Method of drying articles

DOEpatents

Janney, Mark A.; Kiggans, Jr., James O.

1999-01-01

A method of drying a green particulate article includes the steps of: a. Providing a green article which includes a particulate material and a pore phase material, the pore phase material including a solvent; and b. contacting the green article with a liquid desiccant for a period of time sufficient to remove at least a portion of the solvent from the green article, the pore phase material acting as a semipermeable barrier to allow the solvent to be sorbed into the liquid desiccant, the pore phase material substantially preventing the liquid desiccant from entering the pores.

Microbial dispersal in unsaturated porous media: Characteristics of motile bacterial cell motions in unsaturated angular pore networks

NASA Astrophysics Data System (ADS)

Ebrahimi, Ali N.; Or, Dani

2014-09-01

The dispersal rates of self-propelled microorganisms affect their spatial interactions and the ecological functioning of microbial communities. Microbial dispersal rates affect risk of contamination of water resources by soil-borne pathogens, the inoculation of plant roots, or the rates of spoilage of food products. In contrast with the wealth of information on microbial dispersal in water replete systems, very little is known about their dispersal rates in unsaturated porous media. The fragmented aqueous phase occupying complex soil pore spaces suppress motility and limits dispersal ranges in unsaturated soil. The primary objective of this study was to systematically evaluate key factors that shape microbial dispersal in model unsaturated porous media to quantify effects of saturation, pore space geometry, and chemotaxis on characteristics of principles that govern motile microbial dispersion in unsaturated soil. We constructed a novel 3-D angular pore network model (PNM) to mimic aqueous pathways in soil for different hydration conditions; within the PNM, we employed an individual-based model that considers physiological and biophysical properties of motile and chemotactic bacteria. The effects of hydration conditions on first passage times in different pore networks were studied showing that fragmentation of aquatic habitats under dry conditions sharply suppresses nutrient transport and microbial dispersal rates in good agreement with limited experimental data. Chemotactically biased mean travel speed of microbial cells across 9 mm saturated PNM was ˜3 mm/h decreasing exponentially to 0.45 mm/h for the PNM at matric potential of -15 kPa (for -35 kPa, dispersal practically ceases and the mean travel time to traverse the 9 mm PNM exceeds 1 year). Results indicate that chemotaxis enhances dispersal rates by orders of magnitude relative to random (diffusive) motions. Model predictions considering microbial cell sizes relative to available liquid pathways sizes were in good agreement with experimental results for unsaturated soils. The new modeling platform enables quantitative consideration of key biophysical factors (e.g., pore space heterogeneities and hydration conditions) governing microbial interactions in 3-D soil pore spaces.

Synthesis and characterization of nanocrystalline mesoporous zirconia using supercritical drying.

PubMed

Tyagi, Beena; Sidhpuria, Kalpesh; Shaik, Basha; Jasra, Raksh Vir

2006-06-01

Synthesis of nano-crystalline zirconia aerogel was done by sol-gel technique and supercritical drying using n-propanol solvent at and above supercritical temperature (235-280 degrees C) and pressure (48-52 bar) of n-propanol. Zirconia xerogel samples have also been prepared by conventional thermal drying method to compare with the super critically dried samples. Crystalline phase, crystallite size, surface area, pore volume, and pore size distribution were determined for all the samples in detail to understand the effect of gel drying methods on these properties. Supercritical drying of zirconia gel was observed to give thermally stable, nano-crystalline, tetragonal zirconia aerogels having high specific surface area and porosity with narrow and uniform pore size distribution as compared to thermally dried zirconia. With supercritical drying, zirconia samples show the formation of only mesopores whereas in thermally dried samples, substantial amount of micropores are observed along with mesopores. The samples prepared using supercritical drying yield nano-crystalline zirconia with smaller crystallite size (4-6 nm) as compared to higher crystallite size (13-20 nm) observed with thermally dried zirconia.

Product mass transfer resistance directly determined during freeze-drying cycle runs using tunable diode laser absorption spectroscopy (TDLAS) and pore diffusion model.

PubMed

Kuu, Wei Y; O'Bryan, Kevin R; Hardwick, Lisa M; Paul, Timothy W

2011-08-01

The pore diffusion model is used to express the dry layer mass transfer resistance, [Formula: see text], as a function of the ratio r(e)/?, where r(e) is the effective pore radius and ? is the tortuosity factor of the dry layer. Using this model, the effective pore radius of the dry layer can be estimated from the sublimation rate and product temperature profiles measured during primary drying. Freeze-drying cycle runs were performed using the LyoStar II dryer (FTS Systems), with real-time sublimation rate profiles during freeze drying continuously measured by tunable diode laser absorption spectroscopy (TDLAS). The formulations chosen for demonstration of the proposed approach include 5% mannitol, 5% sucrose, 5% lactose, 3% mannitol plus 2% sucrose, and a parenteral nutrition formulation denoted VitaM12. The three different methods used for determination of the product resistance are: (1) Using both the sublimation rate and product temperature profiles, (2) using the sublimation rate profile alone, and (3) using the product temperate profile alone. Unlike the second and third methods, the computation procedure of first method does not need solution of the complex heat and mass transfer equations.

Pore network modeling to explore the effects of compression on multiphase transport in polymer electrolyte membrane fuel cell gas diffusion layers

NASA Astrophysics Data System (ADS)

Fazeli, Mohammadreza; Hinebaugh, James; Fishman, Zachary; Tötzke, Christian; Lehnert, Werner; Manke, Ingo; Bazylak, Aimy

2016-12-01

Understanding how compression affects the distribution of liquid water and gaseous oxygen in the polymer electrolyte membrane fuel cell gas diffusion layer (GDL) is vital for informing the design of improved porous materials for effective water management strategies. Pore networks extracted from synchrotron-based micro-computed tomography images of compressed GDLs were employed to simulate liquid water transport in GDL materials over a range of compression pressures. The oxygen transport resistance was predicted for each sample under dry and partially saturated conditions. A favorable GDL compression value for a preferred liquid water distribution and oxygen diffusion was found for Toray TGP-H-090 (10%), yet an optimum compression value was not recognized for SGL Sigracet 25BC. SGL Sigracet 25BC exhibited lower transport resistance values compared to Toray TGP-H-090, and this is attributed to the additional diffusion pathways provided by the microporous layer (MPL), an effect that is particularly significant under partially saturated conditions.

Machine learning framework for analysis of transport through complex networks in porous, granular media: A focus on permeability

NASA Astrophysics Data System (ADS)

van der Linden, Joost H.; Narsilio, Guillermo A.; Tordesillas, Antoinette

2016-08-01

We present a data-driven framework to study the relationship between fluid flow at the macroscale and the internal pore structure, across the micro- and mesoscales, in porous, granular media. Sphere packings with varying particle size distribution and confining pressure are generated using the discrete element method. For each sample, a finite element analysis of the fluid flow is performed to compute the permeability. We construct a pore network and a particle contact network to quantify the connectivity of the pores and particles across the mesoscopic spatial scales. Machine learning techniques for feature selection are employed to identify sets of microstructural properties and multiscale complex network features that optimally characterize permeability. We find a linear correlation (in log-log scale) between permeability and the average closeness centrality of the weighted pore network. With the pore network links weighted by the local conductance, the average closeness centrality represents a multiscale measure of efficiency of flow through the pore network in terms of the mean geodesic distance (or shortest path) between all pore bodies in the pore network. Specifically, this study objectively quantifies a hypothesized link between high permeability and efficient shortest paths that thread through relatively large pore bodies connected to each other by high conductance pore throats, embodying connectivity and pore structure.

Preparation of high porosity xerogels by chemical surface modification.

DOEpatents

Deshpande, Ravindra; Smith, Douglas M.; Brinker, C. Jeffrey

1996-01-01

This invention provides an extremely porous xerogel dried at vacuum-to-below supercritical pressures but having the properties of aerogels which are typically dried at supercritical pressures. This is done by reacting the internal pore surface of the wet gel with organic substances in order to change the contact angle of the fluid meniscus in the pores during drying. Shrinkage of the gel (which is normally prevented by use of high autoclave pressures, such that the pore fluid is at temperature and pressure above its critical values) is avoided even at vacuum or ambient pressures.

Review of pore network modelling of porous media: Experimental characterisations, network constructions and applications to reactive transport.

PubMed

Xiong, Qingrong; Baychev, Todor G; Jivkov, Andrey P

2016-09-01

Pore network models have been applied widely for simulating a variety of different physical and chemical processes, including phase exchange, non-Newtonian displacement, non-Darcy flow, reactive transport and thermodynamically consistent oil layers. The realism of such modelling, i.e. the credibility of their predictions, depends to a large extent on the quality of the correspondence between the pore space of a given medium and the pore network constructed as its representation. The main experimental techniques for pore space characterisation, including direct imaging, mercury intrusion porosimetry and gas adsorption, are firstly summarised. A review of the main pore network construction techniques is then presented. Particular focus is given on how such constructions are adapted to the data from experimentally characterised pore systems. Current applications of pore network models are considered, with special emphasis on the effects of adsorption, dissolution and precipitation, as well as biomass growth, on transport coefficients. Pore network models are found to be a valuable tool for understanding and predicting meso-scale phenomena, linking single pore processes, where other techniques are more accurate, and the homogenised continuum porous media, used by engineering community. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

Pore Structure Model for Predicting Elastic Wavespeeds in Fluid-Saturated Sandstones

NASA Astrophysics Data System (ADS)

Zimmerman, R. W.; David, E. C.

2011-12-01

During hydrostatic compression, in the elastic regime, ultrasonic P and S wave velocities measured on rock cores generally increase with pressure, and reach asymptotic values at high pressures. The pressure dependence of seismic velocities is generally thought to be due to the closure of compliant cracks, in which case the high-pressure velocities must reflect only the influence of the non-closable, equant "pores". Assuming that pores can be represented by spheroids, we can relate the elastic properties to the pore structure using an effective medium theory. Moreover, the closure pressure of a thin crack-like pore is directly proportional to its aspect ratio. Hence, our first aim is to use the pressure dependence of seismic velocities to invert the aspect ratio distribution. We use a simple analytical algorithm developed by Zimmerman (Compressibility of Sandstones, 1991), which can be used for any effective medium theory. Previous works have used overly restrictive assumptions, such as assuming that the stiff pores are spherical, or that the interactions between pores can be neglected. Here, we assume that the rock contains an exponential distribution of crack aspect ratios, and one family of stiff pores having an aspect ratio lying somewhere between 0.01 and 1. We develop our model in two versions, using the Differential Scheme, and the Mori-Tanaka scheme. The inversion is done using data obtained in dry experiments, since pore fluids have a strong effect on velocities and tend to mask the effect of the pore geometry. This avoids complicated joint inversion of dry and wet data, such as done by Cheng and Toksoz (JGR, 1979). Our results show that for many sets of data on sandstones, we can fit very well the dry velocities. Our second aim is to predict the saturated velocities from our pore structure model, noting that at a given differential stress, the pore structure should be the same as for a dry test. Our results show that the Biot-Gassmann predictions always underpredict the rock stiffness and that, for ultrasonic measurements performed at high frequencies (~MHz), it is more accurate to use the results from effective medium theories, which implicitly assume that the fluid is trapped in the pores. Hence, we use the aspect ratio distribution inverted from dry data, but this time introducing fluid in the pores. For a good number of experimental data on sandstones, our predictions for the saturated velocities match well the experimental data. This validates the use of a spheroidal model for pores. The results are only very weakly dependent on the choice of the effective medium theory. We conclude that our method, which remain relatively simple, is a useful tool to extract the pore aspect ratio distribution, as well as predicting the saturated velocities for sandstones.

Microstructurally tailored ceramics for advanced energy applications by thermoreversible gelcasting

NASA Astrophysics Data System (ADS)

Shanti, Noah Omar

Thermoreversible gelcasting (TRG) is an advantageous technique for rapidly producing bulk, net-shape ceramics and laminates. In this method, ceramic powder is suspended in warm acrylate triblock copolymer/alcohol solutions that reversibly gel upon cooling by the formation of endblock aggregates, to produce slurries which are cast into molds. Gel properties can be tailored by controlling the endblock and midblock lengths of the copolymer network-former and selecting an appropriate alcohol solvent. This research focuses on expanding and improving TRG techniques, focusing specifically on advanced energy applications including the solid oxide fuel cell (SOFC). Rapid drying of filled gels can lead to warping and cracking caused by high differential capillary stresses. A new drying technique using concentrated, alcohol-based solutions as liquid desiccants (LDs) to greatly reduce warping is introduced. The optimal LD is a poly(tert-butyl acrylate)/isopropyl alcohol solution with 5 mol% tert-butyl acrylate units. Alcohol emissions during drying are completely eliminated by combining initial drying in an LD with final stage drying in a vacuum oven having an in-line solvent trap. Porous ceramics are important structures for many applications, including SOFCs. Pore network geometries are tailored by the addition of fugitive fillers to TRG slurries. Uniform spherical, bimodal spherical and uniform fibrous fillers are used. Three-dimensional pore structures are visualized by X-ray computed tomography, allowing for direct measurements of physical parameters such as concentration and morphology as well as transport properties such as tortuosity. Tortuosity values as low as 1.52 are achieved when 60 vol% of solids are uniform spherical filler. Functionally graded laminates with layers ranging from 10 mum to > 1 mm thick are produced with a new technique that combines TRG with tape casting. Gels used for bulk casting are not suitable for use with tape casting, and appropriate base gels are selected for this technique. Each layer is cast in a single pass, and the layers are directly laminated. The anode support, anode functional layer, and electrolyte of anode-supported SOFCs are produced using this technique. The performance of SOFCs produced this way is not yet equal to that of traditionally processed cells, but shows the promise of this technique.

Insight into the wetting of a graphene-mica slit pore with a monolayer of water

NASA Astrophysics Data System (ADS)

Lin, Hu; Schilo, Andre; Kamoka, A. Rauf; Severin, Nikolai; Sokolov, Igor M.; Rabe, Jürgen P.

2017-05-01

Scanning force microscopy (SFM) and Raman spectroscopy allow the unraveling of charge doping and strain effects upon wetting and dewetting of a graphene-mica slit pore with water. SFM reveals a wetting monolayer of water, slightly thinner than a single layer of graphene. The Raman spectrum of the dry pore exhibits the D' peak of graphene, which practically disappears upon wetting, and recurs when the water layer dewets the pore. Based on the 2 D - and G -peak positions, the corresponding peak intensities, and the widths, we conclude that graphene on dry mica is charge-doped and variably strained. A monolayer of water in between graphene and mica removes the doping and reduces the strain. We attribute the D' peak to direct contact of the graphene with the ionic mica surface in dry conditions, and we conclude that a complete monolayer of water wetting the slit pore decouples the graphene from the mica substrate both mechanically and electronically.

Combined Neutron and X-Ray Radiographic/Tomographic Analysis of Dissolution Limestones under Acidic Conditions

NASA Astrophysics Data System (ADS)

Anovitz, L. M.; Cole, D. R.; Hussey, D. S.; LaManna, J.; Swift, A.; Jacobson, D. L.

2016-12-01

Carbon dioxide capture and sequestration in deep geological formations is an important option for reducing greenhouse gas emissions. While the importance of porosity and pore-evolution has long been recognized, the evolution of porosity and permeability in reactive carbonates exposed to CO2-loaded brines is not well constrained. A typical pH range for CO2-acidified brine is 3 to 4.5 depending on alkalinity. This represents a substantial perturbation of typical brines that range from pH 6 to 8. The key questions include how accessible are the pores to fluid transport and how does the pore network evolve as the matrix reacts with the acidic solution? Limestones and dolostones contain nano- to macroscale porosity comprised of cracks, grain boundaries, fluid inclusions, single pores, vugs and networks of pores of random shapes and orientations. Accessible, interconnected pores may act as pore throats, constraining overall flow and are the most likely locations for extensive rock alteration. Neutron imaging is well suited to interrogation of fluid flow in porous media. Because of the large scattering cross section of hydrogen it can be used to directly image water or hydrocarbons without an added contrast medium that might modify interfacial tension and fluid/fluid interactions. In order to understand the reaction of acidified fluids we used simultaneous neutron and X-ray tomography to study the uptake and reaction of water and an acidic fluid (pH 1 HCl) with two types of Indiana limestone, one with a permeability of 2-4 mD, and the other 70 mD. One set of experiments explored capillary uptake in a dry core. These documented rapid uptake and CO2 bubble formation at the inlet. A second set introduced at a constant forced flow rate of 10 ml/min. Both core types exhibited wormhole formation, but the low perm limestone wormhole consisted of one well-delineated channel with a few side "tributaries," whereas the high perm core exhibited a more diffuse array of channels. Post-flow neutron and X-ray tomography showed that grain boundaries and other initial parts of the porous network play an important role in controlling the dissolution process. Neutron radiography and tomography have the potential to significantly advance our understanding of fluid flow and reactive behavior relevant to a wide variety of subsurface applications.

A characterization of the coupled evolution of grain fabric and pore space using complex networks: Pore connectivity and optimized flows in the presence of shear bands

NASA Astrophysics Data System (ADS)

Russell, Scott; Walker, David M.; Tordesillas, Antoinette

2016-03-01

A framework for the multiscale characterization of the coupled evolution of the solid grain fabric and its associated pore space in dense granular media is developed. In this framework, a pseudo-dual graph transformation of the grain contact network produces a graph of pores which can be readily interpreted as a pore space network. Survivability, a new metric succinctly summarizing the connectivity of the solid grain and pore space networks, measures material robustness. The size distribution and the connectivity of pores can be characterized quantitatively through various network properties. Assortativity characterizes the pore space with respect to the parity of the number of particles enclosing the pore. Multiscale clusters of odd parity versus even parity contact cycles alternate spatially along the shear band: these represent, respectively, local jamming and unjamming regions that continually switch positions in time throughout the failure regime. Optimal paths, established using network shortest paths in favor of large pores, provide clues on preferential paths for interstitial matter transport. In systems with higher rolling resistance at contacts, less tortuous shortest paths thread through larger pores in shear bands. Notably the structural patterns uncovered in the pore space suggest that more robust models of interstitial pore flow through deforming granular systems require a proper consideration of the evolution of in situ shear band and fracture patterns - not just globally, but also inside these localized failure zones.

Micro/Nano-pore Network Analysis of Gas Flow in Shale Matrix

PubMed Central

Zhang, Pengwei; Hu, Liming; Meegoda, Jay N.; Gao, Shengyan

2015-01-01

The gas flow in shale matrix is of great research interests for optimized shale gas extraction. The gas flow in the nano-scale pore may fall in flow regimes such as viscous flow, slip flow and Knudsen diffusion. A 3-dimensional nano-scale pore network model was developed to simulate dynamic gas flow, and to describe the transient properties of flow regimes. The proposed pore network model accounts for the various size distributions and low connectivity of shale pores. The pore size, pore throat size and coordination number obey normal distribution, and the average values can be obtained from shale reservoir data. The gas flow regimes were simulated using an extracted pore network backbone. The numerical results show that apparent permeability is strongly dependent on pore pressure in the reservoir and pore throat size, which is overestimated by low-pressure laboratory tests. With the decrease of reservoir pressure, viscous flow is weakening, then slip flow and Knudsen diffusion are gradually becoming dominant flow regimes. The fingering phenomenon can be predicted by micro/nano-pore network for gas flow, which provides an effective way to capture heterogeneity of shale gas reservoir. PMID:26310236

Micro/Nano-pore Network Analysis of Gas Flow in Shale Matrix.

PubMed

Zhang, Pengwei; Hu, Liming; Meegoda, Jay N; Gao, Shengyan

2015-08-27

The gas flow in shale matrix is of great research interests for optimized shale gas extraction. The gas flow in the nano-scale pore may fall in flow regimes such as viscous flow, slip flow and Knudsen diffusion. A 3-dimensional nano-scale pore network model was developed to simulate dynamic gas flow, and to describe the transient properties of flow regimes. The proposed pore network model accounts for the various size distributions and low connectivity of shale pores. The pore size, pore throat size and coordination number obey normal distribution, and the average values can be obtained from shale reservoir data. The gas flow regimes were simulated using an extracted pore network backbone. The numerical results show that apparent permeability is strongly dependent on pore pressure in the reservoir and pore throat size, which is overestimated by low-pressure laboratory tests. With the decrease of reservoir pressure, viscous flow is weakening, then slip flow and Knudsen diffusion are gradually becoming dominant flow regimes. The fingering phenomenon can be predicted by micro/nano-pore network for gas flow, which provides an effective way to capture heterogeneity of shale gas reservoir.

Stabilizing nanocellulose-nonionic surfactant composite foams by delayed Ca-induced gelation.

PubMed

Gordeyeva, Korneliya S; Fall, Andreas B; Hall, Stephen; Wicklein, Bernd; Bergström, Lennart

2016-06-15

Aggregation of dispersed rod-like particles like nanocellulose can improve the strength and rigidity of percolated networks but may also have a detrimental effect on the foamability. However, it should be possible to improve the strength of nanocellulose foams by multivalent ion-induced aggregation if the aggregation occurs after the foam has been formed. Lightweight and highly porous foams based on TEMPO-mediated oxidized cellulose nanofibrils (CNF) were formulated with the addition of a non-ionic surfactant, pluronic P123, and CaCO3 nanoparticles. Foam volume measurements show that addition of the non-ionic surfactant generates wet CNF/P123 foams with a high foamability. Foam bubble size studies show that delayed Ca-induced aggregation of CNF by gluconic acid-triggered dissolution of the CaCO3 nanoparticles significantly improves the long-term stability of the wet composite foams. Drying the Ca-reinforced foam at 60 °C results in a moderate shrinkage and electron microscopy and X-ray tomography studies show that the pores became slightly oblate after drying but the overall microstructure and pore/foam bubble size distribution is preserved after drying. The elastic modulus (0.9-1.4 MPa) of Ca-reinforced composite foams with a density of 9-15 kg/m(3) is significantly higher than commercially available polyurethane foams used for thermal insulation. Copyright © 2016 Elsevier Inc. All rights reserved.

Micromodel observations of evaporative drying and salt deposition in porous media

NASA Astrophysics Data System (ADS)

Rufai, Ayorinde; Crawshaw, John

2017-12-01

Most evaporation experiments using artificial porous media have focused on single capillaries or sand packs. We have carried out, for the first time, evaporation studies on a 2.5D micromodel based on a thin section of a sucrosic dolomite rock. This allowed direct visual observation of pore-scale processes in a network of pores. NaCl solutions from 0 wt. % (de-ionized water) to 36 wt. % (saturated brine) were evaporated by passing dry air through a channel in front of the micromodel matrix. For de-ionized water, we observed the three classical periods of evaporation: the constant rate period (CRP) in which liquid remains connected to the matrix surface, the falling rate period, and the receding front period, in which the capillary connection is broken and water transport becomes dominated by vapour diffusion. However, when brine was dried in the micromodel, we observed that the length of the CRP decreased with increasing brine concentration and became almost non-existent for the saturated brine. In the experiments with brine, the mass lost by evaporation became linear with the square root of time after the short CRP. However, this is unlikely to be due to capillary disconnection from the surface of the matrix, as salt crystals continued to be deposited in the channel above the matrix. We propose that this is due to salt deposition at the matrix surface progressively impeding hydraulic connectivity to the evaporating surface.

Pore-Scale Modeling of Pore Structure Effects on P-Wave Scattering Attenuation in Dry Rocks

PubMed Central

Li, Tianyang; Qiu, Hao; Wang, Feifei

2015-01-01

Underground rocks usually have complex pore system with a variety of pore types and a wide range of pore size. The effects of pore structure on elastic wave attenuation cannot be neglected. We investigated the pore structure effects on P-wave scattering attenuation in dry rocks by pore-scale modeling based on the wave theory and the similarity principle. Our modeling results indicate that pore size, pore shape (such as aspect ratio), and pore density are important factors influencing P-wave scattering attenuation in porous rocks, and can explain the variation of scattering attenuation at the same porosity. From the perspective of scattering attenuation, porous rocks can safely suit to the long wavelength assumption when the ratio of wavelength to pore size is larger than 15. Under the long wavelength condition, the scattering attenuation coefficient increases as a power function as the pore density increases, and it increases exponentially with the increase in aspect ratio. For a certain porosity, rocks with smaller aspect ratio and/or larger pore size have stronger scattering attenuation. When the pore aspect ratio is larger than 0.5, the variation of scattering attenuation at the same porosity is dominantly caused by pore size and almost independent of the pore aspect ratio. These results lay a foundation for pore structure inversion from elastic wave responses in porous rocks. PMID:25961729

Sol-Gel assembly of CdSe nanoparticles to form porous aerogel networks.

PubMed

Arachchige, Indika U; Brock, Stephanie L

2006-06-21

A detailed study of CdSe aerogels prepared by oxidative aggregation of primary nanoparticles (prepared at room temperature and high temperature conditions, >250 degrees C), followed by CO2 supercritical drying, is described. The resultant materials are mesoporous, with an interconnected network of colloidal nanoparticles, and exhibit BET surface areas up to 224 m2/g and BJH average pore diameters in the range of 16-32 nm. Powder X-ray diffraction studies indicate that these materials retain the crystal structure of the primary nanoparticles, with a slight increase in primary particle size upon gelation and aerogel formation. Optical band gap measurements and photoluminescence studies show that the as-prepared aerogels retain the quantum-confined optical properties of the nanoparticle building blocks despite being connected into a 3-D network. The specific optical characteristics of the aerogel can be further modified by surface ligand exchange at the wet-gel stage, without destroying the gel network.

Impact of drying on pore structures in ettringite-rich cements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galan, I., E-mail: isabelgalan@abdn.ac.uk; Beltagui, H.; García-Maté, M.

Drying techniques affect the properties of cement pastes to varying extents. The effect of different drying techniques on calcium sulfoaluminate-based (C$A) cements and their constituent phases is reported for a range of simulated and commercial C$A pastes which are benchmarked against an OPC paste. The recommended methodologies used to dry samples were identified from the literature and include D-drying and solvent exchange. These methods were used in conjunction with mercury intrusion porosimetry (MIP) and X-ray powder diffraction (XRPD) measurements to assess the changes in pore structure and the damage to crystalline phases, respectively. D-drying and isopropanol exchange are the mostmore » satisfactory and least damaging methods for drying C$A based pastes.« less

Strategies for Tailoring the Pore-Size Distribution of Virus Retention Filter Papers.

PubMed

Gustafsson, Simon; Mihranyan, Albert

2016-06-08

The goal of this work is to demonstrate how the pore-size distribution of the nanocellulose-based virus-retentive filter can be tailored. The filter paper was produced using cellulose nanofibers derived from Cladophora sp. green algae using the hot-press drying at varying drying temperatures. The produced filters were characterized using scanning electron microscopy, atomic force microscopy, and N2 gas sorption analysis. Further, hydraulic permeability and retention efficiency toward surrogate 20 nm model particles (fluorescent carboxylate-modified polystyrene spheres) were assessed. It was shown that by controlling the rate of water evaporation during hot-press drying the pore-size distribution can be precisely tailored in the region between 10 and 25 nm. The mechanism of pore formation and critical parameters are discussed in detail. The results are highly valuable for development of advanced separation media, especially for virus-retentive size-exclusion filtration.

Estimating dynamic permeability in fractal pore network saturated by Maxwellian fluid

NASA Astrophysics Data System (ADS)

Sun, W.

2017-12-01

The frequency dependent flow of fluid in porous media is an important issue in geophysical prospecting. Oscillating flow in pipe leads to frequency dependent dynamic permeability and has been studied in pore network containing Newtonian fluid. But there is little work on oscillating complex fluid in pipe network, especially in irregular network. Here we formulated frequency dependent permeability for Maxwellian fluid and estimated the permeability in three-dimensional fractal network model. We consider an infinitely long cylindrical pipe with rigid solid wall. The pipe is filled with Maxwellian fluids. Based on the mass conservation equation, the equilibrium equation of force and Maxwell constitutive relationship, we formulated the flux by integration of axial velocity component over the pipe's cross section. Then we extend single pipe formulation to a 3D irregular network. Flux balance condition yields a set of linear equations whose unknowns are the fluid pressure at each node. By evaluating the total flow flux through the network, the dynamic permeability can be calculated.We investigated the dynamic permeability of brine and CPyCl/NaSal in a 3D porous sample with a cubic side length 1 cm. The pore network is created by a Voronoi cell filling method. The porosity, i.e., volume ratio between pore/pipe network and the overall cubic, is set as 0.1. The irregular pore network has a fractal structure. The dimension d of the pore network is defined by the relation between node number M within a sphere and the radius r of the sphere,M=rd.The results show that both brine and Maxwellian fluid's permeability maintain a stable value at low frequency, then decreases with fluctuating peaks. The dynamic permeability in pore networks saturated by Maxwellian fluid (CPyCl/NaSal (60 mM)) show larger peaks during the decline process at high frequency, which represents the typical resonance behavior. Dynamic permeability shows clear dependence on the dimension of the fractal network. Small-scale network has higher dimension than large-scale networks. The reason is that in larger networks pore and inter-pore connections are so dense that the probability P(r) to have a neighboring pore at distance r decays faster. The proposed model may be used to explain velocity dispersion in unconventional reservoir rocks observed in laboratory.

3-D loaded scaffolds obtained by supercritical CO2 assisted process

NASA Astrophysics Data System (ADS)

Cardea, S.; Reverchon, E.

2014-08-01

In this work, a supercritical CO2 (SC-CO2) drying process for the formation of 3-D PVDF-HFP loaded scaffolds was tested. Experiments at pressures ranging between 150 and 250 bar and at temperatures ranging between 35 and 55°C were performed. The PVDF-HFP- acetone-ethanol solution at 15% w/w polymer was selected as the base case. The drug (amoxicillin) concentration was varied from 20 to 30% w/w with respect to PVDF-HFP. SC- CO2 drying process was confirmed to be a valid alternative to generate loaded structures; indeed, scaffolds characterized by nanometric networks (with mean pore diameter of about 300 nm) with a homogeneous drug distribution were obtained. Drug controlled release experiments were also performed and a quasi-zero order release kinetic was observed.

Sediment entrainment by debris flows: In situ measurements from the headwaters of a steep catchment

USGS Publications Warehouse

McCoy, S.W.; Kean, Jason W.; Coe, Jeffrey A.; Tucker, G.E.; Staley, Dennis M.; Wasklewicz, T.A.

2012-01-01

Debris flows can dramatically increase their volume, and hence their destructive potential, by entraining sediment. Yet quantitative constraints on rates and mechanics of sediment entrainment by debris flows are limited. Using an in situ sensor network in the headwaters of a natural catchment we measured flow and bed properties during six erosive debris-flow events. Despite similar flow properties and thicknesses of bed sediment entrained across all events, time-averaged entrainment rates were significantly faster for bed sediment that was saturated prior to flow arrival compared with rates for sediment that was dry. Bed sediment was entrained from the sediment-surface downward in a progressive fashion and occurred during passage of dense granular fronts as well as water-rich, inter-surge flow.En massefailure of bed sediment along the sediment-bedrock interface was never observed. Large-magnitude, high-frequency fluctuations in total normal basal stress were dissipated within the upper 5 cm of bed sediment. Within this near surface layer, concomitant fluctuations in Coulomb frictional resistance are expected, irrespective of the influence of pore fluid pressure or fluctuations in shear stress. If the near-surface sediment was wet as it was overridden by a flow, additional large-magnitude, high-frequency pore pressure fluctuations were measured in the near-surface bed sediment. These pore pressure fluctuations propagated to depth at subsonic rates and in a diffusive manner. The depth to which large excess pore pressures propagated was typically less than 10 cm, but scaled as (D/fi)0.5, in which D is the hydraulic diffusivity and fi is the frequency of a particular pore pressure fluctuation. Shallow penetration depths of granular-normal-stress fluctuations and excess pore pressures demonstrate that only near-surface bed sediment experiences the full dynamic range of effective-stress fluctuations, and as a result, can be more easily entrained than deeper sediment. These data provide robust tests for mechanical models of entrainment and demonstrate that a debris flow over wet bed sediment will be larger than the same flow over dry bed sediment.

Pore-scale distribution of mucilage affecting water repellency in the rhizosphere

NASA Astrophysics Data System (ADS)

Benard, Pascal; Zarebanadkouki, Mohsen; Hedwig, Clemens; Holz, Maire; Ahmed, Mutez; Carminati, Andrea

2017-04-01

The hydraulic properties of the rhizosphere are altered by plants, fungi and microorganism. Plant roots release different compounds into the soil. One of these substances is mucilage, a gel which turns water repellent upon drying. We introduce a conceptual model of mucilage deposition during soil drying and its impact on the soil wettability. As the soil dries, water menisci recede and draw mucilage towards the contact region between particles where it is deposited. At high mucilage content, mucilage deposits expand into the open pore space and finally block water infiltration when a critical fraction of the pore space is blocked. To test this hypothesis, we mixed mucilage and particles of different grain size, we let them dry and measured the contact angle using the sessile drop method. Mucilage deposition was visualized by light microscopy imaging. Contact angle measurements showed a distinct threshold-like behavior with a sudden increase in apparent contact angle at high mucilage concentrations. Particle roughness induced a more uniform distribution of mucilage. The observed threshold corresponds to the concentration when mucilage deposition occupies a critical fraction of the pore space, as visualized with the microscope images. In conclusion, water repellency is critically affected by the distribution of mucilage on the pore-scale. This microscopic heterogeneity has to be taken into account in the description of macroscopic processes, like water infiltration or rewetting of water repellent soil.

Assessing five evolving microbial enzyme models against field measurements from a semiarid savannah—What are the mechanisms of soil respiration pulses?

NASA Astrophysics Data System (ADS)

Zhang, Xia; Niu, Guo-Yue; Elshall, Ahmed S.; Ye, Ming; Barron-Gafford, Greg A.; Pavao-Zuckerman, Mitch

2014-09-01

Soil microbial respiration pulses in response to episodic rainfall pulses (the "Birch effect") are poorly understood. We developed and assessed five evolving microbial enzyme models against field measurements from a semiarid savannah characterized by pulsed precipitation to understand the mechanisms to generate the Birch pulses. The five models evolve from an existing four-carbon (C) pool model to models with additional C pools and explicit representations of soil moisture controls on C degradation and microbial uptake rates. Assessing the models using techniques of model selection and model averaging suggests that models with additional C pools for accumulation of degraded C in the dry zone of the soil pore space result in a higher probability of reproducing the observed Birch pulses. Degraded C accumulated in dry soil pores during dry periods becomes immediately accessible to microbes in response to rainstorms, providing a major mechanism to generate respiration pulses. Explicitly representing the transition of degraded C and enzymes between dry and wet soil pores in response to soil moisture changes and soil moisture controls on C degradation and microbial uptake rates improve the models' efficiency and robustness in simulating the Birch effect. Assuming that enzymes in the dry soil pores facilitate degradation of complex C during dry periods (though at a lower rate) results in a greater accumulation of degraded C and thus further improves the models' performance. However, the actual mechanism inducing the greater accumulation of labile C needs further experimental studies.

Reservoir depletion at The Geysers geothermal area, California, shown by four-dimensional seismic tomography

USGS Publications Warehouse

Gunasekera, R.C.; Foulger, G.R.; Julian, B.R.

2003-01-01

Intensive geothermal exploitation at The Geysers geothermal area, California, induces myriads of small-magnitude earthquakes that are monitored by a dense, permanent, local seismometer network. Using this network, tomographic inversions were performed for the three-dimensional Vp and Vp/Vs structure of the reservoir for April 1991, February 1993, December 1994, October 1996, and August 1998. The extensive low-Vp/Vs anomaly that occupies the reservoir grew in strength from a maximum of 9% to a maximum of 13.4% during the 7-year study period. This is attributed to depletion of pore liquid water in the reservoir and replacement with steam. This decreases Vp by increasing compressibility, and increases Vs because of reduction in pore pressure and the drying of argillaceous minerals, e.g., illite, which increase the shear modulus. These effects serendipitously combine to lower Vp/Vs, resulting in a strong overall effect that provides a convenient tool for monitoring reservoir depletion. Variations in the Vp and Vs fields indicate that water depletion is the dominant process in the central part of the exploited reservoir, and pressure reduction and mineral drying in the northwest and southeast parts of the reservoir. The rate at which the Vp/Vs anomaly grew in strength in the period 1991-1998 suggests most of the original anomaly was caused by exploitation. Continuous monitoring of Vp, Vs, and Vp/Vs is an effective geothermal reservoir depletion monitoring tool and can potentially provide information about depletion in parts of the reservoir that have not been drilled.

Nanoporous thermosetting polymers.

PubMed

Raman, Vijay I; Palmese, Giuseppe R

2005-02-15

Potential applications of nanoporous thermosetting polymers include polyelectrolytes in fuel cells, separation membranes, adsorption media, and sensors. Design of nanoporous polymers for such applications entails controlling permeability by tailoring pore size, structure, and interface chemistry. Nanoporous thermosetting polymers are often synthesized via free radical mechanisms using solvents that phase separate during polymerization. In this work, a novel technique for the synthesis of nanoporous thermosets is presented that is based on the reactive encapsulation of an inert solvent using step-growth cross-linking polymerization without micro/macroscopic phase separation. The criteria for selecting such a monomer-polymer-solvent system are discussed based on FTIR analysis, observed micro/macroscopic phase separation, and thermodynamics of swelling. Investigation of resulting network pore structures by scanning electron microscopy (SEM) and small-angle X-ray scattering following extraction and supercritical drying using carbon dioxide showed that nanoporous polymeric materials with pore sizes ranging from 1 to 50 nm can be synthesized by varying the solvent content. The differences in the porous morphology of these materials compared to more common free radically polymerized analogues that exhibit phase separation were evident from SEM imaging. Furthermore, it was demonstrated that the chemical activity of the nanoporous materials obtained by our method could be tailored by grafting appropriate functional groups at the pore interface.

Mesoporous Polymer Frameworks from End-Reactive Bottlebrush Copolymers

DOE PAGES

Altay, Esra; Nykypanchuk, Dmytro; Rzayev, Javid

2017-08-07

Reticulated nanoporous materials generated by versatile molecular framework approaches are limited to pore dimensions on the scale of the utilized rigid molecular building blocks (<5 nm). The inherent flexibility of linear polymers precludes their utilization as long framework connectors for the extension of this strategy to larger length scales. We report a method for the fabrication of mesoporous frameworks by using bottlebrush copolymers with reactive end blocks serving as rigid macromolecular interconnectors with directional reactivity. End-reactive bottlebrush copolymers with pendant alkene functionalities were synthesized by a combination of controlled radical polymerization and polymer modification protocols. Ru-catalyzed cross-metathesis cross-linking of bottlebrushmore » copolymers with two reactive end blocks resulted in the formation of polymer frameworks where isolated cross-linked domains were interconnected with bottlebrush copolymer bridges. The resulting materials were characterized by a continuous network pore structure with average pore sizes of 9–50 nm, conveniently tunable by the length of the utilized bottlebrush copolymer building blocks. As a result, the materials fabrication strategy described in this work expands the length scale of molecular framework materials and provides access to mesoporous polymers with a molecularly tunable reticulated pore structure without the need for templating, sacrificial component etching, or supercritical fluid drying.« less

Freeze-drying of “pearl milk tea”: A general strategy for controllable synthesis of porous materials

PubMed Central

Zhou, Yingke; Tian, Xiaohui; Wang, Pengcheng; Hu, Min; Du, Guodong

2016-01-01

Porous materials have been widely used in many fields, but the large-scale synthesis of materials with controlled pore sizes, pore volumes, and wall thicknesses remains a considerable challenge. Thus, the controllable synthesis of porous materials is of key general importance. Herein, we demonstrate the “pearl milk tea” freeze-drying method to form porous materials with controllable pore characteristics, which is realized by rapidly freezing the uniformly distributed template-containing precursor solution, followed by freeze-drying and suitable calcination. This general and convenient method has been successfully applied to synthesize various porous phosphate and oxide materials using different templates. The method is promising for the development of tunable porous materials for numerous applications of energy, environment, and catalysis, etc. PMID:27193866

New families of carbon gels based on natural resources

NASA Astrophysics Data System (ADS)

Szczurek, Andrzej; Amaral-Labat, Gisele; Fierro, Vanessa; Pizzi, Antonio; Celzard, Alain

2013-03-01

Carbon gels are versatile materials which can be used for many applications. They are extremely expensive, because generally prepared from resorcinol - formaldehyde (RF) resins first gelled and next dried with supercritical carbon dioxide. In the present work, resorcinol has been substituted partly or completely by tannins, a family of molecules extracted from mimosa tree barks. Tannins are natural, non-toxic products, typically thirty times cheaper than resorcinol. Their chemical resemblance with the latter makes them be often called natural resorcinol. Using tannins not only substantially decreases the cost but also allows preparing materials in a much wider range of pHs than that usually employed for RF gels. Consequently the main pore size and the fraction of given families of pores, controlling the carbon gels' properties, are tuned in an easier way, and a much wider range of pore structures is obtained. Finally, two alternative ways of drying are suggested for further decreasing the cost: freeze-drying and supercritical drying in acetone. Both are shown to lead, in some conditions described below, to materials having similar characteristics to those of expensive RF carbon aerogels previously dried in supercritical CO2.

Development of Biomimetic Hybrid Porous Scaffold of Chitosan/Polyvinyl Alcohol/Carboxymethyl Cellulose by Freeze-Dried and Salt Leached Technique.

PubMed

Kanimozhi, K; Basha, S Khaleel; Kumari, V Sugantha; Kaviyarasu, K

2018-07-01

Freeze drying and salt leaching methods were applied to fabricate Chitosan/Poly(vinyl alcohol)/Carboxymethyl cellulose (CPCMC) biomimetic porous scaffolds for soft tissue engineering. The properties of these scaffolds were investigated and compared to those by freeze drying and salt leaching methods respectively. The salt-leached CS/PVA/CMC scaffolds were easily formed into desired shapes with a uniformly distributed and interconnected pore structure with an average pore size. The mechanical strength of the scaffolds increased with the porosity, and were easily modulated by the addition of carboxymethyl cellulose. The morphology of the porous scaffolds observed using a SEM exhibited good porosity and interconnectivity of pores. MTT assay using L929 fibroblast cells demonstrated that the cell viability of the porous scaffold was good. Scaffolds prepared by salt leached method show larger swelling capacity, and mechanical strength, potent antibacterial activity and more cell viability than freeze dried method. It is found that salt leaching method has distinguished characteristics of simple, efficient, feasible and less economic than freeze dried scaffolds.

A new challenge: in-situ investigation of the elusive nanostructures in wet halite and clay using BIB/FIB-cryo-SEM methods

NASA Astrophysics Data System (ADS)

Desbois, G.; Urai, J. L.

2009-04-01

Mudrocks and saltrocks form seals for hydrocarbon accumulations, aquitards and chemical barriers. The sealing capacity is controlled either by the rock microstructure or by chemical interactions between minerals and the permeating fluid. A detailed knowledge about the sealing characteristics is of particular interest in Petroleum Sciences. Other fields of interest are the storage of anthropogenic carbon dioxide and radioactive waste in geologic formations. A key factor to the understanding of sealing by mudstones and saltrocks is the study of their porosity. However, Halite and clay are so fluids sensitive that investigation on dried samples required by traditional methods of investigations (metal injection methods [6],[3]; magnetic susceptibility measurement [4]; SEM imaging of broken surfaces [5] and CT scanner computing [7]) are critical for robust interpretation. In one hand, none of these methods is able to directly describe the in-situ porosity at the pore scale and on the other hand, most of these methods require dried samples in which the natural structure of pores could be damaged due to the desiccation, dehydration and dissolution-recrystallisation of the fabric. SEM imaging is certainly the most direct approach to investigate the porosity but it is generally limited by the poor quality of the mechanically prepared surfaces. This problem is solved by the recent development of ion milling tools (FIB: Focussed Ion Beam or BIB: Broad Ion Beam, which allows producing in-situ high quality polished cross-sections suitable for high resolution pores SEM imaging at nano-scale. More over, new and innovative developments of the cryo-SEM approach in the Geosciences allow investigating samples under wet natural conditions. Thus, we are developing the combination of FIB/BIB-cryo-SEM methods ([1],[2]), which combine in one machine the vitrification of the pore fluids by very rapid cooling, the excavation of the sample by ion milling tool and SEM imaging. By these, we are able to stabilize the in-situ fluids in grain boundaries or pores, preserve the natural structures at nano scale, produce high quality polished cross-sections for high resolution SEM imaging and reconstruct accurately the grain boundary and the pore space networks in 3D by serial cross sectioning. Our first investigations on wet halite and wet clay materials produced unprecedented high quality images of fully preserved fluid-filled pore space as appear in nature. We have thus validated the use of the FIB/BIB-cryo-SEM technology for the in-situ investigations of the elusive structures in wet geomaterials paving the way towards a fuller understanding of how pore geometry can affect physical properties of rocks. [1] Desbois G. And Urai J.L. (submitted). In-situ morphology of meso-porosity in Boom clay (Mol site, Belgium) inferred by the innovative FIB-cryo-SEM method. E-earth. [2] Desbois G., Urai J.L., Burkhardt C., Drury M., Hayles M. and Humbel B. (2008). Cryogenic vitrification and 3D serial sectioning using high resolution cryo-FIB-SEM technology for brine-filled grain boundaries in halite: first results. Geofluids, 8: 60-72 [3] Esteban L., Géraud Y. And Bouchez J.L. (2006). Pore network geometry in low permeability argillites from magnetic fabric data and oriented mercury injections. Geophysical Research Letters, vol. 33, L18311, doi : 10.1029/2006GL026908. [4] Esteban L., Géraud Y. And Bouchez J.L. (2007). Pore network connectivity anisotropy in Jurassic argillite specimens from eastern Paris Basin (France). Physics and Chemistry of the Earth, 32(1) :161-169. [5] Hildenbrand A., Krooss B. M. and Urai J. L. (2005). Relationship between pore structure and fluid transport in argillaceous rocks. Solid Mechanics and Its Applications, IUTAM Symposium on Physicochemical and Electromechanical Interactions in Porous Media, 125 : 231-237, doi : 10.1007/1-4020-3865-8_26. [6] Hildenbrand A. and Urai J.L. (2003) Investigation of the morphology of pore space in mudstones—first results. Marine and Petroleum Geology, 20(10):1185-1200. [7] H. Taud H., Martinez-Angeles R., Parrot J.F., Hernandez-Escobedo L. (2005). Porosity estimation method by X-ray computed tomography. Journal of Petroleum Science and Engineering, (47), 3-4, 30: 209-217

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kanna, V.; Olson, R.A.; Jennings, H.M.

The effects of drying on mortars containing Portland cement blended with fly ash or slag on the shrinkage, extent of surface cracking, pore size distribution as measured by mercury intrusion porosimetry, flexural strength, fracture toughness, and Young`s modulus are reported. Specimens were exposed to conditions of 100% relative humidity (RH), 50% RH, and/or oven-drying at 105 C. Drying coarsened the pore structure and increased the density of surface cracks, but surprisingly increased the flexural strength and the fracture toughness, and as anticipated lowered the Young`s modulus. This was regardless of the content of mineral admixture.

Permeability changes induced by microfissure closure and opening in tectonized materials. Effect on slope pore pressure regime.

NASA Astrophysics Data System (ADS)

De la Fuente, Maria; Vaunat, Jean; Pedone, Giuseppe; Cotecchia, Federica; Sollecito, Francesca; Casini, Francesca

2015-04-01

Tectonized clays are complex materials characterized by several levels of structures that may evolve during load and wetting/drying processes. Some microstructural patterns, as microfissures, have a particular influence on the value of permeability which is one of the main factors controlling pore pressure regime in slopes. In this work, the pore pressure regime measured in a real slope of tectonized clay in Southern Italy is analyzed by a numerical model that considers changes in permeability induced by microfissure closure and opening during the wetting and drying processes resulting from climatic actions. Permeability model accounts for the changes in Pore Size Distribution observed by Microscopy Intrusion Porosimetry. MIP tests are performed on representative samples of ground in initial conditions ("in situ" conditions) and final conditions (deformed sample after applying a wetting path that aims to reproduce the saturation of the soil under heavy rains). The resulting measurements allow for the characterization at microstructural level of the soil, identifying the distribution of dominant families pores in the sample and its evolution under external actions. Moreover, comparison of pore size density functions allows defining a microstructural parameter that depends on void ratio and degree of saturation and controls the variation of permeability. Model has been implemented in a thermo-hydro-mechanical code provided with a special boundary condition for climatic actions. Tool is used to analyze pore pressure measurements obtained in the tectonized clay slope. Results are analyzed at the light of the effect that permeability changes during wetting and drying have on the pore pressure regime.

Mechanical behavior of concrete and related porous materials under partial saturation: The effective stress and the viscous softening due to movement of nanometer-scale pore fluid

NASA Astrophysics Data System (ADS)

Vlahinic, Ivan

It has been said that porous materials are like music: the gaps are as important as the filled-in bits. In other words, in addition to the solid structure, pore characteristics such as size and morphology play a crucial role in defining the overall physical properties of the porous materials. This work goes a step further and examines the behaviors of some porous media that arise when the pore network is occupied by two fluids, principally air and water, as a result of drying or wetting. Such a state gives rise to fluid capillarity which can generate significant negative fluid pressures. In the first part, a constitutive model for drying of an elastic porous medium is proposed and then extended to derive a novel expression for effective stress in partially saturated media. The model is motivated by the fact that in a system that is saturated by two different fluids, two different pressure inherently act on the surfaces of the pore network. This causes a non-uniform strain field in the solid structure, something that is not explicitly accounted for in the classic formulations of this problem. We use some standard micromechanical homogenization techniques to estimate the extent of the 'non-uniformity' and on this basis, evaluate the validity of the classic Bishop effective stress expression for partially saturated materials. In the second part, we examine a diverse class of porous materials which behave in an unexpected (and even counterintuitive) way under the internal moisture fluctuations. In particular, during wetting and drying alike, the solid viscosity of these materials appears to soften, sometimes by an order of magnitude or more. Under load, this can lead to significantly increased rates of deformations. On account of the recent experimental and theoretical findings on the nature of water flow in nanometer-size hydrophillic spaces, we provide a physical explanation for the viscous softening and propose a constitutive law on this basis. To this end, it also becomes necessary to describe the fluid flow in a double porosity medium, i.e. a medium containing both macro- and nano-scale porosity. We show that the proposed model can quantitatively capture the key observations that have thus far evaded a simple mechanical description. The materials more closely examined in this work enjoy a wide variety of practical uses. Wood and concrete are used as a basis for infrastructure the world over; porous glass with engineered nanometer-sized openings is used for its sorptive and filtering abilities; KevlarRTM and similar synthetic polymers are used for their high strength-to-weight ratio in creating body armor, ropes, and even sails.

Using synchrotron X-ray microtomography to characterize the pore network of reservoir rocks: A case study on carbonates

NASA Astrophysics Data System (ADS)

Arzilli, F.; Cilona, A.; Mancini, L.; Tondi, E.

2016-09-01

In this work we propose a new methodology to calculate pore connectivity in granular rocks. This method is useful to characterize the pore networks of natural and laboratory compaction bands (CBs), and compare them with the host rock pore network. Data were collected using the synchrotron X-ray microtomography technique and quantitative analyses were carried out using the Pore3D software library. The porosity was calculated from segmented tridimensional images of deformed and pristine rocks. A process of skeletonization of the pore space was used to obtain the number of connected pores within the rock volume. By analyzing the skeletons the differences between natural and laboratory CBs were highlighted. The natural CB has a lower porosity than to the laboratory one. In natural CBs, the grain contacts appear welded, whereas laboratory CBs show irregular pore shape. Moreover, we assessed for the first time how pore connectivity evolves as a function of deformation, documenting the mechanism responsible for pore connectivity drop within the CBs.

A multi-scale network method for two-phase flow in porous media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khayrat, Karim, E-mail: khayratk@ifd.mavt.ethz.ch; Jenny, Patrick

Pore-network models of porous media are useful in the study of pore-scale flow in porous media. In order to extract macroscopic properties from flow simulations in pore-networks, it is crucial the networks are large enough to be considered representative elementary volumes. However, existing two-phase network flow solvers are limited to relatively small domains. For this purpose, a multi-scale pore-network (MSPN) method, which takes into account flow-rate effects and can simulate larger domains compared to existing methods, was developed. In our solution algorithm, a large pore network is partitioned into several smaller sub-networks. The algorithm to advance the fluid interfaces withinmore » each subnetwork consists of three steps. First, a global pressure problem on the network is solved approximately using the multiscale finite volume (MSFV) method. Next, the fluxes across the subnetworks are computed. Lastly, using fluxes as boundary conditions, a dynamic two-phase flow solver is used to advance the solution in time. Simulation results of drainage scenarios at different capillary numbers and unfavourable viscosity ratios are presented and used to validate the MSPN method against solutions obtained by an existing dynamic network flow solver.« less

Capillary-Driven Solute Transport and Precipitation in Porous Media during Dry-Out

NASA Astrophysics Data System (ADS)

Ott, Holger; Andrew, Matthew; Blunt, Martin; Snippe, Jeroen

2014-05-01

The injection of dry or under-saturated gases or supercritical (SC) fluids into water bearing formations might lead to a formation dry-out in the vicinity of the injection well. The dry-out is caused by the evaporation/dissolution of formation water into the injected fluid and the subsequent transport of dissolved water in the injected fluid away from the injection well. Dry-out results in precipitation from solutes of the formation brine and consequently leads to a reduction of the rock's pore space (porosity) and eventually to a reduction of permeability near the injection well, or even to the loss of injectivity. Recently evidence has been found that the complexity of the pore space and the respective capillary driven solute transport plays a key role. While no effective-permeability (Keff) reduction was observed in a single-porosity sandstone, multi porosity carbonate rocks responded to precipitation with a strong reduction of Keff. The reason for the different response of Keff to salt precipitation is suspected to be in the exact location of the precipitate (solid salt) in the pore space. In this study, we investigate dry-out and salt precipitation due to supercritical CO2 injection in single and multi-porosity systems under near well-bore conditions. We image fluid saturation changes by means of μCT scanning during desaturation. We are able to observe capillary driven transport of the brine phase and the respective transport of solutes on the rock's pore scale. Finally we have access to the precipitated solid-salt phase and their distribution. The results can proof the thought models behind permeability porosity relationships K(φ) for injectivity modeling. The topic and the mechanisms we show are of general interest for drying processes in porous material such as soils and paper.

Hornwort Stomata: Architecture and Fate Shared with 400-Million-Year-Old Fossil Plants without Leaves.

PubMed

Renzaglia, Karen S; Villarreal, Juan Carlos; Piatkowski, Bryan T; Lucas, Jessica R; Merced, Amelia

2017-06-01

As one of the earliest plant groups to evolve stomata, hornworts are key to understanding the origin and function of stomata. Hornwort stomata are large and scattered on sporangia that grow from their bases and release spores at their tips. We present data from development and immunocytochemistry that identify a role for hornwort stomata that is correlated with sporangial and spore maturation. We measured guard cells across the genera with stomata to assess developmental changes in size and to analyze any correlation with genome size. Stomata form at the base of the sporophyte in the green region, where they develop differential wall thickenings, form a pore, and die. Guard cells collapse inwardly, increase in surface area, and remain perched over a substomatal cavity and network of intercellular spaces that is initially fluid filled. Following pore formation, the sporophyte dries from the outside inwardly and continues to do so after guard cells die and collapse. Spore tetrads develop in spore mother cell walls within a mucilaginous matrix, both of which progressively dry before sporophyte dehiscence. A lack of correlation between guard cell size and DNA content, lack of arabinans in cell walls, and perpetually open pores are consistent with the inactivity of hornwort stomata. Stomata are expendable in hornworts, as they have been lost twice in derived taxa. Guard cells and epidermal cells of hornworts show striking similarities with the earliest plant fossils. Our findings identify an architecture and fate of stomata in hornworts that is ancient and common to plants without sporophytic leaves. © 2017 American Society of Plant Biologists. All Rights Reserved.

Development of a pore network simulation model to study nonaqueous phase liquid dissolution

USGS Publications Warehouse

Dillard, Leslie A.; Blunt, Martin J.

2000-01-01

A pore network simulation model was developed to investigate the fundamental physics of nonequilibrium nonaqueous phase liquid (NAPL) dissolution. The network model is a lattice of cubic chambers and rectangular tubes that represent pore bodies and pore throats, respectively. Experimental data obtained by Powers [1992] were used to develop and validate the model. To ensure the network model was representative of a real porous medium, the pore size distribution of the network was calibrated by matching simulated and experimental drainage and imbibition capillary pressure‐saturation curves. The predicted network residual styrene blob‐size distribution was nearly identical to the observed distribution. The network model reproduced the observed hydraulic conductivity and produced relative permeability curves that were representative of a poorly consolidated sand. Aqueous‐phase transport was represented by applying the equation for solute flux to the network tubes and solving for solute concentrations in the network chambers. Complete mixing was found to be an appropriate approximation for calculation of chamber concentrations. Mass transfer from NAPL blobs was represented using a corner diffusion model. Predicted results of solute concentration versus Peclet number and of modified Sherwood number versus Peclet number for the network model compare favorably with experimental data for the case in which NAPL blob dissolution was negligible. Predicted results of normalized effluent concentration versus pore volume for the network were similar to the experimental data for the case in which NAPL blob dissolution occurred with time.

A computational geometry approach to pore network construction for granular packings

NASA Astrophysics Data System (ADS)

van der Linden, Joost H.; Sufian, Adnan; Narsilio, Guillermo A.; Russell, Adrian R.; Tordesillas, Antoinette

2018-03-01

Pore network construction provides the ability to characterize and study the pore space of inhomogeneous and geometrically complex granular media in a range of scientific and engineering applications. Various approaches to the construction have been proposed, however subtle implementational details are frequently omitted, open access to source code is limited, and few studies compare multiple algorithms in the context of a specific application. This study presents, in detail, a new pore network construction algorithm, and provides a comprehensive comparison with two other, well-established Delaunay triangulation-based pore network construction methods. Source code is provided to encourage further development. The proposed algorithm avoids the expensive non-linear optimization procedure in existing Delaunay approaches, and is robust in the presence of polydispersity. Algorithms are compared in terms of structural, geometrical and advanced connectivity parameters, focusing on the application of fluid flow characteristics. Sensitivity of the various networks to permeability is assessed through network (Stokes) simulations and finite-element (Navier-Stokes) simulations. Results highlight strong dependencies of pore volume, pore connectivity, throat geometry and fluid conductance on the degree of tetrahedra merging and the specific characteristics of the throats targeted by the merging algorithm. The paper concludes with practical recommendations on the applicability of the three investigated algorithms.

Multiscale pore networks and their effect on deformation and transport property alteration associated with hydraulic fracturing

NASA Astrophysics Data System (ADS)

Daigle, Hugh; Hayman, Nicholas; Jiang, Han; Tian, Xiao; Jiang, Chunbi

2017-04-01

Multiple lines of evidence indicate that, during a hydraulic fracture stimulation, the permeability of the unfractured matrix far from the main, induced tensile fracture increases by one to two orders of magnitude. This permeability enhancement is associated with pervasive shear failure in a large region surrounding the main induced fracture. We have performed low-pressure gas sorption, mercury intrusion, and nuclear magnetic resonance measurements along with high-resolution scanning electron microscope imaging on several preserved and unpreserved shale samples from North American basins before and after inducing failure in confined compressive strength tests. We have observed that the pore structure in intact samples exhibits multiscale behavior, with sub-micron-scale pores in organic matter connected in isolated, micron-scale clusters which themselves are connected to each other through a network of microcracks. The organic-hosted pore networks are poorly connected due to a significant number of dead-end pores within the organic matter. Following shear failure, we often observe an increase in pore volume in the sub-micron range, which appears to be related to the formation of microcracks that propagate along grain boundaries and other planes of mechanical strength contrast. This is consistent with other experimental and field evidence. In some cases these microcracks cross or terminate in organic matter, intersecting the organic-hosted pores. The induced microcrack networks typically have low connectivity and do not appreciably increase the connectivity of the overall pore network. However, in other cases the shear deformation results in an overall pore volume decrease; samples which exhibit this behavior tend to have more clay minerals. Our interpretation of these phenomena is as follows. As organic matter is converted to hydrocarbons, organic-hosted pores develop, and the hydrocarbons contained in these pores are overpressured. The disconnected nature of these clusters of organic-hosted pores prevents the overpressure from dissipating, resulting in localized overpressure at the micron scale. When the rock is subjected to a hydraulic fracture stimulation, the rock surrounding the main induced fracture experiences shear deformation. Those parts of the rock that contain overpressured fluids in the organic-hosted pores will be more likely to experience dilatancy in the form of brittle deformation; the portions of the rock lacking in organic-hosted pores will tend to experience compactive shear failure since the effective normal stresses are larger. The microcrack networks that propagate into the regions of organic-hosted porosity allow the hydrocarbons resident in those pores to migrate to the main induced tensile fractures. The disconnected nature of the microcrack networks causes only a slight increase in permeability, which is consistent with other observations. Our work illustrates how multiscale pore networks in shale interact with in situ stresses to affect the bulk shale rheology.

Upscaling of nanoparticle transport in porous media under unfavorable conditions: Pore scale to Darcy scale

NASA Astrophysics Data System (ADS)

Seetha, N.; Raoof, Amir; Mohan Kumar, M. S.; Majid Hassanizadeh, S.

2017-05-01

Transport and deposition of nanoparticles in porous media is a multi-scale problem governed by several pore-scale processes, and hence, it is critical to link the processes at pore scale to the Darcy-scale behavior. In this study, using pore network modeling, we develop correlation equations for deposition rate coefficients for nanoparticle transport under unfavorable conditions at the Darcy scale based on pore-scale mechanisms. The upscaling tool is a multi-directional pore-network model consisting of an interconnected network of pores with variable connectivities. Correlation equations describing the pore-averaged deposition rate coefficients under unfavorable conditions in a cylindrical pore, developed in our earlier studies, are employed for each pore element. Pore-network simulations are performed for a wide range of parameter values to obtain the breakthrough curves of nanoparticle concentration. The latter is fitted with macroscopic 1-D advection-dispersion equation with a two-site linear reversible deposition accounting for both equilibrium and kinetic sorption. This leads to the estimation of three Darcy-scale deposition coefficients: distribution coefficient, kinetic rate constant, and the fraction of equilibrium sites. The correlation equations for the Darcy-scale deposition coefficients, under unfavorable conditions, are provided as a function of measurable Darcy-scale parameters, including: porosity, mean pore throat radius, mean pore water velocity, nanoparticle radius, ionic strength, dielectric constant, viscosity, temperature, and surface potentials of the particle and grain surfaces. The correlation equations are found to be consistent with the available experimental results, and in qualitative agreement with Colloid Filtration Theory for all parameters, except for the mean pore water velocity and nanoparticle radius.

Microstructure Evolution from X-CT Measurements for Concrete/mortar under Multi-actions of Composite Salts Dry-wet Cycles and Loading

NASA Astrophysics Data System (ADS)

Chen, Yanjuan; Gao, Jianming; Shen, Daman

2017-08-01

Inthis research, microstructure evolution forconcrete/mortar under multi-actions of composite salts dry-wet cycles and loading was investigated through X-CT measurements. The evolution process of pores and micro-cracking with the erosion time were tracked. Compared the different erosion actions, it was found that dry-wet cycles promoted the pores become connected gradually. Besides, the dry-wet cycles accelerated the damage seriously on interface area between concrete and aggregate, whistle, loading contributes to the cracking propagation toward the internal. Moreover, fly ash played a positive role in the increasing of the number of harmless holes again and contributed to the durability of concrete.

Multiscale Pore Throat Network Reconstruction of Tight Porous Media Constrained by Mercury Intrusion Capillary Pressure and Nuclear Magnetic Resonance Measurements

NASA Astrophysics Data System (ADS)

Xu, R.; Prodanovic, M.

2017-12-01

Due to the low porosity and permeability of tight porous media, hydrocarbon productivity strongly depends on the pore structure. Effective characterization of pore/throat sizes and reconstruction of their connectivity in tight porous media remains challenging. Having a representative pore throat network, however, is valuable for calculation of other petrophysical properties such as permeability, which is time-consuming and costly to obtain by experimental measurements. Due to a wide range of length scales encountered, a combination of experimental methods is usually required to obtain a comprehensive picture of the pore-body and pore-throat size distributions. In this work, we combine mercury intrusion capillary pressure (MICP) and nuclear magnetic resonance (NMR) measurements by percolation theory to derive pore-body size distribution, following the work by Daigle et al. (2015). However, in their work, the actual pore-throat sizes and the distribution of coordination numbers are not well-defined. To compensate for that, we build a 3D unstructured two-scale pore throat network model initialized by the measured porosity and the calculated pore-body size distributions, with a tunable pore-throat size and coordination number distribution, which we further determine by matching the capillary pressure vs. saturation curve from MICP measurement, based on the fact that the mercury intrusion process is controlled by both the pore/throat size distributions and the connectivity of the pore system. We validate our model by characterizing several core samples from tight Middle East carbonate, and use the network model to predict the apparent permeability of the samples under single phase fluid flow condition. Results show that the permeability we get is in reasonable agreement with the Coreval experimental measurements. The pore throat network we get can be used to further calculate relative permeability curves and simulate multiphase flow behavior, which will provide valuable insights into the production optimization and enhanced oil recovery design.

Effects of the soil pore network architecture on the soil's physical functionalities

NASA Astrophysics Data System (ADS)

Smet, Sarah; Beckers, Eléonore; Léonard, Angélique; Degré, Aurore

2017-04-01

The soil fluid movement's prediction is of major interest within an agricultural or environmental scope because many processes depend ultimately on the soil fluids dynamic. It is common knowledge that the soil microscopic pore network structure governs the inner-soil convective fluids flow. There isn't, however, a general methodthat consider the pore network structure as a variable in the prediction of thecore scale soil's physical functionalities. There are various possible representations of the microscopic pore network: sample scale averaged structural parameters, extrapolation of theoretic pore network, or use of all the information available by modeling within the observed pore network. Different representations implydifferent analyzing methodologies. To our knowledge, few studies have compared the micro-and macroscopic soil's characteristics for the same soil core sample. The objective of our study is to explore the relationship between macroscopic physical properties and microscopic pore network structure. The saturated hydraulic conductivity, the air permeability, the retention curve, and others classical physical parameters were measured for ten soil samples from an agricultural field. The pore network characteristics were quantified through the analyses of X-ray micro-computed tomographic images(micro-CT system Skyscan-1172) with a voxel size of 22 µm3. Some of the first results confirmed what others studies had reported. Then, the comparison between macroscopic properties and microscopic parameters suggested that the air movements depended mostly on the pore connectivity and tortuosity than on the total porosity volume. We have also found that the fractal dimension calculated from the X-ray images and the fractal dimension calculated from the retention curve were significantly different. Our communication will detailthose results and discuss the methodology: would the results be similar with a different voxel size? What are the calculated and measured parameters uncertainties? Sarah Smet, as a research fellow, acknowledges the support of the National Fund for Scientific Research (Brussels, Belgium).

Fractal Characteristics of the Pore Network in Diatomites Using Mercury Porosimetry and Image Analysis

NASA Astrophysics Data System (ADS)

Stańczak, Grażyna; Rembiś, Marek; Figarska-Warchoł, Beata; Toboła, Tomasz

The complex pore space considerably affects the unique properties of diatomite and its significant potential for many industrial applications. The pore network in the diatomite from the Lower Miocene strata of the Skole nappe (the Jawornik deposit, SE Poland) has been investigated using a fractal approach. The fractal dimension of the pore-space volume was calculated using the Menger sponge as a model of a porous body and the mercury porosimetry data in a pore-throat diameter range between 10,000 and 10 nm. Based on the digital analyses of the two-dimensional images from thin sections taken under a scanning electron microscope at the backscattered electron mode at different magnifications, the authors tried to quantify the pore spaces of the diatomites using the box counting method. The results derived from the analyses of the pore-throat diameter distribution using mercury porosimetry have revealed that the pore space of the diatomite has the bifractal structure in two separated ranges of the pore-throat diameters considerably smaller than the pore-throat sizes corresponding to threshold pressures. Assuming that the fractal dimensions identified for the ranges of the smaller pore-throat diameters characterize the overall pore-throat network in the Jawornik diatomite, we can set apart the distribution of the pore-throat volume (necks) and the pore volume from the distribution of the pore-space volume (pores and necks together).

Controlled nucleation in freeze-drying: effects on pore size in the dried product layer, mass transfer resistance, and primary drying rate.

PubMed

Konstantinidis, Alex K; Kuu, Wei; Otten, Lori; Nail, Steven L; Sever, Robert R

2011-08-01

A novel and scalable method has been developed to enable control of the ice nucleation step for the freezing process during lyophilization. This method manipulates the chamber pressure of the freeze dryer to simultaneously induce nucleation in all product vials at a desired temperature. The effects of controlled nucleation on the drying rate of various formulations including 5% (w/w) mannitol, 5% (w/w) sucrose, and a mixture of 3% (w/w) mannitol and 2% (w/w) sucrose were studied. For a 5% (w/w) mannitol, uncontrolled ice nucleation occurred randomly at product temperatures between -8.0°C and -15.9°C as the vials were cooled to -40°C. Controlled ice nucleation was achieved at product temperatures between -2.3°C and -3.7°C. The effect of nucleation control on the effective pore radius (r(e) ) of the cake was determined from the product temperature profiles using a pore diffusion model in combination with a nonlinear parameter estimation approach reported earlier. Results show that the value of r(e) for 5% (w/w) mannitol was enlarged from 13 to 27 μm by uniformly inducing nucleation at higher temperatures. Applying the resistance parameters obtained from the pore diffusion model for 5% (w/w) mannitol, optimized cycles were theoretically generated and experimentally tested, resulting in a 41% reduction in primary drying time. Copyright © 2011 Wiley-Liss, Inc.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruvinsky, Anatoly M., E-mail: anatoly.ruvinsky@astrazeneca.com; Center for Bioinformatics, The University of Kansas, Lawrence, Kansas 66047; Vakser, Ilya A.

Ferritin-like molecules show a remarkable combination of the evolutionary conserved activity of iron uptake and release that engage different pores in the conserved ferritin shell. It was hypothesized that pore selection and iron traffic depend on dynamic allostery with no conformational changes in the backbone. In this study, we detect the allosteric networks in Pseudomonas aeruginosa bacterioferritin (BfrB), bacterial ferritin (FtnA), and bullfrog M and L ferritins (Ftns) by a network-weaving algorithm (NWA) that passes threads of an allosteric network through highly correlated residues using hierarchical clustering. The residue-residue correlations are calculated in the packing-on elastic network model that introducesmore » atom packing into the common packing-off model. Applying NWA revealed that each of the molecules has an extended allosteric network mostly buried inside the ferritin shell. The structure of the networks is consistent with experimental observations of iron transport: The allosteric networks in BfrB and FtnA connect the ferroxidase center with the 4-fold pores and B-pores, leaving the 3-fold pores unengaged. In contrast, the allosteric network directly links the 3-fold pores with the 4-fold pores in M and L Ftns. The majority of the network residues are either on the inner surface or buried inside the subunit fold or at the subunit interfaces. We hypothesize that the ferritin structures evolved in a way to limit the influence of functionally unrelated events in the cytoplasm on the allosteric network to maintain stability of the translocation mechanisms. We showed that the residue-residue correlations and the resultant long-range cooperativity depend on the ferritin shell packing, which, in turn, depends on protein sequence composition. Switching from the packing-on to the packing-off model reduces correlations by 35%–38% so that no allosteric network can be found. The influence of the side-chain packing on the allosteric networks explains the diversity in mechanisms of iron traffic suggested by experimental approaches.« less

Micro- and nano-X-ray computed-tomography: A step forward in the characterization of the pore network of a leached cement paste

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bossa, Nathan, E-mail: bossanathan@gmail.com; INERIS, Parc Technologique Alata, BP2, 60550 Verneuil-en-Halatte; iCEINT, CNRS, Duke Univ. International Consortium for the Environmental Implications of Nanotechnology, Aix-en-Provence

2015-01-15

Pore structure of leached cement pastes (w/c = 0.5) was studied for the first time from micro-scale down to the nano-scale by combining micro- and nano-X-ray computed tomography (micro- and nano-CT). This allowed assessing the 3D heterogeneity of the pore network along the cement profile (from the core to the altered layer) of almost the entire range of cement pore size, i.e. from capillary to gel pores. We successfully quantified an increase of porosity in the altered layer at both resolutions. Porosity is increasing from 1.8 to 6.1% and from 18 to 58% at the micro-(voxel = 1.81 μm) andmore » nano-scale (voxel = 63.5 nm) respectively. The combination of both CT allowed to circumvent weaknesses inherent of both investigation scales. In addition the connectivity and the channel size of the pore network were also evaluated to obtain a complete 3D pore network characterization at both scales.« less

Impact of pore size variability and network coupling on electrokinetic transport in porous media

NASA Astrophysics Data System (ADS)

Alizadeh, Shima; Bazant, Martin Z.; Mani, Ali

2016-11-01

We have developed and validated an efficient and robust computational model to study the coupled fluid and ion transport through electrokinetic porous media, which are exposed to external gradients of pressure, electric potential, and concentration. In our approach a porous media is modeled as a network of many pores through which the transport is described by the coupled Poisson-Nernst-Planck-Stokes equations. When the pore sizes are random, the interactions between various modes of transport may provoke complexities such as concentration polarization shocks and internal flow circulations. These phenomena impact mixing and transport in various systems including deionization and filtration systems, supercapacitors, and lab-on-a-chip devices. In this work, we present simulations of massive networks of pores and we demonstrate the impact of pore size variation, and pore-pore coupling on the overall electrokinetic transport in porous media.

Assessing the Increase in Specific Surface Area for Electrospun Fibrous Network due to Pore Induction.

PubMed

Katsogiannis, Konstantinos Alexandros G; Vladisavljević, Goran T; Georgiadou, Stella; Rahmani, Ramin

2016-10-26

The effect of pore induction on increasing electrospun fibrous network specific surface area was investigated in this study. Theoretical models based on the available surface area of the fibrous network and exclusion of the surface area lost due to fiber-to-fiber contacts were developed. The models for calculation of the excluded area are based on Hertzian, Derjaguin-Muller-Toporov (DMT), and Johnson-Kendall-Roberts (JKR) contact models. Overall, the theoretical models correlated the network specific surface area to the material properties including density, surface tension, Young's modulus, Poisson's ratio, as well as network physical properties, such as density and geometrical characteristics including fiber radius, fiber aspect ratio and network thickness. Pore induction proved to increase the network specific surface area up to 52%, compared to the maximum surface area that could be achieved by nonporous fiber network with the same physical properties and geometrical characteristics. The model based on Johnson-Kendall-Roberts contact model describes accurately the fiber-to-fiber contact area under the experimental conditions used for pore generation. The experimental results and the theoretical model based on Johnson-Kendall-Roberts contact model show that the increase in network surface area due to pore induction can reach to up to 58%.

High-velocity frictional experiments on dolerite and quartzite under controlled pore pressure

NASA Astrophysics Data System (ADS)

Togo, T.; Shimamoto, T.; Ma, S.

2013-12-01

High-velocity friction experiments on rocks with or without gouge have been conducted mostly under dry conditions and demonstrated dramatic weakening of faults at high velocities (e.g., Di Toro et al., 2011, Nature). Recent experiments under wet conditions (e.g., Ujiie and Tsutsumi, 2010, GRL; Faulkner et al., 2011, GRL) revealed very different behaviors from those of dry faults, but those experiments were done under drained conditions. Experiments with controlled pore pressure Pp are definitely needed to determine mechanical properties of faults under fluid-rich environments such as those in subduction zones. Thus we have developed a pressure vessel that can be attached to our rotary-shear low to high-velocity friction apparatus (Marui Co Ltd., MIS-233-1-76). With a current specimen holder, friction experiments can be done on hollow-cylindrical specimens of 15 and 40 mm in inner and outer diameters, respectively, at controlled Pp to 35 MPa, at effective normal stresses of 3~9 MPa, and at slip rates of 60 mm/year to 2 m/s. An effective normal stress can be applied with a 100 kN hydraulic actuator. We report an outline of the experimental system and preliminary high-velocity experiments on Shanxi dolerite and a quartzite from China that are composed of pyroxene and plagioclase and of almost pure quartz, respectively. High-velocity friction experiments were performed on hollow-cylindrical specimens of Shanxi dolerite at effective normal stresses of 0.13~1.07 MPa and at slip rates of 1, 10, 100 and 1000 mm/sec. All experiments were conducted first with the nitrogen gas filling the pressure vessel (dry tests) and then with a controlled pore-water pressure (wet tests). In the dry tests an axial force was kept at 1 kN and the nitrogen gas pressure was increased in steps to 5 MPa to change an effective normal stress. In the wet tests the specimens were soaked in distilled water in the vessel and Pp was applied by nitrogen gas in a similar manner as in the dry tests. Nitrogen gas acted as buffer to prevent an abrupt changes in the pore-water pressure during experiments. The steady-state friction coefficient (μss) of dry dolerite increased from 0.3~0.35 at 10 mm/s to 0.55~0.8 at 100 mm/s and then decreased down to 0.2~0.6 at 1000 mm/s. The results are quite similar to those of dry granite tested under similar conditions (Reches and Lockner, 2010, Nature). However, the μss of dolerite under a pore-water pressure decreased monotonically from 0.4~0.8 at 1 mm/s to 0.3~0.5 at 1000 mm/s, and the strengthening from 10 to 100 mm/s disappeared with a pore-water pressure. Two experiments were conducted on solid-cylindrical specimens of quartzite at effective normal stresses of 1.39 MPa (a dry test with CO2 gas pressure of 6.22 MPa) and of 0.99 MPa (a wet test with pore-water pressure of 6.1 MPa, also applied with pressurized CO2 gas). In dry and wet tests, the friction coefficient decreases nearly exponentially from about 0.35 at the peak friction to around 0.05 (dry) and 0.03 (wet) at the steady state. A notable difference was that wet quartzite exhibit much more rapid slip weakening with the slip weakening distance Dc of several meters than the dry specimen with Dc of about 15 m. We plan to conduct more experiments with controlled pore-water pressure and to do textural and material analysis of specimens to gain insight on the weakening mechanisms.

Saturation-dependent solute dispersivity in porous media: Pore-scale processes

NASA Astrophysics Data System (ADS)

Raoof, A.; Hassanizadeh, S. M.

2013-04-01

It is known that in variably saturated porous media, dispersion coefficient depends on Darcy velocity and water saturation. In one-dimensional flow, it is commonly assumed that the dispersion coefficient is a linear function of velocity. The coefficient of proportionality, called the dispersivity, is considered to depend on saturation. However, there is not much known about its dependence on saturation. In this study, we investigate, using a pore network model, how the longitudinal dispersivity varies nonlinearly with saturation. We schematize the porous medium as a network of pore bodies and pore throats with finite volumes. The pore space is modeled using the multidirectional pore-network concept, which allows for a distribution of pore coordination numbers. This topological property together with the distribution of pore sizes are used to mimic the microstructure of real porous media. The dispersivity is calculated by solving the mass balance equations for solute concentration in all network elements and averaging the concentrations over a large number of pores. We have introduced a new formulation of solute transport within pore space, where we account for different compartments of residual water within drained pores. This formulation makes it possible to capture the effect of limited mixing due to partial filling of the pores under variably saturated conditions. We found that dispersivity increases with the decrease in saturation, it reaches a maximum value, and then decreases with further decrease in saturation. To show the capability of our formulation to properly capture the effect of saturation on solute dispersion, we applied it to model the results of a reported experimental study.

Generalized network modeling of capillary-dominated two-phase flow

NASA Astrophysics Data System (ADS)

Raeini, Ali Q.; Bijeljic, Branko; Blunt, Martin J.

2018-02-01

We present a generalized network model for simulating capillary-dominated two-phase flow through porous media at the pore scale. Three-dimensional images of the pore space are discretized using a generalized network—described in a companion paper [A. Q. Raeini, B. Bijeljic, and M. J. Blunt, Phys. Rev. E 96, 013312 (2017), 10.1103/PhysRevE.96.013312]—which comprises pores that are divided into smaller elements called half-throats and subsequently into corners. Half-throats define the connectivity of the network at the coarsest level, connecting each pore to half-throats of its neighboring pores from their narrower ends, while corners define the connectivity of pore crevices. The corners are discretized at different levels for accurate calculation of entry pressures, fluid volumes, and flow conductivities that are obtained using direct simulation of flow on the underlying image. This paper discusses the two-phase flow model that is used to compute the averaged flow properties of the generalized network, including relative permeability and capillary pressure. We validate the model using direct finite-volume two-phase flow simulations on synthetic geometries, and then present a comparison of the model predictions with a conventional pore-network model and experimental measurements of relative permeability in the literature.

Confinement of Amorphous Lactose in Pores Formed Upon Co-Spray Drying With Nanoparticles.

PubMed

Hellrup, Joel; Mahlin, Denny

2017-01-01

This study aims at investigating factors influencing humidity-induced recrystallization of amorphous lactose, produced by co-spray drying with particles of cellulose nanocrystals or sodium montmorillonite. In particular, the focus is on how the nanoparticle shape and surface properties influence the nanometer to micrometer length scale nanofiller arrangement in the nanocomposites and how the arrangements influence the mechanisms involved in the inhibition of the amorphous to crystalline transition. The nanocomposites were produced by co-spray drying. Solid-state transformations were analyzed at 60%-94% relative humidity using X-ray powder diffraction, microcalorimetry, and light microscopy. The recrystallization rate constant for the lactose/cellulose nanocrystals and lactose/sodium montmorillonite nanocomposites was lowered at nanofiller contents higher than 60% and was stable for months at 80% nanofiller. The most likely explanation to these results is spontaneous formations of mesoporous particle networks that the lactose is confined upon co-spray drying at high filler content. Compartmentalization and rigidification of the amorphous lactose proved to be less important mechanisms involved in the stabilization of lactose in the nanocomposites. Copyright © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

VISUALIZATION AND SIMULATION OF NON-AQUEOUS PHASE LIQUIDS SOLUBILIZATION IN PORE NETWORKS

EPA Science Inventory

The design of in-situ remediation of contaminated soils is mostly based on a description at the macroscopic scale using a averaged quantities. These cannot address issues at the pore and pore network scales. In this paper, visualization experiments and numerical simulations in ...

Construction of pore network models for Berea and Fontainebleau sandstones using non-linear programing and optimization techniques

NASA Astrophysics Data System (ADS)

Sharqawy, Mostafa H.

2016-12-01

Pore network models (PNM) of Berea and Fontainebleau sandstones were constructed using nonlinear programming (NLP) and optimization methods. The constructed PNMs are considered as a digital representation of the rock samples which were based on matching the macroscopic properties of the porous media and used to conduct fluid transport simulations including single and two-phase flow. The PNMs consisted of cubic networks of randomly distributed pores and throats sizes and with various connectivity levels. The networks were optimized such that the upper and lower bounds of the pore sizes are determined using the capillary tube bundle model and the Nelder-Mead method instead of guessing them, which reduces the optimization computational time significantly. An open-source PNM framework was employed to conduct transport and percolation simulations such as invasion percolation and Darcian flow. The PNM model was subsequently used to compute the macroscopic properties; porosity, absolute permeability, specific surface area, breakthrough capillary pressure, and primary drainage curve. The pore networks were optimized to allow for the simulation results of the macroscopic properties to be in excellent agreement with the experimental measurements. This study demonstrates that non-linear programming and optimization methods provide a promising method for pore network modeling when computed tomography imaging may not be readily available.

Healing kinetics of microneedle-formed pores in PLGA films.

PubMed

Mazzara, J M; Balagna, M A; Thouless, M D; Schwendeman, S P

2013-10-28

The spontaneous healing of aqueous pores in poly(D,L-lactic-co-glycolic acid) (PLGA) drug delivery systems has been identified to play a key role in terminating the burst release of large molecules, and to provide a means for novel aqueous-based microencapsulation. To examine healing of PLGA, pores were created of defined size and depth on the surface of thin PLGA films by stamping with blunt-tip microneedles. Pore dimensions on the micron-scale were relevant to surface pores of common PLGA microspheres and could be easily monitored by light microscopy. Most pores healed reproducibly at temperatures above the glass-transition temperature (T(g)) of the films, with healing times decreasing sharply with increasing temperature according to Williams-Landel-Ferry (WLF) behavior. It is suggested that healing is driven by high surface tension in the films and occurs through viscoelastic creep. Hydrated films healed at lower temperatures than dry films, consistent with a drop in Tg upon polymer hydration. Larger pores took longer to heal than smaller ones, while pores larger than 20 μm did not heal before significant polymer degradation occurred. Films of a less hydrophobic PLGA showed slower healing kinetics, attributed to a weaker surface tension driving force. Deeper pores showed signs of in-plane stress from spin-coating, and either ruptured or only partially healed when incubated wet and dry, respectively. © 2013.

