Microstructure Evolution and Mechanical Behavior of 2219 Aluminum Alloys Additively Fabricated by the Cold Metal Transfer Process

PubMed Central

Fang, Xuewei; Li, Hui; Li, Chaolong; Lu, Bingheng

2018-01-01

In this research, four different welding arc modes including conventional cold metal transfer (CMT), CMT-Pulse (CMT-P), CMT-Advanced (CMT-ADV), and CMT pulse advanced (CMT-PADV) were used to deposit 2219-Al wire. The effects of different arc modes on porosity, pore size distribution, microstructure evolution, and mechanical properties were thoroughly investigated. The statistical analysis of the porosity and its size distribution indicated that the CMT-PADV process gave the smallest pore area percentage and pore aspect ratio, and had almost no larger pores. The results from optical microscopy, scanning electron microscopy, and fractographic morphology proved that uniform and fine equiaxed grains, evenly distributed Al2Cu second phase particles were formed during the CMT-PADV process. Furthermore, the X-ray diffraction test ascertained that the CMT-PADV sample had the smallest lattice parameter and the highest solute Cu content. Besides, the tensile strength could reach 283 MPa, the data scattering was the smallest, and the strength scattering of the sample in the horizontal direction was the shortest. In addition, the strength properties were nearly isotropic, with only 5 MPa difference in the vertical and horizontal directions. The above mentioned results indicated that the mechanical properties of 2219 aluminum alloy was improved using the CMT-PADV arc mode. PMID:29772708

Microstructure Evolution and Mechanical Behavior of 2219 Aluminum Alloys Additively Fabricated by the Cold Metal Transfer Process.

PubMed

Fang, Xuewei; Zhang, Lijuan; Li, Hui; Li, Chaolong; Huang, Ke; Lu, Bingheng

2018-05-16

In this research, four different welding arc modes including conventional cold metal transfer (CMT), CMT-Pulse (CMT-P), CMT-Advanced (CMT-ADV), and CMT pulse advanced (CMT-PADV) were used to deposit 2219-Al wire. The effects of different arc modes on porosity, pore size distribution, microstructure evolution, and mechanical properties were thoroughly investigated. The statistical analysis of the porosity and its size distribution indicated that the CMT-PADV process gave the smallest pore area percentage and pore aspect ratio, and had almost no larger pores. The results from optical microscopy, scanning electron microscopy, and fractographic morphology proved that uniform and fine equiaxed grains, evenly distributed Al₂Cu second phase particles were formed during the CMT-PADV process. Furthermore, the X-ray diffraction test ascertained that the CMT-PADV sample had the smallest lattice parameter and the highest solute Cu content. Besides, the tensile strength could reach 283 MPa, the data scattering was the smallest, and the strength scattering of the sample in the horizontal direction was the shortest. In addition, the strength properties were nearly isotropic, with only 5 MPa difference in the vertical and horizontal directions. The above mentioned results indicated that the mechanical properties of 2219 aluminum alloy was improved using the CMT-PADV arc mode.

High surface area, low weight composite nickel fiber electrodes

NASA Technical Reports Server (NTRS)

Johnson, Bradley A.; Ferro, Richard E.; Swain, Greg M.; Tatarchuk, Bruce J.

1993-01-01

The energy density and power density of light weight aerospace batteries utilizing the nickel oxide electrode are often limited by the microstructures of both the collector and the resulting active deposit in/on the collector. Heretofore, these two microstructures were intimately linked to one another by the materials used to prepare the collector grid as well as the methods and conditions used to deposit the active material. Significant weight and performance advantages were demonstrated by Britton and Reid at NASA-LeRC using FIBREX nickel mats of ca. 28-32 microns diameter. Work in our laboratory investigated the potential performance advantages offered by nickel fiber composite electrodes containing a mixture of fibers as small as 2 microns diameter (Available from Memtec America Corporation). These electrode collectors possess in excess of an order of magnitude more surface area per gram of collector than FIBREX nickel. The increase in surface area of the collector roughly translates into an order of magnitude thinner layer of active material. Performance data and advantages of these thin layer structures are presented. Attributes and limitations of their electrode microstructure to independently control void volume, pore structure of the Ni(OH)2 deposition, and resulting electrical properties are discussed.

Analysis of the ceramic layer microstructure influence on plasma spray thermal barrier coating performance

NASA Astrophysics Data System (ADS)

Bogdanovich, V. I.; Giorbelidze, M. G.

2017-12-01

This paper outlines the results of analysis and describes the structure of the thermal protection coatings formed by atomic ion stream deposition in vacuum, and plasma thermal spraying method. Crystallite structure features are considered along with the crystallite dimensions, spatial orientation, and position of the boundaries between separate crystallites. Discontinuity, volume, and morphology of the pores has been evaluated. Experimental studies have been accomplished using various fractions of the powder-like material ZrO2 - 8%Y2O3. The influence of the coating microstructure on the coating performance has been analyzed, such as adhesive strength, thermal stability, and thermal conductivity.

Characteristics and engineering properties of residual soil of volcanic deposits

NASA Astrophysics Data System (ADS)

Wibawa, Y. S.; Sugiarti, K.; Soebowo, E.

2018-02-01

Residual soil knowledge of volcanic-sedimentary rock products provides important information on the soil bearing capacity and its engineering properties. The residual soil is the result of weathering commonly found in unsaturated conditions, having varied geotechnical characteristics at each level of weathering. This paper summarizes the results of the research from the basic engineering properties of residual soil of volcanic-sedimentary rocks from several different locations. The main engineering properties of residual soil such as specific gravity, porosity, grain size, clay content (X-Ray test) and soil shear strength are performed on volcanic rock deposits. The results show that the variation of the index and engineering properties and the microstructure properties of residual soil have the correlation between the depths of weathering levels. Pore volume and pore size distribution on weathered rock profiles can be used as an indication of weathering levels in the tropics.

Plasma etching a ceramic composite. [evaluating microstructure

NASA Technical Reports Server (NTRS)

Hull, David R.; Leonhardt, Todd A.; Sanders, William A.

1992-01-01

Plasma etching is found to be a superior metallographic technique for evaluating the microstructure of a ceramic matrix composite. The ceramic composite studied is composed of silicon carbide whiskers (SiC(sub W)) in a matrix of silicon nitride (Si3N4), glass, and pores. All four constituents are important in evaluating the microstructure of the composite. Conventionally prepared samples, both as-polished or polished and etched with molten salt, do not allow all four constituents to be observed in one specimen. As-polished specimens allow examination of the glass phase and porosity, while molten salt etching reveals the Si3N4 grain size by removing the glass phase. However, the latter obscures the porosity. Neither technique allows the SiC(sub W) to be distinguished from the Si3N4. Plasma etching with CF4 + 4 percent O2 selectively attacks the Si3N4 grains, leaving SiC(sub W) and glass in relief, while not disturbing the pores. An artifact of the plasma etching reaction is the deposition of a thin layer of carbon on Si3N4, allowing Si3N4 grains to be distinguished from SiC(sub W) by back scattered electron imaging.

Characterization of reactive flow-induced evolution of carbonate rocks using digital core analysis - part 2: Calculation of the evolution of percolation and transport properties.

PubMed

Qajar, Jafar; Arns, Christoph H

2017-09-01

Percolation of reactive fluids in carbonate rocks affects the rock microstructure and hence changes the rock macroscopic properties. In Part 1 paper, we examined the voxel-wise evolution of microstructure of the rock in terms of mineral dissolution/detachment, mineral deposition, and unchanged regions. In the present work, we investigate the relationships between changes in two characteristic transport properties, i.e. permeability and electrical conductivity and two critical parameters of the pore phase, i.e. the fraction of the pore space connecting the inlet and outlet faces of the core sample and the critical pore-throat diameter. We calculate the aforementioned properties on the images of the sample, wherein a homogeneous modification of pore structure occurred in order to ensure the representativeness of the calculated transport properties at the core scale. From images, the evolution of pore connectivity and the potential role of micropores on the connectivity are quantified. It is found that the changing permeability and electrical conductivity distributions along the core length are generally in good agreement with the longitudinal evolution of macro-connected macroporosity and the critical pore-throat diameter. We incorporate microporosity into critical length and permeability calculations and show how microporosity locally plays a role in permeability. It is shown that the Katz-Thompson model reasonably predicts the post-alteration permeability in terms of pre-alteration simulated parameters. This suggests that the evolution of permeability and electrical conductivity of the studied complex carbonate core are controlled by the changes in the macro-connected macroporosity as well as the smallest pore-throats between the connected macropores. Copyright © 2017 Elsevier B.V. All rights reserved.

Generation of random microstructures and prediction of sound velocity and absorption for open foams with spherical pores.

PubMed

Zieliński, Tomasz G

2015-04-01

This paper proposes and discusses an approach for the design and quality inspection of the morphology dedicated for sound absorbing foams, using a relatively simple technique for a random generation of periodic microstructures representative for open-cell foams with spherical pores. The design is controlled by a few parameters, namely, the total open porosity and the average pore size, as well as the standard deviation of pore size. These design parameters are set up exactly and independently, however, the setting of the standard deviation of pore sizes requires some number of pores in the representative volume element (RVE); this number is a procedure parameter. Another pore structure parameter which may be indirectly affected is the average size of windows linking the pores, however, it is in fact weakly controlled by the maximal pore-penetration factor, and moreover, it depends on the porosity and pore size. The proposed methodology for testing microstructure-designs of sound absorbing porous media applies the multi-scale modeling where some important transport parameters-responsible for sound propagation in a porous medium-are calculated from microstructure using the generated RVE, in order to estimate the sound velocity and absorption of such a designed material.

Wear and Corrosion Resistance of Thick Ti-6Al-4V Coating Deposited on Ti-6Al-4V Substrate via High-Pressure Cold Spray

NASA Astrophysics Data System (ADS)

Khun, N. W.; Tan, A. W. Y.; Sun, W.; Liu, E.

2017-08-01

Ti-6Al-4V (Ti64) coating with a thickness of about 9 mm was deposited on commercial Ti64 substrate via a high-pressure cold spray process. The microstructure, hardness, and wear and corrosion resistance of the Ti64 coating were systematically investigated. The hardness of the Ti64 coating was higher than that of the Ti64 substrate due to the cold-worked microstructure of the coating. The tribological results showed that there was no significant difference in the surface wear rates of the Ti64 coating measured on its different layers while the surface wear resistance of the Ti64 coating was lower than its cross-sectional wear resistance. The corrosion results showed that the Ti64 coating did not effectively prevent its underlying Ti64 substrate from corrosion due to the occurrence of pores in the coating microstructure. It could be concluded that the hardness and wear resistance of the Ti64 coating were comparable to those of the commercial Ti64 substrate.

Effects of pore formers on microstructure and performance of cathode membranes for solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Nie, Lifang; Liu, Juncheng; Zhang, Yujun; Liu, Meilin

La 0.6Sr 0.4Co 0.2Fe 0.8O 3- δ (LSCF) is the most widely used cathode material for intermediate temperature solid oxide fuel cells. In the present communication, porous LSCF cathodes are fabricated by tape casting, a low-cost and reproducible fabrication process. The effects of four different pore formers, namely, graphite, carbon black, rice starch, and corn starch, on the microstructure and electrochemical performance of the LSCF cathode are investigated. Examination of the microstructures reveals that the shape of the pores, the pore size, and the pore distribution in the final ceramic are related to the type of pore formers. Impedance analysis and cell testing show that the best performance is obtained from the cathode using graphite as the pore former. The microstructure indicates that graphite results in a porous LSCF cathode with a large surface area and high porosity, which can offer a considerably long triple phase boundary for catalytic reactions as well as channels for gas phase transport.

Multi-scale Multi-dimensional Imaging and Characterization of Oil Shale Pyrolysis

NASA Astrophysics Data System (ADS)

Gao, Y.; Saif, T.; Lin, Q.; Al-Khulaifi, Y.; Blunt, M. J.; Bijeljic, B.

2017-12-01

The microstructural evaluation of fine grained rocks is challenging which demands the use of several complementary methods. Oil shale, a fine-grained organic-rich sedimentary rock, represents a large and mostly untapped unconventional hydrocarbon resource with global reserves estimated at 4.8 trillion barrels. The largest known deposit is the Eocene Green River Formation in Western Colorado, Eastern Utah, and Southern Wyoming. An improved insight into the mineralogy, organic matter distribution and pore network structure before, during and after oil shale pyrolysis is critical to understanding hydrocarbon flow behaviour and improving recovery. In this study, we image Mahogany zone oil shale samples in two dimensions (2-D) using scanning electron microscopy (SEM), and in three dimensions (3-D) using focused ion beam scanning electron microscopy (FIB-SEM), laboratory-based X-ray micro-tomography (µCT) and synchrotron X-ray µCT to reveal a complex and variable fine grained microstructure dominated by organic-rich parallel laminations which are tightly bound in a highly calcareous and heterogeneous mineral matrix. We report the results of a detailed µCT study of the Mahogany oil shale with increasing pyrolysis temperature. The physical transformation of the internal microstructure and evolution of pore space during the thermal conversion of kerogen in oil shale to produce hydrocarbon products was characterized. The 3-D volumes of pyrolyzed oil shale were reconstructed and image processed to visualize and quantify the volume and connectivity of the pore space. The results show a significant increase in anisotropic porosity associated with pyrolysis between 300-500°C with the formation of micron-scale connected pore channels developing principally along the kerogen-rich lamellar structures.

Hydroxyapatite coatings deposited by liquid precursor plasma spraying: controlled dense and porous microstructures and osteoblastic cell responses.

PubMed

Huang, Yi; Song, Lei; Liu, Xiaoguang; Xiao, Yanfeng; Wu, Yao; Chen, Jiyong; Wu, Fang; Gu, Zhongwei

2010-12-01

Hydroxyapatite coatings were deposited on Ti-6Al-4V substrates by a novel plasma spraying process, the liquid precursor plasma spraying (LPPS) process. X-ray diffraction results showed that the coatings obtained by the LPPS process were mainly composed of hydroxyapatite. The LPPS process also showed excellent control on the coating microstructure, and both nearly fully dense and highly porous hydroxyapatite coatings were obtained by simply adjusting the solid content of the hydroxyapatite liquid precursor. Scanning electron microscope observations indicated that the porous hydroxyapatite coatings had pore size in the range of 10-200 µm and an average porosity of 48.26 ± 0.10%. The osteoblastic cell responses to the dense and porous hydroxyapatite coatings were evaluated with human osteoblastic cell MG-63, in respect of the cell morphology, proliferation and differentiation, with the hydroxyapatite coatings deposited by the atmospheric plasma spraying (APS) process as control. The cell experiment results indicated that the heat-treated LPPS coatings with a porous structure showed the best cell proliferation and differentiation among all the hydroxyapatite coatings. Our results suggest that the LPPS process is a promising plasma spraying technique for fabricating hydroxyapatite coatings with a controllable microstructure, which has great potential in bone repair and replacement applications.

Modeling of Processing-Induced Pore Morphology in an Additively-Manufactured Ti-6Al-4V Alloy

PubMed Central

Kabir, Mohammad Rizviul; Richter, Henning

2017-01-01

A selective laser melting (SLM)-based, additively-manufactured Ti-6Al-4V alloy is prone to the accumulation of undesirable defects during layer-by-layer material build-up. Defects in the form of complex-shaped pores are one of the critical issues that need to be considered during the processing of this alloy. Depending on the process parameters, pores with concave or convex boundaries may occur. To exploit the full potential of additively-manufactured Ti-6Al-4V, the interdependency between the process parameters, pore morphology, and resultant mechanical properties, needs to be understood. By incorporating morphological details into numerical models for micromechanical analyses, an in-depth understanding of how these pores interact with the Ti-6Al-4V microstructure can be gained. However, available models for pore analysis lack a realistic description of both the Ti-6Al-4V grain microstructure, and the pore geometry. To overcome this, we propose a comprehensive approach for modeling and discretizing pores with complex geometry, situated in a polycrystalline microstructure. In this approach, the polycrystalline microstructure is modeled by means of Voronoi tessellations, and the complex pore geometry is approximated by strategically combining overlapping spheres of varied sizes. The proposed approach provides an elegant way to model the microstructure of SLM-processed Ti-6Al-4V containing pores or crack-like voids, and makes it possible to investigate the relationship between process parameters, pore morphology, and resultant mechanical properties in a finite-element-based simulation framework. PMID:28772504

Modeling of Processing-Induced Pore Morphology in an Additively-Manufactured Ti-6Al-4V Alloy.

PubMed

Kabir, Mohammad Rizviul; Richter, Henning

2017-02-08

A selective laser melting (SLM)-based, additively-manufactured Ti-6Al-4V alloy is prone to the accumulation of undesirable defects during layer-by-layer material build-up. Defects in the form of complex-shaped pores are one of the critical issues that need to be considered during the processing of this alloy. Depending on the process parameters, pores with concave or convex boundaries may occur. To exploit the full potential of additively-manufactured Ti-6Al-4V, the interdependency between the process parameters, pore morphology, and resultant mechanical properties, needs to be understood. By incorporating morphological details into numerical models for micromechanical analyses, an in-depth understanding of how these pores interact with the Ti-6Al-4V microstructure can be gained. However, available models for pore analysis lack a realistic description of both the Ti-6Al-4V grain microstructure, and the pore geometry. To overcome this, we propose a comprehensive approach for modeling and discretizing pores with complex geometry, situated in a polycrystalline microstructure. In this approach, the polycrystalline microstructure is modeled by means of Voronoi tessellations, and the complex pore geometry is approximated by strategically combining overlapping spheres of varied sizes. The proposed approach provides an elegant way to model the microstructure of SLM-processed Ti-6Al-4V containing pores or crack-like voids, and makes it possible to investigate the relationship between process parameters, pore morphology, and resultant mechanical properties in a finite-element-based simulation framework.

Microstructural Evolution in Solution Heat Treatment of Gas-Atomized Al Alloy (7075) Powder for Cold Spray

NASA Astrophysics Data System (ADS)

Sabard, A.; de Villiers Lovelock, H. L.; Hussain, T.

2018-01-01

Cold gas dynamic spray is being explored as a repair technique for high-value metallic components, given its potential to produce pore and oxide-free deposits of between several micrometers and several millimeters thick with good levels of adhesion and mechanical strength. However, feedstock powders for cold spray experience rapid solidification if manufactured by gas atomization and hence can exhibit non-equilibrium microstructures and localized segregation of alloying elements. Here, we used sealed quartz tube solution heat treatment of a precipitation hardenable 7075 aluminum alloy feedstock to yield a consistent and homogeneous powder phase composition and microstructure prior to cold spraying, aiming for a more controllable heat treatment response of the cold spray deposits. It was shown that the dendritic microstructure and solute segregation in the gas-atomized powders were altered, such that the heat-treated powder exhibits a homogeneous distribution of solute atoms. Micro-indentation testing revealed that the heat-treated powder exhibited a mean hardness decrease of nearly 25% compared to the as-received powder. Deformation of the powder particles was enhanced by heat treatment, resulting in an improved coating with higher thickness ( 300 μm compared to 40 μm for untreated feedstock). Improved particle-substrate bonding was evidenced by formation of jets at the particle boundaries.

Microstructure and Microhardness of 17-4PH Deposited with Co-based Alloy Hardfacing Coating

NASA Astrophysics Data System (ADS)

Deng, D. W.; Zhang, C. P.; Chen, R.; Xia, H. F.

Hardfacing is widely used to improve the performance of components exposed to severe service conditions. In this paper, the surface modification was evaluated for precipitation hardening martensitic stainless steel 17-4PH deposited with Co-based alloy stellite12 by the plasma-transferred arc welding (PTAW). The microstructure and microhardness of coating and heat affected zone(HAZ) of base metal were characterized by optical microscope (OM), scanning electron scanning microscope (SEM), X-ray diffractometer and hardness tester. The results show that the interface between weld metal and base metal is favorable without pore and crack, at the same time elements diffusion is observed in the fusion area. However, as the distance from the interface increases, HAZ comprises three different microstructural zones, namely, zones of coarse overheated structures, quenching martensite and martensite, ferrite. The microhardness decreases gradually from the HAZ near interface to the base metal, except the zone of coarse overheated structures. The microhardness of the coating improves a lot and fluctuates in a definitive range, and microstructural gradient is observed including the fusion area (the planar region and the bulky dendrite in a direction perpendicular to the weld interface), the transition zone (the dendrite in a multi-direction way) and the fine grain zone near the surface in the coating (fine equiaxial structure).

Modeling of phase transformations of Ti6Al4 V during laser metal deposition

NASA Astrophysics Data System (ADS)

Suárez, A.; Tobar, M. J.; Yáñez, A.; Pérez, I.; Sampedro, J.; Amigó, V.; Candel, J. J.

The low density, excellent high temperature mechanical properties and good corrosion resistance of titanium and its alloys have led to a diversified range of successful applications. As a consequence, there is a demand of increasing the capabilities of processing such alloys. The laser cladding technique allows direct metal deposition with an excellent metallurgical bond and a pore free fine grained microstructure. A nonlinear transient thermo-metallurgical model was developed to study the technique with titanium alloys to get a better understanding of the thermal and metallurgical underlying aspects. The calculated temperatures and phase transformations are compared with experimental tests.

Pore- and micro-structural characterization of a novel structural binder based on iron carbonation

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

Das, Sumanta, E-mail: Sumanta.Das@asu.edu; Stone, David, E-mail: dajstone@gmail.com; Convey, Diana, E-mail: Diana.Convey@asu.edu

2014-12-15

The pore- and micro-structural features of a novel binding material based on the carbonation of waste metallic iron powder are reported in this paper. The binder contains metallic iron powder as the major ingredient, followed by additives containing silica and alumina to facilitate favorable reaction product formation. Compressive strengths sufficient for a majority of concrete applications are attained. The material pore structure is investigated primarily through mercury intrusion porosimetry whereas electron microscopy is used for microstructural characterization. Reduction in the overall porosity and the average pore size with an increase in carbonation duration from 1 day to 4 days ismore » noticed. The pore structure features are used in predictive models for gas and moisture transport (water vapor diffusivity and moisture permeability) through the porous medium which dictates its long-term durability when used in structural applications. Comparisons of the pore structure with those of a Portland cement paste are also provided. The morphology of the reaction products in the iron-based binder, and the distribution of constituent elements in the microstructure are also reported. - Highlights: • Carbonation of iron produces a dense microstructure. • Pore volume in iron carbonate lower, critical size higher than those in OPC pastes • Reaction product contains iron, carbon, silicon, aluminum and calcium. • Power-law for porosity-moisture permeability relationship was established.« less

Carbon foam/hydroxyapatite coating for carbon/carbon composites: Microstructure and biocompatibility

NASA Astrophysics Data System (ADS)

Zhang, Leilei; Li, Hejun; Li, Kezhi; Zhang, Shouyang; Lu, Jinhua; Li, Wei; Cao, Sheng; Wang, Bin

2013-12-01

To improve the surface biocompatibility of carbon/carbon composites, a carbon foam/hydroxyapatite coating was applied using a combination method of slurry procedure and ultrasound-assisted electrochemical deposition procedure. The morphology, microstructure and chemical composition of the coating were investigated by scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and X-ray diffraction. The biocompatibility of the carbon foam/hydroxyapatite coating was investigated by osteoblast-like MG63 cell culture tests. The results showed that the carbon foam could provide a large number of pores on the surface of carbon/carbon composites. The hydroxyapatite crystals could infiltrate into the pores and form the carbon foam/hydroxyapatite coating. The coating covered the carbon/carbon composites fully and uniformly with slice morphology. The cell response tests showed that the MG63 cells on carbon foam/hydroxyapatite coating had a better cell adhesion and cell proliferation than those on uncoated carbon/carbon composites. The carbon foam/hydroxyapatite coatings were cytocompatible and were beneficial to improve the biocompatibility. The approach presented here may be exploited for fabrication of carbon/carbon composite implant surfaces.

Porous silicon carbide and aluminum oxide with unidirectional open porosity as model target materials for radioisotope beam production

NASA Astrophysics Data System (ADS)

Czapski, M.; Stora, T.; Tardivat, C.; Deville, S.; Santos Augusto, R.; Leloup, J.; Bouville, F.; Fernandes Luis, R.

2013-12-01

New silicon carbide (SiC) and aluminum oxide (Al2O3) of a tailor-made microstructure were produced using the ice-templating technique, which permits controlled pore formation conditions within the material. These prototypes will serve to verify aging of the new advanced target materials under irradiation with proton beams. Before this, the evaluation of their mechanical integrity was made based on the energy deposition spectra produced by FLUKA codes.

Experimental study on microstructure characters of foamed lightweight soil

NASA Astrophysics Data System (ADS)

Qiu, Youqiang; Li, Yongliang; Li, Meixia; Liu, Yaofu; Zhang, Liujun

2018-01-01

In order to verify the microstructure of foamed lightweight soil and its characters of compressive strength, four foamed lightweight soil samples with different water-soild ratio were selected and the microstructure characters of these samples were scanned by electron microscope. At the same time, the characters of compressive strength of foamed lightweight soil were analyzed from the microstructure. The study results show that the water-soild ratio has a prominent effect on the microstructure and compressive strength of foamed lightweight soil, with the decrease of water-solid ratio, the amount and the perforation of pores would be reduced significantly, thus eventually forming a denser and fuller interior structure. Besides, the denser microstructure and solider pore-pore wall is benefit to greatly increase mechanical intensity of foamed lightweight soil. In addition, there are very few acicular ettringite crystals in the interior of foamed lightweight soil, its number is also reduced with the decrease in water-soild ratio.

Multi-Scale Porous Ultra High Temperature Ceramics

DTIC Science & Technology

2015-01-08

different techniques: replica, particle stabilized foams, ice templating (freeze casting) and partial sintering. The pore morphology (closed-bubble...the porosity, pore size, shape and morphology . X-Ray Tomography was used to study their 3D microstructure. The 3D microstructures captured with...four different techniques: replica, particle stabilized foams, ice templating (freeze casting) and partial sintering. The pore morphology (closed-bubble

3D Analysis of Porosity in a Ceramic Coating Using X-ray Microscopy

NASA Astrophysics Data System (ADS)

Klement, Uta; Ekberg, Johanna; Kelly, Stephen T.