Formation of Molecular Networks: Tailored Quantum Boxes and Behavior of Adsorbed CO in Them

NASA Astrophysics Data System (ADS)

Wyrick, Jon; Sun, Dezheng; Kim, Dae-Ho; Cheng, Zhihai; Lu, Wenhao; Zhu, Yeming; Luo, Miaomiao; Kim, Yong Su; Rotenberg, Eli; Kim, Kwangmoo; Einstein, T. L.; Bartels, Ludwig

2011-03-01

We show that the behavior of CO adsorbed into the pores of large regular networks on Cu(111) is significantly affected by their nano-scale lateral confinement and that formation of the networks themselves is directed by the Shockley surface state. Saturation coverages of CO are found to exhibit persistent dislocation lines; at lower coverages their mobility increases. Individual CO within the pores titrate the surface state, providing crucial information for understanding formation of the network as a result of optimization of the number N of electrons bound within each pore. Determination of N is based on quinone-coverage-dependent UPS data and an analysis of states of particles in a pore-shaped box (verified by CO's titration); a wide range of possible pore shapes and sizes has been considered. Work at UCR supported by NSF CHE 07-49949; at UMD by NSF CHE 07-50334 & UMD NSF-MRSEC DMR 05-20471.

Organic carbon aerogels from the sol-gel polymerization of phenolic-furfural mixtures

DOEpatents

Pekala, R.W.

1998-04-28

The sol-gel polymerization of a phenolic-furfural mixture in dilute solution leads to a highly cross-linked network that can be supercritically dried to form a high surface area foam. These porous materials have cell/pore sizes {<=}1000 {angstrom}, and although they are dark brown in color, they can be classified as a new type of aerogel. The phenolic-furfural aerogel can be pyrolyzed in an inert atmosphere at 1050 C to produce carbon aerogels. This new aerogel may be used for thermal insulation, chromatographic packing, water filtration, ion-exchange, and carbon electrodes for energy storage devices, such as batteries and double-layer capacitors. 8 figs.

Organic carbon aerogels from the sol-gel polymerization of phenolic-furfural mixtures

DOEpatents

Pekala, Richard W.

1998-04-28

The sol-gel polymerization of a phenolic-furfural mixture in dilute solution leads to a highly cross-linked network that can be supercritically dried to form a high surface area foam. These porous materials have cell/pore sizes .ltoreq.1000 .ANG., and although they are dark brown in color, they can be classified as a new type of aerogel. The phenolic-furfural aerogel can be pyrolyzed in an inert atmosphere at 1050.degree. C. to produce carbon aerogels. This new aerogel may be used for thermal insulation, chromatographic packing, water filtration, ion-exchange, and carbon electrodes for energy storage devices, such as batteries and double-layer capacitors.

Organic aerogels from the sol-gel polymerization of phenolic-furfural mixtures

DOEpatents

Pekala, Richard W.

1995-01-01

The sol-gel polymerization of a phenolic-furfural mixture in dilute solution leads to a highly cross-linked network that can be supercritically dried to form a high surface area foam. These porous materials have cell/pore sizes.ltoreq.1000.ANG., and although they are dark brown in color, they can be classified as a new type of aerogel. The phenolic-furfural aerogel can be pyrolyzed in an inert atmosphere at 1050.degree. C. to produce carbon aerogels. This new aerogel may be used for thermal insulation, chromatographic packing, water filtration, ion-exchange, and carbon electrodes for energy storage devices, such as batteries and double-layer capacitors.

Organic aerogels from the sol-gel polymerization of phenolic-furfural mixtures

DOEpatents

Pekala, R.W.

1995-12-19

The sol-gel polymerization of a phenolic-furfural mixture in dilute solution leads to a highly cross-linked network that can be supercritically dried to form a high surface area foam. These porous materials have cell/pore sizes{<=}1000{angstrom}, and although they are dark brown in color, they can be classified as a new type of aerogel. The phenolic-furfural aerogel can be pyrolyzed in an inert atmosphere at 1050 C to produce carbon aerogels. This new aerogel may be used for thermal insulation, chromatographic packing, water filtration, ion-exchange, and carbon electrodes for energy storage devices, such as batteries and double-layer capacitors. 8 figs.

Organic aerogels from the sol-gel polymerization of phenolic-furfural mixtures

DOEpatents

Pekala, Richard W.

1996-01-01

The sol-gel polymerization of a phenolic-furfural mixture in dilute solution leads to a highly cross-linked network that can be supercritically dried to form a high surface area foam. These porous materials have cell/pore sizes .ltoreq.1000.ANG., and although they are dark brown in color, they can be classified as a new type of aerogel. The phenolic-furfural aerogel can be pyrolyzed in an inert atmosphere at 1050.degree. C. to produce carbon aerogels. This new aerogel may be used for thermal insulation, chromatographic packing, water filtration, ion-exchange, and carbon electrodes for energy storage devices, such as batteries and double-layer capacitors.

Evaluating the hydraulic and transport properties of peat soil using pore network modeling and X-ray micro computed tomography

NASA Astrophysics Data System (ADS)

Gharedaghloo, Behrad; Price, Jonathan S.; Rezanezhad, Fereidoun; Quinton, William L.

2018-06-01

Micro-scale properties of peat pore space and their influence on hydraulic and transport properties of peat soils have been given little attention so far. Characterizing the variation of these properties in a peat profile can increase our knowledge on the processes controlling contaminant transport through peatlands. As opposed to the common macro-scale (or bulk) representation of groundwater flow and transport processes, a pore network model (PNM) simulates flow and transport processes within individual pores. Here, a pore network modeling code capable of simulating advective and diffusive transport processes through a 3D unstructured pore network was developed; its predictive performance was evaluated by comparing its results to empirical values and to the results of computational fluid dynamics (CFD) simulations. This is the first time that peat pore networks have been extracted from X-ray micro-computed tomography (μCT) images of peat deposits and peat pore characteristics evaluated in a 3D approach. Water flow and solute transport were modeled in the unstructured pore networks mapped directly from μCT images. The modeling results were processed to determine the bulk properties of peat deposits. Results portray the commonly observed decrease in hydraulic conductivity with depth, which was attributed to the reduction of pore radius and increase in pore tortuosity. The increase in pore tortuosity with depth was associated with more decomposed peat soil and decreasing pore coordination number with depth, which extended the flow path of fluid particles. Results also revealed that hydraulic conductivity is isotropic locally, but becomes anisotropic after upscaling to core-scale; this suggests the anisotropy of peat hydraulic conductivity observed in core-scale and field-scale is due to the strong heterogeneity in the vertical dimension that is imposed by the layered structure of peat soils. Transport simulations revealed that for a given solute, the effective diffusion coefficient decreases with depth due to the corresponding increase of diffusional tortuosity. Longitudinal dispersivity of peat also was computed by analyzing advective-dominant transport simulations that showed peat dispersivity is similar to the empirical values reported in the same peat soil; it is not sensitive to soil depth and does not vary much along the soil profile.

Investigating the relative permeability behavior of microporosity-rich carbonates and tight sandstones with multiscale pore network models

NASA Astrophysics Data System (ADS)

Bultreys, Tom; Stappen, Jeroen Van; Kock, Tim De; Boever, Wesley De; Boone, Marijn A.; Hoorebeke, Luc Van; Cnudde, Veerle

2016-11-01

The relative permeability behavior of rocks with wide ranges of pore sizes is in many cases still poorly understood and is difficult to model at the pore scale. In this work, we investigate the capillary pressure and relative permeability behavior of three outcrop carbonates and two tight reservoir sandstones with wide, multimodal pore size distributions. To examine how the drainage and imbibition properties of these complex rock types are influenced by the connectivity of macropores to each other and to zones with unresolved small-scale porosity, we apply a previously presented microcomputed-tomography-based multiscale pore network model to these samples. The sensitivity to the properties of the small-scale porosity is studied by performing simulations with different artificial sphere-packing-based networks as a proxy for these pores. Finally, the mixed-wet water-flooding behavior of the samples is investigated, assuming different wettability distributions for the microporosity and macroporosity. While this work is not an attempt to perform predictive modeling, it seeks to qualitatively explain the behavior of the investigated samples and illustrates some of the most recent developments in multiscale pore network modeling.

Pore-scale dynamics of salt transport and distribution in drying porous media

NASA Astrophysics Data System (ADS)

Shokri, Nima

2014-01-01

Understanding the physics of water evaporation from saline porous media is important in many natural and engineering applications such as durability of building materials and preservation of monuments, water quality, and mineral-fluid interactions. We applied synchrotron x-ray micro-tomography to investigate the pore-scale dynamics of dissolved salt distribution in a three dimensional drying saline porous media using a cylindrical plastic column (15 mm in height and 8 mm in diameter) packed with sand particles saturated with CaI2 solution (5% concentration by mass) with a spatial and temporal resolution of 12 μm and 30 min, respectively. Every time the drying sand column was set to be imaged, two different images were recorded using distinct synchrotron x-rays energies immediately above and below the K-edge value of Iodine. Taking the difference between pixel gray values enabled us to delineate the spatial and temporal distribution of CaI2 concentration at pore scale. Results indicate that during early stages of evaporation, air preferentially invades large pores at the surface while finer pores remain saturated and connected to the wet zone at bottom via capillary-induced liquid flow acting as evaporating spots. Consequently, the salt concentration increases preferentially in finer pores where evaporation occurs. Higher salt concentration was observed close to the evaporating surface indicating a convection-driven process. The obtained salt profiles were used to evaluate the numerical solution of the convection-diffusion equation (CDE). Results show that the macro-scale CDE could capture the overall trend of the measured salt profiles but fail to produce the exact slope of the profiles. Our results shed new insight on the physics of salt transport and its complex dynamics in drying porous media and establish synchrotron x-ray tomography as an effective tool to investigate the dynamics of salt transport in porous media at high spatial and temporal resolution.

Pore-scale dynamics of salt transport and distribution in drying porous media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shokri, Nima, E-mail: nima.shokri@manchester.ac.uk

2014-01-15

Understanding the physics of water evaporation from saline porous media is important in many natural and engineering applications such as durability of building materials and preservation of monuments, water quality, and mineral-fluid interactions. We applied synchrotron x-ray micro-tomography to investigate the pore-scale dynamics of dissolved salt distribution in a three dimensional drying saline porous media using a cylindrical plastic column (15 mm in height and 8 mm in diameter) packed with sand particles saturated with CaI{sub 2} solution (5% concentration by mass) with a spatial and temporal resolution of 12 μm and 30 min, respectively. Every time the drying sandmore » column was set to be imaged, two different images were recorded using distinct synchrotron x-rays energies immediately above and below the K-edge value of Iodine. Taking the difference between pixel gray values enabled us to delineate the spatial and temporal distribution of CaI{sub 2} concentration at pore scale. Results indicate that during early stages of evaporation, air preferentially invades large pores at the surface while finer pores remain saturated and connected to the wet zone at bottom via capillary-induced liquid flow acting as evaporating spots. Consequently, the salt concentration increases preferentially in finer pores where evaporation occurs. Higher salt concentration was observed close to the evaporating surface indicating a convection-driven process. The obtained salt profiles were used to evaluate the numerical solution of the convection-diffusion equation (CDE). Results show that the macro-scale CDE could capture the overall trend of the measured salt profiles but fail to produce the exact slope of the profiles. Our results shed new insight on the physics of salt transport and its complex dynamics in drying porous media and establish synchrotron x-ray tomography as an effective tool to investigate the dynamics of salt transport in porous media at high spatial and temporal resolution.« less

Detecting Pore Fluid Pressure Changes by Using the Vp/Vs Ratio

NASA Astrophysics Data System (ADS)

Vanorio, T.; Mavko, G.

2006-12-01

A central problem in studies aimed at predicting the dynamic behavior of faults is monitoring and quantifying fluid changes in areas prone to overpressure. Experimental and modeling studies show the Vp/Vs ratio to be a good determinant of the saturation state of a rock formation as well as of its inner pore pressure condition. Dectecting pore pressure changes depends, among other causes, on the reliability of laboratory data to calibrate the in-situ measured velocities. Ideally, laboratory experiments performed under controlled conditions would identify the fundamental mechanisms responsible for changes in the measured acoustic properties. However, technical limitations in the laboratory together with the assumptions driving the experimental and modeling approaches rise spouriuos mechanisms which hinder our present understanding of the actual role of high pore pressure on the elastic and poroelastic parameters. Critical issues unclude: a) the frequencies used in the laboratory are responsible for high-frequency fluid effects which induce velocity dispersion. As a result, both the effective stress parameter and velocities (and their pressure-dependence) estimated from high- frequency ultrasonic data are different from those applicable to crustal low frequency wave propagation; b) laboratory measurements made at dry, drained conditions are assumed to mimic those in gas pressured rocks. However, in dry, drained conditions, no pore pressure is exerted in the pore space, and the pore gas is infinitely compressible; c) when using room-dry, drained measurements as the baseline to model pressured rock formations, the unloading path (i.e. decreasing confining pressure) is supposed to mimic the inflationary path due to pore pressure increase. Doing so, it is assumed that the amount of crack opening due to pore pressure is equal to that of crack closure caused by the overburden stress and thus, the effective stress coefficient is implicitely assumed equal to 1. To minimize the assumptions and limitations described above, we designed a laboratory experiment which used gas as pore fluid medium. Experimental results show that in gas-pressured saturated rocks the Vp/Vs ratio, while remaining lower than values reported for liquid saturation conditions, increases with decreasing differential pressure, similarly to the trend observed in liquid saturated rocks.

A Collaborative US/UK Research Program in Advanced Silica Macromolecular Micro-Optics

DTIC Science & Technology

1990-04-30

is present at the drying temperatures used here then it must be taken into account in determining the true hydraulic radius of the pores. This bound...drying, especially when one includes the effects of a bound water layer on effective evaporation area and the hydraulic radius of the pores. This...f1 ____ 1 , rJm2 ___ __ ____ _______ ______ 1 ,’ ___ ___ _: _ _ _ _’ / I N I _ _ _ I ____.1 0Ŗ 03 L] 05 Figure 2a disft~rre cross frack /m I I E 600

Ion-Exchangeable Molybdenum Sulfide Porous Chalcogel: Gas Adsorption and Capture of Iodine and Mercury.

PubMed

Subrahmanyam, Kota S; Malliakas, Christos D; Sarma, Debajit; Armatas, Gerasimos S; Wu, Jinsong; Kanatzidis, Mercouri G

2015-11-04

We report the synthesis of ion-exchangeable molybdenum sulfide chalcogel through an oxidative coupling process, using (NH4)2MoS4 and iodine. After supercritical drying, the MoS(x) amorphous aerogel shows a large surface area up to 370 m(2)/g with a broad range of pore sizes. X-ray photoelectron spectroscopic and pair distribution function analyses reveal that Mo(6+) species undergo reduction during network assembly to produce Mo(4+)-containing species where the chalcogel network consists of [Mo3S13] building blocks comprising triangular Mo metal clusters and S2(2-) units. The optical band gap of the brown-black chalcogel is ∼1.36 eV. The ammonium sites present in the molybdenum sulfide chalcogel network are ion-exchangeable with K(+) and Cs(+) ions. The molybdenum sulfide aerogel exhibits high adsorption selectivities for CO2 and C2H6 over H2 and CH4. The aerogel also possesses high affinity for iodine and mercury.

Pore-scale modeling of capillary trapping in water-wet porous media: A new cooperative pore-body filling model

NASA Astrophysics Data System (ADS)

Ruspini, L. C.; Farokhpoor, R.; Øren, P. E.

2017-10-01

We present a pore-network model study of capillary trapping in water-wet porous media. The amount and distribution of trapped non-wetting phase is determined by the competition between two trapping mechanisms - snap-off and cooperative pore-body filling. We develop a new model to describe the pore-body filling mechanism in geologically realistic pore-networks. The model accounts for the geometrical characteristics of the pore, the spatial location of the connecting throats and the local fluid topology at the time of the displacement. We validate the model by comparing computed capillary trapping curves with published data for four different water-wet rocks. Computations are performed on pore-networks extracted from micro-CT images and process-based reconstructions of the actual rocks used in the experiments. Compared with commonly used stochastic models, the new model describes more accurately the experimental measurements, especially for well connected porous systems where trapping is controlled by subtleties of the pore structure. The new model successfully predicts relative permeabilities and residual saturation for Bentheimer sandstone using in-situ measured contact angles as input to the simulations. The simulated trapped cluster size distributions are compared with predictions from percolation theory.

Capillary filling rules and displacement mechanisms for spontaneous imbibition of CO2 for carbon storage and EOR using micro-model experiments and pore scale simulation

NASA Astrophysics Data System (ADS)

Chapman, E.; Yang, J.; Crawshaw, J.; Boek, E. S.

2012-04-01

In the 1980s, Lenormand et al. carried out their pioneering work on displacement mechanisms of fluids in etched networks [1]. Here we further examine displacement mechanisms in relation to capillary filling rules for spontaneous imbibition. Understanding the role of spontaneous imbibition in fluid displacement is essential for refining pore network models. Generally, pore network models use simple capillary filling rules and here we examine the validity of these rules for spontaneous imbibition. Improvement of pore network models is vital for the process of 'up-scaling' to the field scale for both enhanced oil recovery (EOR) and carbon sequestration. In this work, we present our experimental microfluidic research into the displacement of both supercritical CO2/deionised water (DI) systems and analogous n-decane/air - where supercritical CO2 and n-decane are the respective wetting fluids - controlled by imbibition at the pore scale. We conducted our experiments in etched PMMA and silicon/glass micro-fluidic hydrophobic chips. We first investigate displacement in single etched pore junctions, followed by displacement in complex network designs representing actual rock thin sections, i.e. Berea sandstone and Sucrosic dolomite. The n-decane/air experiments were conducted under ambient conditions, whereas the supercritical CO2/DI water experiments were conducted under high temperature and pressure in order to replicate reservoir conditions. Fluid displacement in all experiments was captured via a high speed video microscope. The direction and type of displacement the imbibing fluid takes when it enters a junction is dependent on the number of possible channels in which the wetting fluid can imbibe, i.e. I1, I2 and I3 [1]. Depending on the experiment conducted, the micro-models were initially filled with either DI water or air before the wetting fluid was injected. We found that the imbibition of the wetting fluid through a single pore is primarily controlled by the geometry of the pore body rather than the downstream pore throat sizes, contrary to the established capillary filling rules as used in current pore network models. Our experimental observations are confirmed by detailed lattice-Boltzmann pore scale computer simulations of fluid displacement in the same geometries. This suggests that capillary filling rules for imbibition as used in pore network models may need to be revised. [1] G. Lenormand, C. Zarcone and A. Sarr, J. Fluid Mech. 135 , 337-353 (1983).

Morphology of the pore space in claystones - evidence from BIB/FIB ion beam sectioning and cryo-SEM observations

NASA Astrophysics Data System (ADS)

Desbois, G.; Urai, J. L.; Kukla, P. A.

2009-12-01

Mudrocks and clay-rich fault gouges are important mechanical elements in the Earth’s crust and form seals for crustal fluids such as groundwater and hydrocarbons. Other fields of interest are the storage of anthropogenic carbon dioxide and radioactive waste in geologic formations. In addition, coupled flows, capillary processes, and associated deformation are of importance in many applied fields. A key factor to understanding these processes is a detailed understanding of the morphology of the pore space. Classic studies of porosity in fine grained materials are performed on dried or freeze dried samples and include metal injection methods, magnetic susceptibility measurement, SEM and TEM imaging, neutron scattering, NMR spectroscopy, and ESEM. Confocal microscopy and X-ray tomography are used to image porosity in coarse grained sediments but the resolution of these techniques is not sufficient at present for applications to mudrocks or clay-rich fault gouges. Therefore, observations and interpretations remain difficult because none of these approaches is able to directly describe the in-situ porosity at the pore scale. In addition, some methods require dried samples in which the natural structure of pores may have been damaged to some extent due to desiccation and dehydration of the clay minerals. A recently developed alternative is to study wet samples using a cryo-SEM, which allows stabilization of wet media at cryo-temperature, in-situ sample preparation by ion beam cross-sectioning (BIB, FIB) and observations of the stabilized microstructure at high resolution. We report on a study of Boom clay from a proposed disposal site of radioactive waste (Mol site, Belgium) using cryo-SEM at cryogenic temperature, with ion beam cross-sectioning to prepare smooth, damage free surfaces. Pores commonly have crack-like tips, preferred orientation parallel to bedding and power law size distribution. We define a number of pore types depending on shape and location in the microstructure. 3-D reconstruction by serial cross-sectioning shows 3-D connectivity of the pore space. These findings offer a new insight into the morphology of pores down to nano-scale and provide the basis for microstructure-based models of transport in clays. SEM image (SE) of a Broad Ion Beam polished cross-section performed on dry Boom clay (Mol site, Belgium) showing the 2D apparent porosity (26.3%). The cross-section is perpendicular to the bedding.

Molecular Dynamic Simulation of Water Vapor and Determination of Diffusion Characteristics in the Pore

NASA Astrophysics Data System (ADS)

Nikonov, Eduard G.; Pavluš, Miron; Popovičová, Mária

2018-02-01

One of the varieties of pores, often found in natural or artificial building materials, are the so-called blind pores of dead-end or saccate type. Three-dimensional model of such kind of pore has been developed in this work. This model has been used for simulation of water vapor interaction with individual pore by molecular dynamics in combination with the diffusion equation method. Special investigations have been done to find dependencies between thermostats implementations and conservation of thermodynamic and statistical values of water vapor - pore system. The two types of evolution of water - pore system have been investigated: drying and wetting of the pore. Full research of diffusion coefficient, diffusion velocity and other diffusion parameters has been made.

Fiber optic sensor and method for making

DOEpatents

Vartuli, James Scott; Bousman, Kenneth Sherwood; Deng, Kung-Li; McEvoy, Kevin Paul; Xia, Hua

2010-05-18

A fiber optic sensor including a fiber having a modified surface integral with the fiber wherein the modified surface includes an open pore network with optical agents dispersed within the open pores of the open pore network. Methods for preparing the fiber optic sensor are also provided. The fiber optic sensors can withstand high temperatures and harsh environments.

Effect of whey protein isolate and β-cyclodextrin wall systems on stability of microencapsulated vanillin by spray-freeze drying method.

PubMed

Hundre, Swetank Y; Karthik, P; Anandharamakrishnan, C

2015-05-01

Vanillin flavour is highly volatile in nature and due to that application in food incorporation is limited; hence microencapsulation of vanillin is an ideal technique to increase its stability and functionality. In this study, vanillin was microencapsulated for the first time by non-thermal spray-freeze-drying (SFD) technique and its stability was compared with other conventional techniques such as spray drying (SD) and freeze-drying (FD). Different wall materials like β-cyclodextrin (β-cyd), whey protein isolate (WPI) and combinations of these wall materials (β-cyd + WPI) were used to encapsulate vanillin. SFD microencapsulated vanillin with WPI showed spherical shape with numerous fine pores on the surface, which in turn exhibited good rehydration ability. On the other hand, SD powder depicted spherical shape without pores and FD encapsulated powder yielded larger particle sizes with flaky structure. FTIR analysis confirmed that there was no interaction between vanillin and wall materials. Moreover, spray-freeze-dried vanillin + WPI sample exhibited better thermal stability than spray dried and freeze-dried microencapsulated samples. Copyright © 2014 Elsevier Ltd. All rights reserved.

Structural characteristics of gels prepared from sonohydrolysis and conventional hydrolysis of TEOS: an emphasis on the mass fractal as determined from the pore size distribution

NASA Astrophysics Data System (ADS)

Vollet, D. R.; Torres, R. R.; Donatti, D. A.; Ibañez Ruiz, A.

2005-11-01

Silica gels were preparated from fixed proportion mixtures of tetraethoxysilane, water and hydrocloric acid, using either ultrasound stimulation (US) or conventional method (CO) in the hydrolysis step of the process. Wet gels were obtained with the same silica volume concentration and density. According to small-angle X-ray scattering, the structure of the wet gels can be described as mass fractal structures with mass fractal dimension D = 2.20 in a length scale = 7.9 nm, in the case of wet gels US, and D = 2.26 in a length scale = 6.9 nm, in the case of wet gels CO. The mass fractal characteristics of the wet gels US and CO account for the different structures evolved in the drying of the gels US and CO in the obtaining of xerogels and aerogels. The pore structure of the dried gels was studied by nitrogen adsorption as a function of the temperature. Aerogels (US and CO) present high porosity with pore size distribution (PSD) curves in the mesopore region while xerogels (US and CO) present minor porosity with PSD curves mainly in the micropore region. The dried gels US (aerogels and xerogels) generally present pore volume and specific surface area greater than the dried gels CO. The mass fractal structure of the aerogels has been studied from an approach based on the PSD curves exclusively.

The effect of carbon type on arsenic and trichloroethylene removal capabilities of iron (hydr)oxide nanoparticle-impregnated granulated activated carbons.

PubMed

Cooper, Anne Marie; Hristovski, Kiril D; Möller, Teresia; Westerhoff, Paul; Sylvester, Paul

2010-11-15

This study investigates the impact of the type of virgin granular activated carbon (GAC) media used to synthesize iron (hydr)oxide nanoparticle-impregnated granular activated carbon (Fe-GAC) on its properties and its ability to remove arsenate and organic trichloroethylene (TCE) from water. Two Fe-GAC media were synthesized via a permanganate/ferrous ion synthesis method using bituminous and lignite-based virgin GAC. Data obtained from an array of characterization techniques (pore size distribution, surface charge, etc.) in correlation with batch equilibrium tests, and continuous flow modeling suggested that GAC type and pore size distribution control the iron (nanoparticle) contents, Fe-GAC synthesis mechanisms, and contaminant removal performances. Pore surface diffusion model calculations predicted that lignite Fe-GAC could remove ∼6.3 L g(-1) dry media and ∼4 L g(-1) dry media of water contaminated with 30 μg L(-1) TCE and arsenic, respectively. In contrast, the bituminous Fe-GAC could remove only ∼0.2 L/g dry media for TCE and ∼2.8 L/g dry media for As of the same contaminated water. The results show that arsenic removal capability is increased while TCE removal is decreased as a result of Fe nanoparticle impregnation. This tradeoff is related to several factors, of which changes in surface properties and pore size distributions appeared to be the most dominant. Copyright © 2010 Elsevier B.V. All rights reserved.

Effect of cryoprotectants on the porosity and stability of insulin-loaded PLGA nanoparticles after freeze-drying

PubMed Central

Fonte, Pedro; Soares, Sandra; Costa, Ana; Andrade, José Carlos; Seabra, Vítor; Reis, Salette; Sarmento, Bruno

2012-01-01

PLGA nanoparticles are useful to protect and deliver proteins in a localized or targeted manner, with a long-term systemic delivery pattern intended to last for a period of time, depending on polymer bioerosion and biodegradability. However, the principal concern regarding these carriers is the hydrolytic instability of polymer in aqueous suspension. Freeze-drying is a commonly used method to stabilize nanoparticles, and cryoprotectants may be also used, to even increase its physical stability. The aim of the present work was to analyze the influence of cryoprotectants on nanoparticle stability and porosity after freeze-drying, which may influence protein release and stability. It was verified that freeze-drying significantly increased the number of pores on PLGA-NP surface, being more evident when cryoprotectants are added. The presence of pores is important in a lyophilizate to facilitate its reconstitution in water, although this may have consequences to protein release and stability. The release profile of insulin encapsulated into PLGA-NP showed an initial burst in the first 2 h and a sustained release up to 48 h. After nanoparticles freeze-drying the insulin release increased about 18% in the first 2 h due to the formation of pores, maintaining a sustained release during time. After freeze-drying with cryoprotectants, the amount of insulin released was higher for trehalose and lower for sucrose, glucose, fructose and sorbitol comparatively to freeze-dried PLGA-NP with no cryoprotectant added. Besides the porosity, the ability of cryoprotectants to be adsorbed on the nanoparticles surface may also play an important role on insulin release and stability. PMID:23507897

Multiphase flow predictions from carbonate pore space images using extracted network models

NASA Astrophysics Data System (ADS)

Al-Kharusi, Anwar S.; Blunt, Martin J.

2008-06-01

A methodology to extract networks from pore space images is used to make predictions of multiphase transport properties for subsurface carbonate samples. The extraction of the network model is based on the computation of the location and sizes of pores and throats to create a topological representation of the void space of three-dimensional (3-D) rock images, using the concept of maximal balls. In this work, we follow a multistaged workflow. We start with a 2-D thin-section image; convert it statistically into a 3-D representation of the pore space; extract a network model from this image; and finally, simulate primary drainage, waterflooding, and secondary drainage flow processes using a pore-scale simulator. We test this workflow for a reservoir carbonate rock. The network-predicted absolute permeability is similar to the core plug measured value and the value computed on the 3-D void space image using the lattice Boltzmann method. The predicted capillary pressure during primary drainage agrees well with a mercury-air experiment on a core sample, indicating that we have an adequate representation of the rock's pore structure. We adjust the contact angles in the network to match the measured waterflood and secondary drainage capillary pressures. We infer a significant degree of contact angle hysteresis. We then predict relative permeabilities for primary drainage, waterflooding, and secondary drainage that agree well with laboratory measured values. This approach can be used to predict multiphase transport properties when wettability and pore structure vary in a reservoir, where experimental data is scant or missing. There are shortfalls to this approach, however. We compare results from three networks, one of which was derived from a section of the rock containing vugs. Our method fails to predict properties reliably when an unrepresentative image is processed to construct the 3-D network model. This occurs when the image volume is not sufficient to represent the geological variations observed in a core plug sample.

Characterizing particle-scale equilibrium adsorption and kinetics of uranium(VI) desorption from U-contaminated sediments

USGS Publications Warehouse

Stoliker, Deborah L.; Liu, Chongxuan; Kent, Douglas B.; Zachara, John M.

2013-01-01

Rates of U(VI) release from individual dry-sieved size fractions of a field-aggregated, field-contaminated composite sediment from the seasonally saturated lower vadose zone of the Hanford 300-Area were examined in flow-through reactors to maintain quasi-constant chemical conditions. The principal source of variability in equilibrium U(VI) adsorption properties of the various size fractions was the impact of variable chemistry on adsorption. This source of variability was represented using surface complexation models (SCMs) with different stoichiometric coefficients with respect to hydrogen ion and carbonate concentrations for the different size fractions. A reactive transport model incorporating equilibrium expressions for cation exchange and calcite dissolution, along with rate expressions for aerobic respiration and silica dissolution, described the temporal evolution of solute concentrations observed during the flow-through reactor experiments. Kinetic U(VI) desorption was well described using a multirate SCM with an assumed lognormal distribution for the mass-transfer rate coefficients. The estimated mean and standard deviation of the rate coefficients were the same for all <2 mm size fractions but differed for the 2–8 mm size fraction. Micropore volumes, assessed using t-plots to analyze N2 desorption data, were also the same for all dry-sieved <2 mm size fractions, indicating a link between micropore volumes and mass-transfer rate properties. Pore volumes for dry-sieved size fractions exceeded values for the corresponding wet-sieved fractions. We hypothesize that repeated field wetting and drying cycles lead to the formation of aggregates and/or coatings containing (micro)pore networks which provided an additional mass-transfer resistance over that associated with individual particles. The 2–8 mm fraction exhibited a larger average and standard deviation in the distribution of mass-transfer rate coefficients, possibly caused by the abundance of microporous basaltic rock fragments.

Modeling Mass and Thermal Transport in Thin Porous Media of PEM Fuel Cells

NASA Astrophysics Data System (ADS)

Konduru, Vinaykumar

Water transport in the Porous Transport Layer (PTL) plays an important role in the efficient operation of polymer electrolyte membrane fuel cells (PEMFC). Excessive water content as well as dry operating conditions are unfavorable for efficient and reliable operation of the fuel cell. The effect of thermal conductivity and porosity on water management are investigated by simulating two-phase flow in the PTL of the fuel cell using a network model. In the model, the PTL consists of a pore-phase and a solid-phase. Different models of the PTLs are generated using independent Weibull distributions for the pore-phase and the solid-phase. The specific arrangement of the pores and solid elements is varied to obtain different PTL realizations for the same Weibull parameters. The properties of PTL are varied by changing the porosity and thermal conductivity. The parameters affecting operating conditions include the temperature, relative humidity in the flow channel and voltage and current density. In addition, a novel high-speed capable Surface Plasmon Resonance (SPR) microscope was built based on Kretschmann's configuration utilizing a collimated Kohler illumination. The SPR allows thin film characterization in a thickness of approximately 0-200nm by measuring the changes in the refractive index. Various independent experiments were run to measure film thickness during droplet coalescence during condensation.

A kinetic Monte Carlo approach to study fluid transport in pore networks

NASA Astrophysics Data System (ADS)

Apostolopoulou, M.; Day, R.; Hull, R.; Stamatakis, M.; Striolo, A.

2017-10-01

The mechanism of fluid migration in porous networks continues to attract great interest. Darcy's law (phenomenological continuum theory), which is often used to describe macroscopically fluid flow through a porous material, is thought to fail in nano-channels. Transport through heterogeneous and anisotropic systems, characterized by a broad distribution of pores, occurs via a contribution of different transport mechanisms, all of which need to be accounted for. The situation is likely more complicated when immiscible fluid mixtures are present. To generalize the study of fluid transport through a porous network, we developed a stochastic kinetic Monte Carlo (KMC) model. In our lattice model, the pore network is represented as a set of connected finite volumes (voxels), and transport is simulated as a random walk of molecules, which "hop" from voxel to voxel. We simulated fluid transport along an effectively 1D pore and we compared the results to those expected by solving analytically the diffusion equation. The KMC model was then implemented to quantify the transport of methane through hydrated micropores, in which case atomistic molecular dynamic simulation results were reproduced. The model was then used to study flow through pore networks, where it was able to quantify the effect of the pore length and the effect of the network's connectivity. The results are consistent with experiments but also provide additional physical insights. Extension of the model will be useful to better understand fluid transport in shale rocks.

Percolation Network Study on the Gas Apparent Permeability of Rock

NASA Astrophysics Data System (ADS)

Wang, Y.; Tang, Y. B.; Li, M.

2017-12-01

We modeled the gas single phase transport behaviors of monomodal porous media using percolation networks. Different from the liquid absolute permeability, which is only related to topology and morphology of pore space, the gas permeability depends on pore pressure as well. A published gas flow conductance model, included usual viscous flow, slip flow and Knudsen diffusion in cylinder pipe, was used to simulated gas flow in 3D, simple cubic, body-center cubic and face-center cubic networks with different hydraulic radius, different coordination number, and different pipe radius distributions under different average pore pressure. The simulation results showed that the gas apparent permeability kapp obey the `universal' scaling law (independence of network lattices), kapp (z-zc)β, where exponent β is related to pore radius distribution, z is coordination number and zc=1.5. Following up on Bernabé et al.'s (2010) study of the effects of pore connectivity and pore size heterogeneity on liquid absolute permeability, gas apparent permeability kapp model and a new joint gas-liquid permeability (i.e., kapp/k∞) model, which could explain the Klinkenberg phenomenon, were proposed. We satisfactorily tested the models by comparison with published experimental data on glass beads and other datasets.

Influence of Rubber Size on Properties of Crumb Rubber Mortars

PubMed Central

Yu, Yong; Zhu, Han

2016-01-01

Studies on the properties and applications of rubber cement-based materials are well documented. The sizes of rubbers used in these materials varied. However, information about the effects of rubber size on the properties of rubber cement-based materials, especially pore structure, mechanical strengths, and drying shrinkage properties, remains limited. Three groups of rubber with major particle sizes of 2–4 mm, 1–3 mm, and 0–2 mm were selected in this study. This paper presents experimental studies on the effects of rubber size on the consistency, fresh density, pore structure, mechanical properties, and drying shrinkage properties of crumb rubber mortars (CRMs). Results demonstrated that the consistency and fresh density of CRMs decreased with the rubber size. As to the pore structure, the total pore volume increased with the decrease of the rubber size. By contrast, the influence of the rubber size on the mesopore (<50 nm) volume is not as significant as that of the rubber content. The mechanical properties of CRMs decreased with the rubber size. Low rubber stiffness and large pore volumes, especially those of small sized rubbers, contribute to the reduction of CRMs strength. The drying shrinkage of CRM increases as the rubber size decreases. The influences of rubber size on capillary tension are not significant. Thus, the shrinkage increases with the decrease of rubber size mainly because of its function in the deformation modulus reduction of CRMs. PMID:28773649

Silk fibroin nanostructured materials for biomedical applications

NASA Astrophysics Data System (ADS)

Mitropoulos, Alexander N.

Nanostructured biopolymers have proven to be promising to develop novel biomedical applications where forming structures at the nanoscale normally occurs by self-assembly. However, synthesizing these structures can also occur by inducing materials to transition into other forms by adding chemical cross-linkers, changing pH, or changing ionic composition. Understanding the generation of nanostructures in fluid environments, such as liquid organic solvents or supercritical fluids, has not been thoroughly examined, particularly those that are based on protein-based block-copolymers. Here, we examine the transformation of reconstituted silk fibroin, which has emerged as a promising biopolymer due to its biocompatibility, biodegradability, and ease of functionalization, into submicron spheres and gel networks which offer applications in tissue engineering and advanced sensors. Two types of gel networks, hydrogels and aerogels, have small pores and large surface areas that are defined by their structure. We design and analyze silk nanoparticle formation using a microfluidic device while offering an application for drug delivery. Additionally, we provide a model and characterize hydrogel formation from micelles to nanoparticles, while investigating cellular response to the hydrogel in an in vitro cell culture model. Lastly, we provide a second model of nanofiber formation during near-critical and supercritical drying and characterize the silk fibroin properties at different drying pressures which, when acting as a stabilizing matrix, shows to improve the activity of entrapped enzymes dried at different pressures. This work has created new nanostructured silk fibroin forms to benefit biomedical applications that could be applied to other fibrous proteins.

Assessment of critical path analyses of the relationship between permeability and electrical conductivity of pore networks

NASA Astrophysics Data System (ADS)

Skaggs, Todd H.

2011-10-01

Critical path analysis (CPA) is a method for estimating macroscopic transport coefficients of heterogeneous materials that are highly disordered at the micro-scale. Developed originally to model conduction in semiconductors, numerous researchers have noted that CPA might also have relevance to flow and transport processes in porous media. However, the results of several numerical investigations of critical path analysis on pore network models raise questions about the applicability of CPA to porous media. Among other things, these studies found that (i) in well-connected 3D networks, CPA predictions were inaccurate and became worse when heterogeneity was increased; and (ii) CPA could not fully explain the transport properties of 2D networks. To better understand the applicability of CPA to porous media, we made numerical computations of permeability and electrical conductivity on 2D and 3D networks with differing pore-size distributions and geometries. A new CPA model for the relationship between the permeability and electrical conductivity was found to be in good agreement with numerical data, and to be a significant improvement over a classical CPA model. In sufficiently disordered 3D networks, the new CPA prediction was within ±20% of the true value, and was nearly optimal in terms of minimizing the squared prediction errors across differing network configurations. The agreement of CPA predictions with 2D network computations was similarly good, although 2D networks are in general not well-suited for evaluating CPA. Numerical transport coefficients derived for regular 3D networks of slit-shaped pores were found to be in better agreement with experimental data from rock samples than were coefficients derived for networks of cylindrical pores.

Carbon nanotube (CNT) and nanofibrillated cellulose (NFC) reinforcement effect on thermoplastic polyurethane (TPU) scaffolds fabricated via phase separation using dimethyl sulfoxide (DMSO) as solvent.

PubMed

Mi, Hao-Yang; Jing, Xin; Salick, Max R; Cordie, Travis M; Turng, Lih-Sheng

2016-09-01

Although phase separation is a simple method of preparing tissue engineering scaffolds, it suffers from organic solvent residual in the scaffold. Searching for nontoxic solvents and developing effective solvent removal methods are current challenges in scaffold fabrication. In this study, thermoplastic polyurethane (TPU) scaffolds containing carbon nanotubes (CNTs) or nanofibrillated cellulose fibers (NFCs) were prepared using low toxicity dimethyl sulfoxide (DMSO) as a solvent. The effects of two solvent removal approaches on the final scaffold morphology were studied. The freeze drying method caused large pores, with small pores on the pore walls, which created connections between the pores. Meanwhile, the leaching and freeze drying method led to interconnected fine pores with smaller pore diameters. The nucleation effect of CNTs and the phase separation behavior of NFCs in the TPU solution resulted in significant differences in the microstructures of the resulting scaffolds. The mechanical performance of the nanocomposite scaffolds with different morphologies was investigated. Generally, the scaffolds with a fine pore structure showed higher compressive properties, and both the CNTs and NFCs improved the compressive properties of the scaffolds, with greater enhancement found in TPU/NFC nanocomposite scaffolds. In addition, all scaffolds showed good sustainability under cyclical load bearing, and the biocompatibility of the scaffolds was verified via 3T3 fibroblast cell culture. Copyright © 2016 Elsevier Ltd. All rights reserved.

Using Resin-Based 3D Printing to Build Geometrically Accurate Proxies of Porous Sedimentary Rocks.

PubMed

Ishutov, Sergey; Hasiuk, Franciszek J; Jobe, Dawn; Agar, Susan

2018-05-01

Three-dimensional (3D) printing is capable of transforming intricate digital models into tangible objects, allowing geoscientists to replicate the geometry of 3D pore networks of sedimentary rocks. We provide a refined method for building scalable pore-network models ("proxies") using stereolithography 3D printing that can be used in repeated flow experiments (e.g., core flooding, permeametry, porosimetry). Typically, this workflow involves two steps, model design and 3D printing. In this study, we explore how the addition of post-processing and validation can reduce uncertainty in the 3D-printed proxy accuracy (difference of proxy geometry from the digital model). Post-processing is a multi-step cleaning of porous proxies involving pressurized ethanol flushing and oven drying. Proxies are validated by: (1) helium porosimetry and (2) digital measurements of porosity from thin-section images of 3D-printed proxies. 3D printer resolution was determined by measuring the smallest open channel in 3D-printed "gap test" wafers. This resolution (400 µm) was insufficient to build porosity of Fontainebleau sandstone (∼13%) from computed tomography data at the sample's natural scale, so proxies were printed at 15-, 23-, and 30-fold magnifications to validate the workflow. Helium porosities of the 3D-printed proxies differed from digital calculations by up to 7% points. Results improved after pressurized flushing with ethanol (e.g., porosity difference reduced to ∼1% point), though uncertainties remain regarding the nature of sub-micron "artifact" pores imparted by the 3D printing process. This study shows the benefits of including post-processing and validation in any workflow to produce porous rock proxies. © 2017, National Ground Water Association.

Organic aerogels from the sol-gel polymerization of phenolic-furfural mixtures

DOEpatents

Pekala, R.W.

1996-09-17

The sol-gel polymerization of a phenolic-furfural mixture in dilute solution leads to a highly cross-linked network that can be supercritically dried to form a high surface area foam. These porous materials have cell/pore sizes {<=}1,000{angstrom}, and although they are dark brown in color, they can be classified as a new type of aerogel. The phenolic-furfural aerogel can be pyrolyzed in an inert atmosphere at 1,050 C to produce carbon aerogels. This new aerogel may be used for thermal insulation, chromatographic packing, water filtration, ion-exchange, and carbon electrodes for energy storage devices, such as batteries and double-layer capacitors. 8 figs.

Multi-Scale Multi-Physics Modeling of Matrix Transport Properties in Fractured Shale Reservoirs

NASA Astrophysics Data System (ADS)

Mehmani, A.; Prodanovic, M.

2014-12-01

Understanding the shale matrix flow behavior is imperative in successful reservoir development for hydrocarbon production and carbon storage. Without a predictive model, significant uncertainties in flowback from the formation, the communication between the fracture and matrix as well as proper fracturing practice will ensue. Informed by SEM images, we develop deterministic network models that couple pores from multiple scales and their respective fluid physics. The models are used to investigate sorption hysteresis as an affordable way of inferring the nanoscale pore structure in core scale. In addition, restricted diffusion as a function of pore shape, pore-throat size ratios and network connectivity is computed to make correct interpretation of the 2D NMR maps possible. Our novel pore network models have the ability to match sorption hysteresis measurements without any tuning parameters. The results clarify a common misconception of linking type 3 nitrogen hysteresis curves to only the shale pore shape and show promising sensitivty for nanopore structre inference in core scale. The results on restricted diffusion shed light on the importance of including shape factors in 2D NMR interpretations. A priori "weighting factors" as a function of pore-throat and throat-length ratio are presented and the effect of network connectivity on diffusion is quantitatively assessed. We are currently working on verifying our models with experimental data gathered from the Eagleford formation.

Effect of Dihedral Angle and Porosity on Percolating-Sealing Capacity of Texturally Equilibrated Rock Salt

NASA Astrophysics Data System (ADS)

Ghanbarzadeh, S.; Hesse, M. A.; Prodanovic, M.; Gardner, J. E.

2013-12-01

Salt deposits in sedimentary basins have long been considered to be a seal against fluid penetration. However, experimental, theoretical and field evidence suggests brine (and oil) can wet salt crystal surfaces at higher pressures and temperatures, which can form a percolating network. This network may act as flow conduits even at low porosities. The aim of this work is to investigate the effects of dihedral angle and porosity on the formation of percolating paths in different salt network lattices. However, previous studies considered only simple homogeneous and isotropic geometries. This work extends the analysis to realistic salt textures by presenting a novel numerical method to describe the texturally equilibrated pore shapes in polycrystalline rock salt and brine systems. First, a theoretical interfacial topology was formulated to minimize the interfacial surface between brine and salt. Then, the resulting nonlinear system of ordinary differential equations was solved using the Newton-Raphson method. Results show that the formation of connected fluid channels is more probable in lower dihedral angles and at higher porosities. The connectivity of the pore network is hysteretic, because the connection and disconnection at the pore throats for processes with increasing or decreasing porosities occur at different porosities. In porous media with anisotropic solids, pores initially connect in the direction of the shorter crystal axis and only at much higher porosities in the other directions. Consequently, even an infinitesimal elongation of the crystal shape can give rise to very strong anisotropy in permeability of the pore network. Also, fluid flow was simulated in the resulting pore network to calculate permeability, capillary entry pressure and velocity field. This work enabled us to investigate the opening of pore space and sealing capacity of rock salts. The obtained pore geometries determine a wide range of petrophysical properties such as permeability and capillary entry pressure. This expanded knowledge of the salt textural behavior vs. depth could also improve drilling operations in salt. Second, a series of experiments in different P-T conditions was carried out to investigate the actual shape of equilibrated channels in salt. The synthetic salt samples were scanned at the High Resolution X-ray CT Facility at the Department of Geological Science, the University of Texas at Austin with resolution in 1-6 micron range. The experimental results show both equilibrated (tubular pores) and non-equilibrated (planar features) in salt structure. Image processing was carried out by two open source software programs: ImageJ, which is a public domain Java image processing program, and 3DMA-Rock, which is a software package for quantitative analyzing of the pore space in three-dimensional X-ray computed microtomographic images of rock. We obtain medial axis and medial surface of the pore space, as well as find and characterize the corresponding pore-throat network. We also report permeability of the pore space computed using Palabos software.

Production of morphology-controllable porous hyaluronic acid particles using a spray-drying method.

PubMed

Iskandar, Ferry; Nandiyanto, Asep Bayu Dani; Widiyastuti, W; Young, Lee Sin; Okuyama, Kikuo; Gradon, Leon

2009-05-01

Hyaluronic acid (HA) porous particles with controllable porosity and pore size, ranging from 100 to 300 nm, were successfully prepared using a colloidal templating and spray-drying method. HA powder and polystyrene latex (PSL) particles, which were used as the precursor and templating agent, respectively, were mixed in aqueous solution and spray-dried using a two-fluid nozzle system to produce HA and PSL composite particles. Water was evaporated during spray-drying using heated air with a temperature of 120 degrees C. This simple process was completed within several seconds. The prepared particles were collected and washed with an organic solvent to dissolve the PSL templating agent. The porosity and pore size of the resulting particles were easily controlled by changing the initial mass ratio of precursor to templating agent, i.e., HA to PSL, and by altering the size of the PSL template particles.

Temperature gradient effects on vapor diffusion in partially-saturated porous media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Webb, S.W.

1999-07-01

Vapor diffusion in porous media in the presence of its own liquid may be enhanced due to pore-scale processes, such as condensation and evaporation across isolated liquid islands. Webb and Ho (1997) developed one-and two-dimensional mechanistic pore-scale models of these processes in an ideal porous medium. For isothermal and isobaric boundary conditions with a concentration gradient, the vapor diffusion rate was significantly enhanced by these liquid island processes compared to a dry porous media. The influence of a temperature gradient on the enhanced vapor diffusion rate is considered in this paper. The two-dimensional pore network model which is used inmore » the present study is shown. For partially-saturated conditions, a liquid island is introduced into the top center pore. Boundary conditions on the left and right sides of the model are specified to give the desired concentration and temperature gradients. Vapor condenses on one side of the liquid island and evaporates off the other side due to local vapor pressure lowering caused by the interface curvature, even without a temperature gradient. Rather than acting as an impediment to vapor diffusion, the liquid island actually enhances the vapor diffusion rate. The enhancement of the vapor diffusion rate can be significant depending on the liquid saturation. Vapor diffusion is enhanced by up to 40% for this single liquid island compared to a dry porous medium; enhancement factors of up to an order of magnitude have been calculated for other conditions by Webb and Ho (1997). The dominant effect on the enhancement factor is the concentration gradient; the influence of the temperature gradient is smaller. The significance of these results, which need to be confirmed by experiments, is that the dominant model of enhanced vapor diffusion (EVD) by Philip and deVries (1957) predicts that temperature gradients must exist for EVD to occur. If there is no temperature gradient, there is no enhancement. The present results indicate that EVD is predominantly driven by concentration gradients; temperature gradients are less important. Therefore, the EVD model of Philip and deVries may need to be modified to reflect these results.« less

The impact of calcium carbonate as pore forming agent and drug entrapment method towards drug dissolution mechanism of amoxicillin trihydrate encapsulated by chitosan-methyl cellulose semi-IPN hydrogel for floating drug delivery system

NASA Astrophysics Data System (ADS)

Dewantara, Fauzi; Budianto, Emil

2018-04-01

Chitosan-methyl cellulose semi-IPN hydrogel is used as floating drug delivery system, and calcium carbonate also added as pore forming agent. The hydrogel network arranged by not only using biopolymer chitosan and methyl cellulose, but also the crosslink agent that is glutaraldehyde. Amoxicillin trihydrate entrapped into the polymer network with two different method, in situ loading and post loading. Furthermore both method has been tested for drug entrapment efficiency along with drug dissolution test, and the result for drug entrapment efficiency is in situ loading method has highest value of 100%, compared to post loading method which has value only 71%. Moreover, at the final time of drug dissolution test shows in situ loading method has value of 96% for total accumulative of drug dissolution, meanwhile post loading method has 72%. The value of drug dissolution test from both method is used for analyzing drug dissolution mechanism of amoxicillin trihydrate from hydrogel network with four mathematical drug mechanism models as parameter. The polymer network encounter destructive degradation causes by acid solution which used as dissolution medium, and the level of degradation is observed with optical microscope. However the result shows that degradation of the polymer network doesn't affect drug dissolution mechanism directly. Although the pore forming agent causes the pore inside the hydrogel network create interconnection and it was quite influential to drug dissolution mechanism. Interconnected pore is observed with Scanning Electron Microscope (SEM) and shows that the amount and area of interconnected pore inside the hydrogel network is increasing as drug dissolution goes on.

Characteristics of cellulose-microalgae composite

NASA Astrophysics Data System (ADS)

Hwang, Kyo-Jung; Kwon, Gu-Joong; Yang, Ji-Wook; Kim, Sung-yeol; Kim, Dae-Young

2017-10-01

The composites were prepared in order of mixing the cellulose with the N. commune, dissolution-regeneration procedure by LiOH/Urea aqueous solution and freeze-drying. Before the freeze-drying, internal pores of the composites were substituted with an organic solvent. SEM analysis showed that the increase of N. commune results in blockage of cellulose network structure. Brunauer-Emmett-Teller (BET) surface area analysis showed the decrease of mesopore and macropore as the N. commune ratio increases, also the decrease of the specific surface area was shown. The composites appear to have different thermogravimetric analysis properties with the pure N. commune or cellulose itself. Fourier transform infrared spectroscopy (FT-IR) spectra of the composites have specific peaks of the cellulose and N. commune, and increase of N. commune ratio results broadening of peaks relevant to proteins, lipids, and fatty acids. The composites showed higher adsorptivity as the N. commune ratio increases. Especially, the adsorptivity was higher than active carbon before 120 minutes of adsorption. The composite is expected to be used for the situations which need urgent adsorption.

Pore-scale dynamics of salt transport in drying porous media

NASA Astrophysics Data System (ADS)

Shokri, N.

2013-12-01

Understanding the physics of water evaporation from saline porous media is important in many hydrological processes such as land-atmosphere interactions, water management, vegetation, soil salinity, and mineral-fluid interactions. We applied synchrotron x-ray micro-tomography to investigate the pore-scale dynamics of dissolved salt distribution in a three dimensional drying saline porous media using a cylindrical plastic column (15 mm in height and 8 mm in diameter) packed with sand particles saturated with CaI2 solution (5% concentration by mass) with a spatial and temporal resolution of 12 microns and 30 min, respectively. Every time the drying sand column was set to be imaged, two different images were recorded using distinct synchrotron X-rays energies immediately above (33.2690 keV) and below (33.0690 keV) the K-edge value of Iodine (33.1694 keV). Taking the difference between pixel gray values enabled us to delineate the spatial and temporal distribution of CaI2 concentration at pore scale. The experiment was continued for 12 hours. Results indicate that during early stages of evaporation, air preferentially invades large pores at the surface while finer pores remain saturated and connected to the wet zone at bottom via capillary-induced liquid flow. Consequently, the salt concentration increases preferentially in finer pores where evaporation occurs. The Peclet number (describing the competition between convection and diffusion) was greater than one in our experiment resulting in higher salt concentrations closer to the evaporation surface indicating a convection-driven process. The obtained salt profiles were used to evaluate the numerical solution of the convection-diffusion equation (CDE). Results show that the macro-scale CDE could capture the overall trend of the measured salt profiles but fail to produce the exact slope of the profiles. Our results shed new insight on the physics of salt transport and its complex dynamics in drying porous media and establish synchrotron x-ray micro-tomography as an effective tool to investigate the dynamics of dissolved salt transport in porous media with high spatial and temporal resolutions.

Capillary suspensions as beneficial formulation concept for high energy density Li-ion battery electrodes

NASA Astrophysics Data System (ADS)

Bitsch, Boris; Gallasch, Tobias; Schroeder, Melanie; Börner, Markus; Winter, Martin; Willenbacher, Norbert

2016-10-01

We introduce a novel formulation concept to prepare high capacity graphite electrodes for lithium ion batteries. The concept is based on the capillary suspension phenomenon: graphite and conductive agent are dispersed in an aqueous binder solution and the organic solvent octanol is added as immiscible, secondary fluid providing the formation of a sample-spanning network resulting in unique stability and coating properties. No additional processing steps compared to conventional slurry preparation are required. The resulting ultra-thick electrodes comprise mass loadings of about 16.5 mg cm-2, uniform layer thickness, and superior edge contours. The adjustment of mechanical energy input ensures uniform distribution of the conductive agent and sufficient electronic conductivity of the final dry composite electrode. The resulting pore structure is due to the stable network provided by the secondary fluid which evaporates residue-free during drying. Constant current-constant potential (CC-CP) cycling clearly indicates that the corresponding microstructure significantly improves the kinetics of reversible Li+ (de-) intercalation. A double layer electrode combining a conventionally prepared layer coated directly onto the Cu current collector with an upper layer stabilized with octanol was prepared applying wet-on-wet coating. CC-CP cycling data confirms that staged porosity within the electrode cross section results in superior electrochemical performance.

The Effect of Stretching on Ultraviolet Protection of Cotton and Cotton/Coolmax-Blended Weft Knitted Fabric in a Dry State

PubMed Central

Kan, Chi-wai; Yam, Lim-yung; Ng, Sun-pui

2013-01-01

In this paper, the ultraviolet protection factor (UPF) of weft knitted fabrics made from 20Ne cotton yarn, Coolmax yarn and their blends in dry, relaxed and stretched states were studied. According to the fibre composition, samples were divided into three groups: Group I (single cotton yarn); Group II (cotton/cotton combination); and Group III (Coolmax/cotton combination) for discussion. In addition, yarn and fabric properties such as yarn tenacity, yarn strength, fibre combination and water vapour transmission that affect the corresponding UPF values are used for formulating a prediction model in order to determine UPF. Generally speaking, when samples are measured under stretched conditions in a dry state, they exhibit a remarkable reduction in ultraviolet protective power, as pores are opened up and UV radiation can easily penetrate through these pores. In addition, greater stretch percentage came along with greater reduction in UPF. This can be explained by the fact that the amount and the size of pores increase when samples are subjected to greater tension. PMID:28788371

Dissolution Front Instabilities in Reacting Porous Media

NASA Astrophysics Data System (ADS)

Raoof, Amir; Spiers, Chris; Hassanizadeh, Majid

2013-04-01

The main objective of this research is to gain a better understanding of the relation between regime of reaction and dissolution front instability, leading to formation of channels or wormholes. Potential applications are geological sequestration of CO2 and acid-gas injection during enhanced oil recovery. The microscopic pore space is modeled using a multi-directional pore network, allowing for a distribution of pore coordination number, together with distribution of pore sizes. In order to simulate transport of multi-component chemical species, mass balance equations are solved within each element of the network (i.e., pore body and pore throat). We have considered advective and diffusive transport processes within the pore spaces together with multi-component chemical reactions, including both equilibrium and kinetic reactions. Using dimensionless scaling groups (such as Damköhler number and Péclet-Damköhler number) we characterized the dissolution front behavior, and by averaging over the network domain we calculated the evolution of porosity and permeability as well as flux-averaged concentration breakthrough curves. We obtain constitutive relations linking porosity and permeability, under conditions relevant to geological storage of CO2. Effect of distribution of reactive minerals is also evaluated and regime of reaction is shown to play a key role.

Transparent, Superflexible Doubly Cross-Linked Polyvinylpolymethylsiloxane Aerogel Superinsulators via Ambient Pressure Drying.

PubMed

Zu, Guoqing; Shimizu, Taiyo; Kanamori, Kazuyoshi; Zhu, Yang; Maeno, Ayaka; Kaji, Hironori; Shen, Jun; Nakanishi, Kazuki

2018-01-23

Aerogels have many attractive properties but are usually costly and mechanically brittle, which always limit their practical applications. While many efforts have been made to reinforce the aerogels, most of the reinforcement efforts sacrifice the transparency or superinsulating properties. Here we report superflexible polyvinylpolymethylsiloxane, (CH 2 CH(Si(CH 3 )O 2/2 )) n , aerogels that are facilely prepared from a single precursor vinylmethyldimethoxysilane or vinylmethyldiethoxysilane without organic cross-linkers. The method is based on consecutive processes involving radical polymerization and hydrolytic polycondensation, followed by ultralow-cost, highly scalable, ambient-pressure drying directly from alcohol as a drying medium without any modification or additional solvent exchange. The resulting aerogels and xerogels show a homogeneous, tunable, highly porous, doubly cross-linked nanostructure with the elastic polymethylsiloxane network cross-linked with flexible hydrocarbon chains. An outstanding combination of ultralow cost, high scalability, uniform pore size, high surface area, high transparency, high hydrophobicity, excellent machinability, superflexibility in compression, superflexibility in bending, and superinsulating properties has been achieved in a single aerogel or xerogel. This study represents a significant progress of porous materials and makes the practical applications of transparent flexible aerogel-based superinsulators realistic.

Thermal separation of soil particles from thermal conductivity measurement under various air pressures.

PubMed

Lu, Sen; Ren, Tusheng; Lu, Yili; Meng, Ping; Zhang, Jinsong

2017-01-05

The thermal conductivity of dry soils is related closely to air pressure and the contact areas between solid particles. In this study, the thermal conductivity of two-phase soil systems was determined under reduced and increased air pressures. The thermal separation of soil particles, i.e., the characteristic dimension of the pore space (d), was then estimated based on the relationship between soil thermal conductivity and air pressure. Results showed that under both reduced and increased air pressures, d estimations were significantly larger than the geometrical mean separation of solid particles (D), which suggested that conductive heat transfer through solid particles dominated heat transfer in dry soils. The increased air pressure approach gave d values lower than that of the reduced air pressure method. With increasing air pressure, more collisions between gas molecules and solid surface occurred in micro-pores and intra-aggregate pores due to the reduction of mean free path of air molecules. Compared to the reduced air pressure approach, the increased air pressure approach expressed more micro-pore structure attributes in heat transfer. We concluded that measuring thermal conductivity under increased air pressure procedures gave better-quality d values, and improved soil micro-pore structure estimation.

Numerical Simulation of Multiphase Flow in Nanoporous Organic Matter With Application to Coal and Gas Shale Systems

NASA Astrophysics Data System (ADS)

Song, Wenhui; Yao, Jun; Ma, Jingsheng; Sun, Hai; Li, Yang; Yang, Yongfei; Zhang, Lei

2018-02-01

Fluid flow in nanoscale organic pores is known to be affected by fluid transport mechanisms and properties within confined pore space. The flow of gas and water shows notably different characteristics compared with conventional continuum modeling approach. A pore network flow model is developed and implemented in this work. A 3-D organic pore network model is constructed from 3-D image that is reconstructed from 2-D shale SEM image of organic-rich sample. The 3-D pore network model is assumed to be gas-wet and to contain initially gas-filled pores only, and the flow model is concerned with drainage process. Gas flow considers a full range of gas transport mechanisms, including viscous flow, Knudsen diffusion, surface diffusion, ad/desorption, and gas PVT and viscosity using a modified van der Waals' EoS and a correlation for natural gas, respectively. The influences of slip length, contact angle, and gas adsorption layer on water flow are considered. Surface tension considers the pore size and temperature effects. Invasion percolation is applied to calculate gas-water relative permeability. The results indicate that the influences of pore pressure and temperature on water phase relative permeabilities are negligible while gas phase relative permeabilities are relatively larger in higher temperatures and lower pore pressures. Gas phase relative permeability increases while water phase relative permeability decreases with the shrinkage of pore size. This can be attributed to the fact that gas adsorption layer decreases the effective flow area of the water phase and surface diffusion capacity for adsorbed gas is enhanced in small pore size.

Porous poly-ether ether ketone (PEEK) manufactured by a novel powder route using near-spherical salt bead porogens: characterisation and mechanical properties.

PubMed

Siddiq, Abdur R; Kennedy, Andrew R

2015-02-01

Porous PEEK structures with approximately 85% open porosity have been made using PEEK-OPTIMA® powder and a particulate leaching technique using porous, near-spherical, sodium chloride beads. A novel manufacturing approach is presented and compared with a traditional dry mixing method. Irrespective of the method used, the use of near-spherical beads with a fairly narrow size range results in uniform pore structures. However the integration, by tapping, of fine PEEK into a pre-existing network salt beads, followed by compaction and "sintering", produces porous structures with excellent repeatability and homogeneity of density; more uniform pore and strut sizes; an improved and predictable level of connectivity via the formation of "windows" between the cells; faster salt removal rates and lower levels of residual salt. Although tapped samples show a compressive yield stress >1 MPa and stiffness >30 MPa for samples with 84% porosity, the presence of windows in the cell walls means that tapped structures show lower strengths and lower stiffnesses than equivalent structures made by mixing. Copyright © 2014 Elsevier B.V. All rights reserved.

Toward multiscale modelings of grain-fluid systems

NASA Astrophysics Data System (ADS)

Chareyre, Bruno; Yuan, Chao; Montella, Eduard P.; Salager, Simon

2017-06-01

Computationally efficient methods have been developed for simulating partially saturated granular materials in the pendular regime. In contrast, one hardly avoid expensive direct resolutions of 2-phase fluid dynamics problem for mixed pendular-funicular situations or even saturated regimes. Following previous developments for single-phase flow, a pore-network approach of the coupling problems is described. The geometry and movements of phases and interfaces are described on the basis of a tetrahedrization of the pore space, introducing elementary objects such as bridge, meniscus, pore body and pore throat, together with local rules of evolution. As firmly established local rules are still missing on some aspects (entry capillary pressure and pore-scale pressure-saturation relations, forces on the grains, or kinetics of transfers in mixed situations) a multi-scale numerical framework is introduced, enhancing the pore-network approach with the help of direct simulations. Small subsets of a granular system are extracted, in which multiphase scenario are solved using the Lattice-Boltzman method (LBM). In turns, a global problem is assembled and solved at the network scale, as illustrated by a simulated primary drainage.

Minimum requirements for predictive pore-network modeling of solute transport in micromodels

NASA Astrophysics Data System (ADS)

Mehmani, Yashar; Tchelepi, Hamdi A.

2017-10-01

Pore-scale models are now an integral part of analyzing fluid dynamics in porous materials (e.g., rocks, soils, fuel cells). Pore network models (PNM) are particularly attractive due to their computational efficiency. However, quantitative predictions with PNM have not always been successful. We focus on single-phase transport of a passive tracer under advection-dominated regimes and compare PNM with high-fidelity direct numerical simulations (DNS) for a range of micromodel heterogeneities. We identify the minimum requirements for predictive PNM of transport. They are: (a) flow-based network extraction, i.e., discretizing the pore space based on the underlying velocity field, (b) a Lagrangian (particle tracking) simulation framework, and (c) accurate transfer of particles from one pore throat to the next. We develop novel network extraction and particle tracking PNM methods that meet these requirements. Moreover, we show that certain established PNM practices in the literature can result in first-order errors in modeling advection-dominated transport. They include: all Eulerian PNMs, networks extracted based on geometric metrics only, and flux-based nodal transfer probabilities. Preliminary results for a 3D sphere pack are also presented. The simulation inputs for this work are made public to serve as a benchmark for the research community.

Comparison of caprock pore networks which potentially will be impacted by carbon sequestration projects.

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCray, John; Navarre-Sitchler, Alexis; Mouzakis, Katherine

Injection of CO2 into underground rock formations can reduce atmospheric CO2 emissions. Caprocks present above potential storage formations are the main structural trap inhibiting CO2 from leaking into overlying aquifers or back to the Earth's surface. Dissolution and precipitation of caprock minerals resulting from reaction with CO2 may alter the pore network where many pores are of the micrometer to nanometer scale, thus altering the structural trapping potential of the caprock. However, the distribution, geometry and volume of pores at these scales are poorly characterized. In order to evaluate the overall risk of leakage of CO2 from storage formations, amore » first critical step is understanding the distribution and shape of pores in a variety of different caprocks. As the caprock is often comprised of mudstones, we analyzed samples from several mudstone formations with small angle neutron scattering (SANS) and high-resolution transmission electron microscopy (TEM) imaging to compare the pore networks. Mudstones were chosen from current or potential sites for carbon sequestration projects including the Marine Tuscaloosa Group, the Lower Tuscaloosa Group, the upper and lower shale members of the Kirtland Formation, and the Pennsylvanian Gothic shale. Expandable clay contents ranged from 10% to approximately 40% in the Gothic shale and Kirtland Formation, respectively. During SANS, neutrons effectively scatter from interfaces between materials with differing scattering length density (i.e., minerals and pores). The intensity of scattered neutrons, I(Q), where Q is the scattering vector, gives information about the volume and arrangement of pores in the sample. The slope of the scattering data when plotted as log I(Q) vs. log Q provides information about the fractality or geometry of the pore network. On such plots slopes from -2 to -3 represent mass fractals while slopes from -3 to -4 represent surface fractals. Scattering data showed surface fractal dimensions for the Kirtland formation and one sample from the Tuscaloosa formation close to 3, indicating very rough surfaces. In contrast, scattering data for the Gothic shale formation exhibited mass fractal behavior. In one sample of the Tuscaloosa formation the data are described by a surface fractal at low Q (larger pores) and a mass fractal at high Q (smaller pores), indicating two pore populations contributing to the scattering behavior. These small angle neutron scattering results, combined with high-resolution TEM imaging, provided a means for both qualitative and quantitative analysis of the differences in pore networks between these various mudstones.« less

Percolation properties of 3-D multiscale pore networks: how connectivity controls soil filtration processes

NASA Astrophysics Data System (ADS)

Perrier, E. M. A.; Bird, N. R. A.; Rieutord, T. B.

2010-04-01

Quantifying the connectivity of pore networks is a key issue not only for modelling fluid flow and solute transport in porous media but also for assessing the ability of soil ecosystems to filter bacteria, viruses and any type of living microorganisms as well inert particles which pose a contamination risk. Straining is the main mechanical component of filtration processes: it is due to size effects, when a given soil retains a conveyed entity larger than the pores through which it is attempting to pass. We postulate that the range of sizes of entities which can be trapped inside soils has to be associated with the large range of scales involved in natural soil structures and that information on the pore size distribution has to be complemented by information on a Critical Filtration Size (CFS) delimiting the transition between percolating and non percolating regimes in multiscale pore networks. We show that the mass fractal dimensions which are classically used in soil science to quantify scaling laws in observed pore size distributions can also be used to build 3-D multiscale models of pore networks exhibiting such a critical transition. We extend to the 3-D case a new theoretical approach recently developed to address the connectivity of 2-D fractal networks (Bird and Perrier, 2009). Theoretical arguments based on renormalisation functions provide insight into multi-scale connectivity and a first estimation of CFS. Numerical experiments on 3-D prefractal media confirm the qualitative theory. These results open the way towards a new methodology to estimate soil filtration efficiency from the construction of soil structural models to be calibrated on available multiscale data.

Percolation properties of 3-D multiscale pore networks: how connectivity controls soil filtration processes

NASA Astrophysics Data System (ADS)

Perrier, E. M. A.; Bird, N. R. A.; Rieutord, T. B.

2010-10-01

Quantifying the connectivity of pore networks is a key issue not only for modelling fluid flow and solute transport in porous media but also for assessing the ability of soil ecosystems to filter bacteria, viruses and any type of living microorganisms as well inert particles which pose a contamination risk. Straining is the main mechanical component of filtration processes: it is due to size effects, when a given soil retains a conveyed entity larger than the pores through which it is attempting to pass. We postulate that the range of sizes of entities which can be trapped inside soils has to be associated with the large range of scales involved in natural soil structures and that information on the pore size distribution has to be complemented by information on a critical filtration size (CFS) delimiting the transition between percolating and non percolating regimes in multiscale pore networks. We show that the mass fractal dimensions which are classically used in soil science to quantify scaling laws in observed pore size distributions can also be used to build 3-D multiscale models of pore networks exhibiting such a critical transition. We extend to the 3-D case a new theoretical approach recently developed to address the connectivity of 2-D fractal networks (Bird and Perrier, 2009). Theoretical arguments based on renormalisation functions provide insight into multi-scale connectivity and a first estimation of CFS. Numerical experiments on 3-D prefractal media confirm the qualitative theory. These results open the way towards a new methodology to estimate soil filtration efficiency from the construction of soil structural models to be calibrated on available multiscale data.

Experimental and modeling study of Newtonian and non-Newtonian fluid flow in pore network micromodels.

PubMed

Perrin, Christian L; Tardy, Philippe M J; Sorbie, Ken S; Crawshaw, John C

2006-03-15

The in situ rheology of polymeric solutions has been studied experimentally in etched silicon micromodels which are idealizations of porous media. The rectangular channels in these etched networks have dimensions typical of pore sizes in sandstone rocks. Pressure drop/flow rate relations have been measured for water and non-Newtonian hydrolyzed-polyacrylamide (HPAM) solutions in both individual straight rectangular capillaries and in networks of such capillaries. Results from these experiments have been analyzed using pore-scale network modeling incorporating the non-Newtonian fluid mechanics of a Carreau fluid. Quantitative agreement is seen between the experiments and the network calculations in the Newtonian and shear-thinning flow regions demonstrating that the 'shift factor,'alpha, can be calculated a priori. Shear-thickening behavior was observed at higher flow rates in the micromodel experiments as a result of elastic effects becoming important and this remains to be incorporated in the network model.

Fast Two-Dimensional Bubble Analysis of Biopolymer Filamentous Networks Pore Size from Confocal Microscopy Thin Data Stacks

PubMed Central

Molteni, Matteo; Magatti, Davide; Cardinali, Barbara; Rocco, Mattia; Ferri, Fabio

2013-01-01

The average pore size ξ0 of filamentous networks assembled from biological macromolecules is one of the most important physical parameters affecting their biological functions. Modern optical methods, such as confocal microscopy, can noninvasively image such networks, but extracting a quantitative estimate of ξ0 is a nontrivial task. We present here a fast and simple method based on a two-dimensional bubble approach, which works by analyzing one by one the (thresholded) images of a series of three-dimensional thin data stacks. No skeletonization or reconstruction of the full geometry of the entire network is required. The method was validated by using many isotropic in silico generated networks of different structures, morphologies, and concentrations. For each type of network, the method provides accurate estimates (a few percent) of the average and the standard deviation of the three-dimensional distribution of the pore sizes, defined as the diameters of the largest spheres that can be fit into the pore zones of the entire gel volume. When applied to the analysis of real confocal microscopy images taken on fibrin gels, the method provides an estimate of ξ0 consistent with results from elastic light scattering data. PMID:23473499

Cyclic deformation-induced solute transport in tissue scaffolds with computer designed, interconnected, pore networks: experiments and simulations.

PubMed

Den Buijs, Jorn Op; Dragomir-Daescu, Dan; Ritman, Erik L

2009-08-01

Nutrient supply and waste removal in porous tissue engineering scaffolds decrease from the periphery to the center, leading to limited depth of ingrowth of new tissue into the scaffold. However, as many tissues experience cyclic physiological strains, this may provide a mechanism to enhance solute transport in vivo before vascularization of the scaffold. The hypothesis of this study was that pore cross-sectional geometry and interconnectivity are of major importance for the effectiveness of cyclic deformation-induced solute transport. Transparent elastic polyurethane scaffolds, with computer-programmed design of pore networks in the form of interconnected channels, were fabricated using a 3D printing and injection molding technique. The scaffold pores were loaded with a colored tracer for optical contrast, cyclically compressed with deformations of 10 and 15% of the original undeformed height at 1.0 Hz. Digital imaging was used to quantify the spatial distribution of the tracer concentration within the pores. Numerical simulations of a fluid-structure interaction model of deformation-induced solute transport were compared to the experimental data. The results of experiments and modeling agreed well and showed that pore interconnectivity heavily influences deformation-induced solute transport. Pore cross-sectional geometry appears to be of less relative importance in interconnected pore networks. Validated computer models of solute transport can be used to design optimal scaffold pore geometries that will enhance the convective transport of nutrients inside the scaffold and the removal of waste, thus improving the cell survivability deep inside the scaffold.

Pore network quantification of sandstones under experimental CO2 injection using image analysis

NASA Astrophysics Data System (ADS)

Berrezueta, Edgar; González-Menéndez, Luís; Ordóñez-Casado, Berta; Olaya, Peter

2015-04-01

Automated-image identification and quantification of minerals, pores and textures together with petrographic analysis can be applied to improve pore system characterization in sedimentary rocks. Our case study is focused on the application of these techniques to study the evolution of rock pore network subjected to super critical CO2-injection. We have proposed a Digital Image Analysis (DIA) protocol that guarantees measurement reproducibility and reliability. This can be summarized in the following stages: (i) detailed description of mineralogy and texture (before and after CO2-injection) by optical and scanning electron microscopy (SEM) techniques using thin sections; (ii) adjustment and calibration of DIA tools; (iii) data acquisition protocol based on image capture with different polarization conditions (synchronized movement of polarizers); (iv) study and quantification by DIA that allow (a) identification and isolation of pixels that belong to the same category: minerals vs. pores in each sample and (b) measurement of changes in pore network, after the samples have been exposed to new conditions (in our case: SC-CO2-injection). Finally, interpretation of the petrography and the measured data by an automated approach were done. In our applied study, the DIA results highlight the changes observed by SEM and microscopic techniques, which consisted in a porosity increase when CO2 treatment occurs. Other additional changes were minor: variations in the roughness and roundness of pore edges, and pore aspect ratio, shown in the bigger pore population. Additionally, statistic tests of pore parameters measured were applied to verify that the differences observed between samples before and after CO2-injection were significant.

Superporous polyacrylate/chitosan IPN hydrogels for protein delivery.

PubMed

Gümüşderelioğlu, Menemşe; Erce, Deniz; Demirtaş, T Tolga

2011-11-01

In this study, poly(acrylamide), poly(AAm), and poly(acrylamide-co-acrylic acid), poly(AAm-co-AA) superporous hydrogels (SPHs) were synthesized by radical polymerization in the presence of gas blowing agent, sodium bicarbonate. In addition, ionically crosslinked chitosan (CH) superporous hydrogels were synthesized to form interpenetrating superporous hydrogels, i.e. poly(AAm)-CH and poly(AAm-co-AA)-CH SPH-IPNs. The hydrogels have a structure of interconnected pores with pore sizes of approximately 100-150 μm. Although the extent of swelling increased when AA were incorporated to the poly(AAm) structure, the time to reach the equilibrium swelling (~30 s) was not affected so much. In the presence of chitosan network mechanical properties significantly improved when compared with SPHs, however, equilibrium swelling time (~30 min) was prolonged significantly as due to the lower porosities and pore sizes of SPH-IPNs than that of SPHs. Model protein bovine serum albumin (BSA) was loaded into SPHs and SPH-IPNs by solvent sorption in very short time (<1 h) and very high capacities (~30-300 mg BSA/g dry gel) when compared to conventional hydrogels. BSA release profiles from SPHs and SPH-IPNs were characterized by an initial burst of protein during the first 20 min followed by a completed release within 1 h. However, total releasable amount of BSA from SPH-IPNs was lower than that of SPHs as due to the electrostatic interactions between chitosan and BSA.

A streamline splitting pore-network approach for computationally inexpensive and accurate simulation of transport in porous media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mehmani, Yashar; Oostrom, Martinus; Balhoff, Matthew

2014-03-20

Several approaches have been developed in the literature for solving flow and transport at the pore-scale. Some authors use a direct modeling approach where the fundamental flow and transport equations are solved on the actual pore-space geometry. Such direct modeling, while very accurate, comes at a great computational cost. Network models are computationally more efficient because the pore-space morphology is approximated. Typically, a mixed cell method (MCM) is employed for solving the flow and transport system which assumes pore-level perfect mixing. This assumption is invalid at moderate to high Peclet regimes. In this work, a novel Eulerian perspective on modelingmore » flow and transport at the pore-scale is developed. The new streamline splitting method (SSM) allows for circumventing the pore-level perfect mixing assumption, while maintaining the computational efficiency of pore-network models. SSM was verified with direct simulations and excellent matches were obtained against micromodel experiments across a wide range of pore-structure and fluid-flow parameters. The increase in the computational cost from MCM to SSM is shown to be minimal, while the accuracy of SSM is much higher than that of MCM and comparable to direct modeling approaches. Therefore, SSM can be regarded as an appropriate balance between incorporating detailed physics and controlling computational cost. The truly predictive capability of the model allows for the study of pore-level interactions of fluid flow and transport in different porous materials. In this paper, we apply SSM and MCM to study the effects of pore-level mixing on transverse dispersion in 3D disordered granular media.« less

Investigation of Coupled model of Pore network and Continuum in shale gas

NASA Astrophysics Data System (ADS)

Cao, G.; Lin, M.

2016-12-01

Flow in shale spanning over many scales, makes the majority of conventional treatment methods disabled. For effectively simulating, a coupled model of pore-scale and continuum-scale was proposed in this paper. Based on the SEM image, we decompose organic-rich-shale into two subdomains: kerogen and inorganic matrix. In kerogen, the nanoscale pore-network is the main storage space and migration pathway so that the molecular phenomena (slip and diffusive transport) is significant. Whereas, inorganic matrix, with relatively large pores and micro fractures, the flow is approximate to Darcy. We use pore-scale network models (PNM) to represent kerogen and continuum-scale models (FVM or FEM) to represent matrix. Finite element mortars are employed to couple pore- and continuum-scale models by enforcing continuity of pressures and fluxes at shared boundary interfaces. In our method, the process in the coupled model is described by pressure square equation, and uses Dirichlet boundary conditions. We discuss several problems: the optimal element number of mortar faces, two categories boundary faces of pore network, the difference between 2D and 3D models, and the difference between continuum models FVM and FEM in mortars. We conclude that: (1) too coarse mesh in mortars will decrease the accuracy, while too fine mesh will lead to an ill-condition even singular system, the optimal element number is depended on boundary pores and nodes number. (2) pore network models are adjacent to two different mortar faces (PNM to PNM, PNM to continuum model), incidental repeated mortar nodes must be deleted. (3) 3D models can be replaced by 2D models under certain condition. (4) FVM is more convenient than FEM, for its simplicity in assigning interface nodes pressure and calculating interface fluxes. This work is supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB10020302), the 973 Program (2014CB239004), the Key Instrument Developing Project of the CAS (ZDYZ2012-1-08-02), the National Natural Science Foundation of China (41574129).

Liquid bridges at the root-soil interface

NASA Astrophysics Data System (ADS)

Carminati, Andrea; Benard, Pascal; Ahmed, Mutez; Zarebanadkouki, Mohsen

2017-04-01

The role of the root-soil interface on soil-plant water relations is unclear. Despite many experimental studies proved that the soil close to the root surface, the rhizosphere, has different properties compared to the adjacent bulk soil, the mechanisms underlying such differences are poorly understood and the implications for plant-water relations remain largely speculative. The objective of this contribution is to discuss the key elements affecting water dynamics in the rhizosphere. Special attention is dedicated to the role of mucilage exuded by roots in shaping the hydraulic properties of the rhizosphere. We identified three key properties: 1) mucilage adsorbs water decreasing its water potential; 2) mucilage decreases the surface tension of the soil solution; 3) mucilage increases the viscosity of the soil solution. These three properties determine the retention and spatial configuration of the liquid phase in porous media. The increase in viscosity and the decrease in surface tension (quantified by the Ohnesorge number) allow the persistence of long liquid filaments even at very negative water potentials. At high mucilage concentrations these filaments form a network that creates an additional matric potential and maintains the continuity of the liquid phase during drying. The biophysical interactions between mucilage and the pore space determine the physical properties of the rhizosphere. Mucilage forms a network that provides mechanical stability to soils upon drying and that maintains the continuity of the liquid phase across the soil-root interface. Such biophysical properties are functional to create an interconnected matrix that maintains the roots in contact with the soil, which is of particular importance when the soil is drying and the transpiration rate is high.

Simulating secondary waterflooding in heterogeneous rocks with variable wettability using an image-based, multiscale pore network model

NASA Astrophysics Data System (ADS)

Bultreys, Tom; Van Hoorebeke, Luc; Cnudde, Veerle

2016-09-01

The two-phase flow properties of natural rocks depend strongly on their pore structure and wettability, both of which are often heterogeneous throughout the rock. To better understand and predict these properties, image-based models are being developed. Resulting simulations are however problematic in several important classes of rocks with broad pore-size distributions. We present a new multiscale pore network model to simulate secondary waterflooding in these rocks, which may undergo wettability alteration after primary drainage. This novel approach permits to include the effect of microporosity on the imbibition sequence without the need to describe each individual micropore. Instead, we show that fluid transport through unresolved pores can be taken into account in an upscaled fashion, by the inclusion of symbolic links between macropores, resulting in strongly decreased computational demands. Rules to describe the behavior of these links in the quasistatic invasion sequence are derived from percolation theory. The model is validated by comparison to a fully detailed network representation, which takes each separate micropore into account. Strongly and weakly water-and oil-wet simulations show good results, as do mixed-wettability scenarios with different pore-scale wettability distributions. We also show simulations on a network extracted from a micro-CT scan of Estaillades limestone, which yields good agreement with water-wet and mixed-wet experimental results.