2017-02-01

Suspension plasma spraying (SPS) is a new, innovative plasma spray technique using a feedstock consisting of fine powder particles suspended in a liquid. Using SPS, ceramic coatings with columnar microstructures have been produced which are used as topcoats in thermal barrier coatings. The microstructure contains a wide pore size range consisting of inter-columnar spacings, micro-pores and nano-pores. Hence, determination of total porosity and pore size distribution is a challenge. Here, x-ray microscopy (XRM) has been applied for describing the complex pore space of the coatings because of its capability to image the (local) porosity within the coating in 3D at a resolution down to 50 nm. The possibility to quantitatively segment the analyzed volume allows analysis of both open and closed porosity. For an yttria-stabilized zirconia coating with feathery microstructure, both open and closed porosity were determined and it could be revealed that 11% of the pore volumes (1.4% of the total volume) are closed pores. The analyzed volume was reconstructed to illustrate the distribution of open and closed pores in 3D. Moreover, pore widths and pore volumes were determined. The results on the complex pore space obtained by XRM are discussed in connection with other porosimetry techniques.

Microtomographic quantification of hydraulic clay mineral displacement effects during a CO2 sequestration experiment with saline aquifer sandstone.

PubMed

Sell, Kathleen; Enzmann, Frieder; Kersten, Michael; Spangenberg, Erik

2013-01-02

We combined a noninvasive tomographic imaging technique with an invasive open-system core-flooding experiment and compared the results of the pre- and postflooded states of an experimental sandstone core sample from an ongoing field trial for carbon dioxide geosequestration. For the experiment, a rock core sample of 80 mL volume was taken from the 629 m Stuttgart Formation storage domain of a saline sandstone aquifer at the CCS research pilot plant Ketzin, Germany. Supercritical carbon dioxide and synthetical brine were injected under in situ reservoir p/T-conditions at an average flow rate of 0.1 mL/min for 256 h. X-ray computed microtomographic imaging was carried out before and after the core-flooding experiment at a spatial voxel resolution of 27 μm. No significant changes in microstructure were found at the tomographic imaging resolution including porosity and pore size distribution, except of an increase of depositional heterogeneous distribution of clay minerals in the pores. The digitized rock data were used as direct real microstructure input to the GeoDict software package, to simulate Navier-Stokes flow by a lattice Boltzmann equation solver. This procedure yielded 3D pressure and flow velocity fields, and revealed that the migration of clay particles decreased the permeability tensor probably due to clogging of pore openings.

Mechanistic principles of colloidal crystal growth by evaporation-induced convective steering.

PubMed

Brewer, Damien D; Allen, Joshua; Miller, Michael R; de Santos, Juan M; Kumar, Satish; Norris, David J; Tsapatsis, Michael; Scriven, L E

2008-12-02

We simulate evaporation-driven self-assembly of colloidal crystals using an equivalent network model. Relationships between a regular hexagonally close-packed array of hard, monodisperse spheres, the associated pore space, and selectivity mechanisms for face-centered cubic microstructure propagation are described. By accounting for contact line rearrangement and evaporation at a series of exposed menisci, the equivalent network model describes creeping flow of solvent into and through a rigid colloidal crystal. Observations concerning colloidal crystal growth are interpreted in terms of the convective steering hypothesis, which posits that solvent flow into and through the pore space of the crystal may play a major role in colloidal self-assembly. Aspects of the convective steering and deposition of high-Peclet-number rigid spherical particles at a crystal boundary are inferred from spatially resolved solvent flow into the crystal. Gradients in local flow through boundary channels were predicted due to the channels' spatial distribution relative to a pinned free surface contact line. On the basis of a uniform solvent and particle flux as the criterion for stability of a particular growth plane, these network simulations suggest the stability of a declining {311} crystal interface, a symmetry plane which exclusively propagates fcc microstructure. Network simulations of alternate crystal planes suggest preferential growth front evolution to the declining {311} interface, in consistent agreement with the proposed stability mechanism for preferential fcc microstructure propagation in convective assembly.

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.

Effect of heat treatment on the microstructure of Co-Cr-W alloy fabricated by laser additive manufacturing

NASA Astrophysics Data System (ADS)

Ren, Bo; Chen, Changjun; Zhang, Min

2018-04-01

Stellite 6 cobalt-based alloy powder was used to produce Co-Cr-W alloy using laser additive manufacturing technology, and then different heat treatment strategies were carried out on the deposited sample. The characteristics of microstructure under different heat treatment conditions were investigated using scanning electron microscopy with energy dispersive spectroscopy, transmission electron microscope, and x-ray diffraction. The results show that the as-deposited sample has few cracks or pores, and the microstructure is typical dendritic structure, and lamellar eutectic carbides are rich in Cr in interdendritic. The matrix mainly consists of γ phases and a few ɛ phases. Some γ phases transform into ɛ phases after 900°C/6 h aging treatment and lamellar eutectic carbides transform into blocky carbides presenting as a network, most of the carbides are rich in Cr and a few are rich in W. When heat treated at 1200°C/1 h followed by water cooling and then treated at 900°C/6 h followed by furnace cooling, it can be found that some γ phases transform into ɛ phases. The carbides transform into elliptical M23C6 carbides that are rich in Cr with the size of 1 to 3 μm and a part of W-rich carbides.

Spatial variations in a.c. susceptibility and microstructure for the YBa2Cu3O(7-x) superconductor and their correlation with room-temperature ultrasonic measurements

NASA Technical Reports Server (NTRS)

Roth, Don J.; Hepp, Aloysius F.; Deguire, Mark R.; Dolhert, Leonard E.

1991-01-01

The spatial (within-sample) uniformity of superconducting behavior and microstructure in YBa2Cu30(7-x) specimens over the pore fraction range of 0.10 to 0.25 was examined. The viability of using a room-temperature, nondestructive characterization method (ultrasonic velocity imaging) to predict spatial variability was determined. Spatial variations in superconductor properties were observed for specimens containing 0.10 pore fraction. An ultrasonic velocity image constructed from measurements at 1 mm increments across one such specimen revealed microstructural variation between edge and center locations that correlated with variations in alternating-current shielding and loss behavior. Optical quantitative image analysis on sample cross-sections revealed pore fraction to be the varying microstructural feature.

Spatial variations in ac susceptibility and microstructure for the YBa2Cu3O(7-x) superconductor and their correlation with room-temperature ultrasonic measurements

NASA Technical Reports Server (NTRS)

Roth, Don J.; Deguire, Mark R.; Dolhert, Leonard E.; Hepp, Aloysius F.

1991-01-01

The spatial (within-sample) uniformity of superconducting behavior and microstructure in YBa2Cu3O(7-x) specimens over the pore fraction range of 0.10 to 0.25 was examined. The viability of using a room-temperature, nondestructive characterization method (ultrasonic velocity imaging) to predict spatial variability was determined. Spatial variations in superconductor properties were observed for specimens containing 0.10 pore fraction. An ultrasonic velocity image constructed from measurements at 1 mm increments across one such specimen revealed microstructural variation between edge and center locations that correlated with variations in alternating-current shielding and loss behavior. Optical quantitative image analysis on sample cross-sections revealed pore fraction to be the varying microstructural feature.

Effects of Pore Distributions on Ductility of Thin-Walled High Pressure Die-Cast Magnesium

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

Choi, Kyoo Sil; Li, Dongsheng; Sun, Xin

2013-06-01

In this paper, a microstructure-based three-dimensional (3D) finite element modeling method is adopted to investigate the effects of porosity in thin-walled high pressure die-cast (HPDC) Magnesium alloys on their ductility. For this purpose, the cross-sections of AM60 casting samples are first examined using optical microscope and X-ray tomography to obtain the general information on the pore distribution features. The experimentally observed pore distribution features are then used to generate a series of synthetic microstructure-based 3D finite element models with different pore volume fractions and pore distribution features. Shear and ductile damage models are adopted in the finite element analyses tomore » induce the fracture by element removal, leading to the prediction of ductility. The results in this study show that the ductility monotonically decreases as the pore volume fraction increases and that the effect of ‘skin region’ on the ductility is noticeable under the condition of same local pore volume fraction in the center region of the sample and its existence can be beneficial for the improvement of ductility. The further synthetic microstructure-based 3D finite element analyses are planned to investigate the effects of pore size and pore size distribution.« less

Dynamic Heterogeneous Multiscale Filtration Model: Probing Micro- and Macroscopic Filtration Characteristics of Gasoline Particulate Filters.

PubMed

Gong, Jian; Viswanathan, Sandeep; Rothamer, David A; Foster, David E; Rutland, Christopher J

2017-10-03

Motivated by high filtration efficiency (mass- and number-based) and low pressure drop requirements for gasoline particulate filters (GPFs), a previously developed heterogeneous multiscale filtration (HMF) model is extended to simulate dynamic filtration characteristics of GPFs. This dynamic HMF model is based on a probability density function (PDF) description of the pore size distribution and classical filtration theory. The microstructure of the porous substrate in a GPF is resolved and included in the model. Fundamental particulate filtration experiments were conducted using an exhaust filtration analysis (EFA) system for model validation. The particulate in the filtration experiments was sampled from a spark-ignition direct-injection (SIDI) gasoline engine. With the dynamic HMF model, evolution of the microscopic characteristics of the substrate (pore size distribution, porosity, permeability, and deposited particulate inside the porous substrate) during filtration can be probed. Also, predicted macroscopic filtration characteristics including particle number concentration and normalized pressure drop show good agreement with the experimental data. The resulting dynamic HMF model can be used to study the dynamic particulate filtration process in GPFs with distinct microstructures, serving as a powerful tool for GPF design and optimization.

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.

Effect of Micro Porous Shape on Mechanical Properties in Polypropylene Syntactic Foams

NASA Astrophysics Data System (ADS)

Mae, Hiroyuki; Omiya, Masaki; Kishimoto, Kikuo

The objective is to characterize the effect of the microstructure of the micro pores inside the matrix on the mechanical properties of the thermoplastic syntactic polypropylene (PP) foams at the intermediate and high strain rates. Tensile tests are conducted at the nominal strain rates from 3 x 10-1 to 102 s-1. In addition, the dart impact tests are conducted at the impact velocities of 0.1, 1 and 10 m/s. Then, the constitutive law with craze evolution is modified by introducing the relative density, the stress concentration coefficient and the volume fraction of cell edge, and then applied to the dart impact test mode for simulating the macroscopic load displacement history of the dart impact process. Moreover, the microstructural finite element analysis is conducted to characterize the local stress states in the microstructure. In the tensile loading, the elastic modulus is not influenced by the shape of the micro pores in the PP matrix while the yield stress and the strain energy up to failure are relatively influenced by the shape of micro pores. The microstructural finite element analysis shows that the magnitudes of the localized stresses at the edges and the ligaments of the elliptical-shape micro pores are larger than those at the spherical micro pores, leading to the early yielding and the small material ductility. In the case of the dart impact loading, the microstructure of pores has strong effect on the absorbed energy. This is because the elliptical-shape micro pores are very sensitive to the shear deformation, which is revealed by the microstructural finite element analysis. The modified constitutive law with the stress concentration coefficient and the volume fraction of the cell edges successfully predicts the load-displacement curve of the dart impact loading in the spherical micro-porous PP foam. It is concluded that the micro porous shape has strong effect on the material ductility especially in the dart impact test, leading to the possibility to control the material ductility by the shape of the micro pores in the polymeric foams.

Bone regeneration in strong porous bioactive glass (13–93) scaffolds with an oriented microstructure implanted in rat calvarial defects

PubMed Central

Liu, Xin; Rahaman, Mohamed N.; Fu, Qiang

2012-01-01

There is a need for synthetic bone graft substitutes to repair large bone defects resulting from trauma, malignancy, and congenital diseases. Bioactive glass has attractive properties as a scaffold material but factors that influence its ability to regenerate bone in vivo are not well understood. In the present work, the ability of strong porous scaffolds of 13–93 bioactive glass with an oriented microstructure to regenerate bone was evaluated in vivo using a rat calvarial defect model. Scaffolds with an oriented microstructure of columnar pores (porosity = 50%; pore diameter = 50–150 µm) showed mostly osteoconductive bone regeneration, and new bone formation, normalized to the available pore area (volume) of the scaffolds, increased from 37% at 12 weeks to 55% at 24 weeks. Scaffolds of the same glass with a trabecular microstructure (porosity = 80%; pore width = 100–500 µm), used as the positive control, showed bone regeneration in the pores of 25% and 46% at 12 and 24 weeks, respectively. The brittle mechanical response of the as-fabricated scaffolds changed markedly to an elasto-plastic response in vivo at both implantation times. These results indicate that both groups of 13–93 bioactive glass scaffolds could potentially be used to repair large bone defects, but scaffolds with the oriented microstructure could also be considered for the repair of loaded bone. PMID:22922251

Thin-film X-ray filters on microstructured substrates and their thermophysical properties

NASA Astrophysics Data System (ADS)

Mitrofanov, A. V.

2018-02-01

It is shown that structured substrates having micron- or submicron-sized through holes and coated with an ultrathin organic film can be used for the fabrication of thin-film X-ray filters via direct growth of functional layers on a substrate by sputter deposition, without additional complex processing steps. An optimised process is considered for the fabrication of X-ray filters on support structures in the form of electroplated fine nickel grids and on track-etched polymer membranes with micron- and submicrondiameter through pores. 'Optimisation' is here taken to mean matching the sputter deposition conditions with the properties of substrates so as to avoid overheating. The filters in question are intended for both imaging and single-channel detectors operating in the soft X-ray and vacuum UV spectral regions, at wavelengths from 10 to 60 nm. Thermal calculations are presented for the heating of ultrathin layers of organic films and thin-film support substrates during the sputter deposition of aluminium or other functional materials. The paper discusses approaches for cooling thinfilm composites during the sputter deposition process and the service of the filters in experiments and gives a brief overview of the works that utilised filters produced by the described technique on microstructured substrates, including orbital solar X-ray research in the framework of the CORONAS programme and laboratory laser plasma experiments.

Correlation of Thermally Induced Pores with Microstructural Features Using High Energy X-rays

NASA Astrophysics Data System (ADS)

Menasche, David B.; Shade, Paul A.; Lind, Jonathan; Li, Shiu Fai; Bernier, Joel V.; Kenesei, Peter; Schuren, Jay C.; Suter, Robert M.

2016-11-01

Combined application of a near-field High Energy Diffraction Microscopy measurement of crystal lattice orientation fields and a tomographic measurement of pore distributions in a sintered nickel-based superalloy sample allows pore locations to be correlated with microstructural features. Measurements were carried out at the Advanced Photon Source beamline 1-ID using an X-ray energy of 65 keV for each of the measurement modes. The nickel superalloy sample was prepared in such a way as to generate significant thermally induced porosity. A three-dimensionally resolved orientation map is directly overlaid with the tomographically determined pore map through a careful registration procedure. The data are shown to reliably reproduce the expected correlations between specific microstructural features (triple lines and quadruple nodes) and pore positions. With the statistics afforded by the 3D data set, we conclude that within statistical limits, pore formation does not depend on the relative orientations of the grains. The experimental procedures and analysis tools illustrated are being applied to a variety of materials problems in which local heterogeneities can affect materials properties.

Role of SiC substrate surface on local tarnishing of deposited silver mirror stacks

NASA Astrophysics Data System (ADS)

Limam, Emna; Maurice, Vincent; Seyeux, Antoine; Zanna, Sandrine; Klein, Lorena H.; Chauveau, Grégory; Grèzes-Besset, Catherine; Savin De Larclause, Isabelle; Marcus, Philippe

2018-04-01

The role of the SiC substrate surface on the resistance to the local initiation of tarnishing of thin-layered silver stacks for demanding space mirror applications was studied by combined surface and interface analysis on model stack samples deposited by cathodic magnetron sputtering and submitted to accelerated aging in gaseous H2S. It is shown that suppressing the surface pores resulting from the bulk SiC material production process by surface pretreatment eliminates the high aspect ratio surface sites that are imperfectly protected by the SiO2 overcoat after the deposition of silver. The formation of channels connecting the silver layer to its environment through the failing protection layer at the surface pores and locally enabling H2S entry and Ag2S growth as columns until emergence at the stack surface is suppressed, which markedly delays tarnishing initiation and thereby preserves the optical performance. The results revealed that residual tarnishing initiation proceeds by a mechanism essentially identical in nature but involving different pathways short circuiting the protection layer and enabling H2S ingress until the silver layer. These permeation pathways are suggested to be of microstructural origin and could correspond to the incompletely coalesced intergranular boundaries of the SiO2 layer.

Fabrication of porous noble metal thin-film electrode by reactive magnetron sputtering.

PubMed

Cho, Tae-Shin; Choi, Heonjin; Kim, Joosun

2013-06-01

Porous platinum films have been fabricated by reactive sputtering combined with subsequent thermal annealing. Using the SEM, XRD, XPS, and polarization resistance measurement techniques, the microstructural development of the film and its resultant electrochemical properties have been characterized. Pore evolution was understood as a result of the thermal grooving of platinum during annealing process. We demonstrated that crystallization should be followed by agglomeration for the evolution of porous microstructures. Furthermore, reaction sputtering affected the adhesion enhancement between the film and substrate compared to the film deposited by non-reactive sputtering. The polarization resistance of the porous platinum film was five times lower than that of the dense platinum film. At 600 degrees C the resistance of the porous film was 5.67 omega x cm2, and that of the dense film was 38 omega x cm2.

Property and microstructural nonuniformity in the yttrium-barium-copper-oxide superconductor determined from electrical, magnetic, and ultrasonic measurements. Ph.D. Thesis - Case Western Reserve Univ.

NASA Technical Reports Server (NTRS)

Roth, Don J.

1991-01-01

The purpose of this dissertation was the following: (1) to characterize the effect of pore fraction on a comprehensive set of electrical and magnetic properties for the yttrium-barium-copper-oxide (YBCO) high temperature ceramic superconductor; and (2) to determine the viability of using a room-temperature, nondestructive characterization method to aid in the prediction of superconducting (cryogenic) properties. The latter involved correlating ultrasonic velocity measurements at room temperature with property-affecting pore fraction and oxygen content variations. The use of ultrasonic velocity for estimating pore fraction in YBCO is presented, and other polycrystalline materials are reviewed, modeled, and statistically analyzed. This provides the basis for using ultrasonic velocity to interrogate microstructure. The effect of pore fraction (0.10-0.25) on superconductor properties of YBCO samples was characterized. Spatial (within-sample) variations in microstructure and superconductor properties were investigated, and the effect of oxygen content on elastic behavior was examined. Experimental methods used included a.c. susceptibility, electrical, and ultrasonic velocity measurements. Superconductor properties measured included transition temperature, magnetic transition width, transport and magnetic critical current density, magnetic shielding, a.c. loss, and sharpness of the voltage-current characteristics. An ultrasonic velocity image constructed from measurements at 1mm increments across a YBCO sample revealed microstructural variations that correlated with variations in magnetic shielding and a.c. loss behavior. Destructive examination using quantitative image analysis revealed pore fraction to be the varying microstructural feature.

Porous ceramics mimicking nature—preparation and properties of microstructures with unidirectionally oriented pores

PubMed Central

Okada, Kiyoshi; Isobe, Toshihiro; Katsumata, Ken-ichi; Kameshima, Yoshikazu; Nakajima, Akira; MacKenzie, Kenneth J D

2011-01-01

Porous ceramics with unidirectionally oriented pores have been prepared by various methods such as anodic oxidation, templating using wood, unidirectional solidification, extrusion, etc. The templating method directly replicates the porous microstructure of wood to prepare porous ceramics, whereas the extrusion method mimics the microstructures of tracheids and xylems in trees. These two methods are therefore the main focus of this review as they provide good examples of the preparation of functional porous ceramics with properties replicating nature. The well-oriented cylindrical through-hole pores prepared by the extrusion method using fibers as the pore formers provide excellent permeability together with high mechanical strength. Examples of applications of these porous ceramics are given, including their excellent capillary lift of over 1 m height which could be used to counteract urban heat island phenomena, and other interesting properties arising from anisotropic unidirectional porous structures. PMID:27877451

Effect of process parameters on formability of laser melting deposited 12CrNi2 alloy steel

NASA Astrophysics Data System (ADS)

Peng, Qian; Dong, Shiyun; Kang, Xueliang; Yan, Shixing; Men, Ping

2018-03-01

As a new rapid prototyping technology, the laser melting deposition technology not only has the advantages of fast forming, high efficiency, but also free control in the design and production chain. Therefore, it has drawn extensive attention from community.With the continuous improvement of steel performance requirements, high performance low-carbon alloy steel is gradually integrated into high-tech fields such as aerospace, high-speed train and armored equipment.However, it is necessary to further explore and optimize the difficult process of laser melting deposited alloy steel parts to achieve the performance and shape control.This article took the orthogonal experiment on alloy steel powder by laser melting deposition ,and revealed the influence rule of the laser power, scanning speed, powder gas flow on the quality of the sample than the dilution rate, surface morphology and microstructure analysis were carried out.Finally, under the optimum technological parameters, the Excellent surface quality of the alloy steel forming part with high density, no pore and cracks was obtained.

A mathematical multiscale model of bone remodeling, accounting for pore space-specific mechanosensation.

PubMed

Pastrama, Maria-Ioana; Scheiner, Stefan; Pivonka, Peter; Hellmich, Christian

2018-02-01

While bone tissue is a hierarchically organized material, mathematical formulations of bone remodeling are often defined on the level of a millimeter-sized representative volume element (RVE), "smeared" over all types of bone microstructures seen at lower observation scales. Thus, there is no explicit consideration of the fact that the biological cells and biochemical factors driving bone remodeling are actually located in differently sized pore spaces: active osteoblasts and osteoclasts can be found in the vascular pores, whereas the lacunar pores host osteocytes - bone cells originating from former osteoblasts which were then "buried" in newly deposited extracellular bone matrix. We here propose a mathematical description which considers size and shape of the pore spaces where the biological and biochemical events take place. In particular, a previously published systems biology formulation, accounting for biochemical regulatory mechanisms such as the rank-rankl-opg pathway, is cast into a multiscale framework coupled to a poromicromechanical model. The latter gives access to the vascular and lacunar pore pressures arising from macroscopic loading. Extensive experimental data on the biological consequences of this loading strongly suggest that the aforementioned pore pressures, together with the loading frequency, are essential drivers of bone remodeling. The novel approach presented here allows for satisfactory simulation of the evolution of bone tissue under various loading conditions, and for different species; including scenarios such as mechanical dis- and overuse of murine and human bone, or in osteocyte-free bone. Copyright © 2017 Elsevier Inc. All rights reserved.

Pore and grain boundary migration under a temperature gradient: A phase-field model study

DOE PAGES

Biner, S. B.

2016-03-16

In this study, the collective migration behavior of pores and grain boundaries under a temperature gradient is studied for simple single crystal, bi-crystal and polycrystal configurations with a phase-field model formulism. For simulation of the microstructure of solids, composed of pores and grain boundaries, the results indicate that not only the volume fraction of pores, but also its spatial partitioning between the grain boundary junctions and the grain boundary segments appears to be important. In addition to various physical properties, the evolution kinetics, under given temperature gradients, will be strongly influenced with the initial morphology of a poly-crystalline microstructure.

Microstructural aspects in steel fiber reinforced acrylic emulsion polymer modified concrete

NASA Astrophysics Data System (ADS)

Hazimmah, Dayang; Ayob, Afizah; Sie Yee, Lau; Chee Cung, Wong

2018-03-01

Scanning electron microscope observations of polymer-free and polymer-modified cements have shown that the polymer particles are partitioned between the inside of hydrates and the surface of anhydrous cement grains. For optimum dosage of acrylic emulsion polymer with 2.5%, the C-S-H gel in this structure is finer and more acicular. Some polymer adheres or deposit on the surface of the C-S-H gel. The presence of acrylic emulsion polymer confines the ionic diffusion so that the Ca(OH)2 crystallized locally to form fine crystals. The void in the structures seems to be smaller but no polymer films appears to be bridging the walls of pores although many polymer bonds or C-S-H spread into the pore spaces. In addition to porosity reduction, acrylic emulsion polymer modified the hydration products in the steel fiber -matrix ITZ. The hydration product C-S-H appeared as a needle like shape. The needle-shaped C-S-H increases and gradually formed the gel, with needles growing into the pore space. The phenomenon is more obvious as curing age increased.

Electrochemically deposited cobalt/platinum (Co/Pt) film into porous silicon: Structural investigation and magnetic properties

NASA Astrophysics Data System (ADS)

Harraz, F. A.; Salem, A. M.; Mohamed, B. A.; Kandil, A.; Ibrahim, I. A.

2013-01-01

A nanostructured CoPt magnetic film was deposited from a single electrolyte into porous silicon layer by an electrochemical technique, followed by annealing at 600 °C in Ar atmosphere during which the CoPt alloy was converted to L10 ordered phase. Porous silicon with pore diameter between 5 and 100 nm was firstly fabricated by galvanostatic anodization of n-type silicon wafer in the presence of CrO3 as oxidizing agent and ethanol or sodium lauryl sulfate as surfactants. The role of the surfactant on the produced pore size and morphology was investigated by means of UV-vis spectra. As-formed porous silicon was consequently used as a template for the electrodeposition of magnetic CoPt film. The phase formation, microstructure and the magnetic properties were fully analyzed by XRD, FE-SEM, EDS and VSM measurements. It was found that, upon annealing the coercivity was significantly increased due to the transformation to the L10 ordered structure. The saturation magnetization and remanence ratio were also found to increase, indicating no loss of Co content or oxidation reaction after the annealing. Results of synthesis and characterization of CoPt/porous silicon nanocomposite are addressed and thoroughly discussed.

Laser-Assisted Cold-Sprayed Corrosion- and Wear-Resistant Coatings: A Review

NASA Astrophysics Data System (ADS)

Olakanmi, E. O.; Doyoyo, M.

2014-06-01

Laser-assisted cold spray (LACS) process will be increasingly employed for depositing coatings because of its unique advantages: solid-state deposition of dense, homogeneous, and pore-free coatings onto a range of substrates; and high build rate at reduced operating costs without the use of expensive heating and process inert gases. Depositing coatings with excellent performance indicators via LACS demands an accurate knowledge and control of processing and materials' variables. By varying the LACS process parameters and their interactions, the functional properties of coatings can be manipulated. Moreover, thermal effect due to laser irradiation and microstructural evolution complicate the interpretation of LACS mechanical deformation mechanism which is essential for elucidating its physical phenomena. In order to provide a basis for follow-on-research that leads to the development of high-productivity LACS processing of coatings, this review focuses on the latest developments in depositing corrosion- and wear-resistant coatings with the emphasis on the composition, structure, and mechanical and functional properties. Historical developments and fundamentals of LACS are addressed in an attempt to describe the physics behind the process. Typical technological applications of LACS coatings are also identified. The investigations of all process sequences, from laser irradiation of the powder-laden gas stream and the substrate, to the impingement of thermally softened particles on the deposition site, and subsequent further processes, are described. Existing gaps in the literature relating to LACS-dependent microstructural evolution, mechanical deformation mechanisms, correlation between functional properties and process parameters, processing challenges, and industrial applications have been identified in order to provide insights for further investigations and innovation in LACS deposition of wear- and corrosion-resistant coatings.

Processing-Microstructure-Property Relationships for Cold Spray Powder Deposition of Al-Cu Alloys

DTIC Science & Technology

2015-06-01

MICROSTRUCTURE - PROPERTY RELATIONSHIPS FOR COLD SPRAY POWDER DEPOSITION OF Al - Cu ALLOYS by Jeremy D. Leazer June 2015 Thesis Advisor: Sarath K...basic microstructure -mechanical property relationships for cold spray deposited Al - Cu alloy coatings The microstructure of the deposited materials will...the dynamic mechanical

Methods for controlling pore morphology in aerogels using electric fields and products thereof

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

Worsley, Marcus A.; Baumann, Theodore F.; Satcher, Jr., Joe H.

In one embodiment, an aerogel or xerogel includes column structures of a material having minor pores therein and major pores devoid of the material positioned between the column structures, where longitudinal axes of the major pores are substantially parallel to one another. In another embodiment, a method includes heating a sol including aerogel or xerogel precursor materials to cause gelation thereof to form an aerogel or xerogel and exposing the heated sol to an electric field, wherein the electric field causes orientation of a microstructure of the sol during gelation, which is retained by the aerogel or xerogel. In onemore » approach, an aerogel has elongated pores extending between a material arranged in column structures having structural characteristics of being formed from a sol exposed to an electric field that causes orientation of a microstructure of the sol during gelation which is retained by the elongated pores of the aerogel.« less

Microstructural and Microanalytical Study on Concrete Exposed to the Sulfate Environment

NASA Astrophysics Data System (ADS)

Qing, Fang; Beixing, Li; Jiangang, Yin; Xiaolu, Yuan

2017-11-01

Microstructural properties have been examined to investigate the effect of mineral admixtures on the sulfate resistance of concrete. Concrete and cement paste specimens made with ordinary Portland cement (OPC) or ordinary Portland cement incorporating 20% fly ash (FA) or 30% ground blast furnace slag (GBFS), were made and exposed to 250 cycles of the cyclic sulfate environment. Microstructural and Microanalytical study was conducted by means of x-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and mercury intrusion porosimetry (MIP). Results indicate that the pore structure of concrete after sulfate exposure possesses the fractal feature. The OPC concrete presents more complex pore internal surface, higher porosity and less micro-pores than the concrete incorporating fly ash and GBFS. Portlandite in OPC concrete and OPC-FA concrete is mainly converted to gypsum; while for OPC-GBFS concrete, both gypsum and ettringite are formed. In the cyclic sulfate environment, repeated hydration and dehydration of sulfates produce the expansive stress in pores, aggravating the demolishment of concrete structure.

Characterisation of pore structures of pharmaceutical tablets: A review.

PubMed

Markl, Daniel; Strobel, Alexa; Schlossnikl, Rüdiger; Bøtker, Johan; Bawuah, Prince; Ridgway, Cathy; Rantanen, Jukka; Rades, Thomas; Gane, Patrick; Peiponen, Kai-Erik; Zeitler, J Axel

2018-03-01

Traditionally, the development of a new solid dosage form is formulation-driven and less focus is put on the design of a specific microstructure for the drug delivery system. However, the compaction process particularly impacts the microstructure, or more precisely, the pore architecture in a pharmaceutical tablet. Besides the formulation, the pore structure is a major contributor to the overall performance of oral solid dosage forms as it directly affects the liquid uptake rate, which is the very first step of the dissolution process. In future, additive manufacturing is a potential game changer to design the inner structures and realise a tailor-made pore structure. In pharmaceutical development the pore structure is most commonly only described by the total porosity of the tablet matrix. Yet it is of great importance to consider other parameters to fully resolve the interplay between microstructure and dosage form performance. Specifically, tortuosity, connectivity, as well as pore shape, size and orientation all impact the flow paths and play an important role in describing the fluid flow in a pharmaceutical tablet. This review presents the key properties of the pore structures in solid dosage forms and it discusses how to measure these properties. In particular, the principles, advantages and limitations of helium pycnometry, mercury porosimetry, terahertz time-domain spectroscopy, nuclear magnetic resonance and X-ray computed microtomography are discussed. Copyright © 2018 Elsevier B.V. All rights reserved.

Mechanical characterization of collagen-glycosaminoglycan scaffolds.

PubMed

Harley, Brendan A; Leung, Janet H; Silva, Emilio C C M; Gibson, Lorna J

2007-07-01

Tissue engineering scaffolds are used extensively as three-dimensional analogs of the extracellular matrix (ECM). However, less attention has been paid to characterizing the scaffold microstructure and mechanical properties than to the processing and bioactivity of scaffolds. Collagen-glycosaminoglycan (CG) scaffolds have long been utilized as ECM analogs for the regeneration of skin and are currently being considered for the regeneration of nerve and conjunctiva. Recently a series of CG scaffolds with a uniform pore microstructure has been developed with a range of sizes of equiaxed pores. Experimental characterization and theoretical modeling techniques have previously been used to describe the pore microstructure, specific surface area, cell attachment and permeability of these variants. The results of tensile and compressive tests on these CG scaffolds and of bending tests on the individual struts that define the scaffold network are reported here. The CG scaffold variants exhibited stress-strain behavior characteristic of low-density, open-cell foams with distinct linear elastic, collapse plateau and densification regimes. Scaffolds with equiaxed pores were found to be mechanically isotropic. The independent effects of hydration level, pore size, crosslink density and relative density on the mechanical properties was determined. Independent control over scaffold stiffness and pore size was obtained. Good agreement was observed between experimental results of scaffold mechanical characterization and low-density, open-cell foam model predictions for uniform scaffolds. The characterized scaffold variants provide a standardized framework with defined extracellular environments (microstructure, mechanics) for in vitro studies of the mechanical interactions between cells and scaffolds as well as in vivo tissue engineering studies.

Cell wall microstructure, pore size distribution and absolute density of hemp shiv

PubMed Central

Lawrence, M.; Ansell, M. P.; Hussain, A.

2018-01-01

This paper, for the first time, fully characterizes the intrinsic physical parameters of hemp shiv including cell wall microstructure, pore size distribution and absolute density. Scanning electron microscopy revealed microstructural features similar to hardwoods. Confocal microscopy revealed three major layers in the cell wall: middle lamella, primary cell wall and secondary cell wall. Computed tomography improved the visualization of pore shape and pore connectivity in three dimensions. Mercury intrusion porosimetry (MIP) showed that the average accessible porosity was 76.67 ± 2.03% and pore size classes could be distinguished into micropores (3–10 nm) and macropores (0.1–1 µm and 20–80 µm). The absolute density was evaluated by helium pycnometry, MIP and Archimedes' methods. The results show that these methods can lead to misinterpretation of absolute density. The MIP method showed a realistic absolute density (1.45 g cm−3) consistent with the density of the known constituents, including lignin, cellulose and hemi-cellulose. However, helium pycnometry and Archimedes’ methods gave falsely low values owing to 10% of the volume being inaccessible pores, which require sample pretreatment in order to be filled by liquid or gas. This indicates that the determination of the cell wall density is strongly dependent on sample geometry and preparation. PMID:29765652

Cell wall microstructure, pore size distribution and absolute density of hemp shiv

NASA Astrophysics Data System (ADS)

Jiang, Y.; Lawrence, M.; Ansell, M. P.; Hussain, A.

2018-04-01

This paper, for the first time, fully characterizes the intrinsic physical parameters of hemp shiv including cell wall microstructure, pore size distribution and absolute density. Scanning electron microscopy revealed microstructural features similar to hardwoods. Confocal microscopy revealed three major layers in the cell wall: middle lamella, primary cell wall and secondary cell wall. Computed tomography improved the visualization of pore shape and pore connectivity in three dimensions. Mercury intrusion porosimetry (MIP) showed that the average accessible porosity was 76.67 ± 2.03% and pore size classes could be distinguished into micropores (3-10 nm) and macropores (0.1-1 µm and 20-80 µm). The absolute density was evaluated by helium pycnometry, MIP and Archimedes' methods. The results show that these methods can lead to misinterpretation of absolute density. The MIP method showed a realistic absolute density (1.45 g cm-3) consistent with the density of the known constituents, including lignin, cellulose and hemi-cellulose. However, helium pycnometry and Archimedes' methods gave falsely low values owing to 10% of the volume being inaccessible pores, which require sample pretreatment in order to be filled by liquid or gas. This indicates that the determination of the cell wall density is strongly dependent on sample geometry and preparation.

A Study on the Deposition of Al2O3 Coatings on Polymer Substrates by a Plasma Spray/Micro-Arc Oxidation Two-Step Method

NASA Astrophysics Data System (ADS)

Sun, Guanhong; He, Xiaodong; Jiang, Jiuxing; Sun, Yue; Zhong, Yesheng

2013-02-01

To increase the wear resistance of polymer matrix composites, alumina coatings were deposited on polymer substrates by a two-step method combining plasma spraying and micro-arc oxidation. The microstructures and phase compositions of the processed coatings were investigated for different treatment times. Uniformly distributed pores were found in addition to the presence of various coral-like structures and floccules on the surface of the coatings. The presence of α-Al2O3 and γ-Al2O3 phases was identified by XRD. The distribution of alumina was analyzed by EDS and is discussed. The maximum bond strength of the coatings was found to be 5.89 MPa. There was little thermal damage in the polymer substrates after the coatings were produced.

Effect of stress evolution on microstructural behavior in U-Mo/Al dispersion fuel [Effect of stress on microstructural evolution in U-Mo/Al dispersion fuel

DOE PAGES

Jeong, G. Y.; Kim, Yeon Soo; Jamison, L. M.; ...

2017-02-20

U-Mo/Al dispersion fuel irradiated to high burnup at high power (high fission rate) exhibited microstructural changes such as deformation of the fuel particles, pore growth, and rupture of the Al matrix. The driving force for these microstructural changes was meat swelling caused by a combination of fuel particle swelling and interaction layer growth. Five miniplates with well-recorded fabrication data and irradiation conditions were selected, and their PIE data was analyzed. ABAQUS finite element analysis (FEA) was utilized to simulate the microstructural evolution of the plates. Using the simulation results shear stress, effective stress and hydrostatic stress exerted on both themore » fuel particles and the Al matrix were determined. The effects of fabrication and irradiation variables on stress-induced microstructural evolutions, such as pore growth in the interaction layers and Al matrix rupture, were investigated. The observed microstructural changes were consistent with the calculated stress distribution in the meat.« less

Effect of stress evolution on microstructural behavior in U-Mo/Al dispersion fuel [Effect of stress on microstructural evolution in U-Mo/Al dispersion fuel

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

Jeong, G. Y.; Kim, Yeon Soo; Jamison, L. M.

U-Mo/Al dispersion fuel irradiated to high burnup at high power (high fission rate) exhibited microstructural changes such as deformation of the fuel particles, pore growth, and rupture of the Al matrix. The driving force for these microstructural changes was meat swelling caused by a combination of fuel particle swelling and interaction layer growth. Five miniplates with well-recorded fabrication data and irradiation conditions were selected, and their PIE data was analyzed. ABAQUS finite element analysis (FEA) was utilized to simulate the microstructural evolution of the plates. Using the simulation results shear stress, effective stress and hydrostatic stress exerted on both themore » fuel particles and the Al matrix were determined. The effects of fabrication and irradiation variables on stress-induced microstructural evolutions, such as pore growth in the interaction layers and Al matrix rupture, were investigated. The observed microstructural changes were consistent with the calculated stress distribution in the meat.« less

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.

The Effects of Sn Addition on the Microstructure and Surface Properties of Laser Deposited Al-Si-Sn Coatings on ASTM A29 Steel

NASA Astrophysics Data System (ADS)

Fatoba, Olawale S.; Akinlabi, Stephen A.; Akinlabi, Esther T.

2018-03-01

Aluminium and its alloys have been successful metal materials used for many applications like commodity roles, automotive and vital structural components in aircrafts. A substantial portion of Al-Fe-Si alloy is also used for manufacturing the packaging foils and sheets for common heat exchanger applications. The present research was aimed at studying the morphology and surface analyses of laser deposited Al-Sn-Si coatings on ASTM A29 steel. These Fe-intermetallic compounds influence the material properties during rapid cooling by laser alloying technique and play a crucial role for the material quality. Thus, it is of considerable technological interest to control the morphology and distribution of these phases in order to eliminate the negative effects on microstructure. A 3 kW continuous wave ytterbium laser system (YLS) attached to a KUKA robot which controls the movement of the alloying process was utilized for the fabrication of the coatings at optimum laser parameters. The fabricated coatings were investigated for its hardness and wear resistance performance. The field emission scanning electron microscope equipped with energy dispersive spectroscopy (SEM/EDS) was used to study the morphology of the fabricated coatings and X-ray diffractometer (XRD) for the identification of the phases present in the coatings. The coatings were free of cracks and pores with homogeneous and refined microstructures. The enhanced hardness and wear resistance performance were attributed to metastable intermetallic compounds formed.

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.

Effect of Processing Conditions on the Anelastic Behavior of Plasma Sprayed Thermal Barrier Coatings

NASA Astrophysics Data System (ADS)

Viswanathan, Vaishak

2011-12-01

Plasma sprayed ceramic materials contain an assortment of micro-structural defects, including pores, cracks, and interfaces arising from the droplet based assemblage of the spray deposition technique. The defective architecture of the deposits introduces a novel "anelastic" response in the coatings comprising of their non-linear and hysteretic stress-strain relationship under mechanical loading. It has been established that this anelasticity can be attributed to the relative movement of the embedded defects under varying stresses. While the non-linear response of the coatings arises from the opening/closure of defects, hysteresis is produced by the frictional sliding among defect surfaces. Recent studies have indicated that anelastic behavior of coatings can be a unique descriptor of their mechanical behavior and related to the defect configuration. In this dissertation, a multi-variable study employing systematic processing strategies was conducted to augment the understanding on various aspects of the reported anelastic behavior. A bi-layer curvature measurement technique was adapted to measure the anelastic properties of plasma sprayed ceramic. The quantification of anelastic parameters was done using a non-linear model proposed by Nakamura et.al. An error analysis was conducted on the technique to know the available margins for both experimental as well as computational errors. The error analysis was extended to evaluate its sensitivity towards different coating microstructure. For this purpose, three coatings with significantly different microstructures were fabricated via tuning of process parameters. Later the three coatings were also subjected to different strain ranges systematically, in order to understand the origin and evolution of anelasticity on different microstructures. The last segment of this thesis attempts to capture the intricacies on the processing front and tries to evaluate and establish a correlation between them and the anelastic parameters.

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.

Decreased Lamina Cribrosa Beam Thickness and Pore Diameter Relative to Distance From the Central Retinal Vessel Trunk

PubMed Central

Wang, Bo; Lucy, Katie A.; Schuman, Joel S.; Sigal, Ian A.; Bilonick, Richard A.; Kagemann, Larry; Kostanyan, Tigran; Lu, Chen; Liu, Jonathan; Grulkowski, Ireneusz; Fujimoto, James G.; Ishikawa, Hiroshi; Wollstein, Gadi

2016-01-01

Purpose To investigate how the lamina cribrosa (LC) microstructure changes with distance from the central retinal vessel trunk (CRVT), and to determine how this change differs in glaucoma. Methods One hundred nineteen eyes (40 healthy, 29 glaucoma suspect, and 50 glaucoma) of 105 subjects were imaged using swept-source optical coherence tomography (OCT). The CRVT was manually delineated at the level of the anterior LC surface. A line was fit to the distribution of LC microstructural parameters and distance from CRVT to measure the gradient (change in LC microstructure per distance from the CRVT) and intercept (LC microstructure near the CRVT). A linear mixed-effects model was used to determine the effect of diagnosis on the gradient and intercept of the LC microstructure with distance from the CRVT. A Kolmogorov-Smirnov test was applied to determine the difference in distribution between the diagnostic categories. Results The percent of visible LC in all scans was 26 ± 7%. Beam thickness and pore diameter decreased with distance from the CRVT. Glaucoma eyes had a larger decrease in beam thickness (−1.132 ± 0.503 μm, P = 0.028) and pore diameter (−0.913 ± 0.259 μm, P = 0.001) compared with healthy controls per 100 μm from the CRVT. Glaucoma eyes showed increased variability in both beam thickness and pore diameter relative to the distance from the CRVT compared with healthy eyes (P < 0.05). Conclusions These findings results demonstrate the importance of considering the anatomical location of CRVT in the assessment of the LC, as there is a relationship between the distance from the CRVT and the LC microstructure, which differs between healthy and glaucoma eyes. PMID:27286366

Effects of surfactants on the microstructure of porous ceramic scaffolds fabricated by foaming for bone tissue engineering

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

Wang Xi, E-mail: nano-sun@hotmail.com; Ruan Jianming; Chen Qiyuan

2009-06-03

A porous scaffold comprising a {beta}-tricalcium phosphate matrix and bioactive glass powders was fabricated by foaming method and the effects of surfactants as foaming agent on microstructure of scaffolds were investigated. Foaming capacity and foam stability of different surfactants in water firstly were carried out to evaluate their foam properties. The porous structure and pore size distribution of the scaffolds were systematically characterized by scanning electron microscopy (SEM) and an optical microscopy connected to an image analyzer. The results showed that the foam stability of surfactant has more remarkable influence on their microstructure such as pore shape, size and interconnectivitymore » than the foaming ability of one. Porous scaffolds fabricated using nonionic surfactant Tween 80 with large foam stability exhibited higher open and total porosities, and fully interconnected porous structure with a pore size of 750-850 {mu}m.« less

Microstructural effect on radiative scattering coefficient and asymmetry factor of anisotropic thermal barrier coatings

NASA Astrophysics Data System (ADS)

Chen, X. W.; Zhao, C. Y.; Wang, B. X.

2018-05-01

Thermal barrier coatings are common porous materials coated on the surface of devices operating under high temperatures and designed for heat insulation. This study presents a comprehensive investigation on the microstructural effect on radiative scattering coefficient and asymmetry factor of anisotropic thermal barrier coatings. Based on the quartet structure generation set algorithm, the finite-difference-time-domain method is applied to calculate angular scattering intensity distribution of complicated random microstructure, which takes wave nature into account. Combining Monte Carlo method with Particle Swarm Optimization, asymmetry factor, scattering coefficient and absorption coefficient are retrieved simultaneously. The retrieved radiative properties are identified with the angular scattering intensity distribution under different pore shapes, which takes dependent scattering and anisotropic pore shape into account implicitly. It has been found that microstructure significantly affects the radiative properties in thermal barrier coatings. Compared with spherical shape, irregular anisotropic pore shape reduces the forward scattering peak. The method used in this paper can also be applied to other porous media, which designs a frame work for further quantitative study on porous media.

Effect of starting powder morphology on film texture for bismuth layer-structured ferroelectrics prepared by aerosol deposition method

NASA Astrophysics Data System (ADS)

Suzuki, Muneyasu; Tsuchiya, Tetsuo; Akedo, Jun

2017-06-01

We report grain orientation control for bismuth layer-structured ferroelectrics (BLSFs) films deposited by aerosol deposition (AD) method at room temperature. Bi4Ti3O12 (BiT), SrBi2Ta2O9 (SBTa), and SrBi4Ti4O15 (SBTi) starting powders with particles of various shape (plate-like, spherical, and angular) were prepared by solid-state reaction and fused salt synthesis. Their AD films represented fine microstructures without pores, which agrees well with previous reports. Although the SBTa AD films deposited by using spherical particles exhibited an extremely low Lotgering factor (F), the BiT AD films deposited by using plate-like particles exhibited a marked c-axis orientation. The F of BiT and SBTi AD films decreased with increasing film thickness (t). We consider that the dispersion of agglomerated plate-like particles on the film surface and the densification of the compacted powder layer occurring while under particle impact are important in obtaining the grain-oriented AD films. These results of using the AD method with shape-controlled particles are expected to result in open up an innovative functional coating technique.

Freeze extrusion fabrication of 13-93 bioactive glass scaffolds for bone repair.

PubMed

Doiphode, Nikhil D; Huang, Tieshu; Leu, Ming C; Rahaman, Mohamed N; Day, Delbert E

2011-03-01

A solid freeform fabrication technique, freeze extrusion fabrication (FEF), was investigated for the creation of three-dimensional bioactive glass (13-93) scaffolds with pre-designed porosity and pore architecture. An aqueous mixture of bioactive glass particles and polymeric additives with a paste-like consistency was extruded through a narrow nozzle, and deposited layer-by-layer in a cold environment according to a computer-aided design (CAD) file. Following sublimation of the ice in a freeze dryer, the construct was heated according to a controlled schedule to burn out the polymeric additives (below ~500°C), and to densify the glass phase at higher temperature (1 h at 700°C). The sintered scaffolds had a grid-like microstructure of interconnected pores, with a porosity of ~50%, pore width of ~300 μm, and dense glass filaments (struts) with a diameter or width of ~300 μm. The scaffolds showed an elastic response during mechanical testing in compression, with an average compressive strength of 140 MPa and an elastic modulus of 5-6 GPa, comparable to the values for human cortical bone. These bioactive glass scaffolds created by the FEF method could have potential application in the repair of load-bearing bones.

Preparation of foam-like carbon nanotubes/hydroxyapatite composite scaffolds with superparamagnetic properties

NASA Astrophysics Data System (ADS)

Lu, X. Y.; Qiu, T.; Wang, X. F.; Zhang, M.; Gao, X. L.; Li, R. X.; Lu, X.; Weng, J.

2012-12-01

In this paper, the foam-like composite scaffolds composed of hydroxyapatite (HA) and carbon nanotubes (CNTs) were prepared by a new method, where a polymer impregnating method was used for porous HA-based scaffold and a chemical vapor deposition (CVD) method was used for the growth of CNTs from the HA-based scaffold. The process produces the CNTs/HA scaffolds that have a foam-like structure with better mechanical property, better microstructure and a high degree of interconnection. A favorable pore size with big pores of 1-2 mm and small pores of 20-300 μm for osteoconduction and bone ingrowth is presented in these scaffolds. About 2 wt% multi-walled CNTs with the diameter of 60-100 nm are observed to be in situ grown from deficient nano-HA crystallites. Magnetic measurement exhibits these scaffolds are superparamagnetic with a saturation magnetization of 1.14 emu g-1 at a room temperature, benefiting the scaffolds to take up growth factors in vivo, stem cell or other bioactive molecules easily. This new type of CNTs/HA scaffolds is expected to have a promising applications in bone tissue engineering, targeted drug delivery system and other biomedical fields.

Laboratory characterization of shale pores

NASA Astrophysics Data System (ADS)

Nur Listiyowati, Lina

2018-02-01

To estimate the potential of shale gas reservoir, one needs to understand the characteristics of pore structures. Characterization of shale gas reservoir microstructure is still a challenge due to ultra-fine grained micro-fabric and micro level heterogeneity of these sedimentary rocks. The sample used in the analysis is a small portion of any reservoir. Thus, each measurement technique has a different result. It raises the question which methods are suitable for characterizing pore shale. The goal of this paper is to summarize some of the microstructure analysis tools of shale rock to get near-real results. The two analyzing pore structure methods are indirect measurement (MIP, He, NMR, LTNA) and direct observation (SEM, TEM, Xray CT). Shale rocks have a high heterogeneity; thus, it needs multiscale quantification techniques to understand their pore structures. To describe the complex pore system of shale, several measurement techniques are needed to characterize the surface area and pore size distribution (LTNA, MIP), shapes, size and distribution of pore (FIB-SEM, TEM, Xray CT), and total porosity (He pycnometer, NMR). The choice of techniques and methods should take into account the purpose of the analysis and also the time and budget.

Experimental Study on Mechanical Properties and Porosity of Organic Microcapsules Based Self-Healing Cementitious Composite.

PubMed

Wang, Xianfeng; Sun, Peipei; Han, Ningxu; Xing, Feng

2017-01-01

Encapsulation of healing agents embedded in a material matrix has become one of the major approaches for achieving self-healing function in cementitious materials in recent years. A novel type of microcapsules based self-healing cementitious composite was developed in Guangdong Provincial Key Laboratory of Durability for Marine Civil Engineering, Shenzhen University. In this study, both macro performance and the microstructure of the composite are investigated. The macro performance was evaluated by employing the compressive strength and the dynamic modulus, whereas the microstructure was represented by the pore structure parameters such as porosity, cumulative-pore volume, and average-pore diameter, which are significantly correlated to the pore-size distribution and the compressive strength. The results showed that both the compressive strength and the dynamic modulus, as well as the pore structure parameters such as porosity, cumulative-pore volume, and average-pore diameter of the specimen decrease to some extent with the amount of microcapsules. However, the self-healing rate and the recovery rate of the specimen performance and the pore-structure parameters increase with the amount of microcapsules. The results should confirm the self-healing function of microcapsules in the cementitious composite from macroscopic and microscopic viewpoints.

Experimental Study on Mechanical Properties and Porosity of Organic Microcapsules Based Self-Healing Cementitious Composite

PubMed Central

Wang, Xianfeng; Sun, Peipei; Han, Ningxu; Xing, Feng

2017-01-01

Encapsulation of healing agents embedded in a material matrix has become one of the major approaches for achieving self-healing function in cementitious materials in recent years. A novel type of microcapsules based self-healing cementitious composite was developed in Guangdong Provincial Key Laboratory of Durability for Marine Civil Engineering, Shenzhen University. In this study, both macro performance and the microstructure of the composite are investigated. The macro performance was evaluated by employing the compressive strength and the dynamic modulus, whereas the microstructure was represented by the pore structure parameters such as porosity, cumulative-pore volume, and average-pore diameter, which are significantly correlated to the pore-size distribution and the compressive strength. The results showed that both the compressive strength and the dynamic modulus, as well as the pore structure parameters such as porosity, cumulative-pore volume, and average-pore diameter of the specimen decrease to some extent with the amount of microcapsules. However, the self-healing rate and the recovery rate of the specimen performance and the pore-structure parameters increase with the amount of microcapsules. The results should confirm the self-healing function of microcapsules in the cementitious composite from macroscopic and microscopic viewpoints. PMID:28772382

Microstructure design of nanoporous TiO2 photoelectrodes for dye-sensitized solar cell modules.