Hysteresis of liquid adsorption in porous media by coarse-grained Monte Carlo with direct experimental validation

NASA Astrophysics Data System (ADS)

Zeidman, Benjamin D.; Lu, Ning; Wu, David T.

2016-05-01

The effects of path-dependent wetting and drying manifest themselves in many types of physical systems, including nanomaterials, biological systems, and porous media such as soil. It is desirable to better understand how these hysteretic macroscopic properties result from a complex interplay between gasses, liquids, and solids at the pore scale. Coarse-Grained Monte Carlo (CGMC) is an appealing approach to model these phenomena in complex pore spaces, including ones determined experimentally. We present two-dimensional CGMC simulations of wetting and drying in two systems with pore spaces determined by sections from micro X-ray computed tomography: a system of randomly distributed spheres and a system of Ottawa sand. Results for the phase distribution, water uptake, and matric suction when corrected for extending to three dimensions show excellent agreement with experimental measurements on the same systems. This supports the hypothesis that CGMC can generate metastable configurations representative of experimental hysteresis and can also be used to predict hysteretic constitutive properties of particular experimental systems, given pore space images.

Porous PVDF/PANI ion-exchange membrane (IEM) modified by polyvinylpyrrolidone (PVP) and lithium chloride in the application of membrane capacitive deionisation (MCDI).

PubMed

Zhang, Yiming; Zhang, Wei; Cházaro-Ruiz, Luis F

2018-05-01

In this work, polyvinylidene fluoride (PVDF)/polyaniline (PANI) heterogeneous anion-exchange membranes filled with pore-forming agents polyvinylpyrrolidone (PVP) and lithium chloride were prepared by the solution-casting technique using the solvent 1-methyl-2-pyrrolidone (NMP) and a two-step phase inversion procedure. Key properties of the as-prepared membranes, such as hydrophilicity, water content, ion exchange capacity, fixed ion concentration, conductivity and transport number were examined and compared between membranes in different conditions. The pore-forming hydrophilic additives PVP and lithium chloride to the casting solution appeared to improve the ion-exchange membranes (IEMs) by increasing the conductivity, transport number and hydrophilicity. The effects of increasing membrane drying time on the porosity of the as-prepared membranes were found to lower membrane porosity by reducing membrane water content. However, pore-forming agents were found to be able to stabilise membrane transport number with different drying times. As-prepared PVDF/PANI anion-exchange membrane with pore-forming agent is demonstrated to be a more efficient candidate for water purification (e.g. desalination) and other industrial applications.

Hysteresis of liquid adsorption in porous media by coarse-grained Monte Carlo with direct experimental validation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zeidman, Benjamin D.; Lu, Ning; Wu, David T., E-mail: dwu@mines.edu

2016-05-07

The effects of path-dependent wetting and drying manifest themselves in many types of physical systems, including nanomaterials, biological systems, and porous media such as soil. It is desirable to better understand how these hysteretic macroscopic properties result from a complex interplay between gasses, liquids, and solids at the pore scale. Coarse-Grained Monte Carlo (CGMC) is an appealing approach to model these phenomena in complex pore spaces, including ones determined experimentally. We present two-dimensional CGMC simulations of wetting and drying in two systems with pore spaces determined by sections from micro X-ray computed tomography: a system of randomly distributed spheres andmore » a system of Ottawa sand. Results for the phase distribution, water uptake, and matric suction when corrected for extending to three dimensions show excellent agreement with experimental measurements on the same systems. This supports the hypothesis that CGMC can generate metastable configurations representative of experimental hysteresis and can also be used to predict hysteretic constitutive properties of particular experimental systems, given pore space images.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beckingham, Lauren E.; Peters, Catherine A.; Um, Wooyong

Although the impact of subsurface geochemical reactions on porosity is relatively well understood, changes in permeability remain difficult to estimate. In this work, pore-network modeling was used to predict permeability based on pore- and pore-throat size distributions determined from analysis of 2D scanning electron microscopy (SEM) images of thin sections and 3D X-ray computed microtomography (CMT) data. The analyzed specimens were a Viking sandstone sample from the Alberta sedimentary basin and an experimental column of reacted Hanford sediments. For the column, a decrease in permeability due to mineral precipitation was estimated, but the permeability estimates were dependent on imaging techniquemore » and resolution. X-ray CT imaging has the advantage of reconstructing a 3D pore network while 2D SEM imaging can easily analyze sub-grain and intragranular variations in mineralogy. Pore network models informed by analyses of 2D and 3D images at comparable resolutions produced permeability esti- mates with relatively good agreement. Large discrepancies in predicted permeabilities resulted from small variations in image resolution. Images with resolutions 0.4 to 4 lm predicted permeabilities differ- ing by orders of magnitude. While lower-resolution scans can analyze larger specimens, small pore throats may be missed due to resolution limitations, which in turn overestimates permeability in a pore-network model in which pore-to-pore conductances are statistically assigned. Conversely, high-res- olution scans are capable of capturing small pore throats, but if they are not actually flow-conducting predicted permeabilities will be below expected values. In addition, permeability is underestimated due to misinterpreting surface-roughness features as small pore throats. Comparison of permeability pre- dictions with expected and measured permeability values showed that the largest discrepancies resulted from the highest resolution images and the best predictions of permeability will result from images between 2 and 4 lm resolution. To reduce permeability underestimation from analyses of high-resolu- tion images, a resolution threshold between 3 and 15 lm was found to be effective, but it is not known whether this range is applicable beyond the samples studied here.« less

Frictional strength of wet and dry montmorillonite

USGS Publications Warehouse

Morrow, Carolyn A.; Moore, Diane E.; Lockner, David A.

2017-01-01

Montmorillonite is a common mineral in fault zones, and its low strength relative to other common gouge minerals is important in many models of fault rheology. However, the coefficient of friction, μ, varies with degree of saturation and is not well constrained in the literature due to the difficulty of establishing fully drained or fully dried states in the laboratory. We measured μ of both saturated and oven-dried montmorillonite at normal stresses up to 700 MPa. Care was taken to shear saturated samples slowly enough to avoid pore fluid overpressure. For saturated samples, μ increased from 0.10 to 0.28 with applied effective normal stress, while for dry samples μ decreased from 0.78 to 0.45. The steady state rate dependence of friction, (a − b), was positive, promoting stable sliding. The wide disparity in reported frictional strengths can be attributed to experimental procedures that promote differing degrees of partial saturation or overpressured pore fluid conditions.

Analysis of quasi-periodic pore-network structure of centric marine diatom frustules

NASA Astrophysics Data System (ADS)

Cohoon, Gregory A.; Alvarez, Christine E.; Meyers, Keith; Deheyn, Dimitri D.; Hildebrand, Mark; Kieu, Khanh; Norwood, Robert A.

2015-03-01

Diatoms are a common type of phytoplankton characterized by their silica exoskeleton known as a frustule. The diatom frustule is composed of two valves and a series of connecting girdle bands. Each diatom species has a unique frustule shape and valves in particular species display an intricate pattern of pores resembling a photonic crystal structure. We used several numerical techniques to analyze the periodic and quasi-periodic valve pore-network structure in diatoms of the Coscinodiscophyceae order. We quantitatively identify defect locations and pore spacing in the valve and use this information to better understand the optical and biological properties of the diatom.

Measurements of pore-scale flow through apertures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chojnicki, Kirsten

Pore-scale aperture effects on flow in pore networks was studied in the laboratory to provide a parameterization for use in transport models. Four cases were considered: regular and irregular pillar/pore alignment with and without an aperture. The velocity field of each case was measured and simulated, providing quantitatively comparable results. Two aperture effect parameterizations were considered: permeability and transmission. Permeability values varied by an order of magnitude between the cases with and without apertures. However, transmission did not correlate with permeability. Despite having much greater permeability the regular aperture case permitted less transmission than the regular case. Moreover, both irregularmore » cases had greater transmission than the regular cases, a difference not supported by the permeabilities. Overall, these findings suggest that pore-scale aperture effects on flow though a pore-network may not be adequately captured by properties such as permeability for applications that are interested in determining particle transport volume and timing.« less

Improved consolidation of silicon carbide

NASA Technical Reports Server (NTRS)

Freedman, M. R.; Millard, M. L.

1986-01-01

Alpha silicon carbide powder was consolidated by both dry and wet methods. Dry pressing in a double acting steel die yielded sintered test bars with an average flexural strength of 235.6 MPa with a critical flaw size of approximately 100 micro m. An aqueous slurry pressing technique produced sintered test bars with an average flexural strength of 440.8 MPa with a critical flaw size of approximately 25 micro m. Image analysis revealed a reduction in both pore area and pore size distribution in the slurry pressed sintered test bars. The improvements in the slurry pressed material properties are discussed in terms of reduced agglomeration and improved particle packing during consolidation.

Gap-freezing approach for shortening the lyophilization cycle time of pharmaceutical formulations-demonstration of the concept.

PubMed

Kuu, Wei Y; Doty, Mark J; Rebbeck, Christine L; Hurst, William S; Cho, Yong K

2013-08-01

During gap freezing, vials are placed on a metal tray, which is separated from the shelf surface with a small air gap that eliminates significant conductive heat transfer from the shelf to the bottom of the vial. The purpose of this freezing approach is to reduce the lyophilization cycle time of various amorphous formulations by nearly isothermal freezing. Such isothermal freezing promotes the formation of large ice crystals, and thus large pores throughout the cake, which subsequently accelerates the primary drying rate. The nucleation temperature using gap freezing, for the experimental conditions tested, was in the range of -1°C to -6°C, much higher than the range of -10°C to -14°C found using conventional shelf freezing. Isothermal freezing becomes effective when the gap is greater than 3 mm. The pore sizes and cake resistance during primary drying for various formulations were determined using the pore diffusion model developed by Kuu et al. (Pharm Dev Technol, 2011, 16(4): 343-357). Reductions in primary drying time were 42% (for 10% sucrose), 45% (for 10% trehalose), and 33% (for 5% sucrose). Copyright © 2013 Wiley Periodicals, Inc.

Explosion Amplitude Reduction due to Fractures in Water-Saturated and Dry Granite

NASA Astrophysics Data System (ADS)

Stroujkova, A. F.; Leidig, M.; Bonner, J. L.

2013-12-01

Empirical observations made at the Semipalatinsk Test Site suggest that nuclear tests in the fracture zones left by previous explosions ('repeat shots') show reduced seismic amplitudes compared to the nuclear tests in virgin rocks. Likely mechanisms for the amplitude reduction in the repeat shots include increased porosity and reduced strength and elastic moduli, leading to pore closing and frictional sliding. Presence of pore water significantly decreases rock compressibility and strength, thus affecting seismic amplitudes. A series of explosion experiments were conducted in order to define the physical mechanism responsible for the amplitude reduction and to quantify the degree of the amplitude reduction in fracture zones of previously detonated explosions. Explosions in water-saturated granite were conducted in central New Hampshire in 2011 and 2012. Additional explosions in dry granite were detonated in Barre, VT in 2013. The amplitude reduction is different between dry and water-saturated crystalline rocks. Significant reduction in seismic amplitudes (by a factor of 2-3) in water-saturated rocks was achieved only when the repeat shot was detonated in the extensive damage zone created by a significantly larger (by a factor of 5) explosion. In case where the first and the second explosions were similar in yield, the amplitude reduction was relatively modest (5-20%). In dry rocks the amplitude reduction reached a factor of 2 even in less extensive damage zones. In addition there are differences in frequency dependence of the spectral amplitude ratios between explosions in dry and water-saturated rocks. Thus the amplitude reduction is sensitive to the extent of the damage zone as well as the pore water content.

Design and synthesis of inorganic/organic hybrid electrochemical materials

NASA Astrophysics Data System (ADS)

Harreld, John H.

An ambient pressure method for drying sol-gel materials is developed to synthesize high porosity (80--90%), high surface area vanadium oxide and silica aerogel materials (150--300 and 1000 m2/g for vanadium pentoxide and silica, respectively). The synthesis approach uses liquid exchange to replace the pore fluid with a low surface tension, nonpolar solvent which reduces the capillary pressures developed during drying. The Good-Girifalco interaction parameter is used to calculate pore stresses resulting from drying silica gels from various liquids. Vanadium oxide/polypyrrole hybrid aerogels are prepared using three strategies. These approaches focus on either sequential or consecutive polymerization of the inorganic and organic networks. Microcomposite aerogels are synthesized by encapsulating a dispersion of preformed polypyrrole in a vanadium pentoxide gel. In the second approach, pyrrole is polymerized and doped within the pore volume of preformed vanadium pentoxide gel. When the inorganic and organic precursors are polymerized simultaneously, the resulting gels exhibited a nanometer scaled microstructure with homogeneous distributions of either phases. Through this route, a suitable microstructure and composition for a lithium secondary battery cathode is obtained. Lithiated aerogels of hydrated nickel, cobalt, and mixed nickel-cobalt oxides are synthesized from lithium hydroxide and transition metal acetate precursors. The XRD analyses indicate that the nickel containing gels exhibit a lithium deficiency (less than 1 Li/transition metal. By increasing the concentration of the lithium precursor the lithium content in nickel oxides is increased, and additional base solution is no longer required to catalyze gelation. A non-hydrolytic sol-gel approach is utilized to create tin oxide and tin-aluminum binary oxide aerogels with high porosity (90%) and high surface area (300 m2/g). XRD data from single phase tin oxide aerogel indicates the growth of SnO2 crystallites between 150--400°C in air, accompanied by a reduction in surface area (30 m2/g). Heated tin oxide aerogel exhibits comparable reversible specific capacity (390 mAh/g) as that of commercial SnO2 (420 mAh/g). Amorphous tin oxide aerogel is stabilized to higher temperatures when aluminum oxide is incorporated into the structure. The tin oxide phase remains electrochemically active towards lithium insertion and exhibits excellent reversibility during cycling.

Three dimensional characterization of nickel coarsening in solid oxide cells via ex-situ ptychographic nano-tomography

NASA Astrophysics Data System (ADS)

De Angelis, Salvatore; Jørgensen, Peter Stanley; Tsai, Esther Hsiao Rho; Holler, Mirko; Kreka, Kosova; Bowen, Jacob R.

2018-04-01

Nickel coarsening is considered a significant cause of solid oxide cell (SOC) performance degradation. Therefore, understanding the morphological changes in the nickel-yttria stabilized zirconia (Ni-YSZ) fuel electrode is crucial for the wide spread usage of SOC technology. This paper reports a study of the initial 3D microstructure evolution of a SOC analyzed in the pristine state and after 3 and 8 h of annealing at 850 °C, in dry hydrogen. The analysis of the evolution of the same location of the electrode shows a substantial change of the nickel and pore network during the first 3 h of treatment, while only negligible changes are observed after 8 h. The nickel coarsening results in loss of connectivity in the nickel network, reduced nickel specific surface area and decreased total triple phase boundary density. For the condition of this experiment, nickel coarsening is shown to be predominantly curvature driven, and changes in the electrode microstructure parameters are discussed in terms of local microstructural evolution.

Measurement and modelling of reactive transport in geological barriers for nuclear waste containment

DOE PAGES

Xiong, Qingrong; Joseph, Claudia; Schmeide, Katja; ...

2015-10-26

Compacted clays are considered as excellent candidates for barriers to radionuclide transport in future repositories for nuclear waste due to their very low hydraulic permeability. Diffusion is the dominant transport mechanism, controlled by a nano-scale pore system. Assessment of the clays' long-term containment function requires adequate modelling of such pore systems and their evolution. Existing characterisation techniques do not provide complete pore space information for effective modelling, such as pore and throat size distributions and connectivity. Special network models for reactive transport are proposed here using the complimentary character of the pore space and the solid phase. Here, this balancesmore » the insufficient characterisation information and provides the means for future mechanical–physical–chemical coupling. The anisotropy and heterogeneity of clays is represented using different length parameters and percentage of pores in different directions. Resulting networks are described as mathematical graphs with efficient discrete calculus formulation of transport. Opalinus Clay (OPA) is chosen as an example. Experimental data for the tritiated water (HTO) and U(VI) diffusion through OPA are presented. Calculated diffusion coefficients of HTO and uranium species are within the ranges of the experimentally determined data in different clay directions. This verifies the proposed pore network model and validates that uranium complexes are diffusing as neutral species in OPA. In the case of U(VI) diffusion the method is extended to account for sorption and convection. Finally, rather than changing pore radii by coarse grained mathematical formula, physical sorption is simulated in each pore, which is more accurate and realistic.« less

Cyclic Deformation-Induced Solute Transport in Tissue Scaffolds with Computer Designed, Interconnected, Pore Networks: Experiments and Simulations

PubMed Central

Op Den Buijs, Jorn; Dragomir-Daescu, Dan; Ritman, Erik L.

2014-01-01

Nutrient supply and waste removal in porous tissue engineering scaffolds decrease from the periphery to the center, leading to limited depth of ingrowth of new tissue into the scaffold. However, as many tissues experience cyclic physiological strains, this may provide a mechanism to enhance solute transport in vivo before vascularization of the scaffold. The hypothesis of this study was that pore cross-sectional geometry and interconnectivity are of major importance for the effectiveness of cyclic deformation-induced solute transport. Transparent elastic polyurethane scaffolds, with computer-programmed design of pore networks in the form of interconnected channels, were fabricated using a 3D printing and injection molding technique. The scaffold pores were loaded with a colored tracer for optical contrast, cyclically compressed with deformations of 10 and 15% of the original undeformed height at 1.0 Hz. Digital imaging was used to quantify the spatial distribution of the tracer concentration within the pores. Numerical simulations of a fluid–structure interaction model of deformation-induced solute transport were compared to the experimental data. The results of experiments and modeling agreed well and showed that pore interconnectivity heavily influences deformation-induced solute transport. Pore cross-sectional geometry appears to be of less relative importance in interconnected pore networks. Validated computer models of solute transport can be used to design optimal scaffold pore geometries that will enhance the convective transport of nutrients inside the scaffold and the removal of waste, thus improving the cell survivability deep inside the scaffold. PMID:19466547

Measurement and modelling of reactive transport in geological barriers for nuclear waste containment.

PubMed

Xiong, Qingrong; Joseph, Claudia; Schmeide, Katja; Jivkov, Andrey P

2015-11-11

Compacted clays are considered as excellent candidates for barriers to radionuclide transport in future repositories for nuclear waste due to their very low hydraulic permeability. Diffusion is the dominant transport mechanism, controlled by a nano-scale pore system. Assessment of the clays' long-term containment function requires adequate modelling of such pore systems and their evolution. Existing characterisation techniques do not provide complete pore space information for effective modelling, such as pore and throat size distributions and connectivity. Special network models for reactive transport are proposed here using the complimentary character of the pore space and the solid phase. This balances the insufficient characterisation information and provides the means for future mechanical-physical-chemical coupling. The anisotropy and heterogeneity of clays is represented using different length parameters and percentage of pores in different directions. Resulting networks are described as mathematical graphs with efficient discrete calculus formulation of transport. Opalinus Clay (OPA) is chosen as an example. Experimental data for the tritiated water (HTO) and U(vi) diffusion through OPA are presented. Calculated diffusion coefficients of HTO and uranium species are within the ranges of the experimentally determined data in different clay directions. This verifies the proposed pore network model and validates that uranium complexes are diffusing as neutral species in OPA. In the case of U(vi) diffusion the method is extended to account for sorption and convection. Rather than changing pore radii by coarse grained mathematical formula, physical sorption is simulated in each pore, which is more accurate and realistic.

Mechanical instability and percolation of deformable particles through porous networks

NASA Astrophysics Data System (ADS)

Benet, Eduard; Lostec, Guillaume; Pellegrino, John; Vernerey, Franck

2018-04-01

The transport of micron-sized particles such as bacteria, cells, or synthetic lipid vesicles through porous spaces is a process relevant to drug delivery, separation systems, or sensors, to cite a few examples. Often, the motion of these particles depends on their ability to squeeze through small constrictions, making their capacity to deform an important factor for their permeation. However, it is still unclear how the mechanical behavior of these particles affects collective transport through porous networks. To address this issue, we present a method to reconcile the pore-scale mechanics of the particles with the Darcy scale to understand the motion of a deformable particle through a porous network. We first show that particle transport is governed by a mechanical instability occurring at the pore scale, which leads to a binary permeation response on each pore. Then, using the principles of directed bond percolation, we are able to link this microscopic behavior to the probability of permeating through a random porous network. We show that this instability, together with network uniformity, are key to understanding the nonlinear permeation of particles at a given pressure gradient. The results are then summarized by a phase diagram that predicts three distinct permeation regimes based on particle properties and the randomness of the pore network.

Versatile and efficient pore network extraction method using marker-based watershed segmentation

NASA Astrophysics Data System (ADS)

Gostick, Jeff T.

2017-08-01

Obtaining structural information from tomographic images of porous materials is a critical component of porous media research. Extracting pore networks is particularly valuable since it enables pore network modeling simulations which can be useful for a host of tasks from predicting transport properties to simulating performance of entire devices. This work reports an efficient algorithm for extracting networks using only standard image analysis techniques. The algorithm was applied to several standard porous materials ranging from sandstone to fibrous mats, and in all cases agreed very well with established or known values for pore and throat sizes, capillary pressure curves, and permeability. In the case of sandstone, the present algorithm was compared to the network obtained using the current state-of-the-art algorithm, and very good agreement was achieved. Most importantly, the network extracted from an image of fibrous media correctly predicted the anisotropic permeability tensor, demonstrating the critical ability to detect key structural features. The highly efficient algorithm allows extraction on fairly large images of 5003 voxels in just over 200 s. The ability for one algorithm to match materials as varied as sandstone with 20% porosity and fibrous media with 75% porosity is a significant advancement. The source code for this algorithm is provided.

Mechanical, Thermal and Acoustic Properties of Open-pore Phenolic Multi-structured Cryogel

NASA Astrophysics Data System (ADS)

Yao, Rui; Yao, Zhengjun; Zhou, Jintang; Liu, Peijiang; Lei, Yiming

2017-09-01

Open-pore phenolic cryogel acoustic multi-structured plates (OCMPs) were prepared via modified sol gel polymerization and freeze-dried methods. The pore morphology, mechanical, thermal and acoustic properties of the cryogels were investigated. From the experimental results, the cryogels exhibited a porous sandwich microstructure: A nano-micron double-pore structure was observed in the core layer of the plates, and nanosized pores were observed in the inner part of the micron pores. In addtion, compared with cryogel plates with uniform-pore (OCPs), the OCMPs had lower thermal conductivities. What’s more, the compressive and tensile strength of the OCMPs were much higher than those of OCPs. Finally, the OCMPs exhibited superior acoustic performances (20% solid content OCMPs performed the best) as compared with those of OCPs. Moreover, the sound insulation value and sound absorption bandwidth of OCMPs exhibited an improvement of approximately 3 and 2 times as compared with those of OCPs, respectively.

Understanding fluid transport through the multiscale pore network of a natural shale

NASA Astrophysics Data System (ADS)

Davy, Catherine A.; Nguyen Kim, Thang; Song, Yang; Troadec, David; Blanchenet, Anne-Marie; Adler, Pierre M.

2017-06-01

The pore structure of a natural shale is obtained by three imaging means. Micro-tomography results are extended to provide the spatial arrangement of the minerals and pores present at a voxel size of 700 nm (the macroscopic scale). FIB/SEM provides a 3D representation of the porous clay matrix on the so-called mesoscopic scale (10-20 nm); a connected pore network, devoid of cracks, is obtained for two samples out of five, while the pore network is connected through cracks for two other samples out of five. Transmission Electron Microscopy (TEM) is used to visualize the pore space with a typical pixel size of less than 1 nm and a porosity ranging from 0.12 to 0.25. On this scale, in the absence of 3D images, the pore structure is reconstructed by using a classical technique, which is based on truncated Gaussian fields. Permeability calculations are performed with the Lattice Boltzmann Method on the nanoscale, on the mesoscale, and on the combination of the two. Upscaling is finally done (by a finite volume approach) on the bigger macroscopic scale. Calculations show that, in the absence of cracks, the contribution of the nanoscale pore structure on the overall permeability is similar to that of the mesoscale. Complementarily, the macroscopic permeability is measured on a centimetric sample with a neutral fluid (ethanol). The upscaled permeability on the macroscopic scale is in good agreement with the experimental results.

Structure influence on mechanical and acoustic properties of freeze-dried gels obtained with the use of hydrocolloids.

PubMed

Ciurzyńska, Agnieszka; Marzec, Agata; Mieszkowska, Arleta; Lenart, Andrzej

2017-04-01

The influence of the structure formed by the type of hydrocolloids (low-methoxyl pectin, the mixture of xanthan gum, and locust bean gum, and mixture of xanthan gum, and guar gum) and the aeration time (3, 5, 7, and 9 min) on textural properties of freeze-dried gels were investigated. The hardest texture generating the strongest acoustic emission was obtained by freeze-dried pectin gel, characterised by the lowest porosity and the largest pore diameter. Aeration time significantly affected mechanical and acoustic properties of the pectin gel lyophilisate. No effect of gel aeration time on tested characteristics of samples with mixture of hydrocolloids was observed. Strong positive correlations between acoustic energy as well as the maximum force and work and negative ones between porosity and pore diameter indicate that greater resilience and stronger acoustic emission of freeze-dried gels was caused by the reduction of porosity and the increase in the pore size of the material. The research is expected to show the phenomenon of structure formation when preparing and freeze-drying gels and explain the influence of the process parameters (time of aeration, the type of hydrocolloids) on the formation of the internal structure and physical properties of a dried product, especially mechanical and acoustic properties. This achievement will contribute to the development of the science of food and human nutrition, especially within the context of the popular research on aerated diet products. The expected result will be the ability to develop a new technology for producing food with a delicate texture, using the phenomenon of sublimation. As a result, designing changes in the structure of freeze-dried fruit gels with a delicate structure will be possible due to the choice of ingredients and aeration parameters in order to develop innovative food characterised by favorable nutritional, health and functional properties, which will be attractive for the consumers. © 2016 Wiley Periodicals, Inc.

Transport and Deposition of Nanoparticles in the Pore Network of a Reservoir Rock: Effects of Pore Surface Heterogeneity and Radial Diffusion

NASA Astrophysics Data System (ADS)

Pham, Ngoc; Papavassiliou, Dimitrios

2014-03-01

In this study, transport behavior of nanoparticles under different pore surface conditions of consolidated Berea sandstone is numerically investigated. Micro-CT scanning technique is applied to obtain 3D grayscale images of the rock sample geometry. Quantitative characterization, which is based on image analysis is done to obtain physical properties of the pore network, such as the pore size distribution and the type of each pore (dead-end, isolated, and fully connected pore). Transport of water through the rock is simulated by employing a 3D lattice Boltzmann method. The trajectories of nanopaticles moving under convection in the simulated flow field and due to molecular diffusion are monitored in the Lagrangian framework. It is assumed in the model that the particle adsorption on the pore surface, which is modeled as a pseudo-first order adsorption, is the only factor hindering particle propagation. The effect of pore surface heterogeneity to the particle breakthrough is considered, and the role of particle radial diffusion is also addressed in details. The financial support of the Advanced Energy Consortium (AEC BEG08-022) and the computational support of XSEDE (CTS090017) are acknowledged.

Cavitation and pore blocking in nanoporous glasses.

PubMed

Reichenbach, C; Kalies, G; Enke, D; Klank, D

2011-09-06

In gas adsorption studies, porous glasses are frequently referred to as model materials for highly disordered mesopore systems. Numerous works suggest that an accurate interpretation of physisorption isotherms requires a complete understanding of network effects upon adsorption and desorption, respectively. The present article deals with nitrogen and argon adsorption at different temperatures (77 and 87 K) performed on a series of novel nanoporous glasses (NPG) with different mean pore widths. NPG samples contain smaller mesopores and significantly higher microporosity than porous Vycor glass or controlled pore glass. Since the mean pore width of NPG can be tuned sensitively, the evolution of adsorption characteristics with respect to a broadening pore network can be investigated starting from the narrowest nanopore width. With an increasing mean pore width, a H2-type hysteresis develops gradually which finally transforms into a H1-type. In this connection, a transition from a cavitation-induced desorption toward desorption controlled by pore blocking can be observed. Furthermore, we find concrete hints for a pore size dependence of the relative pressure of cavitation in highly disordered pore systems. By comparing nitrogen and argon adsorption, a comprehensive insight into adsorption mechanisms in novel disordered materials is provided. © 2011 American Chemical Society

The influence of shrinkage-cracking on the drying behaviour of White Portland cement using Single-Point Imaging (SPI).

PubMed

Beyea, S D; Balcom, B J; Bremner, T W; Prado, P J; Cross, A R; Armstrong, R L; Grattan-Bellew, P E

1998-11-01

The removal of water from pores in hardened cement paste smaller than 50 nm results in cracking of the cement matrix due to the tensile stresses induced by drying shrinkage. Cracks in the matrix fundamentally alter the permeability of the material, and therefore directly affect the drying behaviour. Using Single-Point Imaging (SPI), we obtain one-dimensional moisture profiles of hydrated White Portland cement cylinders as a function of drying time. The drying behaviour of White Portland cement, is distinctly different from the drying behaviour of related concrete materials containing aggregates.

Comparison of the Modified Biot-Gassmann Theory and the Kuster-Toksoz Theory in Predicting Elastic Velocities of Sediments

USGS Publications Warehouse

Lee, Myung W.

2008-01-01

Elastic velocities of water-saturated sandstones depend primarily on porosity, effective pressure, and the degree of consolidation. If the dry-frame moduli are known, from either measurements or theoretical calculations, the effect of pore water on velocities can be modeled using the Gassmann theory. Kuster and Toksoz developed a theory based on wave-scattering theory for a variety of inclusion shapes, which provides a means for calculating dry- or wet-frame moduli. In the Kuster-Toksoz theory, elastic wave velocities through different sediments can be predicted by using different aspect ratios of the sediment's pore space. Elastic velocities increase as the pore aspect ratio increases (larger pore aspect ratio describes a more spherical pore). On the basis of the velocity ratio, which is assumed to be a function of (1-0)n, and the Biot-Gassmann theory, Lee developed a semi-empirical equation for predicting elastic velocities, which is referred to as the modified Biot-Gassmann theory of Lee. In this formulation, the exponent n, which depends on the effective pressure and the degree of consolidation, controls elastic velocities; as n increases, elastic velocities decrease. Computationally, the role of exponent n in the modified Biot-Gassmann theory by Lee is similar to the role of pore aspect ratios in the Kuster-Toksoz theory. For consolidated sediments, either theory predicts accurate velocities. However, for unconsolidated sediments, the modified Biot-Gassmann theory by Lee performs better than the Kuster-Toksoz theory, particularly in predicting S-wave velocities.

Coverage dependent molecular assembly of anthraquinone on Au(111)

NASA Astrophysics Data System (ADS)

DeLoach, Andrew S.; Conrad, Brad R.; Einstein, T. L.; Dougherty, Daniel B.

2017-11-01

A scanning tunneling microscopy study of anthraquinone (AQ) on the Au(111) surface shows that the molecules self-assemble into several structures depending on the local surface coverage. At high coverages, a close-packed saturated monolayer is observed, while at low coverages, mobile surface molecules coexist with stable chiral hexamer clusters. At intermediate coverages, a disordered 2D porous network interlinking close-packed islands is observed in contrast to the giant honeycomb networks observed for the same molecule on Cu(111). This difference verifies the predicted extreme sensitivity [J. Wyrick et al., Nano Lett. 11, 2944 (2011)] of the pore network to small changes in the surface electronic structure. Quantitative analysis of the 2D pore network reveals that the areas of the vacancy islands are distributed log-normally. Log-normal distributions are typically associated with the product of random variables (multiplicative noise), and we propose that the distribution of pore sizes for AQ on Au(111) originates from random linear rate constants for molecules to either desorb from the surface or detach from the region of a nucleated pore.

Coverage dependent molecular assembly of anthraquinone on Au(111).

PubMed

DeLoach, Andrew S; Conrad, Brad R; Einstein, T L; Dougherty, Daniel B

2017-11-14

A scanning tunneling microscopy study of anthraquinone (AQ) on the Au(111) surface shows that the molecules self-assemble into several structures depending on the local surface coverage. At high coverages, a close-packed saturated monolayer is observed, while at low coverages, mobile surface molecules coexist with stable chiral hexamer clusters. At intermediate coverages, a disordered 2D porous network interlinking close-packed islands is observed in contrast to the giant honeycomb networks observed for the same molecule on Cu(111). This difference verifies the predicted extreme sensitivity [J. Wyrick et al., Nano Lett. 11, 2944 (2011)] of the pore network to small changes in the surface electronic structure. Quantitative analysis of the 2D pore network reveals that the areas of the vacancy islands are distributed log-normally. Log-normal distributions are typically associated with the product of random variables (multiplicative noise), and we propose that the distribution of pore sizes for AQ on Au(111) originates from random linear rate constants for molecules to either desorb from the surface or detach from the region of a nucleated pore.

Application of real rock pore-threat statistics to a regular pore network model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rakibul, M.; Sarker, H.; McIntyre, D.

2011-01-01

This work reports the application of real rock statistical data to a previously developed regular pore network model in an attempt to produce an accurate simulation tool with low computational overhead. A core plug from the St. Peter Sandstone formation in Indiana was scanned with a high resolution micro CT scanner. The pore-throat statistics of the three-dimensional reconstructed rock were extracted and the distribution of the pore-throat sizes was applied to the regular pore network model. In order to keep the equivalent model regular, only the throat area or the throat radius was varied. Ten realizations of randomly distributed throatmore » sizes were generated to simulate the drainage process and relative permeability was calculated and compared with the experimentally determined values of the original rock sample. The numerical and experimental procedures are explained in detail and the performance of the model in relation to the experimental data is discussed and analyzed. Petrophysical properties such as relative permeability are important in many applied fields such as production of petroleum fluids, enhanced oil recovery, carbon dioxide sequestration, ground water flow, etc. Relative permeability data are used for a wide range of conventional reservoir engineering calculations and in numerical reservoir simulation. Two-phase oil water relative permeability data are generated on the same core plug from both pore network model and experimental procedure. The shape and size of the relative permeability curves were compared and analyzed and good match has been observed for wetting phase relative permeability but for non-wetting phase, simulation results were found to be deviated from the experimental ones. Efforts to determine petrophysical properties of rocks using numerical techniques are to eliminate the necessity of regular core analysis, which can be time consuming and expensive. So a numerical technique is expected to be fast and to produce reliable results. In applied engineering, sometimes quick result with reasonable accuracy is acceptable than the more time consuming results. Present work is an effort to check the accuracy and validity of a previously developed pore network model for obtaining important petrophysical properties of rocks based on cutting-sized sample data.« less

Application of real rock pore-throat statistics to a regular pore network model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sarker, M.R.; McIntyre, D.; Ferer, M.

2011-01-01

This work reports the application of real rock statistical data to a previously developed regular pore network model in an attempt to produce an accurate simulation tool with low computational overhead. A core plug from the St. Peter Sandstone formation in Indiana was scanned with a high resolution micro CT scanner. The pore-throat statistics of the three-dimensional reconstructed rock were extracted and the distribution of the pore-throat sizes was applied to the regular pore network model. In order to keep the equivalent model regular, only the throat area or the throat radius was varied. Ten realizations of randomly distributed throatmore » sizes were generated to simulate the drainage process and relative permeability was calculated and compared with the experimentally determined values of the original rock sample. The numerical and experimental procedures are explained in detail and the performance of the model in relation to the experimental data is discussed and analyzed. Petrophysical properties such as relative permeability are important in many applied fields such as production of petroleum fluids, enhanced oil recovery, carbon dioxide sequestration, ground water flow, etc. Relative permeability data are used for a wide range of conventional reservoir engineering calculations and in numerical reservoir simulation. Two-phase oil water relative permeability data are generated on the same core plug from both pore network model and experimental procedure. The shape and size of the relative permeability curves were compared and analyzed and good match has been observed for wetting phase relative permeability but for non-wetting phase, simulation results were found to be deviated from the experimental ones. Efforts to determine petrophysical properties of rocks using numerical techniques are to eliminate the necessity of regular core analysis, which can be time consuming and expensive. So a numerical technique is expected to be fast and to produce reliable results. In applied engineering, sometimes quick result with reasonable accuracy is acceptable than the more time consuming results. Present work is an effort to check the accuracy and validity of a previously developed pore network model for obtaining important petrophysical properties of rocks based on cutting-sized sample data. Introduction« less

Development of nanocomposite scaffolds based on TiO2 doped in grafted chitosan/hydroxyapatite by freeze drying method and evaluation of biocompatibility.

PubMed

Abd-Khorsand, Saber; Saber-Samandari, Samaneh; Saber-Samandari, Saeed

2017-08-01

Porous three-dimensional scaffolds with potential for application as cancellous bone graft substitutes were prepared using the freeze-drying technique. Hydroxyapatite with different weight ratio was embedded in the network of poly(acrylic acid) grafted chitosan accompanied by using TiO 2 as an auxiliary component to fabricate porous nanocomposite bone scaffolds. Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction analysis and mechanical tests were carried out to characterize the prepared scaffolds. These scaffolds showed well-controlled and interconnected porous structures. The pore size and porosity of the scaffolds could be effectively modulated by selecting appropriate amounts of hydroxyapatite. The results obtained from mechanical properties measurements indicated that the scaffolds could basically retain their strength in their dry state and have adequate mechanical properties close to those of cancellous bone. The swelling behavior of the scaffolds was also examined in both water and phosphate buffer saline solution. The cytotoxicity of the scaffold was determined by MTT assays on human fibroblast gum (HuGu) cells for 24, 48 and 72h. In conclusion, this investigation demonstrates that the fabricated nanocomposite scaffolds are suitable for bone tissue engineering. Copyright © 2017 Elsevier B.V. All rights reserved.

The application of A.C. impedance spectroscopy on the durability of hydrated cement paste subjected to various environmental conditions

NASA Astrophysics Data System (ADS)

Perron, Stacey

Harsh Canadian winters cause many problems in reinforced concrete structures due to damaging freezing-thawing cycles which is exacerbated by the heavy use of de-icing salts on roadways. Evaluation of concrete durability with current ASTM methods may give unreliable results and are destructive to the structure. A relatively new and novel approach to evaluating the durability of concrete uses A. C. Impedance Spectroscopy (ACIS). Hydrated cement paste (hcp), mortar, brick and vycor glass were evaluated using ACIS during drying-rewetting and freezing-thawing cycles. Thermal mechanical analysis (TMA), and differential scanning calorimetry (DSC) tests were also conducted and used as references. Results indicate that ACIS can be used to successfully evaluate the pore structure of hcp. The results from the drying-rewetting cycles are consistent with the pore coarsening theory. ACIS revealed pore structure changes consistent with the mechanical strains and pore solution chemistry. Increased pore continuity with each drying-rewetting cycle was indicated by a reduction in sample resistance. Unique tests were conducted on hydrated cement paste, mortar, brick and vycor glass that measured the ACIS and mechanical strains simultaneously while undergoing temperature changes. The temperature was lowered from 5°C to -80°C and then raised to +20°C. The ACIS results indicate that durability of the material can be assessed using the parameters R, material resistance, and phi, indicative of the frequency dispersion angle. The resistance on freezing values correlates with the amount of pore water freezing. The phi values on freezing are representative of the pore size distribution of the test sample. Resistance and phi data from freezing-thawing tests can be analyzed to assess durability of the sample. A material that is durable to freezing-thawing cycles can be described as having a high resistance at room temperature, a low freezing resistance and small changes in phi. Results were consistent among all the materials tested. Freezing-thawing tests were also conducted on specimens resaturated with salt solutions (5%, 10%, 15%). The results of these tests indicated a lower incipient freezing temperature, increase in pore blockage temperatures, and increased mobility of the pore water during freezing (increase in the change to phi). A series of test were conducted to evaluate the electrode polarization effects associated with the permittivity values at low frequencies. Teflon sheets were used to minimize the electrode polarization effects. It is shown that electrode polarization effects dominate over bulk polarization effects. Effects vary with the porosity of the material.

Microorganisms in desert rocks: the edge of life on Earth.

PubMed

Wierzchos, Jacek; de los Ríos, Asunción; Ascaso, Carmen

2012-12-01

This article reviews current knowledge on microbial communities inhabiting endolithic habitats in the arid and hyper-arid regions of our planet. In these extremely dry environments, the most common survival strategy is to colonize the interiors of rocks. This habitat provides thermal buffering, physical stability, and protection against incident UV radiation, excessive photosynthetically active radiation, and freeze-thaw events. Above all, through water retention in the rocks' network of pores and fissures, moisture is made available. Some authors have argued that dry environments pose the most extreme set of conditions faced by microorganisms. Microbial cells need to withstand the biochemical stresses created by the lack of water, along with temperature fluctuations and/or high salinity. In this review, we also address the variety of ways in which microorganisms deal with the lack of moisture in hyper-arid environments and point out the diversity of microorganisms that are able to cope with only the scarcest presence of water. Finally, we discuss the important clues to the history of life on Earth, and perhaps other places in our solar system, that have emerged from the study of extreme microbial ecosystems.

Porosity changes and retention of ginsenosides in North American ginseng root using different dehydration processes.

PubMed

Purnama, Monica; Yaghmaee, Parastoo; Durance, Tim D; Kitts, David D

2010-09-01

Air drying (AD), freeze-drying (FD), and vacuum-microwave drying (VMD) were applied to fresh North American ginseng roots to evaluate the effect of different drying techniques on pore characteristics and the subsequent recovery of ginsenoside content. FD ginseng root produced the lowest reductions in both total moisture content and water activity (P < 0.05), with no differences noted between Ontario or British Columbia ginseng. Ginseng roots from Ontario and British Columbia sources were therefore pooled to conduct the root porosity and ginsenoside measurements. Among samples, FD ginseng obtained the highest total porosity followed by VMD and AD, respectively (P < 0.05). All dehydrated samples had a porous structure with sizes that ranged from 0.002 μm to 172 μm, dominated by macropores (>1.5 μm). Pore characteristics of dried ginseng root were shown to affect recovery of ginsenosides, with the general trend being an increase in total porosity resulting in an increase in total ginsenoside recovered. High performance liquid chromatography results obtained on specific ginsenosides showed that AD of ginseng root resulted in the lowest recovery of total ginsenosides, most notably, Rg1 and Rb1, followed by VMD and FD, respectively. There was no specific difference in total ginsenoside recovery from roots dried at increasing power of VMD.

Transient effects of drying creep in nanoporous solids: understanding the effects of nanoscale energy barriers

NASA Astrophysics Data System (ADS)

Sinko, Robert; Vandamme, Matthieu; Bažant, Zdeněk P.; Keten, Sinan

2016-07-01

The Pickett effect is the phenomenon of creep enhancement during transient drying. It has been observed for many nanoporous solids, including concrete, wood and Kevlar. While the existing micromechanical models can partially explain this effect, they have yet to consider nanoscale dynamic effects of water in nanopores, which are believed to be of paramount importance. Here, we examine how creep deformations in a slit pore are accelerated by the motion of water due to drying forces using coarse-grained molecular dynamics simulations. We find that the drying that drives water flow in the nanopores lowers both the activation energy of pore walls sliding past one another and the apparent viscosity of confined water molecules. This lowering can be captured with an analytical Arrhenius relationship accounting for the role of water flow in overcoming the energy barriers. Notably, we use this model and simulation results to demonstrate that the drying creep strain is not linearly dependent on the applied creep stress at the nanopore level. Our findings establish the scaling relationships that explain how the creep driving force, drying force and fluid properties are related. Thus, we establish the nanoscale origins of the Pickett effect and provide strategies for minimizing the additional displacements arising from this effect.

Transient effects of drying creep in nanoporous solids: understanding the effects of nanoscale energy barriers

PubMed Central

Sinko, Robert; Vandamme, Matthieu; Keten, Sinan

2016-01-01

The Pickett effect is the phenomenon of creep enhancement during transient drying. It has been observed for many nanoporous solids, including concrete, wood and Kevlar. While the existing micromechanical models can partially explain this effect, they have yet to consider nanoscale dynamic effects of water in nanopores, which are believed to be of paramount importance. Here, we examine how creep deformations in a slit pore are accelerated by the motion of water due to drying forces using coarse-grained molecular dynamics simulations. We find that the drying that drives water flow in the nanopores lowers both the activation energy of pore walls sliding past one another and the apparent viscosity of confined water molecules. This lowering can be captured with an analytical Arrhenius relationship accounting for the role of water flow in overcoming the energy barriers. Notably, we use this model and simulation results to demonstrate that the drying creep strain is not linearly dependent on the applied creep stress at the nanopore level. Our findings establish the scaling relationships that explain how the creep driving force, drying force and fluid properties are related. Thus, we establish the nanoscale origins of the Pickett effect and provide strategies for minimizing the additional displacements arising from this effect. PMID:27493584

Transient effects of drying creep in nanoporous solids: understanding the effects of nanoscale energy barriers.

PubMed

Sinko, Robert; Vandamme, Matthieu; Bažant, Zdeněk P; Keten, Sinan

2016-07-01

The Pickett effect is the phenomenon of creep enhancement during transient drying. It has been observed for many nanoporous solids, including concrete, wood and Kevlar. While the existing micromechanical models can partially explain this effect, they have yet to consider nanoscale dynamic effects of water in nanopores, which are believed to be of paramount importance. Here, we examine how creep deformations in a slit pore are accelerated by the motion of water due to drying forces using coarse-grained molecular dynamics simulations. We find that the drying that drives water flow in the nanopores lowers both the activation energy of pore walls sliding past one another and the apparent viscosity of confined water molecules. This lowering can be captured with an analytical Arrhenius relationship accounting for the role of water flow in overcoming the energy barriers. Notably, we use this model and simulation results to demonstrate that the drying creep strain is not linearly dependent on the applied creep stress at the nanopore level. Our findings establish the scaling relationships that explain how the creep driving force, drying force and fluid properties are related. Thus, we establish the nanoscale origins of the Pickett effect and provide strategies for minimizing the additional displacements arising from this effect.

Sorption of water by biochar: Closer look at micropores

NASA Astrophysics Data System (ADS)

Spokas, Kurt; Hall, Kathleen; Joseph, Stephan; Kammann, Claudia; Novak, Jeffrey; Gámiz, Beatriz; Cox, Lucia

2017-04-01

Typically, biochar has been assumed to increase total water content of the soil system and thereby positively influence plant-soil moisture hydraulics. In this work, we focused on water's interaction with micro-pores (<2 nm) and its influence on water availability. In other words, the main question was if the driving force of water's behavior was the physics or chemistry of biochar pores. The temporal scale of liquid water entry into biochar's pore network is very complex, with observed bubbling occurring days, weeks, and even months after a piece of biochar is immersed under water at ambient conditions. Elevated temperature biochar typically has a positive heat of immersion measured calorimetrically, whereas the calculated BET energy of sorption from a water sorption isotherm typically decrease with production temperatures. To further complicate matters, different pieces of biochar interact differently with water even though the entire batch was created in the same reactor at the same time and after liquid water exposure the physical structure of biochar is irreversibly altered, sometimes negligible other times catastrophically. Nevertheless, based on the estimations of diffusion coefficients in biochar from drying curve analyses, pore surface moieties do reduce the effective diffusivity of water vapor in biochar. Contrary to the rule of thumb in soil physics, where higher gas filled porosity correlates with higher soil moisture holding capacities, our results indicate that biochar's water sorption rate and capacity is actually reduced at ambient conditions by an increase in microporous volume. Thereby, biochar's hydrophobic behavior is partly due to the entrapment of gas within the air-filled porosity which prevents liquid water's entry, even though these biochars possess elevated gas phase sorption capacities (e.g., BET N2/CO2 surface areas).

Séchage d'un enduit pigmenté avec application à l'étude d'une couche papetière

NASA Astrophysics Data System (ADS)

Bernada, P.; Bruneau, D.

1996-07-01

Paper color coating drying is investigated from several experimental view points which include drying kinetics and time evolution of moisture content profiles, pore size distribution in the dried coating, and natural binder (starch) distribution in the dried coating. A study of the effects of drying conditions on those experimental parameters is carried out. Furthermore, gelification and consolidation characteristic moisture contents of the coating are determined using a graphical approach. Le séchage d'un enduit pigmenté à l'usage d'une couche papetière est absorbé sous diverts aspects : cinétiques de séchage et évolution temporelle des profils de teneur en eau, profils de répartition de la taille des pores dans la couche séchée, et répartition finale d'un liant hydrophile de la sauce de couchage (amidon). Les conséquences des conditions de séchage sur ces paramètres expérimentaux sont mises en évidence. De plus, les teneurs en eau caractéristiques de gélification et consolidation de la sauce de couchage sont obtenues par une approche graphique.

An investigation into preserving spatially-distinct pore systems in multi-component rocks using a fossiliferous limestone example

NASA Astrophysics Data System (ADS)

Jiang, Zeyun; Couples, Gary D.; Lewis, Helen; Mangione, Alessandro

2018-07-01

Limestones containing abundant disc-shaped fossil Nummulites can form significant hydrocarbon reservoirs but they have a distinctly heterogeneous distribution of pore shapes, sizes and connectivities, which make it particularly difficult to calculate petrophysical properties and consequent flow outcomes. The severity of the problem rests on the wide length-scale range from the millimetre scale of the fossil's pore space to the micron scale of rock matrix pores. This work develops a technique to incorporate multi-scale void systems into a pore network, which is used to calculate the petrophysical properties for subsequent flow simulations at different stages in the limestone's petrophysical evolution. While rock pore size, shape and connectivity can be determined, with varying levels of fidelity, using techniques such as X-ray computed tomography (CT) or scanning electron microscopy (SEM), this work represents a more challenging class where the rock of interest is insufficiently sampled or, as here, has been overprinted by extensive chemical diagenesis. The main challenge is integrating multi-scale void structures derived from both SEM and CT images, into a single model or a pore-scale network while still honouring the nature of the connections across these length scales. Pore network flow simulations are used to illustrate the technique but of equal importance, to demonstrate how supportable earlier-stage petrophysical property distributions can be used to assess the viability of several potential geological event sequences. The results of our flow simulations on generated models highlight the requirement for correct determination of the dominant pore scales (one plus of nm, μm, mm, cm), the spatial correlation and the cross-scale connections.

A facile method for the preparation of monodisperse beads with uniform pore sizes for cell culture.

PubMed

Moon, Seung-Kwan; Oh, Myeong-Jin; Paik, Dong-Hyun; Ryu, Tae-Kyung; Park, Kyeongsoon; Kim, Sung-Eun; Park, Jong-Hoon; Kim, Jung-Hyun; Choi, Sung-Wook

2013-03-12

This paper describes a facile method for the preparation of porous gelatin beads with uniform pore sizes using a simple fluidic device and their application as supporting materials for cell culture. An aqueous gelatin droplet containing many uniform toluene droplets, produced in the fluidic device, is dropped into liquid nitrogen for instant freezing and the small toluene droplets evolve into pores in the gelatin beads after removal of toluene and then freeze-drying. The porous gelatin beads exhibit a uniform pore size and monodisperse diameter as well as large open pores at the surface. Fluorescence microscopy images of fibroblast-loaded gelatin beads confirm the attachment and proliferation of the cells throughout the porous gelatin beads. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mycorrhizal networks and distance from mature trees alter patterns of competition and facilitation in dry Douglas-fir forests.

PubMed

Teste, François P; Simard, Suzanne W

2008-11-01

The distribution of dry Douglas-fir forests in western North America is expected to shift northward with climate change and disappear from the grassland interface in the southern interior of British Columbia. This shift may be accentuated by clearcutting, a common harvesting practice that aims to reduce the competitive effects of residual mature trees on new regeneration, but in so doing, ignores their facilitative effects. In this study, we investigated the net effects of competition from and facilitation by mature trees retained on harvested sites on seedling establishment in the dry interface Douglas-fir forests. We demonstrate that access to a mycorrhizal network (MN) and proximity to trees have important influences on seedling performance. On six sites, we established trenched plots around 24 mature Pseudotsuga menziesii var. glauca (Douglas-fir) trees, then planted Douglas-fir seedlings into four mesh treatments that served to restrict MN access (i.e., planted into mesh bags with 0.5-, 35-, or 250-microm pores, or without mesh) or into impermeable bags (grown in isolation) at four distances (0.5, 1.0, 2.5, or 5.0 m). Seedling survival tended to be greater and water stress lower where seedlings had full access to the MN. Seedling height, shoot biomass, needle biomass, and nutrient uptake peaked at 2.5-5.0 m from mature trees. Seedlings 0.5 m from mature trees had lower CO2 assimilation rates and wood delta(13)C compared to seedlings 5.0 m away. Competition for soil resources was highest near mature trees but facilitation was relatively greater at further distances, resulting in a zone of net benefit for seedlings. These results show that intraspecific tree-seedling interactions are both competitive and facilitative in dry Douglas-fir forests, and that they are spatially dependent. After disturbance, maintaining residual mature trees may be important for their beneficial regeneration zones.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kyakuno, Haruka, E-mail: h-kyakuno@kanagawa-u.ac.jp; Institute of Physics, Faculty of Engineering, Kanagawa University, Yokohama 221-8686; Fukasawa, Mamoru

Single-wall carbon nanotubes (SWCNTs) are a good model system that provides atomically smooth nanocavities. It has been reported that water-SWCNTs exhibit hydrophobicity depending on the temperature T and the SWCNT diameter D. SWCNTs adsorb water molecules spontaneously in their cylindrical pores around room temperature, whereas they exhibit a hydrophilic-hydrophobic transition or wet-dry transition (WDT) at a critical temperature T{sub wd} ≈ 220-230 K and above a critical diameter D{sub c} ≈ 1.4-1.6 nm. However, details of the WDT phenomenon and its mechanism remain unknown. Here, we report a systematic experimental study involving X-ray diffraction, optical microscopy, and differential scanning calorimetry.more » It is found that water molecules inside thick SWCNTs (D > D{sub c}) evaporate and condense into ice Ih outside the SWCNTs at T{sub wd} upon cooling, and the ice Ih evaporates and condenses inside the SWCNTs upon heating. On the other hand, residual water trapped inside the SWCNTs below T{sub wd} freezes. Molecular dynamics simulations indicate that upon lowering T, the hydrophobicity of thick SWCNTs increases without any structural transition, while the water inside thin SWCNTs (D < D{sub c}) exhibits a structural transition, forming an ordered ice. This ice has a well-developed hydrogen bonding network adapting to the cylindrical pores of the SWCNTs. Thus, the unusual diameter dependence of the WDT is attributed to the adaptability of the structure of water to the pore dimension and shape.« less

Pore size engineering applied to starved electrochemical cells and batteries

NASA Technical Reports Server (NTRS)

Abbey, K. M.; Thaller, L. H.

1982-01-01

To maximize performance in starved, multiplate cells, the cell design should rely on techniques which widen the volume tolerance characteristics. These involve engineering capillary pressure differences between the components of an electrochemical cell and using these forces to promote redistribution of electrolyte to the desired optimum values. This can be implemented in practice by prescribing pore size distributions for porous back-up plates, reservoirs, and electrodes. In addition, electrolyte volume management can be controlled by incorporating different pore size distributions into the separator. In a nickel/hydrogen cell, the separator must contain pores similar in size to the small pores of both the nickel and hydrogen electrodes in order to maintain an optimum conductive path for the electrolyte. The pore size distributions of all components should overlap in such a way as to prevent drying of the separator and/or flooding of the hydrogen electrode.

SAPO-34/AlMCM-41, as a novel hierarchical nanocomposite: preparation, characterization and investigation of synthesis factors using response surface methodology

NASA Astrophysics Data System (ADS)

Roohollahi, Hossein; Halladj, Rouein; Askari, Sima; Yaripour, Fereydoon

2018-06-01

SAPO-34/AlMCM-41, as a new hierarchical nanocomposite was successfully synthesized via hydrothermal and dry-gel conversion. In an experimental and statistical study, effect of five input parameters including synthesis period, drying temperature, NaOH/Si, water/dried-gel and SAPO% were investigated on range-order degree of mesochannels and the relative crystallinity. X-ray diffraction (XRD) patterns were recorded to characterize the ordered AlMCM-41 and crystalline SAPO-34 structures. Nitrogen adsorption-desorption technique, scanning electron microscopy (SEM), field-emission SEM (FESEM) equipped with an energy-dispersive X-ray spectroscopy (EDS-Map) and transmission electron microscopy (TEM) were used to study the textural properties, morphology and surface elemental composition. Two reduced polynomials were fitted to the responses with good precision. Further, based on analysis of variances, SAPO% and time duration of dry-gel conversion were observed as the most effective parameters on the composite structure. The hierarchical porosity, narrow pore size distribution, high external surface area and large specific pore volume were of interesting characteristics for this novel nanocomposite.

Response of murine bone marrow-derived mesenchymal stromal cells to dry-etched porous silicon scaffolds.

PubMed

Hajj-Hassan, Mohamad; Khayyat-Kholghi, Maedeh; Wang, Huifen; Chodavarapu, Vamsy; Henderson, Janet E

2011-11-01

Porous silicon shows great promise as a bio-interface material due to its large surface to volume ratio, its stability in aqueous solutions and to the ability to precisely regulate its pore characteristics. In the current study, porous silicon scaffolds were fabricated from single crystalline silicon wafers by a novel xenon difluoride dry etching technique. This simplified dry etch fabrication process allows selective formation of porous silicon using a standard photoresist as mask material and eliminates the post-formation drying step typically required for the wet etching techniques, thereby reducing the risk of damaging the newly formed porous silicon. The porous silicon scaffolds supported the growth of primary cultures of bone marrow derived mesenchymal stromal cells (MSC) plated at high density for up to 21 days in culture with no significant loss of viability, assessed using Alamar Blue. Scanning electron micrographs confirmed a dense lawn of cells at 9 days of culture and the presence of MSC within the pores of the porous silicon scaffolds. Copyright © 2011 Wiley Periodicals, Inc.

Synthesis of silica aerogel monoliths with controlled specific surface areas and pore sizes

NASA Astrophysics Data System (ADS)

Gao, Bingying; Lu, Shaoxiang; Kalulu, Mulenga; Oderinde, Olayinka; Ren, Lili

2017-07-01

To replace traditional preparation methods of silica aerogels, a small-molecule 1,2-epoxypropane (PO) has been introduced into the preparation process instead of using ammonia as the cross-linking agent, thus generating a lightweight, high porosity, and large surface area silica aerogel monolithic. We put forward a simple solution route for the chemical synthesis of silica aerogels, which was characterized by scanning electron microscopy (SEM), TEM, XRD, FTIR, thermogravimetric analysis (TGA) and the Brunauer-Emmett-Teller (BET) method In this paper, the effect of the amount of PO on the microstructure of silica aerogels is discussed. The BET surface areas and pore sizes of the resulting silica aerogels can be freely adjusted by changing the amount of PO, which will be helpful in promoting the development of silica aerogels to fabricate other porous materials with similar requirements. We also adopted a new organic solvent sublimation drying (OSSD) method to replace traditional expensive and dangerous drying methods such as critical point drying and freeze drying. This simple approach is easy to operate and has good repeatability, which will further facilitate actual applications of silica aerogels.

Method for rapidly producing microporous and mesoporous materials

DOEpatents

Coronado, Paul R.; Poco, John F.; Hrubesh, Lawrence W.; Hopper, Robert W.

1997-01-01

An improved, rapid process is provided for making microporous and mesoporous materials, including aerogels and pre-ceramics. A gel or gel precursor is confined in a sealed vessel to prevent structural expansion of the gel during the heating process. This confinement allows the gelation and drying processes to be greatly accelerated, and significantly reduces the time required to produce a dried aerogel compared to conventional methods. Drying may be performed either by subcritical drying with a pressurized fluid to expel the liquid from the gel pores or by supercritical drying. The rates of heating and decompression are significantly higher than for conventional methods.

The Impact of Multiple Freeze-Thaw Cycles on the Microstructure of Aggregates from a Soddy-Podzolic Soil: A Microtomographic Analysis

NASA Astrophysics Data System (ADS)

Skvortsova, E. B.; Shein, E. V.; Abrosimov, K. N.; Romanenko, K. A.; Yudina, A. V.; Klyueva, V. V.; Khaidapova, D. D.; Rogov, V. V.

2018-02-01

With the help of computed X-ray microtomography with a resolution of 2.75 μm, changes in the microstructure and pore space of aggregates of 3 mm in diameter from the virgin soddy-podzolic soil (Glossic Retisol (Loamic)) in the air-dry, capillary-moistened, and frozen states after five freeze-thaw cycles were studied in a laboratory experiment. The freezing of the samples was performed at their capillary moistening. It was shown that capillary moistening of initially air-dry samples from the humus (AY), eluvial (EL), and illuvial (BT1) horizons at room temperature resulted in the development of the platy, fine vesicular, and angular blocky microstructure, respectively. The total volume of tomographically visible pores >10 μm increased by 1.3, 2.2, and 3.4 times, respectively. After freeze-thaw cycles, frozen aggregates partly preserved the structural arrangement formed during the capillary moistening. At the same time, in the frozen aggregate from the AY horizon, the total tomographic porosity decreased to the initial level of the air-dry soil. In the frozen aggregate from the EL horizon, large vesicular pores were formed, owing to which the total pore volume retained its increased values. The resistance of aggregate shape to the action of freeze-thaw cycles differed. The aggregate from the EL horizon completely lost its original configuration by the end of the experiment. The aggregate from the AY horizon displayed definite features of sagging after five freeze-thaw cycles, whereas the aggregate from the BT1 horizon preserved its original configuration.

Pore-Scale Simulation and Sensitivity Analysis of Apparent Gas Permeability in Shale Matrix

PubMed Central

Zhang, Pengwei; Hu, Liming; Meegoda, Jay N.

2017-01-01

Extremely low permeability due to nano-scale pores is a distinctive feature of gas transport in a shale matrix. The permeability of shale depends on pore pressure, porosity, pore throat size and gas type. The pore network model is a practical way to explain the macro flow behavior of porous media from a microscopic point of view. In this research, gas flow in a shale matrix is simulated using a previously developed three-dimensional pore network model that includes typical bimodal pore size distribution, anisotropy and low connectivity of the pore structure in shale. The apparent gas permeability of shale matrix was calculated under different reservoir pressures corresponding to different gas exploitation stages. Results indicate that gas permeability is strongly related to reservoir gas pressure, and hence the apparent permeability is not a unique value during the shale gas exploitation, and simulations suggested that a constant permeability for continuum-scale simulation is not accurate. Hence, the reservoir pressures of different shale gas exploitations should be considered. In addition, a sensitivity analysis was also performed to determine the contributions to apparent permeability of a shale matrix from petro-physical properties of shale such as pore throat size and porosity. Finally, the impact of connectivity of nano-scale pores on shale gas flux was analyzed. These results would provide an insight into understanding nano/micro scale flows of shale gas in the shale matrix. PMID:28772465

Pore-Scale Simulation and Sensitivity Analysis of Apparent Gas Permeability in Shale Matrix.

PubMed

Zhang, Pengwei; Hu, Liming; Meegoda, Jay N

2017-01-25

Extremely low permeability due to nano-scale pores is a distinctive feature of gas transport in a shale matrix. The permeability of shale depends on pore pressure, porosity, pore throat size and gas type. The pore network model is a practical way to explain the macro flow behavior of porous media from a microscopic point of view. In this research, gas flow in a shale matrix is simulated using a previously developed three-dimensional pore network model that includes typical bimodal pore size distribution, anisotropy and low connectivity of the pore structure in shale. The apparent gas permeability of shale matrix was calculated under different reservoir pressures corresponding to different gas exploitation stages. Results indicate that gas permeability is strongly related to reservoir gas pressure, and hence the apparent permeability is not a unique value during the shale gas exploitation, and simulations suggested that a constant permeability for continuum-scale simulation is not accurate. Hence, the reservoir pressures of different shale gas exploitations should be considered. In addition, a sensitivity analysis was also performed to determine the contributions to apparent permeability of a shale matrix from petro-physical properties of shale such as pore throat size and porosity. Finally, the impact of connectivity of nano-scale pores on shale gas flux was analyzed. These results would provide an insight into understanding nano/micro scale flows of shale gas in the shale matrix.

Template-directed assembly of metal-chalcogenide nanocrystals into ordered mesoporous networks.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vamvasakis, Ioannis; Subrahmanyam, Kota S.; Kanatzidis, Mercouri G.

Although great progress in the synthesis of porous networks of metal and metal oxide nanoparticles with highly accessible pore surface and ordered mesoscale pores has been achieved, synthesis of assembled 3D mesostructures of metal-chalcogenide nanocrystals is still challenging. In this work we demonstrate that ordered mesoporous networks, which comprise well-defined interconnected metal sulfide nanocrystals, can be prepared through a polymer-templated oxidative polymerization process. The resulting self-assembled mesostructures that were obtained after solvent extraction of the polymer template impart the unique combination of light-emitting metal chalcogenide nanocrystals, three-dimensional open-pore structure, high surface area, and uniform pores. We show that the poremore » surface of these materials is active and accessible to incoming molecules, exhibiting high photocatalytic activity and stability, for instance, in oxidation of 1-phenylethanol into acetophenone. We demonstrate through appropriate selection of the synthetic components that this method is general to prepare ordered mesoporous materials from metal chalcogenide nanocrystals with various sizes and compositions.« less

Mechanics of membrane bulging during cell-wall disruption in Gram-negative bacteria

NASA Astrophysics Data System (ADS)

Daly, Kristopher E.; Huang, Kerwyn Casey; Wingreen, Ned S.; Mukhopadhyay, Ranjan

2011-04-01

The bacterial cell wall is a network of sugar strands crosslinked by peptides that serve as the primary structure for bearing osmotic stress. Despite its importance in cellular survival, the robustness of the cell wall to network defects has been relatively unexplored. Treatment of the Gram-negative bacterium Escherichia coli with the antibiotic vancomycin, which disrupts the crosslinking of new material during growth, leads to the development of pronounced bulges and eventually of cell lysis. Here, we model the mechanics of the bulging of the cytoplasmic membrane through pores in the cell wall. We find that the membrane undergoes a transition between a nearly flat state and a spherical bulge at a critical pore radius of ~20 nm. This critical pore size is large compared to the typical distance between neighboring peptides and glycan strands, and hence pore size acts as a constraint on network integrity. We also discuss the general implications of our model to membrane deformations in eukaryotic blebbing and vesiculation in red blood cells.

The effect of fluids on the frictional behavior of calcite gouge

NASA Astrophysics Data System (ADS)

Rempe, M.; Di Toro, G.; Mitchell, T. M.; Hirose, T.; Smith, S. A. F.; Renner, J.

2016-12-01

The presence of fluids in fault zones affects the faults' strength and the nucleation and propagation of earthquakes due to mechanical or physico-chemical weakening effects. To better understand the effect of pore fluids on the frictional behavior of gouge-bearing faults, a series of intermediate- to high-velocity experiments was conducted using the Phv rotary-shear apparatus (Kochi Core Center, Japan) equipped with a servo-controlled pore-fluid pressure system. Calcite gouge was sheared up to several meters displacement at room-humidity (dry) and water-saturated conditions. The pore-fluid factor, λ=pf/σn, ranged from 0.15 to 0.7 and the effective normal stress, σn,eff=σn-pf, from 1 to 12 MPa. Sheared samples were analyzed using scanning electron microscopy and Raman spectroscopy. The steady-state shear stress is lower for saturated than for dry gouges sliding at V=1 mm/s, possibly due to higher intergranular lubrication and/or accelerated subcritical crack growth, as evidenced also by the observed higher degree of compaction. At V=1 m/s, dry gouges show a pronounced strengthening phase preceding the onset of dynamic weakening; saturated gouges weaken abruptly. The higher λ, the lower the peak and steady-state shear stress, but -counterintuitively- the less localized deformation. Degree of weakening and localization might be influenced by insufficient drainage at high λ. In undrained experiments, the shear stress is slightly decreased likely due to thermal pressurization of the pore fluid, but the onset of dynamic weakening is not accelerated, indicating that dynamic weakening is due to more efficient mechanisms. For example, amorphous carbon may lubricate the slip surfaces of dry and saturated calcite gouges and cause dynamic weakening, yet Raman spectra only show the presence of disordered carbon on the principal slip surface. Furthermore, the presence of small recrystallized grains suggests that strain accommodation during steady-state slip might occur by non-frictional processes, such as grain-boundary sliding aided by diffusion creep.

Prediction of relative and absolute permeabilities for gas and water from soil water retention curves using a pore-scale network model

NASA Astrophysics Data System (ADS)

Fischer, Ulrich; Celia, Michael A.

1999-04-01

Functional relationships for unsaturated flow in soils, including those between capillary pressure, saturation, and relative permeabilities, are often described using analytical models based on the bundle-of-tubes concept. These models are often limited by, for example, inherent difficulties in prediction of absolute permeabilities, and in incorporation of a discontinuous nonwetting phase. To overcome these difficulties, an alternative approach may be formulated using pore-scale network models. In this approach, the pore space of the network model is adjusted to match retention data, and absolute and relative permeabilities are then calculated. A new approach that allows more general assignments of pore sizes within the network model provides for greater flexibility to match measured data. This additional flexibility is especially important for simultaneous modeling of main imbibition and drainage branches. Through comparisons between the network model results, analytical model results, and measured data for a variety of both undisturbed and repacked soils, the network model is seen to match capillary pressure-saturation data nearly as well as the analytical model, to predict water phase relative permeabilities equally well, and to predict gas phase relative permeabilities significantly better than the analytical model. The network model also provides very good estimates for intrinsic permeability and thus for absolute permeabilities. Both the network model and the analytical model lost accuracy in predicting relative water permeabilities for soils characterized by a van Genuchten exponent n≲3. Overall, the computational results indicate that reliable predictions of both relative and absolute permeabilities are obtained with the network model when the model matches the capillary pressure-saturation data well. The results also indicate that measured imbibition data are crucial to good predictions of the complete hysteresis loop.

A Binomial Modeling Approach for Upscaling Colloid Transport Under Unfavorable Attachment Conditions: Emergent Prediction of Nonmonotonic Retention Profiles

NASA Astrophysics Data System (ADS)

Hilpert, Markus; Johnson, William P.

2018-01-01

We used a recently developed simple mathematical network model to upscale pore-scale colloid transport information determined under unfavorable attachment conditions. Classical log-linear and nonmonotonic retention profiles, both well-reported under favorable and unfavorable attachment conditions, respectively, emerged from our upscaling. The primary attribute of the network is colloid transfer between bulk pore fluid, the near-surface fluid domain (NSFD), and attachment (treated as irreversible). The network model accounts for colloid transfer to the NSFD of downgradient grains and for reentrainment to bulk pore fluid via diffusion or via expulsion at rear flow stagnation zones (RFSZs). The model describes colloid transport by a sequence of random trials in a one-dimensional (1-D) network of Happel cells, which contain a grain and a pore. Using combinatorial analysis that capitalizes on the binomial coefficient, we derived from the pore-scale information the theoretical residence time distribution of colloids in the network. The transition from log-linear to nonmonotonic retention profiles occurs when the conditions underlying classical filtration theory are not fulfilled, i.e., when an NSFD colloid population is maintained. Then, nonmonotonic retention profiles result potentially both for attached and NSFD colloids. The concentration maxima shift downgradient depending on specific parameter choice. The concentration maxima were also shown to shift downgradient temporally (with continued elution) under conditions where attachment is negligible, explaining experimentally observed downgradient transport of retained concentration maxima of adhesion-deficient bacteria. For the case of zero reentrainment, we develop closed-form, analytical expressions for the shape, and the maximum of the colloid retention profile.

Developing an Effective Model for Shale Gas Flow in Nano-scale Pore Clusters based on FIB-SEM Images

NASA Astrophysics Data System (ADS)

Jiang, W. B.; Lin, M.; Yi, Z. X.; Li, H. S.

2016-12-01

Nano-scale pores existed in the form of clusters are the controlling void space in shale gas reservoir. Gas transport in nanopores which has a significant influence on shale gas' recoverability displays multiple transport regimes, including viscous, slippage flow and Knudsen diffusion. In addition, it is also influenced by pore space characteristics. For convenience and efficiency consideration, it is necessary to develop an upscaling model from nano pore to pore cluster scale. Existing models are more like framework functions that provide a format, because the parameters that represent pore space characteristics are underdetermined and may have multiple possibilities. Therefore, it is urgent to make them clear and obtained a model that is closer to reality. FIB-SEM imaging technology is able to acquire three dimensional images with nanometer resolution that nano pores can be visible. Based on the images of two shale samples, we used a high-precision pore network extraction algorithm to generate equivalent pore networks and simulate multiple regime (non-Darcy) flow in it. Several structural parameters can be obtained through pore network modelling. It is found that although the throat-radius distributions are very close, throat flux-radius distributions of different samples can be divided into two categories. The variation of tortuosity with pressure and the overall trend of throat-flux distribution changes with pressure are disclosed. A deeper understanding of shale gas flow in nano-scale pore clusters is obtained. After all, an upscaling model that connects absolute permeability, apparent permeability and other characteristic parameters is proposed, and the best parameter scheme considering throat number-radius distribution and flowing porosity for this model is selected out of three schemes based on pore scale results, and it can avoid multiple-solution problem and is useful in reservoir modelling and experiment result analysis, etc. This work is supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB10020302), the National Natural Science Foundation of China (41574129), the Key Instrument Developing Project of the CAS (ZDYZ2012-1-08-02), the 973 Program (2014CB239004).

Comparison of Two Methods for Determination of Strontium Isotopes in Pore Water at Yucca Mountain, Nevada

NASA Astrophysics Data System (ADS)

Marshall, B. D.; Futa, K.; Scofield, K. M.

2002-12-01

The proposed radioactive waste repository at Yucca Mountain, Nevada would be constructed in the high-silica rhyolite member of the Topopah Spring Tuff, an ash-flow tuff within the ~500-m-thick unsaturated zone. Dry-drilled rock cores from this unit have been packaged to preserve their water content. Two methods have been used to extract the strontium contained in the pore water for isotopic measurements. In the first method, samples of dried core were crushed, and the 0.25 to 2.4 mm size fractions were leached with ultra-pure water for about 1 hour to dissolve the salts left behind by the evaporated pore water. Concentrations of strontium in the pore water were calculated from determinations of porosity and saturation on adjacent core and the measured strontium concentration in the leachate. In the second method, pore water was extracted from sealed core using an ultracentrifuge, minimizing evaporation of water from the core at all steps in the process. The centrifugation of 150 to 200 g of welded tuff at 15,000 rpm for 6 hours typically results in the recovery of as much as 3 ml of pore water for analysis. Strontium isotope compositions were determined by thermal ionization mass spectrometry; 87Sr /86Sr ratios have a reproducibility of 0.00005. The ranges of 87Sr/86Sr ratios determined by the two methods are identical: 0.71215 to 0.71267 in the leachates (n = 35) and 0.71214 to 0.71266 in the extracted pore waters (n = 21). However, the calculated strontium concentrations in the leachates average 300 μg/L, whereas those in the extracted pore water average 1440 μg/L, indicating that a substantial portion of the pore-water salts remain in the crushed rock after leaching. The strontium data determined on extracted pore water shows that the leaching of pore-water salts results in accurate 87Sr/86Sr, but that a substantial correction to the strontium concentration is required due to the inefficiency of the leaching procedure and the small pore sizes in the welded tuffs. The strontium isotope data obtained on leachates can be used to constrain models of water-rock interaction and estimates of travel times in the unsaturated zone.

Pore scale investigation of salt precipitation inside drying porous media resolved by 4D X-ray Microscopy Imaging

NASA Astrophysics Data System (ADS)

Norouzi Rad, M.

2016-12-01

Precipitation and deposition of salts in porous media is important in many natural processes as well as industrial and environmental applications since it can modify the structure and transport properties of porous media. In the presence of soluble salt in water during evaporation from porous media, salt is transported by convection induced by capillary liquid flow toward the evaporating surface where it accumulates, whereas diffusion tends to spread the salt and homogenize concentrations in space. Therefore, the competition between the convection and diffusion (characterized by Peclet number) affects the dynamics of salt distribution in porous media. As shown in previous studies (1-3) salt crust thickness and its coverage on the surface are highly influenced by the pore size distribution on the surface and active evaporation spots. In the current study, we focus on the precipitation dynamics and pattern during diffusion-driven evaporation period (the so-called stage-2 of evaporation) when the surface is dried and vaporization plane moves below the surface. Therefore, precipitation occurs inside the porous media during this period. To investigate the details of this process, 4D X-ray Microscopy was utilized. To do so, a packed bed of silica sand was saturated with 4 Molal NaCl solution and X-ray Microscopy was used to image the sample at well-defined time intervals during the evaporation process to provide pore scale information on evaporation and precipitation dynamics. The resulted 3-D pore-scale images were segmented to quantify the evaporative water losses and the dynamics and patterns of salt precipitation inside porous media with particular focus on the characterization of the processes occurring during stage-2 evaporation affecting the precipitation dynamics. [1] Norouzi Rad, M., N. Shokri, A. Keshmiri, P. Withers (2015), Effects of grain and pore size on salt precipitation during evaporation from porous media: A pore-scale investigation, Trans. Porous. Med., 110(2), 281-294. [2] Norouzi Rad, M., N. Shokri (2014), Effects of grain angularity on NaCl precipitation in porous media during evaporation, Water Resour. Res., 50, 9020-9030. [3] Norouzi Rad, M., N. Shokri, M. Sahimi (2013), Pore-Scale Dynamics of Salt Precipitation in Drying Porous Media, Phys. Rev. E, 88, 032404.

SMALL-ANGLE NEUTRON SCATTERING CHARACTERIZATION OF THE STRUCTURE OF NANOPOROUS CARBONS FOR ENERGY-RELATED APPLICATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

He, Lilin; Mavila Chathoth, Suresh; Melnichenko, Yuri B

2011-01-01

We used small-angle neutron scattering (SANS) and neutron contrast variation to study the structure of four nanoporouscarbons prepared by thermo-chemical etching of titanium carbide TiC in chlorine at 300, 400, 600, and 800 C with pore diameters ranging between -4 and -11 {angstrom}. SANS patterns were obtained from dry samples and samples saturated with deuterium oxide (D{sub 2}O) in order to delineate origin of the power law scattering in the low Q domain as well as to evaluate pore accessibility for D{sub 2}O molecules. SANS cross section of all samples was fitted to Debye-Anderson-Brumberger (DAB), DAB-Kirste-Porod models as well asmore » to the Guinier and modified Guinier formulae for cylindrical objects, which allowed for evaluating the radii of gyration as well as the radii and lengths of the pores under cylindrical shape approximation. SANS data from D{sub 2}O-saturated samples indicate that strong upturn in the low Q limit usually observed in the scattering patterns from microporous carbon powders is due to the scattering from outer surface of the powder particles. Micropores are only partially filled with D{sub 2}O molecules due to geometrical constraints and or partial hydrophobicity of the carbon matrix. Structural parameters of the dry carbons obtained using SANS are compared with the results of the gas sorption measurements and the values agree for carbide-derived carbons (CDCs) obtained at high chlorination temperatures (>600 C). For lower chlorination temperatures, pore radii obtained from gas sorption overestimate the actual pore size as calculated from SANS for two reasons: inaccessible small pores are present and the model-dependent fitting based on density functional theory models assumes non-spherical pores, whereas SANS clearly indicates that the pore shape in microporous CDC obtained at low chlorination temperatures is nearly spherical.« less

Seasonal Effects on the Relationships Between Soil Water Content, Pore Water Pressure and Shear Strength and Their Implications for Slope Stability

NASA Astrophysics Data System (ADS)

Hughes, P. N.

2015-12-01

A soil's shear resistance is mainly dependent upon the magnitude of effective stress. For small to medium height slopes (up to 10m) in clay soils the total stress acting along potential failure planes will be low, therefore the magnitude of effective stress (and hence soil shear strength) will be dominated by the pore-water pressure. The stability of slopes on this scale through periods of increased precipitation is improved by the generation of negative pore pressures (soil suctions) during preceding, warmer, drier periods. These negative pore water pressures increase the effective stress within the soil and cause a corresponding increase in shearing resistance. The relationships between soil water content and pore water pressure (soil water retention curves) are known to be hysteretic, but for the purposes of the majority of slope stability assessments in partially saturated clay soils, these are assumed to be consistent with time. Similarly, the relationship between shear strength and water content is assumed to be consistent over time. This research presents a laboratory study in which specimens of compacted Glacial Till (typical of engineered slopes within the UK) were subjected to repeated cycles of wetting and drying to simulate seasonal cycles. At predetermined water contents, measurements of soil suction were made using tensiometer and dewpoint potentiometer methods. The undrained shear strength of the specimens was then measured using triaxial strength testing equipment. Results indicate that repeated wetting and drying cycles caused a change in the soil water retention behaviour. A reduction in undrained shear strength at corresponding water contents along the wetting and drying paths was also observed. The mechanism for the change in the relationship is believed to be a deterioration in the soil physical structure due to shrink/swell induced micro-cracking. The non-stationarity of these relationships has implications for slope stability assessment.

Unifying Pore Network Modeling, Continuous Time Random Walk Theory and Experiment - Accomplishments and Future Directions

NASA Astrophysics Data System (ADS)

Bijeljic, B.

2008-05-01

This talk will describe and highlight the advantages offered by a methodology that unifies pore network modeling, CTRW theory and experiment in description of solute dispersion in porous media. Solute transport in a porous medium is characterized by the interplay of advection and diffusion (described by Peclet number, Pe) that cause spreading of solute particles. This spreading is traditionally described by dispersion coefficients, D, defined by σ 2 = 2Dt, where σ 2 is the variance of the solute position and t is the time. Using a pore-scale network model based on particle tracking, the rich Peclet- number dependence of dispersion coefficient is predicted from first principles and is shown to compare well with experimental data for restricted diffusion, transition, power-law and mechanical dispersion regimes in the asymptotic limit. In the asymptotic limit D is constant and can be used in an averaged advection-dispersion equation. However, it is highly important to recognize that, until the velocity field is fully sampled, the particle transport is non-Gaussian and D possesses temporal or spatial variation. Furthermore, temporal probability density functions (PDF) of tracer particles are studied in pore networks and an excellent agreement for the spectrum of transition times for particles from pore to pore is obtained between network model results and CTRW theory. Based on the truncated power-law interpretation of PDF-s, the physical origin of the power-law scaling of dispersion coefficient vs. Peclet number has been explained for unconsolidated porous media, sands and a number of sandstones, arriving at the same conclusion from numerical network modelling, analytic CTRW theory and experiment. Future directions for further applications of the methodology presented are discussed in relation to the scale- dependent solute dispersion and reactive transport. Significance of pre-asymptotic dispersion in porous media is addressed from pore-scale upwards and the impact of heterogeneity is discussed. The length traveled by solute plumes before Gaussian behaviour is reached increases with an increase in heterogeneity and/or Pe. This opens up the question on the nature of dispersion in natural systems where the heterogeneities at the larger scales will profoundly increase the range of velocities in the aquifer, thus considerably delaying the asymptotic approach to Gaussian behaviour. As a consequence, the asymptotic behaviour might not be reached at the field scale.

Effect of the aerated structure on selected properties of freeze-dried hydrocolloid gels

NASA Astrophysics Data System (ADS)

Ciurzyńska, Agnieszka; Lenart, Andrzej

2016-01-01

The ability to create diverse structures and studies on the effect of the aerated structure on selected properties with the use of freeze-dried gels may provide knowledge about the properties of dried foods. Such gels can be a basis for obtaining innovative food products. For the gel preparation, 3 types of hydrocolloids were used: low-methoxyl pectin, a mixture of xanthan gum and locust-bean gum, and a mixture of xanthan gum and guar gum. Gels were aerated for 3 and 7 min, frozen at a temperature of -45°C 2 h-1, and freeze-dried at a temperature of 30°C. For the samples obtained, structure, porosity, shrinkage, rehydration, and colour were investigated. It was shown that the type of the hydrocolloid and aeration time influence the structure of freeze-dried gels, which determines such properties of samples as porosity, shrinkage, density, rehydration, and colour. The bigger pores of low-methoxyl pectin gels undergo rehydration in the highest degree. The delicate and aerated structure of gels with the mixture of xanthan gum and locust-bean gum was damaged during freeze-drying and shrinkage exhibited the highest value. Small pores of samples with the mixture of xanthan gum and guar gum were responsible for the lower rehydration properties, but the highest porosity value contributed to the highest lightness value.