PubMed

Hu, Linhua; Dai, Songyuan; Weng, Jian; Xiao, Shangfeng; Sui, Yifeng; Huang, Yang; Chen, Shuanghong; Kong, Fantai; Pan, Xu; Liang, Linyun; Wang, Kongjia

2007-01-18

The optimization of dye-sensitized solar cells, especially the design of nanoporous TiO2 film microstructure, is an urgent problem for high efficiency and future commercial applications. However, up to now, little attention has been focused on the design of nanoporous TiO2 microstructure for a high efficiency of dye-sensitized solar cell modules. The optimization and design of TiO2 photoelectrode microstructure are discussed in this paper. TiO2 photoelectrodes with three different layers, including layers of small pore size films, larger pore size films, and light-scattering particles on the conducting glass with the desirable thickness, were designed and investigated. Moreover, the photovoltaic properties showed that the different porosities, pore size distribution, and BET surface area of each layer have a dramatic influence on short-circuit current, open-circuit voltage, and fill factor of the modules. The optimization and design of TiO2 photoelectrode microstructure contribute a high efficiency of DSC modules. The photoelectric conversion efficiency around 6% with 15 x 20 cm2 modules under illumination of simulated AM1.5 sunlight (100 mW/cm2) and 40 x 60 cm2 panels with the same performance tested outdoor have been achieved by our group.

Interface characterization of Cu-Mo coating deposited on Ti-Al alloys by arc spraying

NASA Astrophysics Data System (ADS)

Bai, Shengqiang; Li, Fei; Wu, Ting; Yin, Xianglin; Shi, Xun; Chen, Lidong

2015-03-01

Cu-Mo pseudobinary alloys are promising candidates as electrode materials in CoSb3-based skutterudite thermoelectric (TE) devices for TE power generation. In this study, Cu-Mo coatings were deposited onto Ti-Al substrates by applying a dual-wire electric arc spraying coating technique. The microstructure of the surfaces, cross sections and coating interfaces were analyzed by scanning electron microscopy (SEM) and energy dispersion spectrometry (EDS). Cu-Mo coatings showed a typical banded splat with compact microstructures, and have no coarse pores nor micro-cracks. The thermal shock resistance of the Cu-Mo coating was also investigated to show good combinations with Ti-Al substrates. After 50 thermal shock cycles, there were no cracks observed at the interface. In contrast, the test of the thermal shock resistance of the Cu coating on the Ti-Al substrate was also investigated. Due to a large difference in the thermal expansion coefficients between Cu and Ti-Al alloys, the Cu coating flaked from the Ti-Al substrate completely after 10 thermal shock cycles. The contact resistivity of the Ti-Al/Cu-Mo interface was about 1.6 μΩṡcm2 and this value was unchanged after 50 thermal shock cycles, indicating the low electric resistance and high thermal stability of the Cu-Mo/Ti-Al interface.

Universal Spatial Correlation Functions for Describing and Reconstructing Soil Microstructure

PubMed Central

Skvortsova, Elena B.; Mallants, Dirk

2015-01-01

Structural features of porous materials such as soil define the majority of its physical properties, including water infiltration and redistribution, multi-phase flow (e.g. simultaneous water/air flow, or gas exchange between biologically active soil root zone and atmosphere) and solute transport. To characterize soil microstructure, conventional soil science uses such metrics as pore size and pore-size distributions and thin section-derived morphological indicators. However, these descriptors provide only limited amount of information about the complex arrangement of soil structure and have limited capability to reconstruct structural features or predict physical properties. We introduce three different spatial correlation functions as a comprehensive tool to characterize soil microstructure: 1) two-point probability functions, 2) linear functions, and 3) two-point cluster functions. This novel approach was tested on thin-sections (2.21×2.21 cm2) representing eight soils with different pore space configurations. The two-point probability and linear correlation functions were subsequently used as a part of simulated annealing optimization procedures to reconstruct soil structure. Comparison of original and reconstructed images was based on morphological characteristics, cluster correlation functions, total number of pores and pore-size distribution. Results showed excellent agreement for soils with isolated pores, but relatively poor correspondence for soils exhibiting dual-porosity features (i.e. superposition of pores and micro-cracks). Insufficient information content in the correlation function sets used for reconstruction may have contributed to the observed discrepancies. Improved reconstructions may be obtained by adding cluster and other correlation functions into reconstruction sets. Correlation functions and the associated stochastic reconstruction algorithms introduced here are universally applicable in soil science, such as for soil classification, pore-scale modelling of soil properties, soil degradation monitoring, and description of spatial dynamics of soil microbial activity. PMID:26010779

Universal spatial correlation functions for describing and reconstructing soil microstructure.

PubMed

Karsanina, Marina V; Gerke, Kirill M; Skvortsova, Elena B; Mallants, Dirk

2015-01-01

Structural features of porous materials such as soil define the majority of its physical properties, including water infiltration and redistribution, multi-phase flow (e.g. simultaneous water/air flow, or gas exchange between biologically active soil root zone and atmosphere) and solute transport. To characterize soil microstructure, conventional soil science uses such metrics as pore size and pore-size distributions and thin section-derived morphological indicators. However, these descriptors provide only limited amount of information about the complex arrangement of soil structure and have limited capability to reconstruct structural features or predict physical properties. We introduce three different spatial correlation functions as a comprehensive tool to characterize soil microstructure: 1) two-point probability functions, 2) linear functions, and 3) two-point cluster functions. This novel approach was tested on thin-sections (2.21×2.21 cm2) representing eight soils with different pore space configurations. The two-point probability and linear correlation functions were subsequently used as a part of simulated annealing optimization procedures to reconstruct soil structure. Comparison of original and reconstructed images was based on morphological characteristics, cluster correlation functions, total number of pores and pore-size distribution. Results showed excellent agreement for soils with isolated pores, but relatively poor correspondence for soils exhibiting dual-porosity features (i.e. superposition of pores and micro-cracks). Insufficient information content in the correlation function sets used for reconstruction may have contributed to the observed discrepancies. Improved reconstructions may be obtained by adding cluster and other correlation functions into reconstruction sets. Correlation functions and the associated stochastic reconstruction algorithms introduced here are universally applicable in soil science, such as for soil classification, pore-scale modelling of soil properties, soil degradation monitoring, and description of spatial dynamics of soil microbial activity.

Liquid Feedstock Plasma Spraying: An Emerging Process for Advanced Thermal Barrier Coatings

NASA Astrophysics Data System (ADS)

Markocsan, Nicolaie; Gupta, Mohit; Joshi, Shrikant; Nylén, Per; Li, Xin-Hai; Wigren, Jan

2017-08-01

Liquid feedstock plasma spraying (LFPS) involves deposition of ultrafine droplets of suspensions or solution precursors (typically ranging from nano- to submicron size) and permits production of coatings with unique microstructures that are promising for advanced thermal barrier coating (TBC) applications. This paper reviews the recent progress arising from efforts devoted to development of high-performance TBCs using the LFPS approach. Advancements in both suspension plasma spraying and solution precursor plasma spraying, which constitute the two main variants of LFPS, are presented. Results illustrating the different types of the microstructures that can be realized in LFPS through appropriate process parameter control, model-assisted assessment of influence of coating defects on thermo-mechanical properties and the complex interplay between pore coarsening, sintering and crystallite growth in governing thermal conductivity are summarized. The enhancement in functional performances/lifetime possible in LFPS TBCs with multilayered architectures and by incorporating new pyrochlore chemistries such as gadolinium zirconate, besides the conventional single 8 wt.% yttria-stabilized zirconia insulating ceramic layer, is specifically highlighted.

Microstructured silicon radiation detector

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

Okandan, Murat; Derzon, Mark S.; Draper, Bruce L.

2017-03-14

A radiation detector comprises a silicon body in which are defined vertical pores filled with a converter material and situated within silicon depletion regions. One or more charge-collection electrodes are arranged to collect current generated when secondary particles enter the silicon body through walls of the pores. The pores are disposed in low-density clusters, have a majority pore thickness of 5 .mu.m or less, and have a majority aspect ratio, defined as the ratio of pore depth to pore thickness, of at least 10.

Micro Mechanics and Microstructures of Major Subsurface Hydraulic Barriers: Shale Caprock vs Wellbore Cement

NASA Astrophysics Data System (ADS)

Radonjic, M.; Du, H.

2015-12-01

Shale caprocks and wellbore cements are two of the most common subsurface impermeable barriers in the oil and gas industry. More than 60% of effective seals for geologic hydrocarbon bearing formations as natural hydraulic barriers constitute of shale rocks. Wellbore cements provide zonal isolation as an engineered hydraulic barrier to ensure controlled fluid flow from the reservoir to the production facilities. Shale caprocks were deposited and formed by squeezing excess formation water and mineralogical transformations at different temperatures and pressures. In a similar process, wellbore cements are subjected to compression during expandable tubular operations, which lead to a rapid pore water propagation and secondary mineral precipitation within the cement. The focus of this research was to investigate the effect of wellbore cement compression on its microstructure and mechanical properties, as well as a preliminary comparison of shale caprocks and hydrated cement. The purpose of comparative evaluation of engineered vs natural hydraulic barrier materials is to further improve wellbore cement durability when in contact with geofluids. The micro-indentation was utilized to evaluate the change in cement mechanical properties caused by compression. Indentation experiments showed an overall increase in hardness and Young's modulus of compressed cement. Furthermore, SEM imaging and Electron Probe Microanalysis showed mineralogical alterations and decrease in porosity. These can be correlated with the cement rehydration caused by microstructure changes as a result of compression. The mechanical properties were also quantitatively compared to shale caprock samples in order to investigate the similarities of hydraulic barrier features that could help to improve the subsurface application of cement in zonal isolation. The comparison results showed that the poro-mechanical characteristics of wellbore cement appear to be improved when inherent pore sizes are shifted to predominantly nano-scale range as characteristic of pore-size distribution typical for shale rocks. The effect of compression on cement appears to petrophysically alter cement towards the properties of shale caprocks, although the process is achieved much faster than in the case of shale diagenesis over geological times.

Microstructural characterization of multiphase chocolate using X-ray microtomography.

PubMed

Frisullo, Pierangelo; Licciardello, Fabio; Muratore, Giuseppe; Del Nobile, Matteo Alessandro

2010-09-01

In this study, X-ray microtomography (μCT) was used for the image analysis of the microstructure of 12 types of Italian aerated chocolate chosen to exhibit variability in terms of cocoa mass content. Appropriate quantitative 3-dimensional parameters describing the microstructure were calculated, for example, the structure thickness (ST), object structure volume ratio (OSVR), and the percentage object volume (POV). Chemical analysis was also performed to correlate the microstructural data to the chemical composition of the samples. Correlation between the μCT parameters acquired for the pore microstructure evaluation and the chemical analysis revealed that the sugar crystals content does not influence the pore structure and content. On the other hand, it revealed that there is a strong correlation between the POV and the sugar content obtained by chemical analysis. The results from this study show that μCT is a suitable technique for the microstructural analysis of confectionary products such as chocolates and not only does it provide an accurate analysis of the pores and microstructure but the data obtained could also be used to aid in the assessment of its composition and consistency with label specifications. X-ray microtomography (μCT) is a noninvasive and nondestructive 3-D imaging technique that has several advantages over other methods, including the ability to image low-moisture materials. Given the enormous success of μCT in medical applications, material science, chemical engineering, geology, and biology, it is not surprising that in recent years much attention has been focused on extending this imaging technique to food science as a useful technique to aid in the study of food microstructure. X-ray microtomography provides in-depth information on the microstructure of the food product being tested; therefore, a better understanding of the physical structure of the product and from an engineering perspective, knowledge about the microstructure of foods can be used to identify the important processing parameters that affect the quality of a product.

Characterizing TPS Microstructure: A Review of Some techniques

NASA Technical Reports Server (NTRS)

Gasch, Matthew; Stackpole, Mairead; Agrawal, Parul; Chavez-Garcie, Jose

2011-01-01

I. When seeking to understand ablator microstructure and morphology there are several useful techniques A. SEM 1) Visual characteriza3on at various length scales. 2) Chemical mapping by backscatter or x-ray highlights areas of interest. 3) Combined with other techniques (density, weight change, chemical analysis) SEM is a powerful tool to aid in explaining thermo/structural data. B. ASAP. 1) Chemical characteriza3on at various length scales. 2) Chemical mapping of pore structure by gas adsorption. 3) Provides a map of pore size vs. pore volume. 4) Provided surface area of exposed TPS. II. Both methods help characterize and understand how ablators react with other chemical species and provides insight into how they oxidize.

Influence of Structure and Microstructure on Deformation Localization and Crack Growth in NiTi Shape Memory Alloys

NASA Astrophysics Data System (ADS)

Paul, Partha P.; Fortman, Margaret; Paranjape, Harshad M.; Anderson, Peter M.; Stebner, Aaron P.; Brinson, L. Catherine

2018-04-01

Porous NiTi shape memory alloys have applications in the biomedical and aerospace fields. Recent developments in metal additive manufacturing have made fabrication of near-net-shape porous products with complicated geometries feasible. There have also been developments in tailoring site-specific microstructures in metals using additive manufacturing. Inspired by these developments, we explore two related mechanistic phenomena in a simplified representation of porous shape memory alloys. First, we computationally elucidate the connection between pore geometry, stress concentration around pores, grain orientation, and strain-band formation during tensile loading of NiTi. Using this, we present a method to engineer local crystal orientations to mitigate the stress concentrations around the pores. Second, we experimentally document the growth of cracks around pores in a cyclically loaded superelastic NiTi specimen. In the areas of stress concentration around holes, cracks are seen to grow in large grains with [1 1 0] oriented along the tensile axis. This combined work shows the potential of local microstructural engineering in reducing stress concentration and increasing resistance to propagation of cracks in porous SMAs, potentially increasing the fatigue life of porous SMA components.

Constrained Sintering in Fabrication of Solid Oxide Fuel Cells

PubMed Central

Lee, Hae-Weon; Park, Mansoo; Hong, Jongsup; Kim, Hyoungchul; Yoon, Kyung Joong; Son, Ji-Won; Lee, Jong-Ho; Kim, Byung-Kook

2016-01-01

Solid oxide fuel cells (SOFCs) are inevitably affected by the tensile stress field imposed by the rigid substrate during constrained sintering, which strongly affects microstructural evolution and flaw generation in the fabrication process and subsequent operation. In the case of sintering a composite cathode, one component acts as a continuous matrix phase while the other acts as a dispersed phase depending upon the initial composition and packing structure. The clustering of dispersed particles in the matrix has significant effects on the final microstructure, and strong rigidity of the clusters covering the entire cathode volume is desirable to obtain stable pore structure. The local constraints developed around the dispersed particles and their clusters effectively suppress generation of major process flaws, and microstructural features such as triple phase boundary and porosity could be readily controlled by adjusting the content and size of the dispersed particles. However, in the fabrication of the dense electrolyte layer via the chemical solution deposition route using slow-sintering nanoparticles dispersed in a sol matrix, the rigidity of the cluster should be minimized for the fine matrix to continuously densify, and special care should be taken in selecting the size of the dispersed particles to optimize the thermodynamic stability criteria of the grain size and film thickness. The principles of constrained sintering presented in this paper could be used as basic guidelines for realizing the ideal microstructure of SOFCs. PMID:28773795

Leaching of Conductive Species: Implications to Measurements of Electrical Resistivity

PubMed Central

Spragg, R; Jones, S; Bu, Y; Lu, Y; Bentz, D; Snyder, K; Weiss, J

2017-01-01

Electrical tests have been used to characterize the microstructure of porous materials, the measured electrical response being determined by the contribution of the microstructure (porosity and tortuosity) and the electrical properties of the solution (conductivity of the pore solution) inside the pores of the material. This study has shown how differences in concentration between the pore solution (i.e., the solution in the pores) and the storage solution surrounding the test specimen leads to significant transport (leaching) of the conductive ionic species between the pore solution and the storage solution. Leaching influences the resistivity of the pore solution, thereby influencing electrical measurements on the bulk material from either a surface or uniaxial bulk resistance test. This paper has three main conclusions: 1.) Leaching of conductive species does occur with concentration gradients and that a diffusion based approach can be used to estimate the time scale associated with this change. 2.) Leaching of ions in the pore solution can influence resistivity measurements, and the ratio of surface to uniaxial resistivity can be used as a method to assess the presence of leaching and 3.) An estimation of the magnitude of leaching for standardized tests of cementitious materials. PMID:28584407

Leaching of Conductive Species: Implications to Measurements of Electrical Resistivity.

PubMed

Spragg, R; Jones, S; Bu, Y; Lu, Y; Bentz, D; Snyder, K; Weiss, J

2017-05-01

Electrical tests have been used to characterize the microstructure of porous materials, the measured electrical response being determined by the contribution of the microstructure (porosity and tortuosity) and the electrical properties of the solution (conductivity of the pore solution) inside the pores of the material. This study has shown how differences in concentration between the pore solution (i.e., the solution in the pores) and the storage solution surrounding the test specimen leads to significant transport (leaching) of the conductive ionic species between the pore solution and the storage solution. Leaching influences the resistivity of the pore solution, thereby influencing electrical measurements on the bulk material from either a surface or uniaxial bulk resistance test. This paper has three main conclusions: 1.) Leaching of conductive species does occur with concentration gradients and that a diffusion based approach can be used to estimate the time scale associated with this change. 2.) Leaching of ions in the pore solution can influence resistivity measurements, and the ratio of surface to uniaxial resistivity can be used as a method to assess the presence of leaching and 3.) An estimation of the magnitude of leaching for standardized tests of cementitious materials.

Modification of Lightweight Aggregates' Microstructure by Used Motor Oil Addition.

PubMed

Franus, Małgorzata; Jozefaciuk, Grzegorz; Bandura, Lidia; Lamorski, Krzysztof; Hajnos, Mieczysław; Franus, Wojciech

2016-10-18

An admixture of lightweight aggregate substrates (beidellitic clay containing 10 wt % of natural clinoptilolite or Na-P1 zeolite) with used motor oil (1 wt %-8 wt %) caused marked changes in the aggregates' microstructure, measured by a combination of mercury porosimetry (MIP), microtomography (MT), and scanning electron microscopy. Maximum porosity was produced at low (1%-2%) oil concentrations and it dropped at higher concentrations, opposite to the aggregates' bulk density. Average pore radii, measured by MIP, decreased with an increasing oil concentration, whereas larger (MT) pore sizes tended to increase. Fractal dimension, derived from MIP data, changed similarly to the MIP pore radius, while that derived from MT remained unaltered. Solid phase density, measured by helium pycnometry, initially dropped slightly and then increased with the amount of oil added, which was most probably connected to changes in the formation of extremely small closed pores that were not available for He atoms.

Modification of Lightweight Aggregates’ Microstructure by Used Motor Oil Addition

PubMed Central

Franus, Małgorzata; Jozefaciuk, Grzegorz; Bandura, Lidia; Lamorski, Krzysztof; Hajnos, Mieczysław; Franus, Wojciech

2016-01-01

An admixture of lightweight aggregate substrates (beidellitic clay containing 10 wt % of natural clinoptilolite or Na-P1 zeolite) with used motor oil (1 wt %–8 wt %) caused marked changes in the aggregates’ microstructure, measured by a combination of mercury porosimetry (MIP), microtomography (MT), and scanning electron microscopy. Maximum porosity was produced at low (1%–2%) oil concentrations and it dropped at higher concentrations, opposite to the aggregates’ bulk density. Average pore radii, measured by MIP, decreased with an increasing oil concentration, whereas larger (MT) pore sizes tended to increase. Fractal dimension, derived from MIP data, changed similarly to the MIP pore radius, while that derived from MT remained unaltered. Solid phase density, measured by helium pycnometry, initially dropped slightly and then increased with the amount of oil added, which was most probably connected to changes in the formation of extremely small closed pores that were not available for He atoms. PMID:28773964

Atomic layer deposition-based functionalization of materials for medical and environmental health applications

PubMed Central

Narayan, Roger J.; Adiga, Shashishekar P.; Pellin, Michael J.; Curtiss, Larry A.; Hryn, Alexander J.; Stafslien, Shane; Chisholm, Bret; Shih, Chun-Che; Shih, Chun-Ming; Lin, Shing-Jong; Su, Yea-Yang; Jin, Chunming; Zhang, Junping; Monteiro-Riviere, Nancy A.; Elam, Jeffrey W.

2010-01-01

Nanoporous alumina membranes exhibit high pore densities, well-controlled and uniform pore sizes, as well as straight pores. Owing to these unusual properties, nanoporous alumina membranes are currently being considered for use in implantable sensor membranes and water purification membranes. Atomic layer deposition is a thin-film growth process that may be used to modify the pore size in a nanoporous alumina membrane while retaining a narrow pore distribution. In addition, films deposited by means of atomic layer deposition may impart improved biological functionality to nanoporous alumina membranes. In this study, zinc oxide coatings and platinum coatings were deposited on nanoporous alumina membranes by means of atomic layer deposition. PEGylated nanoporous alumina membranes were prepared by self-assembly of 1-mercaptoundec-11-yl hexa(ethylene glycol) on platinum-coated nanoporous alumina membranes. The pores of the PEGylated nanoporous alumina membranes remained free of fouling after exposure to human platelet-rich plasma; protein adsorption, fibrin networks and platelet aggregation were not observed on the coated membrane surface. Zinc oxide-coated nanoporous alumina membranes demonstrated activity against two waterborne pathogens, Escherichia coli and Staphylococcus aureus. The results of this work indicate that nanoporous alumina membranes may be modified using atomic layer deposition for use in a variety of medical and environmental health applications. PMID:20308114

3D shape extraction segmentation and representation of soil microstructures using generalized cylinders

NASA Astrophysics Data System (ADS)

Ngom, Ndèye Fatou; Monga, Olivier; Ould Mohamed, Mohamed Mahmoud; Garnier, Patricia

2012-02-01

This paper focuses on the modeling of soil microstructures using generalized cylinders, with a specific application to pore space. The geometric modeling of these microstructures is a recent area of study, made possible by the improved performance of computed tomography techniques. X-scanners provide very-high-resolution 3D volume images ( 3-5μm) of soil samples in which pore spaces can be extracted by thresholding. However, in most cases, the pore space defines a complex volume shape that cannot be approximated using simple analytical functions. We propose representing this shape using a compact, stable, and robust piecewise approximation by means of generalized cylinders. This intrinsic shape representation conserves its topological and geometric properties. Our algorithm includes three main processing stages. The first stage consists in describing the volume shape using a minimum number of balls included within the shape, such that their union recovers the shape skeleton. The second stage involves the optimum extraction of simply connected chains of balls. The final stage copes with the approximation of each simply optimal chain using generalized cylinders: circular generalized cylinders, tori, cylinders, and truncated cones. This technique was applied to several data sets formed by real volume computed tomography soil samples. It was possible to demonstrate that our geometric representation supplied a good approximation of the pore space. We also stress the compactness and robustness of this method with respect to any changes affecting the initial data, as well as its coherence with the intuitive notion of pores. During future studies, this geometric pore space representation will be used to simulate biological dynamics.

The growth of high density network of MOF nano-crystals across macroporous metal substrates - Solvothermal synthesis versus rapid thermal deposition

NASA Astrophysics Data System (ADS)

Maina, James W.; Gonzalo, Cristina Pozo; Merenda, Andrea; Kong, Lingxue; Schütz, Jürg A.; Dumée, Ludovic F.

2018-01-01

Fabrication of metal organic framework (MOF) films and membranes across macro-porous metal substrates is extremely challenging, due to the large pore sizes across the substrates, poor wettability, and the lack of sufficient reactive functional groups on the surface, which prevent high density nucleation of MOF crystals. Herein, macroporous stainless steel substrates (pore size 44 × 40 μm) are functionalized with amine functional groups, and the growth of ZIF-8 crystals investigated through both solvothermal synthesis and rapid thermal deposition (RTD), to assess the role of synthesis routes in the resultant membranes microstructure, and subsequently their performance. Although a high density of well interconnected MOF crystals was observed across the modified substrates following both techniques, RTD was found to be a much more efficient route, yielding high quality membranes under 1 h, as opposed to the 24 h required for solvothermal synthesis. The RTD membranes also exhibited high gas permeance, with He permeance of up to 2.954 ± 0.119 × 10-6 mol m-2 s-1 Pa-1, and Knudsen selectivities for He/N2, Ar/N2 and CO2/N2, suggesting the membranes were almost defect free. This work opens up route for efficient fabrication of MOF films and membranes across macro-porous metal supports, with potential application in electrically mediated separation applications.

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.

Creation of bioactive glass (13-93) scaffolds for structural bone repair using a combined finite element modeling and rapid prototyping approach.

PubMed

Xiao, Wei; Zaeem, Mohsen Asle; Bal, B Sonny; Rahaman, Mohamed N

2016-11-01

There is a clinical need for synthetic bioactive materials that can reliably repair intercalary skeletal tissue loss in load-bearing bones. Bioactive glasses have been investigated as one such material but their mechanical response has been a concern. Previously, we created bioactive silicate glass (13-93) scaffolds with a uniform grid-like microstructure which showed a compressive strength comparable to human cortical bone but a much lower flexural strength. In the present study, finite element modeling (FEM) was used to re-design the scaffold microstructure to improve its flexural strength without significantly lowering its compressive strength and ability to support bone infiltration in vivo. Then scaffolds with the requisite microstructures were created by a robotic deposition method and tested in four-point bending and compression to validate the FEM simulations. In general, the data validated the predictions of the FEM simulations. Scaffolds with a porosity gradient, composed of a less porous outer region and a more porous inner region, showed a flexural strength (34±5MPa) that was more than twice the value for the uniform grid-like microstructure (15±5MPa) and a higher compressive strength (88±20MPa) than the grid-like microstructure (72±10MPa). Upon implantation of the scaffolds for 12weeks in rat calvarial defects in vivo, the amount of new bone that infiltrated the pore space of the scaffolds with the porosity gradient (37±16%) was similar to that for the grid-like scaffolds (35±6%). These scaffolds with a porosity gradient that better mimics the microstructure of human long bone could provide more reliable implants for structural bone repair. Copyright © 2016 Elsevier B.V. All rights reserved.

Provenance study through analysis of microstructural characteristics using an optical microscope and scanning electron microscopy for Goryeo celadon excavated from the seabed.

PubMed

Min-su, Han

2013-08-01

This paper aims at identifying the provenance of Goryeo celadons by understanding its microstructural characteristics, such as particles, blisters, forms and amount of pores, and the presence of crystal formation, bodies, and glazes and its boundary, using an optical microscope and scanning electron microscopy (SEM). The analysis of the reproduced samples shows that the glazed layer of the sherd fired at higher temperatures has lower viscosity and therefore it encourages the blisters to be combined together and the layer to become more transparent. In addition, the result showed that the vitrification and melting process of clay minerals such as feldspars and quartzs on the bodies was accelerated for those samples. To factor such characteristics of the microstructure and apply it to the sherds, the samples could be divided into six categories based on status, such as small particles with many small pores or mainly large and small circular pores in the bodies, only a limited number of varied sized blisters in the glazes, and a few blisters and needle-shaped crystals on the boundary surface. In conclusion, the analysis of the microstructural characteristics using an optical microscope and SEM have proven to be useful as a categorizing reference factor in a provenance study on Goryeo celadons.

Hybrid approach combining multiple characterization techniques and simulations for microstructural analysis of proton exchange membrane fuel cell electrodes

NASA Astrophysics Data System (ADS)

Cetinbas, Firat C.; Ahluwalia, Rajesh K.; Kariuki, Nancy; De Andrade, Vincent; Fongalland, Dash; Smith, Linda; Sharman, Jonathan; Ferreira, Paulo; Rasouli, Somaye; Myers, Deborah J.

2017-03-01

The cost and performance of proton exchange membrane fuel cells strongly depend on the cathode electrode due to usage of expensive platinum (Pt) group metal catalyst and sluggish reaction kinetics. Development of low Pt content high performance cathodes requires comprehensive understanding of the electrode microstructure. In this study, a new approach is presented to characterize the detailed cathode electrode microstructure from nm to μm length scales by combining information from different experimental techniques. In this context, nano-scale X-ray computed tomography (nano-CT) is performed to extract the secondary pore space of the electrode. Transmission electron microscopy (TEM) is employed to determine primary C particle and Pt particle size distributions. X-ray scattering, with its ability to provide size distributions of orders of magnitude more particles than TEM, is used to confirm the TEM-determined size distributions. The number of primary pores that cannot be resolved by nano-CT is approximated using mercury intrusion porosimetry. An algorithm is developed to incorporate all these experimental data in one geometric representation. Upon validation of pore size distribution against gas adsorption and mercury intrusion porosimetry data, reconstructed ionomer size distribution is reported. In addition, transport related characteristics and effective properties are computed by performing simulations on the hybrid microstructure.

The effect of wall thickness distribution on mechanical reliability and strength in unidirectional porous ceramics.

PubMed

Seuba, Jordi; Deville, Sylvain; Guizard, Christian; Stevenson, Adam J

2016-01-01

Macroporous ceramics exhibit an intrinsic strength variability caused by the random distribution of defects in their structure. However, the precise role of microstructural features, other than pore volume, on reliability is still unknown. Here, we analyze the applicability of the Weibull analysis to unidirectional macroporous yttria-stabilized-zirconia (YSZ) prepared by ice-templating. First, we performed crush tests on samples with controlled microstructural features with the loading direction parallel to the porosity. The compressive strength data were fitted using two different fitting techniques, ordinary least squares and Bayesian Markov Chain Monte Carlo, to evaluate whether Weibull statistics are an adequate descriptor of the strength distribution. The statistical descriptors indicated that the strength data are well described by the Weibull statistical approach, for both fitting methods used. Furthermore, we assess the effect of different microstructural features (volume, size, densification of the walls, and morphology) on Weibull modulus and strength. We found that the key microstructural parameter controlling reliability is wall thickness. In contrast, pore volume is the main parameter controlling the strength. The highest Weibull modulus ([Formula: see text]) and mean strength (198.2 MPa) were obtained for the samples with the smallest and narrowest wall thickness distribution (3.1 [Formula: see text]m) and lower pore volume (54.5%).

The effect of wall thickness distribution on mechanical reliability and strength in unidirectional porous ceramics

NASA Astrophysics Data System (ADS)

Seuba, Jordi; Deville, Sylvain; Guizard, Christian; Stevenson, Adam J.

2016-01-01

Macroporous ceramics exhibit an intrinsic strength variability caused by the random distribution of defects in their structure. However, the precise role of microstructural features, other than pore volume, on reliability is still unknown. Here, we analyze the applicability of the Weibull analysis to unidirectional macroporous yttria-stabilized-zirconia (YSZ) prepared by ice-templating. First, we performed crush tests on samples with controlled microstructural features with the loading direction parallel to the porosity. The compressive strength data were fitted using two different fitting techniques, ordinary least squares and Bayesian Markov Chain Monte Carlo, to evaluate whether Weibull statistics are an adequate descriptor of the strength distribution. The statistical descriptors indicated that the strength data are well described by the Weibull statistical approach, for both fitting methods used. Furthermore, we assess the effect of different microstructural features (volume, size, densification of the walls, and morphology) on Weibull modulus and strength. We found that the key microstructural parameter controlling reliability is wall thickness. In contrast, pore volume is the main parameter controlling the strength. The highest Weibull modulus (?) and mean strength (198.2 MPa) were obtained for the samples with the smallest and narrowest wall thickness distribution (3.1 ?m) and lower pore volume (54.5%).

Metallurgical Mechanisms Controlling Mechanical Properties of Aluminum Alloy 2219 Produced by Electron Beam Freeform Fabrication

NASA Technical Reports Server (NTRS)

Domack, Marcia S.; Tainger, Karen M.

2006-01-01

The electron beam freeform fabrication (EBF3) layer-additive manufacturing process has been developed to directly fabricate complex geometry components. EBF3 introduces metal wire into a molten pool created on the surface of a substrate by a focused electron beam. Part geometry is achieved by translating the substrate with respect to the beam to build the part one layer at a time. Tensile properties demonstrated for electron beam deposited aluminum and titanium alloys are comparable to wrought products, although the microstructures of the deposits exhibit cast features. Understanding the metallurgical mechanisms controlling mechanical properties is essential to maximizing application of the EBF3 process. Tensile mechanical properties and microstructures were examined for aluminum alloy 2219 fabricated over a range of EBF3 process variables. Unique microstructures were observed within the deposited layers and at interlayer boundaries, which varied within the deposit height due to microstructural evolution associated with the complex thermal history experienced during subsequent layer deposition. Microstructures exhibited irregularly shaped grains with interior dendritic structures, described based on overall grain size, morphology, distribution, and dendrite spacing, and were correlated with deposition parameters. Fracture features were compared with microstructural elements to define fracture paths and aid in definition of basic processing-microstructure-property correlations.

A fractal model of effective stress of porous media and the analysis of influence factors

NASA Astrophysics Data System (ADS)

Li, Wei; Zhao, Huan; Li, Siqi; Sun, Wenfeng; Wang, Lei; Li, Bing

2018-03-01

The basic concept of effective stress describes the characteristics of fluid and solid interaction in porous media. In this paper, based on the theory of fractal geometry, a fractal model was built to analyze the relationship between the microstructure and the effective stress of porous media. From the microscopic point of view, the influence of effective stress on pore structure of porous media was demonstrated. Theoretical analysis and experimental results show that: (i) the fractal model of effective stress can be used to describe the relationship between effective stress and the microstructure of porous media; (ii) a linear increase in the effective stress leads to exponential increases in fractal dimension, porosity and pore number of the porous media, and causes a decreasing trend in the average pore radius.

Computational and Experimental Studies of Microstructure-Scale Porosity in Metallic Fuels for Improved Gas Swelling Behavior

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

Mllett, Paul; McDeavitt, Sean; Deo, Chaitanya

This proposal will investigate the stability of bimodal pore size distributions in metallic uranium and uranium-zirconium alloys during sintering and re-sintering annealing treatments. The project will utilize both computational and experimental approaches. The computational approach includes both Molecular Dynamics simulations to determine the self-diffusion coefficients in pure U and U-Zr alloys in single crystals, grain boundaries, and free surfaces, as well as calculations of grain boundary and free surface interfacial energies. Phase-field simulations using MOOSE will be conducted to study pore and grain structure evolution in microstructures with bimodal pore size distributions. Experiments will also be performed to validate themore » simulations, and measure the time-dependent densification of bimodal porous compacts.« less

Osteoconductive hydroxyapatite coated PEEK for spinal fusion surgery

NASA Astrophysics Data System (ADS)

Hahn, Byung-Dong; Park, Dong-Soo; Choi, Jong-Jin; Ryu, Jungho; Yoon, Woon-Ha; Choi, Joon-Hwan; Kim, Jong-Woo; Ahn, Cheol-Woo; Kim, Hyoun-Ee; Yoon, Byung-Ho; Jung, In-Kwon

2013-10-01

Polyetheretherketone (PEEK) has attracted much interest as biomaterial for interbody fusion cages due to its similar stiffness to bone and good radio-transparency for post-op visualization. Hydroxyapatite (HA) coating stimulates bone growth to the medical implant. The objective of this work is to make an implant consisting of biocompatible PEEK with an osteoconductive HA surface for spinal or orthopedic applications. Highly dense and well-adhered HA coating was developed on medical-grade PEEK using aerosol deposition (AD) without thermal degradation of the PEEK. The HA coating had a dense microstructure with no cracks or pores, and showed good adhesion to PEEK at adhesion strengths above 14.3 MPa. The crystallinity of the HA coating was remarkably enhanced by hydrothermal annealing as post-deposition heat-treatment. In addition, in vitro and in vivo biocompatibility of PEEK, in terms of cell adhesion morphology, cell proliferation, differentiation, and bone-to-implant contact ratio, were remarkably enhanced by the HA coating through AD.

Micromechanical modeling of elastic properties of cortical bone accounting for anisotropy of dense tissue.

PubMed

Salguero, Laura; Saadat, Fatemeh; Sevostianov, Igor

2014-10-17

The paper analyzes the connection between microstructure of the osteonal cortical bone and its overall elastic properties. The existing models either neglect anisotropy of the dense tissue or simplify cortical bone microstructure (accounting for Haversian canals only). These simplifications (related mostly to insufficient mathematical apparatus) complicate quantitative analysis of the effect of microstructural changes - produced by age, microgravity, or some diseases - on the overall mechanical performance of cortical bone. The present analysis fills this gap; it accounts for anisotropy of the dense tissue and uses realistic model of the porous microstructure. The approach is based on recent results of Sevostianov et al. (2005) and Saadat et al. (2012) on inhomogeneities in a transversely-isotropic material. Bone's microstructure is modeled according to books of Martin and Burr (1989), Currey (2002), and Fung (1993) and includes four main families of pores. The calculated elastic constants for porous cortical bone are in agreement with available experimental data. The influence of each of the pore types on the overall moduli is examined. Copyright © 2014 Elsevier Ltd. All rights reserved.

Study of the Microstructure Evolution of Low-pH Cements Based on Ordinary Portland Cement (OPC) by Mid- and Near-Infrared Spectroscopy, and Their Influence on Corrosion of Steel Reinforcement.

PubMed

García Calvo, José Luis; Sánchez Moreno, Mercedes; Alonso Alonso, María Cruz; Hidalgo López, Ana; García Olmo, Juan

2013-06-18

Low-pH cements are designed to be used in underground repositories for high level waste. When they are based on Ordinary Portland Cements (OPC), high mineral admixture contents must be used which significantly modify their microstructure properties and performance. This paper evaluates the microstructure evolution of low-pH cement pastes based on OPC plus silica fume and/or fly ashes, using Mid-Infrared and Near-Infrared spectroscopy to detect cement pastes mainly composed of high polymerized C-A-S-H gels with low C/S ratios. In addition, the lower pore solution pH of these special cementitious materials have been monitored with embedded metallic sensors. Besides, as the use of reinforced concrete can be required in underground repositories, the influence of low-pH cementitious materials on steel reinforcement corrosion was analysed. Due to their lower pore solution pH and their different pore solution chemical composition a clear influence on steel reinforcement corrosion was detected.

Analyses of microstructural and elastic properties of porous SOFC cathodes based on focused ion beam tomography

NASA Astrophysics Data System (ADS)

Chen, Zhangwei; Wang, Xin; Giuliani, Finn; Atkinson, Alan

2015-01-01

Mechanical properties of porous SOFC electrodes are largely determined by their microstructures. Measurements of the elastic properties and microstructural parameters can be achieved by modelling of the digitally reconstructed 3D volumes based on the real electrode microstructures. However, the reliability of such measurements is greatly dependent on the processing of raw images acquired for reconstruction. In this work, the actual microstructures of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathodes sintered at an elevated temperature were reconstructed based on dual-beam FIB/SEM tomography. Key microstructural and elastic parameters were estimated and correlated. Analyses of their sensitivity to the grayscale threshold value applied in the image segmentation were performed. The important microstructural parameters included porosity, tortuosity, specific surface area, particle and pore size distributions, and inter-particle neck size distribution, which may have varying extent of effect on the elastic properties simulated from the microstructures using FEM. Results showed that different threshold value range would result in different degree of sensitivity for a specific parameter. The estimated porosity and tortuosity were more sensitive than surface area to volume ratio. Pore and neck size were found to be less sensitive than particle size. Results also showed that the modulus was essentially sensitive to the porosity which was largely controlled by the threshold value.

Hollow glass for insulating layers

NASA Astrophysics Data System (ADS)

Merticaru, Andreea R.; Moagar-Poladian, Gabriel

1999-03-01

Common porous materials, some of which will be considered in the chapters of this book, include concrete, paper, ceramics, clays, porous semiconductors, chromotography materials, and natural materials like coral, bone, sponges, rocks and shells. Porous materials can also be reactive, such as in charcoal gasification, acid rock dissolution, catalyst deactivation and concrete. This study continues the investigations about the properties of, so-called, hollow glass. In this paper is presented a computer simulation approach in which the thermo-mechanical behavior of a 3D microstructure is directly computed. In this paper a computer modeling approach of porous glass is presented. One way to test the accuracy of the reconstructed microstructures is to computed their physical properties and compare to experimental measurement on equivalent systems. In this view, we imagine a new type of porous type of glass designed as buffer layer in multilayered printed boards in ICs. Our glass is a variable material with a variable pore size and surface area. The porosity could be tailored early from the deposition phases that permitting us to keep in a reasonable balance the dielectric constant and thermal conductivity.

Detecting diffusion-diffraction patterns in size distribution phantoms using double-pulsed field gradient NMR: Theory and experiments.

PubMed

Shemesh, Noam; Ozarslan, Evren; Basser, Peter J; Cohen, Yoram

2010-01-21

NMR observable nuclei undergoing restricted diffusion within confining pores are important reporters for microstructural features of porous media including, inter-alia, biological tissues, emulsions and rocks. Diffusion NMR, and especially the single-pulsed field gradient (s-PFG) methodology, is one of the most important noninvasive tools for studying such opaque samples, enabling extraction of important microstructural information from diffusion-diffraction phenomena. However, when the pores are not monodisperse and are characterized by a size distribution, the diffusion-diffraction patterns disappear from the signal decay, and the relevant microstructural information is mostly lost. A recent theoretical study predicted that the diffusion-diffraction patterns in double-PFG (d-PFG) experiments have unique characteristics, such as zero-crossings, that make them more robust with respect to size distributions. In this study, we theoretically compared the signal decay arising from diffusion in isolated cylindrical pores characterized by lognormal size distributions in both s-PFG and d-PFG methodologies using a recently presented general framework for treating diffusion in NMR experiments. We showed the gradual loss of diffusion-diffraction patterns in broadening size distributions in s-PFG and the robustness of the zero-crossings in d-PFG even for very large standard deviations of the size distribution. We then performed s-PFG and d-PFG experiments on well-controlled size distribution phantoms in which the ground-truth is well-known a priori. We showed that the microstructural information, as manifested in the diffusion-diffraction patterns, is lost in the s-PFG experiments, whereas in d-PFG experiments the zero-crossings of the signal persist from which relevant microstructural information can be extracted. This study provides a proof of concept that d-PFG may be useful in obtaining important microstructural features in samples characterized by size distributions.

Natural and laboratory compaction bands in porous carbonates: a three-dimensional characterization using synchrotron X-ray computed microtomography

NASA Astrophysics Data System (ADS)

Cilona, A.; Arzilli, F.; Mancini, L.; Emanuele, T.

2014-12-01

Porous carbonates form important reservoirs for water and hydrocarbons. The fluid flow properties of carbonate reservoirs may be affected by post-depositional processes (e.g., mechanical and chemical), which need to be quantified. Field-based studies described bed-parallel compaction bands (CBs) within carbonates with a wide range of porosities. These burial-related structures accommodate volumetric strain by grain rotation, translation, pore collapse and pressure solution. Recently, the same structures have been reproduced for the first time in the laboratory by performing triaxial compaction experiments on porous grainstones. These laboratory studies characterized and compared the microstructures of natural and laboratory CBs, but no analysis of pore connectivity has been performed. In this paper, we use an innovative approach to characterize the pore networks (e.g. porosity, connectivity) of natural and laboratory CBs and compare them with the host rock one. We collected the data using the synchrotron X-ray computed microtomography technique at the SYRMEP beamline of the Elettra-Sincrotrone Trieste Laboratory (Italy). Quantitative analyses of the samples were performed with the Pore3D software library. The porosity was calculated from segmented 3D images of pristine and deformed carbonates. A process of skeletonization was then applied to quantify the number of connected pores within the rock volume. The analysis of the skeleton allowed us to highlight the differences between natural and laboratory CBs, and to investigate how pore connectivity evolves as a function of different deformation pathways. Both pore volume and connectivity are reduced within the CBs respect to the pristine rock and the natural CB has a lower porosity with respect to the laboratory one. The grain contacts in the natural CB are welded, whereas in the laboratory one they have more irregular shapes and grain crushing is the predominant process.

Microstructure of ZnO Thin Films Deposited by High Power Impulse Magnetron Sputtering (Postprint)

DTIC Science & Technology

2015-03-01

AFRL-RX-WP-JA-2015-0185 MICROSTRUCTURE OF ZNO THIN FILMS DEPOSITED BY HIGH POWER IMPULSE MAGNETRON SPUTTERING (POSTPRINT) A. N. Reed...COVERED (From – To) 29 January 2013 – 16 February 2015 4. TITLE AND SUBTITLE MICROSTRUCTURE OF ZNO THIN FILMS DEPOSITED BY HIGH POWER IMPULSE MAGNETRON...ABSTRACT High power impulse magnetron sputtering was used to deposit thin (~100 nm) zinc oxide (ZnO) films from a ceramic ZnO target onto substrates

Effects of collagen microstructure and material properties on the deformation of the neural tissues of the lamina cribrosa.

PubMed

Voorhees, A P; Jan, N-J; Sigal, I A

2017-08-01

It is widely considered that intraocular pressure (IOP)-induced deformation within the neural tissue pores of the lamina cribrosa (LC) contributes to neurodegeneration and glaucoma. Our goal was to study how the LC microstructure and mechanical properties determine the mechanical insult to the neural tissues within the pores of the LC. Polarized light microscopy was used to measure the collagen density and orientation in histology sections of three sheep optic nerve heads (ONH) at both mesoscale (4.4μm) and microscale (0.73μm) resolutions. Mesoscale fiber-aware FE models were first used to calculate ONH deformations at an IOP of 30mmHg. The results were then used as boundary conditions for microscale models of LC regions. Models predicted large insult to the LC neural tissues, with 95th percentile 1st principal strains ranging from 7 to 12%. Pores near the scleral boundary suffered significantly higher stretch compared to pores in more central regions (10.0±1.4% vs. 7.2±0.4%; p=0.014; mean±SD). Variations in material properties altered the minimum, median, and maximum levels of neural tissue insult but largely did not alter the patterns of pore-to-pore variation, suggesting these patterns are determined by the underlying structure and geometry of the LC beams and pores. To the best of our knowledge, this is the first computational model that reproduces the highly heterogeneous neural tissue strain fields observed experimentally. The loss of visual function associated with glaucoma has been attributed to sustained mechanical insult to the neural tissues of the lamina cribrosa due to elevated intraocular pressure. Our study is the first computational model built from specimen-specific tissue microstructure to consider the mechanics of the neural tissues of the lamina separately from the connective tissue. We found that the deformation of the neural tissue was much larger than that predicted by any recent microstructure-aware models of the lamina. These results are consistent with recent experimental data and the highest deformations were found in the region of the lamina where glaucomatous damage first occurs. This study provides new insight into the complex biomechanical environment within the lamina. Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A phase-field approach to model multi-axial and microstructure dependent fracture in nuclear grade graphite

DOE PAGES

Chakraborty, Pritam; Sabharwall, Piyush; Carroll, Mark C.

2016-04-07

The fracture behavior of nuclear grade graphites is strongly influenced by underlying microstructural features such as the character of filler particles, and the distribution of pores and voids. These microstructural features influence the crack nucleation and propagation behavior, resulting in quasi-brittle fracture with a tortuous crack path and significant scatter in measured bulk strength. This paper uses a phase-field method to model the microstructural and multi-axial fracture in H-451, a historic variant of nuclear graphite that provides the basis for an idealized study on a legacy grade. The representative volume elements are constructed from randomly located pores with random sizemore » obtained from experimentally determined log-normal distribution. The representative volume elements are then subjected to simulated multi-axial loading, and a reasonable agreement of the resulting fracture stress with experiments is obtained. Finally, quasi-brittle stress-strain evolution with a tortuous crack path is also observed from the simulations and is consistent with experimental results.« less

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.

Atomic layer deposition of nanoporous biomaterials.

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

Narayan, R. J.; Adiga, S. P.; Pellin, M. J.

2010-03-01

Due to its chemical stability, uniform pore size, and high pore density, nanoporous alumina is being investigated for use in biosensing, drug delivery, hemodialysis, and other medical applications. In recent work, we have examined the use of atomic layer deposition for coating the surfaces of nanoporous alumina membranes. Zinc oxide coatings were deposited on nanoporous alumina membranes using atomic layer deposition. The zinc oxide-coated nanoporous alumina membranes demonstrated antimicrobial activity against Escherichia coli and Staphylococcus aureus bacteria. These results suggest that atomic layer deposition is an attractive technique for modifying the surfaces of nanoporous alumina membranes and other nanostructured biomaterials.more » Nanoporous alumina, also known as anodic aluminum oxide (AAO), is a nanomaterial that exhibits several unusual properties, including high pore densities, straight pores, small pore sizes, and uniform pore sizes. In 1953, Keller et al. showed that anodizing aluminum in acid electrolytes results in a thick layer of nearly cylindrical pores, which are arranged in a close-packed hexagonal cell structure. More recently, Matsuda & Fukuda demonstrated preparation of highly ordered platinum and gold nanohole arrays using a replication process. In this study, a negative structure of nanoporous alumina was initially fabricated and a positive structure of a nanoporous metal was subsequently fabricated. Over the past fifteen years, nanoporous alumina membranes have been used as templates for growth of a variety of nanostructured materials, including nanotubes, nanowires, nanorods, and nanoporous membranes.« less

Effect of sub-pore scale morphology of biological deposits on porous media flow properties

NASA Astrophysics Data System (ADS)

Ghezzehei, T. A.

2012-12-01

Biological deposits often influence fluid flow by altering the pore space morphology and related hydrologic properties such as porosity, water retention characteristics, and permeability. In most coupled-processes models changes in porosity are inferred from biological process models using mass-balance. The corresponding evolution of permeability is estimated using (semi-) empirical porosity-permeability functions such as the Kozeny-Carman equation or power-law functions. These equations typically do not account for the heterogeneous spatial distribution and morphological irregularities of the deposits. As a result, predictions of permeability evolution are generally unsatisfactory. In this presentation, we demonstrate the significance of pore-scale deposit distribution on porosity-permeability relations using high resolution simulations of fluid flow through a single pore interspersed with deposits of varying morphologies. Based on these simulations, we present a modification to the Kozeny-Carman model that accounts for the shape of the deposits. Limited comparison with published experimental data suggests the plausibility of the proposed conceptual model.

Modeling precursor diffusion and reaction of atomic layer deposition in porous structures

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

Keuter, Thomas, E-mail: t.keuter@fz-juelich.de; Menzler, Norbert Heribert; Mauer, Georg

2015-01-01

Atomic layer deposition (ALD) is a technique for depositing thin films of materials with a precise thickness control and uniformity using the self-limitation of the underlying reactions. Usually, it is difficult to predict the result of the ALD process for given external parameters, e.g., the precursor exposure time or the size of the precursor molecules. Therefore, a deeper insight into ALD by modeling the process is needed to improve process control and to achieve more economical coatings. In this paper, a detailed, microscopic approach based on the model developed by Yanguas-Gil and Elam is presented and additionally compared with themore » experiment. Precursor diffusion and second-order reaction kinetics are combined to identify the influence of the porous substrate's microstructural parameters and the influence of precursor properties on the coating. The thickness of the deposited film is calculated for different depths inside the porous structure in relation to the precursor exposure time, the precursor vapor pressure, and other parameters. Good agreement with experimental results was obtained for ALD zirconiumdioxide (ZrO{sub 2}) films using the precursors tetrakis(ethylmethylamido)zirconium and O{sub 2}. The derivation can be adjusted to describe other features of ALD processes, e.g., precursor and reactive site losses, different growth modes, pore size reduction, and surface diffusion.« less

Effect of Fe- and Si-Enriched Secondary Precipitates and Surface Roughness on Pore Formation on Aluminum Plate Surfaces During Anodizing

NASA Astrophysics Data System (ADS)

Zhu, Yuanzhi; Wang, Shizhi; Yang, Qingda; Zhou, Feng

2014-09-01

Two twin roll casts (TRCs) and one hot rolled (HR) AA 1235 aluminum alloy plates with different microstructures are prepared. The plates were electrolyzed in a 1.2 wt% HCl solution with a voltage of 21 V and a current of 1.9 mA. The shape, size, and number of pores formed on the surfaces of these plates were analyzed and correlated with the microstructures of the plates. It is found that pores are easier to form on the alloy plates containing subgrains with a lower dislocation density inside the subgrains, rather than along the grain boundaries. Furthermore, Fe- and Si-enriched particles in the AA1235 aluminum alloys lead to the formation of pores on the surface during electrolyzing; the average precipitate sizes of 4, 3.5, and 2 μm in Alloy 1#, Alloy 2# and Alloy 3# result in the average pore sizes of 3.78, 2.76, and 1.9 μm on the surfaces of the three alloys, respectively; The G.P zone in the alloy also facilitates the surface pore formation. High-surface roughness enhances the possibility of entrapping more lubricants into the plate surface, which eventually blocks the formation of the pores on the surface of the aluminum plates in the following electrolyzing process.

Analysis on the overpressure characterization with respect to depositional environment facies: Case Study in Miri Area, Baram Delta

NASA Astrophysics Data System (ADS)

Mhd Hanapiah, N.; Yusoff, W. I. Wan; Zakariah, M. N. A.

2017-10-01

Overpressure studies in oil and gas exploration and production are carried out in order to mitigate any losses that could happen while drilling. These concerns can be addressed by enhancing the understanding of overpressure characterization in the fields. This research emphasizes in determining the pore pressure trend in Miri area to assist pore pressure prediction for future hydrocarbon exploration and production. Generally, pore pressure trends are related to mechanisms that contribute to the overpressure generation. In the region predominant overpressure are disequilibrium compaction within the prodelta shales meanwhile in outer shelf overpressure generation controlled by fluid expansion in deltaic sequence of inner shelf area. The objective of this research is to analyze the pore pressure profile of wells for determining vertical trends of pore pressure for various depositional environment facies of Miri area. Integration of rock physics and pore pressure analysis and relating the trends to environment depositional environment facies within shale underlying sand interval. Analysis done shows that overpressure top is characterize by depositional environment facies within shale underlying sand interval.