Reconstruction of three-dimensional porous media using generative adversarial neural networks

NASA Astrophysics Data System (ADS)

Mosser, Lukas; Dubrule, Olivier; Blunt, Martin J.

2017-10-01

To evaluate the variability of multiphase flow properties of porous media at the pore scale, it is necessary to acquire a number of representative samples of the void-solid structure. While modern x-ray computer tomography has made it possible to extract three-dimensional images of the pore space, assessment of the variability in the inherent material properties is often experimentally not feasible. We present a method to reconstruct the solid-void structure of porous media by applying a generative neural network that allows an implicit description of the probability distribution represented by three-dimensional image data sets. We show, by using an adversarial learning approach for neural networks, that this method of unsupervised learning is able to generate representative samples of porous media that honor their statistics. We successfully compare measures of pore morphology, such as the Euler characteristic, two-point statistics, and directional single-phase permeability of synthetic realizations with the calculated properties of a bead pack, Berea sandstone, and Ketton limestone. Results show that generative adversarial networks can be used to reconstruct high-resolution three-dimensional images of porous media at different scales that are representative of the morphology of the images used to train the neural network. The fully convolutional nature of the trained neural network allows the generation of large samples while maintaining computational efficiency. Compared to classical stochastic methods of image reconstruction, the implicit representation of the learned data distribution can be stored and reused to generate multiple realizations of the pore structure very rapidly.

Confinement properties of 2D porous molecular networks on metal surfaces

NASA Astrophysics Data System (ADS)

Müller, Kathrin; Enache, Mihaela; Stöhr, Meike

2016-04-01

Quantum effects that arise from confinement of electronic states have been extensively studied for the surface states of noble metals. Utilizing small artificial structures for confinement allows tailoring of the surface properties and offers unique opportunities for applications. So far, examples of surface state confinement include thin films, artificial nanoscale structures, vacancy and adatom islands, self-assembled 1D chains, vicinal surfaces, quantum dots and quantum corrals. In this review we summarize recent achievements in changing the electronic structure of surfaces by adsorption of nanoporous networks whose design principles are based on the concepts of supramolecular chemistry. Already in 1993, it was shown that quantum corrals made from Fe atoms on a Cu(1 1 1) surface using single atom manipulation with a scanning tunnelling microscope confine the Shockley surface state. However, since the atom manipulation technique for the construction of corral structures is a relatively time consuming process, the fabrication of periodic two-dimensional (2D) corral structures is practically impossible. On the other side, by using molecular self-assembly extended 2D porous structures can be achieved in a parallel process, i.e. all pores are formed at the same time. The molecular building blocks are usually held together by non-covalent interactions like hydrogen bonding, metal coordination or dipolar coupling. Due to the reversibility of the bond formation defect-free and long-range ordered networks can be achieved. However, recently also examples of porous networks formed by covalent coupling on the surface have been reported. By the choice of the molecular building blocks, the dimensions of the network (pore size and pore to pore distance) can be controlled. In this way, the confinement properties of the individual pores can be tuned. In addition, the effect of the confined state on the hosting properties of the pores will be discussed in this review article.

Confinement properties of 2D porous molecular networks on metal surfaces.

PubMed

Müller, Kathrin; Enache, Mihaela; Stöhr, Meike

2016-04-20

Quantum effects that arise from confinement of electronic states have been extensively studied for the surface states of noble metals. Utilizing small artificial structures for confinement allows tailoring of the surface properties and offers unique opportunities for applications. So far, examples of surface state confinement include thin films, artificial nanoscale structures, vacancy and adatom islands, self-assembled 1D chains, vicinal surfaces, quantum dots and quantum corrals. In this review we summarize recent achievements in changing the electronic structure of surfaces by adsorption of nanoporous networks whose design principles are based on the concepts of supramolecular chemistry. Already in 1993, it was shown that quantum corrals made from Fe atoms on a Cu(1 1 1) surface using single atom manipulation with a scanning tunnelling microscope confine the Shockley surface state. However, since the atom manipulation technique for the construction of corral structures is a relatively time consuming process, the fabrication of periodic two-dimensional (2D) corral structures is practically impossible. On the other side, by using molecular self-assembly extended 2D porous structures can be achieved in a parallel process, i.e. all pores are formed at the same time. The molecular building blocks are usually held together by non-covalent interactions like hydrogen bonding, metal coordination or dipolar coupling. Due to the reversibility of the bond formation defect-free and long-range ordered networks can be achieved. However, recently also examples of porous networks formed by covalent coupling on the surface have been reported. By the choice of the molecular building blocks, the dimensions of the network (pore size and pore to pore distance) can be controlled. In this way, the confinement properties of the individual pores can be tuned. In addition, the effect of the confined state on the hosting properties of the pores will be discussed in this review article.

Ceramic membranes: The effects of deposition and drying conditions on membrane morphology and performance

NASA Astrophysics Data System (ADS)

Webster, Elizabeth T.

Sol-gel methods for fabricating ceramic membranes on porous supports include dip coating, evaporative drying, and sintering. The ceramic membranes of interest in the present research were prepared from aqueous sols of silica, titania, or iron oxide nano-particles which were deposited on porous alumina supports. Physisorption measurements indicate that the diameters of the pores in the resulting membranes are 20 A or smaller. Defect formation during fabrication is particularly problematic for ceramic membranes with pore diameters in the nanometer range. Solutions to these problems would greatly enhance the commercial potential of nano-filtration membranes for gas-phase separations. Cracks are debilitating defects which originate during the drying and firing phases of fabrication. As water evaporates during drying, the sol-gel film is subjected to large capillary forces. Unchecked, these tensile forces result in catastrophic cracking across the membrane. A novel technique called internal deposition can be employed to deposit the sol particles within the pores of the support rather than on its surface. Internal deposition obstructs the propagation of cracks, thereby reducing the impact of crack-type defects. A patent for demonstration of proof of concept of the internal deposition technique has been received. Experimental difficulties associated with the nonuniform morphology of the tubular alumina support hindered further development of the internal deposition protocol. The final phase of the research incorporated a support containing uniform capillaries (Anotec(TM) disks). Two-level factorial experiments were conducted to determine the effects of various deposition and drying conditions (viz., speed and method of deposition, surface charge, humidity, and drying rate) on membrane performance. Membrane performance was characterized in terms of the permeabilities of nitrogen and helium in the resulting membranes. The permeability and pressure data were incorporated in a transport model to characterize the mechanisms of fluid flow and the morphologies of the membranes. Electron microscopy was employed to evaluate membrane coverage and to identify defects in the membranes. The results of the factorial experiments indicate that membrane performance is strongly affected by humidity during deposition and drying. These results underscore the importance of controlling process humidity during fabrication of ceramic membranes.

Validation of model predictions of pore-scale fluid distributions during two-phase flow

NASA Astrophysics Data System (ADS)

Bultreys, Tom; Lin, Qingyang; Gao, Ying; Raeini, Ali Q.; AlRatrout, Ahmed; Bijeljic, Branko; Blunt, Martin J.

2018-05-01

Pore-scale two-phase flow modeling is an important technology to study a rock's relative permeability behavior. To investigate if these models are predictive, the calculated pore-scale fluid distributions which determine the relative permeability need to be validated. In this work, we introduce a methodology to quantitatively compare models to experimental fluid distributions in flow experiments visualized with microcomputed tomography. First, we analyzed five repeated drainage-imbibition experiments on a single sample. In these experiments, the exact fluid distributions were not fully repeatable on a pore-by-pore basis, while the global properties of the fluid distribution were. Then two fractional flow experiments were used to validate a quasistatic pore network model. The model correctly predicted the fluid present in more than 75% of pores and throats in drainage and imbibition. To quantify what this means for the relevant global properties of the fluid distribution, we compare the main flow paths and the connectivity across the different pore sizes in the modeled and experimental fluid distributions. These essential topology characteristics matched well for drainage simulations, but not for imbibition. This suggests that the pore-filling rules in the network model we used need to be improved to make reliable predictions of imbibition. The presented analysis illustrates the potential of our methodology to systematically and robustly test two-phase flow models to aid in model development and calibration.

Pore-scale simulation of liquid CO2 displacement of water using a two-phase lattice Boltzmann model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Haihu; Valocchi, Albert J.; Werth, Charles J.

A lattice Boltzmann color-fluid model, which was recently proposed by Liu et al. [H. Liu, A.J. Valocchi, and Q. Kang. Three-dimensional lattice Boltzmann model for immiscible two-phase flow simulations. Phys. Rev. E, 85:046309, 2012.] based on a concept of continuum surface force, is improved to simulate immiscible two-phase flows in porous media. The new improvements allow the model to account for different kinematic viscosities of both fluids and to model fluid-solid interactions. The capability and accuracy of this model is first validated by two benchmark tests: a layered two-phase flow with a viscosity ratio, and a dynamic capillary intrusion. Thismore » model is then used to simulate liquid CO2 (LCO2) displacing water in a dual-permeability pore network. The extent and behavior of LCO2 preferential flow (i.e., fingering) is found to depend on the capillary number (Ca), and three different displacement patterns observed in previous micromodel experiments are reproduced. The predicted variation of LCO2 saturation with Ca, as well as variation of specific interfacial length with LCO2 saturation, are both in good agreement with the experimental observations. To understand the effect of heterogeneity on pore-scale displacement, we also simulate LCO2 displacing water in a randomly heterogeneous pore network, which has the same size and porosity as the dual-permeability pore network. In comparison to the dual-permeability case, the transition from capillary fingering to viscous fingering occurs at a higher Ca, and LCO2 saturation is higher at low Ca but lower at high Ca. In either pore network, the LCO2-water specific interfacial length is found to obey a power-law dependence on LCO2 saturation.« less

A FUNCTIONAL RELATION FOR FIELD-SCALE NONAQUEOUS PHASE LIQUID DISSOLUTION DEVELOPED USING A PORE NETWORK MODEL. (R825689C080)

EPA Science Inventory

Abstract

A pore network model with cubic chambers and rectangular tubes was used to estimate the nonaqueous phase liquid (NAPL) dissolution rate coefficient, K_dissa_i, and NAPL/water total specific interfacial area, a_i

A FUNCTIONAL RELATION FOR FIELD-SCALE NONAQUEOUS PHASE LIQUID DISSOLUTION DEVELOPED USING A PORE NETWORK MODEL. (R825689C079)

EPA Science Inventory

Abstract

A pore network model with cubic chambers and rectangular tubes was used to estimate the nonaqueous phase liquid (NAPL) dissolution rate coefficient, K_dissa_i, and NAPL/water total specific interfacial area, a_i

Morphological analysis of pore size and connectivity in a thick mixed-culture biofilm.

PubMed

Rosenthal, Alex F; Griffin, James S; Wagner, Michael; Packman, Aaron I; Balogun, Oluwaseyi; Wells, George F

2018-05-19

Morphological parameters are commonly used to predict transport and metabolic kinetics in biofilms. Yet, quantification of biofilm morphology remains challenging due to imaging technology limitations and lack of robust analytical approaches. We present a novel set of imaging and image analysis techniques to estimate internal porosity, pore size distributions, and pore network connectivity to a depth of 1 mm at a resolution of 10 µm in a biofilm exhibiting both heterotrophic and nitrifying activity. Optical coherence tomography (OCT) scans revealed an extensive pore network with diameters as large as 110 µm directly connected to the biofilm surface and surrounding fluid. Thin section fluorescence in situ hybridization microscopy revealed ammonia oxidizing bacteria (AOB) distributed through the entire thickness of the biofilm. AOB were particularly concentrated in the biofilm around internal pores. Areal porosity values estimated from OCT scans were consistently lower than those estimated from multiphoton laser scanning microscopy, though the two imaging modalities showed a statistically significant correlation (r = 0.49, p<0.0001). Estimates of areal porosity were moderately sensitive to grey level threshold selection, though several automated thresholding algorithms yielded similar values to those obtained by manually thresholding performed by a panel of environmental engineering researchers (±25% relative error). These findings advance our ability to quantitatively describe the geometry of biofilm internal pore networks at length scales relevant to engineered biofilm reactors and suggest that internal pore structures provide crucial habitat for nitrifier growth. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

A Novel Nano/Micro-Fluidic Reactor for Evaluation of Pore-Scale Reactive Transport

NASA Astrophysics Data System (ADS)

Werth, C. J.; Alcalde, R.; Ghazvini, S.; Sanford, R. A.; Fouke, B. W.; Valocchi, A. J.

2017-12-01

The reactive transport of pollutants in groundwater can be affected by the presence of stressor chemicals, which inhibit microbial functions. The stressor can be a primary reactant (e.g., trichloroethene), a reaction product (e.g., nitrite from nitrate), or some other chemical present in groundwater (e.g., antibiotic). In this work, a novel nano/microfluidic cell was developed to examine the effect of the antibiotic ciprofloxacin on nitrate reduction coupled to lactate oxidation. The reactor contains parallel boundary channels that deliver flow and solutes on either side of a pore network. The boundary channels are separated from the pore network by one centimeter-long, one micrometer-thick walls perforated by hundreds of nanoslits. The nanoslits allow solute mass transfer from the boundary channels to the pore network, but not microbial passage. The pore network was inoculated with a pure culture of Shewanella oneidensis MR-1, and this was allowed to grow on lactate and nitrate in the presence of ciprofloxacin, all delivered through the boundary channels. Microbial growth patterns suggest inhibition from ciprofloxacin and the nitrate reduction product nitrite, and a dependence on nitrate and lactate mass transfer rates from the boundary channels. A numerical model was developed to interpret the controlling mechanisms, and results indicate cell chemotaxis also affects nitrate reduction and microbial growth. The results are broadly relevant to bioremediation efforts where one or more chemicals that inhibit microbial growth are present and inhibit pollutant degradation rates.

Adsorption of sulfur dioxide on ammonia-treated activated carbon fibers

USGS Publications Warehouse

Mangun, C.L.; DeBarr, J.A.; Economy, J.

2001-01-01

A series of activated carbon fibers (ACFs) and ammonia-treated ACFs prepared from phenolic fiber precursors have been studied to elucidate the role of pore size, pore volume, and pore surface chemistry on adsorption of sulfur dioxide and its catalytic conversion to sulfuric acid. As expected, the incorporation of basic functional groups into the ACFs was shown as an effective method for increasing adsorption of sulfur dioxide. The adsorption capacity for dry SO2 did not follow specific trends; however the adsorption energies calculated from the DR equation were found to increase linearly with nitrogen content for each series of ACFs. Much higher adsorption capacities were achieved for SO2 in the presence of oxygen and water due to its catalytic conversion to H2SO4. The dominant factor for increasing adsorption of SO2 from simulated flue gas for each series of fibers studied was the weight percent of basic nitrogen groups present. In addition, the adsorption energies calculated for dry SO2 were shown to be linearly related to the adsorption capacity of H2SO4 from this flue gas for all fibers. It was shown that optimization of this parameter along with the pore volume results in higher adsorption capacities for removal of SO2 from flue gases. ?? 2001 Elsevier Science Ltd. All rights reserved.

Characterization of the intragranular water regime within subsurface sediments: Pore volume, surface area, and mass transfer limitations

USGS Publications Warehouse

Hay, M.B.; Stoliker, D.L.; Davis, J.A.; Zachara, J.M.

2011-01-01

Although "intragranular" pore space within grain aggregates, grain fractures, and mineral surface coatings may contain a relatively small fraction of the total porosity within a porous medium, it often contains a significant fraction of the reactive surface area, and can thus strongly affect the transport of sorbing solutes. In this work, we demonstrate a batch experiment procedure using tritiated water as a high-resolution diffusive tracer to characterize the intragranular pore space. The method was tested using uranium-contaminated sediments from the vadose and capillary fringe zones beneath the former 300A process ponds at the Hanford site (Washington). Sediments were contacted with tracers in artificial groundwater, followed by a replacement of bulk solution with tracer-free groundwater and the monitoring of tracer release. From these data, intragranular pore volumes were calculated and mass transfer rates were quantified using a multirate first-order mass transfer model. Tritium-hydrogen exchange on surface hydroxyls was accounted for by conducting additional tracer experiments on sediment that was vacuum dried after reaction. The complementary ("wet" and "dry") techniques allowed for the simultaneous determination of intragranular porosity and surface area using tritium. The Hanford 300A samples exhibited intragranular pore volumes of ???1% of the solid volume and intragranular surface areas of ???20%-35% of the total surface area. Analogous experiments using bromide ion as a tracer yielded very different results, suggesting very little penetration of bromide into the intragranular porosity. Copyright 2011 by the American Geophysical Union.

Characterization of the intragranular water regime within subsurface sediments: pore volume, surface area, and mass transfer limitations

USGS Publications Warehouse

Hay, Michael B.; Stoliker, Deborah L.; Davis, James A.; Zachara, John M.

2011-01-01

Although "intragranular" pore space within grain aggregates, grain fractures, and mineral surface coatings may contain a relatively small fraction of the total porosity within a porous medium, it often contains a significant fraction of the reactive surface area, and can thus strongly affect the transport of sorbing solutes. In this work, we demonstrate a batch experiment procedure using tritiated water as a high-resolution diffusive tracer to characterize the intragranular pore space. The method was tested using uranium-contaminated sediments from the vadose and capillary fringe zones beneath the former 300A process ponds at the Hanford site (Washington). Sediments were contacted with tracers in artificial groundwater, followed by a replacement of bulk solution with tracer-free groundwater and the monitoring of tracer release. From these data, intragranular pore volumes were calculated and mass transfer rates were quantified using a multirate first-order mass transfer model. Tritium-hydrogen exchange on surface hydroxyls was accounted for by conducting additional tracer experiments on sediment that was vacuum dried after reaction. The complementary ("wet" and "dry") techniques allowed for the simultaneous determination of intragranular porosity and surface area using tritium. The Hanford 300A samples exhibited intragranular pore volumes of ~1% of the solid volume and intragranular surface areas of ~20%–35% of the total surface area. Analogous experiments using bromide ion as a tracer yielded very different results, suggesting very little penetration of bromide into the intragranular porosity.

Method for rapidly producing microporous and mesoporous materials

DOEpatents

Coronado, P.R.; Poco, J.F.; Hrubesh, L.W.; Hopper, R.W.

1997-11-11

An improved, rapid process is provided for making microporous and mesoporous materials, including aerogels and pre-ceramics. A gel or gel precursor is confined in a sealed vessel to prevent structural expansion of the gel during the heating process. This confinement allows the gelation and drying processes to be greatly accelerated, and significantly reduces the time required to produce a dried aerogel compared to conventional methods. Drying may be performed either by subcritical drying with a pressurized fluid to expel the liquid from the gel pores or by supercritical drying. The rates of heating and decompression are significantly higher than for conventional methods. 3 figs.

The effect of moisture on the methane adsorption capacity of shales: A study case in the eastern Qaidam Basin in China

NASA Astrophysics Data System (ADS)

Wang, Lu; Yu, Qingchun

2016-11-01

This study investigated the effects of moisture on high-pressure methane adsorption in carboniferous shales from the Qaidam Basin, China. The shale characteristics, including the organic/inorganic compositions and pore structure (volume and surface) distribution, were obtained using various techniques. Gibbs adsorption measurements were performed over a pressure range up to 6 MPa and temperatures of 308.15 K on dry samples and moisture-equilibrated samples to analyze the correlations between organic/inorganic matter, pore structure, and moisture content on the methane sorption capacity. Compared to dry samples, the sorption capacity of wet samples (0.44-2.52% of water content) is reduced from 19.7 ± 5.3% to 36.1% ± 6.1%. Langmuir fitting is conducted to investigate moisture-dependent variations of adsorbed methane density, Langmuir pressure, and volume. By combining the pore volume and surface distribution analyses, our observations suggested that the main competition sites for CH4-H2O covered pores of approximately 2-7 nm, whereas the effective sites for methane and water were predominantly distributed within smaller (<4 nm) and larger pores (>10 nm), respectively. Regarding the compositional correlations, the impact of moisture on the amount of adsorbed methane shows a roughly linearly decreasing trend with increasing TOC content ranging from 0.62 to 2.88%, whereas the correlation between the moisture effect and various inorganic components is more complicated. Further fitting results indicate that illite/smectite mixed formations are closely related to the methane capacity, whereas the illite content show an evident connection to the pore structural (volume and surface) variations in the presence of moisture.

Freeze-cast alumina pore networks: Effects of freezing conditions and dispersion medium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller, S. M.; Xiao, X.; Faber, K. T.

Alumina ceramics were freeze-cast from water- and camphene-based slurries under varying freezing conditions and examined using X-ray computed tomography (XCT). Pore network characteristics, i.e., porosity, pore size, geometric surface area, and tortuosity, were measured from XCT reconstructions and the data were used to develop a model to predict feature size from processing conditions. Classical solidification theory was used to examine relationships between pore size, temperature gradients, and freezing front velocity. Freezing front velocity was subsequently predicted from casting conditions via the two-phase Stefan problem. Resulting models for water-based samples agreed with solidification-based theories predicting lamellar spacing of binary eutectic alloys,more » and models for camphene-based samples concurred with those for dendritic growth. Relationships between freezing conditions and geometric surface area were also modeled by considering the inverse relationship between pore size and surface area. Tortuosity was determined to be dependent primarily on the type of dispersion medium. (C) 2015 Elsevier Ltd. All rights reserved.« less

Laboratory measurements of shock propagation through spherical cavities in an optically accessible polymer.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chojnicki, Kirsten; Cooper, Marcia A.; Guo, Shuyue

Pore-scale aperture effects on flow in pore networks was studied in the laboratory to provide a parameterization for use in transport models. Four cases were considered: regular and irregular pillar/pore alignment with and without an aperture. The velocity field of each case was measured and simulated, providing quantitatively comparable results. Two aperture effect parameterizations were considered: permeability and transmission. Permeability values varied by an order of magnitude between the cases with and without apertures. However, transmission did not correlate with permeability. Despite having much greater permeability the regular aperture case permitted less transmission than the regular case. Moreover, both irregularmore » cases had greater transmission than the regular cases, a difference not supported by the permeabilities. Overall, these findings suggest that pore-scale aperture effects on flow though a pore-network may not be adequately captured by properties such as permeability for applications that are interested in determining particle transport volume and timing.« less

Method for producing hydrophobic aerogels

DOEpatents

Hrubesh, Lawrence W.; Poco, John F.; Coronado, Paul R.

1999-01-01

A method for treating a dried monolithic aerogel containing non-dispersed particles, with an organometallic surface modifying agent to produce hydrophobic aerogels. The dried, porous hydrophobic aerogels contain a protective layer of alkyl groups, such as methyl groups, on the modified surfaces of the pores of the aerogel. The alkyl groups at the aerogel surface typically contain at least one carbon-metal bond per group.

Pore pressure control on faulting behavior in a block-gouge system

NASA Astrophysics Data System (ADS)

Yang, Z.; Juanes, R.

2016-12-01

Pore fluid pressure in a fault zone can be altered by natural processes (e.g., mineral dehydration and thermal pressurization) and industrial operations involving subsurface fluid injection/extraction for the development of energy and water resources. However, the effect of pore pressure change on the stability and slip motion of a preexisting geologic fault remain poorly understood; yet they are critical for the assessment of seismic risk. In this work, we develop a micromechanical model to investigate the effect of pore pressure on faulting behavior. The model couples pore network fluid flow and mechanics of the solid grains. We conceptualize the fault zone as a gouge layer sandwiched between two blocks; the block material is represented by a group of contact-bonded grains and the gouge is composed of unbonded grains. A pore network is extracted from the particulate pack of the block-gouge system with pore body volumes and pore throat conductivities calculated rigorously based on the geometry of the local pore space. Pore fluid exerts pressure force onto the grains, the motion of which is solved using the discrete element method (DEM). The model updates the pore network regularly in response to deformation of the solid matrix. We study the fault stability in the presence of a pressure inhomogeneity (gradient) across the gouge layer, and compare it with the case of homogeneous pore pressure. We consider both normal and thrust faulting scenarios with a focus on the onset of shear failure along the block-gouge interfaces. Numerical simulations show that the slip behavior is characterized by intermittent dynamics, which is evident in the number of slipping contacts at the block-gouge interfaces and the total kinetic energy of the gouge particles. Numerical results also show that, for the case of pressure inhomogeneity, the onset of slip occurs earlier for the side with higher pressure, and that this onset appears to be controlled by the maximum pressure of both sides of the fault. We conclude that the stability of the fault should be evaluated separately for both sides of the gouge layer, a result that sheds new light on the use of the effective stress principle and the Coulomb failure criterion in evaluating the stability of a complex fault zone.

Experimental impact crater morphology

NASA Astrophysics Data System (ADS)

Dufresne, A.; Poelchau, M. H.; Hoerth, T.; Schaefer, F.; Thoma, K.; Deutsch, A.; Kenkmann, T.

2012-04-01

The research group MEMIN (Multidisciplinary Experimental and Impact Modelling Research Network) is conducting impact experiments into porous sandstones, examining, among other parameters, the influence of target pore-space saturation with water, and projectile velocity, density and mass, on the cratering process. The high-velocity (2.5-7.8 km/s) impact experiments were carried out at the two-stage light-gas gun facilities of the Fraunhofer Institute EMI (Germany) using steel, iron meteorite (Campo del Cielo IAB), and aluminium projectiles with Seeberg Sandstone as targets. The primary objectives of this study within MEMIN are to provide detailed morphometric data of the experimental craters, and to identify trends and characteristics specific to a given impact parameter. Generally, all craters, regardless of impact conditions, have an inner depression within a highly fragile, white-coloured centre, an outer spallation (i.e. tensile failure) zone, and areas of arrested spallation (i.e. spall fragments that were not completely dislodged from the target) at the crater rim. Within this general morphological framework, distinct trends and differences in crater dimensions and morphological characteristics are identified. With increasing impact velocity, the volume of craters in dry targets increases by a factor of ~4 when doubling velocity. At identical impact conditions (steel projectiles, ~5km/s), craters in dry and wet sandstone targets differ significantly in that "wet" craters are up to 76% larger in volume, have depth-diameter ratios generally below 0.19 (whereas dry craters are almost consistently above this value) at significantly larger diameters, and their spallation zone morphologies show very different characteristics. In dry craters, the spall zone surfaces dip evenly at 10-20° towards the crater centre. In wet craters, on the other hand, they consist of slightly convex slopes of 10-35° adjacent to the inner depression, and of sub-horizontal tensile failure planes ("terraces") in the outer, near-surface region of the crater. We suggest that these differences are due to a reduction in tensile strength in pore-space saturated sandstone. Linking morphological characteristics to impact conditions might provide a tool to help reconstruct impact conditions in small, more strength- than gravity-dominated impact craters in nature. Findings in small-scale experiments can aid the identification of particular structures in the field, such as spallation induced uplift of strata outside of the crater margins.

Bioinspired Synthesis of Monolithic and Layered Aerogels.

PubMed

Han, Xiao; Hassan, Khalil T; Harvey, Alan; Kulijer, Dejan; Oila, Adrian; Hunt, Michael R C; Šiller, Lidija

2018-06-01

Aerogels are the least dense and most porous materials known to man, with potential applications from lightweight superinsulators to smart energy materials. To date their use has been seriously hampered by their synthesis methods, which are laborious and expensive. Taking inspiration from the life cycle of the damselfly, a novel ambient pressure-drying approach is demonstrated in which instead of employing low-surface-tension organic solvents to prevent pore collapse during drying, sodium bicarbonate solution is used to generate pore-supporting carbon dioxide in situ, significantly reducing energy, time, and cost in aerogel production. The generic applicability of this readily scalable new approach is demonstrated through the production of granules, monoliths, and layered solids with a number of precursor materials. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Silica aerogel films prepared at ambient pressure by using surface derivatization to induce reversible drying shrinkage

NASA Astrophysics Data System (ADS)

Prakash, Sai S.; Brinker, C. Jeffrey; Hurd, Alan J.; Rao, Sudeep M.

1995-03-01

HIGHLY porous inorganic films have potential applications as dielectric materials, reflective and anti-reflective coatings, flat-panel displays, sensors, catalyst supports and super-insulating architectural glazings1-3. Aerogels4 are the most highly porous solids known, and can now be prepared from inorganic5 and organic6,7 precursors with volume-fraction porosities of up to 99.9% (ref. 8). Aerogels are normally prepared by supercritical extraction of the pore fluid from a wet gel1, which prevents the network collapse that is otherwise induced by capillary forces. But supercritical processing is expensive, hazardous and incompatible with the processing requirements of many potential applications,thus severely restricting the commercial exploitation of aerogels. Here we describe a means of preparing aerogels by a simple dip-coating method at ambient pressure without the need for supercriti-cal extraction. We add surface groups to the inorganic gel which make drying shrinkage reversible9: as the solvent is withdrawn, the gel springs back to a porous state. We can generate aerogel films with 98.5% porosity using this approach. We anticipate that it will greatly expand the commercial applications of these materials.

The effect of the pore-fluid factor on strength and failure mechanism of Wilkeson sandstone

NASA Astrophysics Data System (ADS)

Kätker, A. K.; Rempe, M.; Renner, J.

2016-12-01

The effective stress law, σn,eff = σn - αpf, is a central tool in analysing phenomena related to hydromechanical coupling, such as fluid-induced seismicity or aftershock activity. The effective-stress coefficient α assumes different values for specific physical properties and may deviate from 1. The limited number of studies suggest that brittle compressive strength obeys an effective-stress law when effective drainage is achieved. Yet, open questions remain regarding, e.g., the role of the loading path. We performed suites of triaxial compression tests on samples of Wilkeson sandstone at a range of pore-fluid pressures but identical effective confining pressure (60, 100, and 120 MPa) maintaining the pore-fluid factor λ = pf / pc constant (0.05, 0.2, 0.4, 0.55) during the isostatic loading stage to ensure uniform loading paths. Samples were shortened with a strain rate of 4×10-7 s-1 yielding drained conditions. All tests were terminated at a total axial strain of 4.5% for comparability of microstructures. The tests also included continuous permeability determination and ultrasonic p-wave-velocity measurements to monitor microstructural evolution. Results from experiments conducted at peff = 100 MPa show that dry samples exhibit a higher peak strength and brittle failure while water-saturated samples tend to deform at lower stress by cataclastic flow indicating physico-chemical weakening. Regardless of pore-fluid factor, the saturated experiments exhibit similar peak and residual strength. Differences in failure mechanism (degree of macroscopic localization) and volumetric strain evolution are however noticed, albeit without systematic relation to pore-fluid factor. Microstructure analyses by optical and scanning electron microscopy revealed an evolution from localized shear zones in dry experiments and experiments with a low pore-fluid factor to rather distributed cataclastic flow for experiments with high pore fluid factors. Yet, mechanical and structural differences observed so far may result from sample-to-sample variability and the proximity of the experimental conditions to the brittle-ductile transition.

A New Dual-Pore Formation Factor Model: A Percolation Network Study and Comparison to Experimental Data

NASA Astrophysics Data System (ADS)

Tang, Y. B.; Li, M.; Bernabe, Y.

2014-12-01

We modeled the electrical transport behavior of dual-pore carbonate rocks in this paper. Based on experimental data of a carbonate reservoir in China, we simply considered the low porosity samples equivalent to the matrix (micro-pore system) of the high porosity samples. For modeling the bimodal porous media, we considered that the matrix is homogeneous and interconnected. The connectivity and the pore size distribution of macro-pore system are varied randomly. Both pore systems are supposed to act electrically in parallel, connected at the nodes, where the fluid exchange takes place, an approach previously used by Bauer et al. (2012). Then, the effect of the properties of matrix, the pore size distribution and connectivity of macro-pore system on petrophysical properties of carbonates can be investigated. We simulated electrical current through networks in three-dimensional simple cubic (SC) and body-center cubic (BCC) with different coordination numbers and different pipe radius distributions of macro-pore system. Based on the simulation results, we found that the formation factor obeys a "universal" scaling relationship (i.e. independent of lattice type), 1/F∝eγz, where γ is a function of the normalized standard deviation of the pore radius distribution of macro-pore system and z is the coordination number of macro-pore system. This relationship is different from the classic "universal power law" in percolation theory. A formation factor model was inferred on the basis of the scaling relationship mentioned above and several scale-invariant quantities (such as hydraulic radius rH and throat length l of macro-pore). Several methods were developed to estimate corresponding parameters of the new model with conventional core analyses. It was satisfactorily tested against experimental data, including some published experimental data. Furthermore, the relationship between water saturation and resistivity in dual-pore carbonates was discussed based on the new model.

A dynamic wicking technique for determining the effective pore radius of pregelatinized starch sheets.

PubMed

Kalogianni, E P; Savopoulos, T; Karapantsios, T D; Raphaelides, S N

2004-06-01

A dynamic wicking technique is employed for the first time for the determination of the effective mean pore radius of a thin-layer porous food: drum dried pregelatinized starch sheets. The technique consists of measuring the penetration rate of various n-alkanes in the porous matrix of the starch sheets and using this data to calculate the effective pore radius via the Washburn equation. Pore sizes in the order of a few nanometers have been determined in the starch sheets depending on the drum dryer's operating variables (drum rotation speed, steam pressure and starch feed concentration). The conditions for the application of the technique in porous foods are discussed as compared to the conditions for single capillaries and inorganic porous material measured in other studies.

The effects of pressure, temperature, and pore water on velocities in Westerly granite. [for seismic wave propagation

NASA Technical Reports Server (NTRS)

Spencer, J. W., Jr.; Nur, A. M.

1976-01-01

A description is presented of an experimental assembly which has been developed to conduct concurrent measurements of compressional and shear wave velocities in rocks at high temperatures and confining pressures and with independent control of the pore pressure. The apparatus was used in studies of the joint effects of temperature, external confining pressure, and internal pore water on sonic velocities in Westerly granite. It was found that at a given temperature, confining pressure has a larger accelerating effect on compressional waves in dry rock, whereas at a given confining pressure, temperature has a larger retarding effect on shear waves.

Comparison of three-dimensional printing and vacuum freeze-dried techniques for fabricating composite scaffolds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Kai; Li, Ruixin; Jiang, Wenxue, E-mail: jiangortholivea@sina.cn

In this study, the performances of different preparation methods of the scaffolds were analyzed for chondrocyte tissue engineering. Silk fibroin/collagen (SF/C) was fabricated using a vacuum freeze-dried technique and by 3D printing. The porosity, water absorption expansion rates, mechanical properties, and pore sizes of the resulting materials were evaluated. The proliferation and metabolism of the cells was detected at different time points using an MTT assay. Cell morphologies and distributions were observed by histological analysis and scanning electron microscopy (SEM). The porosity, water absorption expansion rate, and Young’s modulus of the material obtained via 3D printing were significantly higher thanmore » those obtained by the freeze-dried method, while the pore size did not differ significantly between the two methods. MTT assay results showed that the metabolism of cells seeded on the 3D printed scaffolds was more viable than the metabolism on the freeze-dried material. H&E staining of the scaffolds revealed that the number of cells in the 3D printed scaffold was higher in comparison to a similar measurement on the freeze-dried material. Consequently, stem cells grew well inside the 3D printed scaffolds, as measured by SEM, while the internal structure of the freeze-dried scaffold was disordered. Compared with the freeze-dried technique, the 3D printed scaffold exhibited better overall performance and was more suitable for cartilage tissue engineering. - Highlights: • Silk fibroin/collagen was fabricated using 3D printing. • Physical characterization and Cell compatibility were compared. • 3D printed scaffold exhibited better overall performance.« less

Lattice Boltzmann simulation of immiscible fluid displacement in porous media: Homogeneous versus heterogeneous pore network

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Haihu, E-mail: haihu.liu@mail.xjtu.edu.cn; James Weir Fluids Laboratory, Department of Mechanical and Aerospace Engineering, University of Strathclyde, Glasgow G1 1XJ; Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801

Injection of anthropogenic carbon dioxide (CO{sub 2}) into geological formations is a promising approach to reduce greenhouse gas emissions into the atmosphere. Predicting the amount of CO{sub 2} that can be captured and its long-term storage stability in subsurface requires a fundamental understanding of multiphase displacement phenomena at the pore scale. In this paper, the lattice Boltzmann method is employed to simulate the immiscible displacement of a wetting fluid by a non-wetting one in two microfluidic flow cells, one with a homogeneous pore network and the other with a randomly heterogeneous pore network. We have identified three different displacement patterns,more » namely, stable displacement, capillary fingering, and viscous fingering, all of which are strongly dependent upon the capillary number (Ca), viscosity ratio (M), and the media heterogeneity. The non-wetting fluid saturation (S{sub nw}) is found to increase nearly linearly with logCa for each constant M. Increasing M (viscosity ratio of non-wetting fluid to wetting fluid) or decreasing the media heterogeneity can enhance the stability of the displacement process, resulting in an increase in S{sub nw}. In either pore networks, the specific interfacial length is linearly proportional to S{sub nw} during drainage with equal proportionality constant for all cases excluding those revealing considerable viscous fingering. Our numerical results confirm the previous experimental finding that the steady state specific interfacial length exhibits a linear dependence on S{sub nw} for either favorable (M ≥ 1) or unfavorable (M < 1) displacement, and the slope is slightly higher for the unfavorable displacement.« less

Micro-CT scan reveals an unexpected high-volume and interconnected pore network in a Cretaceous Sanagasta dinosaur eggshell.

PubMed

Hechenleitner, E Martín; Grellet-Tinner, Gerald; Foley, Matthew; Fiorelli, Lucas E; Thompson, Michael B

2016-03-01

The Cretaceous Sanagasta neosauropod nesting site (La Rioja, Argentina) was the first confirmed instance of extinct dinosaurs using geothermal-generated heat to incubate their eggs. The nesting strategy and hydrothermal activities at this site led to the conclusion that the surprisingly 7 mm thick-shelled eggs were adapted to harsh hydrothermal microenvironments. We used micro-CT scans in this study to obtain the first three-dimensional microcharacterization of these eggshells. Micro-CT-based analyses provide a robust assessment of gas conductance in fossil dinosaur eggshells with complex pore canal systems, allowing calculation, for the first time, of the shell conductance through its thickness. This novel approach suggests that the shell conductance could have risen during incubation to seven times more than previously estimated as the eggshell erodes. In addition, micro-CT observations reveal that the constant widening and branching of pore canals form a complex funnel-like pore canal system. Furthermore, the high density of pore canals and the presence of a lateral canal network in the shell reduce the risks of pore obstruction during the extended incubation of these eggs in a relatively highly humid and muddy nesting environment. © 2016 The Author(s).

Structural determinants of hydration, mechanics and fluid flow in freeze-dried collagen scaffolds.

PubMed

Offeddu, G S; Ashworth, J C; Cameron, R E; Oyen, M L

2016-09-01

Freeze-dried scaffolds provide regeneration templates for a wide range of tissues, due to their flexibility in physical and biological properties. Control of structure is crucial for tuning such properties, and therefore scaffold functionality. However, the common approach of modeling these scaffolds as open-cell foams does not fully account for their structural complexity. Here, the validity of the open-cell model is examined across a range of physical characteristics, rigorously linking morphology to hydration and mechanical properties. Collagen scaffolds with systematic changes in relative density were characterized using Scanning Electron Microscopy, X-ray Micro-Computed Tomography and spherical indentation analyzed in a time-dependent poroelastic framework. Morphologically, all scaffolds were mid-way between the open- and closed-cell models, approaching the closed-cell model as relative density increased. Although pore size remained constant, transport pathway diameter decreased. Larger collagen fractions also produced greater volume swelling on hydration, although the change in pore diameter was constant, and relatively small at ∼6%. Mechanically, the dry and hydrated scaffold moduli varied quadratically with relative density, as expected of open-cell materials. However, the increasing pore wall closure was found to determine the time-dependent nature of the hydrated scaffold response, with a decrease in permeability producing increasingly elastic rather than viscoelastic behavior. These results demonstrate that characterizing the deviation from the open-cell model is vital to gain a full understanding of scaffold biophysical properties, and provide a template for structural studies of other freeze-dried biomaterials. Freeze-dried collagen sponges are three-dimensional microporous scaffolds that have been used for a number of exploratory tissue engineering applications. The characterization of the structure-properties relationships of these scaffolds is necessary to understand their biophysical behavior in vivo. In this work, the relationship between morphology and physical properties in the dry and hydrated states was investigated across a range of solid concentrations in the scaffolds. The quantitative results provided can aid the design of scaffolds with a target trade-off between mechanical properties and structural features important for their biological activity. Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Pore networks and polymer rearrangement on a drug-eluting stent as revealed by correlated confocal Raman and atomic force microscopy.

PubMed

Biggs, Kevin B; Balss, Karin M; Maryanoff, Cynthia A

2012-05-29

Drug release from and coating morphology on a CYPHER sirolimus-eluting coronary stent (SES) during in vitro elution were studied by correlated confocal Raman and atomic force microscopy (CRM and AFM, respectively). Chemical surface and subsurface maps of the SES were generated in the same region of interest by CRM and were correlated with surface topography measured by AFM at different elution times. For the first time, a direct correlation between drug-rich regions and the coating morphology was made on a drug-eluting medical device, linking drug release with pore formation, pore throats, and pore networks. Drug release was studied on a drug-eluting stent (DES) system with a multicomponent carrier matrix (poly(n-butyl methacrylate) [PBMA] and poly(ethylene-co-vinyl acetate) [PEVA]). The polymer was found to rearrange postelution because confluence of the carrier polymer matrix reconstituted the voids created by drug release.

Bio-inspired Murray materials for mass transfer and activity

NASA Astrophysics Data System (ADS)

Zheng, Xianfeng; Shen, Guofang; Wang, Chao; Li, Yu; Dunphy, Darren; Hasan, Tawfique; Brinker, C. Jeffrey; Su, Bao-Lian

2017-04-01

Both plants and animals possess analogous tissues containing hierarchical networks of pores, with pore size ratios that have evolved to maximize mass transport and rates of reactions. The underlying physical principles of this optimized hierarchical design are embodied in Murray's law. However, we are yet to realize the benefit of mimicking nature's Murray networks in synthetic materials due to the challenges in fabricating vascularized structures. Here we emulate optimum natural systems following Murray's law using a bottom-up approach. Such bio-inspired materials, whose pore sizes decrease across multiple scales and finally terminate in size-invariant units like plant stems, leaf veins and vascular and respiratory systems provide hierarchical branching and precise diameter ratios for connecting multi-scale pores from macro to micro levels. Our Murray material mimics enable highly enhanced mass exchange and transfer in liquid-solid, gas-solid and electrochemical reactions and exhibit enhanced performance in photocatalysis, gas sensing and as Li-ion battery electrodes.

Nanoporous mannitol carrier prepared by non-organic solvent spray drying technique to enhance the aerosolization performance for dry powder inhalation

PubMed Central

Peng, Tingting; Zhang, Xuejuan; Huang, Ying; Zhao, Ziyu; Liao, Qiuying; Xu, Jing; Huang, Zhengwei; Zhang, Jiwen; Wu, Chuan-yu; Pan, Xin; Wu, Chuanbin

2017-01-01

An optimum carrier rugosity is essential to achieve a satisfying drug deposition efficiency for the carrier based dry powder inhalation (DPI). Therefore, a non-organic spray drying technique was firstly used to prepare nanoporous mannitol with small asperities to enhance the DPI aerosolization performance. Ammonium carbonate was used as a pore-forming agent since it decomposed with volatile during preparation. It was found that only the porous structure, and hence the specific surface area and carrier density were changed at different ammonium carbonate concentration. Furthermore, the carrier density was used as an indication of porosity to correlate with drug aerosolization. A good correlation between the carrier density and fine particle fraction (FPF) (r2 = 0.9579) was established, suggesting that the deposition efficiency increased with the decreased carrier density. Nanoporous mannitol with a mean pore size of about 6 nm exhibited 0.24-fold carrier density while 2.16-fold FPF value of the non-porous mannitol. The enhanced deposition efficiency was further confirmed from the pharmacokinetic studies since the nanoporous mannitol exhibited a significantly higher AUC0-8h value than the non-porous mannitol and commercial product Pulmicort. Therefore, surface modification by preparing nanoporous carrier through non-organic spray drying showed to be a facile approach to enhance the DPI aerosolization performance. PMID:28462948

Water retention of repellent and subcritical repellent soils: New insights from model and experimental investigations

NASA Astrophysics Data System (ADS)

Czachor, H.; Doerr, S. H.; Lichner, L.

2010-01-01

SummarySoil organic matter can modify the surface properties of the soil mineral phase by changing the surface tension of the mineral surfaces. This modifies the soil's solid-water contact angle, which in turn would be expected to affect its water retention curve (SWRC). Here we model the impact of differences in the soil pore-water contact angle on capillarity in non-cylindrical pores by accounting for their complex pore geometry. Key outcomes from the model include that (i) available methods for measuring the Young's wetting angle on soil samples are insufficient in representing the wetting angle in the soil pore space, (ii) the wetting branch of water retention curves is strongly affected by the soil pore-water contact angle, as manifest in the wetting behavior of water repellent soils, (iii) effects for the drying branch are minimal, indicating that both wettable and water repellent soils should behave similarly, and (vi) water retention is a feature not of only wettable soils, but also soils that are in a water repellent state. These results are tested experimentally by determining drying and wetting branches for (a) 'model soil' (quartz sands with four hydrophobization levels) and (b) five field soil samples with contrasting wettability, which were used with and without the removal of the soil organic matter. The experimental results support the theoretical predictions and indicate that small changes in wetting angle can cause switches between wettable and water repellent soil behavior. This may explain the common observation that relatively small changes in soil water content can cause substantial changes in soil wettability.

Macroscopic modeling of heat and water vapor transfer with phase change in dry snow based on an upscaling method: Influence of air convection

NASA Astrophysics Data System (ADS)

Calonne, N.; Geindreau, C.; Flin, F.

2015-12-01

At the microscopic scale, i.e., pore scale, dry snow metamorphism is mainly driven by the heat and water vapor transfer and the sublimation-deposition process at the ice-air interface. Up to now, the description of these phenomena at the macroscopic scale, i.e., snow layer scale, in the snowpack models has been proposed in a phenomenological way. Here we used an upscaling method, namely, the homogenization of multiple-scale expansions, to derive theoretically the macroscopic equivalent modeling of heat and vapor transfer through a snow layer from the physics at the pore scale. The physical phenomena under consideration are steady state air flow, heat transfer by conduction and convection, water vapor transfer by diffusion and convection, and phase change (sublimation and deposition). We derived three different macroscopic models depending on the intensity of the air flow considered at the pore scale, i.e., on the order of magnitude of the pore Reynolds number and the Péclet numbers: (A) pure diffusion, (B) diffusion and moderate convection (Darcy's law), and (C) strong convection (nonlinear flow). The formulation of the models includes the exact expression of the macroscopic properties (effective thermal conductivity, effective vapor diffusion coefficient, and intrinsic permeability) and of the macroscopic source terms of heat and vapor arising from the phase change at the pore scale. Such definitions can be used to compute macroscopic snow properties from 3-D descriptions of snow microstructures. Finally, we illustrated the precision and the robustness of the proposed macroscopic models through 2-D numerical simulations.

Single-phase and two-phase flow properties of mesaverde tight sandstone formation; random-network modeling approach

NASA Astrophysics Data System (ADS)

Bashtani, Farzad; Maini, Brij; Kantzas, Apostolos

2016-08-01

3D random networks are constructed in order to represent the tight Mesaverde formation which is located in north Wyoming, USA. The porous-space is represented by pore bodies of different shapes and sizes which are connected to each other by pore throats of varying length and diameter. Pore bodies are randomly distributed in space and their connectivity varies based on the connectivity number distribution which is used in order to generate the network. Network representations are then validated using publicly available mercury porosimetry experiments. The network modeling software solves the fundamental equations of two-phase immiscible flow incorporating wettability and contact angle variability. Quasi-static displacement is assumed. Single phase macroscopic properties (porosity, permeability) are calculated and whenever possible are compared to experimental data. Using this information drainage and imbibition capillary pressure, and relative permeability curves are predicted and (whenever possible) compared to experimental data. The calculated information is grouped and compared to available literature information on typical behavior of tight formations. Capillary pressure curve for primary drainage process is predicted and compared to experimental mercury porosimetry in order to validate the virtual porous media by history matching. Relative permeability curves are also calculated and presented.

Multi-scale mechanical response of freeze-dried collagen scaffolds for tissue engineering applications.

PubMed

Offeddu, Giovanni S; Ashworth, Jennifer C; Cameron, Ruth E; Oyen, Michelle L

2015-02-01

Tissue engineering has grown in the past two decades as a promising solution to unresolved clinical problems such as osteoarthritis. The mechanical response of tissue engineering scaffolds is one of the factors determining their use in applications such as cartilage and bone repair. The relationship between the structural and intrinsic mechanical properties of the scaffolds was the object of this study, with the ultimate aim of understanding the stiffness of the substrate that adhered cells experience, and its link to the bulk mechanical properties. Freeze-dried type I collagen porous scaffolds made with varying slurry concentrations and pore sizes were tested in a viscoelastic framework by macroindentation. Membranes made up of stacks of pore walls were indented using colloidal probe atomic force microscopy. It was found that the bulk scaffold mechanical response varied with collagen concentration in the slurry consistent with previous studies on these materials. Hydration of the scaffolds resulted in a more compliant response, yet lesser viscoelastic relaxation. Indentation of the membranes suggested that the material making up the pore walls remains unchanged between conditions, so that the stiffness of the scaffolds at the scale of seeded cells is unchanged; rather, it is suggested that thicker pore walls or more of these result in the increased moduli for the greater slurry concentration conditions. Copyright © 2014 The Authors. Published by Elsevier Ltd.. All rights reserved.

Pore architecture and cell viability on freeze dried 3D recombinant human collagen-peptide (RHC)-chitosan scaffolds.

PubMed

Zhang, Jing; Zhou, Aimei; Deng, Aipeng; Yang, Yang; Gao, Lihu; Zhong, Zhaocai; Yang, Shulin

2015-04-01

Pore architecture of 3D scaffolds used in tissue engineering plays a critical role in the maintenance of cell survival, proliferation and further promotion of tissue regeneration. We investigated the pore size and structure, porosity, swelling as well as cell viability of a series of recombinant human collagen-peptide-chitosan (RHCC) scaffolds fabricated by lyophilization. In this paper, freezing regime containing a final temperature of freezing (Tf) and cooling rates was applied to obtain scaffolds with pore size ranging from 100μm to 120μm. Other protocols of RHC/chitosan suspension concentration and ratio modification were studied to produce more homogenous and appropriate structural scaffolds. The mean pore size decreased along with the decline of Tf at a slow cooling rate of 0.7°C/min; a more rapid cooling rate under 5°C/min resulted to a smaller pore size and more homogenous microstructure. High concentration could reduce pore size and lead to thick well of scaffold, while improved the ratio of RHC, lamellar and fiber structure coexisted with cellular pores. Human umbilical vein endothelial cells (HUVECs) were seeded on these manufactured scaffolds, the cell viability represented a negative correlation to the pore size. This study provides an alternative method to fabricate 3D RHC-chitosan scaffolds with appropriate pores for potential tissue engineering. Copyright © 2014 Elsevier B.V. All rights reserved.

Geometric and topological characterization of porous media: insights from eigenvector centrality

NASA Astrophysics Data System (ADS)

Jimenez-Martinez, J.; Negre, C.

2017-12-01

Solving flow and transport through complex geometries such as porous media involves an extreme computational cost. Simplifications such as pore networks, where the pores are represented by nodes and the pore throats by edges connecting pores, have been proposed. These models have the ability to preserve the connectivity of the medium. However, they have difficulties capturing preferential paths (high velocity) and stagnation zones (low velocity), as they do not consider the specific relations between nodes. Network theory approaches, where the complex network is conceptualized like a graph, can help to simplify and better understand fluid dynamics and transport in porous media. To address this issue, we propose a method based on eigenvector centrality. It has been corrected to overcome the centralization problem and modified to introduce a bias in the centrality distribution along a particular direction which allows considering the flow and transport anisotropy in porous media. The model predictions are compared with millifluidic transport experiments, showing that this technique is computationally efficient and has potential for predicting preferential paths and stagnation zones for flow and transport in porous media. Entropy computed from the eigenvector centrality probability distribution is proposed as an indicator of the "mixing capacity" of the system.

Pore-Lining Composition and Capillary Breakthrough Pressure of Mudstone Caprocks: Sealing Efficiency of Geologic CO2 Storage Sites

NASA Astrophysics Data System (ADS)

Heath, J. E.; Dewers, T. A.; McPherson, B. J.; Kotula, P. G.

2010-12-01

Subsurface containment of CO2 is predicated on effective caprock sealing. Many previous studies have relied on macroscopic measurements of capillary breakthrough pressure and other petrophysical properties without direct examination of solid phases that line pore networks and directly contact fluids. However, pore-lining phases strongly contribute to sealing behavior through interfacial interactions among CO2, brine, and the mineral or non-mineral phases. Our high resolution (i.e., sub-micron) examination of the composition of pore-lining phases of several continental and marine mudstones indicates that sealing efficiency (i.e., breakthrough pressure) is governed by pore shapes and pore-lining phases that are not identifiable except through direct characterization of pores. Bulk X-ray diffraction data does not indicate which phases line the pores and may be especially lacking for mudstones with organic material. Organics can line pores and may represent once-mobile phases that modify the wettability of an originally clay-lined pore network. For shallow formations (i.e., < ~800 m depth), interfacial tension and contact angles result in breakthrough pressures that may be as high as those needed to fracture the rock—thus, in the absence of fractures, capillary sealing efficiency is indicated. Deeper seals have poorer capillary sealing if mica-like wetting dominates the wettability. We thank the U.S. Department of Energy’s National Energy Technology Laboratory and the Office of Basic Energy Sciences, and the Southeast and Southwest Carbon Sequestration Partnerships for supporting this work. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

Polyimide Aerogels with Three-Dimensional Cross-Linked Structure

NASA Technical Reports Server (NTRS)

Panek, John

2010-01-01

Polyimide aerogels with three-dimensional cross-linked structure are made using linear oligomeric segments of polyimide, and linked with one of the following into a 3D structure: trifunctional aliphatic or aromatic amines, latent reactive end caps such as nadic anhydride or phenylethynylphenyl amine, and silica or silsesquioxane cage structures decorated with amine. Drying the gels supercritically maintains the solid structure of the gel, creating a polyimide aerogel with improved mechanical properties over linear polyimide aerogels. Lightweight, low-density structures are desired for acoustic and thermal insulation for aerospace structures, habitats, astronaut equipment, and aeronautic applications. Aerogels are a unique material for providing such properties because of their extremely low density and small pore sizes. However, plain silica aerogels are brittle. Reinforcing the aerogel structure with a polymer (X-Aerogel) provides vast improvements in strength while maintaining low density and pore structure. However, degradation of polymers used in cross-linking tends to limit use temperatures to below 150 C. Organic aerogels made from linear polyimide have been demonstrated, but gels shrink substantially during supercritical fluid extraction and may have lower use temperature due to lower glass transition temperatures. The purpose of this innovation is to raise the glass transition temperature of all organic polyimide aerogel by use of tri-, tetra-, or poly-functional units in the structure to create a 3D covalently bonded network. Such cross-linked polyimides typically have higher glass transition temperatures in excess of 300 400 C. In addition, the reinforcement provided by a 3D network should improve mechanical stability, and prevent shrinkage on supercritical fluid extraction. The use of tri-functional aromatic or aliphatic amine groups in the polyimide backbone will provide such a 3D structure.

High rate capacitive performance of single-walled carbon nanotube aerogels

DOE PAGES

Van Aken, Katherine L.; Pérez, Carlos R.; Oh, Youngseok; ...

2015-05-30

Single-walled carbon nanotube (SWCNT) aerogels produced by critical-point-drying of wet-gel precursors exhibit unique properties, such as high surface-area-to-volume and strength-to-weight ratios. They are free-standing, are binder-free, and can be scaled to thicknesses of more than 1 mm. In this paper, we examine the electric double layer capacitive behavior of these materials using a common room temperature ionic liquid electrolyte, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI). Electrochemical performance is assessed through galvanostatic cycling, cyclic voltammetry and impedance spectroscopy. Results indicate stable capacitive performance over 10,000 cycles as well as an impressive performance at high charge and discharge rates, due to accessible pore networks andmore » enhanced electronic and ionic conductivities of SWCNT aerogels. Finally, these materials can find applications in mechanically compressible and flexible supercapacitor devices with high power requirements.« less

Controle de la morphologie d'hydrogels poreux a partir de structures polymeres

NASA Astrophysics Data System (ADS)

Esquirol, Anne-Laure

This master thesis presents a new fabrication method to prepare hydrogels with fully interconnected and tunable macropore networks prepared with co-continuous polymer blends. The main contributions are: (1) a hydrogel fabrication process providing a high control over the average pore size diameter, their volume fraction and their interconnectivity; (2) the microstructural characterization of porous hydrogels with new techniques such as X-ray microtomography and (3) the preparation of porous gels with industrial equipment such as extruders and injection molding presses. The development and improvement of methods and techniques to prepare porous polymers and porous gels have been intensive areas of research in materials science over the past 20 years because of their potential use in fields as diverse as high performance membranes and filtration devices, supports for catalysis and biochemical reactions, encapsulating devices for drug release, and scaffolds for cells seeding and proliferation. For this last application, in tissue engineering, some typical parameters related to porosity must be rigorously controlled: (1) the average pore size diameter; (2) the pore volume fraction; (3) the pore interconnectivity. Porous hydrogels are excellent candidates due to their similarities with the extracellular matrix (composition, mechanical properties and diffusion properties). A certain number of methods and techniques have been developed and studied to prepare gels comprising microstructured 3-D networks of (more or less) interconnected pores (also called sometimes microfluidic gels or (macro)porous gels). Poly(L-lactide) (PLA) porous materials were realized from immiscible and co-continuous binary blends of polystyrene/poly(L-lactide) (PS/PLA) at 50/50 %vol prepared by different methods : (1) internal mixer (cubic samples with 0.8 mm sides) and (2) extrusion followed by injection molding which allows the fabrication of bars with superior dimensions (0.95 cm x 1.25 cm x 6.3 cm). Quiescent annealing of the binary blends was performed at 190 °C to tune the characteristic dimensions of the co-continuous morphology: (1) 0, 10, 30, 60 and 90 min for cubic samples and (2) 0, 10, 20 and 30 min for bars. Afterwards, the PLA phase has been isolated by a specific solvent extraction of the PS phase to obtain porous PLA molds. Gravimetric analysis have demonstrated a co-continuity superior to 95% for cubic samples and superior to 85% for the bars. This morphology was analyzed by scanning electron microscopy (SEM) for each annealing time (for the cubic samples). Image analysis performed on the SEM micrographs have demonstrated that the average pore diameter can range from 3 mum to over 400 mum and that the specific interfacial area ranges from 5800 cm-1 to 45 cm-1, for annealing times going from 0 min to 90 min). The porosity of the bars was observed by X-ray microtomography and shows that the average pore diameter ranges from 10 mum to 500 mum (annealing from 10 min to 30 min). Solutions of agar or alginate were subsequently injected into the PLA porous molds by using a manual injection system, followed by an in situ gelification. Visual inspections and optical microscope observations show a complete injection for molds with average pore sizes over 20 mum (cubic samples) and over 300 mum (for bars). These assumptions are also supported by the gels morphology characterization. The second polymer phase (PLA) was subsequently dissolved using a second selective solvent, leaving only the porous gel structures. X-ray microtomography analysis, which provide 2-D and 3-D images, have demonstrated that the morphologies of the porous gels are similar to the PLA molds microstructures. For example, porous gels prepared with cubic PLA molds annealed during 60 min, show an average pore size of about 285 mum (as compared to 200 mum for the PLA molds) and a specific interfacial area of 70 cm -1 (as compared to 100 cm-1 for the PLA molds). Similar results were obtained for the porous gels prepared with the porous PLA bars (qualitative observation). The effectiveness of two sterilization methods has been proven on nutrient agar (NA) and "Brain Heart Infusion" (BHI) with no bacterial colonies apparition. The first method is the freeze-drying followed by an oven treatment at 120 °C in a sterile environment. The porous gel morphology was characterized by X-ray microtomography before and after freeze-drying, and after rehydration, demonstrating the conservation of the macroscopic dimensions of the gels, of their morphologies and porosities. The second method is the successive baths in an ethanol solution. Finally mechanical compression tests have shown that porous gels, as can be expected, have a lower compressive resistance as compared to non-porous hydrogels. (Abstract shortened by UMI.).

Process for disposing of radioactive wastes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grantham, L.F.; Gray, R.L.; McCoy, L.R.

1988-05-03

A process for removing water from the pores of spent, contaminated radioactive ion exchange resins and encasing radionuclides entrapped within the pores of the resins, the process is described consisting essentially of the sequential steps of: (a) heating the spent ion exchange resins at a temperature of from about 100/sup 0/C to about 150/sup 0/C to remove water from within and fill the pores of the ion exchange resins by heating the ion exchange resins for from about 46 to about 610 hours at a temperature at which the pores of the resins are sealed while avoiding any fusing ormore » melting of the ion exchange resins to encase radionuclides contained within the resins; and (b) cooling the resins to obtain dry, flowable ion exchange resins having radionuclides encased within sealed polymeric spheres.« less

Inter-subunit interactions across the upper voltage sensing-pore domain interface contribute to the concerted pore opening transition of Kv channels.

PubMed

Shem-Ad, Tzilhav; Irit, Orr; Yifrach, Ofer

2013-01-01

The tight electro-mechanical coupling between the voltage-sensing and pore domains of Kv channels lies at the heart of their fundamental roles in electrical signaling. Structural data have identified two voltage sensor pore inter-domain interaction surfaces, thus providing a framework to explain the molecular basis for the tight coupling of these domains. While the contribution of the intra-subunit lower domain interface to the electro-mechanical coupling that underlies channel opening is relatively well understood, the contribution of the inter-subunit upper interface to channel gating is not yet clear. Relying on energy perturbation and thermodynamic coupling analyses of tandem-dimeric Shaker Kv channels, we show that mutation of upper interface residues from both sides of the voltage sensor-pore domain interface stabilizes the closed channel state. These mutations, however, do not affect slow inactivation gating. We, moreover, find that upper interface residues form a network of state-dependent interactions that stabilize the open channel state. Finally, we note that the observed residue interaction network does not change during slow inactivation gating. The upper voltage sensing-pore interaction surface thus only undergoes conformational rearrangements during channel activation gating. We suggest that inter-subunit interactions across the upper domain interface mediate allosteric communication between channel subunits that contributes to the concerted nature of the late pore opening transition of Kv channels.

A thermodynamic approach to alamethicin pore formation.

PubMed

Rahaman, Asif; Lazaridis, Themis

2014-01-01

The structure and energetics of alamethicin Rf30 monomer to nonamer in cylindrical pores of 5 to 11Å radius are investigated using molecular dynamics simulations in an implicit membrane model that includes the free energy cost of acyl chain hydrophobic area exposure. Stable, low energy pores are obtained for certain combinations of radius and oligomeric number. The trimer and the tetramer formed 6Å pores that appear closed while the larger oligomers formed open pores at their optimal radius. The hexamer in an 8Å pore and the octamer in an 11Å pore give the lowest effective energy per monomer. However, all oligomers beyond the pentamer have comparable energies, consistent with the observation of multiple conductance levels. The results are consistent with the widely accepted "barrel-stave" model. The N terminal portion of the molecule exhibits smaller tilt with respect to the membrane normal than the C terminal portion, resulting in a pore shape that is a hybrid between a funnel and an hourglass. Transmembrane voltage has little effect on the structure of the oligomers but enhances or decreases their stability depending on its orientation. Antiparallel bundles are lower in energy than the commonly accepted parallel ones and could be present under certain experimental conditions. Dry aggregates (without an aqueous pore) have lower average effective energy than the corresponding aggregates in a pore, suggesting that alamethicin pores may be excited states that are stabilized in part by voltage and in part by the ion flow itself. © 2013.

Water Displacement in Oil-Wet Tight Reservoirs by Dynamic Network Simulation

NASA Astrophysics Data System (ADS)

Wang, Y.; Li, M.; Chen, M.

2017-12-01

Pore network simulation is an effective tool for studying the multiphase flow in porous media. Based on the topological information and pore-throat size distribution obtained from the analysis of Scanning Electron Microscope (SEM) and constant-rate mercury injection (CRMI) for tight cores (composed by micro-nano scale throats and micro scale pores), a simple cubic (SC) pore-throat network was built with equilateral triangular cross-section throats and cubic bodies. Rules for oil and water movement and redistribution were devised in accordance with the physics process at pore-throat scale. Water flooding from oil-saturated under irreducible water were simulated by considering the changing displacement rate and viscosity ratio at the slightly oil-wet condition (the static contact angle ranges between π/2 to 2π/3). Different from the double pressure field algorithm, a single pressure field which solved by using successive over relaxation method was used with the flow of irreducible water in corners was ignored while its swilling was take into consideration. Dynamic of displacement fronts, relative permeability curves and residual oil saturation were obtained. It showed that there were obviously snap-off at low capillary number (Nc<10-5) and fingering at high capillary number (Nc<10-4) even at a favorable viscosity ratio (M=1). The magnitude of viscosity ratio effect on relative permeability depended largely on the capillary number, which the effect wasn't noticeable for a high capillary number. For residual oil saturation Sor, it showed that Sor decreased with the increase of capillary number at different viscosity ratio. Changing of residual oil saturation from simulation was in good agreement with the experimental results in a certain range, which indicated that this network model could be used to character the water flooding in tight reservoirs.

Three-dimensionally networked graphene hydroxide with giant pores and its application in supercapacitors

PubMed Central

Lee, Dongwook; Seo, Jiwon

2014-01-01

The three-dimensionally networked and layered structure of graphene hydroxide (GH) was investigated. After lengthy immersion in a NaOH solution, most of the epoxy groups in the graphene oxide were destroyed, and more hydroxyl groups were generated, transforming the graphene oxide into graphene hydroxide. Additionally, benzoic acid groups were formed, and the ether groups link the neighboring layers, creating a near-3D structure in the GH. To utilize these unique structural features, electrodes with large pores for use in supercapacitors were fabricated using thermal reduction in vacuum. The reduced GH maintained its layered structure and developed a lot of large of pores between/inside the layers. The GH electrodes exhibited high gravimetric as well as high volumetric capacitance. PMID:25492227

Three-dimensionally networked graphene hydroxide with giant pores and its application in supercapacitors

NASA Astrophysics Data System (ADS)

Lee, Dongwook; Seo, Jiwon

2014-12-01

The three-dimensionally networked and layered structure of graphene hydroxide (GH) was investigated. After lengthy immersion in a NaOH solution, most of the epoxy groups in the graphene oxide were destroyed, and more hydroxyl groups were generated, transforming the graphene oxide into graphene hydroxide. Additionally, benzoic acid groups were formed, and the ether groups link the neighboring layers, creating a near-3D structure in the GH. To utilize these unique structural features, electrodes with large pores for use in supercapacitors were fabricated using thermal reduction in vacuum. The reduced GH maintained its layered structure and developed a lot of large of pores between/inside the layers. The GH electrodes exhibited high gravimetric as well as high volumetric capacitance.

Three-dimensionally networked graphene hydroxide with giant pores and its application in supercapacitors.

PubMed

Lee, Dongwook; Seo, Jiwon

2014-12-10

The three-dimensionally networked and layered structure of graphene hydroxide (GH) was investigated. After lengthy immersion in a NaOH solution, most of the epoxy groups in the graphene oxide were destroyed, and more hydroxyl groups were generated, transforming the graphene oxide into graphene hydroxide. Additionally, benzoic acid groups were formed, and the ether groups link the neighboring layers, creating a near-3D structure in the GH. To utilize these unique structural features, electrodes with large pores for use in supercapacitors were fabricated using thermal reduction in vacuum. The reduced GH maintained its layered structure and developed a lot of large of pores between/inside the layers. The GH electrodes exhibited high gravimetric as well as high volumetric capacitance.

Effect of spatial restriction on the photoluminescent properties of carbon nanomaterials

NASA Astrophysics Data System (ADS)

Vostrikova, A. M.; Nikolaeva, A. N.; Bakal, A. A.; Shpuntova, D. V.; Mordovina, E. A.; Sukhorukov, G. B.; Sapelkin, A. V.; Goryacheva, I. Yu.

2018-04-01

Photoluminescent (PL) properties of carbon-based nanomaterials obtained on the base of sodium dextran sulfate (DS) were compared. DS water solution, dry powder and co-precipitated inside pores of CaCO3 microparticles solution were thermally treated and clear difference between these materials was found. Effect of spatial restriction of CaCO3 pores showed itself in the identity of PL properties for material, obtained by thermal and hydrothermal treatment; in the absence of CaCO3 microparticles the PL spectra were quite different.

Determination of relative phase permeabilities in stochastic model of pore channel distribution by diameter

NASA Astrophysics Data System (ADS)

Zemenkova, M. Y.; Shabarov, A.; Shatalov, A.; Puldas, L.

2018-05-01

The problem of the pore space description and the calculation of relative phase permeabilities (RPP) for two-phase filtration is considered. A technique for constructing a pore-network structure for constant and variable channel diameters is proposed. A description of the design model of RPP based on the capillary pressure curves is presented taking into account the variability of diameters along the length of pore channels. By the example of the calculation analysis for the core samples of the Urnenskoye and Verkhnechonskoye deposits, the possibilities of calculating RPP are shown when using the stochastic distribution of pores by diameters and medium-flow diameters.

Synthesis and characterization of binary titania-silica mixed oxides

NASA Astrophysics Data System (ADS)

Budhi, Sridhar

A series of binary titania-silica mixed oxides were synthesized by the sol-gel method at room temperature. The mixed oxides were prepared that involved the hydrolysis of titanium isopropoxide and tetraethylorthosilicate (TEOS) by co-solvent induced gelation usually in acidic media. The resulting gels were dried, calcined and then characterized by powder X-ray diffractometric studies, nitrogen sorption studies (at 77K), diffuse reflectance spectroscopy, Raman microscopy and transmission electron microscopic studies. The nitrogen sorption studies indicate that the specific surface areas, pore volume, pore diameter and pore size distribution of the mixed oxides were substantially enhanced when non-polar solvents such as toluene, p-xylene or mesitylene were added as co-solvents to the synthesis gel. Transmission electron microscopic (TEM) studies confirm the results obtained from the nitrogen sorption studies. Our results indicate that we can obtain binary metal oxides possessing high surface area and large pore volumes with tunable pore size distribution at room temperature. Photocatalytic evaluation of the mixed oxides is currently in progress.

Adsorbates in a Box: Titration of Substrate Electronic States

NASA Astrophysics Data System (ADS)

Cheng, Zhihai; Wyrick, Jonathan; Luo, Miaomiao; Sun, Dezheng; Kim, Daeho; Zhu, Yeming; Lu, Wenhao; Kim, Kwangmoo; Einstein, T. L.; Bartels, Ludwig

2010-08-01

Nanoscale confinement of adsorbed CO molecules in an anthraquinone network on Cu(111) with a pore size of ≈4nm arranges the CO molecules in a shell structure that coincides with the distribution of substrate confined electronic states. Molecules occupy the states approximately in the sequence of rising electron energy. Despite the sixfold symmetry of the pore boundary itself, the adsorbate distribution adopts the threefold symmetry of the network-substrate system, highlighting the importance of the substrate even for such quasi-free-electron systems.

Fracturing of porous rock induced by fluid injection

NASA Astrophysics Data System (ADS)

Stanchits, Sergei; Mayr, Sibylle; Shapiro, Serge; Dresen, Georg

2011-04-01

We monitored acoustic emission (AE) activity and brittle failure initiated by water injection into initially dry critically stressed cylindrical specimens of Flechtingen sandstone of 50 mm diameter and 105-125 mm length. Samples were first loaded in axial direction at 40-50 MPa confining pressure at dry conditions close to peak stress. Subsequently distilled water was injected either at the bottom of specimen or via a central borehole at pore pressures of 5-30 MPa. Water injection into stressed porous sandstone induced a cloud of AE events located close to the migrating water front. Water injection was monitored by periodic ultrasonic velocity measurements across the sample. Propagation of the induced cloud of AE was faster in the direction parallel to bedding than normal to it, indicating permeability anisotropy. Water injection was associated with significant AE activity demonstrating increased contribution of tensile source type. Brittle failure was accompanied by increased contribution of shear and pore collapse source types. At a critical pore pressure, a brittle fault nucleated from a cloud of induced AE events in all samples. Microstructural analysis of fractured samples shows excellent agreement between location of AE hypocenters and macroscopic faults.

Upscaling pore pressure-dependent gas permeability in shales

NASA Astrophysics Data System (ADS)

Ghanbarian, Behzad; Javadpour, Farzam

2017-04-01

Upscaling pore pressure dependence of shale gas permeability is of great importance and interest in the investigation of gas production in unconventional reservoirs. In this study, we apply the Effective Medium Approximation, an upscaling technique from statistical physics, and modify the Doyen model for unconventional rocks. We develop an upscaling model to estimate the pore pressure-dependent gas permeability from pore throat size distribution, pore connectivity, tortuosity, porosity, and gas characteristics. We compare our adapted model with six data sets: three experiments, one pore-network model, and two lattice-Boltzmann simulations. Results showed that the proposed model estimated the gas permeability within a factor of 3 of the measurements/simulations in all data sets except the Eagle Ford experiment for which we discuss plausible sources of discrepancies.

Powder processing of hybrid titanium neural electrodes

NASA Astrophysics Data System (ADS)

Lopez, Jose Luis, Jr.

A preliminary investigation into the powder production of a novel hybrid titanium neural electrode for EEG is presented. The rheological behavior of titanium powder suspensions using sodium alginate as a dispersant are examined for optimal slip casting conditions. Electrodes were slip cast and sintered at 950°C for 1 hr, 1000°C for 1, 3, and 6 hrs, and 1050°C for 1 hr. Residual porosities from sintering are characterized using Archimedes' technique and image analysis. The pore network is gel impregnated by submerging the electrodes in electrically conductive gel and placing them in a chamber under vacuum. Gel evaporation of the impregnated electrodes is examined. Electrodes are characterized in the dry and gelled states using impedance spectrometry and compared to a standard silver- silver chloride electrode. Power spectral densities for the sensors in the dry and gelled state are also compared. Residual porosities for the sintered specimens were between 50.59% and 44.81%. Gel evaporation tests show most of the impregnated gel evaporating within 20 min of exposure to atmospheric conditions with prolonged evaporation times for electrodes with higher impregnated gel mass. Impedance measurements of the produced electrodes indicate the low impedance of the hybrid electrodes are due to the increased contact area of the porous electrode. Power spectral densities of the titanium electrode behave similar to a standard silver-silver chloride electrode. Tests suggest the powder processed hybrid titanium electrode's performance is better than current dry contact electrodes and comparable to standard gelled silver-silver chloride electrodes.

Comparison of Mathematical Equation and Neural Network Modeling for Drying Kinetic of Mendong in Microwave Oven

NASA Astrophysics Data System (ADS)

Maulidah, Rifa'atul; Purqon, Acep

2016-08-01

Mendong (Fimbristylis globulosa) has a potentially industrial application. We investigate a predictive model for heat and mass transfer in drying kinetics during drying a Mendong. We experimentally dry the Mendong by using a microwave oven. In this study, we analyze three mathematical equations and feed forward neural network (FNN) with back propagation to describe the drying behavior of Mendong. Our results show that the experimental data and the artificial neural network model has a good agreement and better than a mathematical equation approach. The best FNN for the prediction is 3-20-1-1 structure with Levenberg- Marquardt training function. This drying kinetics modeling is potentially applied to determine the optimal parameters during mendong drying and to estimate and control of drying process.

The phenotype of cancer cell invasion controlled by fibril diameter and pore size of 3D collagen networks.

PubMed

Sapudom, Jiranuwat; Rubner, Stefan; Martin, Steve; Kurth, Tony; Riedel, Stefanie; Mierke, Claudia T; Pompe, Tilo

2015-06-01

The behavior of cancer cells is strongly influenced by the properties of extracellular microenvironments, including topology, mechanics and composition. As topological and mechanical properties of the extracellular matrix are hard to access and control for in-depth studies of underlying mechanisms in vivo, defined biomimetic in vitro models are needed. Herein we show, how pore size and fibril diameter of collagen I networks distinctively regulate cancer cell morphology and invasion. Three-dimensional collagen I matrices with a tight control of pore size, fibril diameter and stiffness were reconstituted by adjustment of concentration and pH value during matrix reconstitution. At first, a detailed analysis of topology and mechanics of matrices using confocal laser scanning microscopy, image analysis tools and force spectroscopy indicate pore size and not fibril diameter as the major determinant of matrix elasticity. Secondly, by using two different breast cancer cell lines (MDA-MB-231 and MCF-7), we demonstrate collagen fibril diameter--and not pore size--to primarily regulate cell morphology, cluster formation and invasion. Invasiveness increased and clustering decreased with increasing fibril diameter for both, the highly invasive MDA-MB-231 cells with mesenchymal migratory phenotype and the MCF-7 cells with amoeboid migratory phenotype. As this behavior was independent of overall pore size, matrix elasticity is shown to be not the major determinant of the cell characteristics. Our work emphasizes the complex relationship between structural-mechanical properties of the extracellular matrix and invasive behavior of cancer cells. It suggests a correlation of migratory and invasive phenotype of cancer cells in dependence on topological and mechanical features of the length scale of single fibrils and not on coarse-grained network properties. Copyright © 2015 Elsevier Ltd. All rights reserved.

Pore-wall roughness as a fractal surface and theoretical simulation of mercury intrusion/retraction in porous media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsakiroglou, C.D.; Payatakes, A.C.

The mercury intrusion/retraction curves of many types of porous materials (e.g., sandstones) have sections of finite slope in the region of high and very high pressure. This feature is attributed to the existence of microroughness on the pore walls. In the present work pore-wall roughness features are added to a three-dimensional primary network of chambers-and-throats using ideas of fractal geometry. The roughness of the throats is modeled with a finite number of self-similar triangular prisms of progressively smaller sizes. The roughness of the chambers is modeled in a similar way using right circular cones instead of prisms. Three parameters sufficemore » for the complete characterization of the model of fractal roughness, namely, the number of features per unit length, the common angle of sharpness, and the number of layers (which is taken to be the same for throats and chambers). Analytical relations that give the surface area, pore volume, and mercury saturation of the pore network as functions of the fractal roughness parameters are developed for monolayer and multilayer arrangements. The chamber-and-throat network with fractal pore-wall roughness is used to develop an extended version of the computer-aided simulator of mercury porosimetry that has been reported in previous publications. This new simulator is used to investigate the effects of the roughness features on the form of mercury intrusion/retraction curves. It turns out that the fractal model of the porewall roughness gives an adequate representation of real porous media, and capillary pressure curves which are similar to the experimental ones for many typical porous materials such as sandstones. The method is demonstrated with the analysis of a Greek sandstone.« less

Fault gouge rheology under confined, high-velocity conditions

NASA Astrophysics Data System (ADS)

Reches, Z.; Madden, A. S.; Chen, X.

2012-12-01

We recently developed the experimental capability to investigate the shear properties of fine-grain gouge under confined conditions and high-velocity. The experimental system includes a rotary apparatus that can apply large displacements of tens of meters, slip velocity of 0.001- 2.0 m/s, and normal stress of 35 MPa (Reches and Lockner, 2010). The key new component is a Confined ROtary Cell (CROC) that can shear a gouge layer either dry or under pore-pressure. The pore pressure is controlled by two syringe pumps. CROC includes a ring-shape gouge chamber of 62.5 mm inner diameter, 81.25 mm outer diameter, and up to 3 mm thick gouge sample. The lower, rotating part of CROC contains the sample chamber, and the upper, stationary part includes the loading, hollow cylinder and setting for temperature, and dilation measurements, and pore-pressure control. Each side of the gouge chamber has two pairs of industrial, spring-energized, self-lubricating, teflon-graphite seals, built for particle media and can work at temperature up to 250 ded C. The space between each of the two sets of seals is pressurized by nitrogen. This design generates 'zero-differential pressure' on the inner seal (which is in contact with the gouge powder), and prevents gouge leaks. For the preliminary dry experiments, we used ~2.0 mm thick layers of room-dry kaolinite powder. Total displacements were on the order of meters and normal stress up to 4 MPa. The initial shear was accommodated by multiple internal slip surfaces within the kaolinite layer accommodated as oriented Riedel shear structures. Later, the shear was localized within a thin, plate-parallel Y-surface. The kaolinite layer was compacted at a quasi-asymptotic rate, and displayed a steady-state friction coefficient of ~ 0.5 with no clear dependence on slip velocity up to 0.15 m/s. Further experiments with loose quartz sand (grain size ~ 125 micron) included both dry runs and pore-pressure (distilled water) controlled runs. The sand was pressurized through a porous metal (Mott) plug. Comparison with effective stress calculations indicates the same friction coefficient of ~ 1.0 for the sand layer under dry and pressurized conditions. Both kaolinite and quartz sand experiments developed localized shear zones that were examined at the nano- and micro- scales with AFM, SEM and TEM. These zones displayed reduced grain sizes and cementation by local agglomeration. Kaolinite grains sheared in CROC experiment; scale bar = 1 micron.

Dispersion in 2D network: Effects of mixing rule at nodes and molecular diffusion

NASA Astrophysics Data System (ADS)

Wang, Y.; Tao, Q.; Li, M.

2017-12-01

We simulate solute transport in 2D network backbone characterized by pore connectivity and pore heterogeneity by particle-tracking method. In order to ensure the dispersion coefficient reaching an asymptotic value, we upscale dispersion from pore-scale to meter-scale by using periodic boundary condition. As comparison, two different flow mechanisms without or with dispersion in a capillary tube, namely mean flow and Taylor-Aris dispersion, are introduced to investigate the evolution of solute spreading. The longitudinal dispersion coefficient DLM without dispersion in a pipe can roughly be regarded as a parameter to quantify the impact of microscopic structure of porous media on solute spreading, which is smaller than that value DL of Taylor-Aris dispersion. The difference between them decreases with the enhancement of the disorder. The mixing rule at nodes has a minor effect on longitudinal spreading, but has a significant effect on transverse spreading, especially for the nearly homogeneous media. An increase of the disorder in network achieved by increasing pore size heterogeneity or/and decreasing pore connectivity diminishes the difference between two mixing rules. Besides, the evolution of longitudinal dispersion coefficient over diffusion presents three different patterns at different velocities for homogenous media, such as monotonically increasing trend, decreasing first and then increasing trend and monotonically decreasing trend. But all are replaced by power law for a high disorder. The simulation results also accurately predict the experimental dependence of the longitudinal coefficient on Peclet number Pe.

Initiation and Activation of Faults in Dry and Wet Rock by Fluid Injection

NASA Astrophysics Data System (ADS)

Stanchits, S.; Mayr, S.; Shapiro, S. A.; Dresen, G.

2008-12-01

We studied fracturing of rock samples induced by water injection in axial compression tests on cylindrical specimens of Flechtingen sandstone and Aue granite of 50 mm diameter and 105-125 mm length. Samples were intact solid rock cylinders and cylinders with central boreholes of 5 mm diameter and 52 mm length or through-boreholes of 2.5 mm diameter. To monitor acoustic emissions (AE) and ultrasonic velocities, twelve P-wave and six polarized S-wave sensors were glued to the cylindrical surface of the rock. Full waveforms were stored in a 12 channel transient recording system (PROEKEL, Germany). Polarity of AE first motion was used to discriminate source types associated with tensile, shear and pore-collapse cracking. To monitor strain, two pairs of orthogonally oriented strain-gages were glued onto the specimen surface. Samples were deformed in two consecutive loading steps: 1) Initial triaxial loading was performed at 20-50 MPa confining pressure on dry (under vacuum) or fully saturated samples until the yield point was reached. 2) In a second stage distilled water was injected into the samples with pore pressure increasing up to 20 MPa. For saturated samples the pore pressure was increased in steps and in periodic pulses. Injection of water into dry porous sandstone resulted in propagation of an AE hypocenter cloud closely linked to propagation of the water front. Position of the migrating water front was estimated from ultrasonic velocity measurements and measurements of the injected water volume. Propagation rate of AE-induced cloud parallel to bedding was higher than perpendicular to bedding, possibly related to permeability anisotropy. Nucleation of a brittle shear fault occurred at a critical pore pressure level with a nucleation patch located at the central borehole. Micro-structural analysis of fractured samples shows excellent agreement between location of AE hypocenters and macroscopic faults.

A green salt-leaching technique to produce sericin/PVA/glycerin scaffolds with distinguished characteristics for wound-dressing applications.