Deposition Nucleation or Pore Condensation and Freezing?

NASA Astrophysics Data System (ADS)

David, Robert O.; Mahrt, Fabian; Marcolli, Claudia; Fahrni, Jonas; Brühwiler, Dominik; Lohmann, Ulrike; Kanji, Zamin A.

2017-04-01

Ice nucleation plays an important role in moderating Earth's climate and precipitation formation. Over the last century of research, several mechanisms for the nucleation of ice have been identified. Of the known mechanisms for ice nucleation, only deposition nucleation occurs below water saturation. Deposition nucleation is defined as the formation of ice from supersaturated water vapor on an insoluble particle without the prior formation of liquid. However, recent work has found that the efficiency of so-called deposition nucleation shows a dependence on the homogeneous freezing temperature of water even though no liquid phase is presumed to be present. Additionally, the ability of certain particles to nucleate ice more efficiently after being pre-cooled (pre-activation) raises questions on the true mechanism when ice nucleation occurs below water saturation. In an attempt to explain the dependence of the efficiency of so-called deposition nucleation on the onset of homogeneous freezing of liquid water, pore condensation and freezing has been proposed. Pore condensation and freezing suggests that the liquid phase can exist under sub-saturated conditions with respect to liquid in narrow confinements or pores due to the inverse Kelvin effect. Once the liquid-phase condenses, it is capable of nucleating ice either homogeneously or heterogeneously. The role of pore condensation and freezing is assessed in the Zurich Ice Nucleation Chamber, a continuous flow diffusion chamber, using spherical nonporous and mesoporous silica particles. The mesoporous silica particles have a well-defined particle size range of 400 to 600nm with discreet pore sizes of 2.5, 2.8, 3.5 and 3.8nm. Experiments conducted between 218K and 238K show that so-called deposition nucleation only occurs below the homogenous freezing temperature of water and is highly dependent on the presence of pores and their size. The results strongly support pore condensation and freezing, questioning the role of deposition nucleation as an ice nucleation pathway.

Fabrication of nanobaskets by sputter deposition on porous substrates and uses thereof

NASA Technical Reports Server (NTRS)

Johnson, Paige Lea (Inventor); Teeters, Dale (Inventor)

2010-01-01

A method of producing a nanobasket and the applications or uses thereof. The method includes the steps of providing a substrate with at least one (1) pore having diameters of about one (1) nanometer to about ten (10) micrometers. Material is deposited by sputter-coating techniques along continuous edges of the pores to form a capped or partially capped nanotube or microtube structure, termed a nanobasket. Either a single material may be used to form nanobaskets over the pores or, alternately, a layered structure may be created wherein an initial material is deposited followed by one or more other materials to form nanobaskets over the pores.

Permeability and microstructural changes due to weathering of pyroclastic rocks in Cappadocia, central Turkey

NASA Astrophysics Data System (ADS)

Sato, M.; Takahashi, M.; Anma, R.; Shiomi, K.

2014-12-01

Studies of permeability changes of rocks during weathering are important to understand the processes of geomorphological development and how they are influenced by cyclic climatic conditions. Especially volcanic tuffs and pyroclastic flow deposits are easily affected by water absorption and freezing-thawing cycle (Erguler. 2009, Çelik and Ergül 2014). Peculiar erosional landscapes of Cappadocia, central Turkey, with numerous underground cities and carved churches, that made this area a world heritage site, are consists of volcanic tuffs and pyroclastic flow deposits. Understanding permeability changes of such rocks under different conditions are thus important not only to understand fundamental processes of weathering, but also to protect the landscapes of the world heritage sites and archaeological remains. In this study, we aim to evaluate internal void structures and bulk permeability of intact and weathered pyroclastic rocks from Cappadocia using X-ray CT, mercury intrusion porosimetry data and permeability measurement method of flow pump test. Samples of pyroclastic deposits that comprise the landscapes of Rose Valley and Ihlara Valley, were collected from the corresponding strata outside of the preservation areas. Porosity and pore-size distribution for the same samples measured by mercury intrusion porosimetry, indicate that the intact samples have lower porosity than weathered samples and pore sizes were dominantly 1-10μm in calculated radii, whereas weathered samples have more micropores (smaller than 1 μm). X-ray CT images were acquired to observe internal structure of samples. Micro-fractures, probably caused by repeated expansion and contraction due to temperature changes, were observed around clast grains. The higher micropore ratio in weathered samples could be attributed to the development of the micro-farctures. We will discuss fundamental processes of weathering and geomorphological development models using these data.

Catalytic nanoporous membranes

DOEpatents

Pellin, Michael J; Hryn, John N; Elam, Jeffrey W

2013-08-27

A nanoporous catalytic membrane which displays several unique features Including pores which can go through the entire thickness of the membrane. The membrane has a higher catalytic and product selectivity than conventional catalysts. Anodic aluminum oxide (AAO) membranes serve as the catalyst substrate. This substrate is then subjected to Atomic Layer Deposition (ALD), which allows the controlled narrowing of the pores from 40 nm to 10 nm in the substrate by deposition of a preparatory material. Subsequent deposition of a catalytic layer on the inner surfaces of the pores reduces pore sizes to less than 10 nm and allows for a higher degree of reaction selectivity. The small pore sizes allow control over which molecules enter the pores, and the flow-through feature can allow for partial oxidation of reactant species as opposed to complete oxidation. A nanoporous separation membrane, produced by ALD is also provided for use in gaseous and liquid separations. The membrane has a high flow rate of material with 100% selectivity. Also provided is a method for producing a catalytic membrane having flow-through pores and discreet catalytic clusters adhering to the inside surfaces of the pores.

Mechanics of dual-mode dilative failure in subaqueous sediment deposits

NASA Astrophysics Data System (ADS)

You, Yao; Flemings, Peter; Mohrig, David

2014-07-01

We introduce dual-mode dilative failure with flume experiments. Dual-mode dilative failure combines slow and steady release of sediments by breaching with periodic sliding, which rapidly releases an internally coherent wedge of sediments. It occurs in dilative sandy deposits. This periodic slope failure results from cyclic evolution of the excess pore pressure in the deposit. Sliding generates large, transient, negative excess pore pressure that strengthens the deposit and allows breaching to occur. During breaching, negative excess pore pressure dissipates, the deposit weakens, and ultimately sliding occurs once again. We show that the sliding frequency is proportional to the coefficient of consolidation. We find that thicker deposits are more susceptible to dual-mode dilative failure. Discovery of dual-mode dilative failure provides a new mechanism to consider when interpreting the sedimentary deposits linked to submarine slope failures.

Metallurgical Mechanisms Controlling Mechanical Properties of Aluminum Alloy 2219 Produced By Electron Beam Freeform Fabrication

NASA Technical Reports Server (NTRS)

Domack, Marcia S.; Taminger, Karen M. B.; Begley, Matthew

2006-01-01

The electron beam freeform fabrication (EBF3) layer-additive manufacturing process has been developed to directly fabricate complex geometry components. EBF3 introduces metal wire into a molten pool created on the surface of a substrate by a focused electron beam. Part geometry is achieved by translating the substrate with respect to the beam to build the part one layer at a time. Tensile properties have been demonstrated for electron beam deposited aluminum and titanium alloys that are comparable to wrought products, although the microstructures of the deposits exhibit features more typical of cast material. Understanding the metallurgical mechanisms controlling mechanical properties is essential to maximizing application of the EBF3 process. In the current study, mechanical properties and resulting microstructures were examined for aluminum alloy 2219 fabricated over a range of EBF3 process variables. Material performance was evaluated based on tensile properties and results were compared with properties of Al 2219 wrought products. Unique microstructures were observed within the deposited layers and at interlayer boundaries, which varied within the deposit height due to microstructural evolution associated with the complex thermal history experienced during subsequent layer deposition. Microstructures exhibited irregularly shaped grains, typically with interior dendritic structures, which were described based on overall grain size, morphology, distribution, and dendrite spacing, and were correlated with deposition parameters. Fracture features were compared with microstructural elements to define fracture paths and aid in definition of basic processing-microstructure-property correlations.

Microstructural and associated chemical changes during the composting of a high temperature biochar: Mechanisms for nitrate, phosphate and other nutrient retention and release.

PubMed

Joseph, Stephen; Kammann, Claudia I; Shepherd, Jessica G; Conte, Pellegrino; Schmidt, Hans-Peter; Hagemann, Nikolas; Rich, Anne M; Marjo, Christopher E; Allen, Jessica; Munroe, Paul; Mitchell, David R G; Donne, Scott; Spokas, Kurt; Graber, Ellen R

2018-03-15

Recent studies have demonstrated the importance of the nutrient status of biochar and soils prior to its inclusion in particular agricultural systems. Pre-treatment of nutrient-reactive biochar, where nutrients are loaded into pores and onto surfaces, gives improved yield outcomes compared to untreated biochar. In this study we have used a wide selection of spectroscopic and microscopic techniques to investigate the mechanisms of nutrient retention in a high temperature wood biochar, which had negative effects on Chenopodium quinoa above ground biomass yield when applied to the system without prior nutrient loading, but positive effects when applied after composting. We have compared non-composted biochar (BC) with composted biochar (BCC) to elucidate the differences which may have led to these results. The results of our investigation provide evidence for a complex series of reactions during composting, where dissolved nutrients are first taken up into biochar pores along a concentration gradient and through capillary action, followed by surface sorption and retention processes which block biochar pores and result in deposition of a nutrient-rich organomineral (plaque) layer. The lack of such pretreatment in the BC samples would render it reactive towards nutrients in a soil-fertilizer system, making it a competitor for, rather than provider of, nutrients for plant growth. Copyright © 2017 Elsevier B.V. All rights reserved.

Optical waveguiding properties into porous gallium nitride structures investigated by prism coupling technique

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

Alshehri, Bandar; Dogheche, Elhadj, E-mail: elhadj.dogheche@univ-valenciennes.fr; Lee, Seung-Min

2014-08-04

In order to modulate the refractive index and the birefringence of Gallium Nitride (GaN), we have developed a chemical etching method to perform porous structures. The aim of this research is to demonstrate that optical properties of GaN can be tuned by controlling the pores density. GaN films are prepared on sapphire by metal organic chemical vapor deposition and the microstructure is characterized by transmission electron microscopy, and scanning electron microscope analysis. Optical waveguide experiment is demonstrated here to determine the key properties as the ordinary (n{sub 0}) and extraordinary (n{sub e}) refractive indices of etched structures. We report heremore » the dispersion of refractive index for porous GaN and compare it to the bulk material. We observe that the refractive index decreases when the porous density p is increased: results obtained at 0.975 μm have shown that the ordinary index n{sub 0} is 2.293 for a bulk layer and n{sub 0} is 2.285 for a pores density of 20%. This value corresponds to GaN layer with a pore size of 30 nm and inter-distance of 100 nm. The control of the refractive index into GaN is therefore fundamental for the design of active and passive optical devices.« less

The effect of preparation conditions on the structure and mechanical properties of reaction-sintered silicon nitride

NASA Technical Reports Server (NTRS)

Heinrich, J.

1980-01-01

The microstructure of reaction sintered silicon nitride (RSSN) was changed over a wide range by varying the grain density, grain size of the silicon starting powder, nitriding conditions, and by introducing artificial pores. The influence of single microstructural parameters on mechanical properties like room temperature strength, creep behavior, and resistance to thermal shock was investigated. The essential factors influencing these properties were found to be total porosity, pore size distribution, and the fractions of alpha and beta Si3N4. In view of high temperature engineering applications of RSSN, potentials for optimizing the material's properties by controlled processing are discussed.

[The effect of technological parameters of wide-band laser cladding on microstructure and sinterability of gradient bioceramics composite coating].

PubMed

Liu, Qibin; Zhu, Weidong; Zou, Longjiang; Zheng, Min; Dong, Chuang

2005-12-01

The gradient bioceramics coating was prepared on the surface of Ti-6Al-4V alloy by using wide-band laser cladding. And the effect of technological parameters of wide-band laser cladding on microstructure and sinterability of gradient bioceramics composite coating was studied. The experimental results indicated that in the circumstances of size of laser doze D and scanning velocity V being fixed, with the increasement of power P, the density of microstructure in bioceramics coating gradually degraded; with the increasement of power P, the pore rate of bioceramics gradually became high. While P = 2.3 KW, the bioceramics coating with dense structure and lower pore rate (5.11%) was obtained; while P = 2.9 KW, the bioceramics coating with disappointing density was formed and its pore rate was up to 21.32%. The microhardness of bioceramics coating demonstrated that while P = 2.3 KW, the largest value of microhardness of bioceramics coating was 1100 HV. Under the condition of our research work, the optimum technological parameters for preparing gradient bioceramics coating by wide-band laser cladding are: P = 2.3 KW, V = 145 mm/min, D = 16 mm x 2 mm.

Microstructural and Optical Properties of Porous Alumina Elaborated on Glass Substrate

NASA Astrophysics Data System (ADS)

Zaghdoudi, W.; Gaidi, M.; Chtourou, R.

2013-03-01

A transparent porous anodized aluminum oxide (AAO) nanostructure was formed on a glass substrate using the anodization of a highly pure evaporated aluminum layer. A parametric study was carried out in order to achieve a fine control of the microstructural and optical properties of the elaborated films. The microstructural and surface morphologies of the porous alumina films were characterized by x-ray diffraction and atomic force microscopy. Pore diameter, inter-pore separation, and the porous structure as a function of anodization conditions were investigated. It was then found that the pores density decreases with increasing the anodization time. Regular cylindrical porous AAO films with a flat bottom structure were formed by chemical etching and anodization. A high transmittance in the 300-900 nm range is reported, indicating a fulfilled growth of the transparent sample (alumina) from the aluminum metal. The data showed typical interference oscillations as a result of the transparent characteristics of the film throughout the visible spectral range. The thickness and the optical constants ( n and k) of the porous anodic alumina films, as a function of anodizing time, were obtained using spectroscopic ellipsometry in the ultraviolet-visible-near infrared (UV-vis-NIR) regions.

Evaluation of borate bioactive glass scaffolds with different pore sizes in a rat subcutaneous implantation model.

PubMed

Deliormanli, Aylin M; Liu, Xin; Rahaman, Mohamed N

2014-01-01

Borate bioactive glass has been shown to convert faster and more completely to hydroxyapatite and enhance new bone formation in vivo when compared to silicate bioactive glass (such as 45S5 and 13-93 bioactive glass). In this work, the effects of the borate glass microstructure on its conversion to hydroxyapatite (HA) in vitro and its ability to support tissue ingrowth in a rat subcutaneous implantation model were investigated. Bioactive borate glass scaffolds, designated 13-93B3, with a grid-like microstructure and pore widths of 300, 600, and 900 µm were prepared by a robocasting technique. The scaffolds were implanted subcutaneously for 4 weeks in Sprague Dawley rats. Silicate 13-93 glass scaffolds with the same microstructure were used as the control. The conversion of the scaffolds to HA was studied as a function of immersion time in a simulated body fluid. Histology and scanning electron microscopy were used to evaluate conversion of the bioactive glass implants to hydroxyapatite, as well as tissue ingrowth and blood vessel formation in the implants. The pore size of the scaffolds was found to have little effect on tissue infiltration and angiogenesis after the 4-week implantation.

Shaping thin film growth and microstructure pathways via plasma and deposition energy: a detailed theoretical, computational and experimental analysis.

PubMed

Sahu, Bibhuti Bhusan; Han, Jeon Geon; Kersten, Holger

2017-02-15

Understanding the science and engineering of thin films using plasma assisted deposition methods with controlled growth and microstructure is a key issue in modern nanotechnology, impacting both fundamental research and technological applications. Different plasma parameters like electrons, ions, radical species and neutrals play a critical role in nucleation and growth and the corresponding film microstructure as well as plasma-induced surface chemistry. The film microstructure is also closely associated with deposition energy which is controlled by electrons, ions, radical species and activated neutrals. The integrated studies on the fundamental physical properties that govern the plasmas seek to determine their structure and modification capabilities under specific experimental conditions. There is a requirement for identification, determination, and quantification of the surface activity of the species in the plasma. Here, we report a detailed study of hydrogenated amorphous and crystalline silicon (c-Si:H) processes to investigate the evolution of plasma parameters using a theoretical model. The deposition processes undertaken using a plasma enhanced chemical vapor deposition method are characterized by a reactive mixture of hydrogen and silane. Later, various contributions of energy fluxes on the substrate are considered and modeled to investigate their role in the growth of the microstructure of the deposited film. Numerous plasma diagnostic tools are used to compare the experimental data with the theoretical results. The film growth and microstructure are evaluated in light of deposition energy flux under different operating conditions.

Bioceramic coating of hydroxyapatite fabricated on Ti-6Al-4V with Nd-YAG laser

NASA Astrophysics Data System (ADS)

Tlotleng, Monnamme; Akinlabi, Esther T.; Shukla, Mukul; Pityana, Sisa

2015-03-01

This paper presents on the direct laser melted hydroxyapatite coatings achieved by melting the pre-placed powder beds using Nd-YAG laser. The process development and optimized parameters are reported. The results show that by changing the laser power and the beam inclined plane it is possible that a desirable coating of HAP that is rich on the surface can be produced. The microstructures of the coatings showed balling and cracking at beam angles between 0-15° and at 27° a successful coating was achieved with laser power and scanning speed of 750W and 5mm/s respectively. The said coating was pore and crack free while it retained non-decomposed HAP crystallites on the surface (mixed). The microstructure of the transition layer concluded a moderate temperature process since the formed dendrites did not develop or form secondary arms. The Ca/P conducted on the coating using EDS concluded Ca/P ratio of 8.04 and the absence of titanium phosphates phase (TiP2). TiP2 is typically associated with the decomposition of HAP and indicate the presence of high processing temperatures. Even so, the current results indicated that the investigated process was successful in depositing HAP coating with desirable microstructures even though its bio-corrosion properties still need to be ascertained before it could be qualified as suitable for biomedical applications.

Gasification Reaction Characteristics of Ferro-Coke at Elevated Temperatures

NASA Astrophysics Data System (ADS)

Wang, Peng; Zhang, Jian-liang; Gao, Bing

2017-01-01

In this paper, the effects of temperature and atmosphere on the gasification reaction of ferro-coke were investigated in consideration of the actual blast furnace conditions. Besides, the microstructure of the cokes was observed by scanning electron microscope (SEM). It is found that the weight loss of ferro-coke during the gasification reaction is significantly enhanced in the case of increasing either the reaction temperature or the CO2 concentration. Furthermore, compared with the normal type of metallurgical coke, ferro-coke exhibits a higher weight loss when they are gasified at the same temperature or under the same atmosphere. As to the microstructure, inside the reacted ferro-coke are a large amount of pores. Contrary to the normal coke, the proportions of the large-size pores and the through holes are greatly increased after gasification, giving rise to thinner pore walls and hence a degradation in coke strength after reaction (CSR).

Microstructure and Properties of Zircon-Added Carbon Refractories for Blast Furnace

NASA Astrophysics Data System (ADS)

Zhu, Tianbin; Li, Yawei; Sang, Shaobai; Chen, Xilai; Zhao, Lei; Li, Yuanbing; Li, Shujing

2012-11-01

Microstructure and properties of zircon-added carbon refractory specimens for blast furnace (BF) were investigated with the aid of X-ray diffraction (XRD), a scanning electron microscope (SEM), energy-dispersive X-ray, mercury porosimetry, and a laser thermal conductivity (TC) meter. Additives could influence the matrix structures and improve the properties of specimens. With the increase of zircon powder content, the amount of SiC whiskers formed increased and their aspect ratio became larger, and the SiC whiskers tended to be distributed homogeneously. Zircon powder additions decreased the mean pore diameter and increased <1- μm pore volume by filling in pores via SiC, improved the TC and the cold crushing strength (CCS) due to the in-situ formation of the more well-developed SiC whiskers with high TC, and significantly reduced the molten iron attack to carbon specimens.

Residual stress in obliquely deposited MgF2 thin films.

PubMed

Jaing, Cheng-Chung; Liu, Ming-Chung; Lee, Cheng-Chung; Cho, Wen-Hao; Shen, Wei-Ting; Tang, Chien-Jen; Liao, Bo-Huei

2008-05-01

MgF(2) films with a columnar microstructure are obliquely deposited on glass substrates by resistive heating evaporation. The columnar angles of the films increases with the deposition angle. Anisotropic stress does not develop in the films with tilted columns. The residual stresses in the films depend on the deposition and columnar angles in a columnar microstructure.

Microstructure-related properties of magnesium fluoride films at 193nm by oblique-angle deposition.

PubMed

Guo, Chun; Kong, Mingdong; Lin, Dawei; Liu, Cunding; Li, Bincheng

2013-01-14

Magnesium fluoride (MgF2) films deposited by resistive heating evaporation with oblique-angle deposition have been investigated in details. The optical and micro-structural properties of single-layer MgF2 films were characterized by UV-VIS and FTIR spectrophotometers, scanning electron microscope (SEM), atomic force microscope (AFM), and x-ray diffraction (XRD), respectively. The dependences of the optical and micro-structural parameters of the thin films on the deposition angle were analyzed. It was found that the MgF2 film in a columnar microstructure was negatively inhomogeneous of refractive index and polycrystalline. As the deposition angle increased, the optical loss, extinction coefficient, root-mean-square (rms) roughness, dislocation density and columnar angle of the MgF2 films increased, while the refractive index, packing density and grain size decreased. Furthermore, IR absorption of the MgF2 films depended on the columnar structured growth.

Electrically conductive anodized aluminum coatings

NASA Technical Reports Server (NTRS)

Alwitt, Robert S. (Inventor); Liu, Yanming (Inventor)

2001-01-01

A process for producing anodized aluminum with enhanced electrical conductivity, comprising anodic oxidation of aluminum alloy substrate, electrolytic deposition of a small amount of metal into the pores of the anodized aluminum, and electrolytic anodic deposition of an electrically conductive oxide, including manganese dioxide, into the pores containing the metal deposit; and the product produced by the process.

High-volume-fraction Cu/Al2O3-SiC hybrid interpenetrating phase composite

NASA Astrophysics Data System (ADS)

Saidi, Hesam; Roudini, Ghodratollah; Afarani, Mahdi Shafiee

2015-10-01

Metal matrix particulate interpenetrating phase composites are a class of composites materials with three-dimensional internal connections of matrix and reinforcements. This kind of microstructure affects the mechanical and physical properties of the composites. In this study, Al2O3-SiC hybrid preforms were produced by polyurethane foams removal (replica method) within mean pore size of 30 pores per inch (ppi), and sintering at 1200 °C. Subsequently, the molten copper was infiltrated into the preforms by squeeze casting method. The microstructure, density, porosity, bending strength and thermal shock resistance of the preforms were investigated. Then, the composites microstructure and compressive strength were studied. The results showed that with SiC concentration increasing, the density, flexural strength and thermal shock resistance of the preforms were improved. Also the composites compressive strengths were changed with variation of SiC concentration.

Three-dimensional numerical simulation of water droplet emerging from a gas diffusion layer surface in micro-channels

NASA Astrophysics Data System (ADS)

Ding, Y.; Bi, H. T.; Wilkinson, D. P.

The dynamic formation of water droplets emerging from a gas diffusion layer (GDL) surface in micro-channels was simulated using the volume of fluid (VOF) method. The influence of GDL surface microstructure was investigated by changing the pore diameter and the number of pore openings on the GDL surface. Simulation results show that the microstructure of the GDL surface has a significant impact on the two-phase flow patterns in gas flow channels. For a non-uniform GDL surface, three stages were identified, namely emergence and merging on the GDL surface, accumulation on the channel sidewalls and detachment from the top wall. It was also found that if the pore size is small enough, the flow pattern in the channel does not change with further reduction in the pore diameter. However, the two-phase flow patterns change significantly with the wettability of the GDL surface and sidewalls, but remain the same when the liquid flow rate is reduced by two orders of magnitude from the reference case.

Fine tuning of nanopipettes using atomic layer deposition for single molecule sensing.

PubMed

Sze, Jasmine Y Y; Kumar, Shailabh; Ivanov, Aleksandar P; Oh, Sang-Hyun; Edel, Joshua B

2015-07-21

Nanopipettes are an attractive single-molecule tool for identification and characterisation of nucleic acids and proteins in solutions. They enable label-free analysis and reveal individual molecular properties, which are generally masked by ensemble averaging. Having control over the pore dimensions is vital to ensure that the dimensions of the molecules being probed match those of the pore for optimization of the signal to noise. Although nanopipettes are simple and easy to fabricate, challenges exist, especially when compared to more conventional solid-state analogues. For example, a sub-20 nm pore diameter can be difficult to fabricate and the batch-to-batch reproducibility is often poor. To improve on this limitation, atomic layer deposition (ALD) is used to deposit ultrathin layers of alumina (Al2O3) on the surface of the quartz nanopipettes enabling sub-nm tuning of the pore dimensions. Here, Al2O3 with a thickness of 8, 14 and 17 nm was deposited onto pipettes with a starting pore diameter of 75 ± 5 nm whilst a second batch had 5 and 8 nm Al2O3 deposited with a starting pore diameter of 25 ± 3 nm respectively. This highly conformal process coats both the inner and outer surfaces of pipettes and resulted in the fabrication of pore diameters as low as 7.5 nm. We show that Al2O3 modified pores do not interfere with the sensing ability of the nanopipettes and can be used for high signal-to-noise DNA detection. ALD provides a quick and efficient (batch processing) for fine-tuning nanopipettes for a broad range of applications including the detection of small biomolecules like RNA, aptamers and DNA-protein interactions at the single molecule level.

Catalytic nanoporous membranes

DOEpatents

Pellin, Michael J [Naperville, IL; Hryn, John N [Naperville, IL; Elam, Jeffrey W [Elmhurst, IL

2009-12-01

A nanoporous catalytic membrane which displays several unique features including pores which can go through the entire thickness of the membrane. The membrane has a higher catalytic and product selectivity than conventional catalysts. Anodic aluminum oxide (AAO) membranes serve as the catalyst substrate. This substrate is then subjected to Atomic Layer Deposition (ALD), which allows the controlled narrowing of the pores from 40 nm to 10 nm in the substrate by deposition of a preparatory material. Subsequent deposition of a catalytic layer on the inner surfaces of the pores reduces pore sizes to less than 10 nm and allows for a higher degree of reaction selectivity. The small pore sizes allow control over which molecules enter the pores, and the flow-through feature can allow for partial oxidation of reactant species as opposed to complete oxidation. A nanoporous separation membrane, produced by ALD is also provided for use in gaseous and liquid separations. The membrane has a high flow rate of material with 100% selectivity.

Microstructural characterization of dental zinc phosphate cements using combined small angle neutron scattering and microfocus X-ray computed tomography.

PubMed

Viani, Alberto; Sotiriadis, Konstantinos; Kumpová, Ivana; Mancini, Lucia; Appavou, Marie-Sousai

2017-04-01

To characterize the microstructure of two zinc phosphate cement formulations in order to investigate the role of liquid/solid ratio and composition of powder component, on the developed porosity and, consequently, on compressive strength. X-ray powder diffraction with the Rietveld method was used to study the phase composition of zinc oxide powder and cements. Powder component and cement microstructure were investigated with scanning electron microscopy. Small angle neutron scattering (SANS) and microfocus X-ray computed tomography (XmCT) were together employed to characterize porosity and microstructure of dental cements. Compressive strength tests were performed to evaluate their mechanical performance. The beneficial effects obtained by the addition of Al, Mg and B to modulate powder reactivity were mitigated by the crystallization of a Zn aluminate phase not involved in the cement setting reaction. Both cements showed spherical pores with a bimodal distribution at the micro/nano-scale. Pores, containing a low density gel-like phase, developed through segregation of liquid during setting. Increasing liquid/solid ratio from 0.378 to 0.571, increased both SANS and XmCT-derived specific surface area (by 56% and 22%, respectively), porosity (XmCT-derived porosity increased from 3.8% to 5.2%), the relative fraction of large pores ≥50μm, decreased compressive strength from 50±3MPa to 39±3MPa, and favored microstructural and compositional inhomogeneities. Explain aspects of powder design affecting the setting reaction and, in turn, cement performance, to help in optimizing cement formulation. The mechanism behind development of porosity and specific surface area explains mechanical performance, and processes such as erosion and fluoride release/uptake. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

Review of Relationship Between Particle Deformation, Coating Microstructure, and Properties in High-Pressure Cold Spray

NASA Astrophysics Data System (ADS)

Rokni, M. R.; Nutt, S. R.; Widener, C. A.; Champagne, V. K.; Hrabe, R. H.

2017-08-01

In the cold spray (CS) process, deposits are produced by depositing powder particles at high velocity onto a substrate. Powders deposited by CS do not undergo melting before or upon impacting the substrate. This feature makes CS suitable for deposition of a wide variety of materials, most commonly metallic alloys, but also ceramics and composites. During processing, the particles undergo severe plastic deformation and create a more mechanical and less metallurgical bond with the underlying material. The deformation behavior of an individual particle depends on multiple material and process parameters that are classified into three major groups—powder characteristics, geometric parameters, and processing parameters, each with their own subcategories. Changing any of these parameters leads to evolution of a different microstructure and consequently changes the mechanical properties in the deposit. While cold spray technology has matured during the last decade, the process is inherently complex, and thus, the effects of deposition parameters on particle deformation, deposit microstructure, and mechanical properties remain unclear. The purpose of this paper is to review the parameters that have been investigated up to now with an emphasis on the existent relationships between particle deformation behavior, microstructure, and mechanical properties of various cold spray deposits.

Epitaxial thin films

DOEpatents

Hunt, Andrew Tye; Deshpande, Girish; Lin, Wen-Yi; Jan, Tzyy-Jiuan

2006-04-25

Epitatial thin films for use as buffer layers for high temperature superconductors, electrolytes in solid oxide fuel cells (SOFC), gas separation membranes or dielectric material in electronic devices, are disclosed. By using CCVD, CACVD or any other suitable deposition process, epitaxial films having pore-free, ideal grain boundaries, and dense structure can be formed. Several different types of materials are disclosed for use as buffer layers in high temperature superconductors. In addition, the use of epitaxial thin films for electrolytes and electrode formation in SOFCs results in densification for pore-free and ideal gain boundary/interface microstructure. Gas separation membranes for the production of oxygen and hydrogen are also disclosed. These semipermeable membranes are formed by high-quality, dense, gas-tight, pinhole free sub-micro scale layers of mixed-conducting oxides on porous ceramic substrates. Epitaxial thin films as dielectric material in capacitors are also taught herein. Capacitors are utilized according to their capacitance values which are dependent on their physical structure and dielectric permittivity. The epitaxial thin films of the current invention form low-loss dielectric layers with extremely high permittivity. This high permittivity allows for the formation of capacitors that can have their capacitance adjusted by applying a DC bias between their electrodes.

Geochemical impacts of waste disposal on the abyssal seafloor

NASA Astrophysics Data System (ADS)

Jahnke, Richard A.

1998-05-01

The response of pore water oxygen, nitrate, sulfate, sulfide, ammonium and methane and particulate organic carbon distributions to the input of 8.5 million m 3 (3.8×10 12 g) of organic-rich waste materials is simulated. The deposit is assumed to be conical with a maximum thickness of approximately 20 m. Remineralization reactions within the deposit rapidly deplete any initially available pore water oxidants such as oxygen, nitrate and sulfate, and are subsequently dominated by fermentation reactions. Diffusion downward of reduced metabolites, sulfide, ammonium and methane, depletes the available oxidants in the pore waters below the waste pile, increasing the thickness of the anoxic layer. While the impacted region is limited to essentially the deposition site, recovery of the pore waters is estimated to be >10 4 years. The overall computational results are corroborated by the pore water distributions observed at turbidite boundaries. Numerous uncertainties in the parameterizations limit the overall accuracy of the calculations presented. The most significant of these are: (1) A quantitatively accurate assessment of the remineralization rate of the deposited organic matter including its rate of inoculation by abyssal microorganisms; (2) a detailed assessment of potential non-diffusive pore water transport processes including advection due to compaction and buoyancy-driven flows and enhanced exchange due to macrobenthic irrigation activities and (3) an assessment of the potential alteration of pore space and methane reactivity due to gas hydrate formation.

A novel open-porous magnesium scaffold with controllable microstructures and properties for bone regeneration

PubMed Central

Cheng, Meng-qi; Wahafu, Tuerhongjiang; Jiang, Guo-feng; Liu, Wei; Qiao, Yu-qin; Peng, Xiao-chun; Cheng, Tao; Zhang, Xian-long; He, Guo; Liu, Xuan-yong

2016-01-01

The traditional production methods of porous magnesium scaffolds are difficult to accurately control the pore morphologies and simultaneously obtain appropriate mechanical properties. In this work, two open-porous magnesium scaffolds with different pore size but in the nearly same porosity are successfully fabricated with high-purity Mg ingots through the titanium wire space holder (TWSH) method. The porosity and pore size can be easily, precisely and individually controlled, as well as the mechanical properties also can be regulated to be within the range of human cancellous bone by changing the orientation of pores without sacrifice the requisite porous structures. In vitro cell tests indicate that the scaffolds have good cytocompatibility and osteoblastic differentiation properties. In vivo findings demonstrate that both scaffolds exhibit acceptable inflammatory responses and can be almost fully degraded and replaced by newly formed bone. More importantly, under the same porosity, the scaffolds with larger pore size can promote early vascularization and up-regulate collagen type 1 and OPN expression, leading to higher bone mass and more mature bone formation. In conclusion, a new method is introduced to develop an open-porous magnesium scaffold with controllable microstructures and mechanical properties, which has great potential clinical application for bone reconstruction in the future. PMID:27071777

A novel open-porous magnesium scaffold with controllable microstructures and properties for bone regeneration

NASA Astrophysics Data System (ADS)

Cheng, Meng-Qi; Wahafu, Tuerhongjiang; Jiang, Guo-Feng; Liu, Wei; Qiao, Yu-Qin; Peng, Xiao-Chun; Cheng, Tao; Zhang, Xian-Long; He, Guo; Liu, Xuan-Yong

2016-04-01

The traditional production methods of porous magnesium scaffolds are difficult to accurately control the pore morphologies and simultaneously obtain appropriate mechanical properties. In this work, two open-porous magnesium scaffolds with different pore size but in the nearly same porosity are successfully fabricated with high-purity Mg ingots through the titanium wire space holder (TWSH) method. The porosity and pore size can be easily, precisely and individually controlled, as well as the mechanical properties also can be regulated to be within the range of human cancellous bone by changing the orientation of pores without sacrifice the requisite porous structures. In vitro cell tests indicate that the scaffolds have good cytocompatibility and osteoblastic differentiation properties. In vivo findings demonstrate that both scaffolds exhibit acceptable inflammatory responses and can be almost fully degraded and replaced by newly formed bone. More importantly, under the same porosity, the scaffolds with larger pore size can promote early vascularization and up-regulate collagen type 1 and OPN expression, leading to higher bone mass and more mature bone formation. In conclusion, a new method is introduced to develop an open-porous magnesium scaffold with controllable microstructures and mechanical properties, which has great potential clinical application for bone reconstruction in the future.

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.

Characterizing Suspension Plasma Spray Coating Formation Dynamics through Curvature Measurements

NASA Astrophysics Data System (ADS)

Chidambaram Seshadri, Ramachandran; Dwivedi, Gopal; Viswanathan, Vaishak; Sampath, Sanjay

2016-12-01

Suspension plasma spraying (SPS) enables the production of variety of microstructures with unique mechanical and thermal properties. In SPS, a liquid carrier (ethanol/water) is used to transport the sub-micrometric feedstock into the plasma jet. Considering complex deposition dynamics of SPS technique, there is a need to better understand the relationships among spray conditions, ensuing particle behavior, deposition stress evolution and resultant properties. In this study, submicron yttria-stabilized zirconia particles suspended in ethanol were sprayed using a cascaded arc plasma torch. The stresses generated during the deposition of the layers (termed evolving stress) were monitored via the change in curvature of the substrate measured using an in situ measurement apparatus. Depending on the deposition conditions, coating microstructures ranged from feathery porous to dense/cracked deposits. The evolving stresses and modulus were correlated with the observed microstructures and visualized via process maps. Post-deposition bi-layer curvature measurement via low temperature thermal cycling was carried out to quantify the thermo-elastic response of different coatings. Lastly, preliminary data on furnace cycle durability of different coating microstructures were evaluated. This integrated study involving in situ diagnostics and ex situ characterization along with process maps provides a framework to describe coating formation mechanisms, process parametrics and microstructure description.

Electrodeposition of platinum and silver into chemically modified microporous silicon electrodes

PubMed Central

2012-01-01

Electrodeposition of platinum and silver into hydrophobic and hydrophilic microporous silicon layers was investigated using chemically modified microporous silicon electrodes. Hydrophobic microporous silicon enhanced the electrodeposition of platinum in the porous layer. Meanwhile, hydrophilic one showed that platinum was hardly deposited within the porous layer, and a film of platinum on the top of the porous layer was observed. On the other hand, the electrodeposition of silver showed similar deposition behavior between these two chemically modified electrodes. It was also found that the electrodeposition of silver started at the pore opening and grew toward the pore bottom, while a uniform deposition from the pore bottom was observed in platinum electrodeposition. These electrodeposition behaviors are explained on the basis of the both effects, the difference in overpotential for metal deposition on silicon and on the deposited metal, and displacement deposition rate of metal. PMID:22720690

Thermal conductivity of zirconia thermal barrier coatings

NASA Technical Reports Server (NTRS)

Dinwiddie, R. B.; Beecher, S. C.; Nagaraj, B. A.; Moore, C. S.

1995-01-01

Thermal barrier coatings (TBC's) applied to the hot gas components of turbine engines lead to enhanced fuel efficiency and component reliability. Understanding the mechanisms which control the thermal transport behavior of the TBC's is of primary importance. Physical vapor deposition (PVD) and plasma spraying (PS) are the two most commonly used coating techniques. These techniques produce coatings with unique microstructures which control their performance and stability. The PS coatings were applied with either standard powder or hollow sphere particles. The hollow sphere particles yielded a lower density and lower thermal conductivity coating. The thermal conductivity of both fully and partially stabilized zirconia, before and after thermal aging, will be compared. The thermal conductivity of the coatings permanently increases upon exposed to high temperatures. These increases are attributed to microstructural changes within the coatings. Sintering of the as-fabricated plasma sprayed lamellar structure is observed by scanning electron microscopy of coatings isothermally heat treated at temperatures greater than 1100 C. During this sintering process the planar porosity between lamella is converted to a series of small spherical pores. The change in pore morphology is the primary reason for the observed increase in thermal conductivity. This increase in thermal conductivity can be modeled using a relationship which depends on both the temperature and time of exposure. Although the PVD coatings are less susceptible to thermal aging effects, preliminary results suggest that they have a higher thermal conductivity than PS coatings, both before and after thermal aging. The increases in thermal conductivity due to thermal aging for partially stabilized plasma sprayed zirconia have been found to be less than for fully stabilized plasma sprayed zirconia coatings. The high temperature thermal diffusivity data indicate that if these coatings reach a temperature above 1100 C during operation, they will begin to lose their effectiveness as a thermal barrier.

Additive Manufacturing of AlSi10Mg Alloy Using Direct Energy Deposition: Microstructure and Hardness Characterization

NASA Astrophysics Data System (ADS)

Javidani, M.; Arreguin-Zavala, J.; Danovitch, J.; Tian, Y.; Brochu, M.

2017-04-01

This paper aims to study the manufacturing of the AlSi10Mg alloy with direct energy deposition (DED) process. Following fabrication, the macro- and microstructural evolution of the as-processed specimens was initially investigated using optical microscopy and scanning electron microscopy. Columnar dendritic structure was the dominant solidification feature of the deposit; nevertheless, detailed microstructural analysis revealed cellular morphology near the substrate and equiaxed dendrites at the top end of the deposit. Moreover, the microstructural morphology in the melt pool boundary of the deposit differed from the one in the core of the layers. The remaining porosity of the deposit was evaluated by Archimedes' principle and by image analysis of the polished surface. Crystallographic texture in the deposit was also assessed using electron backscatter diffraction and x-ray diffraction analysis. The dendrites were unidirectionally oriented at an angle of 80° to the substrate. EPMA line scans were performed to evaluate the compositional variation and elemental segregation in different locations. Eventually, microhardness (HV) tests were conducted in order to study the hardness gradient in the as-DED-processed specimen along the deposition direction. The presented results, which exhibited a deposit with an almost defect free structure, indicate that the DED process can suitable for the deposition of Al-Si-based alloys with a highly consolidated structure.

Morphology, microstructure, and magnetic properties of ordered large-pore mesoporous cadmium ferrite thin film spin glasses.

PubMed

Reitz, Christian; Suchomski, Christian; Chakravadhanula, Venkata Sai Kiran; Djerdj, Igor; Jagličić, Zvonko; Brezesinski, Torsten

2013-04-01

Herein, we report the synthesis, microstructure, and magnetic properties of cadmium ferrite (CdFe2O4) thin films with both an ordered cubic network of 18 nm diameter pores and single-phase spinel grains averaging 13 nm in diameter. These mesoporous materials were produced through facile polymer templating of hydrated nitrate salt precursors. Both the morphology and the microstructure, including cation site occupancy and electronic bonding configuration, were analyzed in detail by electron microscopy, grazing incidence small-angle X-ray scattering, Raman and X-ray photoelectron spectroscopy, and N2-physisorption. The obtained data demonstrate that the network of pores is retained up to annealing temperatures as high as 650 °C--the onset of crystallization is at ϑ = (590 ± 10) °C. Furthermore, they show that the polymer-templated samples exhibit a "partially" inverted spinel structure with inversion parameter λ = 0.40 ± 0.02. This differs from microcrystalline CdFe2O4 which shows virtually no inversion. Magnetic susceptibility studies reveal ferrimagnetic spin coupling below 147 K and further point to the likelihood of glassy behavior at low temperature (T(f) ≈ 60 K). In addition, analysis of room temperature magnetization data indicates the presence of sub-10 nm diameter superparamagnetic clusters in an otherwise paramagnetic environment.

Water evaporation in silica colloidal deposits.

PubMed

Peixinho, Jorge; Lefèvre, Grégory; Coudert, François-Xavier; Hurisse, Olivier

2013-10-15

The results of an experimental study on the evaporation and boiling of water confined in the pores of deposits made of mono-dispersed silica colloidal micro-spheres are reported. The deposits are studied using scanning electron microscopy, adsorption of nitrogen, and adsorption of water through attenuated total reflection-infrared spectroscopy. The evaporation is characterized using differential scanning calorimetry and thermal gravimetric analysis. Optical microscopy is used to observe the patterns on the deposits after evaporation. When heating at a constant rate and above boiling temperature, the release of water out of the deposits is a two step process. The first step is due to the evaporation and boiling of the surrounding and bulk water and the second is due to the desorption of water from the pores. Additional experiments on the evaporation of water from membranes having cylindrical pores and of heptane from silica deposits suggest that the second step is due to the morphology of the deposits. Copyright © 2013 Elsevier Inc. All rights reserved.

Iron films deposited on porous alumina substrates

NASA Astrophysics Data System (ADS)

Yamada, Yasuhiro; Tanabe, Kenichi; Nishida, Naoki; Kobayashi, Yoshio

2016-12-01

Iron films were deposited on porous alumina substrates using an arc plasma gun. The pore sizes (120 - 250 nm) of the substrates were controlled by changing the temperature during the anodic oxidation of aluminum plates. Iron atoms penetrated into pores with diameters of less than 160 nm, and were stabilized by forming γ-Fe, whereas α-Fe was produced as a flat plane covering the pores. For porous alumina substrates with pore sizes larger than 200 nm, the deposited iron films contained many defects and the resulting α-Fe had smaller hyperfine magnetic fields. In addition, only a very small amount of γ-Fe was obtained. It was demonstrated that the composition and structure of an iron film can be affected by the surface morphology of the porous alumina substrate on which the film is grown.

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.

Melt infiltration of silicon carbide compacts. II - Evaluation of solidification microstructures

NASA Technical Reports Server (NTRS)

Asthana, Rajiv; Rohatgi, Pradeep K.

1993-01-01

Microstructural aspects of alloy solidification within the interstices of porous compacts of platelet-shaped single crystals of alpha-SiC, when the latter are infiltrated with a hot metal under pressure, have been described. Microstructural evidence is presented of selective reorientation of platelets and nonhomogeneous solute distribution under shear of pressurized melt, of constrained growth of primary solid within finite width zones, and of the modulation of coring due to microsegregation as a result of variations in the pore size of compacts.

Microstructural and strength improvements through the use of Na{sub 2}CO{sub 3} in a cementless Ca(OH){sub 2}-activated Class F fly ash system

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

Jeon, Dongho; Jun, Yubin; Jeong, Yeonung

2015-01-15

This study explores the beneficial effects of Na{sub 2}CO{sub 3} as an additive for microstructural and strength improvements in a Ca(OH){sub 2}-activated fly ash system. NaOH-activated fly ash samples were also tested to compare the effect of Na{sub 2}CO{sub 3}. Compressive strength testing, XRD, SEM/BSE/EDS, {sup 29}Si/{sup 27}Al MAS-NMR, MIP and TGA were performed. The testing results indicate that the use of Na{sub 2}CO{sub 3} for Ca(OH){sub 2}-activation led to a noticeable improvement in strength and microstructure, primarily due to (1) more dissolution of raw fly ash at an early age, (2) more formation of C–S–H [or C–S–H(I)], (3) porositymore » reduction, and (4) pore-size refinement. We also found that (1) an early high alkalinity from the NaOH formation was not a major cause of strength, (2) geopolymer was not formed despite the early NaOH formation, and (3) no visible pore-filling action of CaCO{sub 3} was observed. However, Na{sub 2}CO{sub 3} did not produce any improvement in strength for NaOH-activated fly ash. -- Highlights: •The use of Na{sub 2}CO{sub 3} significantly improved strength and microstructure. •The use of Na{sub 2}CO{sub 3} induced more dissolution of raw fly ash at early ages. •The use of Na{sub 2}CO{sub 3} promoted more C–S–H [or C–S–H(I)] formation. •The use of Na{sub 2}CO{sub 3} reduced total porosity and refined pore-size distribution. •The use of Na{sub 2}CO{sub 3} produced neither geopolymer formations nor pore-filling actions from CaCO{sub 3}.« less

3D printing of novel osteochondral scaffolds with graded microstructure

NASA Astrophysics Data System (ADS)

Nowicki, Margaret A.; Castro, Nathan J.; Plesniak, Michael W.; Zhang, Lijie Grace

2016-10-01

Osteochondral tissue has a complex graded structure where biological, physiological, and mechanical properties vary significantly over the full thickness spanning from the subchondral bone region beneath the joint surface to the hyaline cartilage region at the joint surface. This presents a significant challenge for tissue-engineered structures addressing osteochondral defects. Fused deposition modeling (FDM) 3D bioprinters present a unique solution to this problem. The objective of this study is to use FDM-based 3D bioprinting and nanocrystalline hydroxyapatite for improved bone marrow human mesenchymal stem cell (hMSC) adhesion, growth, and osteochondral differentiation. FDM printing parameters can be tuned through computer aided design and computer numerical control software to manipulate scaffold geometries in ways that are beneficial to mechanical performance without hindering cellular behavior. Additionally, the ability to fine-tune 3D printed scaffolds increases further through our investment casting procedure which facilitates the inclusion of nanoparticles with biochemical factors to further elicit desired hMSC differentiation. For this study, FDM was used to print investment-casting molds innovatively designed with varied pore distribution over the full thickness of the scaffold. The mechanical and biological impacts of the varied pore distributions were compared and evaluated to determine the benefits of this physical manipulation. The results indicate that both mechanical properties and cell performance improve in the graded pore structures when compared to homogeneously distributed porous and non-porous structures. Differentiation results indicated successful osteogenic and chondrogenic manipulation in engineered scaffolds.

Dependence of Capillary Properties of Contemporary Clinker Bricks on Their Microstructure

NASA Astrophysics Data System (ADS)

Wesołowska, Maria; Kaczmarek, Anna

2017-10-01

Contemporary clinker bricks are applied for outer layers of walls built from other materials and walls which should have high durability and aesthetic qualities. The intended effect depends not only on the mortar applied but also on clinker properties. Traditional macroscopic tests do not allow to predict clinker behaviour in contact with mortars and external environment. The basic information for this issue is open porosity of material. It defines the material ability to absorb liquids: rain water (through the face wall surface) and grout from mortar (through base surface). The main capillary flow goes on in pores with diameters from 300 to 3000nm. It is possible to define pore distribution and their size using the Mercury Intrusion Porosimetry method. The aim of these research is evaluation of clinker brick capillary properties (initial water absorption and capillary rate) and analysis of differences in microstructure of the face and base wall of a product. Detailed results allowed to show pore distribution in function of their diameters and definition of pore amount responsible for capillary flow. Based on relation between volume function differential and pore diameter, a differential distribution curve was obtained which helped to determine the dominant diameters. The results obtained let us state that face wall of bricks was characterized with the lowest material density and open porosity. In this layer (most burnt) part of pores could be closed by locally appearing liquid phase during brick burning. Thus density is lower comparing to other part of the product.

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.

Predicting Stress vs. Strain Behaviors of Thin-Walled High Pressure Die Cast Magnesium Alloy with Actual Pore Distribution

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

Choi, Kyoo Sil; Barker, Erin; Cheng, Guang

2016-01-06

In this paper, a three-dimensional (3D) microstructure-based finite element modeling method (i.e., extrinsic modeling method) is developed, which can be used in examining the effects of porosity on the ductility/fracture of Mg castings. For this purpose, AM60 Mg tensile samples were generated under high-pressure die-casting in a specially-designed mold. Before the tensile test, the samples were CT-scanned to obtain the pore distributions within the samples. 3D microstructure-based finite element models were then developed based on the obtained actual pore distributions of the gauge area. The input properties for the matrix material were determined by fitting the simulation result to themore » experimental result of a selected sample, and then used for all the other samples’ simulation. The results show that the ductility and fracture locations predicted from simulations agree well with the experimental results. This indicates that the developed 3D extrinsic modeling method may be used to examine the influence of various aspects of pore sizes/distributions as well as intrinsic properties (i.e., matrix properties) on the ductility/fracture of Mg castings.« less

Non-Linear Association between Cerebral Amyloid Deposition and White Matter Microstructure in Cognitively Healthy Older Adults.

PubMed

Wolf, Dominik; Fischer, Florian U; Scheurich, Armin; Fellgiebel, Andreas

2015-01-01

Cerebral amyloid-β accumulation and changes in white matter (WM) microstructure are imaging characteristics in clinical Alzheimer's disease and have also been reported in cognitively healthy older adults. However, the relationship between amyloid deposition and WM microstructure is not well understood. Here, we investigated the impact of quantitative cerebral amyloid load on WM microstructure in a group of cognitively healthy older adults. AV45-positron emission tomography and diffusion tensor imaging (DTI) scans of forty-four participants (age-range: 60 to 89 years) from the Alzheimer's Disease Neuroimaging Initiative were analyzed. Fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (DR), and axial diffusivity (DA) were calculated to characterize WM microstructure. Regression analyses demonstrated non-linear (quadratic) relationships between amyloid deposition and FA, MD, as well as RD in widespread WM regions. At low amyloid burden, higher deposition was associated with increased FA as well as decreased MD and DR. At higher amyloid burden, higher deposition was associated with decreased FA as well as increased MD and DR. Additional regression analyses demonstrated an interaction effect between amyloid load and global WM FA, MD, DR, and DA on cognition, suggesting that cognition is only affected when amyloid is increasing and WM integrity is decreasing. Thus, increases in FA and decreases in MD and RD with increasing amyloid load at low levels of amyloid burden may indicate compensatory processes that preserve cognitive functioning. Potential mechanisms underlying the observed non-linear association between amyloid deposition and DTI metrics of WM microstructure are discussed.

Impact of pore space topology on permeability, cut-off frequencies and validity of wave propagation theories

NASA Astrophysics Data System (ADS)

Sarout, Joël.

2012-04-01

For the first time, a comprehensive and quantitative analysis of the domains of validity of popular wave propagation theories for porous/cracked media is provided. The case of a simple, yet versatile rock microstructure is detailed. The microstructural parameters controlling the applicability of the scattering theories, the effective medium theories, the quasi-static (Gassmann limit) and dynamic (inertial) poroelasticity are analysed in terms of pores/cracks characteristic size, geometry and connectivity. To this end, a new permeability model is devised combining the hydraulic radius and percolation concepts. The predictions of this model are compared to published micromechanical models of permeability for the limiting cases of capillary tubes and penny-shaped cracks. It is also compared to published experimental data on natural rocks in these limiting cases. It explicitly accounts for pore space topology around the percolation threshold and far above it. Thanks to this permeability model, the scattering, squirt-flow and Biot cut-off frequencies are quantitatively compared. This comparison leads to an explicit mapping of the domains of validity of these wave propagation theories as a function of the rock's actual microstructure. How this mapping impacts seismic, geophysical and ultrasonic wave velocity data interpretation is discussed. The methodology demonstrated here and the outcomes of this analysis are meant to constitute a quantitative guide for the selection of the most suitable modelling strategy to be employed for prediction and/or interpretation of rocks elastic properties in laboratory-or field-scale applications when information regarding the rock's microstructure is available.