PubMed

Aramwit, Pornanong; Ratanavaraporn, Juthamas; Ekgasit, Sanong; Tongsakul, Duangta; Bang, Nipaporn

2015-05-01

Sericin/PVA/glycerin scaffolds could be fabricated using the freeze-drying technique; they showed good physical and biological properties and can be applied as wound dressings. However, freeze-drying is an energy- and time-consuming process with a high associated cost. In this study, an alternative, solvent-free, energy- and time-saving, low-cost salt-leaching technique is introduced as a green technology to produce sericin/PVA/glycerin scaffolds. We found that sericin/PVA/glycerin scaffolds were successfully fabricated without any crosslinking using a salt-leaching technique. The salt-leached sericin/PVA/glycerin scaffolds had a porous structure with pore interconnectivity. The sericin in the salt-leached scaffolds had a crystallinity that was as high as that of the freeze-dried scaffolds. Compared to the freeze-dried scaffolds with the same composition, the salt-leached sericin/PVA/glycerin scaffolds has larger pores, a lower Young's modulus, and faster rates of biodegradation and sericin release. When cultured with L929 mouse fibroblast cells, a higher number of cells were found in the salt-leached scaffolds. Furthermore, the salt-leached scaffolds were less adhesive to the wound, which would reduce pain upon removal. Therefore, salt-leached sericin/PVA/glycerin scaffolds with distinguished characteristics were introduced as another choice of wound dressing, and their production process was simpler, more energy efficient, and saved time and money compared to the freeze-dried scaffolds. © 2014 Wiley Periodicals, Inc.

Scalable synthesis of mesoporous titania microspheres via spray-drying method.

PubMed

Pal, Manas; Wan, Li; Zhu, Yongheng; Liu, Yupu; Liu, Yang; Gao, Wenjun; Li, Yuhui; Zheng, Gengfeng; Elzatahry, Ahmed A; Alghamdi, Abdulaziz; Deng, Yonghui; Zhao, Dongyuan

2016-10-01

Mesoporous TiO2 has several potential applications due to its unique electronic and optical properties, although its structures and morphologies are typically difficult to tune because of its uncontrollable and fast sol-gel reaction. In this study we have coupled the template-directed-sol-gel-chemistry with the low-cost, scalable, and environmentally benign aerosol (spray-drying) one-pot preparation technique for the fabrication of hierarchically mesoporous TiO2 microspheres and Fe3O4@mesoporous TiO2-x microspheres in a large scale. Parameters during the pre-hydrolysis and spray-drying treatment were varied to successfully control the bead diameter, morphology, monodispersity, surface area and pore size for improving their effectiveness for better application. Unlike to the previous aerosol synthetic approaches, where mainly quite a high temperature gradient with the strict control of spray-drying precursor concentration is implied, our strategy is lying on comparatively low drying temperature with an additional post-ultrasonication (further hydrolysis and condensation) route of the pre-calcined TiO2 samples. As-synthesized mesoporous microspheres have a size distribution from 500nm to 5μm, specific surface areas ranging from 150 to 162m(2)g(-1) and mean pore sizes of several nanometers (4-6nm). Further Fe3O4@mesoporous TiO2-x microspheres were observed to show remarkable selective phosphopeptide-enrichment activity which might have significant importance in disease diagnosis and other biomedical applications. Copyright © 2016. Published by Elsevier Inc.

Comparison of Pore-Network and Lattice Boltzmann Models for Pore-Scale Modeling of Geological Storage of CO2 in Natural Reservoir Rocks

NASA Astrophysics Data System (ADS)

Kohanpur, A. H.; Chen, Y.; Valocchi, A. J.; Tudek, J.; Crandall, D.

2016-12-01

CO2-brine flow in deep natural rocks is the focus of attention in geological storage of CO2. Understanding rock/flow properties at pore-scale is a vital component in field-scale modeling and prediction of fate of injected CO2. There are many challenges in working at the pore scale, such as size and selection of representative elementary volume (REV), particularly for material with complex geometry and heterogeneity, and the high computational costs. These issues factor into trade-offs that need to be made in choosing and applying pore-scale models. On one hand, pore-network modeling (PNM) simplifies the geometry and flow equations but can provide characteristic curves on fairly large samples. On the other hand, the lattice Boltzmann method (LBM) solves Navier-Stokes equations on the real geometry but is limited to small samples due to its high computational costs. Thus, both methods have some advantages but also face some challenges, which warrants a more detailed comparison and evaluation. In this study, we used industrial and micro-CT scans of actual reservoir rock samples to characterize pore structure at different resolutions. We ran LBM models directly on the characterized geometry and PNM on the equivalent 3D extracted network to determine single/two-phase flow properties during drainage and imbibition processes. Specifically, connectivity, absolute permeability, relative permeability curve, capillary pressure curve, and interface location are compared between models. We also did simulations on several subsamples from different locations including different domain sizes and orientations to encompass analysis of heterogeneity and isotropy. This work is primarily supported as part of the Center for Geologic Storage of CO2, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science and partially supported by the International Institute for Carbon-Neutral Energy Research (WPI-I2CNER) based at Kyushu University, Japan.

Multi-scale modeling of multi-component reactive transport in geothermal aquifers

NASA Astrophysics Data System (ADS)

Nick, Hamidreza M.; Raoof, Amir; Wolf, Karl-Heinz; Bruhn, David

2014-05-01

In deep geothermal systems heat and chemical stresses can cause physical alterations, which may have a significant effect on flow and reaction rates. As a consequence it will lead to changes in permeability and porosity of the formations due to mineral precipitation and dissolution. Large-scale modeling of reactive transport in such systems is still challenging. A large area of uncertainty is the way in which the pore-scale information controlling the flow and reaction will behave at a larger scale. A possible choice is to use constitutive relationships relating, for example the permeability and porosity evolutions to the change in the pore geometry. While determining such relationships through laboratory experiments may be limited, pore-network modeling provides an alternative solution. In this work, we introduce a new workflow in which a hybrid Finite-Element Finite-Volume method [1,2] and a pore network modeling approach [3] are employed. Using the pore-scale model, relevant constitutive relations are developed. These relations are then embedded in the continuum-scale model. This approach enables us to study non-isothermal reactive transport in porous media while accounting for micro-scale features under realistic conditions. The performance and applicability of the proposed model is explored for different flow and reaction regimes. References: 1. Matthäi, S.K., et al.: Simulation of solute transport through fractured rock: a higher-order accurate finite-element finite-volume method permitting large time steps. Transport in porous media 83.2 (2010): 289-318. 2. Nick, H.M., et al.: Reactive dispersive contaminant transport in coastal aquifers: Numerical simulation of a reactive Henry problem. Journal of contaminant hydrology 145 (2012), 90-104. 3. Raoof A., et al.: PoreFlow: A Complex pore-network model for simulation of reactive transport in variably saturated porous media, Computers & Geosciences, 61, (2013), 160-174.

Development of a New Analog Test System Capable of Modeling Tectonic Deformation Incorporating the Effects of Pore Fluid Pressure

NASA Astrophysics Data System (ADS)

Zhang, M.; Nakajima, H.; Takeda, M.; Aung, T. T.

2005-12-01

Understanding and predicting the tectonic deformation within geologic strata has been a very important research subject in many fields such as structural geology and petroleum geology. In recent years, such research has also become a fundamental necessity for the assessment of active fault migration, site selection for geological disposal of radioactive nuclear waste and exploration for methane hydrate. Although analog modeling techniques have played an important role in the elucidation of the tectonic deformation mechanisms, traditional approaches have typically used dry materials and ignored the effects of pore fluid pressure. In order for analog models to properly depict the tectonic deformation of the targeted, large-prototype system within a small laboratory-scale configuration, physical properties of the models, including geometry, force, and time, must be correctly scaled. Model materials representing brittle rock behavior require an internal friction identical to the prototype rock and virtually zero cohesion. Granular materials such as sand, glass beads, or steel beads of dry condition have been preferably used for this reason in addition to their availability and ease of handling. Modeling protocols for dry granular materials have been well established but such model tests cannot account for the pore fluid effects. Although the concept of effective stress has long been recognized and the role of pore-fluid pressure in tectonic deformation processes is evident, there have been few analog model studies that consider the effects of pore fluid movement. Some new applications require a thorough understanding of the coupled deformation and fluid flow processes within the strata. Taking the field of waste management as an example, deep geological disposal of radioactive waste has been thought to be an appropriate methodology for the safe isolation of the wastes from the human environment until the toxicity of the wastes decays to non-hazardous levels. For the deep geological disposal concept, besides containing the wastes with engineering methods such as the glassification of the radioactive wastes, the geological formation itself is expected to serve as a natural barrier that retards migration of radionuclides. To evaluate the long-term safety of deep geological disposal, a better understanding of the fate and transport of radionuclides in a geologically heterogeneous environment is necessary. To meet such requirements, a new analog test sandbox model system was developed. This model system allows the pore fluid flows to be controlled during the model tests and permits the study of flow and transport phenomena in the deformed heterogeneous model. One- or two-dimensional fluid flow is controlled using a side-wall piston. Deformation processes can be observed through a transparent front panel, and pore fluid movement can be also visualized using a color tracer. In this study, the scaling requirements for analog modeling, including pore water pressure, are discussed based on the theory of dimensional analysis, supplemented by data from a series of laboratory shear tests, and a detailed description of the model system. Preliminary experimental results are presented.

Microstructure, chemical composition and mucilage exudation of chia (Salvia hispanica L.) nutlets from Argentina.

PubMed

Capitani, Marianela I; Ixtaina, Vanesa Y; Nolasco, Susana M; Tomás, Mabel C

2013-12-01

The micromorphology and anatomy of nutlets, myxocarpy (mucilage exudation) and mucilage structure of Argentinean chia were described using scanning electron microscopy (SEM). The proximal composition of nutlets and mucilage was also studied. Chia nutlets are made up of a true seed and a pericarp enclosing the seed; they are small, glabrous, elliptic and apically rounded. The pericarp has cuticle, exocarp, mesocarp and bone cells vertically arranged and endocarp. The myxocarpy was carefully recorded by SEM. After 5 min in contact with water, the cuticle of nutlets is broken and the exocarp cell content gradually surrounds the rest of the nutlet. The proximal composition of chia nutlets was studied; fat is the major component (327 ± 8.0 g kg(-1)) followed by protein (293 ± 4.0 g kg(-1)) and fiber (276 ± 1.0 g kg(-1)). Extractions of chia nutlets with water at room temperature yielded 38 ± 1.0 g kg(-1) (dry basis) of mucilage. The fresh mucilage structure was similar to a network of open pores. The freeze-dried crude mucilage contained more ash, residual fat and protein than commercial guar and locust bean gum. The solubility of 10.0 g L(-1) w/v solution of chia freeze-dried crude mucilage in water increased with temperature, being maximal at 60 °C (870 g kg(-1)). The results obtained show a fast exudation of chia mucilage when nutlets are in contact with water. The freeze-dried crude mucilage hydrates easily in water, even at low temperatures. Chia nutlets have mucilaginous substances, with interesting functional properties from a technological and physiological point of view. © 2013 Society of Chemical Industry.

Hydro-mechanical model for wetting/drying and fracture development in geomaterials

DOE PAGES

Asahina, D.; Houseworth, J. E.; Birkholzer, J. T.; ...

2013-12-28

This study presents a modeling approach for studying hydro-mechanical coupled processes, including fracture development, within geological formations. This is accomplished through the novel linking of two codes: TOUGH2, which is a widely used simulator of subsurface multiphase flow based on the finite volume method; and an implementation of the Rigid-Body-Spring Network (RBSN) method, which provides a discrete (lattice) representation of material elasticity and fracture development. The modeling approach is facilitated by a Voronoi-based discretization technique, capable of representing discrete fracture networks. The TOUGH–RBSN simulator is intended to predict fracture evolution, as well as mass transport through permeable media, under dynamicallymore » changing hydrologic and mechanical conditions. Numerical results are compared with those of two independent studies involving hydro-mechanical coupling: (1) numerical modeling of swelling stress development in bentonite; and (2) experimental study of desiccation cracking in a mining waste. The comparisons show good agreement with respect to moisture content, stress development with changes in pore pressure, and time to crack initiation. Finally, the observed relationship between material thickness and crack patterns (e.g., mean spacing of cracks) is captured by the proposed modeling approach.« less

Reply to 'Comments on upscaling geochemical reaction rates usingpore-scale network modeling' by Peter C. Lichtner and Qinjun Kang

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Li; Peters, Catherine A.; Celia, Michael A.

2006-05-03

Our paper "Upscaling geochemical reaction rates usingpore-scale network modeling" presents a novel application of pore-scalenetwork modeling to upscale mineral dissolution and precipitationreaction rates from the pore scale to the continuum scale, anddemonstrates the methodology by analyzing the scaling behavior ofanorthite and kaolinite reaction kinetics under conditions related to CO2sequestration. We conclude that under highly acidic conditions relevantto CO2 sequestration, the traditional continuum-based methodology may notcapture the spatial variation in concentrations from pore to pore, andscaling tools may be important in correctly modeling reactive transportprocesses in such systems. This work addresses the important butdifficult question of scaling mineral dissolution and precipitationreactionmore » kinetics, which is often ignored in fields such as geochemistry,water resources, and contaminant hydrology. Although scaling of physicalprocesses has been studied for almost three decades, very few studieshave examined the scaling issues related to chemical processes, despitetheir importance in governing the transport and fate of contaminants insubsurface systems.« less

Pore-scale modeling of saturated permeabilities in random sphere packings.

PubMed

Pan, C; Hilpert, M; Miller, C T

2001-12-01

We use two pore-scale approaches, lattice-Boltzmann (LB) and pore-network modeling, to simulate single-phase flow in simulated sphere packings that vary in porosity and sphere-size distribution. For both modeling approaches, we determine the size of the representative elementary volume with respect to the permeability. Permeabilities obtained by LB modeling agree well with Rumpf and Gupte's experiments in sphere packings for small Reynolds numbers. The LB simulations agree well with the empirical Ergun equation for intermediate but not for small Reynolds numbers. We suggest a modified form of Ergun's equation to describe both low and intermediate Reynolds number flows. The pore-network simulations agree well with predictions from the effective-medium approximation but underestimate the permeability due to the simplified representation of the porous media. Based on LB simulations in packings with log-normal sphere-size distributions, we suggest a permeability relation with respect to the porosity, as well as the mean and standard deviation of the sphere diameter.

Bio-inspired Murray materials for mass transfer and activity

PubMed Central

Zheng, Xianfeng; Shen, Guofang; Wang, Chao; Li, Yu; Dunphy, Darren; Hasan, Tawfique; Brinker, C. Jeffrey; Su, Bao-Lian

2017-01-01

Both plants and animals possess analogous tissues containing hierarchical networks of pores, with pore size ratios that have evolved to maximize mass transport and rates of reactions. The underlying physical principles of this optimized hierarchical design are embodied in Murray's law. However, we are yet to realize the benefit of mimicking nature's Murray networks in synthetic materials due to the challenges in fabricating vascularized structures. Here we emulate optimum natural systems following Murray's law using a bottom-up approach. Such bio-inspired materials, whose pore sizes decrease across multiple scales and finally terminate in size-invariant units like plant stems, leaf veins and vascular and respiratory systems provide hierarchical branching and precise diameter ratios for connecting multi-scale pores from macro to micro levels. Our Murray material mimics enable highly enhanced mass exchange and transfer in liquid–solid, gas–solid and electrochemical reactions and exhibit enhanced performance in photocatalysis, gas sensing and as Li-ion battery electrodes. PMID:28382972

Anhidrosis (Hypohidrosis)

MedlinePlus

... Fabry's disease Connective tissue diseases, such as Sjogren's syndrome, which causes dry eyes and mouth Skin damage, such as from burns or radiation therapy, or diseases that clog your pores (poral occlusion), such as ... syndrome Certain drugs, such as morphine and botulinum toxin ...

Method for Making a Fuel Cell

NASA Technical Reports Server (NTRS)

Cable, Thomas L. (Inventor); Setlock, John A. (Inventor); Farmer, Serene C. (Inventor)

2014-01-01

The invention is a novel solid oxide fuel cell (SOFC) stack comprising individual bi-electrode supported fuel cells in which an electrolyte layer is supported between porous electrodes. The porous electrodes may be made from graded pore ceramic tape that has been created by the freeze cast method followed by freeze-drying. Each piece of graded pore tape later becomes a graded pore electrode scaffold that, subsequent to sintering, is made into either an anode or a cathode. The electrode scaffold comprising the anode includes a layer of liquid metal. The pores of the electrode scaffolds gradually increase in diameter as the layer extends away from the electrolyte layer. As a result of this diameter increase, any forces that would tend to pull the liquid metal away from the electrolyte are reduced while maintaining a diffusion path for the fuel. Advantageously, the fuel cell of the invention may utilize a hydrocarbon fuel without pre-processing to remove sulfur.

Hierarchically porous structure, mechanical strength and cell biological behaviors of calcium phosphate composite scaffolds prepared by combination of extrusion and porogen burnout technique and enhanced by gelatin.

PubMed

Feng, Shenglei; He, Fupo; Ye, Jiandong

2018-01-01

In this study, hierarchically porous calcium phosphate scaffolds (HTCP) with unidirectional pores, transversely interconnected pores, and micropores were fabricated by the combination of extrusion and porogen burnout technique. Gelatin was incorporated into the HTCP scaffolds by vacuum-impregnation of gelatin solution and subsequent freeze-drying. The phase composition, microstructure, physical and cytobiological properties were analyzed. The results showed that the HTCP scaffolds were composed of β-tricalcium phosphate with minor hydroxyapatite. The HTCP scaffolds had unidirectional pores (~400μm), transversely interconnected pores (~130μm) and micropores (~1μm). The incorporation of gelatin significantly increased the compressive strength, toughness, and cell seeding of the HTCP scaffolds. The composite scaffolds showed excellent cytocompatibility. The hierarchically porous calcium phosphate composite scaffolds may have potential application prospects in bone tissue engineering. Copyright © 2017 Elsevier B.V. All rights reserved.

Effect of rainfall infiltration into unsaturated soil using soil column

NASA Astrophysics Data System (ADS)

Ibrahim, A.; Mukhlisin, M.; Jaafar, O.

2018-02-01

Rainfall especially in tropical region caused infiltration to the soil slope. The infiltration may change pore water pressure or matric suction of the soil. The event of rainfall infiltration into soil is a complex mechanism. Therefore, the main objectives of this research paper is to study the influence of rainfall intensity and duration that changed pore water pressure to soil. There are two types of soils used in this study; forest soil and kaolin. Soil column apparatus is used for experiments. Rainfall were applied to the soil and result for 3, 6, 12, 24, 72, 120 and 168 hours were retrieved. Result shows that for the both types of soil, the negative pore water pressures were increased during wetting process and gradually decreased towards drying process. The results also show that pore water pressure at top part was increased greatly as the wetting process started compared to the middle and bottom part of the column.

Covalent immobilization of penicillin G acylase on aminopropyl-functionalized mesostructured cellular foams.

PubMed

Zhao, Junqi; Wang, Yujun; Luo, Guangsheng; Zhu, Shenlin

2010-10-01

Mesostructured cellular foams (MCFs) are suitable for biomolecular immobilization because of their relatively large-pore diameter and pore volume. Penicillin G acylase (PGA) was immobilized on aminopropyl-functionalized MCFs through Schiff base reaction. It is shown that PGA could be fixed more firmly through the covalent immobilization on aminopropyl-functionalized MCFs support than through the adsorption immobilization on blank MCFs. The PGA loading amount on the aminopropyl-functionalized MCFs could reach 443 mg/g (dry support), and the apparent activity could achieve up to 4138 U/g (dry support). The influence of the amount of grafted aminopropyl group was studied, and it is found that the optimal molar ratio of MCFs to APTS was 15/1; in addition, the suitable enzyme distribution density for the specific activity of the immobilized PGA was 0.7 mg enzyme per m(2) of specific area of MCFs. Copyright 2010 Elsevier Ltd. All rights reserved.

Synthesis and characterization of nanoporous silica aerogel beads using cheap industrial grade sodium silacte precursor

NASA Astrophysics Data System (ADS)

Khan, Tasneem M. A.; Khan, Asiya; Sarawade, Pradip B.

2018-05-01

We report a method to synthesize low-density transparent mesoporous silica aerogel beads by ambient pressure drying (APD). The beads were prepared by acid-base sol-gel polymerization of sodium silicate in via the ball dropping method (BDM). To minimize shrinkage during drying, wet silica beads were initially prepared; their surfaces were then modified using trimethylchlorosilane (TMCS) via simultaneous solvent exchange and surface modification. The specific surface area and cumulative pore volume of the silica aerogel beads increased with an increase in the %V of TMCS. Silica aerogel beads with low packing bed density, high surface area, and large cumulative pore volume was obtained when TMCS was used. Properties of the final product were examined by BET, and TG-DT analyses. The hydrophobic silica aerogel beads were thermally stable up to 350°C. We discuss our results and compare our findings for modified versus unmodified silica beads.

The physics of debris flows

NASA Astrophysics Data System (ADS)

Iverson, Richard M.

1997-08-01

Recent advances in theory and experimentation motivate a thorough reassessment of the physics of debris flows. Analyses of flows of dry, granular solids and solid-fluid mixtures provide a foundation for a comprehensive debris flow theory, and experiments provide data that reveal the strengths and limitations of theoretical models. Both debris flow materials and dry granular materials can sustain shear stresses while remaining static; both can deform in a slow, tranquil mode characterized by enduring, frictional grain contacts; and both can flow in a more rapid, agitated mode characterized by brief, inelastic grain collisions. In debris flows, however, pore fluid that is highly viscous and nearly incompressible, composed of water with suspended silt and clay, can strongly mediate intergranular friction and collisions. Grain friction, grain collisions, and viscous fluid flow may transfer significant momentum simultaneously. Both the vibrational kinetic energy of solid grains (measured by a quantity termed the granular temperature) and the pressure of the intervening pore fluid facilitate motion of grains past one another, thereby enhancing debris flow mobility. Granular temperature arises from conversion of flow translational energy to grain vibrational energy, a process that depends on shear rates, grain properties, boundary conditions, and the ambient fluid viscosity and pressure. Pore fluid pressures that exceed static equilibrium pressures result from local or global debris contraction. Like larger, natural debris flows, experimental debris flows of ˜10 m³ of poorly sorted, water-saturated sediment invariably move as an unsteady surge or series of surges. Measurements at the base of experimental flows show that coarse-grained surge fronts have little or no pore fluid pressure. In contrast, finer-grained, thoroughly saturated debris behind surge fronts is nearly liquefied by high pore pressure, which persists owing to the great compressibility and moderate permeability of the debris. Realistic models of debris flows therefore require equations that simulate inertial motion of surges in which high-resistance fronts dominated by solid forces impede the motion of low-resistance tails more strongly influenced by fluid forces. Furthermore, because debris flows characteristically originate as nearly rigid sediment masses, transform at least partly to liquefied flows, and then transform again to nearly rigid deposits, acceptable models must simulate an evolution of material behavior without invoking preternatural changes in material properties. A simple model that satisfies most of these criteria uses depth-averaged equations of motion patterned after those of the Savage-Hutter theory for gravity-driven flow of dry granular masses but generalized to include the effects of viscous pore fluid with varying pressure. These equations can describe a spectrum of debris flow behaviors intermediate between those of wet rock avalanches and sediment-laden water floods. With appropriate pore pressure distributions the equations yield numerical solutions that successfully predict unsteady, nonuniform motion of experimental debris flows.

The physics of debris flows

USGS Publications Warehouse

Iverson, R.M.

1997-01-01

Recent advances in theory and experimentation motivate a thorough reassessment of the physics of debris flows. Analyses of flows of dry, granular solids and solid-fluid mixtures provide a foundation for a comprehensive debris flow theory, and experiments provide data that reveal the strengths and limitations of theoretical models. Both debris flow materials and dry granular materials can sustain shear stresses while remaining static; both can deform in a slow, tranquil mode characterized by enduring, frictional grain contacts; and both can flow in a more rapid, agitated mode characterized by brief, inelastic grain collisions. In debris flows, however, pore fluid that is highly viscous and nearly incompressible, composed of water with suspended silt and clay, can strongly mediate intergranular friction and collisions. Grain friction, grain collisions, and viscous fluid flow may transfer significant momentum simultaneously. Both the vibrational kinetic energy of solid grains (measured by a quantity termed the granular temperature) and the pressure of the intervening pore fluid facilitate motion of grains past one another, thereby enhancing debris flow mobility. Granular temperature arises from conversion of flow translational energy to grain vibrational energy, a process that depends on shear rates, grain properties, boundary conditions, and the ambient fluid viscosity and pressure. Pore fluid pressures that exceed static equilibrium pressures result from local or global debris contraction. Like larger, natural debris flows, experimental debris flows of ???10 m3 of poorly sorted, water-saturated sediment invariably move as an unsteady surge or series of surges. Measurements at the base of experimental flows show that coarse-grained surge fronts have little or no pore fluid pressure. In contrast, finer-grained, thoroughly saturated debris behind surge fronts is nearly liquefied by high pore pressure, which persists owing to the great compressibility and moderate permeability of the debris. Realistic models of debris flows therefore require equations that simulate inertial motion of surges in which high-resistance fronts dominated by solid forces impede the motion of low-resistance tails more strongly influenced by fluid forces. Furthermore, because debris flows characteristically originate as nearly rigid sediment masses, transform at least partly to liquefied flows, and then transform again to nearly rigid deposits, acceptable models must simulate an evolution of material behavior without invoking preternatural changes in material properties. A simple model that satisfies most of these criteria uses depth-averaged equations of motion patterned after those of the Savage-Hutter theory for gravity-driven flow of dry granular masses but generalized to include the effects of viscous pore fluid with varying pressure. These equations can describe a spectrum of debris flow behaviors intermediate between those of wet rock avalanches and sediment-laden water floods. With appropriate pore pressure distributions the equations yield numerical solutions that successfully predict unsteady, nonuniform motion of experimental debris flows.

Dendritic silica nanomaterials (KCC-1) with fibrous pore structure possess high DNA adsorption capacity and effectively deliver genes in vitro.

PubMed

Huang, Xiaoxi; Tao, Zhimin; Praskavich, John C; Goswami, Anandarup; Al-Sharab, Jafar F; Minko, Tamara; Polshettiwar, Vivek; Asefa, Tewodros

2014-09-16

The pore size and pore structure of nanoporous materials can affect the materials' physical properties, as well as potential applications in different areas, including catalysis, drug delivery, and biomolecular therapeutics. KCC-1, one of the newest members of silica nanomaterials, possesses fibrous, large pore, dendritic pore networks with wide pore entrances, large pore size distribution, spacious pore volume and large surface area--structural features that are conducive for adsorption and release of large guest molecules and biomacromolecules (e.g., proteins and DNAs). Here, we report the results of our comparative studies of adsorption of salmon DNA in a series of KCC-1-based nanomaterials that are functionalized with different organoamine groups on different parts of their surfaces (channel walls, external surfaces or both). For comparison the results of our studies of adsorption of salmon DNA in similarly functionalized, MCM-41 mesoporous silica nanomaterials with cylindrical pores, some of the most studied silica nanomaterials for drug/gene delivery, are also included. Our results indicate that, despite their relatively lower specific surface area, the KCC-1-based nanomaterials show high adsorption capacity for DNA than the corresponding MCM-41-based nanomaterials, most likely because of KCC-1's large pores, wide pore mouths, fibrous pore network, and thereby more accessible and amenable structure for DNA molecules to diffuse through. Conversely, the MCM-41-based nanomaterials adsorb much less DNA, presumably because their outer surfaces/cylindrical channel pore entrances can get blocked by the DNA molecules, making the inner parts of the materials inaccessible. Moreover, experiments involving fluorescent dye-tagged DNAs suggest that the amine-grafted KCC-1 materials are better suited for delivering the DNAs adsorbed on their surfaces into cellular environments than their MCM-41 counterparts. Finally, cellular toxicity tests show that the KCC-1-based materials are biocompatible. On the basis of these results, the fibrous and porous KCC-1-based nanomaterials can be said to be more suitable to carry, transport, and deliver DNAs and genes than cylindrical porous nanomaterials such as MCM-41.

Processes controlling the seasonal and spatial variations in sulfate profiles in the pore water of the sediments surrounding Qi'ao Island, Pearl River Estuary, Southern China

NASA Astrophysics Data System (ADS)

Wu, Zijun; Zhou, Huaiyang; Ren, Dezhang; Gao, Hang; Li, Jiangtao

2015-04-01

Marine sediments are the main sink for seawater sulfate and bacterial sulfate reduction is a major component of the global sulfur cycle. Nevertheless, the factors controlling sulfate reduction in the coastal estuary sediments that undergo spatial and temporal variations are still not fully understood. In this study, we measured the concentrations of SO42-, Cl-, CH4, and DIC, and the δ13C of DIC in the pore water of five sampling stations surrounding the Qi'ao Island, Pearl River Estuary, Southern China during the dry season in November 2011 and during the wet season in May 2012. The results showed that the dilution-mixing of the Pearl River with low-concentration sulfate significantly affects the downcore profiles of the sulfate concentrations in the pore water of these estuary sediments. During the wet season, the dilution-mixing of the layers from the top of the sediments to a depth of 14-18 cm occurred at the different sampling stations. In this layer, the sulfate reduction is not appreciable based on the plot of the pore water Cl- and SO42-. Below the dilution-mixing layers, however, sulfate reduction that is driven by the anaerobic oxidation of methane (AOM) occurs. In our comparison, it appeared that the AOM played more important role in the consumption of the pore water sulfate in May 2012 than in November 2011. Meanwhile, we observed a relatively good correlation (r2=0.64) between the depth of the sulfate-methane interface (SMI) and the sulfate concentration in the pore water of the top sediments in dry season, indicating that the pore water sulfate concentration appears to be a primary controlling factor for the depth of the SMI in this estuary. These results highlight the need for an integrated analysis of the hydrologically driven the variations in the sulfate profiles to improve our understanding of the biogeochemical cycling of C, Fe and S and their budgets in estuarine environments.

Unifying Pore Network Modeling, Continuous Time Random Walk (CTRW) Theory and Experiment to Describe Impact of Spatial Heterogeneities on Solute Dispersion at Multiple Length-scales

NASA Astrophysics Data System (ADS)

Bijeljic, B.; Blunt, M. J.; Rhodes, M. E.

2009-04-01

This talk will describe and highlight the advantages offered by a novel methodology that unifies pore network modeling, CTRW theory and experiment in description of solute dispersion in porous media. Solute transport in a porous medium is characterized by the interplay of advection and diffusion (described by Peclet number, Pe) that cause dispersion of solute particles. Dispersion is traditionally described by dispersion coefficients, D, that are commonly calculated from the spatial moments of the plume. Using a pore-scale network model based on particle tracking, the rich Peclet-number dependence of dispersion coefficient is predicted from first principles and is shown to compare well with experimental data for restricted diffusion, transition, power-law and mechanical dispersion regimes in the asymptotic limit. In the asymptotic limit D is constant and can be used in an averaged advection-dispersion equation. However, it is highly important to recognize that, until the velocity field is fully sampled, the particle transport is non-Gaussian and D possesses temporal or spatial variation. Furthermore, temporal probability density functions (PDF) of tracer particles are studied in pore networks and an excellent agreement for the spectrum of transition times for particles from pore to pore is obtained between network model results and CTRW theory. Based on the truncated power-law interpretation of PDF-s, the physical origin of the power-law scaling of dispersion coefficient vs. Peclet number has been explained for unconsolidated porous media, sands and a number of sandstones, arriving at the same conclusion from numerical network modelling, analytic CTRW theory and experiment. The length traveled by solute plumes before Gaussian behaviour is reached increases with an increase in heterogeneity and/or Pe. This opens up the question on the nature of dispersion in natural systems where the heterogeneities at the larger scales will significantly increase the range of velocities in the reservoir, thus significantly delaying the asymptotic approach to Gaussian behaviour. As a consequence, the asymptotic behaviour might not be reached at the field scale. This is illustrated by the multi-scale approach in which transport at core, gridblock and field scale is viewed as a series of particle transitions between discrete nodes governed by probability distributions. At each scale of interest a distribution that represents transport physics (and the heterogeneity) is used as an input to model a subsequent reservoir scale. The extensions to reactive transport are discussed.

Coverage Dependent Assembly of Anthraquinone on Au(111)

NASA Astrophysics Data System (ADS)

Conrad, Brad; Deloach, Andrew; Einstein, Theodore; Dougherty, Daniel

A study of adsorbate-adsorbate and surface state mediated interactions of anthraquinone (AnQ) on Au(111) is presented. We utilize scanning tunneling microscopy (STM) to characterize the coverage dependence of AnQ structure formation. Ordered structures are observed up to a single monolayer (ML) and are found to be strongly dependent on molecular surface density. While the complete ML forms a well-ordered close-packed layer, for a narrow range of sub-ML coverages irregular close-packed islands are observed to coexist with a disordered pore network linking neighboring islands. This network displays a characteristic pore size and at lower coverages, the soliton walls of the herringbone reconstruction are shown to promote formation of distinct pore nanostructures. We will discuss these nanostructure formations in the context of surface mediated and more direct adsorbate interactions.

Pore Distribution Characteristics of the Igneous Reservoirs in the Eastern Sag of the Liaohe Depression

NASA Astrophysics Data System (ADS)

Zongli, Liu; Zhuwen, Wang; Dapeng, Zhou; Shuqin, Zhao; Min, Xiang

2017-05-01

In the Es3 formation (third section of the Shahejie) of the Eastern sag section of the Liaohe Depression, basalt and trachyte are predominant in the igneous rock. The reservoir consists of complex reservoir space types. Based on the porosity bins of nuclear magnetic logging and the porosity distribution of electric imaging logging, the pores' sizes and distribution, as well as the mutual connectivity of the reservoir, were analyzed. Also, the characteristics of the different reservoirs were summarized. In regards to the oil reservoirs, large pores (PS>10) were found to account for the majority of the reservoir spaces, and the pore distribution was concentrated and well connected. However, for the poor oil reservoirs, the large and small pores were found to alternate, and the pore distribution was scattered and poorly connected. Within the dry layers, the smaller pores (PS<10) were predominant. The pore distributions were found to be influenced by lithology, facies, and tectonism. The reservoirs of the pyroclastic flow of the explosive facies had good connectivity, and the interlayer heterogeneity was relatively weak. This reservoir's pore distributions were found to be mainly dominated by the larger pores (PS10-PS13), which displayed a concentrated distribution mainly in one porosity bin. Therefore, it was taken as a favorable facie belt in the eastern sag of the Liaohe Depression. The examination of the pore distribution characteristics of the igneous rock was the key to the evaluation of the properties and effectiveness of the igneous reservoirs in this study, which potentially has great significance to the future exploration and development of igneous rock.

Dual FIB-SEM 3D imaging and lattice boltzmann modeling of porosimetry and multiphase flow in chalk.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rinehart, Alex; Petrusak, Robin; Heath, Jason E.

2010-12-01

Mercury intrusion porosimetry (MIP) is an often-applied technique for determining pore throat distributions and seal analysis of fine-grained rocks. Due to closure effects, potential pore collapse, and complex pore network topologies, MIP data interpretation can be ambiguous, and often biased toward smaller pores in the distribution. We apply 3D imaging techniques and lattice-Boltzmann modeling in interpreting MIP data for samples of the Cretaceous Selma Group Chalk. In the Mississippi Interior Salt Basin, the Selma Chalk is the apparent seal for oil and gas fields in the underlying Eutaw Fm., and, where unfractured, the Selma Chalk is one of the regional-scalemore » seals identified by the Southeast Regional Carbon Sequestration Partnership for CO2 injection sites. Dual focused ion - scanning electron beam and laser scanning confocal microscopy methods are used for 3D imaging of nanometer-to-micron scale microcrack and pore distributions in the Selma Chalk. A combination of image analysis software is used to obtain geometric pore body and throat distributions and other topological properties, which are compared to MIP results. 3D data sets of pore-microfracture networks are used in Lattice Boltzmann simulations of drainage (wetting fluid displaced by non-wetting fluid via the Shan-Chen algorithm), which in turn are used to model MIP procedures. Results are used in interpreting MIP results, understanding microfracture-matrix interaction during multiphase flow, and seal analysis for underground CO2 storage.« less

Formation, Structure and Electrochemical Impedance Analysis of Microporous Polyelectrolyte Multilayers

NASA Astrophysics Data System (ADS)

Lutkenhaus, Jodie; McEnnis, Kathleen; Hammond, Paula

2007-03-01

Microporous networks are of interest as electrolyte materials, gas separation membranes and catalytic nanoparticle templates. Here, we create microporous polyelectrolyte networks of tunable pore size and connectivity using the layer-by-layer (LBL) technique. In this method, a film is formed from the alternate adsorption of oppositely charged polyelectrolytes from aqueous solution to create a cohesive thin film. Using poly(ethylene imine) (PEI) and poly(acrylic acid) (PAA), LBL thin films of variable composition and charge density were assembled; then, the films were treated in an acidic bath, which ionizes PEI and de-ionizes PAA. This shift in charge density induces morphological rearrangement realized by a microporous network. Depending on the assembly pH and acidic bath pH, we are able to precisely tune the morphology, which is characterized by atomic force microscopy and scanning electron microscopy. To demonstrate the porous nature of the polyelectrolyte multilayer, the pores were filled with non-aqueous electrolyte (i.e. ethylene carbonate, dimethyl carbonate and lithium hexafluorophosphate) and probed with electrochemical impedance spectroscopy. These microporous networks exhibited two time constants, indicative of ions traveling through the liquid-filled pores and ions traveling through the polyelectrolyte matrix.

EVALUATION AND ANALYSIS OF MICROSCALE FLOW AND TRANSPORT DURING REMEDIATION

EPA Science Inventory

The design of in-situ remediation is currently based on a description at the macroscopic scale. Phenomena at the pore and pore-network scales are typically lumped in terms of averaged quantities, using empirical or ad hoc expressions. These models cannot address fundamental rem...

Mechanistic modelling of fluidized bed drying processes of wet porous granules: a review.

PubMed

Mortier, Séverine Thérèse F C; De Beer, Thomas; Gernaey, Krist V; Remon, Jean Paul; Vervaet, Chris; Nopens, Ingmar

2011-10-01

Fluidized bed dryers are frequently used in industrial applications and also in the pharmaceutical industry. The general incentives to develop mechanistic models for pharmaceutical processes are listed, and our vision on how this can particularly be done for fluidized bed drying processes of wet granules is given. This review provides a basis for future mechanistic model development for the drying process of wet granules in pharmaceutical processes. It is intended for a broad audience with a varying level of knowledge on pharmaceutical processes and mathematical modelling. Mathematical models are powerful tools to gain process insight and eventually develop well-controlled processes. The level of detail embedded in such a model depends on the goal of the model. Several models have therefore been proposed in the literature and are reviewed here. The drying behaviour of one single granule, a porous particle, can be described using the continuum approach, the pore network modelling method and the shrinkage of the diameter of the wet core approach. As several granules dry at a drying rate dependent on the gas temperature, gas velocity, porosity, etc., the moisture content of a batch of granules will reside in a certain interval. Population Balance Model (ling) (PBM) offers a tool to describe the distribution of particle properties which can be of interest for the application. PBM formulation and solution methods are therefore reviewed. In a fluidized bed, the granules show a fluidization pattern depending on the geometry of the gas inlet, the gas velocity, characteristics of the particles, the dryer design, etc. Computational Fluid Dynamics (CFD) allows to model this behaviour. Moreover, turbulence can be modelled using several approaches: Reynolds-averaged Navier-Stokes Equations (RANS) or Large Eddy Simulation (LES). Another important aspect of CFD is the choice between the Eulerian-Lagrangian and the Eulerian-Eulerian approach. Finally, the PBM and CFD frameworks can be integrated, to describe the evolution of the moisture content of granules during fluidized bed drying. Copyright © 2011 Elsevier B.V. All rights reserved.

Steam stable mesoporous silica MCM-41 stabilized by trace amounts of Al.

PubMed

Tompkins, Jordan T; Mokaya, Robert

2014-02-12

Evaluation of low and ultralow Al content (Si/Al between 50 and 412) aluminosilicate Al-MCM-41 materials synthesized via three contrasting alumination routes, namely, direct mixed-gel synthesis, post-synthesis wet grafting, and post-synthesis dry grafting, indicates that trace amounts of Al introduced via dry grafting can stabilize mesoporous silica MCM-41 to steaming at 900 °C for 4 h. It was found that trace amounts of Al (Si/Al > 400) introduced via so-called dry grafting of Al stabilize the virtually purely siliceous MCM-41 to steaming, whereas Al incorporated via other methods that involve aqueous media such as direct mixed gel synthesis or wet grafting of Al offer only limited protection at low Al content. It is particularly remarkable that a post-synthesis dry grafted Al-MCM-41 material possessing trace amounts of Al (i.e., Si/Al ratio of 412) and surface area and pore volume of 1112 m(2)/g and 1.20 cm(3)/g, respectively, retains 90% (998 m(2)/g) of the surface area and 85% (1.03 cm(3)/g) of the pore volume after exposure to steaming at 900 °C for 4 h. Under similar steam treatment conditions, the mesostructure of pure silica Si-MCM-41 is virtually destroyed and undergoes a 93% reduction in surface area (958 m(2)/g to 69 m(2)/g) and 88% decrease in pore volume (0.97 cm(3)/g to 0.12 cm(3)/g). The steam stable ultralow (i.e., trace) Al containing MCM-41 materials is found to be virtually similar to mesoporous pure silica Si-MCM-41 with hardly any detectable acidity. The improvement in steam stability arises from not only the presence of trace amounts of Al, but also from an apparent increase in the level of silica condensation that is specific to dry grafted alluminosilicate MCM-41 materials. The more highly condensed framework has fewer silanol groups and therefore is more resistant to hydrolysis under steaming conditions.

An Amorphous Network Model for Capillary Flow and Dispersion in a Partially Saturated Porous Medium

NASA Astrophysics Data System (ADS)

Simmons, C. S.; Rockhold, M. L.

2013-12-01

Network models of capillary flow are commonly used to represent conduction of fluids at pore scales. Typically, a flow system is described by a regular geometric lattice of interconnected tubes. Tubes constitute the pore throats, while connection junctions (nodes) are pore bodies. Such conceptualization of the geometry, however, is questionable for the pore scale, where irregularity clearly prevails, although prior published models using a regular lattice have demonstrated successful descriptions of the flow in the bulk medium. Here a network is allowed to be amorphous, and is not subject to any particular lattice structure. Few network flow models have treated partially saturated or even multiphase conditions. The research trend is toward using capillary tubes with triangular or square cross sections that have corners and always retain some fluid by capillarity when drained. In contrast, this model uses only circular capillaries, whose filled state is controlled by a capillary pressure rule for the junctions. The rule determines which capillary participate in the flow under an imposed matric potential gradient during steady flow conditions. Poiseuille's Law and Laplace equation are used to describe flow and water retention in the capillary units of the model. A modified conjugate gradient solution for steady flow that tracks which capillary in an amorphous network contribute to fluid conduction was devised for partially saturated conditions. The model thus retains the features of classical capillary models for determining hydraulic flow properties under unsaturated conditions based on distribution of non-interacting tubes, but now accounts for flow exchange at junctions. Continuity of the flow balance at every junction is solved simultaneously. The effective water retention relationship and unsaturated permeability are evaluated for an extensive enough network to represent a small bulk sample of porous medium. The model is applied for both a hypothetically randomly generate network and for a directly measured porous medium structure, by means of xray-CT scan. A randomly generated network has the benefit of providing ensemble averages for sample replicates of a medium's properties, whereas network structure measurements are expected to be more predictive. Dispersion of solute in a network flow is calculate by using particle tracking to determine the travel time breakthrough between inflow and outflow boundaries. The travel time distribution can exhibit substantial skewness that reflects both network velocity variability and mixing dilution at junctions. When local diffusion is not included, and transport is strictly advective, then the skew breakthrough is not due to mobile-immobile flow region behavior. The approach of dispersivity to its asymptotic value with sample size is examined, and may be only an indicator of particular stochastic flow variation. It is not proven that a simplified network flow model can accurately predict the hydraulic properties of a sufficiently large-size medium sample, but such a model can at least demonstrate macroscopic flow resulting from the interaction of physical processes at pore scales.

Electrical resistivity characteristics of diesel oil-contaminated kaolin clay and a resistivity-based detection method.

PubMed

Liu, Zhibin; Liu, Songyu; Cai, Yi; Fang, Wei

2015-06-01

As the dielectric constant and conductivity of petroleum products are different from those of the pore water in soil, the electrical resistivity characteristics of oil-contaminated soil will be changed by the corresponding oil type and content. The contaminated soil specimens were manually prepared by static compaction method in the laboratory with commercial kaolin clay and diesel oil. The water content and dry density of the first group of soil specimens were controlled at 10 % and 1.58 g/cm(3). Corresponding electrical resistivities of the contaminated specimens were measured at the curing periods of 7, 14, and 28 and 90, 120, and 210 days on a modified oedometer cell with an LCR meter. Then, the electrical resistivity characteristics of diesel oil-contaminated kaolin clay were discussed. In order to realize a resistivity-based oil detection method, the other group of oil-contaminated kaolin clay specimens was also made and tested, but the initial water content, oil content, and dry density were controlled at 0~18 %, 0~18 %, 1.30~1.95 g/cm(3), respectively. Based on the test data, a resistivity-based artificial neural network (ANN) was developed. It was found that the electrical resistivity of kaolin clay decreased with the increase of oil content. Moreover, there was a good nonlinear relationship between electrical resistivity and corresponding oil content when the water content and dry density were kept constant. The decreasing velocity of the electrical resistivity of oil-contaminated kaolin clay was higher before the oil content of 12 % than after 12 %, which indicated a transition of the soil from pore water-controlled into oil-controlled electrical resistivity characteristics. Through microstructural analysis, the decrease of electrical resistivity could be explained by the increase of saturation degree together with the collapse of the electrical double layer. Environmental scanning electron microscopy (ESEM) photos indicated that the diesel oil in kaolin clay normally had three kinds of effects including oil filling, coating, and bridging. Finally, a resistivity-based ANN model was established based on the database collected from the experiment data. The performance of the model was proved to be reasonably accepted, which puts forward a possible simple, economic, and effective tool to detect the oil content in contaminated clayey soils just with four basic parameters: wet density, dry density, measured moisture content, and electrical resistivity.

Retention of antioxidant capacity of vacuum microwave dried cranberry.

PubMed

Leusink, Gwen J; Kitts, David D; Yaghmaee, Parastoo; Durance, Tim

2010-04-01

In this study, cranberries were dried by vacuum-microwave drying (VMD), freeze-drying (FD), or hot air-drying (AD), to compare the effects of different drying processes on both physical changes as well as the retention of bioactive components in dried samples. Total porosity (%) and average pore radius of dehydrated cranberries were greater using VMD compared to FD and AD (P < 0.05). Crude methanol cranberry powdered extracts were fractionated by solid phase extraction (SPE) into organic acid-, total phenolics-, anthocyanin-, or proanthocyanidin-enriched extracts, respectively. The chemical composition of the 60% acidified methanol fractions contained cyanidin-3-galactoside, cyanidin-3-arabinoside, peonidin-3-galactoside, and peonidin-3-arabinoside, as assessed by HPLC. Antioxidant activities of cranberry fractions were measured using chemical ORAC and ABTS methods. The 60% acidified methanol fraction had a significantly higher (P < 0.05) antioxidant potential than the other chemical fractions, which was largely attributed to the relatively higher anthocyanin content. In general, vacuum-microwave drying and freeze-drying resulted in similar retention of anthocyanins and antioxidant activity, which were both relatively higher (P < 0.05) than that recovered from cranberries dried by hot air drying.

Access to mycorrhizal networks and roots of trees: importance for seedling survival and resource transfer.

PubMed

Teste, François P; Simard, Suzanne W; Durall, Daniel M; Guy, Robert D; Jones, Melanie D; Schoonmaker, Amanda L

2009-10-01

Mycorrhizal networks (MNs) are fungal hyphae that connect roots of at least two plants. It has been suggested that these networks are ecologically relevant because they may facilitate interplant resource transfer and improve regeneration dynamics. This study investigated the effects of MNs on seedling survival, growth and physiological responses, interplant resource (carbon and nitrogen) transfer, and ectomycorrhizal (EM) fungal colonization of seedlings by trees in dry interior Douglas-fir (Pseudotsuga menziesii var. glauca) forests. On a large, recently harvested site that retained some older trees, we established 160 isolated plots containing pairs of older Douglas-fir "donor" trees and either manually sown seed or planted Douglas-fir "receiver" seedlings. Seed- and greenhouse-grown seedlings were sown and planted into four mesh treatments that served to restrict MN access (i.e., planted into mesh bags with 0.5-, 35-, 250-microm pores, or without mesh). Older trees were pulse labeled with carbon (13CO2) and nitrogen (15NH4(15)NO3) to quantify resource transfer. After two years, seedlings grown from seed in the field had the greatest survival and received the greatest amounts of transferred carbon (0.0063% of donor photo-assimilates) and nitrogen (0.0018%) where they were grown without mesh; however, planted seedlings were not affected by access to tree roots and hyphae. Size of "donor" trees was inversely related to the amount of carbon transferred to seedlings. The potential for MNs to form was high (based on high similarity of EM communities between hosts), and MN-mediated colonization appeared only to be important for seedlings grown from seed in the field. These results demonstrate that MNs and mycorrhizal roots of trees may be ecologically important for natural regeneration in dry forests, but it is still uncertain whether resource transfer is an important mechanism underlying seedling establishment.

Prediction of some physical and drying properties of terebinth fruit (Pistacia atlantica L.) using Artificial Neural Networks.

PubMed

Kaveh, Mohammad; Chayjan, Reza Amiri

2014-01-01

Drying of terebinth fruit was conducted to provide microbiological stability, reduce product deterioration due to chemical reactions, facilitate storage and lower transportation costs. Because terebinth fruit is susceptible to heat, the selection of a suitable drying technology is a challenging task. Artificial neural networks (ANNs) are used as a nonlinear mapping structures for modelling and prediction of some physical and drying properties of terebinth fruit. Drying characteristics of terebinth fruit with an initial moisture content of 1.16 (d.b.) was studied in an infrared fluidized bed dryer. Different levels of air temperatures (40, 55 and 70°C), air velocities (0.93, 1.76 and 2.6 m/s) and infrared (IR) radiation powers (500, 1000 and 1500 W) were applied. In the present study, the application of Artificial Neural Network (ANN) for predicting the drying moisture diffusivity, energy consumption, shrinkage, drying rate and moisture ratio (output parameter for ANN modelling) was investigated. Air temperature, air velocity, IR radiation and drying time were considered as input parameters. The results revealed that to predict drying rate and moisture ratio a network with the TANSIG-LOGSIG-TANSIG transfer function and Levenberg-Marquardt (LM) training algorithm made the most accurate predictions for the terebinth fruit drying. The best results for ANN at predications were R2 = 0.9678 for drying rate, R2 = 0.9945 for moisture ratio, R2 = 0.9857 for moisture diffusivity and R2 = 0.9893 for energy consumption. Results indicated that artificial neural network can be used as an alternative approach for modelling and predicting of terebinth fruit drying parameters with high correlation. Also ANN can be used in optimization of the process.

The effects of wettability and trapping on relationships between interfacial area, capillary pressure and saturation in porous media: A pore-scale network modeling approach

NASA Astrophysics Data System (ADS)

Raeesi, Behrooz; Piri, Mohammad

2009-10-01

SummaryWe use a three-dimensional mixed-wet random pore-scale network model to investigate the impact of wettability and trapping on the relationship between interfacial area, capillary pressure and saturation in two-phase drainage and imbibition processes. The model is a three-dimensional network of interconnected pores and throats of various geometrical shapes. It allows multiple phases to be present in each capillary element in wetting and spreading layers, as well as occupying the center of the pore space. Two different random networks that represent the pore space in Berea and a Saudi Arabia reservoir sandstone are used in this study. We allow the wettability of the rock surfaces contacted by oil to alter after primary drainage. The model takes into account both contact angle and trapping hystereses. We model primary oil drainage and water flooding for mixed-wet conditions, and secondary oil injection for a water-wet system. The total interfacial area for pores and throats are calculated when the system is at capillary equilibrium. They include contributions from the arc menisci (AMs) between the bulk and corner fluids, and from the main terminal menisci (MTMs) between different bulk fluids. We investigate hysteresis in these relationships by performing water injection into systems of varying wettability and initial water saturation. We show that trapping and contact angle hystereses significantly affect the interfacial area. In a strongly water-wet system, a sharp increase is observed at the beginning of water flood, which shifts the area to a higher level than primary drainage. As we change the wettability of the system from strongly water-wet to strongly oil-wet, the trapped oil saturation decreases significantly. Starting water flood from intermediate water saturations, greater than the irreducible water saturation, can also affect the non-wetting phase entrapment, resulting in different interfacial area behaviors. This can increase the interfacial area significantly in oil-wet systems. A qualitative comparison of our results with the experimental data available in literature for glass beads shows, with some expected differences, an encouraging agreement. Also, our results agree well with those generated by the previously developed models.

Unlocking the Physiochemical Controls on Organic Carbon Dynamics from the Soil Pore- to Core-Scale

NASA Astrophysics Data System (ADS)

Smith, A. P.; Tfaily, M. M.; Bond-Lamberty, B. P.; Todd-Brown, K. E.; Bailey, V. L.

2015-12-01

The physical organization of soil includes pore networks of varying size and connectivity. These networks control microbial access to soil organic carbon (C) by spatially separating microorganisms and C by both distance and size exclusion. The extent to which this spatially isolated C is vulnerable to microbial transformation under hydrologically dynamic conditions is unknown, and limits our ability to predict the source and sink capacity of soils. We investigated the effects of shifting hydrologic connectivity and soil structure on greenhouse gas C emissions from surface soils collected from the Disney Wilderness Preserve (Florida, USA). We subjected intact soil cores and re-packed homogenized soil cores to simulated groundwater rise or precipitation, monitoring their CO2 and CH4 emissions over 24 hours. Soil pore water was then extracted from each core using different suctions to sample water retained by pore throats of different sizes and then characterized by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Greater respiration rates were observed from homogenized cores compared to intact cores, and from soils wet from below, in which the wetting front is driven by capillary forces, filling fine pores first. This suggests that C located in fine pores may turn over via diffusion processes that lead to the colocation of this C with other resources and microorganisms. Both the complexity and concentration of soluble-C increased with decreasing pore size domains. Pore water extracted from homogenized cores had greater C concentrations than from intact cores, with the greatest concentrations in pore waters sampled from very fine pores, highlighting the importance of soil structure in physically protecting C. These results suggest that the spatial separation of decomposers from C is a key mechanism stabilizing C in these soils. Further research is ongoing to accurately represent this protection mechanism, and the conditions under which it breaks down, in new and improved Earth system models.

FIB and MIP: understanding nanoscale porosity in molecularly imprinted polymers via 3D FIB/SEM tomography.

PubMed

Neusser, G; Eppler, S; Bowen, J; Allender, C J; Walther, P; Mizaikoff, B; Kranz, C

2017-10-05

We present combined focused ion beam/scanning electron beam (FIB/SEM) tomography as innovative method for differentiating and visualizing the distribution and connectivity of pores within molecularly imprinted polymers (MIPs) and non-imprinted control polymers (NIPs). FIB/SEM tomography is used in cell biology for elucidating three-dimensional structures such as organelles, but has not yet been extensively applied for visualizing the heterogeneity of nanoscopic pore networks, interconnectivity, and tortuosity in polymers. To our best knowledge, the present study is the first application of this strategy for analyzing the nanoscale porosity of MIPs. MIPs imprinted for propranolol - and the corresponding NIPs - were investigated establishing FIB/SEM tomography as a viable future strategy complementing conventional isotherm studies. For visualizing and understanding the properties of pore networks in detail, polymer particles were stained with osmium tetroxide (OsO 4 ) vapor, and embedded in epoxy resin. Staining with OsO 4 provides excellent contrast during high-resolution SEM imaging. After optimizing the threshold to discriminate between the stained polymer matrix, and pores filled with epoxy resin, a 3D model of the sampled volume may be established for deriving not only the pore volume and pore surface area, but also to visualize the interconnectivity and tortuosity of the pores within the sampled polymer volume. Detailed studies using different types of cross-linkers and the effect of hydrolysis on the resulting polymer properties have been investigated. In comparison of MIP and NIP, it could be unambiguously shown that the interconnectivity of the visualized pores in MIPs is significantly higher vs. the non-imprinted polymer, and that the pore volume and pore area is 34% and approx. 35% higher within the MIP matrix. This confirms that the templating process not only induces selective binding sites, but indeed also affects the physical properties of such polymers down to the nanoscale, and that additional chemical modification, e.g., via hydrolysis clearly affects that nature of the polymer.

Synthesis, characterization, and catalytic activity of type 2 crystalline titanates prepared with supercritical drying

NASA Astrophysics Data System (ADS)

Al-Adwani, Hamad A. H.

Supercritically dried silico-alumino-titanate (Si-Al-Ti) mixed oxides (T2CT) were successfully synthesized by a sol-gel method with hydrothermal synthesis temperatures less than 200°C and autogenic pressure. High-surface-area T2CT aerogels with meso- to macroporosity were obtained. All solid products, after calcination at 450°C, are semicrystalline. In addition, successful scale-up of T2CT synthesis in a one-gallon reactor yielding 500 g was achieved. Surface areas, pore volumes, and average pore diameters are greatly influenced by the drying method. Supercritical drying had no effect on the crystalline or molecular structure of the materials. The synthesized materials were characterized by means of nitrogen physisorption, X-ray diffraction (XRD), thermal analysis, and diffuse reflectance FTIR spectroscopy. The addition of different amounts of phosphorous and antimony affected neither the textural nor the structural aspects of T2CT. However, a decrease in surface area occurred. The catalytic activity of these materials was evaluated after being loaded with nickel and molybdenum by the incipient wetness method. Cyclohexene hydrogenation and thiophene hydrodesulfurization reactions are used in the catalytic activity study. The activities of some of the catalyst prepared in this study are in the same range as the commercial catalyst, Shell 324, but with lower metal loadings than the commercial catalysts. Thus, more efficient use of Mo and Ni was observed.

Capabilities of ICP-RIE cryogenic dry etching of silicon: review of exemplary microstructures

NASA Astrophysics Data System (ADS)

Sökmen, Ü.; Stranz, A.; Fündling, S.; Wehmann, H.-H.; Bandalo, V.; Bora, A.; Tornow, M.; Waag, A.; Peiner, E.

2009-10-01

Inductively coupled plasma (ICP) cryogenic dry etching was used to etch submicron pores, nano contact lines, submicron diameter pillars, thin and thick cantilevers, membrane structures and anisotropic deep structures with high aspect ratios in silicon for bio-nanoelectronics, optoelectronics and nano-micro electromechanical systems (NMEMS). The ICP cryogenic dry etching gives us the advantage of switching plasmas between etch rates of 13 nm min-1 and 4 µm min-1 for submicron pores and for membrane structures, respectively. A very thin photoresist mask can endure at -75 °C even during etching 70 µm deep for cantilevers and 300 µm deep for membrane structures. Coating the backsides of silicon membrane substrates with a thin photoresist film inhibited the lateral etching of cantilevers during their front release. Between -95 °C and -140 °C, we realized crystallographic-plane-dependent etching that creates facets only at the etch profile bottom. By varying the oxygen content and the process temperature, we achieved good control over the shape of the etched structures. The formation of black silicon during membrane etching down to 300 µm was delayed by reducing the oxygen content.

Ambient pressure dried tetrapropoxysilane-based silica aerogels with high specific surface area

NASA Astrophysics Data System (ADS)

Parale, Vinayak G.; Han, Wooje; Jung, Hae-Noo-Ree; Lee, Kyu-Yeon; Park, Hyung-Ho

2018-01-01

In the present paper, we report the synthesis of tetrapropoxysilane (TPOS)-based silica aerogels with high surface area and large pore volume. The silica aerogels were prepared by a two-step sol-gel process followed by surface modification via a simple ambient pressure drying approach. In order to minimize drying shrinkage and obtain hydrophobic aerogels, the surface of the alcogels was modified using trichloromethylsilane as a silylating agent. The effect of the sol-gel compositional parameters on the polymerization of aerogels prepared by TPOS, one of the precursors belonging to the Si(OR)4 family, was reported for the first time. The oxalic acid and NH4OH concentrations were adjusted to achieve good-quality aerogels with high surface area, low density, and high transparency. Controlling the hydrolysis and condensation reactions of the TPOS precursor turned out to be the most important factor to determine the pore characteristics of the aerogel. Highly transparent aerogels with high specific surface area (938 m2/g) and low density (0.047 g/cm3) could be obtained using an optimized TPOS/MeOH molar ratio with appropriate concentrations of oxalic acid and NH4OH.

Partial Removal of Pore and Loosely Bound Water by Low-Energy Drying Decreases Cortical Bone Toughness in Young and Old Donors

PubMed Central

Nyman, Jeffry S.; Gorochow, Lacey E.; Horch, R. Adam; Uppuganti, Sasidhar; Zein-Sabatto, Ahbid; Manhard, Mary Katherine; Does, Mark D.

2012-01-01

With an ability to quantify matrix-bound and pore water in bone, 1H nuclear magnetic resonance (NMR) relaxometry can potentially be implemented in clinical imaging to assess the fracture resistance of bone in a way that is independent of current X-ray techniques, which assess bone mineral density as a correlate of bone strength. Working towards that goal, we quantified the effect of partial dehydration in air on the mechanical and NMR properties of human cortical bone in order to understand whether NMR is sensitive to water-bone interactions at low energy and whether such interactions contribute to the age-related difference in the toughness of bone. Cadaveric femurs were collected from male and female donors falling into two age groups: 21 to 60 years of age (young) and 74 to 99 years of age (old). After extracting two samples from the medial cortex of the mid-shaft, tensile tests were conducted on Wet specimens and paired, Partially Dry (PtlD) specimens (prepared by low-energy drying in air to remove ~3% of original mass before testing). Prior analysis by micro-computed tomography found that there were no differences in intra-cortical porosity between the Wet and PtlD specimens nor did an age-related difference in porosity exist. PtlD specimens from young and old donors had significantly less toughness than Wet specimens, primarily due to a dehydration-related decrease in post-yield strain. The low-energy drying protocol did not affect the modulus and yield strength of bone. Subsequent dehydration of the PtlD specimens in a vacuum oven at 62 °C and then 103 °C, with quantification of water loss at each temperature, revealed an age-related shift from more loosely bound water to more tightly bound water. NMR detected a change in both bound and pore water pools with low-energy air-drying, and both pools were effectively removed when bone was oven-dried at 62 °C, irrespective of donor age. Although not strictly significant due to variability in the drying and testing conditions, the absolute difference in toughness between Wet and PtlD tended to be greater for the younger donors that had higher bone toughness and more bound water for the wet condition than did the older donors. With sensitivity to low-energy bone-water interactions, NMR, which underpins magnetic resonance imaging, has potential to assess fracture resistance of bone as it relates to bone toughness. PMID:23631897

Partial removal of pore and loosely bound water by low-energy drying decreases cortical bone toughness in young and old donors.

PubMed

Nyman, Jeffry S; Gorochow, Lacey E; Adam Horch, R; Uppuganti, Sasidhar; Zein-Sabatto, Ahbid; Manhard, Mary Katherine; Does, Mark D

2013-06-01

With an ability to quantify matrix-bound and pore water in bone, (1)H nuclear magnetic resonance (NMR) relaxometry can potentially be implemented in clinical imaging to assess the fracture resistance of bone in a way that is independent of current X-ray techniques, which assess bone mineral density as a correlate of bone strength. Working towards that goal, we quantified the effect of partial dehydration in air on the mechanical and NMR properties of human cortical bone in order to understand whether NMR is sensitive to water-bone interactions at low energy and whether such interactions contribute to the age-related difference in the toughness of bone. Cadaveric femurs were collected from male and female donors falling into two age groups: 21-60 years of age (young) and 74-99 years of age (old). After extracting two samples from the medial cortex of the mid-shaft, tensile tests were conducted on Wet specimens and paired, Partially Dry (PtlD) specimens (prepared by low-energy drying in air to remove ∼3% of original mass before testing). Prior analysis by micro-computed tomography found that there were no differences in intra-cortical porosity between the Wet and PtlD specimens nor did an age-related difference in porosity exist. PtlD specimens from young and old donors had significantly less toughness than Wet specimens, primarily due to a dehydration-related decrease in post-yield strain. The low-energy drying protocol did not affect the modulus and yield strength of bone. Subsequent dehydration of the PtlD specimens in a vacuum oven at 62°C and then 103°C, with quantification of water loss at each temperature, revealed an age-related shift from more loosely bound water to more tightly bound water. NMR detected a change in both bound and pore water pools with low-energy air-drying, and both pools were effectively removed when bone was oven-dried at 62°C, irrespective of donor age. Although not strictly significant due to variability in the drying and testing conditions, the absolute difference in toughness between Wet and PtlD tended to be greater for the younger donors that had higher bone toughness and more bound water for the wet condition than did the older donors. With sensitivity to low-energy bone-water interactions, NMR, which underpins magnetic resonance imaging, has potential to assess fracture resistance of bone as it relates to bone toughness. Published by Elsevier Ltd.

Biphasic response of cell invasion to matrix stiffness in 3-dimensional biopolymer networks

PubMed Central

Lang, Nadine R.; Skodzek, Kai; Hurst, Sebastian; Mainka, Astrid; Steinwachs, Julian; Schneider, Julia; Aifantis, Katerina E.; Fabry, Ben

2015-01-01

When cells come in contact with an adhesive matrix, they begin to spread and migrate with a speed that depends on the stiffness of the extracellular matrix. On a flat surface, migration speed decreases with matrix stiffness mainly due to an increased stability of focal adhesions. In a 3-dimensional (3D) environment, cell migration is thought to be additionally impaired by the steric hindrance imposed by the surrounding matrix. For porous 3D biopolymer networks such as collagen gels, however, the effect of matrix stiffness on cell migration is difficult to separate from effects of matrix pore size and adhesive ligand density, and is therefore unknown. Here we used glutaraldehyde as a crosslinker to increase the stiffness of self-assembled collagen biopolymer networks independently of collagen concentration or pore size. Breast carcinoma cells were seeded onto the surface of 3D collagen gels, and the invasion depth was measured after 3 days of culture. Cell invasion in gels with pore sizes larger than 5 μm increased with higher gel stiffness, whereas invasion in gels with smaller pores decreased with higher gel stiffness. These data show that 3D cell invasion is enhanced by higher matrix stiffness, opposite to cell behavior in 2D, as long as the pore size does not fall below a critical value where it causes excessive steric hindrance. These findings may be important for optimizing the recellularization of soft tissue implants or for the design of 3D invasion models in cancer research. PMID:25462839

Micro-computed tomography pore-scale study of flow in porous media: Effect of voxel resolution

NASA Astrophysics Data System (ADS)

Shah, S. M.; Gray, F.; Crawshaw, J. P.; Boek, E. S.

2016-09-01

A fundamental understanding of flow in porous media at the pore-scale is necessary to be able to upscale average displacement processes from core to reservoir scale. The study of fluid flow in porous media at the pore-scale consists of two key procedures: Imaging - reconstruction of three-dimensional (3D) pore space images; and modelling such as with single and two-phase flow simulations with Lattice-Boltzmann (LB) or Pore-Network (PN) Modelling. Here we analyse pore-scale results to predict petrophysical properties such as porosity, single-phase permeability and multi-phase properties at different length scales. The fundamental issue is to understand the image resolution dependency of transport properties, in order to up-scale the flow physics from pore to core scale. In this work, we use a high resolution micro-computed tomography (micro-CT) scanner to image and reconstruct three dimensional pore-scale images of five sandstones (Bentheimer, Berea, Clashach, Doddington and Stainton) and five complex carbonates (Ketton, Estaillades, Middle Eastern sample 3, Middle Eastern sample 5 and Indiana Limestone 1) at four different voxel resolutions (4.4 μm, 6.2 μm, 8.3 μm and 10.2 μm), scanning the same physical field of view. Implementing three phase segmentation (macro-pore phase, intermediate phase and grain phase) on pore-scale images helps to understand the importance of connected macro-porosity in the fluid flow for the samples studied. We then compute the petrophysical properties for all the samples using PN and LB simulations in order to study the influence of voxel resolution on petrophysical properties. We then introduce a numerical coarsening scheme which is used to coarsen a high voxel resolution image (4.4 μm) to lower resolutions (6.2 μm, 8.3 μm and 10.2 μm) and study the impact of coarsening data on macroscopic and multi-phase properties. Numerical coarsening of high resolution data is found to be superior to using a lower resolution scan because it avoids the problem of partial volume effects and reduces the scaling effect by preserving the pore-space properties influencing the transport properties. This is evidently compared in this study by predicting several pore network properties such as number of pores and throats, average pore and throat radius and coordination number for both scan based analysis and numerical coarsened data.

The impact of fluid topology on residual saturations - A pore-network model study

NASA Astrophysics Data System (ADS)

Doster, F.; Kallel, W.; van Dijke, R.

2014-12-01

In two-phase flow in porous media only fractions of the resident fluid are mobilised during a displacement process and, in general, a significant amount of the resident fluid remains permanently trapped. Depending on the application, entrapment is desirable (geological carbon storage), or it should be obviated (enhanced oil recovery, contaminant remediation). Despite its utmost importance for these applications, predictions of trapped fluid saturations for macroscopic systems, in particular under changing displacement conditions, remain challenging. The models that aim to represent trapping phenomena are typically empirical and require tracking of the history of the state variables. This exacerbates the experimental verification and the design of sophisticated displacement technologies that enhance or impede trapping. Recently, experiments [1] have suggested that a macroscopic normalized Euler number, quantifying the topology of fluid distributions, could serve as a parameter to predict residual saturations based on state variables. In these experiments the entrapment of fluids was visualised through 3D micro CT imaging. However, the experiments are notoriously time consuming and therefore only allow for a sparse sampling of the parameter space. Pore-network models represent porous media through an equivalent network structure of pores and throats. Under quasi-static capillary dominated conditions displacement processes can be modeled through simple invasion percolation rules. Hence, in contrast to experiments, pore-network models are fast and therefore allow full sampling of the parameter space. Here, we use pore-network modeling [2] to critically investigate the knowledge gained through observing and tracking the normalized Euler number. More specifically, we identify conditions under which (a) systems with the same saturations but different normalized Euler numbers lead to different residual saturations and (b) systems with the same saturations and the same normalized Euler numbers but different process histories yield the same residual saturations. Special attention is given to contact angle and process histories with varying drainage and imbibition periods. [1] Herring et al., Adv. Water. Resour., 62, 47-58 (2013) [2] Ryazanov et al., Transp. Porous Media, 80, 79-99 (2009).

Adsorption of CO2 from flue gas streams by a highly efficient and stable aminosilica adsorbent.

PubMed

Liu, Shou-Heng; Lin, Yuan-Chung; Chien, Yi-Chi; Hyu, Han-Ren

2011-02-01

Three ordered mesoporous silicas (OMSs) with different pore sizes and pore architectures were prepared and modified with amine functional groups by a postgrafting method. The carbon dioxide (CO2) adsorption on these amine-modified OMSs was measured by using microbalances at 348 K, and their adsorption capacities were found to be 0.2-1.4 mmol g(-1) under ambient pressure using dry 15% CO2. It was found experimentally that the CO2 adsorption capacity and adsorption rate were attributed to the density of amine groups and pore volume, respectively. A simple method is described for the production of densely anchored amine groups on a solid adsorbent invoking direct incorporation of tetraethylenepentamine onto the as-synthesized OMSs. Unlike conventional amine-modified OMSs, which typically show CO2 adsorption capacity less than 2 mmol g(-1), such organic template occluded amine-OMS composites possessed remarkably high CO2 uptake of approximately 4.6 mmol g(-1) at 348 K and 1 atm for a dry 15% CO2/nitrogen feed mixture. The enhancement of 8% in CO2 adsorption capacity was also observed in the presence of 10.6% water vapor. Durability tests done by cyclic adsorption-desorption revealed that these adsorbents also possess excellent stability.

Synthesis and hydrophobic adsorption properties of microporous/mesoporous hybrid materials.

PubMed

Hu, Qin; Li, Jinjun; Qiao, Shizhang; Hao, Zhengping; Tian, Hua; Ma, Chunyan; He, Chi

2009-05-30

Hybrid materials of silicalite-1 (Sil-1)-coated SBA-15 particles (MSs) have been successfully synthesized by crystallization process under hydrothermal conditions. These MSs materials were characterized by X-ray diffraction, nitrogen adsorption/desorption and TEM techniques, which illustrated that the silicalite-1-coated SBA-15 particles were successfully prepared and had large pore volume and hierarchical pore size distribution. Further experimental studies indicated that longer crystallization time under basic condition caused the mesostructure of SBA-15 materials to collapse destructively and higher calcination temperature tended to disrupt the long-range mesoscopic order while they had little influence on the phase of microcrystalline silicalite-1 zeolite. The resultant MSs materials were investigated by estimating dynamic adsorption capacity under dry and wet conditions to evaluate their adsorptive and hydrophobic properties. The hydrophobicity index (HI) value followed the sequence of silicalite-1>MSs>SBA-15, which revealed that the SBA-15 particles coated with the silicalite-1 seeds enhanced the surface hydrophobicity, and also were consistent with FTIR results. Our studies show that MSs materials combined the advantages of the ordered mesoporous material (high adsorptive capacity, large pore volume) and silicalite-1 zeolite (super-hydrophobic property, high hydrothermal stability), and the presence of micropores directly led to an increase in the dynamic adsorption capacity of benzene under dry and wet conditions.

Macroscopic modeling for heat and water vapor transfer in dry snow by homogenization.

PubMed

Calonne, Neige; Geindreau, Christian; Flin, Frédéric

2014-11-26

Dry snow metamorphism, involved in several topics related to cryospheric sciences, is mainly linked to heat and water vapor transfers through snow including sublimation and deposition at the ice-pore interface. In this paper, the macroscopic equivalent modeling of heat and water vapor transfers through a snow layer was derived from the physics at the pore scale using the homogenization of multiple scale expansions. The microscopic phenomena under consideration are heat conduction, vapor diffusion, sublimation, and deposition. The obtained macroscopic equivalent model is described by two coupled transient diffusion equations including a source term arising from phase change at the pore scale. By dimensional analysis, it was shown that the influence of such source terms on the overall transfers can generally not be neglected, except typically under small temperature gradients. The precision and the robustness of the proposed macroscopic modeling were illustrated through 2D numerical simulations. Finally, the effective vapor diffusion tensor arising in the macroscopic modeling was computed on 3D images of snow. The self-consistent formula offers a good estimate of the effective diffusion coefficient with respect to the snow density, within an average relative error of 10%. Our results confirm recent work that the effective vapor diffusion is not enhanced in snow.

A functional relation for field-scale nonaqueous phase liquid dissolution developed using a pore network model

USGS Publications Warehouse

Dillard, L.A.; Essaid, H.I.; Blunt, M.J.

2001-01-01

A pore network model with cubic chambers and rectangular tubes was used to estimate the nonaqueous phase liquid (NAPL) dissolution rate coefficient, Kdissai, and NAPL/water total specific interfacial area, ai. Kdissai was computed as a function of modified Peclet number (Pe???) for various NAPL saturations (SN) and ai during drainage and imbibition and during dissolution without displacement. The largest contributor to ai was the interfacial area in the water-filled corners of chambers and tubes containing NAPL. When Kdissai was divided by ai, the resulting curves of dissolution coefficient, Kdiss versus Pe??? suggested that an approximate value of Kdiss could be obtained as a weak function of hysteresis or SN. Spatially and temporally variable maps of Kdissai calculated using the network model were used in field-scale simulations of NAPL dissolution. These simulations were compared to simulations using a constant value of Kdissai and the empirical correlation of Powers et al. [Water Resour. Res. 30(2) (1994b) 321]. Overall, a methodology was developed for incorporating pore-scale processes into field-scale prediction of NAPL dissolution. Copyright ?? 2001 .

Block copolymer hollow fiber membranes with catalytic activity and pH-response.

PubMed

Hilke, Roland; Pradeep, Neelakanda; Madhavan, Poornima; Vainio, Ulla; Behzad, Ali Reza; Sougrat, Rachid; Nunes, Suzana P; Peinemann, Klaus-Viktor

2013-08-14

We fabricated block copolymer hollow fiber membranes with self-assembled, shell-side, uniform pore structures. The fibers in these membranes combined pores able to respond to pH and acting as chemical gates that opened above pH 4, and catalytic activity, achieved by the incorporation of gold nanoparticles. We used a dry/wet spinning process to produce the asymmetric hollow fibers and determined the conditions under which the hollow fibers were optimized to create the desired pore morphology and the necessary mechanical stability. To induce ordered micelle assembly in the doped solution, we identified an ideal solvent mixture as confirmed by small-angle X-ray scattering. We then reduced p-nitrophenol with a gold-loaded fiber to confirm the catalytic performance of the membranes.

Biofoam II

DOEpatents

Morrison, R.L.

1994-11-01

Biofoam is a rigid, microcellular organic foam made from organic materials derived from natural products and biological organisms. Starting materials include agar, agarose, gelatin, algin, alginates, gellan gum, and microcrystalline cellulose. The organic material is dissolved in a polar solvent, typically water, and the mixture is gelled. The water in the gel pores is replaced at least once with another solvent to reduce the pore size of the final biofoam. The solvent in the gel pores may be replaced several times. After the final replacement of solvent, the gel is frozen and freeze-dried to form a biofoam. Translucent biofoams are formed by selecting a final solvent that forms very small crystals. A variety of crystalline, fibrous, amorphous, or metallic additives may be incorporated into the foam structure to produce lightweight composite materials with enhanced strength and insulating properties. 1 fig.

Biofoam II

DOEpatents

Morrison, Robert L.

1994-01-01

Biofoam is a rigid, microcellular organic foam made from organic materials derived from natural products and biological organisms. Starting materials include agar, agarose, gelatin, algin, alginates, gellan gum, and microcrystalline cellulose. The organic material is dissolved in a polar solvent, typically water, and the mixture is gelled. The water in the gel pores is replaced at least once with another solvent to reduce the pore size of the final biofoam. The solvent in the gel pores may be replaced several times. After the final replacement of solvent, the gel is frozen and freeze-dried to form a biofoam. Translucent biofoams are formed by selecting a final solvent that forms very small crystals. A variety of crystalline, fibrous, amorphous, or metallic additives may be incorporated into the foam structure to produce lightweight composite materials with enhanced strength and insulating properties.

Wildfire effects on vadose zone hydrology in forested boreal peatland microforms

NASA Astrophysics Data System (ADS)

Thompson, Dan K.; Waddington, James M.

2013-04-01

SummaryPeatland vulnerability to wildfire disturbance has been shown to vary as a function of hummock and hollow microforms and vadose zone hydrology, with low-lying hollow microforms most susceptible to deep combustion of peat. To better understand how this microform induced pattern of burning alters vadose water storage, pore-water pressure, and water table relationships, we examined a paired burned and unburned peatland in the boreal plain region of north central Alberta. Water table response to rain events increased significantly after wildfire, resulting in a more variable unsaturated zone thickness that was more responsive to smaller rain events. Water storage losses in the vadose zone occurred primarily at depths greater than 15 cm. Large peat surface water loss occurred in hummock microforms in the early spring due to the presence of unsaturated frozen peat at depth, likely a result of a vapour gradient from the unfrozen peat into the frozen peat underneath. During this period, the loss of water storage in the vadose zone satisfied up to 25% of daily evaporative demand, compared to only 3-5% during ice-free periods. A similar but less severe drying was observed late in summer, with burned hummocks the most vulnerable with high pore-water pressures. The enhanced surface drying observed is a precursor to high pore-water pressure conditions that inhibit Sphagnum regeneration. Our observations point to a paradox where the hummocks, being most resistant to combustion, are themselves most prone to high pore-water pressures following wildfire. The harsher hummock environment may contribute to the observed delay in post-fire Sphagnum regeneration in hummocks compared to hollows.

Critical Evaluation of Soil Pore Water Extraction Methods on a Natural Soil

NASA Astrophysics Data System (ADS)

Orlowski, Natalie; Pratt, Dyan; Breuer, Lutz; McDonnell, Jeffrey

2017-04-01

Soil pore water extraction is an important component in ecohydrological studies for the measurement of δ2H and δ18O. The effect of pore water extraction technique on resultant isotopic signature is poorly understood. Here we present results of an intercomparison of commonly applied lab-based soil water extraction techniques on a natural soil: high pressure mechanical squeezing, centrifugation, direct vapor equilibration, microwave extraction, and two types of cryogenic extraction systems. We applied these extraction methods to a natural summer-dry (gravimetric water contents ranging from 8% to 15%) glacio-lacustrine, moderately fine textured clayey soil; excavated in 10 cm sampling increments to a depth of 1 meter. Isotope results were analyzed via OA-ICOS and compared for each extraction technique that produced liquid water. From our previous intercomparison study among the same extraction techniques but with standard soils, we discovered that extraction methods are not comparable. We therefore tested the null hypothesis that all extraction techniques would be able to replicate the natural evaporation front in a comparable manner occurring in a summer-dry soil. Our results showed that the extraction technique utilized had a significant effect on the soil water isotopic composition. High pressure mechanical squeezing and vapor equilibration techniques produced similar results with similarly sloped evaporation lines. Due to the nature of soil properties and dryness, centrifugation was unsuccessful in obtaining pore water for isotopic analysis. Cryogenic extraction on both tested techniques produced similar results to each other on a similar sloping evaporation line, but dissimilar with depth.

A new species of Xenoturbella from the western Pacific Ocean and the evolution of Xenoturbella.

PubMed

Nakano, Hiroaki; Miyazawa, Hideyuki; Maeno, Akiteru; Shiroishi, Toshihiko; Kakui, Keiichi; Koyanagi, Ryo; Kanda, Miyuki; Satoh, Noriyuki; Omori, Akihito; Kohtsuka, Hisanori

2017-12-18

Xenoturbella is a group of marine benthic animals lacking an anus and a centralized nervous system. Molecular phylogenetic analyses group the animal together with the Acoelomorpha, forming the Xenacoelomorpha. This group has been suggested to be either a sister group to the Nephrozoa or a deuterostome, and therefore it may provide important insights into origins of bilaterian traits such as an anus, the nephron, feeding larvae and centralized nervous systems. However, only five Xenoturbella species have been reported and the evolutionary history of xenoturbellids and Xenacoelomorpha remains obscure. Here we describe a new Xenoturbella species from the western Pacific Ocean, and report a new xenoturbellid structure - the frontal pore. Non-destructive microCT was used to investigate the internal morphology of this soft-bodied animal. This revealed the presence of a frontal pore that is continuous with the ventral glandular network and which exhibits similarities with the frontal organ in acoelomorphs. Our results suggest that large size, oval mouth, frontal pore and ventral glandular network may be ancestral features for Xenoturbella. Further studies will clarify the evolutionary relationship of the frontal pore and ventral glandular network of xenoturbellids and the acoelomorph frontal organ. One of the habitats of the newly identified species is easily accessible from a marine station and so this species promises to be valuable for research on bilaterian and deuterostome evolution.

Eigenvector centrality for geometric and topological characterization of porous media

NASA Astrophysics Data System (ADS)

Jimenez-Martinez, Joaquin; Negre, Christian F. A.

2017-07-01

Solving flow and transport through complex geometries such as porous media is computationally difficult. Such calculations usually involve the solution of a system of discretized differential equations, which could lead to extreme computational cost depending on the size of the domain and the accuracy of the model. Geometric simplifications like pore networks, where the pores are represented by nodes and the pore throats by edges connecting pores, have been proposed. These models, despite their ability to preserve the connectivity of the medium, have difficulties capturing preferential paths (high velocity) and stagnation zones (low velocity), as they do not consider the specific relations between nodes. Nonetheless, network theory approaches, where a complex network is a graph, can help to simplify and better understand fluid dynamics and transport in porous media. Here we present an alternative method to address these issues based on eigenvector centrality, which has been corrected to overcome the centralization problem and modified to introduce a bias in the centrality distribution along a particular direction to address the flow and transport anisotropy in porous media. We compare the model predictions with millifluidic transport experiments, which shows that, albeit simple, this technique is computationally efficient and has potential for predicting preferential paths and stagnation zones for flow and transport in porous media. We propose to use the eigenvector centrality probability distribution to compute the entropy as an indicator of the "mixing capacity" of the system.

Synthesis of pore-variable mesoporous CdS and evaluation of its photocatalytic activity in degrading methylene blue

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Wei-Min, E-mail: chm_zhangwm@ujn.edu.cn; Jiang, Yao-Quan; Cao, Xiao-Yan

2013-10-15

Graphical abstract: - Highlights: • Self-templated synthesis of tubular CdS. • Cadmium complexes of aliphatic acids sustain the network of mesoporous structures. • Aliphatic acids affect the phase composition and particle size. • Pore size and volume vary with aliphatic acids having different hydrocarbonyl. - Abstract: In this study, mesoporous CdS polycrystallites have been synthesized using aliphatic acids of hexanoic acid, octanoic acid, and oleic acid as coordinating and capping agents, respectively. The fibrous Cd–fatty acid salts act as a template to form the tubular CdS. The organic species are found to be necessary for maintaining the network of mesoporousmore » CdS. The characterization results indicate that the shorter carbon chain length in aliphatic acids favors the wurtzite phase and particle size growth the specific surface area, pore diameter and pore volume show a monotonic raise with increasing carbon chain. The photocatalytic activities of mesoporous CdS tubes exhibit much higher efficiency than those of nanosized CdS powders in decolorizing methylene blue under simulated visible light.« less

Influence of Soil Management on Water Retention from Saturation to Oven Dryness and Dominant Soil Water States in a Vertisol under Crop Rotation

NASA Astrophysics Data System (ADS)

Vanderlinden, Karl; Pachepsky, Yakov; Pederera, Aura; Martinez, Gonzalo; Espejo, Antonio Jesus; Giraldez, Juan Vicente

2014-05-01

Unique water transfer and retention properties of Vertisols strongly affect their use in rainfed agriculture in water-limited environments. Despite the agricultural importance of the hydraulic properties of those soils, water retention data dryer than the wilting point are generally scarce, mainly as a result of practical constraints of traditional water retention measurement methods. In this work we provide a detailed description of regionalized water retention data from saturation to oven dryness, obtained from 54 minimally disturbed topsoil (0-0.05m) samples collected at a 3.5-ha experimental field in SW Spain where conventional tillage (CT) and direct drilling (DD) is compared in a wheat-sunflower-legume crop rotation on a Vertisol. Water retention was measured from saturation to oven dryness using sand and sand-kaolin boxes, a pressure plate apparatus and a dew point psychrometer, respectively. A common shape of the water retention curve (WRC) was observed in both tillage systems, with a strong discontinuity in its slope near -0.4 MPa and a decreasing spread from the wet to the dry end. A continuous function, consisting of the sum of a double exponential model (Dexter et al, 2008) and the Groenevelt and Grant (2004) model could be fitted successfully to the data. Two inflection points in the WRC were interpreted as boundaries between the structural and the textural pore spaces and between the textural and the intra-clay aggregate pore spaces. Water retention was significantly higher in DD (p<0.05) for pressure heads ranging from -0.006 to -0.32 MPa, and from -1.8 to -3.3 MPa. The magnitude of these differences ranged from 0.006 to 0.015 kg kg-1. The differential water capacity and associated equivalent pore-size distribution showed that these differences could be attributed to a combined effect of tillage and compaction, increasing and decreasing the amount of the largest pores in CT and DD, respectively, but resulting in a proportionally larger pore space with relevant pore-sizes for water dynamics and agronomic performance. Significant differences in water retention and equivalent pore-sizes at the dry end of the WRC could be associated with the higher organic matter content found in DD. These results explain the superior performance of DD over CT in satisfying high crop water demands, especially at the end of spring when atmospheric water demands become very high, resulting in an extension of the growing period under DD. The results provide also an explanation for the observed soil water dynamics pattern in the field, with rapid transitions between persistent wet and dry water content states. References Dexter, A.R., E.A. Czyż, G. Richard, A. Reszkowska, 2008. A user-friendly water retention function that takes account of the textural and structural pore spaces in soil. Geoderma, 143:243-253. Groenevelt, P.A., C.D. Grant, 2004. A new model for the soil-water retention curve that solves the problem of residual water contents. Eur. J. Soil Sci. 55:479-485.

Monitoring of stainless-steel slag carbonation using X-ray computed microtomography.

PubMed

Boone, Marijn A; Nielsen, Peter; De Kock, Tim; Boone, Matthieu N; Quaghebeur, Mieke; Cnudde, Veerle

2014-01-01

Steel production is one of the largest contributors to industrial CO2 emissions. This industry also generates large amounts of solid byproducts, such as slag and sludge. In this study, fine grained stainless-steel slag (SSS) is valorized to produce compacts with high compressive strength without the use of a hydraulic binder. This carbonation process is investigated on a pore-scale level to identify how the mineral phases in the SSS react with CO2, where carbonates are formed, and what the impact of these changes is on the pore network of the carbonated SSS compact. In addition to conventional research techniques, high-resolution X-ray computed tomography (HRXCT) is applied to visualize and quantify the changes in situ during the carbonation process. The results show that carbonates mainly precipitate at grain contacts and in capillary pores and this precipitation has little effect on the connectivity of the pore space. This paper also demonstrates the use of a custom-designed polymer reaction cell that allows in situ HRXCT analysis of the carbonation process. This shows the distribution and influence of water and CO2 in the pore network on the carbonate precipitation and, thus, the influence on the compressive strength development of the waste material.

Topological characteristics underpin intermittency and anomalous transport behavior in soil-like porous media

NASA Astrophysics Data System (ADS)

Holzner, M.; Morales, V.; Willmann, M.; Jerjen, I.; Kaufmann, R.; Dentz, M.

2016-12-01

Continuum models of porous media are based on the validity of the Darcy equation for fluid and Fick's law for scalar fluxes on a representative elementary volume. Fluctuations of pore-scale flow and scalar transport are averaged out and represented in terms of effective parameters such as hydrodynamic dispersion. However, the intermittent behavior of pore-scale flow impacts on the nature of particle and scalar transport, and it determines the way dissolved substances mix and react. The understanding of the origin of these processes is of both fundamental and practical importance in applications ranging from reactive transport in groundwater flow to diffusion in fuel cells or biological systems. A central issue in porous medium flow is therefore to relate intermittent behavior of Lagrangian velocity at pore scale imposed by the complex pore network geometry to transport properties at larger scales. Lagrangian measurements in porous systems are nonetheless scarce and most experimental techniques do not provide access to all three velocity components. In this contribution we report 3D measurements of Lagrangian velocity in soil-like porous media. We complement these measurements with detailed X-ray scans of the pore network. We find sharp velocity transitions close to pore throats, and low flow variability in the pore bodies, which gives rise to stretched exponential Lagrangian velocity and acceleration distributions characterized by a sharp peak at low velocity and a superlinear evolution of particle dispersion. We demonstrate that porosity and pore size distribution alone cannot explain the observed features of the flow. Rather, anomalous transport is better interpreted in terms of how pores of various geometries are interconnected. We reproduce the main observations using a continuous-time random walk (CTRW) model revealing the main features that control the system and showing the potential of this simple model to capture transport in complex geometries.

Porosity and water activity effects on stability of crystalline β-carotene in freeze-dried solids.

PubMed

Harnkarnsujarit, Nathdanai; Charoenrein, Sanguansri; Roos, Yrjö H

2012-11-01

Stability of entrapped crystalline β-carotene as affected by water activity, solids microstructure, and composition of freeze-dried systems was investigated. Aliquots (1000 mm(3) , 20% w/w solids) of solutions of maltodextrins of various dextrose equivalents (M040:DE6, M100:DE11, and M250:DE25.5), M100-sugars (1:1 glucose, fructose and sucrose), and agar for gelation with dispersed β-carotene were frozen at -20, -40, or -80 °C and freeze-dried. Glass transition and α-relaxation temperatures were determined with differential scanning calorimetry and dynamic mechanical analysis, respectively. β-Carotene contents were monitored spectrophotometrically. In the glassy solids, pore microstructure had a major effect on β-carotene stability. Small pores with thin walls and large surface area allowed β-carotene exposure to oxygen which led to a higher loss, whereas structural collapse enhanced stability of β-carotene by decreasing exposure to oxygen. As water plasticized matrices, an increase in molecular mobility in the matrix enhanced β-carotene degradation. Stability of dispersed β-carotene was highest at around 0.2 a(w) , but decreasing structural relaxation times above the glass transition correlated well with the rate of β-carotene degradation at higher a(w) . Microstructure, a(w) , and component mobility are important factors in the control of stability of β-carotene in freeze-dried solids. β-Carotene expresses various nutritional benefits; however, it is sensitive to oxygen and the degradation contributes to loss of nutritional values as well as product color. To increase stability of β-carotene in freeze-dried foods, the amount of oxygen penetration need to be limited. The modification of freeze-dried food structures, for example, porosity and structural collapse, components, and humidity effectively enhance the stability of dispersed β-carotene in freeze-dried solids. © 2012 Institute of Food Technologists®

PBO Borehole Strainmeters and Pore Pressure Sensors: Recording Hydrological Strain Signals

NASA Astrophysics Data System (ADS)

Gottlieb, M. H.; Hodgkinson, K. M.; Mencin, D.; Henderson, D. B.; Johnson, W.; Van Boskirk, E.; Pyatt, C.; Mattioli, G. S.

2017-12-01

UNAVCO operates a network of 75 borehole strainmeters along the west coast of the United States and Vancouver Island, Canada as part of the Plate Boundary Observatory (PBO), the geodetic component of the NSF-funded Earthscope program. Borehole strainmeters are designed to detect variations in the strain field at the nanostrain level and can easily detect transient strains caused by aseismic creep events, Episodic Tremor and Slip (ETS) events and seismically induced co- and post-seimic signals. In 2016, one strainmeter was installed in an Oklahoma oil field to characterize in-situ deformation during CO2 injection. Twenty-three strainmeter sites also have pore pressure sensors to measure fluctuations in groundwater pressure. Both the strainmeter network and the pore pressure sensors provide unique data against which those using water-level measurements, GPS time-series or InSAR data can compare possible subsidence signals caused by groundwater withdrawal or fluid re-injection. Operating for 12 years, the PBO strainmeter and pore pressure network provides a long-term, continuous, 1-sps record of deformation. PBO deploys GTSM21 tensor strainmeters from GTSM Technologies, which consist of four horizontal strain gauges stacked vertically, at different orientations, within a single 2 m-long instrument. The strainmeters are typically installed at depths of 200 to 250 m and grouted into the bottom of 15 cm diameter boreholes. The pore pressure sensors are Digiquartz Depth Sensors from Paros Scientific. These sensors are installed in 2" PVC, sampling groundwater through a screened section 15 m above the co-located strainmeter. These sensors are also recording at 1-sps with a resolution in the hundredths of hPa. High-rate local barometric pressure data and low-rate rainfall data also available at all locations. PBO Strainmeter and pore pressure data are available in SEED, SAC-ASCII and time-stamped ASCII format from the IRIS Data Managements Center. Strainmeter data are available at 2-hour latency while the pore pressure data are available in real-time. Links for data access, instrument and borehole information and station histories are available from UNAVCO's Borehole Data web page (https://www.unavco.org/data/strain-seismic/bsm-data/bsm-data.html ).

Tailoring physical properties of transglutaminase-modified gelatin films by varying drying temperature

USDA-ARS?s Scientific Manuscript database

Gelatin films prepared with or without transglutaminase (TGase) and dried at 15, 25 and 35 °C were analyzed for polymeric network structure, chemical composition and physical properties. Differences in protein network structure were observed by optical microscopy analysis in freeze-dried film-formin...

PRECISION OF ATMOSPHERIC DRY DEPOSITION DATA FROM THE CLEAN AIR STATUS AND TRENDS NETWORK (CASTNET)

EPA Science Inventory

A collocated, dry deposition sampling program was begun in January 1987 by the US Environmental Protection Agency to provide ongoing estimates of the overall precision of dry deposition and supporting data entering the Clean Air Status and Trends Network (CASTNet) archives Duplic...

Computation of three-phase capillary entry pressures and arc menisci configurations in pore geometries from 2D rock images: A combinatorial approach

NASA Astrophysics Data System (ADS)

Zhou, Yingfang; Helland, Johan Olav; Hatzignatiou, Dimitrios G.

2014-07-01

We present a semi-analytical, combinatorial approach to compute three-phase capillary entry pressures for gas invasion into pore throats with constant cross-sections of arbitrary shapes that are occupied by oil and/or water. For a specific set of three-phase capillary pressures, geometrically allowed gas/oil, oil/water and gas/water arc menisci are determined by moving two circles in opposite directions along the pore/solid boundary for each fluid pair such that the contact angle is defined at the front circular arcs. Intersections of the two circles determine the geometrically allowed arc menisci for each fluid pair. The resulting interfaces are combined systematically to allow for all geometrically possible three-phase configuration changes. The three-phase extension of the Mayer and Stowe - Princen method is adopted to calculate capillary entry pressures for all determined configuration candidates, from which the most favorable gas invasion configuration is determined. The model is validated by comparing computed three-phase capillary entry pressures and corresponding fluid configurations with analytical solutions in idealized triangular star-shaped pores. It is demonstrated that the model accounts for all scenarios that have been analyzed previously in these shapes. Finally, three-phase capillary entry pressures and associated fluid configurations are computed in throat cross-sections extracted from segmented SEM images of Bentheim sandstone. The computed gas/oil capillary entry pressures account for the expected dependence of oil/water capillary pressure in spreading and non-spreading fluid systems at the considered wetting conditions. Because these geometries are irregular and include constrictions, we introduce three-phase displacements that have not been identified previously in pore-network models that are based on idealized pore shapes. However, in the limited number of pore geometries considered in this work, we find that the favorable displacements are not generically different from those already encountered in network models previously, except that the size and shape of oil layers that are surrounded by gas and water are described more realistically. The significance of the results for describing oil connectivity in porous media accurately can only be evaluated by including throats with more complex cross-sections in three-phase pore-network models.

Whey protein aerogel as blended with cellulose crystalline particles or loaded with fish oil.

PubMed

Ahmadi, Maede; Madadlou, Ashkan; Saboury, Ali Akbar

2016-04-01

Whey protein hydrogels blended with nanocrystalline and microcrystalline cellulose particles (NCC and MCC, respectively) were prepared, followed by freeze-drying, to produce aerogels. NCC blending increased the Young's modulus, and elastic character, of the protein aerogel. Aerogels were microporous and mesoporous materials, as characterized by the pores sizing 1.2 nm and 12.2 nm, respectively. Blending with NCC decreased the count of both microporous and mesoporous-classified pores at the sub-100 nm pore size range investigated. In contrast, MCC blending augmented the specific surface area and pores volume of the aerogel. It also increased moisture sorption affinity of aerogel. The feasibility of conveying hydrophobic nutraceuticals by aerogels was evaluated through loading fish oil into the non-blended aerogel. Oil loading altered its microstructure, corresponding to a peak displacement in Fourier-transform infra-red spectra, which was ascribed to increased hydrophobic interactions. Surface coating of aerogel with zein decreased the oxidation susceptibility of the loaded oil during subsequent storage. Copyright © 2015 Elsevier Ltd. All rights reserved.

High-resolution synchrotron imaging shows that root hairs influence rhizosphere soil structure formation.

PubMed

Koebernick, Nicolai; Daly, Keith R; Keyes, Samuel D; George, Timothy S; Brown, Lawrie K; Raffan, Annette; Cooper, Laura J; Naveed, Muhammad; Bengough, Anthony G; Sinclair, Ian; Hallett, Paul D; Roose, Tiina

2017-10-01

In this paper, we provide direct evidence of the importance of root hairs on pore structure development at the root-soil interface during the early stage of crop establishment. This was achieved by use of high-resolution (c. 5 μm) synchrotron radiation computed tomography (SRCT) to visualise both the structure of root hairs and the soil pore structure in plant-soil microcosms. Two contrasting genotypes of barley (Hordeum vulgare), with and without root hairs, were grown for 8 d in microcosms packed with sandy loam soil at 1.2 g cm -3 dry bulk density. Root hairs were visualised within air-filled pore spaces, but not in the fine-textured soil regions. We found that the genotype with root hairs significantly altered the porosity and connectivity of the detectable pore space (> 5 μm) in the rhizosphere, as compared with the no-hair mutants. Both genotypes showed decreasing pore space between 0.8 and 0.1 mm from the root surface. Interestingly the root-hair-bearing genotype had a significantly greater soil pore volume-fraction at the root-soil interface. Effects of pore structure on diffusion and permeability were estimated to be functionally insignificant under saturated conditions when simulated using image-based modelling. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.

A network model for characterizing brine channels in sea ice

NASA Astrophysics Data System (ADS)

Lieblappen, Ross M.; Kumar, Deip D.; Pauls, Scott D.; Obbard, Rachel W.

2018-03-01

The brine pore space in sea ice can form complex connected structures whose geometry is critical in the governance of important physical transport processes between the ocean, sea ice, and surface. Recent advances in three-dimensional imaging using X-ray micro-computed tomography have enabled the visualization and quantification of the brine network morphology and variability. Using imaging of first-year sea ice samples at in situ temperatures, we create a new mathematical network model to characterize the topology and connectivity of the brine channels. This model provides a statistical framework where we can characterize the pore networks via two parameters, depth and temperature, for use in dynamical sea ice models. Our approach advances the quantification of brine connectivity in sea ice, which can help investigations of bulk physical properties, such as fluid permeability, that are key in both global and regional sea ice models.

Synthesis of thick mesoporous gamma-alumina films, loading of Pt nanoparticles, and use of the composite film as a reusable catalyst.

PubMed

Dandapat, Anirban; Jana, Debrina; De, Goutam

2009-04-01

Nanocrystalline mesoporous gamma-Al2O3 film of high thickness has been developed and characterized. The films were prepared on ordinary glass substrates by a single dip-coating method using boehmite (AlOOH) sols derived from aluminum tri-sec-butoxide in presence of cetyltrimethylammonium bromide (CTAB) as structure-directing agent. The dried films were heat-treated at 500 degrees C in air to remove the organics and strengthen the network. The GIXRD of the heat-treated (500 degrees C) film shows a broad peak in the low-angle region supporting the formation of worm-hole-like disordered mesostructures. The high-angle GIXRD, FTIR, and TEM of the films confirm the formation of gamma-Al2O3. N2 adsorption-desorption analyses showed that the heat-treated (500 degrees C) film has a BET surface area of 171 m(2) g(-1) with a pore volume of 0.188 cm(3) g(-1) and mean pore diameter 4.3 nm. Pt nanoparticles (NPs) (approximately 2.7 mol % with respect to the equivalent AlO(1.5)) were generated inside the mesopores of the heat-treated films simply by soaking H2PtCl6 solutions into it, and followed by thermal decomposition at 500 degrees C. The surface area and pore volume of the Pt-incorporated film have been reduced to 101 m(2) g(-1) and 0.119 cm(3) g(-1) respectively, confirming the inclusion of Pt NPs inside the pores. FESEM and TEM studies revealed uniform distribution of Pt NPs (2-8.5 nm; average diameter 4.9 nm) in the films. Catalytic properties of the Pt-incorporated films were investigated in two model (one inorganic and other organic) systems: reduction of hexacyanoferrate(III) ions by thiosulfate to ferrocyanide, and p-nitrophenol to p-aminophenol. In both the cases, the catalyst showed excellent activities, and the reduction reactions followed smoothly, showing isosbestic points in the UV-visible spectra. The catalyst films can be separated easily after the reactions and reused several times.

Pore structure characterization of Chang-7 tight sandstone using MICP combined with N2GA techniques and its geological control factors

NASA Astrophysics Data System (ADS)

Cao, Zhe; Liu, Guangdi; Zhan, Hongbin; Li, Chaozheng; You, Yuan; Yang, Chengyu; Jiang, Hang

2016-11-01

Understanding the pore networks of unconventional tight reservoirs such as tight sandstones and shales is crucial for extracting oil/gas from such reservoirs. Mercury injection capillary pressure (MICP) and N2 gas adsorption (N2GA) are performed to evaluate pore structure of Chang-7 tight sandstone. Thin section observation, scanning electron microscope, grain size analysis, mineral composition analysis, and porosity measurement are applied to investigate geological control factors of pore structure. Grain size is positively correlated with detrital mineral content and grain size standard deviation while negatively related to clay content. Detrital mineral content and grain size are positively correlated with porosity, pore throat radius and withdrawal efficiency and negatively related to capillary pressure and pore-to-throat size ratio; while interstitial material is negatively correlated with above mentioned factors. Well sorted sediments with high debris usually possess strong compaction resistance to preserve original pores. Although many inter-crystalline pores are produced in clay minerals, this type of pores is not the most important contributor to porosity. Besides this, pore shape determined by N2GA hysteresis loop is consistent with SEM observation on clay inter-crystalline pores while BJH pore volume is positively related with clay content, suggesting N2GA is suitable for describing clay inter-crystalline pores in tight sandstones.

Pore structure characterization of Chang-7 tight sandstone using MICP combined with N2GA techniques and its geological control factors

PubMed Central

Cao, Zhe; Liu, Guangdi; Zhan, Hongbin; Li, Chaozheng; You, Yuan; Yang, Chengyu; Jiang, Hang

2016-01-01

Understanding the pore networks of unconventional tight reservoirs such as tight sandstones and shales is crucial for extracting oil/gas from such reservoirs. Mercury injection capillary pressure (MICP) and N2 gas adsorption (N2GA) are performed to evaluate pore structure of Chang-7 tight sandstone. Thin section observation, scanning electron microscope, grain size analysis, mineral composition analysis, and porosity measurement are applied to investigate geological control factors of pore structure. Grain size is positively correlated with detrital mineral content and grain size standard deviation while negatively related to clay content. Detrital mineral content and grain size are positively correlated with porosity, pore throat radius and withdrawal efficiency and negatively related to capillary pressure and pore-to-throat size ratio; while interstitial material is negatively correlated with above mentioned factors. Well sorted sediments with high debris usually possess strong compaction resistance to preserve original pores. Although many inter-crystalline pores are produced in clay minerals, this type of pores is not the most important contributor to porosity. Besides this, pore shape determined by N2GA hysteresis loop is consistent with SEM observation on clay inter-crystalline pores while BJH pore volume is positively related with clay content, suggesting N2GA is suitable for describing clay inter-crystalline pores in tight sandstones. PMID:27830731

Synthesis and characterization of nanoparticulate MnS within the pores of mesoporous silica

NASA Astrophysics Data System (ADS)

Barry, Louse; Copley, Mark; Holmes, Justin D.; Otway, David J.; Kazakova, Olga; Morris, Michael A.

2007-12-01

Mesoporous silica was loaded with nanoparticulate MnS via a simple post-synthesis treatment. The mesoporous material that still contained surfactant was passivated to prevent MnS formation at the surface. The surfactant was extracted and a novel manganese ethylxanthate was used to impregnate the pore network. This precursor thermally decomposes to yield MnS particles that are smaller or equal to the pore size. The particles exhibit all three common polymorphs. The passivation treatment is most effective at lower loadings because at the highest loadings (SiO 2:MnS molar ratio of 6:1) large particles (>50 nm) form at the exterior of the mesoporous particles. The integrity of the mesoporous network is maintained through the preparation and high order is maintained. The MnS particles exhibit unexpected ferromagnetism at low temperatures. Strong luminescence of these samples is observed and this suggests that they may have a range of important application areas.

Evaluation of Data Replacement Strategies for CASTNET Dry Deposition Modeling

EPA Science Inventory

The U.S. Environmental Protection Agency (EPA) established the Clean Air Status and Trends Network (CASTNET) and its predecessor, the National Dry Deposition Network (NDDN), as national air quality and meteorological monitoring networks. The purpose of CASTNET is to track the pr...

Passive advection-dispersion in networks of pipes: Effect of connectivity and relationship to permeability

NASA Astrophysics Data System (ADS)

Bernabé, Y.; Wang, Y.; Qi, T.; Li, M.

2016-02-01

The main purpose of this work is to investigate the relationship between passive advection-dispersion and permeability in porous materials presumed to be statistically homogeneous at scales larger than the pore scale but smaller than the reservoir scale. We simulated fluid flow through pipe network realizations with different pipe radius distributions and different levels of connectivity. The flow simulations used periodic boundary conditions, allowing monitoring of the advective motion of solute particles in a large periodic array of identical network realizations. In order to simulate dispersion, we assumed that the solute particles obeyed Taylor dispersion in individual pipes. When a particle entered a pipe, a residence time consistent with local Taylor dispersion was randomly assigned to it. When exiting the pipe, the particle randomly proceeded into one of the pipes connected to the original one according to probabilities proportional to the outgoing volumetric flow in each pipe. For each simulation we tracked the motion of at least 6000 solute particles. The mean fluid velocity was 10-3 ms-1, and the distance traveled was on the order of 10 m. Macroscopic dispersion was quantified using the method of moments. Despite differences arising from using different types of lattices (simple cubic, body-centered cubic, and face-centered cubic), a number of general observations were made. Longitudinal dispersion was at least 1 order of magnitude greater than transverse dispersion, and both strongly increased with decreasing pore connectivity and/or pore size variability. In conditions of variable hydraulic radius and fixed pore connectivity and pore size variability, the simulated dispersivities increased as power laws of the hydraulic radius and, consequently, of permeability, in agreement with previously published experimental results. Based on these observations, we were able to resolve some of the complexity of the relationship between dispersivity and permeability.

Multiscale approach to (micro)porosity quantification in continental spring carbonate facies: Case study from the Cakmak quarry (Denizli, Turkey)

NASA Astrophysics Data System (ADS)

De Boever, Eva; Foubert, Anneleen; Oligschlaeger, Dirk; Claes, Steven; Soete, Jeroen; Bertier, Pieter; Özkul, Mehmet; Virgone, Aurélien; Swennen, Rudy

2016-07-01

Carbonate spring deposits gained renewed interest as potential contributors to subsurface reservoirs and as continental archives of environmental changes. In contrast to their fabrics, petrophysical characteristics - and especially the importance of microporosity (< 1µm) - are less understood. This study presents the combination of advanced petrophysical and imaging techniques to investigate the pore network characteristics of three, common and widespread spring carbonate facies, as exposed in the Pleistocene Cakmak quarry (Denizli, Turkey): the extended Pond, the dipping crystalline Proximal Slope Facies and the draping Apron and Channel Facies deposits formed by encrustation of biological substrate. Integrating mercury injection capillary pressure, bulk and diffusion Nuclear Magnetic Resonance (NMR), NMR profiling and Brunauer-Emmett-Teller (BET) measurements with microscopy and micro-computer tomography (µ-CT), shows that NMR T2 distributions systematically display a single group of micro-sized pore bodies, making up between 6 and 33% of the pore space (average NMR T2 cut-off value: 62 ms). Micropore bodies are systematically located within cloudy crystal cores of granular and dendritic crystal textures in all facies. The investigated properties therefore do not reveal differences in micropore size or shape with respect to more or less biology-associated facies. The pore network of the travertine facies is distinctive in terms of (i) the percentage of microporosity, (ii) the connectivity of micropores with meso- to macropores, and (ii) the degree of heterogeneity at micro- and macroscale. Results show that an approach involving different NMR experiments provided the most complete view on the 3-D pore network especially when microporosity and connectivity are of interest.

Control of cell proliferation by a porous chitosan scaffold with multiple releasing capabilities

NASA Astrophysics Data System (ADS)

Cai, Shu-Jyun; Li, Ching-Wen; Weihs, Daphne; Wang, Gou-Jen

2017-12-01

The aim of this study was to develop a porous chitosan scaffold with long-acting drug release as an artificial dressing to promote skin wound healing. The dressing was fabricated by pre-freezing at different temperatures (-20 and -80 °C) for different periods of time, followed by freeze-drying to form porous chitosan scaffolds with different pore sizes. The chitosan scaffolds were then used to investigate the effect of the controlled release of fibroblast growth factor-basic (bFGF) and transforming growth factor-β1 (TGFβ1) on mouse fibroblast cells (L929) and bovine carotid endothelial cells (BEC). The biocompatibility of the prepared chitosan scaffold was confirmed with WST-1 proliferation and viability assay, which demonstrated that the material is suitable for cell growth. The results of this study show that the pore sizes of the porous scaffolds prepared by freeze-drying can change depending on the pre-freezing temperature and time via the formation of ice crystals. In this study, the scaffolds with the largest pore size were found to be 153 ± 32 μm and scaffolds with the smallest pores to be 34 ± 9 μm. Through cell culture analysis, it was found that the concentration that increased proliferation of L929 cells for bFGF was 0.005 to 0.1 ng/mL, and the concentration for TGFβ1 was 0.005 to 1 ng/mL. The cell culture of the chitosan scaffold and growth factors shows that 3.75 ng of bFGF in scaffolds with pore sizes of 153 ± 32 μm can promote L929 cell proliferation, while 400 pg of TGFβ1 in scaffolds with pore size of 34 ± 9 μm can enhance the proliferation of L929 cells, but also inhibit BEC proliferation. It is proposed that the prepared chitosan scaffolds can form a multi-drug (bFGF and TGFβ1) release dressing that has the ability to control wound healing via regulating the proliferation of different cell types.

Control of cell proliferation by a porous chitosan scaffold with multiple releasing capabilities

PubMed Central

Cai, Shu-Jyun; Li, Ching-Wen; Weihs, Daphne; Wang, Gou-Jen

2017-01-01

Abstract The aim of this study was to develop a porous chitosan scaffold with long-acting drug release as an artificial dressing to promote skin wound healing. The dressing was fabricated by pre-freezing at different temperatures (−20 and −80 °C) for different periods of time, followed by freeze-drying to form porous chitosan scaffolds with different pore sizes. The chitosan scaffolds were then used to investigate the effect of the controlled release of fibroblast growth factor-basic (bFGF) and transforming growth factor-β1 (TGFβ1) on mouse fibroblast cells (L929) and bovine carotid endothelial cells (BEC). The biocompatibility of the prepared chitosan scaffold was confirmed with WST-1 proliferation and viability assay, which demonstrated that the material is suitable for cell growth. The results of this study show that the pore sizes of the porous scaffolds prepared by freeze-drying can change depending on the pre-freezing temperature and time via the formation of ice crystals. In this study, the scaffolds with the largest pore size were found to be 153 ± 32 μm and scaffolds with the smallest pores to be 34 ± 9 μm. Through cell culture analysis, it was found that the concentration that increased proliferation of L929 cells for bFGF was 0.005 to 0.1 ng/mL, and the concentration for TGFβ1 was 0.005 to 1 ng/mL. The cell culture of the chitosan scaffold and growth factors shows that 3.75 ng of bFGF in scaffolds with pore sizes of 153 ± 32 μm can promote L929 cell proliferation, while 400 pg of TGFβ1 in scaffolds with pore size of 34 ± 9 μm can enhance the proliferation of L929 cells, but also inhibit BEC proliferation. It is proposed that the prepared chitosan scaffolds can form a multi-drug (bFGF and TGFβ1) release dressing that has the ability to control wound healing via regulating the proliferation of different cell types. PMID:29230255

Inorganic dual-layer microporous supported membranes

DOEpatents

Brinker, C. Jeffrey; Tsai, Chung-Yi; Lu, Yungfeng

2003-03-25

The present invention provides for a dual-layer inorganic microporous membrane capable of molecular sieving, and methods for production of the membranes. The inorganic microporous supported membrane includes a porous substrate which supports a first inorganic porous membrane having an average pore size of less than about 25 .ANG. and a second inorganic porous membrane coating the first inorganic membrane having an average pore size of less than about 6 .ANG.. The dual-layered membrane is produced by contacting the porous substrate with a surfactant-template polymeric sol, resulting in a surfactant sol coated membrane support. The surfactant sol coated membrane support is dried, producing a surfactant-templated polymer-coated substrate which is calcined to produce an intermediate layer surfactant-templated membrane. The intermediate layer surfactant-templated membrane is then contacted with a second polymeric sol producing a polymeric sol coated substrate which is dried producing an inorganic polymeric coated substrate. The inorganic polymeric coated substrate is then calcined producing an inorganic dual-layered microporous supported membrane in accordance with the present invention.

How do roll compaction/dry granulation affect the tableting behaviour of inorganic materials? Microhardness of ribbons and mercury porosimetry measurements of tablets.

PubMed

Freitag, Franziska; Reincke, Katrin; Runge, Jürgen; Grellmann, Wolfgang; Kleinebudde, Peter

2004-07-01

The effect of roll compaction/dry granulation on the ribbon and tablet properties produced using different magnesium carbonates was evaluated. The ribbon microhardness and the pore size distribution of tablets were used as evaluation factors. Increasing the specific compaction force resulted in higher microhardness for ribbons prepared with all four magnesium carbonates accompanied with decreased part of fine. Consequently, the corresponding produced tablets displayed a lower tensile strength. A possible correlation between the particle shape, surface area and the resulting pore structure of tablets produced with the four different types of magnesium carbonate was observed. The tensile strength of tablets prepared using granules was lower than tensile strength of tablets produced using starting materials. The partial loss of compactibility resulted in a demand of low loads during roll compaction. However, the impact of changes in the material properties during the roll compaction depended greatly on the type of magnesium carbonate, the specific compaction force and the tableting pressure applied.

The specificity of host-bat fly interaction networks across vegetation and seasonal variation.

PubMed

Zarazúa-Carbajal, Mariana; Saldaña-Vázquez, Romeo A; Sandoval-Ruiz, César A; Stoner, Kathryn E; Benitez-Malvido, Julieta

2016-10-01

Vegetation type and seasonality promote changes in the species composition and abundance of parasite hosts. However, it is poorly known how these variables affect host-parasite interaction networks. This information is important to understand the dynamics of parasite-host relationships according to biotic and abiotic changes. We compared the specialization of host-bat fly interaction networks, as well as bat fly and host species composition between upland dry forest and riparian forest and between dry and rainy seasons in a tropical dry forest in Jalisco, Mexico. Bat flies were surveyed by direct collection from bats. Our results showed that host-bat fly interaction networks were more specialized in upland dry forest compared to riparian forest. Bat fly species composition was different between the dry and rainy seasons, while host species composition was different between upland dry forest and riparian forest. The higher specialization in upland dry forest could be related to the differences in bat host species composition and their respective roosting habits. Variation in the composition of bat fly species between dry and rainy seasons coincides with the seasonal shifts in their species richness. Our study confirms the high specialization of host-bat fly interactions and shows the importance of biotic and abiotic factors to understand the dynamics of parasite-host interactions.

Quantitative Mapping of Pore Fraction Variations in Silicon Nitride Using an Ultrasonic Contact Scan Technique

NASA Technical Reports Server (NTRS)

Roth, Don J.; Kiser, James D.; Swickard, Suzanne M.; Szatmary, Steven A.; Kerwin, David P.

1993-01-01

An ultrasonic scan procedure using the pulse-echo contact configuration was employed to obtain maps of pore fraction variations in sintered silicon nitride samples in terms of ultrasonic material properties. Ultrasonic velocity, attenuation coefficient, and reflection coefficient images were obtained simultaneously over a broad band of frequencies (e.g., 30 to 110 MHz) by using spectroscopic analysis. Liquid and membrane (dry) coupling techniques and longitudinal and shear-wave energies were used. The major results include the following: Ultrasonic velocity (longitudinal and shear wave) images revealed and correlated with the extent of average through-thickness pore fraction variations in the silicon nitride disks. Attenuation coefficient images revealed pore fraction nonuniformity due to the scattering that occurred at boundaries between regions of high and low pore fraction. Velocity and attenuation coefficient images were each nearly identical for machined and polished disks, making the method readily applicable to machined materials. Velocity images were similar for wet and membrane coupling. Maps of apparent Poisson's ratio constructed from longitudinal and shear-wave velocities quantified Poisson's ratio variations across a silicon nitride disk. Thermal wave images of a disk indicated transient thermal behavior variations that correlated with observed variations in pore fraction and velocity and attenuation coefficients.

Solvent and solute ingress into hydrogels resolved by a combination of imaging techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wagner, D.; Burbach, J.; Egelhaaf, S. U.

2016-05-28

Using simultaneous neutron, fluorescence, and optical brightfield transmission imaging, the diffusion of solvent, fluorescent dyes, and macromolecules into a crosslinked polyacrylamide hydrogel was investigated. This novel combination of different imaging techniques enables us to distinguish the movements of the solvent and fluorescent molecules. Additionally, the swelling or deswelling of the hydrogels can be monitored. From the sequence of images, dye and solvent concentrations were extracted spatially and temporally resolved. Diffusion equations and different boundary conditions, represented by different models, were used to quantitatively analyze the temporal evolution of these concentration profiles and to determine the diffusion coefficients of solvent andmore » solutes. Solute size and network properties were varied and their effect was investigated. Increasing the crosslinking ratio or partially drying the hydrogel was found to hinder solute diffusion due to the reduced pore size. By contrast, solvent diffusion seemed to be slightly faster if the hydrogel was only partially swollen and hence solvent uptake enhanced.« less

Process for preparing energetic materials

DOEpatents

Simpson, Randall L [Livermore, CA; Lee, Ronald S [Livermore, CA; Tillotson, Thomas M [Tracy, CA; Hrubesh, Lawrence W [Pleasanton, CA; Swansiger, Rosalind W [Livermore, CA; Fox, Glenn A [Livermore, CA

2011-12-13

Sol-gel chemistry is used for the preparation of energetic materials (explosives, propellants and pyrotechnics) with improved homogeneity, and/or which can be cast to near-net shape, and/or made into precision molding powders. The sol-gel method is a synthetic chemical process where reactive monomers are mixed into a solution, polymerization occurs leading to a highly cross-linked three dimensional solid network resulting in a gel. The energetic materials can be incorporated during the formation of the solution or during the gel stage of the process. The composition, pore, and primary particle sizes, gel time, surface areas, and density may be tailored and controlled by the solution chemistry. The gel is then dried using supercritical extraction to produce a highly porous low density aerogel or by controlled slow evaporation to produce a xerogel. Applying stress during the extraction phase can result in high density materials. Thus, the sol-gel method can be used for precision detonator explosive manufacturing as well as producing precision explosives, propellants, and pyrotechnics, along with high power composite energetic materials.

Sol-Gel Manufactured Energetic Materials

DOEpatents

Simpson, Randall L.; Lee, Ronald S.; Tillotson, Thomas M.; Hrubesh, Lawrence W.; Swansiger, Rosalind W.; Fox, Glenn A.

2005-05-17

Sol-gel chemistry is used for the preparation of energetic materials (explosives, propellants and pyrotechnics) with improved homogeneity, and/or which can be cast to near-net shape, and/or made into precision molding powders. The sol-gel method is a synthetic chemical process where reactive monomers are mixed into a solution, polymerization occurs leading to a highly cross-linked three dimensional solid network resulting in a gel. The energetic materials can be incorporated during the formation of the solution or during the gel stage of the process. The composition, pore, and primary particle sizes, gel time, surface areas, and density may be tailored and controlled by the solution chemistry. The gel is then dried using supercritical extraction to produce a highly porous low density aerogel or by controlled slow evaporation to produce a xerogel. Applying stress during the extraction phase can result in high density materials. Thus, the sol-gel method can be used for precision detonator explosive manufacturing as well as producing precision explosives, propellants, and pyrotechnics, along with high power composite energetic materials.

Sol-gel manufactured energetic materials

DOEpatents

Simpson, Randall L.; Lee, Ronald S.; Tillotson, Thomas M.; Hrubesh, Lawrence W.; Swansiger, Rosalind W.; Fox, Glenn A.

2003-12-23

Sol-gel chemistry is used for the preparation of energetic materials (explosives, propellants and pyrotechnics) with improved homogeneity, and/or which can be cast to near-net shape, and/or made into precision molding powders. The sol-gel method is a synthetic chemical process where reactive monomers are mixed into a solution, polymerization occurs leading to a highly cross-linked three dimensional solid network resulting in a gel. The energetic materials can be incorporated during the formation of the solution or during the gel stage of the process. The composition, pore, and primary particle sizes, gel time, surface areas, and density may be tailored and controlled by the solution chemistry. The gel is then dried using supercritical extraction to produce a highly porous low density aerogel or by controlled slow evaporation to produce a xerogel. Applying stress during the extraction phase can result in high density materials. Thus, the sol-gel method can be used for precision detonator explosive manufacturing as well as producing precision explosives, propellants, and pyrotechnics, along with high power composite energetic materials.

Nano-engineered intrapores in nanoparticles of PtNi networks for increased oxygen reduction reaction activity

NASA Astrophysics Data System (ADS)

Ding, Jieting; Ji, Shan; Wang, Hui; Key, Julian; Brett, Dan J. L.; Wang, Rongfang

2018-01-01

Network-like metallic alloys of solid nanoparticles have been frequently reported as promising electrocatalysts for fuel cells. The three-dimensional structure of such networks is rich in pores in the form of voids between nanoparticles, which collectively expose a large surface area for catalytic activity. Herein, we present a novel solution to this problem using a precursor comprising a flocculent core-shell PtNi@Ni to produce PtNi network catalysts with nanoparticle intraporosity after carefully controlled electrochemical dealloying. Physical characterization shows a hierarchical level of nanoporosity (intrapores within nanoparticles and pores between them) evolves during the controlled electrochemical dealloying, and that a Pt-rich surface also forms after 22 cycles of Ni leaching. In ORR cycling, the PtNi networks gain 4-fold activity in both jECSA and jmass over a state of the art Pt/C electrocatalyst, and also significantly exceed previously reported PtNi networks. In ORR degradation tests, the PtNi networks also proved stable, dropping by 30.4% and 62.6% in jECSA and jmass respectively. The enhanced performance of the catalyst is evident, and we also propose that the presented synthesis procedure can be generally applied to developing other metallic networks.

Process for forming integral edge seals in porous gas distribution plates utilizing a vibratory means

NASA Technical Reports Server (NTRS)

Feigenbaum, Haim (Inventor); Pudick, Sheldon (Inventor)

1988-01-01

A process for forming an integral edge seal in a gas distribution plate for use in a fuel cell. A seal layer is formed along an edge of a porous gas distribution plate by impregnating the pores in the layer with a material adapted to provide a seal which is operative dry or when wetted by an electrolyte of a fuel cell. Vibratory energy is supplied to the sealing material during the step of impregnating the pores to provide a more uniform seal throughout the cross section of the plate.

Environmental and management impacts on temporal variability of soil hydraulic properties

NASA Astrophysics Data System (ADS)

Bodner, G.; Scholl, P.; Loiskandl, W.; Kaul, H.-P.

2012-04-01

Soil hydraulic properties underlie temporal changes caused by different natural and management factors. Rainfall intensity, wet-dry cycles, freeze-thaw cycles, tillage and plant effects are potential drivers of the temporal variability. For agricultural purposes it is important to determine the possibility of targeted influence via management. In no-till systems e.g. root induced soil loosening (biopores) is essential to counteract natural soil densification by settling. The present work studies two years of temporal evolution of soil hydraulic properties in a no-till crop rotation (durum wheat-field pea) with two cover crops (mustard and rye) having different root systems (taproot vs. fibrous roots) as well as a bare soil control. Soil hydraulic properties such as near-saturated hydraulic conductivity, flow weighted pore radius, pore number and macroporosity are derived from measurements using a tension infiltrometer. The temporal dynamics are then analysed in terms of potential driving forces. Our results revealed significant temporal changes of hydraulic conductivity. When approaching saturation, spatial variability tended to dominate over the temporal evolution. Changes in near-saturated hydraulic conductivity were mainly a result of changing pore number, while the flow weighted mean pore radius showed less temporal dynamic in the no-till system. Macroporosity in the measured range of 0 to -10 cm pressure head ranged from 1.99e-4 to 8.96e-6 m3m-3. The different plant coverage revealed only minor influences on the observed system dynamics. Mustard increased slightly the flow weighted mean pore radius, being 0.090 mm in mustard compared to 0.085 mm in bare soil and 0.084 mm in rye. Still pore radius changes were of minor importance for the overall temporal dynamics. Rainfall was detected as major driving force of the temporal evolution of structural soil hydraulic properties at the site. Soil hydraulic conductivity in the slightly unsaturated range (-7 cm to -10 cm) showed a similar time course as a moving average of rainfall. Drying induced a decrease in conductivity while wetting of the soil resulted in higher conductivity values. Approaching saturation however, the drying phase showed a different behaviour with increasing values of hydraulic conductivity. This may be explained probably by formation of cracks acting as large macropores. We concluded that aggregate coalescence as a function of capillary forces and soil rheologic properties (cf. Or et al., 2002) are a main predictor of temporal dynamics of near saturated soil hydraulic properties while different plant covers only had a minor effect on the observed system dynamics. Or, D., Ghezzehei, T.A. 2002. Modeling post-tillage soil structural dynamics. a review. Soil Till Res. 64, 41-59.

Influence of Solutocapillary Convection on Macrovoid Defect Formation in Polymeric Membranes

NASA Technical Reports Server (NTRS)

Greenberg, Alan R.; Krantz, William B.; Todd, Paul

2003-01-01

The focus of this research project involved the dry-cast process for polymeric membrane formation, whereby evaporation of solvent from an initially homogeneous polymer/solvent/ nonsolvent solution results in phase separation and the formation of polymer-rich and polymer-lean phases. Under certain conditions the polymer-lean phase gives rise to very large and usually undesirable, tear-drop-shaped pores (size approx. 10 - 50 microns) termed macrovoids (MVs). Although in many cases the presence of MV pores has deleterious effects on membrane performance, there are a number of innovative applications where the presence of such pores is highly desirable. Although researchers have proposed a variety of mechanisms for MV formation over the past three decades, two main hypotheses are currently favored: one asserts that MV growth can be attributed solely to diffusion (the diffusive growth hypothesis), whereas the other states that solutocapillary convection (the SC hypothesis) at the MV interface contributes to growth. The overall goal of this research was to obtain a more comprehensive understanding of the fundamental mechanism of MV growth. This research incorporates a coupled modeling and experimental approach to test a solutocapillary convection hypothesis for the growth of macrovoid pores in polymeric membranes. Specifically, we utilized a modification of the first principles model developed by two of the PIs (ARG and WBK) for dry-cast CA membranes. For the experimental component, two separate and mutually complementary approaches were used to study MV growth. In the first, membranes cast in a zero-g environment aboard the NASA KC-135 aircraft were compared with those cast on the ground to assess the effect of the buoyancy force on membrane morphology and MV size and shape. In the second approach, videomicroscopy flow visualization (VMFV) was utilized to observe MV formation and growth in real time and to assess the effect of surface tension on the MV growth dynamics. As a result of these fundamental studies, our research group advanced a new hypothesis for MV pore development in polymeric membranes.

A Histidine Aspartate Ionic Lock Gates the Iron Passage in Miniferritins from Mycobacterium smegmatis*

PubMed Central

Williams, Sunanda Margrett; Chandran, Anu V.; Vijayabaskar, Mahalingam S.; Roy, Sourav; Balaram, Hemalatha; Vishveshwara, Saraswathi; Vijayan, Mamannamana; Chatterji, Dipankar

2014-01-01

Dps (DNA-binding protein from starved cells) are dodecameric assemblies belonging to the ferritin family that can bind DNA, carry out ferroxidation, and store iron in their shells. The ferritin-like trimeric pore harbors the channel for the entry and exit of iron. By representing the structure of Dps as a network we have identified a charge-driven interface formed by a histidine aspartate cluster at the pore interface unique to Mycobacterium smegmatis Dps protein, MsDps2. Site-directed mutagenesis was employed to generate mutants to disrupt the charged interactions. Kinetics of iron uptake/release of the wild type and mutants were compared. Crystal structures were solved at a resolution of 1.8–2.2 Å for the various mutants to compare structural alterations vis à vis the wild type protein. The substitutions at the pore interface resulted in alterations in the side chain conformations leading to an overall weakening of the interface network, especially in cases of substitutions that alter the charge at the pore interface. Contrary to earlier findings where conserved aspartate residues were found crucial for iron release, we propose here that in the case of MsDps2, it is the interplay of negative-positive potentials at the pore that enables proper functioning of the protein. In similar studies in ferritins, negative and positive patches near the iron exit pore were found to be important in iron uptake/release kinetics. The unique ionic cluster in MsDps2 makes it a suitable candidate to act as nano-delivery vehicle, as these gated pores can be manipulated to exhibit conformations allowing for slow or fast rates of iron release. PMID:24573673

Differences in soluble organic carbon chemistry in pore waters sampled from different pore size domains

DOE PAGES

Bailey, Vanessa L.; Smith, A. P.; Tfaily, Malak; ...

2017-01-11

Spatial isolation of soil organic carbon (SOC) in different sized pores may be a mechanism by which otherwise labile carbon (C) could be protected in soils. When soil water content increases, the hydrologic connectivity of soil pores also increases, allowing greater transport of SOC and other resources from protected locations, to microbially colonized locations more favorable to decomposition. The heterogeneous distribution of specialized decomposers, C, and other resources throughout the soil indicates that the metabolism or persistence of soil C compounds is highly dependent on short-distance transport processes. The objective of this research was to characterize the complexity of Cmore » in pore waters held at weak and strong water tensions (effectively soil solution held behind coarse- and fine-pore throats, respectively) and evaluate the microbial decomposability of these pore waters. We saturated intact soil cores and extracted pore waters with increasing suction pressures to sequentially sample pore waters from increasingly fine pore domains. Ultrahigh resolution mass spectrometry of the SOC was used to profile the major biochemical classes (i.e., lipids, proteins, lignin, carbohydrates, and condensed aromatics) of compounds present in the pore waters; some of these samples were then used as substrates for growth of Cellvibrio japonicus (DSMZ 16018), Streptomyces cellulosae (ATCC ® 25439™), and Trichoderma reseei (QM6a) in 7 day incubations. The soluble C in finer pores was more complex than the soluble C in coarser pores, and the incubations revealed that the more complex C in these fine pores is not recalcitrant. The decomposition of this complex C led to greater losses of C through respiration than the simpler C from coarser pore waters. Our research suggests that soils that experience repeated cycles of drying and wetting may be accompanied by repeated cycles of increased CO 2 fluxes that are driven by i) the transport of C from protected pools into active, ii) the chemical quality of the potentially soluble C, and iii) the type of microorganisms most likely to metabolize this C.« less

Differences in soluble organic carbon chemistry in pore waters sampled from different pore size domains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bailey, Vanessa L.; Smith, A. P.; Tfaily, Malak

Spatial isolation of soil organic carbon (SOC) in different sized pores may be a mechanism by which otherwise labile carbon (C) could be protected in soils. When soil water content increases, the hydrologic connectivity of soil pores also increases, allowing greater transport of SOC and other resources from protected locations, to microbially colonized locations more favorable to decomposition. The heterogeneous distribution of specialized decomposers, C, and other resources throughout the soil indicates that the metabolism or persistence of soil C compounds is highly dependent on short-distance transport processes. The objective of this research was to characterize the complexity of Cmore » in pore waters held at weak and strong water tensions (effectively soil solution held behind coarse- and fine-pore throats, respectively) and evaluate the microbial decomposability of these pore waters. We saturated intact soil cores and extracted pore waters with increasing suction pressures to sequentially sample pore waters from increasingly fine pore domains. Ultrahigh resolution mass spectrometry of the SOC was used to profile the major biochemical classes (i.e., lipids, proteins, lignin, carbohydrates, and condensed aromatics) of compounds present in the pore waters; some of these samples were then used as substrates for growth of Cellvibrio japonicus (DSMZ 16018), Streptomyces cellulosae (ATCC ® 25439™), and Trichoderma reseei (QM6a) in 7 day incubations. The soluble C in finer pores was more complex than the soluble C in coarser pores, and the incubations revealed that the more complex C in these fine pores is not recalcitrant. The decomposition of this complex C led to greater losses of C through respiration than the simpler C from coarser pore waters. Our research suggests that soils that experience repeated cycles of drying and wetting may be accompanied by repeated cycles of increased CO 2 fluxes that are driven by i) the transport of C from protected pools into active, ii) the chemical quality of the potentially soluble C, and iii) the type of microorganisms most likely to metabolize this C.« less

Ternary Phase-Separation Investigation of Sol-Gel Derived Silica from Ethyl Silicate 40

PubMed Central

Wang, Shengnan; Wang, David K.; Smart, Simon; Diniz da Costa, João C.

2015-01-01

A ternary phase-separation investigation of the ethyl silicate 40 (ES40) sol-gel process was conducted using ethanol and water as the solvent and hydrolysing agent, respectively. This oligomeric silica precursor underwent various degrees of phase separation behaviour in solution during the sol-gel reactions as a function of temperature and H2O/Si ratios. The solution composition within the immiscible region of the ES40 phase-separated system shows that the hydrolysis and condensation reactions decreased with decreasing reaction temperature. A mesoporous structure was obtained at low temperature due to weak drying forces from slow solvent evaporation on one hand and formation of unreacted ES40 cages in the other, which reduced network shrinkage and produced larger pores. This was attributed to the concentration of the reactive sites around the phase-separated interface, which enhanced the condensation and crosslinking. Contrary to dense silica structures obtained from sol-gel reactions in the miscible region, higher microporosity was produced via a phase-separated sol-gel system by using high H2O/Si ratios. This tailoring process facilitated further condensation reactions and crosslinking of silica chains, which coupled with stiffening of the network, made it more resistant to compression and densification. PMID:26411484

Influence of hydraulic hysteresis on the mechanical behavior of unsaturated soils and interfaces

NASA Astrophysics Data System (ADS)

Khoury, Charbel N.

Unsaturated soils are commonly widespread around the world, especially at shallow depths from the surface. The mechanical behavior of this near surface soil is influenced by the seasonal variations such as rainfall or drought, which in turn may have a detrimental effect on many structures (e.g. retaining walls, shallow foundations, mechanically stabilized earth walls, soil slopes, and pavements) in contact with it. Thus, in order to better understand this behavior, it is crucial to study the complex relationship between soil moisture content and matric suction (a stress state variable defined as pore air pressure minus pore water pressure) known as the Soil Water Characteristic Curve (SWCC). In addition, the influence of hydraulic hysteresis on the behavior of unsaturated soils, soil-structure interaction (i.e. rough and smooth steel interfaces, soil-geotextile interfaces) and pavement subgrade (depicted herein mainly by resilient modulus, Mr) was also studied. To this end, suction-controlled direct shear tests were performed on soils, rough and smooth steel interfaces and geotextile interface under drying (D) and wetting after drying (DW). The shearing behavior is examined in terms of the two stress state variables, matric suction and net normal stress. Results along the D and DW paths indicated that peak shear strength increased with suction and net normal stress; while in general, the post peak shear strength was not influenced by suction for rough interfaces and no consistent trend was observed for soils and soil-geotextiles interfaces. Contrary to saturated soils, results during shearing at higher suction values (i.e. 25 kPa and above) showed a decrease in water content eventhough the sample exhibited dilation. A behavior postulated to be related to disruption of menisci and/or non-uniformity of pore size which results in an increase in localized pore water pressures. Interestingly, wetting after drying (DW) test results showed higher peak and post peak shear strength than that of the drying (D) tests. This is believed to be the result of many factors such as: (1) cyclic suction stress loading, (2) water content (less on wetting than drying), and (3) type of soil. The cyclic suction loading may have induced irrecoverable plastic strains, resulting in stiffer samples for wetting tests as compared to drying. Additionally, water may be acting as a lubricant and thus resulting in lower shear strength for test samples D with higher water contents than DW samples. Furthermore, various shear strength models were investigated for their applicability to the experimental data. Models were proposed for the prediction of shear strength with suction based on the SWCC. The models are able to predict the shear strength of unsaturated soil and interfaces due to drying and wetting (i.e. hydraulic hysteresis) by relating directly to the SWCC. The proposed models were used and partly validated by predicting different test results from the literature. In addition, an existing elastoplastic constitutive model was investigated and validated by comparing the predicted and experimental (stress-displacement, volume change behavior) results obtained from rough and geotextile interface tests. This study also explores the effect of hydraulic hysteresis on the resilient modulus (Mr) of subgrade soils. Suction-controlled Mr tests were performed on compacted samples along the primary drying, wetting, secondary drying and wetting paths. Two test types were performed to check the effect of cyclic deviatoric stress loading on the results. First, M r tests were performed on the same sample at each suction (i.e. 25, 50, 75, 100 kPa) value along all the paths (drying, wetting etc.). A relationship between resilient modulus (Mr) and matric suction was obtained and identified as the resilient modulus characteristic curve (MRCC). MRCC results indicated that Mr increased with suction along the drying curve. On the other hand, results on the primary wetting indicated higher Mr than that of the primary drying and the secondary drying. The second type of test was performed at selected suction without subjecting the sample to previous Mr tests. Results indicated that Mr compared favorably with the other type of test (i.e. with previous M r testing), which indicates that the cyclic deviatoric stress loading influence was not as significant as the hydraulic hysteresis (i.e. cyclic suction stress loading). A new model to predict the MRCC results during drying and wetting (i.e., hydraulic hysteresis) is proposed based on the SWCC hysteresis. The model predicted favorably the drying and then the wetting results using the SWCC at all stress levels. (Abstract shortened by UMI.)

Supported inorganic membranes

DOEpatents

Sehgal, Rakesh; Brinker, Charles Jeffrey

1998-01-01

Supported inorganic membranes capable of molecular sieving, and methods for their production, are provided. The subject membranes exhibit high flux and high selectivity. The subject membranes are substantially defect free and less than about 100 nm thick. The pores of the subject membranes have an average critical pore radius of less than about 5 .ANG., and have a narrow pore size distribution. The subject membranes are prepared by coating a porous substrate with a polymeric sol, preferably under conditions of low relative pressure of the liquid constituents of the sol. The coated substrate is dried and calcined to produce the subject supported membrane. Also provided are methods of derivatizing the surface of supported inorganic membranes with metal alkoxides. The subject membranes find use in a variety of applications, such as the separation of constituents of gaseous streams, as catalysts and catalyst supports, and the like.

Structural properties and adsorption capacity of holocellulose aerogels synthesized from an alkali hydroxide-urea solution

NASA Astrophysics Data System (ADS)

Kwon, Gu-Joong; Kim, Dae-Young; Hwang, Jae-Hyun; Kang, Joo-Hyon

2014-05-01

A tulip tree was used to synthesize a holocellulose aerogel from an aqueous alkali hydroxide-urea solution with the substitution of an organic solvent followed by freeze-drying. For comparison, the synthesized holocellulose aerogels were divided into two groups according to the source of the hydrogel, an upper suspended layer and a bottom concentrated layer of the centrifuged solution of cellulose and NaOH/urea solvents. We investigated the effects of the temperature of the pre-cooled NaOH/urea solution ( i.e., dissolution temperature) on the pore structure and the adsorption capacity of the holocellulose aerogel. A nano-fibrillar network structure of the holocellulose aerogel was observed, with little morphological difference in pore structure for different dissolution temperatures. Both micropores and mesopores were observed in the holocellulose aerogel. The specific surface area of the holocellulose aerogel was generally greater at lower dissolution temperatures. In a series of adsorption tests using methylene blue, the holocellulose aerogel showed the greatest adsorption capacity at the lowest dissolution temperature tested (-2°C). However, the dissolution temperature generally had little effect on the adsorption capacity. The holocellulose aerogel produced from the upper suspended layer of the centrifuged hydrogel solution showed a greater porosity and adsorption capacity than the one produced from the bottom concentrated layer. Overall, the aerogel made by utilizing a delignified tulip tree display a high surface area and a high adsorption property, indicating its possible application in eco-friendly adsorption materials.

Nanoindentation of dry and fluid-saturated micro-porous rocks

NASA Astrophysics Data System (ADS)

Mighani, S.; Bernabe, Y.; Schwartzman, A. F.; Evans, J. B.

2017-12-01

In this report we explore the ability of nanoindentation technique to evaluate the pore-scale solid-fluid interactions in micro-porous rocks. We measure the creep deformation of a porous rock sample over a period of 3 minutes under a constant maximum force. The indentation tip is instrumented with a nano-DMA transducer which efficiently compensates for the thermal drifts. The candidate rock is a carbonate with micro-porous micritic cement. Secondary Electron (SE) images revealed a bimodal pore structure for this rock-type: regions (A) of micritic cement with micropores, and (B) with large grains and vuggy pores. The experiments were performed on dry rock samples as well as saturated with water (1 cp and buffered with 30 ppm calcite powder) and silicone oil (100 cp). Thus, the fluids presented a wide variation in viscosity and chemical reactivity. We then explored the size (maximum forces of 2, 4, and 8 mN) and loading rate (0.2-2 mN/sec) dependency of the observed creep behavior. The amount of total deformation within the 3 minutes of creep showed a uniform increase with a tendency to reach an equilibrium depth with creep rates (dh/h) below 5×10-3. The indentations in the water-saturated carbonate showed a 6-fold decrease in the Young's modulus (from 38 to 6 GPa) and 2-fold increase in creep magnitude (from 59 to 119 nm) compared with the dry indentations. We attribute these large differences to the possible chemical reaction of water and carbonate. This is further confirmed by comparing the hardness values, which showed that water softened the rock matrix by a factor of 4 (from 0.87 to 0.22 GPa). The carbonate sample saturated with oil, on the other hand, showed a higher modulus (47 GPa) and greater hardness (1.39 GPa), while the creep magnitude (31 nm) was half that observed in dry rock. We attribute this behavior to the viscous displacement of the pore fluid during consolidation of the poroelastic matrix. The loading rate-dependency and size (maximum load) sensitivity of the observed creep appear consistent with poroelasticity. We used Agbezuge and Deresiewicz's (1974) solution to derive poroelastic constants based on the recorded amount of creep. The analysis yields estimates of the diffusivity constant of the rock and the equilibrium creep depth. (We would like to acknowledge The U.S. Department of Energy (DOE) for their support)

Methods of synthesizing hydroxyapatite powders and bulk materials

DOEpatents

Luo, Ping

1999-01-12

Methods are provided for producing non-porous controlled morphology hydroxyapatite granules of less than 8 .mu.m by a spray-drying process. Solid or hollow spheres or doughnuts can be formed by controlling the volume fraction and viscosity of the slurry as well as the spray-drying conditions. Methods of providing for homogenous cellular structure hydroxyapatite granules are also provided. Pores or channels or varying size and number can be formed by varying the temperature at which a hydroxyapatite slurry formed in basic, saturated ammonium hydroxide is spray-dried. Methods of providing non-porous controlled morphology hydroxyapatite granules in ammonium hydroxide are also provided. The hydroxyapatite granules and bulk materials formed by these methods are also provided.

Methods of synthesizing hydroxyapatite powders and bulk materials

DOEpatents

Luo, P.

1999-01-12

Methods are provided for producing non-porous controlled morphology hydroxyapatite granules of less than 8 {micro}m by a spray-drying process. Solid or hollow spheres or doughnuts can be formed by controlling the volume fraction and viscosity of the slurry as well as the spray-drying conditions. Methods of providing for homogeneous cellular structure hydroxyapatite granules are also provided. Pores or channels or varying size and number can be formed by varying the temperature at which a hydroxyapatite slurry formed in basic, saturated ammonium hydroxide is spray-dried. Methods of providing non-porous controlled morphology hydroxyapatite granules in ammonium hydroxide are also provided. The hydroxyapatite granules and bulk materials formed by these methods are also provided. 26 figs.

Hydrologic monitoring of a landslide-prone hillslope in the Elliott State Forest, Southern Coast Range, Oregon, 2009-2012

USGS Publications Warehouse

Smith, Joel B.; Godt, Jonathan W.; Baum, Rex L.; Coe, Jeffrey A.; Burns, William J.; Morse, Michael M.; Sener-Kaya, Basak; Kaya, Murat

2014-01-01

The Oregon Coast Range is dissected by numerous unchanneled headwater basins, which can generate shallow landslides and debris flows during heavy or prolonged rainfall. An automated monitoring system was installed in an unchanneled headwater basin to measure rainfall, volumetric water content, groundwater temperature, and pore pressures at 15-minute intervals. The purpose of this report is to describe and present the methods used for the monitoring as well as the preliminary data collected during the period from 2009 to 2012. Observations show a pronounced seasonal variation in volumetric water content and pore pressures. Increases in pore pressures and volumetric water content from dry-season values begin with the onset of the rainy season in the fall (typically early to mid October). High water contents and pore pressures tend to persist throughout the rainy season, which typically ends in May. Heavy or prolonged rainfall during the wet season that falls on already moist soils often generates positive pore pressures that are observed in the deeper instruments. These data provide a record of the basin’s hydrologic response to rainfall and provide a foundation for understanding the conditions that lead to landslide and debris-flow occurrence.

Structure modification of natural zeolite for waste removal application

NASA Astrophysics Data System (ADS)

Widayatno, W. B.

2018-03-01

Tremendous industrialization in the last century has led to the generation of huge amount of waste. One of the recent hot research topics is utilizing any advance materials and methods for waste removal. Natural zeolite as an inexpensive porous material with a high abundance holds a key for efficient waste removal owing to its high surface area. However, the microporous structure of natural zeolite hinders the adsorption of waste with a bigger molecular size. In addition, the recovery of natural zeolite after waste adsorption into its pores should also be considered for continuous utilization of this material. In this study, the porosity of natural zeolite from Tasikmalaya, Indonesia, was hydrothermally-modified in a Teflon-lined autoclave filled with certain pore directing agent such as distilled water, KOH, and NH4OH to obtain hierarchical pore structure. After proper drying process, the as-treated natural zeolite is impregnated with iron cation and heat-treated at specified temperature to get Fe-embedded zeolite structure. XRD observation is carried out to ensure the formation of magnetic phase within the zeolite pores. The analysis results show the formation of maghemite phase (γ-Fe2O3) within the zeolite pore structure.

Development of gelatin/carboxymethyl chitosan/nano-hydroxyapatite composite 3D macroporous scaffold for bone tissue engineering applications.

PubMed

Maji, Somnath; Agarwal, Tarun; Das, Joyjyoti; Maiti, Tapas Kumar

2018-06-01

The present study delineates a relatively simpler approach for fabrication of a macroporous three-dimensional scaffold for bone tissue engineering. The novelty of the work is to obtain a scaffold with macroporosity (interconnected networks) through a combined approach of high stirring induced foaming of the gelatin/carboxymethyl chitosan (CMC)/nano-hydroxyapatite (nHAp) matrix followed by freeze drying. The fabricated macroporous (SGC) scaffold had a greater pore size, higher porosity, higher water retention capacity, slow and sustained enzymatic degradation rate along with higher compressive strength compared to that of non-macroporous (NGC, prepared by conventional freeze drying methodology) scaffold. The biological studies revealed the increased percentage of viability, proliferation, and differentiation as well as higher mineralization of differentiated human Wharton's jelly MSC microtissue (wjhMSC-MT) on SGC as compared to NGC scaffold. RT-PCR also showed enhanced expression level of collagen type I, osteocalcin and Runx2 when seeded on SGC. μCT and histological analysis further revealed a penetration of cellular spheroid to a greater depth in SGC scaffold than NGC scaffold. Furthermore, the effect of cryopreservation on microtissue survival on the three-dimensional construct revealed significant higher viability upon revival in macroporous SGC scaffolds. These results together suggest that high stirring based macroporous scaffolds could have a potential application in bone tissue engineering. Copyright © 2018 Elsevier Ltd. All rights reserved.

Rapid Fabrication of Silver Nanowires through Photoreduction of Silver Nitrate from an Anodic-Aluminum-Oxide Template

NASA Astrophysics Data System (ADS)

Lin, Yu-Hsuan; Chen, Kun-Tso; Ho, Jeng-Rong

2011-06-01

A method for rapidly fabricating dense and high-aspect-ratio silver nanowires, with wire diameter of 200 nm and wire length more than 30 µm, is reported. The fabrication process simply involves filling the silver nitrate solution into the pores of an anodic-aluminum-oxide (AAO) membrane through capillary attraction and irradiating the dried template AAO membrane using a pulsed ArF excimer laser. Through varying the thickness and pore diameter of the employed AAO membrane, the primary dimensions of the targeted silver nanowires can be plainly specified; and, by amending the initial concentration of the silver nitrate solution and adjusting the laser operation parameters, laser fluence and number of laser pulses, the surface morphology and size of the resulting nanowires can be finely regulated. The wire formation mechanism is considered through two stages: the period of precipitation of silver particles from the dried silver nitrate film through the laser-induced photoreduction; and, the phase of clustering, merging and fusing of the reduced particles to form nanowires in the template pores by the thermal energy owing to photothermal effect. This approach is straightforward and takes the advantage that all the fabrication processes can be executed in an ambient environment and at room temperature. In addition, by the excellence in local processing that the laser possesses, this method is suitable for precisely growing nanowires.

Thermal-hydraulic performance of metal foam heat exchangers under dry operating conditions

DOE PAGES

Nawaz, Kashif; Bock, Jessica; Jacobi, Anthony M.

2017-03-14

High porosity metal foams with novel thermal, mechanical, electrical, and acoustic properties are being more widely adopted for application. Due to their large surface-area-to-volume ratio and complex structure which induces better fluid mixing, boundary layer restarting and wake destruction, they hold promise for heat transfer applications. In this study, the thermal-hydraulic performance of open-cell aluminum metal foam heat exchanger has been evaluated. The impact of flow conditions and metal foam geometry on the heat transfer coefficient and gradient have been investigated. Metal foam heat exchanger with same geometry (face area, flow depth and fin dimensions) consisting of four different typemore » of metal foams have been built for the study. Experiments are conducted in a closed-loop wind tunnel at different flow rate under dry operating condition. Metal foams with a smaller pore size (40 PPI) have a larger heat transfer coefficient compared to foams with a larger pore size (5 PPI). However, foams with larger pores result in relatively smaller pressure gradients. Current thermal-hydraulic modeling practices have been reviewed and potential issues have been identified. Permeability and inertia coefficients are determined and compared to data reported in open literature. Finally, on the basis of the new experimental results, correlations are developed relating the foam characteristics and flow conditions through the friction factor f and the Colburn j factor.« less

Thermal-hydraulic performance of metal foam heat exchangers under dry operating conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nawaz, Kashif; Bock, Jessica; Jacobi, Anthony M.

High porosity metal foams with novel thermal, mechanical, electrical, and acoustic properties are being more widely adopted for application. Due to their large surface-area-to-volume ratio and complex structure which induces better fluid mixing, boundary layer restarting and wake destruction, they hold promise for heat transfer applications. In this study, the thermal-hydraulic performance of open-cell aluminum metal foam heat exchanger has been evaluated. The impact of flow conditions and metal foam geometry on the heat transfer coefficient and gradient have been investigated. Metal foam heat exchanger with same geometry (face area, flow depth and fin dimensions) consisting of four different typemore » of metal foams have been built for the study. Experiments are conducted in a closed-loop wind tunnel at different flow rate under dry operating condition. Metal foams with a smaller pore size (40 PPI) have a larger heat transfer coefficient compared to foams with a larger pore size (5 PPI). However, foams with larger pores result in relatively smaller pressure gradients. Current thermal-hydraulic modeling practices have been reviewed and potential issues have been identified. Permeability and inertia coefficients are determined and compared to data reported in open literature. Finally, on the basis of the new experimental results, correlations are developed relating the foam characteristics and flow conditions through the friction factor f and the Colburn j factor.« less

A study of clay pore water and sporopollens for characterizing paleoenvironments in the Hebei Plain, Northern China

NASA Astrophysics Data System (ADS)

Niu, Hong; Liang, Xing; Lu, Guoping; Peng, Fei; Jin, Menggui; Gu, Yansheng

2017-08-01

We developed a clay pore water (CPW) isotopic method for tracing paleoenvironments characterized by sporopollens. The thick clayey layers have the advantage of preserving pore water regardless of whether the water is inherent in the clayey layers or not. Therefore, the clayey layers are a suitable target from which paleoenvironmental information can be extracted. Sediment sporopollens as well as CPW deuterium and oxygen isotopes were investigated in drilling cores obtained from a 130-m borehole at a field site in Hengshui in the North China Plain. Our interpretation of δ18O in CPW was consistent with sporopollens climate indices, indicating that CPW was an effective proxy for obtaining paleoenvironmental information. Sporopollens species were abundant in the cores, but the quantity of each species was low. Furthermore, mean annual temperature and precipitation curves were established using a pollen-climatic response surface model. The results indicated two warm-humid periods (5.2-0 m, 22.6-11 m) and one cold-dry period (8.8-6.4 m) in the Holocene as well as two warm-humid periods (90.6-83 m, 110.6-108.2 m) and three cold-dry periods (approximately 40 m, 66.4-56.8 m, approximately 100 m) in the Late Pleistocene. Data derived from the sporopollens and CPW cumulatively elucidate the environmental change in Northern China.

A pore-scale study of fracture dynamics in rock using X-ray micro-CT under ambient freeze-thaw cycling.

PubMed

De Kock, Tim; Boone, Marijn A; De Schryver, Thomas; Van Stappen, Jeroen; Derluyn, Hannelore; Masschaele, Bert; De Schutter, Geert; Cnudde, Veerle

2015-03-03

Freeze-thaw cycling stresses many environments which include porous media such as soil, rock and concrete. Climate change can expose new regions and subject others to a changing freeze-thaw frequency. Therefore, understanding and predicting the effect of freeze-thaw cycles is important in environmental science, the built environment and cultural heritage preservation. In this paper, we explore the possibilities of state-of-the-art micro-CT in studying the pore scale dynamics related to freezing and thawing. The experiments show the development of a fracture network in a porous limestone when cooling to -9.7 °C, at which an exothermal temperature peak is a proxy for ice crystallization. The dynamics of the fracture network are visualized with a time frame of 80 s. Theoretical assumptions predict that crystallization in these experiments occurs in pores of 6-20.1 nm under transient conditions. Here, the crystallization-induced stress exceeds rock strength when the local crystal fraction in the pores is 4.3%. The location of fractures is strongly related to preferential water uptake paths and rock texture, which are visually identified. Laboratory, continuous X-ray micro-CT scanning opens new perspectives for the pore-scale study of ice crystallization in porous media as well as for environmental processes related to freeze-thaw fracturing.

Modeling Bacteria-Water Interactions in Soil: EPS Dynamics Under Evaporative Conditions

NASA Astrophysics Data System (ADS)

Furrer, J.; Hinestroza, H. F.; Guo, Y. S.; Gage, D. J.; Cho, Y. K.; Shor, L. M.

2017-12-01

The soil habitat represents a major linkage between the water and carbon cycles: the ability of soils to sequester or release carbon is determined primarily by soil moisture. Water retention and distribution in soils controls the abundance and activity of soil microbes. Microbes in turn impact water retention by creating biofilms, composed of extracellular polymeric substances (EPS). We model the effects of bacterial EPS on water retention at the pore scale. We use the lattice Boltzmann method (LBM), a well-established fluid dynamics modeling platform, and modify it to include the effects of water uptake and release by the swelling/shrinking EPS phase. The LB model is implemented in 2-D, with a non-ideal gas equation of state that allows condensation and evaporation of fluid in pore spaces. Soil particles are modeled according to experimentally determined particle size distributions and include realistic pore geometries, in contrast to many soil models which use spherical soil particles for simplicity. Model results are compared with evaporation experiments in soil micromodels and other simpler experimental systems, and model parameters are tuned to match experimental results. Drying behavior and solid-gel contact angle of EPS produced by the soil bacteria Sinorhizobium meliloti has been characterized and compared to the behavior of deionized water under the same conditions. The difference in behavior between the fluids is used to parameterize the model. The model shows excellent qualitative agreement for soil micromodels with both aggregated and non-aggregated particle arrangements under no-EPS conditions, and reproduces realistic drying behavior for EPS. This work represents a multi-disciplinary approach to understanding microbe-soil interactions at the pore scale.

3D reconstruction of the porous microstructure of Al2O3-coatings based on sequentially revealed surface data

NASA Astrophysics Data System (ADS)

Loftfield, Nina; Kästner, Markus; Reithmeier, Eduard

2018-06-01

Local and global liquid transport properties correlate strongly with the morphology of porous materials. Therefore, by characterizing the porous network information is indirectly gained on the materials properties. Properties like the open-porosity are easily accessible with techniques like mercury porosimetry. However, the 3D image reconstruction, destructive or non-destructive, holds advantages like an accurate spatially resolved representation of the investigated material. Common 3D data acquisition is done by x-ray microtomography or a combination of focused ion beam based milling and scanning electron microscopy. In this work a reconstruction approach similar to the latter one is implemented. The porous network is reconstructed based on an alternating process of milling the surface by fly cutting and measuring the surface data with a confocal laser scanning microscope. This has the benefit of reconstructing the pore network on the basis of surface height data, measuring the structure boundaries directly. The stack of milled surface height data needs to be registered and the pore structure to be segmented. The segmented pore structure is connected throughout each height layer and afterwards meshed. The investigated materials are porous surface coatings of aluminum oxide for the usage in tribological pairings.

The origins of microstructure in phase inversion coatings or membranes: Snapshots of the transient from time-sectioning cryo-SEM

NASA Astrophysics Data System (ADS)

Prakash, Sai Sivasankaran

2001-11-01

Time-sectioning cryogenic scanning electron microscopy (cryo-SEM) is a unique method of visualizing how the microstructure of liquid coatings evolves during processing. Time-sectioning means rapidly freezing (nearly) identical specimens at successively later stages of the process; doing this requires that coating and drying be well controlled in the dry phase inversion process, and solvents exchange likewise in the wet phase inversion process. With control, frozen specimens are fractured, etched by limited sublimation, sputter-coated, and imaged at temperatures of ca -175°C. The coatings examined were of cellulose acetate, of high and low molecular weights, and polysulfone in mixed solvents and nonsolvents: acetone and water with cellulose acetate undergoing dry phase inversion; and tetrahydrofuran, dimethylacetamide, ethanol with polysulfone undergoing dry-wet phase inversion. All coatings, cast on silicon substrates, were initially homogeneous. The initial compositions of the high and low molecular weight cellulose acetate ternary solutions were "off-critical" and "near-critical", respectively, connoting their proximities to the critical or plait point of the phase diagram. The initial composition of the polysulfone quaternary solution was located near the binodal of the pseudo-ternary phase diagram. It appeared that as the higher molecular weight cellulose acetate coating dries, it nucleates and grows polymer-poor droplets that coalesce into a bicontinuous structure underlying a thin, dense skin. Bicontinuity of structure was verified by stereomicroscopy of the dry sample. The lower molecular weight cellulose acetate coating phase-separates, seemingly spinodally, directly into a bicontinuous structure whose polymer-rich network, stressed by frustrated in-plane shrinkage, ruptures far beneath the skin in some locales to form macrovoids. When, after partial drying, the polysulfone coating was immersed in a bath of water, a nonsolvent, it appeared to swell in thickness as it phase-separates. A dense skin, thinner than a micron, appeared to overlie a two-phase substructure that is punctuated with pear-shaped macrovoids. At early immersion times, this substructure is visibly bicontinuous or open-celled near the bath-side, and dispersion-like (droplets dispersed in a polymeric matrix) or closed-celled near the substrate-side. Moreover, in the bicontinuous regions, length-scales of the individual phases seem to increase across the coating thickness from the bath-side to the substrate-side. After prolonged immersion, the substructure, excluding the macrovoids, is entirely bicontinuous. The bicontinuity presumably results from a combination of spinodal decomposition and nucleation and growth plus coalescence. Quite strikingly, macrovoids are present exclusively in regions where phases are bicontinuous, and are absent where droplets are dispersed in the polymeric matrix. Evidence suggests that macrovoids result from an instability caused by a progressive rupture of polymer-rich links deeper and deeper beneath the skin, aggravated by stress localization in the rupturing network and a buildup of pressure in the polymer-poor phase (the pore space), as suspected by Grobe and Meyer in 1959.

Sliding-surface-liquefaction of sand-dry ice mixture and submarine landslides

NASA Astrophysics Data System (ADS)

Fukuoka, H.; Tsukui, A.

2010-12-01

In the historic records of off-shore mega-earthquakes along the subduction zone offshore Japan, there are a lot of witnesses about large-scale burning of flammable gas possibly ejected from sea floor. This gas was supposed to be the dissolved methane hydrates (MH), which have been found in the soundings of IODP and other oceanology projects. Since the vast distribution of the BSR in the continental margins, a lot of papers have been published which pointed out the possibilities of that gasification of those hydrates could have triggered gigantic submarine landslides. Global warming or large earthquake or magma intrusion may trigger extremely deep gigantic landslides in continental margins that which could cause catastrophic tsunami. However, recent triaxial compression tests on artificially prepared sand-MH-mixture samples revealed that the they have slightly higher strength than the ones of only sands and MH’s endothermal characteristics may resist against accelerating shear and large-displacement landslides as well. While, the stress-controlled undrained ring shear apparatuses have been developed by Sassa and Fukuoka at Disaster Prevention Research Institute, Kyoto University to reproduce subaerial landslides induced by earthquakes and rainfalls. Using the apparatuses, they found localized liquefaction phenomenon along the deep saturated potential sliding surface due to excess pore pressure generation during the grain crushing induced bulk volume change. This phenomenon was named as “sliding surface liquefaction.” Similar sudden large pore pressure generation was observed in pore pressure control test simulating rain-induced landslides. In this paper, authors examined the shear behavior of the dry sand-dry ice mixture under constant normal stress and shear speed control tests using the latest ring shear apparatus. Sample was mixture of silica sands and dry-ice pellets (frozen carbon-dioxide). Those mixtures are often used for studying the mechanism of the methane hydrates in laboratories because no explosion protection facility is required. In order to prevent rapid gasification, the specimen was prepared without water. Applied total normal stress was 200 kPa and initial normal stress was maintained at about 70 kPa by slightly opening the drainage valve to vent pressured CO2 gas. When the sample was sheared at 30 cm/s, the stress path reached failure line of friction angle of about 37 degrees immediately. However, excess pore air pressure increased soon after and the stress path moved to the origin along the failure line. This means rapid shearing generates frictional heat and it accelerates the gasification of dry ice quickly. On the other hand, crushing of pellets may contribute to increase the total surface area of dry ice and to acceleration of gasification, to some extent. Authors are conducting to examine the velocity weakening characteristics of the samples and upcoming results will give more detail of the mechanism. But this sliding-surface-liquefaction in the mixture supports the possibility of similar accelerating displacement in the sand-MH mixture or boundaries between MH and sand layer induced by certain strong ground motion under sea floor.

Nonlinear transport of soft droplets in pore networks

NASA Astrophysics Data System (ADS)

Vernerey, Franck; Benet Cerda, Eduard; Koo, Kanghyeon

A large number of biological and technological processes depend on the transport of soft colloidal particles through porous media; this includes the transport and separation of cells, viruses or drugs through tissues, membranes and microfluidic devices. In these systems, the interactions between soft particles, background fluid and the surrounding pore space yield complex, nonlinear behaviors such as non-Darcy flows, localization and jamming. We devise a computational strategy to investigate the transport of non-wetting and deformable water droplets in a microfluidic device made of a random distribution of cylindrical obstacles. We first derive scaling laws for the entry of the droplet in a single pore and discuss the role of surface tension, contact angle and size in this process. This information is then used to study the transport of multiple droplets in an obstacle network. We find that when the droplet size is close to the pore size, fluid flow and droplet trafficking strongly interact, leading to local redistributions in pressure fields, intermittent clogging and jamming. Importantly, it is found that the overall droplet and fluid transport display three different scaling regimes depending on the forcing pressure, and that these regimes can be related to droplet properties.

Supported microporous ceramic membranes

DOEpatents

Webster, Elizabeth; Anderson, Marc

1993-01-01

A method for permformation of microporous ceramic membranes onto a porous support includes placing a colloidal suspension of metal or metal oxide particles on one side of the porous support and exposing the other side of the porous support to a drying stream of gas or a reactive gas stream so that the particles are deposited on the drying side of the support as a gel. The gel so deposited can be sintered to form a supported ceramic membrane useful for ultrafiltration, reverse osmosis, or molecular sieving having mean pore sizes less than 100 Angstroms.

Metal oxide membranes for gas separation

DOEpatents

Anderson, Marc A.; Webster, Elizabeth T.; Xu, Qunyin

1994-01-01

A method for permformation of a microporous ceramic membrane onto a porous support includes placing a colloidal suspension of metal oxide particles on one side of the porous support and exposing the other side of the porous support to a drying stream of gas or a reactive gas stream so that the particles are deposited on the drying side of the support as a gel. The gel so deposited can be sintered to form a supported ceramic membrane having mean pore sizes less than 30 Angstroms and useful for ultrafiltration, reverse osmosis, or gas separation.

Supported microporous ceramic membranes

DOEpatents

Webster, E.; Anderson, M.

1993-12-14

A method for the formation of microporous ceramic membranes onto a porous support includes placing a colloidal suspension of metal or metal oxide particles on one side of the porous support and exposing the other side of the porous support to a drying stream of gas or a reactive gas stream so that the particles are deposited on the drying side of the support as a gel. The gel so deposited can be sintered to form a supported ceramic membrane useful for ultrafiltration, reverse osmosis, or molecular sieving having mean pore sizes less than 100 Angstroms. 4 figures.

Metal oxide membranes for gas separation

DOEpatents

Anderson, M.A.; Webster, E.T.; Xu, Q.

1994-08-30

A method for formation of a microporous ceramic membrane onto a porous support includes placing a colloidal suspension of metal oxide particles on one side of the porous support and exposing the other side of the porous support to a drying stream of gas or a reactive gas stream so that the particles are deposited on the drying side of the support as a gel. The gel so deposited can be sintered to form a supported ceramic membrane having mean pore sizes less than 30 Angstroms and useful for ultrafiltration, reverse osmosis, or gas separation. 4 figs.

Synthesis and characterization of high-surface-area millimeter-sized silica beads with hierarchical multi-modal pore structure by the addition of agar

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, Yosep; Choi, Junhyun; Tong, Meiping, E-mail: tongmeiping@iee.pku.edu.cn

2014-04-01

Millimeter-sized spherical silica foams (SSFs) with hierarchical multi-modal pore structure featuring high specific surface area and ordered mesoporous frameworks were successfully prepared using aqueous agar addition, foaming and drop-in-oil processes. The pore-related properties of the prepared spherical silica (SSs) and SSFs were systematically characterized by field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), small-angle X-ray diffraction (SAXRD), Hg intrusion porosimetry, and N{sub 2} adsorption–desorption isotherm measurements. Improvements in the BET surface area and total pore volume were observed at 504 m{sup 2} g{sup −1} and 5.45 cm{sup 3} g{sup −1}, respectively, after an agar addition and foaming process. Despitemore » the increase in the BET surface area, the mesopore wall thickness and the pore size of the mesopores generated from the block copolymer with agar addition were unchanged based on the SAXRD, TEM, and BJH methods. The SSFs prepared in the present study were confirmed to have improved BET surface area and micropore volume through the agar loading, and to exhibit interconnected 3-dimensional network macropore structure leading to the enhancement of total porosity and BET surface area via the foaming process. - Highlights: • Millimeter-sized spherical silica foams (SSFs) are successfully prepared. • SSFs exhibit high BET surface area and ordered hierarchical pore structure. • Agar addition improves BET surface area and micropore volume of SSFs. • Foaming process generates interconnected 3-D network macropore structure of SSFs.« less

Pore-scale simulation of calcium carbonate precipitation and dissolution under highly supersaturated conditions in a microfludic pore network

NASA Astrophysics Data System (ADS)

Yoon, H.; Dewers, T. A.; Valocchi, A. J.; Werth, C. J.

2011-12-01

Dissolved CO2 during geological CO2 storage may react with minerals in fractured rocks or confined aquifers and cause mineral precipitation. The overall rate of reaction can be affected by coupled processes among hydrodynamics, transport, and reactions at pore-scale. Pore-scale models of coupled fluid flow, reactive transport, and CaCO3 precipitation and dissolution are applied to account for transient experimental results of CaCO3 precipitation and dissolution under highly supersaturated conditions in a microfluidic pore network (i.e., micromodel). Pore-scale experiments in the micromodel are used as a basis for understanding coupled physics of systems perturbed by geological CO2 injection. In the micromodel, precipitation is induced by transverse mixing along the centerline in pore bodies. Overall, the pore-scale model qualitatively captured the governing physics of reactions such as precipitate morphology, precipitation rate, and maximum precipitation area in first few pore spaces. In particular, we found that proper estimation of the effective diffusion coefficient and the reactive surface area is necessary to adequately simulate precipitation and dissolution rates. As the model domain increases, the effect of flow patterns affected by precipitation on the overall reaction rate also increases. The model is also applied to account for the effect of different reaction rate laws on mineral precipitation and dissolution at pore-scale. Reaction rate laws tested include the linear rate law, nonlinear power law, and newly-developed rate law based on in-situ measurements at nano scale in the literature. Progress on novel methods for upscaling pore-scale models for reactive transport are discussed, and are being applied to mineral precipitation patterns observed in natural analogues. H.Y. and T. D. were supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001114. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Hydrocarbon saturation determination using acoustic velocities obtained through casing

DOEpatents

Moos, Daniel

2010-03-09

Compressional and shear velocities of earth formations are measured through casing. The determined compressional and shear velocities are used in a two component mixing model to provides improved quantitative values for the solid, the dry frame, and the pore compressibility. These are used in determination of hydrocarbon saturation.

Building solids inside nano-space: from confined amorphous through confined solvate to confined 'metastable' polymorph.

PubMed

Nartowski, K P; Tedder, J; Braun, D E; Fábián, L; Khimyak, Y Z

2015-10-14

The nanocrystallisation of complex molecules inside mesoporous hosts and control over the resulting structure is a significant challenge. To date the largest organic molecule crystallised inside the nano-pores is a known pharmaceutical intermediate - ROY (259.3 g mol(-1)). In this work we demonstrate smart manipulation of the phase of a larger confined pharmaceutical - indomethacin (IMC, 357.8 g mol(-1)), a substance with known conformational flexibility and complex polymorphic behaviour. We show the detailed structural analysis and the control of solid state transformations of encapsulated molecules inside the pores of mesoscopic cellular foam (MCF, pore size ca. 29 nm) and controlled pore glass (CPG, pore size ca. 55 nm). Starting from confined amorphous IMC we drive crystallisation into a confined methanol solvate, which upon vacuum drying leads to the stabilised rare form V of IMC inside the MCF host. In contrast to the pure form, encapsulated form V does not transform into a more stable polymorph upon heating. The size of the constraining pores and the drug concentration within the pores determine whether the amorphous state of the drug is stabilised or it recrystallises into confined nanocrystals. The work presents, in a critical manner, an application of complementary techniques (DSC, PXRD, solid-state NMR, N2 adsorption) to confirm unambiguously the phase transitions under confinement and offers a comprehensive strategy towards the formation and control of nano-crystalline encapsulated organic solids.

Research Opportunities for Materials with Ultrafine Microstructures

DTIC Science & Technology

1989-12-31

monodispersed particles and hydrothermal synthesis of composites. Of recent interest in polymeric materials has been the development of rigid-rod...network with uniformly large pores (see Figure 2). An acidic DCCA, such as oxalic acid, in contrast, results in a somewhat smaller-scale network

Micro-fabric damages in Boom Clay inferred from cryo-BIB-SEM experiment: recent results

NASA Astrophysics Data System (ADS)

Desbois, Guillaume; Schmatz, Joyce; Klaver, Jop; Urai, Janos L.

2017-04-01

The Boom Clay is considered as a potential host rock in Belgium for nuclear waste disposal in a deep geological formation. One of the keys to understand the long-term performance of such a host rock is the fundamental understanding of coupling between microstructural evolution, poromechanical behaviour and the state of hydration of the system. At in situ conditions, Boom Clay is a nearly water-saturated (>94%) clay-rich geomaterial. Subsequently, for measurement of mechanical and transport properties in laboratory, cores of Boom Clay are vacuum-packed in Al-coated-poly-ethylene barrier foil to be best preserved at original hydric state. Because clay microstructures are very sensitive to dehydration, the validity of investigations done on such preserved or/and dried samples is often questionable. Desbois et al. (2009, 2013, 2014) showed the possibility to image fluid-filled porosity in Boom Clay, by using the FIB-cryo-SEM (FIB: Focussed Ion Beam) and FIB-cryo-SEM (BIB: Broad Ion Beam) techniques. However, surprisingly in Desbois et al. (2014), BIB-cryo-SEM experiments on Boom Clay, shown that the majority of the pores were fluid-free, contrasting with result in Desbois et al. (2009). In Desbois et al. (2014), several reasons were discussed to explain such discrepancies. The likely ones are the sealing efficiency of the Al-barrier foil at long term and the volume expansion due to the release of in-situ stress after core extraction, contributing both to dehydration and microfabric damage. This contribution presents the newest results based on cryo-BIB-SEM. Small pieces (30 mm3) of Boom Clay were preserved in liquid nitrogen after the core extraction at the MOL/Dessel Underground Research Laboratory in Belgium. A maximum of ten minutes time span was achieved between opening the core, the sub-sample extraction and the quenching of sub-samples in liquid nitrogen. First results show that all pores visible at cryo-SEM resolution are water saturated. However, water-filled micro-cracks are also present and they are interpreted to result from the releasing of in-situ stress after the core extraction. Moreover, the comparison of the clay micro-fabrics in the same preserved and dried sample suggests collapsing of the clay aggregates' pores in dried sample. These newest results are still preliminary and they need to be analysed in more details. However, if they are confirmed they may be important input to discuss about the validity of measurement of mechanical and transport properties done in laboratory. Desbois G., Urai J.L. and Kukla P.A. (2009). Morphology of the pore space in claystones - evidence from BIB/FIB ion beam sectioning and cryo-SEM observations. E-Earth, 4 :15-22. Desbois G., J.L. Urai, F. Pérez-Willard, Z. Radi, S. van Offern, I. Burkart, P.A. Kukla, U. Wollenberg (2013). Argon broad ion beam tomography in a cryogenic scanning electron microscope: a novel tool for the investigation of representative microstructures in sedimentary rocks containing pore fluid. Journal of Microscopy, 249(3): 215-235. Desbois G., Urai J.L., Hemes S., Brassinnes S., De Craen M., Sillen X. (2014). Nanometer-scale pore fluid distribution and drying damage in preserved clay cores from Belgian clay formations inferred by BIB-cryo-SEM. Engineering Geology, 170:117-131.

Upscaling of spectral induced polarization response using random tube networks

NASA Astrophysics Data System (ADS)

Maineult, Alexis; Revil, André; Camerlynck, Christian; Florsch, Nicolas; Titov, Konstantin

2017-05-01

In order to upscale the induced polarization (IP) response of porous media, from the pore scale to the sample scale, we implement a procedure to compute the macroscopic complex resistivity response of random tube networks. A network is made of a 2-D square-meshed grid of connected tubes, which obey to a given tube radius distribution. In a simplified approach, the electrical impedance of each tube follows a local Pelton resistivity model, with identical resistivity, chargeability and Cole-Cole exponent values for all the tubes-only the time constant varies, as it depends on the radius of each tube and on a diffusion coefficient also identical for all the tubes. By solving the conservation law for the electrical charge, the macroscopic IP response of the network is obtained. We fit successfully the macroscopic complex resistivity also by a Pelton resistivity model. Simulations on uncorrelated and correlated networks, for which the tube radius distribution is so that the decimal logarithm of the radius is normally distributed, evidence that the local and macroscopic model parameters are the same, except the Cole-Cole exponent: its macroscopic value diminishes with increasing heterogeneity (i.e. with increasing standard deviation of the radius distribution), compared to its local value. The methodology is also applied to six siliciclastic rock samples, for which the pore radius distributions from mercury porosimetry are available. These samples exhibit the same behaviour as synthetic media, that is, the macroscopic Cole-Cole exponent is always lower than the local one. As a conclusion, the pore network method seems to be a promising tool for studying the upscaling of the IP response of porous media.

Ultrasonic sensing of powder densification

NASA Technical Reports Server (NTRS)

Lu, Yichi; Wadley, Haydn N. G.; Parthasarathi, Sanjai

1992-01-01

An independent scattering theory has been applied to the interpretation of ultrasonic velocity measurements made on porous metal samples produced either by a cold or a high-temperature compaction process. The results suggest that the pores in both processes are not spherical, an aspect ration of 1:3 fitting best with the data for low (less than 4 percent) pore volume fractions. For the hot compacted powders, the pores are smooth due to active diffusional processes during processing. For these types of voids, the results can be extended to a pore fraction of 10 percent, at which point voids form an interconnected network that violates the model assumptions. The cold pressed samples are not as well predicted by the theory because of poor particle bonding.

Exceptional arsenic (III,V) removal performance of highly porous, nanostructured ZrO2 spheres for fixed bed reactors and the full-scale system modeling.

PubMed

Cui, Hang; Su, Yu; Li, Qi; Gao, Shian; Shang, Jian Ku

2013-10-15

Highly porous, nanostructured zirconium oxide spheres were fabricated from ZrO2 nanoparticles with the assistance of agar powder to form spheres with size at millimeter level followed with a heat treatment at 450 °C to remove agar network, which provided a simple, low-cost, and safe process for the synthesis of ZrO2 spheres. These ZrO2 spheres had a dual-pore structure, in which interconnected macropores were beneficial for liquid transport and the mesopores could largely increase their surface area (about 98 m(2)/g) for effective contact with arsenic species in water. These ZrO2 spheres demonstrated an even better arsenic removal performance on both As(III) and As(V) than ZrO2 nanoparticles, and could be readily applied to commonly used fixed-bed adsorption reactors in the industry. A short bed adsorbent test was conducted to validate the calculated external mass transport coefficient and the pore diffusion coefficient. The performance of full-scale fixed bed systems with these ZrO2 spheres as the adsorber was estimated by the validated pore surface diffusion modeling. With the empty bed contact time (EBCT) at 10 min and the initial arsenic concentration at 30 ppb, the number of bed volumes that could be treated by these dry ZrO2 spheres reached ~255,000 BVs and ~271,000 BVs for As(III) and As(V), respectively, until the maximum contaminant level of 10 ppb was reached. These ZrO2 spheres are non-toxic, highly stable, and resistant to acid and alkali, have a high arsenic adsorption capacity, and could be easily adapted for various arsenic removal apparatus. Thus, these ZrO2 spheres may have a promising potential for their application in water treatment practice. Copyright © 2013 Elsevier Ltd. All rights reserved.

Laboratory triggering of stick-slip events by oscillatory loading in the presence of pore fluid with implications for physics of tectonic tremor

USGS Publications Warehouse

Bartlow, Noel M.; Lockner, David A.; Beeler, Nicholas M.

2012-01-01

The physical mechanism by which the low-frequency earthquakes (LFEs) that make up portions of tectonic (also called non-volcanic) tremor are created is poorly understood. In many areas of the world, tectonic tremor and LFEs appear to be strongly tidally modulated, whereas ordinary earthquakes are not. Anomalous seismic wave speeds, interpreted as high pore fluid pressure, have been observed in regions that generate tremor. Here we build upon previous laboratory studies that investigated the response of stick-slip on artificial faults to oscillatory, tide-like loading. These previous experiments were carried out using room-dry samples of Westerly granite, at one effective stress. Here we augment these results with new experiments on Westerly granite, with the addition of varying effective stress using pore fluid at two pressures. We find that raising pore pressure, thereby lowering effective stress can significantly increase the degree of correlation of stick-slip to oscillatory loading. We also find other pore fluid effects that become important at higher frequencies, when the period of oscillation is comparable to the diffusion time of pore fluid into the fault. These results help constrain the conditions at depth that give rise to tidally modulated LFEs, providing confirmation of the effective pressure law for triggering and insights into why tremor is tidally modulated while earthquakes are at best only weakly modulated.

Solubility of hydrogen in metals and its effect of pore-formation and embrittlement. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Shahani, H. R.

1984-01-01

The effect of alloying elements on hydrogen solubility were determined by evaluating solubility equations and interaction coefficients. The solubility of dry hydrogen at one atmosphere was investigated in liquid aluminum, Al-Ti, Al-Si, Al-Fe, liquid gold, Au-Cu, and Au-Pd. The design of rapid heating and high pressure casting furnaces used in meta foam experiments is discussed as well as the mechanism of precipitation of pores in melts, and the effect of hydrogen on the shrinkage porosity of Al-Cu and Al-Si alloys. Hydrogen embrittlement in iron base alloys is also examined.

Changes in pore structure of coal caused by coal-to-gas bioconversion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Rui; Liu, Shimin; Bahadur, Jitendra

Microbial enhanced coalbed methane (ME-CBM) recovery is critically examined as a viable technology for natural gas recovery from coalbed methane (CBM) reservoirs. Since the majority of gas-in-place (GIP) is stored as an adsorbed phase in fine pores of coal matrix, the nano-pore structure directly influences gas storage and transport properties. Only limited studies have quantified the alteration of the nano-pore structure due to ME-CBM treatment. This study examines the evolution of the pore structure using a combination of small angle X-ray scattering (SAXS), low-pressure N 2 and CO 2 adsorption (LPGA) and high-pressure methane adsorption methods. The results show thatmore » the surface fractal dimension decreases for the two bioconverted coals compared to the untreated coal. After bio-treatment, the mesopore surface area and pore volume decrease with the average pore diameter increases, while the micropore surface area increases with pore volume decreases. Both inaccessible meso-/micropore size distributions decrease after bioconversion, while the accessible micropore size distribution increases, making a portion of closed micropore network accessible. In addition, the methane adsorption capacities increase after bio-treatment, which is confirmed by the increase of micropore surface area. A conceptual physical model of methanogenesis is proposed based on the evolution of the pore structure.« less

Changes in pore structure of coal caused by coal-to-gas bioconversion

DOE PAGES

Zhang, Rui; Liu, Shimin; Bahadur, Jitendra; ...

2017-06-19

Microbial enhanced coalbed methane (ME-CBM) recovery is critically examined as a viable technology for natural gas recovery from coalbed methane (CBM) reservoirs. Since the majority of gas-in-place (GIP) is stored as an adsorbed phase in fine pores of coal matrix, the nano-pore structure directly influences gas storage and transport properties. Only limited studies have quantified the alteration of the nano-pore structure due to ME-CBM treatment. This study examines the evolution of the pore structure using a combination of small angle X-ray scattering (SAXS), low-pressure N 2 and CO 2 adsorption (LPGA) and high-pressure methane adsorption methods. The results show thatmore » the surface fractal dimension decreases for the two bioconverted coals compared to the untreated coal. After bio-treatment, the mesopore surface area and pore volume decrease with the average pore diameter increases, while the micropore surface area increases with pore volume decreases. Both inaccessible meso-/micropore size distributions decrease after bioconversion, while the accessible micropore size distribution increases, making a portion of closed micropore network accessible. In addition, the methane adsorption capacities increase after bio-treatment, which is confirmed by the increase of micropore surface area. A conceptual physical model of methanogenesis is proposed based on the evolution of the pore structure.« less

Water permeability in hydrate-bearing sediments: A pore-scale study

NASA Astrophysics Data System (ADS)

Dai, Sheng; Seol, Yongkoo

2014-06-01

Permeability is a critical parameter governing methane flux and fluid flow in hydrate-bearing sediments; however, limited valid data are available due to experimental challenges. Here we investigate the relationship between apparent water permeability (k') and hydrate saturation (Sh), accounting for hydrate pore-scale growth habit and meso-scale heterogeneity. Results from capillary tube models rely on cross-sectional tube shapes and hydrate pore habits, thus are appropriate only for sediments with uniform hydrate distribution and known hydrate pore character. Given our pore network modeling results showing that accumulating hydrate in sediments decreases sediment porosity and increases hydraulic tortuosity, we propose a modified Kozeny-Carman model to characterize water permeability in hydrate-bearing sediments. This model agrees well with experimental results and can be easily implemented in reservoir simulators with no empirical variables other than Sh. Results are also relevant to flow through other natural sediments that undergo diagenesis, salt precipitation, or bio-clogging.

Fabrication of hydroxyapatite ceramics with controlled pore characteristics by slip casting.

PubMed

Yao, Xiumin; Tan, Shouhong; Jiang, Dongliang

2005-02-01

Porous hydroxyapatite (HAp) ceramics with controlled pore characteristics were fabricated using slip casting method by mixing PMMA with HAp powder. The optimum conditions of HAp slip for slip casting was achieved by employing various experimental techniques, zeta potential and sedimentation, as a function of pH of the slips in the pH range of 4-12. HAp suspensions displayed an absolute maximum in zeta potential values and a minimum in sedimentation height at pH 11.5. The optimal amount of dispersant for the HAp suspensions was found at 1.0 wt% according to the viscosity of 25 vol% HAp slurry. The rheological behaviour of HAp slurry displays a shear-thinning behavior without thixotropy, which is needed in slip casting processing. The pore characteristics of sintered porous hydroxyapatite bioceramics can be controlled by added PMMA particle size and volume. The obtained ceramics exhibit higher strength than those obtained by dry pressing.

Radical re-appraisal of water structure in hydrophilic confinement.

PubMed

Soper, Alan K

2013-12-18

The structure of water confined in MCM41 silica cylindrical pores is studied to determine whether confined water is simply a version of the bulk liquid which can be substantially supercooled without crystallisation. A combination of total neutron scattering from the porous silica, both wet and dry, and computer simulation using a realistic model of the scattering substrate is used. The water in the pore is divided into three regions: core, interfacial and overlap. The average local densities of water in these simulations are found to be about 20% lower than bulk water density, while the density in the core region is below, but closer to, the bulk density. There is a decrease in both local and core densities when the temperature is lowered from 298 K to 210 K. The radical proposal is made here that water in hydrophilic confinement is under significant tension, around -100 MPa, inside the pore.

Tunable Impedance Spectroscopy Sensors via Selective Nanoporous Materials.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nenoff, Tina M.; Small, Leo J

Impedance spectroscopy was leveraged to directly detect the sorption of I 2 by selective adsorption into nanoporous metal organic frameworks (MOF). Films of three different types of MOF frameworks, respectively, were drop cast onto platinum interdigitated electrodes, dried, and exposed to gaseous I 2 at 25, 40, or 70 C. The MOF frameworks varied in topology from small pores (equivalent to I 2 diameter) to large pore frameworks. The combination of the chemistry of the framework and pore size dictated quantity and kinetics of I 2 adsorption. Air, argon, methanol, and water were found to produce minimal changes in ZIF-8more » impedance. Independent of MOF framework characteristics, all resultant sensors showed high response to I 2 in air. As an example of sensor output, I 2 was readily detected at 25 C in air within 720 s of exposure, using an un-optimized sensor geometry with a small pored MOF. Further optimization of sensor geometry, decreasing MOF film thicknesses and maximizing sensor capacitance, will enable faster detection of trace I 2 .« less

Dynamic Pore-Scale Imaging of Reactive Transport in Heterogeneous Carbonates at Reservior Conditions

NASA Astrophysics Data System (ADS)

Menke, Hannah; Bijeljic, Branko; Andrew, Matthew; Blunt, Martin

2014-05-01

Sequestering carbon in deep geologic formations is one way of reducing anthropogenic CO2 emissions. Carbon capture, Utilization, and Storage (CCUS) in carbonate reservoirs has the added benefit of mobilizing more oil for extraction, increasing oil reservoir yield, and generating revenue while also mitigating climate change. The magnitude, speed, and type of dissolution are dependent the intrinsic properties of the rock. Understanding how small changes in the pore structure affect dissolution is paramount for successful predictive modelling both on the pore-scale and for up-scaled reservoir simulations. We propose an experimental method whereby both 'Pink Beam' synchrotron radiation and a Micro-CT lab source are used in dynamic X-ray microtomography to investigate the pore structure changes in carbonate rocks of varying heterogeneity at high temperatures and pressures. Four carbonate rock types were studied, two relatively homogeneous carbonates, Ketton and Mt. Gambier, and two very heterogeneous carbonates, Estalliades and Portland Basebed. Each rock type was imaged under the same reservoir and flow conditions to gain insight into the impact of heterogeneity. A 4-mm carbonate core was injected with CO2-saturated brine at 10 MPa and 50oC for 2 hours. Depending on sample heterogeneity and X-ray source, tomographic images were taken at between 30-second and 20-minute time-resolutions and a 4-micron spatial resolution during injection. Changes in porosity, permeability, and structure were obtained by first binning and filtering the images, then binarizing them with watershed segmentation, and finally extracting a pore/throat network. Furthermore, pore-scale flow modelling was performed directly on the binarized image and used to track velocity distributions as the pore network evolved. Significant differences in dissolution type and magnitude were found for each rock type. The most homogeneous carbonate, Ketton, was seen to have predominately uniform dissolution with minor dissolution rate differences between the pores and pore throats. This was not true for the heterogeneous carbonates, Estalliades and Portland Basebed, which formed wormholes. Pore-scale modelling of flow directly on the voxels showed the differences in the evolution of complex flow fields with changes in dissolution regime. The PDFs of normalized velocity for uniform dissolution showed that the maximum pore velocity within the system decreased as dissolution occurred. This is due to dissolution enlarging pores and pore throats. However, in the wormholing regime, there was a large increase in maximum velocity once the wormhole broke through the length of the core and a preferential flow path was created. Additionally, this study serves as a unique benchmark for pore-scale reactive transport modelling directly on the binarized Micro-CT images. This dynamic pore-scale imaging method offers advantages in helping fully explain the dominant physical and chemical processes at the pore scale so that they may be up-scaled to the reservoir scale for increased accuracy in model prediction.

Hybrid response surface methodology-artificial neural network optimization of drying process of banana slices in a forced convective dryer.

PubMed

Taheri-Garavand, Amin; Karimi, Fatemeh; Karimi, Mahmoud; Lotfi, Valiullah; Khoobbakht, Golmohammad

2018-06-01

The aim of the study is to fit models for predicting surfaces using the response surface methodology and the artificial neural network to optimize for obtaining the maximum acceptability using desirability functions methodology in a hot air drying process of banana slices. The drying air temperature, air velocity, and drying time were chosen as independent factors and moisture content, drying rate, energy efficiency, and exergy efficiency were dependent variables or responses in the mentioned drying process. A rotatable central composite design as an adequate method was used to develop models for the responses in the response surface methodology. Moreover, isoresponse contour plots were useful to predict the results by performing only a limited set of experiments. The optimum operating conditions obtained from the artificial neural network models were moisture content 0.14 g/g, drying rate 1.03 g water/g h, energy efficiency 0.61, and exergy efficiency 0.91, when the air temperature, air velocity, and drying time values were equal to -0.42 (74.2 ℃), 1.00 (1.50 m/s), and -0.17 (2.50 h) in the coded units, respectively.

The NEST Dry-Run Mode: Efficient Dynamic Analysis of Neuronal Network Simulation Code.

PubMed

Kunkel, Susanne; Schenck, Wolfram

2017-01-01

NEST is a simulator for spiking neuronal networks that commits to a general purpose approach: It allows for high flexibility in the design of network models, and its applications range from small-scale simulations on laptops to brain-scale simulations on supercomputers. Hence, developers need to test their code for various use cases and ensure that changes to code do not impair scalability. However, running a full set of benchmarks on a supercomputer takes up precious compute-time resources and can entail long queuing times. Here, we present the NEST dry-run mode, which enables comprehensive dynamic code analysis without requiring access to high-performance computing facilities. A dry-run simulation is carried out by a single process, which performs all simulation steps except communication as if it was part of a parallel environment with many processes. We show that measurements of memory usage and runtime of neuronal network simulations closely match the corresponding dry-run data. Furthermore, we demonstrate the successful application of the dry-run mode in the areas of profiling and performance modeling.

The NEST Dry-Run Mode: Efficient Dynamic Analysis of Neuronal Network Simulation Code

PubMed Central

Kunkel, Susanne; Schenck, Wolfram

2017-01-01

NEST is a simulator for spiking neuronal networks that commits to a general purpose approach: It allows for high flexibility in the design of network models, and its applications range from small-scale simulations on laptops to brain-scale simulations on supercomputers. Hence, developers need to test their code for various use cases and ensure that changes to code do not impair scalability. However, running a full set of benchmarks on a supercomputer takes up precious compute-time resources and can entail long queuing times. Here, we present the NEST dry-run mode, which enables comprehensive dynamic code analysis without requiring access to high-performance computing facilities. A dry-run simulation is carried out by a single process, which performs all simulation steps except communication as if it was part of a parallel environment with many processes. We show that measurements of memory usage and runtime of neuronal network simulations closely match the corresponding dry-run data. Furthermore, we demonstrate the successful application of the dry-run mode in the areas of profiling and performance modeling. PMID:28701946

Aerogel Projects Ongoing in MSFC's Engineering Directorate

NASA Technical Reports Server (NTRS)

Shular, David A.; Smithers, Gweneth A.; Plawsky, Joel L.; Whitaker, Ann F. (Technical Monitor)

2000-01-01

When we speak of an aerogel material, we are referring more to process and structure am to a specific substance. Aerogel, considered the lightest solid material, has been made from silica for seventy years. Resorcinol-formaldehyde, organic aerogels have been developed more recently. However, aerogel can be made from almost any type of substance, even lead. Because an aerogel is mostly air (about 99 %), the solid substance used will affect the weight very little. The term "aerogel" connotes the sol-gel process used to manufacture the material. The aerogel begins as a liquid "sol," becomes a solid "alcogel," and is then dried to become an "aerogel." The final product has a unique structure, useful for exploitation. It is an "open pore" system with nano-sized particles and pores, has very high surface area, and is highly interconnected. Besides low weight, aerogels have ultimate (lowest) values in other properties: thermal conductivity, refractive index, sound speed, and dielectric constant. Aerogels were first prepared in 1931 by Steven Kistler, who used a supercritical drying step to replace the liquid in a gel with air, preserving the structure (1). Kistler's procedure involved a water-to-alcohol exchange step; in the 1970's, this step was eliminated when a French investigator introduced the use of tetramethylorthosilicate. Still, alcohol drying involved dangerously high temperatures and pressures. In the 1980's, the Microstructured Materials Group at Berkeley Laboratory found that the alcohol in the gel could be replaced with liquid carbon dioxide before supercritical drying, which greatly improved safety (2). 'Me most recent major contribution has been that of Deshpande, Smith and Brinker in New Mexico, who are working to eliminate the supercritical drying step (3). When aerogels were first being developed, they were evaporatively dried. However, the wet gel, when dried, underwent severe shrinkage and cracking; this product was termed "xerogel." When the autoclave drying step was introduced, the final product was without cracks and showed only minimal shrinkage; this product was termed "aerogel." In the 1990's, Deshpande, Smith and Brinker developed an evaporative drying procedure in which the wet gel is chemically "capped" so that the material, which undergoes shrinkage, springs back to its original size when evaporatively dried. This new type of xerogel, while uncracked and almost the same size as the wet gel, differs from the autoclave-dried product in that it is less porous (approximately 70%, as compared to 99% for aerogels).

Drying Affects the Fiber Network in Low Molecular Weight Hydrogels

PubMed Central

2017-01-01

Low molecular weight gels are formed by the self-assembly of a suitable small molecule gelator into a three-dimensional network of fibrous structures. The gel properties are determined by the fiber structures, the number and type of cross-links and the distribution of the fibers and cross-links in space. Probing these structures and cross-links is difficult. Many reports rely on microscopy of dried gels (xerogels), where the solvent is removed prior to imaging. The assumption is made that this has little effect on the structures, but it is not clear that this assumption is always (or ever) valid. Here, we use small angle neutron scattering (SANS) to probe low molecular weight hydrogels formed by the self-assembly of dipeptides. We compare scattering data for wet and dried gels, as well as following the drying process. We show that the assumption that drying does not affect the network is not always correct. PMID:28631478

A mesocosm study of the effects of wet-dry cycles on nutrient release from constructed wetlands in agricultural landscapes.

PubMed

Smith, Allyson S; Jacinthe, Pierre-Andre

2014-01-01

Given the projection that wet-dry periods will be more frequent in the US Midwest, a study was conducted to understand the impact of these hydro-climatic alterations on nutrient dynamics in wetlands constructed on former croplands in the region. Soil cores were collected from two constructed wetlands and a wooded riparian area (surface: 0-20 cm; subsurface: 40-60 cm) downslope from an agricultural field. Cores were either kept moist or subjected to a 5-week drying treatment, after which all cores were flooded for 36 days. Initial nitrate flux was significantly (p < 0.001) higher in the dry than in the moist treatment (44.5 vs. 1.9 mg N m(-2) per day), likely due to mineralization of organic matter. The NO3(-) released was rapidly denitrified (N2O flux: 18.9 mg N m(-2) per day), except in the subsurface soil cores in which processing of available N (N2O flux: 0.33 mg N m(-2) per day) was limited by low microbial activity (4 times lower CO2 production rate). The dry treatment also resulted in significantly (p < 0.01) higher inorganic P (Pi) flux (3.1 versus 1 mg P m(-2) per day in moist cores), with water-extractable soil P being the best predictor (r(2): 0.93, p < 0.03) of that flux. Despite a decline in redox potential (as low as -36.4 mv) and progressive increase in pore-water dissolved Fe, no relationship between floodwater Pi and dissolved Fe was observed, suggesting either limited contribution of reductive dissolution to Pi dynamics or rapid adsorption of the Pi released within the cores. Compared to the moist cores, geochemical modeling showed a consistent shift toward greater solubility of the calcium-phosphate minerals controlling pore-water Pi concentration in the dry treatment cores. These results suggest that dissolution of Ca-phosphate minerals could be a key factor controlling Pi mobility in constructed wetlands subjected to wet-dry cycles.

Multi-scale characterization of pore evolution in a combustion metamorphic complex, Hatrurim basin, Israel: Combining (ultra) small-angle neutron scattering and image analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Hsiu-Wen; Anovitz, Lawrence; Burg, Avihu

Backscattered scanning electron micrograph and ultra small- and small-angle neutron scattering data have been combined to provide statistically meaningful data on the pore/grain structure and pore evolution of combustion metamorphic complexes from the Hatrurim basin, Israel. Three processes, anti-sintering roughening, alteration of protolith (dehydration, decarbonation, and oxidation) and crystallization of high-temperature minerals, occurred simultaneously, leading to significant changes in observed pore/grain structures. Pore structures in the protoliths, and in lowand high-grade metamorphic rocks show surface (Ds) and mass (Dm) pore fractal geometries with gradual increases in both Ds and Dm values as a function of metamorphic grade. This suggests thatmore » increases in pore volume and formation of less branching pore networks are accompanied by a roughening of pore/grain interfaces. Additionally, pore evolution during combustion metamorphism is also characterized by reduced contributions from small-scale pores to the cumulative porosity in the high-grade rocks. At high temperatures, small-scale pores may be preferentially closed by the formation of high-temperature minerals, producing a rougher morphology with increasing temperature. Alternatively, large-scale pores may develop at the expense of small-scale pores. These observations (pore fractal geometry and cumulative porosity) indicate that the evolution of pore/grain structures is correlated with the growth of high-temperature phases and is a consequence of the energy balance between pore/grain surface energy and energy arising from heterogeneous phase contacts. The apparent pore volume density further suggests that the localized time/temperature development of the high-grade Hatrurim rocks is not simply an extension of that of the low-grade rocks. The former likely represents the "hot spots (burning foci)" in the overall metamorphic terrain while the latter may represent contact aureoles.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vyas, S.N.; Patwardhan, S.R.; Vijayalakshmi, S.

Adsorption on carbon molecular sieves (CMS) prepared by coke deposition has become an interesting area of adsorption due to its microporous nature and favorable separation factor on size and shape selectivity basis for many gaseous systems. In the present work CMS was synthesized from coconut shell through three major steps, namely, carbonization, activation, and coke deposition by hydrocarbon cracking. The crushed, washed, and sieved granules of coconut shell (particle size 2--3 mm) were pretreated with sodium silicate solution and oven-dried at 150 C to create the inorganic sites necessary for coke deposition. Carbonization and activation of the dried granules weremore » carried out at 800 C, for 30 min each. The activated char thus produced was subjected to hydrocarbon cracking at 600 C for periods varying from 30 to 180 min. The product samples were characterized in terms of adsorption isotherm, kinetic adsorption curve, surface area, pore volume, pore size distribution, and characteristic energy for adsorption by using O[sub 2], N[sub 2], C[sub 2]H[sub 2], CO[sub 2], C[sub 3]H[sub 6], and CH[sub 4].« less

Structural evolution of nanoporous silica thin films studied by positron annihilation spectroscopy and Fourier transform infrared spectroscopy

NASA Astrophysics Data System (ADS)

Patel, N.; Mariazzi, S.; Toniutti, L.; Checchetto, R.; Miotello, A.; Dirè, S.; Brusa, R. S.

2007-09-01

Three series of silica thin films with thicknesses in the 300 nm range were deposited by spin coating on Si substrates using different compositions of the sol precursors. Film samples were thermally treated in static air at temperatures ranging from 300 to 900 °C. The effect of sol precursors and thermal treatment temperature on the film porosity was analysed by Fourier transform infrared (FTIR) spectroscopy, depth profiling with positron annihilation spectroscopy (DP-PAS) and the analysis of the capacitance-voltage (C-V) characteristic. The maximum of the total porosity was found to occur at a temperature of 600 °C when removal of porogen and OH groups was completed. Film densification due to the collapsing of the pores was observed after drying at 900 °C. DP-PAS provides evidence that the increase in the total porosity is related to a progressive increase in the pore size. The increase in the pore size never gives rise to the onset of connected porosity. In the silica film samples prepared using a low acidity sol precursor, the pore size is always lower than 1 nm. By increasing the acid catalyst ratio in the sol, larger pores are formed. Pores with size larger than 2.3 nm can be obtained by adding porogen to the sol. In each series of silica film samples the shift of the antisymmetric Si-O-Si transversal optical (TO3) mode upon thermal treatment correlates with a change of the pore size as evidenced by DP-PAS analysis. The pore microstructure of the three series of silica films is different at all the examined treatment temperatures and depends on the composition of the precursor sol.

A nanoscale perspective on the effects of transverse microprestress on drying creep of nanoporous solids

NASA Astrophysics Data System (ADS)

Sinko, Robert; Bažant, Zdeněk P.; Keten, Sinan

2018-01-01

The Pickett effect describes the excess non-additive strain developed during drying of a nanoporous solid material under creep. One explanation for its origins, developed using micromechanical models, is the progressive relaxation of internally developed microprestress. However, these models have not explicitly considered the effects of this microprestress on nanoscale energy barriers that govern the relative motion and displacement between nanopore walls during deformation. Here, we evaluate the nanoscale effects of transverse microprestresses on the drying creep behaviour of a nanoscale slit pore using coarse-grained molecular dynamics. We find that the underlying energy barrier depends exponentially on the transverse microprestress, which is attributed to changes in the effective viscosity and degree of nanoconfinement of molecules in the water interlayer. Specifically, as the transverse microprestress is relaxed (i.e. its magnitude decreases), the activation energy barrier is reduced, thereby leading to an acceleration of the creep behaviour and a stronger Pickett effect. Based on our simulation results, we introduce a new microprestress-dependent energy term into our existing Arrhenius model, which describes the relative displacement of pore walls as a function of the underlying activation energy barriers. Our findings further verify the existing micromechanical theories for the origin of the Pickett effect and establish a quantitative relationship between the transverse microprestress and the intensity of the Pickett effect.

Absorption of water and lubricating oils into porous nylon

NASA Technical Reports Server (NTRS)

Bertrand, P. A.

1995-01-01

Oil and water absorption from air into sintered porous nylon can be described by infiltration into the pores of the material. This process can be modeled by a diffusion-like mechanism. For water absorption, we find a formal diffusion coefficient of 1.5 x 10(exp -4)sq cm/min when the nylon is initially dry. The diffusion coefficient is 4 x 10(exp -6)sq cm/min when the nylon is oil-impregnated prior to air exposure. In a 52% RH atmosphere, dry nylon absorbs 3% w/w water, and oil-impregnated nylon absorbs 0.6% w/w water. For oil absorption there are three steps: (1) surface absorption and infiltration into (2) larger and (3) smaller pores. Surface absorption is too fast to be measured in these experiments. The diffusion coefficient for the second step is 6 x 10(exp -4)sq cm/min for SRG-60 oil into dry nylon and 4 x 10(exp -4)sq cm/min for air-equilibrated nylon. The diffusion coefficient for the third step is about 1 x 10(exp -6)sq cm/min for both cases. The total amount of oil absorbed is 31% w/w. The interaction between water and nylon is not as strong as that between water and cotton-phenolic: oil can replace water, and only a small amount of water can enter previously oil-impregnated nylon.

Influence of internal pore architecture on biological and mechanical properties of three-dimensional fiber deposited scaffolds for bone regeneration.

PubMed

Ostrowska, Barbara; Di Luca, Andrea; Szlazak, Karol; Moroni, Lorenzo; Swieszkowski, Wojciech

2016-04-01

Fused deposition modeling has been used to fabricate three-dimensional (3D) scaffolds for tissue engineering applications, because it allows to tailor their pore network. Despite the proven flexibility in doing so, a limited amount of studies have been performed to evaluate whether specific pore shapes have an influence on cell activity and tissue formation. Our study aimed at investigating the influence of internal pore architecture on the biological and mechanical properties of 3D scaffolds seeded with mesenchymal stromal cells. Polycaprolactone scaffolds with six different geometries were fabricated. The 3D samples were manufactured with different lay-down pattern of the fibers by varying the layer deposition angle from 0°/15°/30°, to 0°/30°/60°, 0°/45°/90°, 0°/60°/120°, 0°/75°/150°, and 0°/90°/180°. The scaffolds were investigated by scanning electron microscopy and micro computed tomographical analysis and displayed a fully interconnected pore network. Cell proliferation and differentiation toward the osteogenic lineage were evaluated by DNA, alkaline phosphatase activity, and polymerase chain reaction. The obtained scaffolds had structures with open porosity (50%-60%) and interconnected pores ranging from 380 to 400 µm. Changing the angle deposition affected significantly the mechanical properties of the scaffolds. With increasing the angle deposition between successive layers, the elastic modulus increased as well. Cellular studies also showed influence of the internal architecture on cell adhesion and proliferation within the 3D construct, yet limited influence on cell differentiation was observed. © 2016 Wiley Periodicals, Inc.

High Fidelity Computational Analysis of CO2 Trapping at Pore Scales

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Vinod

2013-07-13

With an alarming rise in carbon dioxide (CO2) emission from anthropogenic sources, CO2 sequestration has become an attractive choice to mitigate the emission. Some popular storage media for CO{sub 2} are oil reservoirs, deep coal-bed, and deep oceanic-beds. These have been used for the long term CO{sub 2} storage. Due to special lowering viscosity and surface tension property of CO{sub 2}, it has been widely used for enhanced oil recovery. The sites for CO{sub 2} sequestration or enhanced oil recovery mostly consist of porous rocks. Lack of knowledge of molecular mobility under confinement and molecule-surface interactions between CO2 and naturalmore » porous media results in generally governed by unpredictable absorption kinetics and total absorption capacity for injected fluids, and therefore, constitutes barriers to the deployment of this technology. Therefore, it is important to understand the flow dynamics of CO{sub 2} through the porous microstructures at the finest scale (pore-scale) to accurately predict the storage potential and long-term dynamics of the sequestered CO{sub 2}. This report discusses about pore-network flow modeling approach using variational method and analyzes simulated results this method simulations at pore-scales for idealized network and using Berea Sandstone CT scanned images. Variational method provides a promising way to study the kinetic behavior and storage potential at the pore scale in the presence of other phases. The current study validates variational solutions for single and two-phase Newtonian and single phase non-Newtonian flow through angular pores for special geometries whose analytical and/or empirical solutions are known. The hydraulic conductance for single phase flow through a triangular duct was also validated against empirical results derived from lubricant theory.« less

Concerted Motions Networking Pores and Distant Ferroxidase Centers Enable Bacterioferritin Function and Iron Traffic£ξ

PubMed Central

Yao, Huili; Rui, Huan; Kumar, Ritesh; Eshelman, Kate; Lovell, Scott; Battaile, Kevin P.; Im, Wonpil; Rivera, Mario

2015-01-01

X-ray crystallography, molecular dynamics (MD) simulations and biochemistry were utilized to investigate the effect of introducing hydrophobic interactions in the 4-fold (N148L and Q151L) and B-pores (D34F) of Pseudomonas aeruginosa bacterioferritin B (BfrB) on BfrB function. The structures show only local structural perturbations and confirm the anticipated hydrophobic interactions. Surprisingly, structures obtained after soaking crystals in Fe2+-containing crystallization solution revealed that although iron loads into the ferroxidase centers of the mutants, the side chains of ferroxidase ligands E51 and H130 do not reorganize to bind the iron ions, as is seen in the wt BfrB structures. Similar experiments with a double mutant (C89S/K96C) prepared to introduce changes outside the pores show competent ferroxidase centers that function akin to those in wt BfrB. MD simulations comparing wt BfrB with the D34F and N148L mutants show that the mutants exhibit significantly reduced flexibility, and reveal a network of concerted motions linking ferroxidase centers and 4-fold and B-pores, which are important for imparting ferroxidase centers in BfrB with the required flexibility to function efficiently. In agreement, the efficiency of Fe2+ oxidation and uptake of the 4-fold and B-pore mutants in solution is significantly compromised relative to wt or C89S/K96C BfrB. Finally, our structures show a large number of previously unknown iron binding sites in the interior cavity and B-pores of BfrB, which reveal in unprecedented detail conduits followed by iron and phosphate ions across the BfrB shell, as well as paths in the interior cavity that may facilitate nucleation of the iron phosphate mineral. PMID:25640193

X-ray Computed Tomography and Pore Network Modeling to Assess the Impact of Biochar on Saturated Hydraulic Conductivity of Stormwater Infiltration Media

NASA Astrophysics Data System (ADS)

Imhoff, P. T.; Nakhli, S. A. A.; Mills, G.; Yudi, Y.; Abera, K.; Williams, R.; Manahiloh, K. N.; Willson, C. S.

2017-12-01

Biochar has been proposed as an amendment to stormwater infiltration media to enhance pollutant capture (metals, organics) or transformation (e.g., nitrate). Because stormwater media must maintain sufficient infiltration capacity, it is critical that biochar amendment not reduce saturated hydraulic conductivity. We present experimental measurements of saturated hydraulic conductivity for mixtures of wood biochar, sieved to various size fractions, and uniform sands or bioretention media (mixtures of sand, clay, and sawdust). While the influence of biochar on the inter particle pore volume of the mixtures explained most changes in hydraulic conductivity, for mixtures containing large biochar particles results were unexpected. For example, while large biochar particles (2 - 4.75 mm) increased inter particle porosity from 0.35 to 0.48 for a sand/biochar mixture, hydraulic conductivity decreased from 820 ± 90 cm/h to 323 ± 2 cm/h. To understand this and other unusual data, biochar was doped with 3% CsCl, mixed with uniform sand using different packing techniques, and analyzed with X-ray computed tomography to assess biochar distribution and pore structure. Depending on packing technique, biochar particles were either segregated or uniformly mixed, which influenced pore structure. Biochar content and inter particle pore volume determined from X-ray images were in excellent agreement with experimental data (< 5% difference). Grain-based algorithms were then used to generate physically-representative pore networks, and single-phase permeability models were employed to estimate saturated hydraulic conductivity of sand and biochar-amended sand packings for specimens prepared with different packing techniques. Results from these analyses will be presented and compared with experimental measurements to elucidate the mechanisms by which large biochar particles alter the saturated hydraulic conductivity of engineered media.

Mesoporous carbon spheres with controlled porosity for high-performance lithium-sulfur batteries

NASA Astrophysics Data System (ADS)

Wang, Dexian; Fu, Aiping; Li, Hongliang; Wang, Yiqian; Guo, Peizhi; Liu, Jingquan; Zhao, Xiu Song

2015-07-01

Mesoporous carbon (MC) spheres with hierarchical pores, controlled pore volume and high specific surface areas have been prepared by a mass-producible spray drying assisted template method using sodium alginate as carbon precursor and commercial colloidal silica particles as hard template. The resulting MC spheres, possessing hierarchical pores in the range of 3-30 nm, are employed as conductive matrices for the preparation of cathode materials for lithium-sulfur batteries. A high pressure induced one-step impregnation of elemental sulfur into the pore of the MC spheres has been exploited. The electrochemical performances of sulfur-impregnated MC spheres (S-MC) derived from MC spheres with different pore volume and specific surface area but with the same sulfur loading ratio of 60 wt% (S-MC-X-60) have been investigated in details. The S-MC-4-60 composite cathode material displayed a high initial discharge capacity of 1388 mAhg-1 and a good cycling stability of 857 mAhg-1 after 100 cycles at 0.2C, and shows also excellent rate capability of 864 mAhg-1 at 2C. More importantly, the sulfur loading content in MC-4 spheres can reach as high as 80%, and it still can deliver a capacity of 569 mAhg-1 after 100 cycles at 0.2C.

Hybrid Drying of Carrot Preliminary Processed with Ultrasonically Assisted Osmotic Dehydration

PubMed Central

2017-01-01

Summary In this paper the kinetics of osmotic dehydration of carrot and the influence of this pretreatment on the post-drying processes and the quality of obtained products are analysed. Osmotic dehydration was carried out in the aqueous fructose solution in two different ways: with and without ultrasound assistance. In the first part of the research, the kinetics of osmotic dehydration was analysed on the basis of osmotic dewatering rate, water loss and solid gain. Next, the effective time of dehydration was determined and in the second part of research samples were initially dehydrated for 30 min and dried. Five different procedures of drying were established on the grounds of convective method enhanced with microwave and infrared radiation. The influence of osmotic dehydration on the drying kinetics and final product quality was analysed. It was found that it did not influence the drying kinetics significantly but positively affected the final product quality. Negligible influence on the drying kinetics was attributed to solid uptake, which may block the pores, hindering heat and mass transfer. It was also concluded that the application of microwave and/or infrared radiation during convective drying significantly influenced the kinetics of the final stage of drying. A proper combination of aforementioned techniques of hybrid drying allows reducing the drying time. Differences between the particular dehydration methods and drying schedules were discussed. PMID:28867949

A new method of evaluating tight gas sands pore structure from nuclear magnetic resonance (NMR) logs

NASA Astrophysics Data System (ADS)

Xiao, Liang; Mao, Zhi-qiang; Xie, Xiu-hong

2016-04-01

Tight gas sands always display such characteristics of ultra-low porosity, permeability, high irreducible water, low resistivity contrast, complicated pore structure and strong heterogeneity, these make that the conventional methods are invalid. Many effective gas bearing formations are considered as dry zones or water saturated layers, and cannot be identified and exploited. To improve tight gas sands evaluation, the best method is quantitative characterizing rock pore structure. The mercury injection capillary pressure (MICP) curves are advantageous in predicting formation pore structure. However, the MICP experimental measurements are limited due to the environment and economy factors, this leads formation pore structure cannot be consecutively evaluated. Nuclear magnetic resonance (NMR) logs are considered to be promising in evaluating rock pore structure. Generally, to consecutively quantitatively evaluate tight gas sands pore structure, the best method is constructing pseudo Pc curves from NMR logs. In this paper, based on the analysis of lab experimental results for 20 core samples, which were drilled from tight gas sandstone reservoirs of Sichuan basin, and simultaneously applied for lab MICP and NMR measurements, the relationships of piecewise power function between nuclear magnetic resonance (NMR) transverse relaxation T2 time and pore-throat radius Rc are established. A novel method, which is used to transform NMR reverse cumulative curve as pseudo capillary pressure (Pc) curve is proposed, and the corresponding model is established based on formation classification. By using this model, formation pseudo Pc curves can be consecutively synthesized. The pore throat radius distribution, and pore structure evaluation parameters, such as the average pore throat radius (Rm), the threshold pressure (Pd), the maximum pore throat radius (Rmax) and so on, can also be precisely extracted. After this method is extended into field applications, several tight gas sandstone reservoirs are processed, and the predicted results are compared with core derived results. Good consistency between evaluated results with core derived results illustrates the dependability of the proposed method. Comparing with the previous methods, this presented model is much more theoretical, and the applicability is much improved. Combining with the evaluated results, our target tight gas sands are well evaluated, and many potential gas-bearing layers are effectively identified.

The Oxidation of AlN in Dry and Wet Oxygen

NASA Technical Reports Server (NTRS)

Opila, Elizabeth; Humphrey, Donald; Jacobson, Nathan; Yoshio, Tetsuo; Oda, Kohei

1998-01-01

The oxidation kinetics of AlN containing 3.5 wt% Y2O3 were studied by thermogravimetric analysis in dry oxygen and 10% H2O/balance oxygen at temperatures between 1000 and 1200 C for times between 48 and 100 h. The oxidation kinetics for AlN in dry oxygen were parabolic and of approximately the same magnitude and temperature dependence as other alumina forming materials. In this case, diffusion of oxygen and/or aluminum through the alumina scale is the rate limiting mechanism. The oxidation kinetics for AlN in wet oxygen were nearly linear and much more rapid than rates observed in dry oxygen. Numerous micropores were observed in the alumina formed on AIN in wet oxygen. These pores provide a fast path for oxygen transport. The linear kinetics observed in this case suggest that the interface reaction rate of AlN with wet oxygen is the oxidation rate limiting step.

Adsorptive Water Removal from Dichloromethane and Vapor-Phase Regeneration of a Molecular Sieve 3A Packed Bed

PubMed Central

2017-01-01

The drying of dichloromethane with a molecular sieve 3A packed bed process is modeled and experimentally verified. In the process, the dichloromethane is dried in the liquid phase and the adsorbent is regenerated by water desorption with dried dichloromethane product in the vapor phase. Adsorption equilibrium experiments show that dichloromethane does not compete with water adsorption, because of size exclusion; the pure water vapor isotherm from literature provides an accurate representation of the experiments. The breakthrough curves are adequately described by a mathematical model that includes external mass transfer, pore diffusion, and surface diffusion. During the desorption step, the main heat transfer mechanism is the condensation of the superheated dichloromethane vapor. The regeneration time is shortened significantly by external bed heating. Cyclic steady-state experiments demonstrate the feasibility of this novel, zero-emission drying process. PMID:28539701

Characterization of a gel in the cell wall to elucidate the paradoxical shrinkage of tension wood.

PubMed

Clair, Bruno; Gril, Joseph; Di Renzo, Francesco; Yamamoto, Hiroyuki; Quignard, Françoise

2008-02-01

Wood behavior is characterized by high sensibility to humidity and strongly anisotropic properties. The drying shrinkage along the fibers, usually small due to the reinforcing action of cellulosic microfibrils, is surprisingly high in the so-called tension wood, produced by trees to respond to strong reorientation requirements. In this study, nitrogen adsorption-desorption isotherms of supercritically dried tension wood and normal wood show that the tension wood cell wall has a gel-like structure characterized by a pore surface more than 30 times higher than that in normal wood. Syneresis of the tension wood gel explains its paradoxical drying shrinkage. This result could help to reduce technological problems during drying. Potential applications in biomechanics and biomimetics are worth investigating, considering that, in living trees, tension wood produces tensile growth stresses 10 times higher than that of normal wood.

Development of hierarchical, tunable pore size polymer foams for ICF targets

DOE PAGES

Hamilton, Christopher E.; Lee, Matthew Nicholson; Parra-Vasquez, A. Nicholas Gerardo

2016-08-01

In this study, one of the great challenges of inertial confinement fusion experiments is poor understanding of the effects of reactant heterogeneity on fusion reactions. The Marble campaign, conceived at Los Alamos National Laboratory, aims to gather new insights into this issue by utilizing target capsules containing polymer foams of variable pore sizes, tunable over an order of magnitude. Here, we describe recent and ongoing progress in the development of CH and CH/CD polymer foams in support of Marble. Hierarchical and tunable pore sizes have been achieved by utilizing a sacrificial porogen template within an open-celled poly(divinylbenzene) or poly(divinylbenzene-co-styrene) aerogelmore » matrix, resulting in low-density foams (~30 mg/ml) with continuous multimodal pore networks.« less

Dual FIB-SEM 3D Imaging and Lattice Boltzmann Modeling of Porosimetry and Multiphase Flow in Chalk

NASA Astrophysics Data System (ADS)

Rinehart, A. J.; Yoon, H.; Dewers, T. A.; Heath, J. E.; Petrusak, R.

2010-12-01

Mercury intrusion porosimetry (MIP) is an often-applied technique for determining pore throat distributions and seal analysis of fine-grained rocks. Due to closure effects, potential pore collapse, and complex pore network topologies, MIP data interpretation can be ambiguous, and often biased toward smaller pores in the distribution. We apply 3D imaging techniques and lattice-Boltzmann modeling in interpreting MIP data for samples of the Cretaceous Selma Group Chalk. In the Mississippi Interior Salt Basin, the Selma Chalk is the apparent seal for oil and gas fields in the underlying Eutaw Fm., and, where unfractured, the Selma Chalk is one of the regional-scale seals identified by the Southeast Regional Carbon Sequestration Partnership for CO2 injection sites. Dual focused ion - scanning electron beam and laser scanning confocal microscopy methods are used for 3D imaging of nanometer-to-micron scale microcrack and pore distributions in the Selma Chalk. A combination of image analysis software is used to obtain geometric pore body and throat distributions and other topological properties, which are compared to MIP results. 3D data sets of pore-microfracture networks are used in Lattice Boltzmann simulations of drainage (wetting fluid displaced by non-wetting fluid via the Shan-Chen algorithm), which in turn are used to model MIP procedures. Results are used in interpreting MIP results, understanding microfracture-matrix interaction during multiphase flow, and seal analysis for underground CO2 storage. This work was supported by the US Department of Energy, Office of Basic Energy Sciences as part of an Energy Frontier Research Center. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

Characterizing 3-D flow velocity in evolving pore networks driven by CaCO3 precipitation and dissolution

NASA Astrophysics Data System (ADS)

Chojnicki, K. N.; Yoon, H.; Martinez, M. J.

2015-12-01

Understanding reactive flow in geomaterials is important for optimizing geologic carbon storage practices, such as using pore space efficiently. Flow paths can be complex in large degrees of geologic heterogeneities across scales. In addition, local heterogeneity can evolve as reactive transport processes alter the pore-scale morphology. For example, dissolved carbon dioxide may react with minerals in fractured rocks, confined aquifers, or faults, resulting in heterogeneous cementation (and/or dissolution) and evolving flow conditions. Both path and flow complexities are important and poorly characterized, making it difficult to determine their evolution with traditional 2-D transport models. Here we characterize the development of 3-D pore-scale flow with an evolving pore configuration due to calcium carbonate (CaCO3) precipitation and dissolution. A simple pattern of a microfluidic pore network is used initially and pore structures will become more complex due to precipitation and dissolution processes. At several stages of precipitation and dissolution, we directly visualize 3-D velocity vectors using micro particle image velocimetry and a laser scanning confocal microscope. Measured 3-D velocity vectors are then compared to 3-D simulated flow fields which will be used to simulate reactive transport. Our findings will highlight the importance of the 3-D flow dynamics and its impact on estimating reactive surface area over time. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. This material is based upon work supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001114.

Simulation of solute transport through heterogeneous networks: analysis using the method of moments and the statistics of local transport characteristics.

PubMed

Li, Min; Qi, Tao; Bernabé, Yves; Zhao, Jinzhou; Wang, Ying; Wang, Dong; Wang, Zheming

2018-02-28

We used a time domain random walk approach to simulate passive solute transport in networks. In individual pores, solute transport was modeled as a combination of Poiseuille flow and Taylor dispersion. The solute plume data were interpreted via the method of moments. Analysis of the first and second moments showed that the longitudinal dispersivity increased with increasing coefficient of variation of the pore radii CV and decreasing pore coordination number Z. The third moment was negative and its magnitude grew linearly with time, meaning that the simulated dispersion was intrinsically non-Fickian. The statistics of the Eulerian mean fluid velocities [Formula: see text], the Taylor dispersion coefficients [Formula: see text] and the transit times [Formula: see text] were very complex and strongly affected by CV and Z. In particular, the probability of occurrence of negative velocities grew with increasing CV and decreasing Z. Hence, backward and forward transit times had to be distinguished. The high-τ branch of the transit-times probability curves had a power law form associated to non-Fickian behavior. However, the exponent was insensitive to pore connectivity, although variations of Z affected the third moment growth. Thus, we conclude that both the low- and high-τ branches played a role in generating the observed non-Fickian behavior.

The Status of Water in Swelling Shales: An Insight from the Water Retention Properties of the Callovo-Oxfordian Claystone

NASA Astrophysics Data System (ADS)

Menaceur, Hamza; Delage, Pierre; Tang, Anh Minh; Talandier, Jean

2016-12-01

The Callovo-Oxfordian (COx) claystone is considered in France as a possible host rock for the disposal of high-level long-lived radioactive waste at great depth. During the operational phase, the walls of the galleries and of the disposal cells will be successively subjected to desaturation induced by ventilation followed by resaturation once the galleries are closed. To better understand this phenomenon, a sound understanding of the water retention properties of the COx claystone is necessary. Following a previous study by the same group, this paper presents an investigation of microstructure changes in COx claystone under suction changes. Microstructure was investigated by means of mercury intrusion porosimetry tests on freeze-dried specimens previously submitted to various suctions. Along the drying path, the initial microstructure, characterised by a well-classified unimodal pore population around a mean diameter value of 32 nm, slightly changed with the same shape of the PSD curve and slightly moved towards smaller diameters (27-28 nm) at suctions of 150 and 331 MPa, respectively. The infra-porosity too small to be intruded by mercury (diameter smaller than 5.5 nm) reduced from 4.3 to 3.3 %. Oven drying reduced the mean diameter to 20 nm and the infra-porosity to 1 %. Wetting up to 9 MPa suction leads to saturation with no significant change in the PSD curve, whereas wetting at zero suction gave rise to the appearance of a large pore population resulting from the development of cracks with width of several micrometres, together with an enlargement of the initial pore population above the mean diameter. The concepts describing the step hydration of smectites (by the successive placement within the clay platelets along the smectite faces of 1, 2, 3 and 4 layers of water molecules with respect to the suction applied) appeared relevant to better understand the changes in microstructure of the COx claystone under suction changes. This also allowed to better define the status of water in claystones and shales containing smectite, with a distinction made between the water adsorbed within the clay platelets, and the free inter-platelet water involved in hydromechanical couplings through changes in pore pressure and water transfers.

Multiscale modeling of fluid flow and mass transport

NASA Astrophysics Data System (ADS)

Masuoka, K.; Yamamoto, H.; Bijeljic, B.; Lin, Q.; Blunt, M. J.

2017-12-01

In recent years, there are some reports on a simulation of fluid flow in pore spaces of rocks using Navier-Stokes equations. These studies mostly adopt a X-ray CT to create 3-D numerical grids of the pores in micro-scale. However, results may be of low accuracy when the rock has a large pore size distribution, because pores, whose size is smaller than resolution of the X-ray CT may be neglected. We recently found out by tracer tests in a laboratory using a brine saturated Ryukyu limestone and inject fresh water that a decrease of chloride concentration took longer time. This phenomenon can be explained due to weak connectivity of the porous networks. Therefore, it is important to simulate entire pore spaces even those of very small sizes in which diffusion is dominant. We have developed a new methodology for multi-level modeling for pore scale fluid flow in porous media. The approach is to combine pore-scale analysis with Darcy-flow analysis using two types of X-ray CT images in different resolutions. Results of the numerical simulations showed a close match with the experimental results. The proposed methodology is an enhancement for analyzing mass transport and flow phenomena in rocks with complicated pore structure.

Pore Helices Play a Dynamic Role as Integrators of Domain Motion during Kv11.1 Channel Inactivation Gating*

PubMed Central

Perry, Matthew D.; Ng, Chai Ann; Vandenberg, Jamie I.

2013-01-01

Proteins that form ion-selective pores in the membrane of cells are integral to many rapid signaling processes, including regulating the rhythm of the heartbeat. In potassium channels, the selectivity filter is critical for both endowing an exquisite selectivity for potassium ions, as well as for controlling the flow of ions through the pore. Subtle rearrangements in the complex hydrogen-bond network that link the selectivity filter to the surrounding pore helices differentiate conducting (open) from nonconducting (inactivated) conformations of the channel. Recent studies suggest that beyond the selectivity filter, inactivation involves widespread rearrangements of the channel protein. Here, we use rate equilibrium free energy relationship analysis to probe the structural changes that occur during selectivity filter gating in Kv11.1 channels, at near atomic resolution. We show that the pore helix plays a crucial dynamic role as a bidirectional interface during selectivity filter gating. We also define the molecular bases of the energetic coupling between the pore helix and outer helix of the pore domain that occurs early in the transition from open to inactivated states, as well as the coupling between the pore helix and inner helix late in the transition. Our data demonstrate that the pore helices are more than just static structural elements supporting the integrity of the selectivity filter; instead they play a crucial dynamic role during selectivity filter gating. PMID:23471968

Numerous nanopores developed in organo-clay complexes during the shale formations

NASA Astrophysics Data System (ADS)

Wang, Q.; Wang, T.; Lu, H.; Liao, J.

2017-12-01

Shale gas as new energy resource is either stored in nano pores and microfractures or absorbed on the surface of kerogen and clay aggregate (Chalmers et al., 2012). Nano pores developed in organic matters is very important, because these organic pores have better connectivity than inorganic pores (Loucks et al., 2012) and can form an effective pore system where shale gas flows dominantly (Curtis et al., 2010). In order to figure out how the organic pores is affected by shale compositions, we conduct in-situ FE-SEM and EDS analysis on organic-rich Longmaxi shales. The data indicate that 1) organic matter, mixed with clay minerals, can form an organo-clay complex containing many nanopores; 2)furthermore, larger organic pores are developed in organo-clay complexes with higher clay content than in those with lower clay content(Wang et al., 2017). It seems that the presence of organo-clay complex raises the heterogeneous than pure organic matters. Organo-clay complex may bring in lots of intergranular nanopores between organic matter and clay minerals. Another potential interpretation is that clay minerals may influence kerogen thermal decomposition, generation of hydrocarbons and thus the development of organic pores. The presence of numerous nanopores in organo-clay complexes may promote the connectivity of the pore network and enhance the hydrocarbon production efficiency for shale gas field.

Pore-Scale X-ray Micro-CT Imaging and Analysis of Oil Shales

NASA Astrophysics Data System (ADS)

Saif, T.

2015-12-01

The pore structure and the connectivity of the pore space during the pyrolysis of oil shales are important characteristics which determine hydrocarbon flow behaviour and ultimate recovery. We study the effect of temperature on the evolution of pore space and subsequent permeability on five oil shale samples: (1) Vernal Utah United States, (2) El Lajjun Al Karak Jordan, (3) Gladstone Queensland Australia (4) Fushun China and (5) Kimmerdige United Kingdom. Oil Shale cores of 5mm in diameter were pyrolized at 300, 400 and 500 °C. 3D imaging of 5mm diameter core samples was performed at 1μm voxel resolution using X-ray micro computed tomography (CT) and the evolution of the pore structures were characterized. The experimental results indicate that the thermal decomposition of kerogen at high temperatures is a major factor causing micro-scale changes in the internal structure of oil shales. At the early stage of pyrolysis, micron-scale heterogeneous pores were formed and with a further increase in temperature, the pores expanded and became interconnected by fractures. Permeability for each oil shale sample at each temperature was computed by simulation directly on the image voxels and by pore network extraction and simulation. Future work will investigate different samples and pursue insitu micro-CT imaging of oil shale pyrolysis to characterize the time evolution of the pore space.

Nuclear pore complex tethers to the cytoskeleton.

PubMed

Goldberg, Martin W

2017-08-01

The nuclear envelope is tethered to the cytoskeleton. The best known attachments of all elements of the cytoskeleton are via the so-called LINC complex. However, the nuclear pore complexes, which mediate the transport of soluble and membrane bound molecules, are also linked to the microtubule network, primarily via motor proteins (dynein and kinesins) which are linked, most importantly, to the cytoplasmic filament protein of the nuclear pore complex, Nup358, by the adaptor BicD2. The evidence for such linkages and possible roles in nuclear migration, cell cycle control, nuclear transport and cell architecture are discussed. Copyright © 2017. Published by Elsevier Ltd.

Multiscale modelling of dual-porosity porous media; a computational pore-scale study for flow and solute transport

NASA Astrophysics Data System (ADS)

de Vries, Enno T.; Raoof, Amir; van Genuchten, Martinus Th.

2017-07-01

Many environmental and agricultural applications involve the transport of water and dissolved constituents through aggregated soil profiles, or porous media that are structured, fractured or macroporous in other ways. During the past several decades, various process-based macroscopic models have been used to simulate contaminant transport in such media. Many of these models consider advective-dispersive transport through relatively large inter-aggregate pore domains, while exchange with the smaller intra-aggregate pores is assumed to be controlled by diffusion. Exchange of solute between the two domains is often represented using a first-order mass transfer coefficient, which is commonly obtained by fitting to observed data. This study aims to understand and quantify the solute exchange term by applying a dual-porosity pore-scale network model to relatively large domains, and analysing the pore-scale results in terms of the classical dual-porosity (mobile-immobile) transport formulation. We examined the effects of key parameters (notably aggregate porosity and aggregate permeability) on the main dual-porosity model parameters, i.e., the mobile water fraction (ϕm) and the mass transfer coefficient (α). Results were obtained for a wide range of aggregate porosities (between 0.082 and 0.700). The effect of aggregate permeability was explored by varying pore throat sizes within the aggregates. Solute breakthrough curves (BTCs) obtained with the pore-scale network model at several locations along the domain were analysed using analytical solutions of the dual-porosity model to obtain estimates of ϕm and α. An increase in aggregate porosity was found to decrease ϕm and increase α, leading to considerable tailing in the BTCs. Changes in the aggregate pore throat size affected the relative flow velocity between the intra- and inter-aggregate domains. Higher flow velocities within the aggregates caused a change in the transport regime from diffusion dominated to more advection dominated. This change increased the exchange rate of solutes between the mobile and immobile domains, with a related increase in the value of the mass transfer coefficient and less tailing in the BTCs.

Transverse thermal conductivity of porous materials made from aligned nano- and microcylindrical pores

NASA Astrophysics Data System (ADS)

Prasher, Ravi

2006-09-01

Nanoporous and microporous materials made from aligned cylindrical pores play important roles in present technologies and will play even bigger roles in future technologies. The insight into the phonon thermal conductivity of these materials is important and relevant in many technologies and applications. Since the mean free path of phonons can be comparable to the pore size and interpore distance, diffusion-approximation based effective medium models cannot be used to predict the thermal conductivity of these materials. Strictly speaking, the Boltzmann transport equation (BTE) must be solved to capture the ballistic nature of thermal transport; however, solving BTE in such a complex network of pores is impractical. As an alternative, we propose an approximate ballistic-diffusive microscopic effective medium model for predicting the thermal conductivity of phonons in two-dimensional nanoporous and microporous materials made from aligned cylindrical pores. The model captures the size effects due to the pore diameter and the interpore distance and reduces to diffusion-approximation based models for macroporous materials. The results are in good agreement with experimental data.

Understanding the role of hydrogen bonding in the aggregation of fumed silica particles in triglyceride solvents.

PubMed

Whitby, Catherine P; Krebsz, Melinda; Booty, Samuel J

2018-10-01

Fumed silica particles are thought to thicken organic solvents into gels by aggregating to form networks. Hydrogen bonding between silanol groups on different particle surfaces causes the aggregation. The gel structure and hence flow behaviour is altered by varying the proportion of silanol groups on the particle surfaces. However, characterising the gel using rheology measurements alone is not sufficient to optimise the aggregation. We have used confocal microscopy to characterise the changes in the network microstructure caused by altering the particle surface chemistry. Organogels were formed by dispersing fumed silica nanoparticles in a triglyceride solvent. The particle surface chemistry was systematically varied from oleophobic to oleophilic by functionalisation with hydrocarbons. We directly visualised the particle networks using confocal scanning laser microscopy and investigated the correlations between the network structure and the shear response of the organogels. Our key finding is that the sizes of the pore spaces in the networks depend on the fraction of silanol groups available to form hydrogen bonds. The reduction in the network elasticity of gels formed by methylated particles can be accounted for by the increasing pore size and tenuous nature of the networks. This is the first report that characterises the changes in the microstructure of fumed silica particle networks in non-polar solvents caused by manipulating the particle surface chemistry. Copyright © 2018 Elsevier Inc. All rights reserved.

Pore-scale supercritical CO 2 dissolution and mass transfer under drainage conditions

DOE PAGES

Chang, Chun; Zhou, Quanlin; Oostrom, Mart; ...

2016-12-05

Recently, both core- and pore-scale imbibition experiments have shown non-equilibrium dissolution of supercritical CO 2 (scCO 2) and a prolonged depletion of residual scCO 2. In this paper, pore-scale scCO 2 dissolution and mass transfer under drainage conditions were investigated using a two-dimensional heterogeneous micromodel and a novel fluorescent water dye with a sensitive pH range between 3.7 and 6.5. Drainage experiments were conducted at 9 MPa and 40 °C by injecting scCO 2 into the sandstone-analogue pore network initially saturated by water without dissolved CO 2 (dsCO 2). During the experiments, time-lapse images of dye intensity, reflecting water pH,more » were obtained. These images show non-uniform pH in individual pores and pore clusters, with average pH levels gradually decreasing with time. Further analysis on selected pores and pore clusters shows that (1) rate-limited mass transfer prevails with slowly decreasing pH over time when the scCO 2-water interface area is low with respect to the volume of water-filled pores and pore clusters, (2) fast scCO 2 dissolution and phase equilibrium occurs when scCO 2 bubbles invade into water-filled pores, significantly enhancing the area-to-volume ratio, and (3) a transition from rate-limited to diffusion-limited mass transfer occurs in a single pore when a medium area-to-volume ratio is prevalent. The analysis also shows that two fundamental processes – scCO 2 dissolution at phase interfaces and diffusion of dsCO 2 at the pore scale (10–100 µm) observed after scCO 2 bubble invasion into water-filled pores without pore throat constraints – are relatively fast. The overall slow dissolution of scCO 2 in the millimeter-scale micromodel can be attributed to the small area-to-volume ratios that represent pore-throat configurations and characteristics of phase interfaces. Finally, this finding is applicable for the behavior of dissolution at pore, core, and field scales when water-filled pores and pore clusters of varying size are surrounded by scCO 2 at narrow pore throats.« less

Pore-scale supercritical CO 2 dissolution and mass transfer under drainage conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Chun; Zhou, Quanlin; Oostrom, Mart

Recently, both core- and pore-scale imbibition experiments have shown non-equilibrium dissolution of supercritical CO 2 (scCO 2) and a prolonged depletion of residual scCO 2. In this paper, pore-scale scCO 2 dissolution and mass transfer under drainage conditions were investigated using a two-dimensional heterogeneous micromodel and a novel fluorescent water dye with a sensitive pH range between 3.7 and 6.5. Drainage experiments were conducted at 9 MPa and 40 °C by injecting scCO 2 into the sandstone-analogue pore network initially saturated by water without dissolved CO 2 (dsCO 2). During the experiments, time-lapse images of dye intensity, reflecting water pH,more » were obtained. These images show non-uniform pH in individual pores and pore clusters, with average pH levels gradually decreasing with time. Further analysis on selected pores and pore clusters shows that (1) rate-limited mass transfer prevails with slowly decreasing pH over time when the scCO 2-water interface area is low with respect to the volume of water-filled pores and pore clusters, (2) fast scCO 2 dissolution and phase equilibrium occurs when scCO 2 bubbles invade into water-filled pores, significantly enhancing the area-to-volume ratio, and (3) a transition from rate-limited to diffusion-limited mass transfer occurs in a single pore when a medium area-to-volume ratio is prevalent. The analysis also shows that two fundamental processes – scCO 2 dissolution at phase interfaces and diffusion of dsCO 2 at the pore scale (10–100 µm) observed after scCO 2 bubble invasion into water-filled pores without pore throat constraints – are relatively fast. The overall slow dissolution of scCO 2 in the millimeter-scale micromodel can be attributed to the small area-to-volume ratios that represent pore-throat configurations and characteristics of phase interfaces. Finally, this finding is applicable for the behavior of dissolution at pore, core, and field scales when water-filled pores and pore clusters of varying size are surrounded by scCO 2 at narrow pore throats.« less

Pore-scale supercritical CO 2 dissolution and mass transfer under drainage conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Chun; Zhou, Quanlin; Oostrom, Mart

Abstract: Recently, both core- and pore-scale imbibition experiments have shown non-equilibrium dissolution of supercritical CO 2 (scCO 2) and a prolonged depletion of residual scCO 2. In this study, pore-scale scCO 2 dissolution and mass transfer under drainage conditions were investigated using a two-dimensional heterogeneous micromodel and a novel fluorescent water dye with a sensitive pH range between 3.7 and 6.5. Drainage experiments were conducted at 9 MPa and 40 °C by injecting scCO 2 into the sandstone-analogue pore network initially saturated by water without dissolved CO 2 (dsCO 2). During the experiments, time-lapse images of dye intensity, reflecting watermore » pH, were obtained. These images show non-uniform pH in individual pores and pore clusters, with average pH levels gradually decreasing with time. Further analysis on selected pores and pore clusters shows that (1) rate-limited mass transfer prevails with slowly decreasing pH over time when the scCO 2-water interface area is low with respect to the volume of water-filled pores and pore clusters, (2) fast scCO 2 dissolution and phase equilibrium occurs when scCO 2 bubbles invade into water-filled pores, significantly enhancing the area-to-volume ratio, and (3) a transition from rate-limited to diffusion-limited mass transfer occurs in a single pore when a medium area-to-volume ratio is prevalent. The analysis also shows that two fundamental processes – scCO 2 dissolution at phase interfaces and diffusion of dsCO 2 at the pore scale (10-100 µm) observed after scCO 2 bubble invasion into water-filled pores without pore throat constraints – are relatively fast. The overall slow dissolution of scCO 2 in the millimeter-scale micromodel can be attributed to the small area-to-volume ratios that represent pore-throat configurations and characteristics of phase interfaces. This finding is applicable for the behavior of dissolution at pore, core, and field scales when water-filled pores and pore clusters of varying size are surrounded by scCO 2 at narrow pore throats.« less

Multi-scale Pore Imaging Techniques to Characterise Heterogeneity Effects on Flow in Carbonate Rock

NASA Astrophysics Data System (ADS)

Shah, S. M.

2017-12-01

Digital rock analysis and pore-scale studies have become an essential tool in the oil and gas industry to understand and predict the petrophysical and multiphase flow properties for the assessment and exploitation of hydrocarbon reserves. Carbonate reservoirs, accounting for majority of the world's hydrocarbon reserves, are well known for their heterogeneity and multiscale pore characteristics. The pore sizes in carbonate rock can vary over orders of magnitudes, the geometry and topology parameters of pores at different scales have a great impact on flow properties. A pore-scale study is often comprised of two key procedures: 3D pore-scale imaging and numerical modelling techniques. The fundamental problem in pore-scale imaging and modelling is how to represent and model the different range of scales encountered in porous media, from the pore-scale to macroscopic petrophysical and multiphase flow properties. However, due to the restrictions of image size vs. resolution, the desired detail is rarely captured at the relevant length scales using any single imaging technique. Similarly, direct simulations of transport properties in heterogeneous rocks with broad pore size distributions are prohibitively expensive computationally. In this study, we present the advances and review the practical limitation of different imaging techniques varying from core-scale (1mm) using Medical Computed Tomography (CT) to pore-scale (10nm - 50µm) using Micro-CT, Confocal Laser Scanning Microscopy (CLSM) and Focussed Ion Beam (FIB) to characterise the complex pore structure in Ketton carbonate rock. The effect of pore structure and connectivity on the flow properties is investigated using the obtained pore scale images of Ketton carbonate using Pore Network and Lattice-Boltzmann simulation methods in comparison with experimental data. We also shed new light on the existence and size of the Representative Element of Volume (REV) capturing the different scales of heterogeneity from the pore-scale imaging.

Optimality in Microwave-Assisted Drying of Aloe Vera ( Aloe barbadensis Miller) Gel using Response Surface Methodology and Artificial Neural Network Modeling

NASA Astrophysics Data System (ADS)

Das, Chandan; Das, Arijit; Kumar Golder, Animes

2016-10-01

The present work illustrates the Microwave-Assisted Drying (MWAD) characteristic of aloe vera gel combined with process optimization and artificial neural network modeling. The influence of microwave power (160-480 W), gel quantity (4-8 g) and drying time (1-9 min) on the moisture ratio was investigated. The drying of aloe gel exhibited typical diffusion-controlled characteristics with a predominant interaction between input power and drying time. Falling rate period was observed for the entire MWAD of aloe gel. Face-centered Central Composite Design (FCCD) developed a regression model to evaluate their effects on moisture ratio. The optimal MWAD conditions were established as microwave power of 227.9 W, sample amount of 4.47 g and 5.78 min drying time corresponding to the moisture ratio of 0.15. A computer-stimulated Artificial Neural Network (ANN) model was generated for mapping between process variables and the desired response. `Levenberg-Marquardt Back Propagation' algorithm with 3-5-1 architect gave the best prediction, and it showed a clear superiority over FCCD.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bakina, O. V., E-mail: ovbakina@ispms.tsc.ru; Glazkova, E. A., E-mail: eagl@ispms.tsc.ru; Svarovskaya, N. V., E-mail: nvsv@ispms.tsc.ru

In the current paper, the mixed SiO{sub 2}/Al{sub 2}O{sub 3} aerogel was synthesized by sol-gel method with subcritical drying and characterized. Tetraethoxysilane was used as a precursor of silicon sol. The flower-shaped alumina suspension was peptized to produce alumina sol. The aerogel texture, morphology, and structure were determined using scanning electron microscopy, X-ray diffraction, low-temperature nitrogen adsorption, and high-resolution spectroscopy. A special attention was paid to the pore structure of aerogel, and aerogel framework was formed by the spherical agglomerates containing spherical particles of silicon oxide and alumina nanopetals. The pore size distribution was bimodal with peaks of 5.5 nm andmore » 77 nm.« less

Influence of power ultrasound application on mass transport and microstructure of orange peel during hot air drying

NASA Astrophysics Data System (ADS)

Ortuño, Carmen; Pérez-Munuera, Isabel; Puig, Ana; Riera, Enrique; Garcia-Perez, J. V.

2010-01-01

Power ultrasound application on convective drying of foodstuffs may be considered an emergent technology. This work deals with the influence of power ultrasound on drying of natural materials addressing the kinetic as well as the product's microstructure. Convective drying kinetics of orange peel slabs (thickness 5.95±0.41 mm) were carried out at 40 ∘C and 1 m/s with (US) and without (AIR) power ultrasound application. A diffusion model considering external resistance to mass transfer was considered to describe drying kinetics. Fresh, US and AIR dried samples were analyzed using Cryo-SEM. Results showed that drying kinetics of orange peel were significantly improved by the application of power ultrasound. From modeling, it was observed a significant (p¡0.05) increase in both mass transfer coefficient and effective moisture diffusivity. The effects on mass transfer properties were confirmed from microestructural observations. In the cuticle surface, the pores were obstructed by wax components scattering, which evidence the ultrasonic effects on the interfaces. The cells of the flavedo were compressed and large intercellular air spaces were generated in the albedo facilitating water transfer through it.

Intercomparison of 3D pore-scale flow and solute transport simulation methods

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Xiaofan; Mehmani, Yashar; Perkins, William A.

2016-09-01

Multiple numerical approaches have been developed to simulate porous media fluid flow and solute transport at the pore scale. These include methods that 1) explicitly model the three-dimensional geometry of pore spaces and 2) those that conceptualize the pore space as a topologically consistent set of stylized pore bodies and pore throats. In previous work we validated a model of class 1, based on direct numerical simulation using computational fluid dynamics (CFD) codes, against magnetic resonance velocimetry (MRV) measurements of pore-scale velocities. Here we expand that validation to include additional models of class 1 based on the immersed-boundary method (IMB),more » lattice Boltzmann method (LBM), smoothed particle hydrodynamics (SPH), as well as a model of class 2 (a pore-network model or PNM). The PNM approach used in the current study was recently improved and demonstrated to accurately simulate solute transport in a two-dimensional experiment. While the PNM approach is computationally much less demanding than direct numerical simulation methods, the effect of conceptualizing complex three-dimensional pore geometries on solute transport in the manner of PNMs has not been fully determined. We apply all four approaches (CFD, LBM, SPH and PNM) to simulate pore-scale velocity distributions and nonreactive solute transport, and intercompare the model results with previously reported experimental observations. Experimental observations are limited to measured pore-scale velocities, so solute transport comparisons are made only among the various models. Comparisons are drawn both in terms of macroscopic variables (e.g., permeability, solute breakthrough curves) and microscopic variables (e.g., local velocities and concentrations).« less

Induced Seismicity at the UK "Hot Dry Rock" Test Site for Geothermal Energy Production

NASA Astrophysics Data System (ADS)

Li, Xun; Main, Ian; Jupe, Andrew

2018-03-01

In enhanced geothermal systems (EGS), fluid is injected at high pressure in order to stimulate fracturing and/or fluid flow through otherwise relatively impermeable underlying hot rocks to generate power and/or heat. The stimulation induces micro-earthquakes whose precise triggering mechanism and relationship to new and pre-existing fracture networks are still the subject of some debate. Here we analyse the dataset for induced micro-earthquakes at the UK "hot dry rock" experimental geothermal site (Rosemanowes, Cornwall). We quantify the evolution of several metrics used to characterise induced seismicity, including the seismic strain partition factor and the "seismogenic index". The results show a low strain partition factor of 0.01% and a low seismogenenic index indicating that aseismic processes dominate. We also analyse the spatio-temporal distribution of hypocentres, using simple models for the evolution of hydraulic diffusivity by (a) isotropic and (b) anisotropic pore-pressure relaxation. The principal axes of the diffusivity or permeability tensor inferred from the spatial distribution of earthquake foci are aligned parallel to the present-day stress field, although the maximum permeability is vertical, whereas the maximum principal stress is horizontal. Our results are consistent with a triggering mechanism that involves (a) seismic shear slip along optimally-oriented pre-existing fractures, (b) a large component of aseismic slip with creep (c) activation of tensile fractures as hydraulic conduits created by both the present-day stress field and by the induced shear slip, both exploiting pre-existing joint sets exposed in borehole data.

Composite fiber structures for catalysts and electrodes

NASA Technical Reports Server (NTRS)

Marrion, Christopher J.; Cahela, Donald R.; Ahn, Soonho; Tatarchuk, Bruce J.

1993-01-01

We have recently envisioned a process wherein fibers of various metals in the 0.5 to 15 micron diameter range are slurried in concert with cellulose fibers and various other materials in the form of particulates and/or fibers. The resulting slurry is cast via a wet-lay process into a sheet and dried to produce a free-standing sheet of 'composite paper.' When the 'preform' sheet is sintered in hydrogen, the bulk of the cellulose is removed with the secondary fibers and/or particulates being entrapped by the sinter-locked network provided by the metal fibers. The resulting material is unique, in that it allows the intimate contacting and combination of heretofore mutually exclusive materials and properties. Moreover, due to the ease of paper manufacture and processing, the resulting materials are relatively inexpensive and can be fabricated into a wide range of three-dimensional structures. Also, because cellulose is both a binder and a pore-former, structures combining high levels of active surface area and high void volume (i.e., low pressure drop) can be prepared as freestanding flow through monoliths.

Mineral oil barrier sequential polymer treatment for recycled paper products in food packaging

NASA Astrophysics Data System (ADS)

Paul, Uttam C.; Fragouli, Despina; Bayer, Ilker S.; Mele, Elisa; Conchione, Chiara; Cingolani, Roberto; Moret, Sabrina; Athanassiou, Athanassia

2017-01-01

Recycled cellulosic paperboards may include mineral oils after the recycle process, which together with their poor water resistance limit their use as food packaging materials. In this work, we demonstrate that a proper functionalization of the recycled paper with two successive polymer treatments, imposes a mineral oil migration barrier and simultaneously renders it waterproof and grease resistant, making it an ideal material for food contact. The first poly (methyl methacrylate) treatment penetrates the paper network and creates a protective layer around every fiber, permitting thus the transformation of the paperboard to a hydrophobic material throughout its thickness, reducing at the same time the mineral oil migration. Subsequently, the second layer with a cyclic olefin copolymer fills the open pores of the surface, and reduces the mineral oil hydrocarbons migration at levels below those proposed by the BMEL. Online liquid chromatography-gas chromatography coupled with flame ionization detection quantitatively demonstrate that this dual functional treatment prevents the migration of both saturated (mineral oil saturated hydrocarbons) and aromatic hydrocarbon (mineral oil aromatic hydrocarbons) mineral oils from the recycled paperboard to a dry food simulant.

A novel hybrid approach for estimating total deposition in the United States

NASA Astrophysics Data System (ADS)

Schwede, Donna B.; Lear, Gary G.

2014-08-01

Atmospheric deposition of nitrogen and sulfur causes many deleterious effects on ecosystems including acidification and excess eutrophication. Assessments to support development of strategies to mitigate these effects require spatially and temporally continuous values of nitrogen and sulfur deposition. In the U.S., national monitoring networks exist that provide values of wet and dry deposition at discrete locations. While wet deposition can be interpolated between the monitoring locations, dry deposition cannot. Additionally, monitoring networks do not measure the complete suite of chemicals that contribute to total sulfur and nitrogen deposition. Regional air quality models provide spatially continuous values of deposition of monitored species as well as important unmeasured species. However, air quality modeling values are not generally available for an extended continuous time period. Air quality modeling results may also be biased for some chemical species. We developed a novel approach for estimating dry deposition using data from monitoring networks such as the Clean Air Status and Trends Network (CASTNET), the National Atmospheric Deposition Program (NADP) Ammonia Monitoring Network (AMoN), and the Southeastern Aerosol Research and Characterization (SEARCH) network and modeled data from the Community Multiscale Air Quality (CMAQ) model. These dry deposition values estimates are then combined with wet deposition values from the NADP National Trends Network (NTN) to develop values of total deposition of sulfur and nitrogen. Data developed using this method are made available via the CASTNET website.

A Hybrid Approach for Estimating Total Deposition in the ...

EPA Pesticide Factsheets

Atmospheric deposition of nitrogen and sulfur causes many deleterious effects on ecosystems including acidification and excess eutrophication. Assessments to support development of strategies to mitigate these effects require spatially and temporally continuous values of nitrogen and sulfur deposition. In the U.S., national monitoring networks exist that provide values of wet and dry deposition at discrete locations. While wet deposition can be interpolated between the monitoring locations, dry deposition cannot. Additionally, monitoring networks do not measure the complete suite of chemicals that contribute to total sulfur and nitrogen deposition. Regional air quality models provide spatially continuous values of deposition of monitored species as well as important unmeasured species. However, air quality modeling values are not generally available for an extended continuous time period. Air quality modeling results may also be biased for some chemical species. We developed a novel approach for estimating dry deposition using data from monitoring networks such as the Clean Air Status and Trends Network (CASTNET), the National Atmospheric Deposition Program (NADP) Ammonia Monitoring Network (AMoN), and the Southeastern Aerosol Research and Characterization (SEARCH) network and modeled data from the Community Multiscale Air Quality (CMAQ) model. These dry deposition values estimates are then combined with wet deposition values from the NADP National Trends Networ

A Novel Hybrid Approach for Estimating Total Deposition in ...

EPA Pesticide Factsheets

Atmospheric deposition of nitrogen and sulfur causes many deleterious effects on ecosystems including acidification and excess eutrophication. Assessments to support development of strategies to mitigate these effects require spatially and temporally continuous values of nitrogen and sulfur deposition. In the U.S., national monitoring networks exist that provide values of wet and dry deposition at discrete locations. While wet deposition can be interpolated between the monitoring locations, dry deposition cannot. Additionally, monitoring networks do not measure the complete suite of chemicals that contribute to total sulfur and nitrogen deposition. Regional air quality models provide spatially continuous values of deposition of monitored species as well as important unmeasured species. However, air quality modeling values are not generally available for an extended continuous time period. Air quality modeling results may also be biased for some chemical species. We developed a novel approach for estimating dry deposition using data from monitoring networks such as the Clean Air Status and Trends Network (CASTNET), the National Atmospheric Deposition Program (NADP) Ammonia Monitoring Network (AMoN), and the Southeastern Aerosol Research and Characterization (SEARCH) network and modeled data from the Community Multiscale Air Quality (CMAQ) model. These dry deposition values estimates are then combined with wet deposition values from the NADP National Trends Networ

Porous structure and fluid partitioning in polyethylene cores from 3D X-ray microtomographic imaging.

PubMed

Prodanović, M; Lindquist, W B; Seright, R S

2006-06-01

Using oil-wet polyethylene core models, we present the development of robust throat finding techniques for the extraction, from X-ray microtomographic images, of a pore network description of porous media having porosity up to 50%. Measurements of volume, surface area, shape factor, and principal diameters are extracted for pores and area, shape factor and principal diameters for throats. We also present results on the partitioning of wetting and non-wetting phases in the pore space at fixed volume increments of the injected fluid during a complete cycle of drainage and imbibition. We compare these results with fixed fractional flow injection, where wetting and non-wetting phase are simultaneously injected at fixed volume ratio. Finally we demonstrate the ability to differentiate three fluid phases (oil, water, air) in the pore space.

Nanostructured silicon membranes for control of molecular transport.

PubMed

Srijanto, Bernadeta R; Retterer, Scott T; Fowlkes, Jason D; Doktycz, Mitchel J

2010-11-01

A membrane that allows selective transport of molecular species requires precise engineering on the nanoscale. Membrane permeability can be tuned by controlling the physical structure and surface chemistry of the pores. Here, a combination of electron beam and optical lithography, along with cryogenic deep reactive ion etching, has been used to fabricate silicon membranes that are physically robust, have uniform pore sizes, and are directly integrated into a microfluidic network. Additional reductions in pore size were achieved using plasma enhanced chemical vapor deposition and atomic layer deposition of silicon dioxide to coat membrane surfaces. Cross sectioning of the membranes using focused ion beam milling was used to determine the physical shape of the membrane pores before and after coating. Functional characterization of the membranes was performed by using quantitative fluorescence microscopy to document the transport of molecular species across the membrane.

Evaluation of Micro- and Macro-Scale Petrophysical Characteristics of Lower Cretaceous Sandstone with Flow Modeling in µ-CT Imaged Geometry

NASA Astrophysics Data System (ADS)

Katsman, R.; Haruzi, P.; Waldmann, N.; Halisch, M.

2017-12-01

In this study petrophysical characteristics of rock samples from 3 successive outcrop layers of Hatira Formation Lower Cretaceous Sandstone in northen Israel were evaluated at micro- and macro-scales. The study was carried out by two complementary methods: using conventional experimental measurements of porosity, pore size distribution and permeability; and using a 3D µCT imaging and modeling of signle-phase flow in the real micro-scale sample geometry. The workfow included µ-CT scanning, image processing, image segmentation, and image analyses of pore network, followed by fluid flow simulations at a pore-scale. Upscaling the results of the micro-scale flow simulations yielded a macroscopic permeabilty tensor. Comparison of the upscaled and the experimentally measured rock properties demonstrated a reasonable agreement. In addition, geometrical (pore size distribution, surface area and tortuosity) and topological (Euler characteristic) characteristics of the grains and of the pore network were evaluated at a micro-scale. Statistical analyses of the samples for estimation of anisotropy and inhomogeneity of the porous media were conducted and the results agree with anisotropy and inhomogeneity of the upscaled permeabilty tensor. Isotropic pore orientation of the primary inter-granular porosity was identified in all three samples, whereas the characteristics of the secondary porosity were affected by precipitated cement and clay matrix within the primary pore network. Results of this study provide micro- and macro-scale characteristics of the Lower Cretaceous sandstone that is used in different places over the world as a reservoir for petroleum production and sequestration.

Fibril growth kinetics link buffer conditions and topology of 3D collagen I networks.

PubMed

Kalbitzer, Liv; Pompe, Tilo

2018-02-01

Three-dimensional fibrillar networks reconstituted from collagen I are widely used as biomimetic scaffolds for in vitro and in vivo cell studies. Various physicochemical parameters of buffer conditions for in vitro fibril formation are well known, including pH-value, ion concentrations and temperature. However, there is a lack of a detailed understanding of reconstituting well-defined 3D network topologies, which is required to mimic specific properties of the native extracellular matrix. We screened a wide range of relevant physicochemical buffer conditions and characterized the topology of the reconstituted 3D networks in terms of mean pore size and fibril diameter. A congruent analysis of fibril formation kinetics by turbidimetry revealed the adjustment of the lateral growth phase of fibrils by buffer conditions to be key in the determination of pore size and fibril diameter of the networks. Although the kinetics of nucleation and linear growth phase were affected by buffer conditions as well, network topology was independent of those two growth phases. Overall, the results of our study provide necessary insights into how to engineer 3D collagen matrices with an independent control over topology parameters, in order to mimic in vivo tissues in in vitro experiments and tissue engineering applications. The study reports a comprehensive analysis of physicochemical conditions of buffer solutions to reconstitute defined 3D collagen I matrices. By a combined analysis of network topology, i.e., pore size and fibril diameter, and the kinetics of fibril formation we can reveal the dependence of 3D network topology on buffer conditions, such as pH-value, phosphate concentration and sodium chloride content. With those results we are now able to provide engineering strategies to independently tune the topology parameters of widely used 3D collagen scaffolds based on the buffer conditions. By that, we enable the straightforward mimicking of extracellular matrices of in vivo tissues for in vitro cell culture experiments and tissue engineering applications. Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Gelatin Scaffolds with Controlled Pore Structure and Mechanical Property for Cartilage Tissue Engineering.

PubMed

Chen, Shangwu; Zhang, Qin; Nakamoto, Tomoko; Kawazoe, Naoki; Chen, Guoping

2016-03-01

Engineering of cartilage tissue in vitro using porous scaffolds and chondrocytes provides a promising approach for cartilage repair. However, nonuniform cell distribution and heterogeneous tissue formation together with weak mechanical property of in vitro engineered cartilage limit their clinical application. In this study, gelatin porous scaffolds with homogeneous and open pores were prepared using ice particulates and freeze-drying. The scaffolds were used to culture bovine articular chondrocytes to engineer cartilage tissue in vitro. The pore structure and mechanical property of gelatin scaffolds could be well controlled by using different ratios of ice particulates to gelatin solution and different concentrations of gelatin. Gelatin scaffolds prepared from ≥70% ice particulates enabled homogeneous seeding of bovine articular chondrocytes throughout the scaffolds and formation of homogeneous cartilage extracellular matrix. While soft scaffolds underwent cellular contraction, stiff scaffolds resisted cellular contraction and had significantly higher cell proliferation and synthesis of sulfated glycosaminoglycan. Compared with the gelatin scaffolds prepared without ice particulates, the gelatin scaffolds prepared with ice particulates facilitated formation of homogeneous cartilage tissue with significantly higher compressive modulus. The gelatin scaffolds with highly open pore structure and good mechanical property can be used to improve in vitro tissue-engineered cartilage.

Pore blocking: An innovative formulation strategy for the design of alcohol resistant multi-particulate dosage forms.

PubMed

Schrank, Simone; Jedinger, Nicole; Wu, Shengqian; Piller, Michael; Roblegg, Eva

2016-07-25

In this work calcium stearate (CaSt) multi-particulates loaded with codeine phosphate (COP) were developed in an attempt to provide extended release (ER) combined with alcohol dose dumping (ADD) resistance. The pellets were prepared via wet/extrusion spheronization and ER characteristics were obtained after fluid bed drying at 30°C. Pore blockers (i.e., xanthan, guar gum and TiO2) were integrated to control the uptake of ethanolic media, the CaSt swelling and consequently, the COP release. While all three pore blockers are insoluble in ethanol, xanthan dissolves, guar gum swells and TiO2 does not interact with water. The incorporation of 10 and 15% TiO2 still provided ER characteristics and yielded ADD resistance in up to 40v% ethanol. The in-vitro data were subjected to PK simulations, which revealed similar codeine plasma levels when the medication is used concomitantly with alcoholic beverages. Taken together the in-vitro and in-silico results demonstrate that the incorporation of appropriate pore blockers presents a promising strategy to provide ADD resistance of multi-particulate systems. Copyright © 2016 Elsevier B.V. All rights reserved.

Modification of electrical properties of silicon dioxide through intrinsic nano-patterns

NASA Astrophysics Data System (ADS)

Majee, Subimal; Barshilia, Devesh; Banerjee, Debashree; Kumar, Sanjeev; Mishra, Prabhash; Akhtar, Jamil

2018-05-01

The inherent network of nanopores and voids in silicon dioxide (SiO2) is generally undesirable for aspects of film quality, electrical insulation and dielectric performance. However, if we view these pores as natural nano-patterns embedded in a dielectric matrix then that opens up new vistas for exploration. The nano-pattern platform can be used to tailor electrical, optical, magnetic and mechanical properties of the carrier film. In this article we report the tunable electrical properties of thermal SiO2 thin-film achieved through utilization of the metal-nanopore network where the pores are filled with metallic Titanium (Ti). Without any intentional chemical doping, we have shown that the electrical resistivity of the oxide film can be controlled through physical filling up of the intrinsic oxide nanopores with Ti. The electrical resistivity of the composite film remains constant even after complete removal of the metal from the film surface except the pores. Careful morphological, electrical and structural analyses are carried out to establish that the presence of Ti in the nanopores play a crucial role in the observed conductive nature of the nanoporous film.

Effects of chronic anthropogenic disturbance and rainfall on the specialization of ant-plant mutualistic networks in the Caatinga, a Brazilian dry forest.

PubMed

Câmara, Talita; Leal, Inara R; Blüthgen, Nico; Oliveira, Fernanda M P; Queiroz, Rubens T de; Arnan, Xavier

2018-03-05

Anthropogenic disturbance and climate change might negatively affect the ecosystem services provided by mutualistic networks. However, the effects of such forces remain poorly characterized. They may be especially important in dry forests, which (1) experience chronic anthropogenic disturbances (CADs) as human populations exploit forest resources, and (2) are predicted to face a 22% decline in rainfall under climate change. In this study, we investigated the separate and combined effects of CADs and rainfall levels on the specialization of mutualistic networks in the Caatinga, a seasonally dry tropical forest typical of north-eastern Brazil. More specifically, we examined interactions between plants bearing extrafloral nectaries (EFNs) and ants. We analysed whether differences in network specialization could arise from environmentally mediated variation in the species composition, namely via the replacement of specialist by generalist species. We characterized these ant-plant networks in 15 plots (20 × 20 m) that varied in CAD intensity and mean annual rainfall. We quantified CAD intensity by calculating three indices related to the main sources of disturbance in the Caatinga: livestock grazing (LG), wood extraction (WE) and miscellaneous resource use (MU). We determined the degree of ant-plant network specialization using four metrics: generality, vulnerability, interaction evenness and H 2 '. Our results indicate that CADs differentially influenced network specialization: we observed positive, negative, and neutral responses along LG, MU and WE gradients, respectively. The pattern was most pronounced with LG. Rainfall also shaped network specialization, markedly increasing it. While LG and rainfall were associated with changes in network species composition, this trend was not related to the degree of species specialization. This result suggests that shifts in network specialization might be related to changes in species behaviour, not species composition. Our study highlights the vulnerability of such dry forest ant-plant networks to climate change. Moreover, dry forests experience highly heterogeneous anthropogenic disturbances, creating a geographic mosaic of selective forces that may shape the co-evolution of interactions between ants and EFN-bearing plants. © 2018 The Authors. Journal of Animal Ecology © 2018 British Ecological Society.

Dry Juan de Fuca slab revealed by quantification of water entering Cascadia subduction zone

NASA Astrophysics Data System (ADS)

Canales, J. P.; Carbotte, S. M.; Nedimovic, M. R.; Carton, H. D.

2017-12-01

Water is carried by subducting slabs as a pore fluid and in structurally bound minerals, yet no comprehensive quantification of water content and how it is stored and distributed at depth within incoming plates exists for any segment of the global subduction system. Here we use controlled-source seismic data collected in 2012 as part of the Ridge-to-Trench seismic experiment to quantify the amount of pore and structurally bound water in the Juan de Fuca plate entering the Cascadia subduction zone. We use wide-angle OBS seismic data along a 400-km-long margin-parallel profile 10-15 km seaward from the Cascadia deformation front to obtain P-wave tomography models of the sediments, crust, and uppermost mantle, and effective medium theory combined with a stochastic description of crustal properties (e.g., temperature, alteration assemblages, porosity, pore aspect ratio), to analyze the pore fluid and structurally bound water reservoirs in the sediments, crust and lithospheric mantle, and their variations along the Cascadia margin. Our results demonstrate that the Juan de Fuca lower crust and mantle are much drier than at any other subducting plate, with most of the water stored in the sediments and upper crust. Previously documented, variable but limited bend faulting along the margin, which correlates with degree of plate locking, limits slab access to water, and a warm thermal structure resulting from a thick sediment cover and young plate age prevents significant serpentinization of the mantle. Our results have important implications for a number of subduction processes at Cascadia, such as: (1) the dryness of the lower crust and mantle indicates that fluids that facilitate episodic tremor and slip must be sourced from the subducted upper crust; (2) decompression rather than hydrous melting must dominate arc magmatism in northern-central Cascadia; and (3) dry subducted lower crust and mantle can explain the low levels of intermediate-depth seismicity in the Juan de Fuca slab.

Development of Multiscale Materials in Microfluidic Devices: Case Study for Viral Separation from Whole Blood

NASA Astrophysics Data System (ADS)

Surawathanawises, Krissada

Separation and concentration of nanoscale species play an important role in various fields such as biotechnology, nanotechnology and environmental science. Inevitably, the separation efficiency strongly affects the quality of downstream detections or productions. Innovations in materials science that can separate bionanoparticles efficiently and do not require complex setups, reagents or external fields are highly demanded. This work focuses on developing new materials for the affinity separation of bio-nanoparticles such as viruses or macromolecules from a complex mixture, such as whole blood. To enhance the interaction between target nanoparticles and the capture bed, methods to produce porous matrices with a uniform pore size matching the dimension of targets are studied. Furthermore, regarding viral separation from whole blood, macroporous materials are further patterned into microarrays to allow multiscale separation. Considering the needs in resource-limited settings, these materials are integrated with microfluidic technologies to reduce the volume of samples and reagents, simplify operating processes, and enable the use of inexpensive and portable components. Beyond the application of viral separation as demonstrated in the work, the fundamental study of macroporous material formation and transport in these materials also shed light to the separation of many other nanospecies in multiscale materials. Specifically, two macroporous materials, based on template synthesis, are created in this work. The first type employs porous anodic aluminum oxide (AAO) films as the template to create hexagonal arrays of nanoposts. However, pore sizes and interpore distances (cell size) of ordered porous AAO films are limited by the conventional fabrication process. Moreover, the process usually yields defective pore morphologies and large pore and cell size distributions. To overcome these limitations, a patterning method using nanobead indentation on aluminum substrate prior to anodization is evaluated to control the growth of AAO. Together with controlled anodizing voltages and electrolytic concentrations, AAO pore and cell sizes are shown to be tunable and controllable with narrow size distributions within submicron range. A high degree of order of AAO pore arrangement is also demonstrated. In addition, overall anodization becomes more time-efficient and stable at high anodizing voltages. Secondly, a three-dimensional (3D) assembly of microbeads is used as a template to fabricate a spherical pore network with small interconnected openings. After depositing and drying a suspension containing both micro- and nanobeads, the microbeads assemble into a 3D close-packed structure while the nanobeads fill the interstitial space. When the nanobeads are melted and microbeads are removed, a spherical pore matrix then form with small interconnected openings. Such the opening size is in submicron range can be adjusted depending on the size of microbead. The advantages of the two macroporous materials are not only controllable and tunable pore size, but also high surface-to-volume ratio due to the nanoscale features. With a ratio on the order of ~1 microm-1, the porous materials provide a significantly large binding surface. Computational and experimental results reveal that porous materials with a pore size matching the nanoparticle size are suitable for their capture. Separation of human immunodeficiency virus (HIV) is used as a model and capture yields of ~99 % and ~80 % are achieved in the nanopost structure and spherical pore network, respectively, after treated with a functional chemistry. Hence, the properties of these two macroporous materials are suitable as a size-exclusion and affinity separation for viral particles. To further explore multiscale separation, i.e. capturing viruses from whole blood, micropatterned arrays of macroporous materials have been designed. In this design, a microscale gap allows the passage of microparticles such as blood cells, and the nanoscale pores promote permeation for affinity capture of bionanoparticles. Consequently, particles with a size difference of 3--4 orders of magnitude can be separated in a simple flow-through process. Computational analyses are employed to study the effect of micropattern shape and layout. A half-ring pattern is shown to reduce flow resistance and promote fluid permeation compared to a circular pattern. In the experiment, the micropatterned porous arrays yield around 4 times higher viral capture from whole blood compared with a micropatterned solid array. The micropatterned porous devices are capable of handling a large volume of fluid sample without clogging by cells. Therefore they can be used for nanoparticle concentration. Our study also indicates that the layout of micropatterns can be adjusted to improve the capture yield. For example, an increase in pattern radius, or a decrease in gap distance between each post and in width of half ring will enhance fluid permeation in the porous structure. When combined with downstream detection, these materials integrated into microfluidic platforms can be created as point-of-care diagnostics, as well as other applications for particle separation and analysis. (Abstract shortened by UMI.).

Using Artificial Neural Networks to Predict the Presence of Overpressured Zones in the Anadarko Basin, Oklahoma

NASA Astrophysics Data System (ADS)

Cranganu, Constantin

2007-10-01

Many sedimentary basins throughout the world exhibit areas with abnormal pore-fluid pressures (higher or lower than normal or hydrostatic pressure). Predicting pore pressure and other parameters (depth, extension, magnitude, etc.) in such areas are challenging tasks. The compressional acoustic (sonic) log (DT) is often used as a predictor because it responds to changes in porosity or compaction produced by abnormal pore-fluid pressures. Unfortunately, the sonic log is not commonly recorded in most oil and/or gas wells. We propose using an artificial neural network to synthesize sonic logs by identifying the mathematical dependency between DT and the commonly available logs, such as normalized gamma ray (GR) and deep resistivity logs (REID). The artificial neural network process can be divided into three steps: (1) Supervised training of the neural network; (2) confirmation and validation of the model by blind-testing the results in wells that contain both the predictor (GR, REID) and the target values (DT) used in the supervised training; and 3) applying the predictive model to all wells containing the required predictor data and verifying the accuracy of the synthetic DT data by comparing the back-predicted synthetic predictor curves (GRNN, REIDNN) to the recorded predictor curves used in training (GR, REID). Artificial neural networks offer significant advantages over traditional deterministic methods. They do not require a precise mathematical model equation that describes the dependency between the predictor values and the target values and, unlike linear regression techniques, neural network methods do not overpredict mean values and thereby preserve original data variability. One of their most important advantages is that their predictions can be validated and confirmed through back-prediction of the input data. This procedure was applied to predict the presence of overpressured zones in the Anadarko Basin, Oklahoma. The results are promising and encouraging.

Impact of matric potential and pore size distribution on growth dynamics of filamentous and non-filamentous soil bacteria.

PubMed

Wolf, Alexandra B; Vos, Michiel; de Boer, Wietse; Kowalchuk, George A

2013-01-01

The filamentous growth form is an important strategy for soil microbes to bridge air-filled pores in unsaturated soils. In particular, fungi perform better than bacteria in soils during drought, a property that has been ascribed to the hyphal growth form of fungi. However, it is unknown if, and to what extent, filamentous bacteria may also display similar advantages over non-filamentous bacteria in soils with low hydraulic connectivity. In addition to allowing for microbial interactions and competition across connected micro-sites, water films also facilitate the motility of non-filamentous bacteria. To examine these issues, we constructed and characterized a series of quartz sand microcosms differing in matric potential and pore size distribution and, consequently, in connection of micro-habitats via water films. Our sand microcosms were used to examine the individual and competitive responses of a filamentous bacterium (Streptomyces atratus) and a motile rod-shaped bacterium (Bacillus weihenstephanensis) to differences in pore sizes and matric potential. The Bacillus strain had an initial advantage in all sand microcosms, which could be attributed to its faster growth rate. At later stages of the incubation, Streptomyces became dominant in microcosms with low connectivity (coarse pores and dry conditions). These data, combined with information on bacterial motility (expansion potential) across a range of pore-size and moisture conditions, suggest that, like their much larger fungal counterparts, filamentous bacteria also use this growth form to facilitate growth and expansion under conditions of low hydraulic conductivity. The sand microcosm system developed and used in this study allowed for precise manipulation of hydraulic properties and pore size distribution, thereby providing a useful approach for future examinations of how these properties influence the composition, diversity and function of soil-borne microbial communities.

The effect of water-soluble polymers on the microstructure and properties of freeze-cast alumina ceramics

NASA Astrophysics Data System (ADS)

Pekor, Christopher Michael

Porous ceramics can be divided into three separate classes based on their pore size: microporous ceramics with pores less than 2 nm, mesoporous ceramics with pores in the range of 2--50 nm and macroporous ceramics with pores that are greater than 50 nm. In particular, macroporous ceramics are used in a variety of applications such as refractories, molten metal filtration, diesel particulate filters, heterogeneous catalyst supports and biomedical scaffolds. Freeze casting is a novel method used to create macroporous ceramics. In this method growing ice crystals act as a template for the pores and are solidified, often directionally, through a ceramic dispersion and removed from the green body through a freeze drying procedure. This method has attracted some attention over the past few years due to its relative simplicity, flexibility and environmental friendliness. On top of this freeze casting is capable of producing materials with high pore volume fractions, which is an advantage over processing by packing and necking of particles, where the pore volume fraction is typically less than 50%. Many of the basic processing variables that affect the freeze cast microstructure, such as the temperature gradient, interfacial velocity and solid loading of the dispersion have been well established in the literature. On the other hand, areas such as the effect of additives on the microstructure and mechanical properties have not been covered in great detail. In this study the concept of constitutional supercooling from basic solidification theory is used to explain the effects of two water-soluble polymers, polyethylene glycol and polyvinyl alcohol, on the microstructure of freeze cast alumina ceramics. In addition, changes in the observed microstructure will be related to experimentally determined values of permeability and compressive strength.

Microstructure and Mechanical Properties of Porous Mullite

NASA Astrophysics Data System (ADS)

Hsiung, Chwan-Hai Harold

Mullite (3 Al2O3 : 2 SiO2) is a technologically important ceramic due to its thermal stability, corrosion resistance, and mechanical robustness. One variant, porous acicular mullite (ACM), has a unique needle-like microstructure and is the material platform for The Dow Chemical Company's diesel particulate filter AERIFY(TM). The investigation described herein focuses on the microstructure-mechanical property relationships in acicular mullites as well as those with traditional porous microstructures with the goal of illuminating the critical factors in determining their modulus, strength, and toughness. Mullites with traditional pore morphologies were made to serve as references via slipcasting of a kaolinite-alumina-starch slurry. The starch was burned out to leave behind a pore network, and the calcined body was then reaction-sintered at 1600C to form mullite. The samples had porosities of approximately 60%. Pore size and shape were altered by using different starch templates, and pore size was found to influence the stiffness and toughness. The ACM microstructure was varied along three parameters: total porosity, pore size, and needle size. Total porosity was found to dominate the mechanical behavior of ACM, while increases in needle and pore size increased the toughness at lower porosities. ACM was found to have much improved (˜130%) mechanical properties relative to its non-acicular counterpart at the same porosity. A second set of investigations studied the role of the intergranular glassy phase which wets the needle intersections of ACM. Removal of the glassy phase via an HF etch reduced the mechanical properties by ˜30%, highlighting the intergranular phase's importance to the enhanced mechanical properties of ACM. The composition of the glassy phase was altered by doping the ACM precursor with magnesium and neodymium. Magnesium doping resulted in ACM with greatly reduced fracture strength and toughness. Studies showed that the mechanical properties of the two doped intergranular glasses and their interfaces with mullite were quite similar. The reductions in strength and toughness were traced to differences in the ACM network structure and mass-distribution that are hypothesized to result from dopant-altered ACM nucleation and growth kinetics. X-ray computed tomography, a non-destructive 3-D imaging technique, played a key role in this work, enabling the measurement of needle diameters, quantification of the ACM structural network, and finite element analysis of ACM's mechanical response.

A binomial modeling approach for upscaling colloid transport under unfavorable conditions: Emergent prediction of extended tailing

NASA Astrophysics Data System (ADS)

Hilpert, Markus; Rasmuson, Anna; Johnson, William P.

2017-07-01

Colloid transport in saturated porous media is significantly influenced by colloidal interactions with grain surfaces. Near-surface fluid domain colloids experience relatively low fluid drag and relatively strong colloidal forces that slow their downgradient translation relative to colloids in bulk fluid. Near-surface fluid domain colloids may reenter into the bulk fluid via diffusion (nanoparticles) or expulsion at rear flow stagnation zones, they may immobilize (attach) via primary minimum interactions, or they may move along a grain-to-grain contact to the near-surface fluid domain of an adjacent grain. We introduce a simple model that accounts for all possible permutations of mass transfer within a dual pore and grain network. The primary phenomena thereby represented in the model are mass transfer of colloids between the bulk and near-surface fluid domains and immobilization. Colloid movement is described by a Markov chain, i.e., a sequence of trials in a 1-D network of unit cells, which contain a pore and a grain. Using combinatorial analysis, which utilizes the binomial coefficient, we derive the residence time distribution, i.e., an inventory of the discrete colloid travel times through the network and of their probabilities to occur. To parameterize the network model, we performed mechanistic pore-scale simulations in a single unit cell that determined the likelihoods and timescales associated with the above colloid mass transfer processes. We found that intergrain transport of colloids in the near-surface fluid domain can cause extended tailing, which has traditionally been attributed to hydrodynamic dispersion emanating from flow tortuosity of solute trajectories.

One-Dimension Diffusion Preparation of Concentration-Gradient Fe₂O₃/SiO₂ Aerogel.

PubMed

Zhang, Ting; Wang, Haoran; Zhou, Bin; Ji, Xiujie; Wang, Hongqiang; Du, Ai

2018-06-21

Concentration-gradient Fe₂O₃/SiO₂ aerogels were prepared by placing an MTMS (methyltrimethoxysilane)-derived SiO₂ aerogel on an iron gauze with an HCl atmosphere via one-dimensional diffusion, ammonia-atmosphere fixing, supercritical fluid drying and thermal treatment. The energy dispersive spectra show that the Fe/Si molar ratios change gradually from 2.14% to 18.48% with a height of 40 mm. Pore-size distribution results show that the average pore size of the sample decreases from 15.8 nm to 3.1 nm after diffusion. This corresponds well with TEM results, indicating a pore-filling effect of the Fe compound. In order to precisely control the gradient, diffusion kinetics are further studied by analyzing the influence of time and position on the concentration of the wet gel. At last, it is found that the diffusion process could be fitted well with the one-dimensional model of Fick’s second law, demonstrating the feasibility of the precise design and control of the concentration gradient.

Tissue Reaction to a Novel Bone Substitute Material Fabricated With Biodegradable Polymer-Calcium Phosphate Nanoparticle Composite.

PubMed

Shimizu, Hideo; Jinno, Yohei; Ayukawa, Yasunori; Atsuta, Ikiru; Arahira, Takaaki; Todo, Mitsugu; Koyano, Kiyoshi

2016-10-01

The aim of this study was to evaluate the effectiveness of a novel bone substitute material fabricated using a biodegradable polymer-calcium phosphate nanoparticle composite. Porous structured poly-L-lactic acid (PLLA) and hydroxyapatite (HA) nanoparticle composite, which was fabricated using solid-liquid phase separation and freeze-drying methods, was grafted into bone defects created in rat calvarium or tibia. Rats were killed 4 weeks after surgery, and histological analyses were performed to evaluate new bone formation. Scanning electron microscopic observation showed the interconnecting pores within the material and the pore diameter was approximately 100 to 300 μm. HA nanoparticles were observed to be embedded into the PLLA beams. In the calvarial implantation model, abundant blood vessels and fibroblastic cells were observed penetrating into pores, and in the tibia model, newly formed bone was present around and within the composite. The PLLA-HA nanoparticle composite bone substitute developed in this study showed biocompatibility, elasticity, and operability and thus has potential as a novel bone substitute.

Agarose drug delivery systems upgraded by surfactants inclusion: critical role of the pore architecture.

PubMed

Marras-Marquez, T; Peña, J; Veiga-Ochoa, M D

2014-03-15

Anionic or non-ionic surfactants have been introduced in agarose-based hydrogels aiming to tailor the release of drugs with different solubility. The release of a hydrophilic model drug, Theophylline, shows the predictable release enhancement that varies depending on the surfactant. However, when the hydrophobic Tolbutamide is considered, an unexpected retarded release is observed. This effect can be explained not only considering the interactions established between the drug loaded micelles and agarose but also to the alteration of the freeze-dried hydrogels microstructure. It has been observed that the modification of the porosity percentage as well as the pore size distribution during the lyophilization plays a critical role in the different phenomena that take place as soon as desiccated hydrogel is rehydrated. The possibility of tailoring the pore architecture as a function of the surfactant nature and percentage can be applied from drug control release to the widespread and growing applications of materials based on hydrogel matrices. Copyright © 2013 Elsevier Ltd. All rights reserved.

Effects of pore topology and iron oxide core on doxorubicin loading and release from mesoporous silica nanoparticles

NASA Astrophysics Data System (ADS)

Ronhovde, Cicily J.; Baer, John; Larsen, Sarah C.

2017-06-01

Mesoporous silica nanoparticles (MSNs) have a network of pores that give rise to extremely high specific surface areas, making them attractive materials for applications such as adsorption and drug delivery. The pore topology can be readily tuned to achieve a variety of structures such as the hexagonally ordered Mobil Crystalline Material 41 (MCM-41) and the disordered "wormhole" (WO) mesoporous silica (MS) structure. In this work, the effects of pore topology and iron oxide core on doxorubicin loading and release were investigated using MSNs with pore diameters of approximately 3 nm and sub-100 nm particle diameters. The nanoparticles were loaded with doxorubicin, and the drug release into phosphate-buffered saline (PBS, 10 mM, pH 7.4) at 37 °C was monitored by fluorescence spectroscopy. The release profiles were fit using the Peppas model. The results indicated diffusion-controlled release for all samples. Statistically significant differences were observed in the kinetic host-guest parameters for each sample due to the different pore topologies and the inclusion of an iron oxide core. Applying a static magnetic field to the iron oxide core WO-MS shell materials did not have a significant impact on the doxorubicin release. This is the first time that the effects of pore topology and iron oxide core have been isolated from pore diameter and particle size for these materials.

Variational-based segmentation of bio-pores in tomographic images

NASA Astrophysics Data System (ADS)

Bauer, Benjamin; Cai, Xiaohao; Peth, Stephan; Schladitz, Katja; Steidl, Gabriele

2017-01-01

X-ray computed tomography (CT) combined with a quantitative analysis of the resulting volume images is a fruitful technique in soil science. However, the variations in X-ray attenuation due to different soil components keep the segmentation of single components within these highly heterogeneous samples a challenging problem. Particularly demanding are bio-pores due to their elongated shape and the low gray value difference to the surrounding soil structure. Recently, variational models in connection with algorithms from convex optimization were successfully applied for image segmentation. In this paper we apply these methods for the first time for the segmentation of bio-pores in CT images of soil samples. We introduce a novel convex model which enforces smooth boundaries of bio-pores and takes the varying attenuation values in the depth into account. Segmentation results are reported for different real-world 3D data sets as well as for simulated data. These results are compared with two gray value thresholding methods, namely indicator kriging and a global thresholding procedure, and with a morphological approach. Pros and cons of the methods are assessed by considering geometric features of the segmented bio-pore systems. The variational approach features well-connected smooth pores while not detecting smaller or shallower pores. This is an advantage in cases where the main bio-pores network is of interest and where infillings, e.g., excrements of earthworms, would result in losing pore connections as observed for the other thresholding methods.

Spectro-microscopic study of the formation of supramolecular networks

NASA Astrophysics Data System (ADS)

Sadowski, Jerzy T.

2015-03-01

Metal-organic frameworks (MOFs) are emerging as a new class of materials for CO2 capture. There are many fundamental questions, including the optimum pore size and arrangement of the molecules in the structure to achieve highest CO2 uptake. As only the surface is of interest for potential applications such as heterogeneous catalysis, nano-templating, and sensing, 2D analogs of MOFs can serve as good model systems. Utilizing capabilities of LEEM/PEEM for non-destructive interrogation of the real-time molecular self-assembly, we investigated supramolecular systems based on carboxylic acid-metal complexes, such as trimesic and mellitic acid, doped with transition metals. Such 2D networks act as host systems for transition-metal phthalocyanines (MPc; M = Fe, Ti, Sc) and the electrostatic interactions of CO2 molecules with transition metal ions, can be tuned by controlling the type of TM ion and the size of the pore in the host network. The understanding of directed self-assembly by controlling the molecule-substrate interaction can enable us to engineer the pore size and density, and thus tune the host's chemical activity. Research carried out at the Center for Functional Nanomaterials and National Synchrotron Light Source, Brookhaven National Laboratory, which are supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10.

Porous Electrodes I: Numerical Simulation Using Random Network and Single Pore Models.

DTIC Science & Technology

1984-01-31

characteristic of Zn and ZnO ) and scaling them down to the magnitude of a unit pore size- approximately 10i in diameter. We define a characteristic...supported by the Office of Naval Research under contract N00014-81-K-0339. 11 - 15 - REFERENCES 1. R. de Levis in Advances in Electrochemistry and...P. 3. Hendra Dr. C. E. Mueller Department of Chemistry The Electrochemistry Branch University of Southampton Naval Surface Weapons Center

Proceedings of the SERDP Coral Reef Monitoring and Assessment Workshop

DTIC Science & Technology

2009-12-01

the U.S. that have coral reefs within their jurisdictions. Biscayne National Park, the Dry Tortugas , and U.S. Virgin Island parks at St. John and...Signs Monitoring Networks Dry Tortugas NP Buck Island Reef NM Virgin Islands National Park Biscayne NP South Florida/Caribbean Network Florida/Caribbean...Buck Island, Dry Tortugas and Biscayne • Extensive sites – 4 10m permanent transects per site – 18 sites in DRTO Virgin Islands NP % l i v e c o r

Preparation of amine-impregnated silica foams using agar as the gelling agent

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jardim, Iara M., E-mail: iaramj01@yahoo.com.br

In this work we successfully prepared amine-impregnated gel-cast silica foams using agar and atmospheric air as the gelling agent and heat treatment atmosphere, respectively. The concentration of 3,6-anhydrogalactose in agar was evaluated by ultraviolet–visible spectroscopy (UV–Vis). The obtained foams were examined by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG) coupled to mass spectrometry (TG-MS), scanning electron microscopy (SEM), X-ray microtomography (micro-CT), and Archimedes method. The cold crushing strength of the materials prepared in this work was assessed using a mechanical testing stage available in the micro-CT system. The obtained foams exhibited a highly interconnected pore network, with an expressivemore » presence of open pores. Samples heat-treated at 1300 °C for 2 h showed both an expressive porosity (≈ 77%) and a significant cold crushing strength (≈ 1.4 MPa). It was observed that the calcination of the prepared materials at 1200 °C for times as long as 16 h may lead to the rupture of pore walls. FTIR and TG-MS revealed that amine groups were properly incorporated into the foams structure. - Highlights: •Successful preparation of amine-impregnated gel-cast silica foams •Agar used as the gelling agent •Samples with expressive porosity and cold crushing strength •Sintering times as long as 16 h led to the rupture of the pore network.« less

Electrical conductivity of Icelandic deep geothermal reservoirs: insight from HT-HP laboratory experiments

NASA Astrophysics Data System (ADS)

Nono, Franck; Gibert, Benoit; Loggia, Didier; Parat, Fleurice; Azais, Pierre; Cichy, Sarah

2016-04-01

Although the Icelandic geothermal system has been intensively investigated over the years, targeting increasingly deeper reservoirs (i.e. under supercritical conditions) requires a good knowledge of the behaviour of physical properties of the host rock in order to better interpret large scale geophysical observations. In particular, the interpretation of deep electrical soundings remains controversial as only few studies have investigated the influence of altered minerals and pore fluid properties on electrical properties of rocks at high temperature and pressure. In this study, we investigate the electrical conductivity of drilled samples from different Icelandic geothermal fields at elevated temperature, confining pressure and pore pressure conditions (100°C < T < 600°C, confining pressure up to 100 MPa and pore pressure up to 35 MPa). The investigated rocks are composed of hyaloclastites, dolerites and basalts taken from depths of about 800 m for the hyaloclastites, to almost 2500 m for the dolerites. They display different porosity structures, from vuggy and intra-granular to micro-cracked porosities, and have been hydrothermally alterated in the chlorite to amphibolite facies. Electrical conductivity measurements are first determined at ambient conditions as a function of pore fluid conductivity in order to establish their relationships with lithology and pore space topology, prior to the high pressure and temperature measurements. Cementation factor varies from 1.5 for the dolerites to 2.83 for the basalt, reflecting changes in the shape of the conductive channels. The surface conductivities, measured at very low fluid conductivity, increases with the porosity and is correlated with the cation exchange capacity. At high pressure and temperature, we used the two guard-ring electrodes system. Measurements have been performed in dry and saturated conditions as a function of temperature and pore pressure. The supercritical conditions have been investigated and temperature cycles have been performed systematically. Dry electrical conductivity measurements show for most of the samples irreversible changes when temperatures exceed 500°C. These changes are interpreted as destabilization/dehydration of alteration minerals that could lead to the presence of a conductive fluid phase in the samples. Very low and high salinity (NaCl) electrical conductivity measurements have been performed as a function of temperature. At supercritical conditions, electrical conductivity at low salinity is not pore pressure dependent and surface conduction is preponderant. At saturated conditions, the rock's electrical conductivity increases linearly (as a function of T-1) until 350°C. Above 350°C, the conductivity decreases. All rock types exhibit the same increasing rate. This work was funded by the of the EC project IMAGE (Integrated Methods for Advanced Geothermal Exploration, grant agreement No. 608553).

Characterization of Pores in Dense Nanopapers and Nanofibrillated Cellulose Membranes: A Critical Assessment of Established Methods.

PubMed

Orsolini, Paola; Michen, Benjamin; Huch, Anja; Tingaut, Philippe; Caseri, Walter R; Zimmermann, Tanja

2015-11-25

Nanofibrillated cellulose (NFC) is a natural fibrous material that can be readily processed into membranes. NFC membranes for fluid separation work in aqueous medium, thus in their swollen state. The present study is devoted to a critical investigation of porosity, pore volume, specific surface area, and pore size distribution of dry and wet NFC nanopapers, also known as membranes, with various established techniques, such as electron microscopy, helium pycnometry, mercury intrusion, gas adsorption (N2 and Kr), and thermoporometry. Although these techniques can be successfully applied to inorganic materials (e.g., mesoporous silica), it is necessary to appraise them for organic and hydrophilic products such as NFC membranes. This is due to different phenomena occurring at the materials interfaces with the probing fluids. Mercury intrusion and gas adsorption are often used for the characterization of porosity-related properties; nevertheless, both techniques characterize materials in the dry state. In parallel, thermoporometry was employed to monitor the structure changes upon swelling, and a water permeance test was run to show the accessibility of the membranes to fluids. For the first time, the methods were systematically screened, and we highlighted the need of uniform sample treatments prior to the measurements (i.e., sample cutting and outgassing protocols) in order to harmonize results from the literature. The need for revising the applicability range of mercury intrusion and the inappropriateness of nitrogen adsorption were pointed out. We finally present a table for selecting the most appropriate method to determine a desired property and propose guidelines for results interpretation from which future users could profit.

Colloid Mobilization in a Fractured Soil during Dry-Wet Cycles: Role of Drying Duration and Flow Path Permeability.

PubMed

Mohanty, Sanjay K; Saiers, James E; Ryan, Joseph N

2015-08-04

In subsurface soils, colloids are mobilized by infiltrating rainwater, but the source of colloids and the process by which colloids are generated between rainfalls are not clear. We examined the effect of drying duration and the spatial variation of soil permeability on the mobilization of in situ colloids in intact soil cores (fractured and heavily weathered saprolite) during dry-wet cycles. Measuring water flux at multiple sampling ports at the core base, we found that water drained through flow paths of different permeability. The duration of antecedent drying cycles affected the amount of mobilized colloids, particularly in high-flux ports that received water from soil regions with a large number of macro- and mesopores. In these ports, the amount of mobilized colloids increased with increased drying duration up to 2.5 days. For drying durations greater than 2.5 days, the amount of mobilized colloids decreased. In contrast, increasing drying duration had a limited effect on colloid mobilization in low-flux ports, which presumably received water from soil regions with fewer macro- and mesopores. On the basis of these results, we attribute this dependence of colloid mobilization upon drying duration to colloid generation from dry pore walls and distribution of colloids in flow paths, which appear to be sensitive to the moisture content of soil after drying and flow path permeability. The results are useful for improving the understanding of colloid mobilization during fluctuating weather conditions.

Pore-Confined Carriers and Biomolecules in Mesoporous Silica for Biomimetic Separation and Targeting

NASA Astrophysics Data System (ADS)

Zhou, Shanshan

Selectively permeable biological membranes composed of lipophilic barriers inspire the design of biomimetic carrier-mediated membranes for aqueous solute separation. This work imparts selective permeability to lipid-filled pores of silica thin film composite membranes using carrier molecules that reside in the lipophilic self-assemblies. The lipids confined inside the pores of silica are proven to be a more effective barrier than bilayers formed on the porous surface through vesicle fusion, which is critical for quantifying the function of an immobilized carrier. The ability of a lipophilic carrier embedded in the lipid bilayer to reversibly bind the target solute and transport it through the membrane is demonstrated. Through the functionalization of the silica surface with enzymes, enzymatic catalysis and biomimetic separations can be combined on this nanostructured composite platform. The successful development of biomimetic nanocomposite membrane can provide for efficient dilute aqueous solute upgrading or separations using engineered carrier/catalyst/support systems. While the carrier-mediated biomimetic membranes hold great potential, fully understanding of the transport processes in composite synthetic membranes is essential for improve the membrane performance. Electrochemical impedance spectroscopy (EIS) technique is demonstrated to be a useful tool for characterizing the thin film pore accessibility. Furthermore, the effect of lipid bilayer preparation methods on the silica thin film (in the form of pore enveloping, pore filling) on ion transport is explored, as a lipid bilayer with high electrically insulation is essential for detecting activity of proteins or biomimetic carriers in the bilayer. This study provides insights for making better barriers on mesoporous support for carrier-mediated membrane separation process. Porous silica nanoparticles (pSNPs) with pore sizes appropriate for biomolecule loading are potential for encapsulating dsRNA within the pores to achieve effective delivery of dsRNA to insects for RNA interference (RNAi). The mobility of dsRNA in the nanopores of the pSNPs is expected to have a functional effect on delivery of dsRNA to insects. The importance of pores to a mobile dsRNA network is demonstrated by the lack of measurable mobility for both lengths of RNA on nonporous materials. In addition, when the dsRNA could not penetrate the pores, dsRNA mobility is also not measurable at the surface of the particle. Thus, the pores seem to serve as a "sink" in providing a mobile network of dsRNA on the surface of the particle. This work successfully demonstrates the loading of RNA on functionalized pSNPs and identified factors that affects RNA loading and releasing, which provides basis for the delivery of RNA-loaded silica particles in vivo.

Nutrient Recovery from the Dry Grind Process Using Sequential Micro and Ultrafiltration of Thin Stillage

USDA-ARS?s Scientific Manuscript database

The effectiveness of microfiltration (MF) and ultrafiltration (UF) for nutrient recovery from a thin stillage stream was determined. When a stainless steel MF membrane (0.1 um pore size) was used, the content of solids increased from 7.0% to 22.8% with a mean permeate flux rate of 45 L/m**2/h (LMH)...

Water storage characteristics of several peats in situ

Treesearch

D.H. Boelter

1964-01-01

Water storage characteristics of the various horizons in a northern Minnesota bog were found to vary considerably with peat type. Surface horizons of sphagnum moss contain 0.020 g. per cc. of dry material and 95 to nearly 100% water by volume at saturation. Its total porosity consisted primarily of large pores which released 0.80 cc. of water per cc. between saturation...

Fabrication of Activated Rice Husk Charcoal by Slip Casting as a Hybrid Material for Water Filter Aid

NASA Astrophysics Data System (ADS)

Tuaprakone, T.; Wongphaet, N.; Wasanapiarnpong, T.

2011-04-01

Activated charcoal has been widely used as an odor absorbent in household and water purification industry. Filtration equipment for drinking water generally consists of four parts, which are microporous membrane (porous alumina ceramic or diatomite, or porous polymer), odor absorbent (activated carbon), hard water treatment (ion exchange resin), and UV irradiation. Ceramic filter aid is usually prepared by slip casting of alumina or diatomite. The membrane offers high flux, high porosity and maximum pore size does not exceed 0.3 μm. This study investigated the fabrication of hybrid activated charcoal tube for water filtration and odor absorption by slip casting. The suitable rice husk charcoal and water ratio was 48 to 52 wt% by weight with 1.5wt% (by dry basis) of CMC binder. The green rice husk charcoal bodies were dried and fired between 700-900 °C in reduction atmosphere. The resulting prepared slip in high speed porcelain pot for 60 min and sintered at 700 °C for 1 h showed the highest specific surface area as 174.95 m2/g. The characterizations of microstructure and pore size distribution as a function of particle size were investigated.

Reticular synthesis of porous molecular 1D nanotubes and 3D networks.

PubMed

Slater, A G; Little, M A; Pulido, A; Chong, S Y; Holden, D; Chen, L; Morgan, C; Wu, X; Cheng, G; Clowes, R; Briggs, M E; Hasell, T; Jelfs, K E; Day, G M; Cooper, A I

2017-01-01

Synthetic control over pore size and pore connectivity is the crowning achievement for porous metal-organic frameworks (MOFs). The same level of control has not been achieved for molecular crystals, which are not defined by strong, directional intermolecular coordination bonds. Hence, molecular crystallization is inherently less controllable than framework crystallization, and there are fewer examples of 'reticular synthesis', in which multiple building blocks can be assembled according to a common assembly motif. Here we apply a chiral recognition strategy to a new family of tubular covalent cages to create both 1D porous nanotubes and 3D diamondoid pillared porous networks. The diamondoid networks are analogous to MOFs prepared from tetrahedral metal nodes and linear ditopic organic linkers. The crystal structures can be rationalized by computational lattice-energy searches, which provide an in silico screening method to evaluate candidate molecular building blocks. These results are a blueprint for applying the 'node and strut' principles of reticular synthesis to molecular crystals.

Reticular synthesis of porous molecular 1D nanotubes and 3D networks

NASA Astrophysics Data System (ADS)

Slater, A. G.; Little, M. A.; Pulido, A.; Chong, S. Y.; Holden, D.; Chen, L.; Morgan, C.; Wu, X.; Cheng, G.; Clowes, R.; Briggs, M. E.; Hasell, T.; Jelfs, K. E.; Day, G. M.; Cooper, A. I.

2017-01-01

Synthetic control over pore size and pore connectivity is the crowning achievement for porous metal-organic frameworks (MOFs). The same level of control has not been achieved for molecular crystals, which are not defined by strong, directional intermolecular coordination bonds. Hence, molecular crystallization is inherently less controllable than framework crystallization, and there are fewer examples of 'reticular synthesis', in which multiple building blocks can be assembled according to a common assembly motif. Here we apply a chiral recognition strategy to a new family of tubular covalent cages to create both 1D porous nanotubes and 3D diamondoid pillared porous networks. The diamondoid networks are analogous to MOFs prepared from tetrahedral metal nodes and linear ditopic organic linkers. The crystal structures can be rationalized by computational lattice-energy searches, which provide an in silico screening method to evaluate candidate molecular building blocks. These results are a blueprint for applying the 'node and strut' principles of reticular synthesis to molecular crystals.

Mesoporous Silicate Materials in Sensing

PubMed Central

Melde, Brian J.; Johnson, Brandy J.; Charles, Paul T.

2008-01-01

Mesoporous silicas, especially those exhibiting ordered pore systems and uniform pore diameters, have shown great potential for sensing applications in recent years. Morphological control grants them versatility in the method of deployment whether as bulk powders, monoliths, thin films, or embedded in coatings. High surface areas and pore sizes greater than 2 nm make them effective as adsorbent coatings for humidity sensors. The pore networks also provide the potential for immobilization of enzymes within the materials. Functionalization of materials by silane grafting or through co-condensation of silicate precursors can be used to provide mesoporous materials with a variety of fluorescent probes as well as surface properties that aid in selective detection of specific analytes. This review will illustrate how mesoporous silicas have been applied to sensing changes in relative humidity, changes in pH, metal cations, toxic industrial compounds, volatile organic compounds, small molecules and ions, nitroenergetic compounds, and biologically relevant molecules. PMID:27873810

Water retention curve for hydrate-bearing sediments

NASA Astrophysics Data System (ADS)

Dai, Sheng; Santamarina, J. Carlos

2013-11-01

water retention curve plays a central role in numerical algorithms that model hydrate dissociation in sediments. The determination of the water retention curve for hydrate-bearing sediments faces experimental difficulties, and most studies assume constant water retention curves regardless of hydrate saturation. This study employs network model simulation to investigate the water retention curve for hydrate-bearing sediments. Results show that (1) hydrate in pores shifts the curve to higher capillary pressures and the air entry pressure increases as a power function of hydrate saturation; (2) the air entry pressure is lower in sediments with patchy rather than distributed hydrate, with higher pore size variation and pore connectivity or with lower specimen slenderness along the flow direction; and (3) smaller specimens render higher variance in computed water retention curves, especially at high water saturation Sw > 0.7. Results are relevant to other sediment pore processes such as bioclogging and mineral precipitation.

A level set method for determining critical curvatures for drainage and imbibition.

PubMed

Prodanović, Masa; Bryant, Steven L

2006-12-15

An accurate description of the mechanics of pore level displacement of immiscible fluids could significantly improve the predictions from pore network models of capillary pressure-saturation curves, interfacial areas and relative permeability in real porous media. If we assume quasi-static displacement, at constant pressure and surface tension, pore scale interfaces are modeled as constant mean curvature surfaces, which are not easy to calculate. Moreover, the extremely irregular geometry of natural porous media makes it difficult to evaluate surface curvature values and corresponding geometric configurations of two fluids. Finally, accounting for the topological changes of the interface, such as splitting or merging, is nontrivial. We apply the level set method for tracking and propagating interfaces in order to robustly handle topological changes and to obtain geometrically correct interfaces. We describe a simple but robust model for determining critical curvatures for throat drainage and pore imbibition. The model is set up for quasi-static displacements but it nevertheless captures both reversible and irreversible behavior (Haines jump, pore body imbibition). The pore scale grain boundary conditions are extracted from model porous media and from imaged geometries in real rocks. The method gives quantitative agreement with measurements and with other theories and computational approaches.

Molecular accessibility in solvent swelled coal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kispert, L.D.

1991-08-01

Research continued on the determination of pore size and number distribution changes after swelling the coal samples with various solvents. A paper has just been submitted to the journal Fuel on the Low temperature Swelling of Argonne Premium Coal samples using solvents of varying polarity. The variation in the shape of the pore was followed as a function of temperature and swelling solvent polarity. This change in pore structure was attributed to break-up of the hydrogen bonding network in coal by polar solvents. The modification in pore shape from spherical to cylindrical was attributed to anisotropy in hydrogen bond densities.more » A copy of this paper has been attached to this report. Wojciech Sady has determine the structural changes in the pores that occur when APCS coal is dehydrated prior to swelling with polar solvents. These changes are different from those that occur in the absence of prior dehydration. He has also completed a study on the variation in the hydrogen bonding character of the pore wall as the coals are swelled with various polar solvents. A statistical analysis of the data is currently underway to determine important trends in his data. 9 refs.« less

Modeling of submicrometer aerosol penetration through sintered granular membrane filters.

PubMed

Marre, Sonia; Palmeri, John; Larbot, André; Bertrand, Marielle

2004-06-01

We present a deep-bed aerosol filtration model that can be used to estimate the efficiency of sintered granular membrane filters in the region of the most penetrating particle size. In this region the capture of submicrometer aerosols, much smaller than the filter pore size, takes place mainly via Brownian diffusion and direct interception acting in synergy. By modeling the disordered sintered grain packing of such filters as a simple cubic lattice, and mapping the corresponding 3D connected pore volume onto a discrete cylindrical pore network, the efficiency of a granular filter can be estimated, using new analytical results for the efficiency of cylindrical pores. This model for aerosol penetration in sintered granular filters includes flow slip and the kinetics of particle capture by the pore surface. With a unique choice for two parameters, namely the structural tortuosity and effective kinetic coefficient of particle adsorption, this semiempirical model can account for the experimental efficiency of a new class of "high-efficiency particulate air" ceramic membrane filters as a function of particle size over a wide range of filter thickness and texture (pore size and porosity) and operating conditions (face velocity).

Sol-gel processed porous silica carriers for the controlled release of diclofenac diethylamine.

PubMed

Czarnobaj, Katarzyna; Czarnobaj, Joanna

2008-10-01

Silica xerogels doped with diclofenac diethylamine were prepared by the sol-gel method from a hydrolysed tetraethoxysilane (TEOS) solution containing diclofenac diethylamine. Two different catalysts, drying conditions and levels of water content were used to alter the microstructure of the silica xerogels. The aim of this study was to determine the rate of Diclofenac release from the silica xerogels. This in vitro study showed that the sol-gel method is useful for entrapping Diclofenac in the pores of xerogels. It also showed that, in vitro, Diclofenac is released from the silica xerogel, through the pores, by diffusion. Base-catalysed gels proved to be much more effective than acid-catalyzed gels. (c) 2008 Wiley Periodicals, Inc.

Drying techniques for the visualisation of agarose-based chromatography media by scanning electron microscopy.

PubMed

Nweke, Mauryn C; Turmaine, Mark; McCartney, R Graham; Bracewell, Daniel G

2017-03-01

The drying of chromatography resins prior to scanning electron microscopy is critical to image resolution and hence understanding of the bead structure at sub-micron level. Achieving suitable drying conditions is especially important with agarose-based chromatography resins, as over-drying may cause artefact formation, bead damage and alterations to ultrastructural properties; and under-drying does not provide sufficient resolution for visualization under SEM. This paper compares and contrasts the effects of two drying techniques, critical point drying and freeze drying, on the morphology of two agarose based resins (MabSelect™/d w ≈85 µm and Capto™ Adhere/d w ≈75 µm) and provides a complete method for both. The results show that critical point drying provides better drying and subsequently clearer ultrastructural visualization of both resins under SEM. Under this protocol both the polymer fibers (thickness ≈20 nm) and the pore sizes (diameter ≈100 nm) are clearly visible. Freeze drying is shown to cause bead damage to both resins, but to different extents. MabSelect resin encounters extensive bead fragmentation, whilst Capto Adhere resin undergoes partial bead disintegration, corresponding with the greater extent of agarose crosslinking and strength of this resin. While freeze drying appears to be the less favorable option for ultrastructural visualization of chromatography resin, it should be noted that the extent of fracturing caused by the freeze drying process may provide some insight into the mechanical properties of agarose-based chromatography media. © 2017 The Authors. Biotechnology Journal published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Modeling of a heat sink and high heat flux vapor chamber

NASA Astrophysics Data System (ADS)

Vadnjal, Aleksander

An increasing demand for a higher heat flux removal capability within a smaller volume for high power electronics led us to focus on a novel cold plate design. A high heat flux evaporator and micro channel heat sink are the main components of a cold plate which is capable of removing couple of 100 W/cm2. In order to describe performance of such porous media device a proper modeling has to be addressed. A universal approach based on the volume average theory (VAT) to transport phenomena in porous media is shown. An approach on how to treat the closure for momentum and energy equations is addressed and a proper definition for friction factors and heat transfer coefficients are discussed. A numerical scheme using a solution to Navier-Stokes equations over a representative elementary volume (REV) and the use of VAT is developed to show how to compute friction factors and heat transfer coefficients. The calculation show good agreement with the experimental data. For the heat transfer coefficient closure, a proper average for both fluid and solid is investigated. Different types of heating are also investigated in order to determine how it influences the heat transfer coefficient. A higher heat fluxes in small area condensers led us to the micro channels in contrast to the classical heat fin design. A micro channel can have various shapes to enhance heat transfer, but the shape that will lead to a higher heat flux removal with a moderate pumping power needs to be determined. The standard micro-channel terminology is usually used for channels with a simple cross section, e.g. square, round, triangle, etc., but here the micro channel cross section is going to be expanded to describe more complicated and interconnected micro scale channel cross sections. The micro channel geometries explored are pin fins (in-line and staggered) and sintered porous micro channels. The problem solved here is a conjugate problem involving two heat transfer mechanisms; (1) porous media conductivity and (2) internal heat transfer coefficient. Volume averaging theory (VAT) is used to rigorously cast the point wise conservation of energy, momentum and mass equations into a form that represents the thermal and hydraulic properties of the micro channel (porous media) morphology. Using the resulting VAT based field equations, optimization of a micro channel heated from one side is used to determine the optimum micro channel morphology. A small square of 1 cm2 is chosen as an example and the thermal resistance, 0C/W, and pressure drop are shown as a function of Reynolds number. The high heat flux removal on small surfaces at moderately small temperatures is achieved by bi-porous evaporator The device was analyzed with the possibility of heat flux magnitudes exceeding 1kW/cm2 by using advantages of a dual pore structure of a bi-porous wick. The heat transfer model of a thin bi-porous wick is developed and it incorporates thermo-physical properties of a bi-porous media. It is shown that physics of heat removal is characterized in three stages; conduction, big pore drying out and small pore drying out. The operating conditions of the wick have to be in a safe margin away from the total dry out. A complete dry out of the wick inevitably leads to the burn out, therefore more concern has been added to modeling of big pore dry out, since this will be a desired operational. The construction of the boiling/evaporation curves was successfully constructed by the model showing that the physic of heat removal on two different length scales is governed by thermo-physical properties for the appropriate scale. The model shows good prediction for various combinations of big and small pores size in the bi-porous wicks tested.

Dynamic pore-scale network model (PNM) of water imbibition in porous media

NASA Astrophysics Data System (ADS)

Li, J.; McDougall, S. R.; Sorbie, K. S.

2017-09-01

A dynamic pore-scale network model is presented which simulates 2-phase oil/water displacement during water imbibition by explicitly modelling intra-pore dynamic bulk and film flows using a simple local model. A new dynamic switching parameter, λ, is proposed within this model which is able to simulate the competition between local capillary forces and viscous forces over a very wide range of flow conditions. This quantity (λ) determines the primary pore filling mechanism during imbibition; i.e. whether the dominant force is (i) piston-like displacement under viscous forces, (ii) film swelling/collapse and snap-off due to capillary forces, or (iii) some intermediate local combination of both mechanisms. A series of 2D dynamic pore network simulations is presented which shows that the λ-model can satisfactorily reproduce and explain different filling regimes of water imbibition over a wide range of capillary numbers (Ca) and viscosity ratios (M). These imbibition regimes are more complex than those presented under drainage by (Lenormand et al. (1983)), since they are determined by a wider group of control parameters. Our simulations show that there is a coupling between viscous and capillary forces that is much less important in drainage. The effects of viscosity ratio during imbibition are apparent even under conditions of very slow flow (low Ca)-displacements that would normally be expected to be completely capillary dominated. This occurs as a result of the wetting films having a much greater relative mobility in the higher M cases (e.g. M = 10) thus leading to a higher level of film swelling/snap-off, resulting in local oil cluster bypassing and trapping, and hence a poorer oil recovery. This deeper coupled viscous mechanism is the underlying reason why the microscopic displacement efficiency is lower for higher M cases in water imbibition processes. Additional results are presented from the dynamic model on the corresponding effluent fractional flows (fw) and global pressure drops (ΔP) as functions of capillary number and viscosity ratio. These results indicate that unsteady-state (USS) relatively permeabilities in imbibition should be inherently rate dependent.

Pore-scale simulations of drainage in granular materials: Finite size effects and the representative elementary volume

NASA Astrophysics Data System (ADS)

Yuan, Chao; Chareyre, Bruno; Darve, Félix

2016-09-01

A pore-scale model is introduced for two-phase flow in dense packings of polydisperse spheres. The model is developed as a component of a more general hydromechanical coupling framework based on the discrete element method, which will be elaborated in future papers and will apply to various processes of interest in soil science, in geomechanics and in oil and gas production. Here the emphasis is on the generation of a network of pores mapping the void space between spherical grains, and the definition of local criteria governing the primary drainage process. The pore space is decomposed by Regular Triangulation, from which a set of pores connected by throats are identified. A local entry capillary pressure is evaluated for each throat, based on the balance of capillary pressure and surface tension at equilibrium. The model reflects the possible entrapment of disconnected patches of the receding wetting phase. It is validated by a comparison with drainage experiments. In the last part of the paper, a series of simulations are reported to illustrate size and boundary effects, key questions when studying small samples made of spherical particles be it in simulations or experiments. Repeated tests on samples of different sizes give evolution of water content which are not only scattered but also strongly biased for small sample sizes. More than 20,000 spheres are needed to reduce the bias on saturation below 0.02. Additional statistics are generated by subsampling a large sample of 64,000 spheres. They suggest that the minimal sampling volume for evaluating saturation is one hundred times greater that the sampling volume needed for measuring porosity with the same accuracy. This requirement in terms of sample size induces a need for efficient computer codes. The method described herein has a low algorithmic complexity in order to satisfy this requirement. It will be well suited to further developments toward coupled flow-deformation problems in which evolution of the microstructure require frequent updates of the pore network.

Dual porosity gas evolving electrode

DOEpatents

Townsend, Carl W.

1994-01-01

A dual porosity electrode for use in thermoelectrochemical systems where simultaneous transport of gas and liquid into and/or out of the electrode is required. The electrode includes catalytic electrode particles having diameters ranging from about 25 to 100 angstroms. The catalytic electrode particles are anchored to a support network in clusters which have internal pores ranging in size from 25 to 100 angstroms. The pores between the clusters range in size from between about 1 to 20 microns. A method for making the dual porosity electrodes is also disclosed.

Real rock-microfluidic flow cell: A test bed for real-time in situ analysis of flow, transport, and reaction in a subsurface reactive transport environment.

PubMed

Singh, Rajveer; Sivaguru, Mayandi; Fried, Glenn A; Fouke, Bruce W; Sanford, Robert A; Carrera, Martin; Werth, Charles J

2017-09-01

Physical, chemical, and biological interactions between groundwater and sedimentary rock directly control the fundamental subsurface properties such as porosity, permeability, and flow. This is true for a variety of subsurface scenarios, ranging from shallow groundwater aquifers to deeply buried hydrocarbon reservoirs. Microfluidic flow cells are now commonly being used to study these processes at the pore scale in simplified pore structures meant to mimic subsurface reservoirs. However, these micromodels are typically fabricated from glass, silicon, or polydimethylsiloxane (PDMS), and are therefore incapable of replicating the geochemical reactivity and complex three-dimensional pore networks present in subsurface lithologies. To address these limitations, we developed a new microfluidic experimental test bed, herein called the Real Rock-Microfluidic Flow Cell (RR-MFC). A porous 500μm-thick real rock sample of the Clair Group sandstone from a subsurface hydrocarbon reservoir of the North Sea was prepared and mounted inside a PDMS microfluidic channel, creating a dynamic flow-through experimental platform for real-time tracking of subsurface reactive transport. Transmitted and reflected microscopy, cathodoluminescence microscopy, Raman spectroscopy, and confocal laser microscopy techniques were used to (1) determine the mineralogy, geochemistry, and pore networks within the sandstone inserted in the RR-MFC, (2) analyze non-reactive tracer breakthrough in two- and (depth-limited) three-dimensions, and (3) characterize multiphase flow. The RR-MFC is the first microfluidic experimental platform that allows direct visualization of flow and transport in the pore space of a real subsurface reservoir rock sample, and holds potential to advance our understandings of reactive transport and other subsurface processes relevant to pollutant transport and cleanup in groundwater, as well as energy recovery. Copyright © 2017 Elsevier B.V. All rights reserved.

Evolutionarily Conserved Sequence Features Regulate the Formation of the FG Network at the Center of the Nuclear Pore Complex

PubMed Central

Peyro, M.; Soheilypour, M.; Lee, B.L.; Mofrad, M.R.K.

2015-01-01

The nuclear pore complex (NPC) is the portal for bidirectional transportation of cargos between the nucleus and the cytoplasm. While most of the structural elements of the NPC, i.e. nucleoporins (Nups), are well characterized, the exact transport mechanism is still under much debate. Many of the functional Nups are rich in phenylalanine-glycine (FG) repeats and are believed to play the key role in nucleocytoplasmic transport. We present a bioinformatics study conducted on more than a thousand FG Nups across 252 species. Our results reveal the regulatory role of polar residues and specific sequences of charged residues, named ‘like charge regions’ (LCRs), in the formation of the FG network at the center of the NPC. Positively charged LCRs prepare the environment for negatively charged cargo complexes and regulate the size of the FG network. The low number density of charged residues in these regions prevents FG domains from forming a relaxed coil structure. Our results highlight the significant role of polar interactions in FG network formation at the center of the NPC and demonstrate that the specific localization of LCRs, FG motifs, charged, and polar residues regulate the formation of the FG network at the center of the NPC. PMID:26541386

Anisotropic Dye Adsorption and Anhydrous Proton Conductivity in Smectic Liquid Crystal Networks: The Role of Cross-Link Density, Order, and Orientation.

PubMed

Liang, Ting; van Kuringen, Huub P C; Mulder, Dirk J; Tan, Shuai; Wu, Yong; Borneman, Zandrie; Nijmeijer, Kitty; Schenning, Albertus P H J

2017-10-11

In this work, the decisive role of rigidity, orientation, and order in the smectic liquid crystalline network on the anisotropic proton and adsorbent properties is reported. The rigidity in the hydrogen-bonded polymer network has been altered by changing the cross-link density, the order by using different mesophases (smectic, nematic, and isotropic phases), whereas the orientation of the mesogens was controlled by alignment layers. Adding more cross-linkers improved the integrity of the polymer films. For the proton conduction, an optimum was found in the amount of cross-linker and the smectic organization results in the highest anhydrous proton conduction. The polymer films show anisotropic proton conductivity with a 54 times higher conductivity in the direction perpendicular to the molecular director. After a base treatment of the smectic liquid crystalline network, a nanoporous polymer film is obtained that also shows anisotropic adsorption of dye molecules and again straight smectic pores are favored over disordered pores in nematic and isotropic networks. The highly cross-linked films show size-selective adsorption of dyes. Low cross-linked materials do not show this difference due to swelling, which decreases the order and creates openings in the two-dimensional polymer layers. The latter is, however, beneficial for fast adsorption kinetics.

Artificial neural network modeling of DDGS flowability with varying process and storage parameters

USDA-ARS?s Scientific Manuscript database

Neural Network (NN) modeling techniques were used to predict flowability behavior in distillers dried grains with solubles (DDGS) prepared with varying CDS (10, 15, and 20%, wb), drying temperature (100, 200, and 300°C), cooling temperature (-12, 0, and 35°C) and cooling time (0 and 1 month) levels....

Diffusion Dominant Solute Transport Modelling In Deep Repository Under The Effect of Emplacement Media Degradation - 13285

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kwong, S.; Jivkov, A.P.

2013-07-01

Deep geologic disposal of high activity and long-lived radioactive waste is being actively considered and pursued in many countries, where low permeability geological formations are used to provide long term waste contaminant with minimum impact to the environment and risk to the biosphere. A multi-barrier approach that makes use of both engineered and natural barriers (i.e. geological formations) is often used to further enhance the containment performance of the repository. As the deep repository system subjects to a variety of thermo-hydro-chemo-mechanical (THCM) effects over its long 'operational' lifespan (e.g. 0.1 to 1.0 million years, the integrity of the barrier systemmore » will decrease over time (e.g. fracturing in rock or clay)). This is broadly referred as media degradation in the present study. This modelling study examines the effects of media degradation on diffusion dominant solute transport in fractured media that are typical of deep geological environment. In particular, reactive solute transport through fractured media is studied using a 2-D model, that considers advection and diffusion, to explore the coupled effects of kinetic and equilibrium chemical processes, while the effects of degradation is studied using a pore network model that considers the media diffusivity and network changes. Model results are presented to demonstrate the use of a 3D pore-network model, using a novel architecture, to calculate macroscopic properties of the medium such as diffusivity, subject to pore space changes as the media degrade. Results from a reactive transport model of a representative geological waste disposal package are also presented to demonstrate the effect of media property change on the solute migration behaviour, illustrating the complex interplay between kinetic biogeochemical processes and diffusion dominant transport. The initial modelling results demonstrate the feasibility of a coupled modelling approach (using pore-network model and reactive transport model) to examine the long term behaviour of deep geological repositories with media property change under complex geochemical conditions. (authors)« less

A forward analysis on the applicability of tracer breakthrough profiles in revealing the pore structure of tight gas sandstone and carbonate rocks

NASA Astrophysics Data System (ADS)

Mehmani, Ayaz; Mehmani, Yashar; Prodanović, Maša.; Balhoff, Matthew

2015-06-01

We explore tracer breakthrough profiles (TBP) as a macroscopic property to infer the pore-space topology of tight gas sandstone and carbonate rocks at the core scale. The following features were modeled via three-dimensional multiscale networks: microporosity within dissolved grains and pore-filling clay, cementation in the absence and presence of microporosity (each classified into uniform, pore-preferred, and throat-preferred modes), layering, vug, and microcrack inclusion. A priori knowledge of the extent and location of each process was assumed to be known. With the exception of an equal importance of macropores and pore-filling micropores, TBPs show little sensitivity to the fraction of micropores present. In general, significant sensitivity of the TBPs was observed for uniform and throat-preferred cementation. Layering parallel to the fluid flow direction had a considerable impact on TBPs whereas layering perpendicular to flow did not. Microcrack orientations seemed of minor importance in affecting TBPs. This article was corrected on 9 Nov 2015. See the end of the full text for details.

Enrichment of pasta with faba bean does not impact glycemic or insulin response but can enhance satiety feeling and digestive comfort when dried at very high temperature.

PubMed

Greffeuille, Valérie; Marsset-Baglieri, Agnès; Molinari, Nicolas; Cassan, Denis; Sutra, Thibault; Avignon, Antoine; Micard, Valérie

2015-09-01

Enrichment of durum wheat pasta with legume flour enhances their protein and essential amino acid content, especially lysine content. However, despite its nutritional potential, the addition of a legume alters the rheological properties of pasta. High temperature drying of pasta reduces this negative effect by strengthening its protein network. The aim of our study was to determine if these changes in the pasta structure alter its in vitro carbohydrate digestibility, in vivo glycemic, insulin and satiety responses. We also investigated if high temperature drying of pasta can reduce the well-known digestive discomfort associated with the consumption of legume grains. Fifteen healthy volunteers consumed three test meals: durum wheat pasta dried at a low temperature (control), and pasta enriched with 35% faba bean dried at a low and at a very high temperature. When enriched with 35% legume flour, pasta maintained its nutritionally valuable low glycemic and insulin index, despite its weaker protein network. Drying 35% faba bean pasta at a high temperature strengthened its protein network, and decreased its in vitro carbohydrate digestion with no further decrease in its in vivo glycemic or insulin index. Drying pasta at a very high temperature reduced digestive discomfort and enhanced self-reported satiety, and was not associated with a modification of energy intake in the following meal.

Triconstituent co-assembly to ordered mesostructured polymer-silica and carbon-silica nanocomposites and large-pore mesoporous carbons with high surface areas.

PubMed

Liu, Ruili; Shi, Yifeng; Wan, Ying; Meng, Yan; Zhang, Fuqiang; Gu, Dong; Chen, Zhenxia; Tu, Bo; Zhao, Dongyuan

2006-09-06

Highly ordered mesoporous polymer-silica and carbon-silica nanocomposites with interpenetrating networks have been successfully synthesized by the evaporation-induced triconstituent co-assembly method, wherein soluble resol polymer is used as an organic precursor, prehydrolyzed TEOS is used as an inorganic precursor, and triblock copolymer F127 is used as a template. It is proposed for the first time that ordered mesoporous nanocomposites have "reinforced concrete"-structured frameworks. By adjusting the initial mass ratios of TEOS to resol, we determined the obtained nanocomposites possess continuous composition with the ratios ranging from zero to infinity for the two constituents that are "homogeneously" dispersed inside the pore walls. The presence of silicates in nanocomposites dramatically inhibits framework shrinkage during the calcination, resulting in highly ordered large-pore mesoporous carbon-silica nanocomposites. Combustion in air or etching in HF solution can remove carbon or silica from the carbon-silica nanocomposites and yield ordered mesoporous pure silica or carbon frameworks. The process generates plenty of small pores in carbon or/and silica pore walls. Ordered mesoporous carbons can then be obtained with large pore sizes of approximately 6.7 nm, pore volumes of approximately 2.0 cm(3)/g, and high surface areas of approximately 2470 m(2)/g. The pore structures and textures can be controlled by varying the sizes and polymerization degrees of two constituent precursors. Accordingly, by simply tuning the aging time of TEOS, ordered mesoporous carbons with evident bimodal pores at 2.6 and 5.8 nm can be synthesized.

Fluid displacement fronts in porous media: pore scale interfacial jumps, pressure bursts and acoustic emissions

NASA Astrophysics Data System (ADS)

Moebius, Franziska; Or, Dani

2014-05-01

The macroscopically smooth and regular motion of fluid fronts in porous media is composed of numerous rapid pore-scale interfacial jumps and pressure bursts that involve intense interfacial energy release in the form of acoustic emissions. The characteristics of these pore scale events affect residual phase entrapment and transport properties behind the front. We present experimental studies using acoustic emission technique (AE), rapid imaging, and liquid pressure measurements to characterize these processes during drainage and imbibition in simple porous media. Imbibition and drainage produce different AE signatures (AE amplitudes obey a power law). For rapid drainage, AE signals persist long after cessation of front motion reflecting fluid redistribution and interfacial relaxation. Imaging revealed that the velocity of interfacial jumps often exceeds front velocity by more than 50 fold and is highly inertial component (Re>1000). Pore invasion volumes reduced deduced from pressure fluctuations waiting times (for constant withdrawal rates) show remarkable agreement with geometrically-deduced pore volumes. Discrepancies between invaded volumes and geometrical pores increase with increasing capillary numbers due to constraints on evacuation opportunity times and simultaneous invasion events. A mechanistic model for interfacial motions in a pore-throat network was developed to investigate interfacial dynamics focusing on the role of inertia. Results suggest that while pore scale dynamics were sensitive to variations in pore geometry and boundary conditions, inertia exerted only a minor effect on phase entrapment. The study on pore scale invasion events paints a complex picture of rapid and inertial motions and provides new insights on mechanisms at displacement fronts that are essential for improved macroscopic description of multiphase flows in porous media.

Localization and Instability in Sheared Granular Materials: Role of Pore Fluids and Non-monotonic Rate Dependent Rheology

NASA Astrophysics Data System (ADS)

Ma, X.; Elbanna, A. E.; Kothari, K.

2017-12-01

Fault zone dynamics hold the key to resolving many outstanding geophysical problems including the heat flow paradox, discrepancy between fault static and dynamic strength, and energy partitioning. Most fault zones that generate tectonic events are gouge filled and fluid saturated posing the need for formulating gouge-specific constitutive models that capture spatially heterogeneous compaction and dilation, non-monotonic rate dependence, and transition between localized and distributed deformation. In this presentation, we focus primarily on elucidating microscopic underpinnings for shear banding and stick-slip instabilities in sheared saturated granular materials and explore their implications for earthquake dynamics. We use a non-equilibrium thermodynamics model, the Shear Transformation Zone theory, to investigate the dynamics of strain localization and its connection to stability of sliding in the presence and absence of pore fluids. We also consider the possible influence of self-induced mechanical vibrations as well as the role of external acoustic vibrations as analogue for triggering by a distant event. For the dry case, our results suggest that at low and intermediate strain rates, persistent shear bands develop only in the absence of vibrations. Vibrations tend to fluidize the granular network and de-localize slip at these rates. Stick-slip is only observed for rough grains and it is confined to the shear band. At high strain rates, stick-slip disappears and the different systems exhibit similar stress-slip response. Changing the vibration intensity, duration or time of application alters the system response and may cause long-lasting rheological changes. The presence of pore fluids modifies the stick slip pattern and may lead to both loss and development of slip instability depending on the value of the confining pressure, imposed strain rate and hydraulic parameters. We analyze these observations in terms of possible transitions between rate strengthening and rate weakening response facilitated by a competition between shear induced dilation and acoustic compaction. We discuss the implications of our results on dynamic triggering, quiescence and strength evolution in gouge filled fault zones.