Deformation Behavior and Microstructure of Ti6Al4V Manufactured by SLM

NASA Astrophysics Data System (ADS)

Krakhmalev, P.; Fredriksson, G.; Yadroitsava, I.; Kazantseva, N.; Plessis, A. du; Yadroitsev, I.

Mechanical properties, porosity, and microstructure of Ti6Al4V (ELI) material produced by Selective Laser Melting (SLM) under controlled oxygen content were analyzed. Fully martensitic α'structure with high dislocation density and stacking faults was observed in both as-built and stress relieved samples by means of XRD and TEM. Tensile {101 ̅2} twinning was identified by TEM and electron diffraction. Accommodation of thermal stresses during manufacturing was suggested as a possible reason for twinning. Computed tomography of pores was carried out. Pores in the specimens were evenly distributed and mostly had an elongated shape. Defect analysis by micro CT scans in pre-strained samples confirmed that the pore coalescence was the main crack formation mechanism in the final fracture with typical cup-and-cone fracture morphology. Additionally, typical dimples and quasi-cleavage were revealed. Mechanical properties of the samples after stress relieving heat treatment at 650°C for 3 h are complied with the international standard for Ti alloys for biomedical applications.

Deposition nucleation viewed as homogeneous or immersion freezing in pores and cavities

NASA Astrophysics Data System (ADS)

Marcolli, C.

2013-06-01

Heterogeneous ice nucleation is an important mechanism for the glaciation of mixed phase clouds and may also be relevant for cloud formation and dehydration at the cirrus cloud level. It is thought to proceed through different mechanisms, namely contact, condensation, immersion and deposition nucleation. Supposedly, deposition nucleation is the only pathway which does not involve liquid water but occurs by direct water vapor deposition on a surface. This study challenges this classical view by putting forward the hypothesis that what is called deposition nucleation is in fact homogeneous or immersion nucleation occurring in pores and cavities that may form between aggregated primary particles and fill with water at relative humidity RHw < 100% because of the inverse Kelvin effect. Evidence for this hypothesis of pore condensation and freezing (PCF) originates from a number of only loosely connected scientific areas. The prime example for PCF is ice nucleation in clay minerals and mineral dusts, for which the data base is best. Studies on freezing in confinement carried out on mesoporous silica materials such as SBA-15, SBA-16, MCM-41, zeolites and KIT have shown that homogeneous ice nucleation occurs abruptly at T=230-235 K in pores with diameters (D) of 3.5-4 nm or larger but only gradually at T=210-230 K in pores with D=2.5-3.5 nm. Melting temperatures in pores are depressed by an amount that can be described by the Gibbs-Thomson equation. Water adsorption isotherms of MCM-41 show that pores with D=3.5-4 nm fill with water at RHw = 56-60% in accordance with an inverse Kelvin effect. Water in such pores should freeze homogeneously for T < 235 K even before relative humidity with respect to ice (RHi) reaches ice saturation. Ice crystal growth by water vapor deposition from the gas phase is therefore expected to set in as soon as RHw > 100%. Pores with D > 7.5 nm fill with water at RHi > 100% for T < 235 K and are likely to freeze homogeneously as soon as they are filled with water. Water in pores can freeze in immersion mode at T > 235 K if the pore walls contain an active site. Pore analysis of clay minerals shows that kaolinites exhibit pore structures with pore diameters of 20-50 nm. The mesoporosity of illites and montmorillonites is characterized by pores with T = 2-5 nm. The number and size of pores is distinctly increased in acid treated montmorillonites like K10. Many clay minerals and mineral dusts show a strong increase in ice nucleation efficiency when temperature is decreased below 235 K. Such an increase is difficult to explain when ice nucleation is supposed to occur by a deposition mechanism, but evident when assuming freezing in pores, because for homogeneous ice nucleation only small pore volumes are needed, while heterogeneous ice nucleation requires larger pore structures to contain at least one active site for immersion nucleation. Together, these pieces of evidence strongly suggest that ice nucleation within pores should be the prevailing freezing mechanism of clay minerals for RHw below water saturation. Extending the analysis to other types of ice nuclei shows that freezing in pores and cracks is probably the prevailing ice nucleation mechanism for glassy and volcanic ash aerosols at RHw below water saturation. Freezing of water in carbon nanotubes might be of significance for ice nucleation by soot aerosols. No case could be identified that gives clear evidence of ice nucleation by water vapor deposition on a solid surface. Inspection of ice nuclei with a close lattice match to ice, such as silver iodide or SnomaxTM, show that for high ice nucleation efficiency below water saturation the presence of impurities or cracks on the surface may be essential. Soluble impurities promote the formation of a liquid phase below water saturation in patches on the surface or as a complete surface layer that offers an environment for immersion freezing. If porous aerosol particles come in contact with semivolatile vapors, these will condense preferentially in pores before a coating on the surface of the particles is formed. A pore partially filled with condensed species attracts water at lower RHw than an empty pore, but the aqueous solution that forms in the pore will freeze at a higher RHi than pure water. The ice nucleation ability of pores completely filled with condensed organic species might be totally impeded. Pores might also be important for preactivation, the capability of a particle to nucleate ice at lower RHi in subsequent experiments when compared to the first initial ice nucleation event. Preactivation has often been explained by persistence of ice embryos at specific sites like dislocations, steps, kinks or pores. However, it is not clear how such features can preserve an ice embryo at RHi < 100%. Rather, ice embryos could be preserved when embedded in water. To keep liquid water at RHw well below 100%, narrow pores are needed but to avoid a strong melting point depression large pores are favorable. A narrow pore opening and a large inner volume are combined in "ink bottle" pores. Such "ink bottle" pores would be suited to preserve ice at RHi < 100% and can arise e.g. in spaces between aggregated particles.

Effective properties of a fly ash geopolymer: Synergistic application of X-ray synchrotron tomography, nanoindentation, and homogenization models

DOE PAGES

Das, Sumanta; Yang, Pu; Singh, Sudhanshu S.; ...

2015-09-02

Microstructural and micromechanical investigation of a fly ash-based geopolymer using: (i) synchrotron x-ray tomography (XRT) to determine the volume fraction and tortuosity of pores that are influential in fluid transport, (ii) mercury intrusion porosimetry (MIP) to capture the volume fraction of smaller pores, (iii) scanning electron microscopy (SEM) combined with multi-label thresholding to identify and characterize the solid phases in the microstructure, and (iv) nanoindentation to determine the component phase elastic properties using statistical deconvolution, is reported in this paper. The phase volume fractions and elastic properties are used in multi-step mean field homogenization (Mori- Tanaka and double inclusion) modelsmore » to determine the homogenized macroscale elastic modulus of the composite. The homogenized elastic moduli are in good agreement with the flexural elastic modulus determined on macroscale paste beams. As a result, the combined use of microstructural and micromechanical characterization tools at multiple scales provides valuable information towards the material design of fly ash geopolymers.« less

Multi-modal porous microstructure for high temperature fuel cell application

NASA Astrophysics Data System (ADS)

Wejrzanowski, T.; Haj Ibrahim, S.; Cwieka, K.; Loeffler, M.; Milewski, J.; Zschech, E.; Lee, C.-G.

2018-01-01

In this study, the effect of microstructure of porous nickel electrode on the performance of high temperature fuel cell is investigated and presented based on a molten carbonate fuel cell (MCFC) cathode. The cathode materials are fabricated from slurry consisting of nickel powder and polymeric binder/solvent mixture, using the tape casting method. The final pore structure is shaped through modifying the slurry composition - with or without the addition of porogen(s). The manufactured materials are extensively characterized by various techniques involving: micro-computed tomography (micro-XCT), scanning electron microscopy (SEM), mercury porosimetry, BET and Archimedes method. Tomographic images are also analyzed and quantified to reveal the evolution of pore space due to nickel in situ oxidation to NiO, and infiltration by the electrolyte. Single-cell performance tests are carried out under MCFC operation conditions to estimate the performance of the manufactured materials. It is found that the multi-modal microstructure of MCFC cathode results in a significant enhancement of the power density generated by the reference cell. To give greater insight into the understanding of the effect of microstructure on the properties of the cathode, a model based on 3D tomography image transformation is proposed.

Effect of sintering temperature on the electrolysis of TiO2

NASA Astrophysics Data System (ADS)

Li, Ze-quan; Ru, Li-yue; Bai, Cheng-guang; Zhang, Na; Wang, Hai-hua

2012-07-01

The effects of sintering temperature on the microstructure and the conductivity of TiO2 cathodes were studied by examining the phase composition, microstructure, and element contents of the sintered cathodes and the cathodic products using X-ray diffraction and scanning electronic microscopy-energy dispersive spectrometry. The oxygen vacancy, conductivity, average pore diameter, and specific surface area of the sintered cathodes were detected by X-ray photoelectron spectroscopy, four-point probe, and ASPA 2010. The results showed that TiO2 phase transformations occurred, and oxygen vacancies formed with the increase of sintering temperature. The cathodic conductivity improved, but the average pore diameter and the effective response area of the TiO2 cathode were reduced when the sintering temperature increased. These phenomena could weaken the contact between reaction ions and electrons and also had the same effect on the cathodes and the molten salt. Moreover, they were disadvantageous to ion migration, so a lower sintering temperature was favorable for the microstructure of electrolysis. Consequently, the cathodic conductivity may be improved, but the microstructure became compact with the increase of sintering temperature. The cathodic products at different temperatures indicated that the cathodic conductivity was more important for electrolysis.

Theory and experimental technique for nondestructive evaluation of ceramic composites

NASA Technical Reports Server (NTRS)

Generazio, Edward R.

1990-01-01

The important ultrasonic scattering mechanisms for SiC and Si3N4 ceramic composites were identified by examining the interaction of ultrasound with individual fibers, pores, and grains. The dominant scattering mechanisms were identified as asymmetric refractive scattering due to porosity gradients in the matrix material, and symmetric diffractive scattering at the fiber-to-matrix interface and at individual pores. The effect of the ultrasonic reflection coefficient and surface roughness in the ultrasonic evaluation was highlighted. A new nonintrusive ultrasonic evaluation technique, angular power spectrum scanning (APSS), was presented that is sensitive to microstructural variations in composites. Preliminary results indicate that APSS will yield information on the composite microstructure that is not available by any other nondestructive technique.

Effect of heat treatment on the characteristics of tool steel deposited by the directed energy deposition process

NASA Astrophysics Data System (ADS)

Park, Jun Seok; Lee, Min-Gyu; Cho, Yong-Jae; Sung, Ji Hyun; Jeong, Myeong-Sik; Lee, Sang-Kon; Choi, Yong-Jin; Kim, Da Hye

2016-01-01

The directed energy deposition process has been mainly applied to re-work and the restoration of damaged steel. Differences in material properties between the base and the newly deposited materials are unavoidable, which may affect the mechanical properties and durability of the part. We investigated the effect of heat treatment on the characteristics of tool steel deposited by the DED process. We prepared general tool steel materials of H13 and D2 that were deposited onto heat-treated substrates of H13 and D2, respectively, using a direct metal tooling process. The hardness and microstructure of the deposited steel before and after heat treatment were investigated. The hardness of the deposited H13 steel was higher than that of wrought H13 steel substrate, while that of the deposited D2 was lower than that of wrought D2. The evolution of the microstructures by deposition and heat treatment varied depending on the materials. In particular, the microstructure of the deposited D2 steel after heat treatment consisted of fine carbides in tempered martensite and it is expected that the deposited D2 steel will have isotropic properties and high hardness after heat treatment.

Membranous glomerulopathy with spherules: an uncommon variant with obscure pathogenesis.

PubMed

Kowalewska, Jolanta; Smith, Kelly D; Hudkins, Kelly L; Chang, Anthony; Fogo, Agnes B; Houghton, Donald; Leslie, Deena; Aitchison, John; Nicosia, Roberto F; Alpers, Charles E

2006-06-01

Occasional case reports of membranous glomerulopathy described unique subepithelial accumulations of an unusual type of immune deposit composed of spherular structures. The identity of such structures as nuclear pores has been suggested, but not established. We identified a cohort of patients (n = 14, including 1 patient with disease recurrence in an allograft) who presented with nephrotic syndrome and had renal biopsy specimens with light and immunofluorescence microscopic findings characteristic of membranous glomerulopathy. These patients were distinguished by ultrastructural studies that showed glomerular capillary wall accumulations of subepithelial immune deposits composed of uniform spherular structures, while lacking the typical granular electron-dense deposits seen in membranous glomerulopathy. The molecular identity of these spherular structures as nuclear pores was tested by using immunofluorescence microscopy and immunohistochemistry with mouse monoclonal antinuclear pore antibodies (Covance, Princeton, NJ) and anti-Nuclear Pore-O-Linked Glycoprotein (Affinity BioReagents Inc, Golden, CO) antibodies. Measurement of spherular structures by using high-magnification electron microscopy showed an average diameter of 84.5 nm, which correlated well with accepted diameters of nuclear pores (80 to 120 nm). Immunofluorescence microscopy and immunoperoxidase staining with both antibodies showed characteristic beaded staining of nuclear membranes of multiple cell types within normal control kidney, but no staining of immune-type deposits within glomerular basement membranes. These cases form a rare, but distinctive, morphological subclass of membranous glomerulopathy. The antigenic specificity of immune deposits in these cases remains elusive.

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.

Microstructure and permeability of the Whitby Mudstone (UK) as an analogue for the Posidonia shale (NL)

NASA Astrophysics Data System (ADS)

Houben, Maartje; Barnhoorn, Auke; Drury, Martyn; Peach, Colin; Spiers, Christopher

2015-04-01

In order to make gas productivity from a shale economically interesting we should find ways to better connect the in-situ pore network to the natural occurring and mechanical induced fractures in the rock. When trying to improve gas productivity a first aim is to understand gas storage and gas flow potential through the rock by investigating the microstructure and measure the matrix porosity and permeability of the unfractured shales. Using a combination of methods we have characterized the porosity and permeability of the Jet Dogger section of the Whitby Mudstone Formation (UK), which we use as an analogue for the Posidonia Shale (NL). The Posidonia shale is a possible unconventional source for gas in Northern Europe. A combination of Precision Ion Polishing (PIPS) and Scanning Electron Microscopy (SEM) has been used to investigate the microstructure and the pores. Microstructurally the circa 8 meter thick Jet section of the Whitby Mudstone Formation can be subdivided into a fossil rich (>15 %) top half with an organic matter content of 7-10% and a sub-mm laminated (alternating clay-rich, carbonate-rich, not necessarily fossils, layers) lower half were the organic matter content varies from 0.3-16%. In addition, any possible flow in the rock has to go through the fine-grained clay matrix (all grains < 2 μm) due to the fact that all larger grains are completely surround by this matrix. Visible PIPS-SEM porosity (pore diameter > 100 nm) is in the order of 0.5-2.5% and is not connected in 2D. Furthermore, overall more than 40% of the visible porosity is present within the clay matrix (sometimes even up to 80%). Porosity and pore size distributions for pores with smaller diameters (2 < diameter < 100 nm) were determined using Ar and N2 gas adsorption. The adsorption porosity was in the order of 1-5%, were we found 1-2.5% porosity for the top half of the section and 2-5% porosity for the bottom half. Ar gas permeability of the samples was measured on 1-inch diameter cores using Ar-gas-permeametry with a pressure step of 0.2 MPa. The permeability measured was in the order of 2•10-19 - 1•10-17 m2 at a confining pressure of 0.8 MPa. The top half of the section (less porous) showed a slightly lower permeability (2•10-19 -3•10-18 m2) than the lower half of the Jet Dogger section (1•10-18 - 1•10-17m2). The PIPS-SEM porosity is apparently unconnected on the scale used for imaging and any flow through these rocks has to go through the clay matrix. A connected network of nano-scale pores connected to the micro-scale (PIPS-SEM) pores should be present because of the fact that we measured a through flow of gas. Relationships between the permeability and Ar-porosity and permeability and microstructure were, however, not systematic.

Limits of ZnO Electrodeposition in Mesoporous Tin Doped Indium Oxide Films in View of Application in Dye-Sensitized Solar Cells

PubMed Central

Dunkel, Christian; von Graberg, Till; Smarsly, Bernd M.; Oekermann, Torsten; Wark, Michael

2014-01-01

Well-ordered 3D mesoporous indium tin oxide (ITO) films obtained by a templated sol-gel route are discussed as conductive porous current collectors. This paper explores the use of such films modified by electrochemical deposition of zinc oxide (ZnO) on the pore walls to improve the electron transport in dye-sensitized solar cells (DSSCs). Mesoporous ITO film were dip-coated with pore sizes of 20–25 nm and 40–45 nm employing novel poly(isobutylene)-b-poly(ethylene oxide) block copolymers as structure-directors. After electrochemical deposition of ZnO and sensitization with the indoline dye D149 the films were tested as photoanodes in DSSCs. Short ZnO deposition times led to strong back reaction of photogenerated electrons from non-covered ITO to the electrolyte. ITO films with larger pores enabled longer ZnO deposition times before pore blocking occurred, resulting in higher efficiencies, which could be further increased by using thicker ITO films consisting of five layers, but were still lower compared to nanoporous ZnO films electrodeposited on flat ITO. The major factors that currently limit the application are the still low thickness of the mesoporous ITO films, too small pore sizes and non-ideal geometries that do not allow obtaining full coverage of the ITO surface with ZnO before pore blocking occurs. PMID:28788618

Macromolecular shape and interactions in layer-by-layer assemblies within cylindrical nanopores.

PubMed

Lazzara, Thomas D; Lau, K H Aaron; Knoll, Wolfgang; Janshoff, Andreas; Steinem, Claudia

2012-01-01

Layer-by-layer (LbL) deposition of polyelectrolytes and proteins within the cylindrical nanopores of anodic aluminum oxide (AAO) membranes was studied by optical waveguide spectroscopy (OWS). AAO has aligned cylindrical, nonintersecting pores with a defined pore diameter d(0) and functions as a planar optical waveguide so as to monitor, in situ, the LbL process by OWS. The LbL deposition of globular proteins, i.e., avidin and biotinylated bovine serum albumin was compared with that of linear polyelectrolytes (linear-PEs), both species being of similar molecular weight. LbL deposition within the cylindrical AAO geometry for different pore diameters (d(0) = 25-80 nm) for the various macromolecular species, showed that the multilayer film growth was inhibited at different maximum numbers of LbL steps (n(max)). The value of n(max) was greatest for linear-PEs, while proteins had a lower value. The cylindrical pore geometry imposes a physical limit to LbL growth such that n(max) is strongly dependent on the overall internal structure of the LbL film. For all macromolecular species, deposition was inhibited in native AAO, having pores of d(0) = 25-30 nm. Both, OWS and scanning electron microscopy showed that LbL growth in larger AAO pores (d(0) > 25-30 nm) became inhibited when approaching a pore diameter of d(eff,n_max) = 25-35 nm, a similar size to that of native AAO pores, with d(0) = 25-30 nm. For a reasonable estimation of d(eff,n_max), the actual volume occupied by a macromolecular assembly must be taken into consideration. The results clearly show that electrostatic LbL allowed for compact macromolecular layers, whereas proteins formed loosely packed multilayers.

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.

Direct Numerical Simulations of Microstructure Effects During High-Rate Loading of Additively Manufactured Metals

NASA Astrophysics Data System (ADS)

Battaile, Corbett; Owen, Steven; Moore, Nathan

2017-06-01

The properties of most engineering materials depend on the characteristics of internal microstructures and defects. In additively manufactured (AM) metals, these can include polycrystalline grains, impurities, phases, and significant porosity that qualitatively differ from conventional engineering materials. The microscopic details of the interactions between these internal defects, and the propagation of applied loads through the body, act in concert to dictate macro-observable properties like strength and compressibility. In this work, we used Sandia's ALEGRA finite element software to simulate the high-strain-rate loading of AM metals from laser engineered net shaping (LENS) and thermal spraying. The microstructural details of the material were represented explicitly, such that internal features like second phases and pores are captured and meshed as individual entities in the computational domain. We will discuss the dependence of the high-strain-rate mechanical properties on microstructural characteristics such as the shapes, sizes, and volume fractions of second phases and pores. In addition, we will examine how the details of the microstructural representation affect the microscopic material response to dynamic loads, and the effects of using ``stair-step'' versus conformal interfaces smoothed via the SCULPT tool in Sandia's CUBIT software. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US DOE NNSA under contract DE-AC04-94AL85000.

Tomographic analysis of reactive flow induced pore structure changes in column experiments

NASA Astrophysics Data System (ADS)

Cai, Rong; Lindquist, W. Brent; Um, Wooyong; Jones, Keith W.

2009-09-01

We utilize synchrotron X-ray computed micro-tomography to capture and quantify snapshots in time of dissolution and secondary precipitation in the microstructure of Hanford sediments exposed to simulated caustic waste in flow-column experiments. The experiment is complicated somewhat as logistics dictated that the column spent significant amounts of time in a sealed state (acting as a batch reactor). Changes accompanying a net reduction in porosity of 4% were quantified including: (1) a 25% net decrease in pores resulting from a 38% loss in the number of pores <10-4mm in volume and a 13% increase in the number of pores of larger size; and (2) a 38% decrease in the number of throats. The loss of throats resulted in decreased coordination number for pores of all sizes and significant reduction in the number of pore pathways.

Formation of Foam-like Microstructural Carbon Material by Carbonization of Porous Coordination Polymers through a Ligand-Assisted Foaming Process.

PubMed

Kongpatpanich, Kanokwan; Horike, Satoshi; Fujiwara, Yu-Ichi; Ogiwara, Naoki; Nishihara, Hirotomo; Kitagawa, Susumu

2015-09-14

Porous carbon material with a foam-like microstructure has been synthesized by direct carbonization of porous coordination polymer (PCP). In situ generation of foaming agents by chemical reactions of ligands in PCP during carbonization provides a simple way to create lightweight carbon material with a foam-like microstructure. Among several substituents investigated, the nitro group has been shown to be the key to obtain the unique foam-like microstructure, which is due to the fast kinetics of gas evolution during carbonization. Foam-like microstructural carbon materials showed higher pore volume and specific capacitance compared to a microporous carbon. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Shock Wave Propagation in Cementitious Materials at Micro/Meso Scales

DTIC Science & Technology

2015-08-31

ABSTRACT 16. SECURITY CLASSIFICATION OF: Shock wave response of heterogeneous materials like cement and concrete is greatly influenced by the...constituents and their statistical distributions. The microstructure of cement is complex due to the presence of unhydrated water, nano /micro pores, and other...heterogeneous materials like cement and concrete is greatly influenced by the constituents and their statistical distributions. The microstructure of cement

Anomalous Annealing Response of Directed Energy Deposited Type 304L Austenitic Stainless Steel

NASA Astrophysics Data System (ADS)

Smith, Thale R.; Sugar, Joshua D.; Schoenung, Julie M.; San Marchi, Chris

2018-03-01

Directed energy deposited (DED) and forged austenitic stainless steels possess dissimilar microstructures but can exhibit similar mechanical properties. In this study, annealing was used to evolve the microstructure of both conventional wrought and DED type 304L austenitic stainless steels, and significant differences were observed. In particular, the density of geometrically necessary dislocations and hardness were used to probe the evolution of the microstructure and properties. Forged type 304L exhibited the expected decrease in measured dislocation density and hardness as a function of annealing temperature. The more complex microstructure-property relationship observed in the DED type 304L material is attributed to compositional heterogeneities in the solidification microstructure.

Fabrication and Properties of Plasma-Sprayed Al2O3/ZrO2 Composite Coatings

NASA Astrophysics Data System (ADS)

Dejang, N.; Limpichaipanit, A.; Watcharapasorn, A.; Wirojanupatump, S.; Niranatlumpong, P.; Jiansirisomboon, S.

2011-12-01

Al2O3 /xZrO2 (where x = 0, 3, 13, and 20 wt.%) composite coatings were deposited onto mild steel substrates by atmospheric plasma spraying of mixed α-Al2O3 and nano-sized monoclinic-ZrO2 powders. Microstructural investigation showed that the coatings comprised well-separated Al2O3 and ZrO2 lamellae, pores, and partially molten particles. The coating comprised mainly of metastable γ-Al2O3 and tetragonal-ZrO2 with trace of original α-Al2O3 and monoclinic-ZrO2 phases. The effect of ZrO2 addition on the properties of coatings were investigated in terms of microhardness, fracture toughness, and wear behavior. It was found that ZrO2 improved the fracture toughness, reduced friction coefficient, and wear rate of the coatings.

Plasma-Sprayed Fine-grained Zirconium Silicate and Its Dielectric Properties

NASA Astrophysics Data System (ADS)

Ctibor, P.; Pala, Z.; Nevrlá, B.; Neufuss, K.

2017-05-01

The article is focused on selected dielectric and electrical properties of ZrSiO4, which was plasma sprayed by a water-stabilized plasma system. A combination of two feeding distances and three spray distances was utilized for spraying and the structure and properties of samples evaluated. The coatings were tested in alternating electric field to determine capacity and loss factor with the frequency from 100 Hz to 100 kHz. Relative permittivity was calculated from the capacity. Volume resistivity and dielectric strength of ZrSiO4 were measured in a direct current regime. The aim was to test electrically this natural silicate material in the form of plasma-sprayed deposits. Microstructure was characterized by relatively large and non-globular pores. Crystallites were very small, about 10-20 nm. Dielectric losses were small, resistivity as well as strength relatively high. This silicate ceramic was recognized to be prospective for electrical engineering.

High-temperature frictional wear behavior of MCrAlY-based coatings deposited by atmosphere plasma spraying

NASA Astrophysics Data System (ADS)

Tao, Chong; Wang, Lei; Song, Xiu

2017-02-01

Al2O3-Cr2O3/NiCoCrAlYTa coatings were prepared via atmosphere plasma spraying (APS). The microstructure and phase composition of the coatings were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), laser confocal scanning microscopy (LSCM), and transmission electron microscopy (TEM). The dry frictional wear behavior of the coatings at 500°C in static air was investigated and compared with that of 0Cr25Ni20 steel. The results show that the coatings comprise the slatted layers of oxide phases, unmelted particles, and pores. The hot abrasive resistance of the coatings is enhanced compared to that of 0Cr25Ni20, and their mass loss is approximately one-fifteenth that of 0Cr25Ni20 steel. The main wear failure mechanisms of the coatings are abrasive wear, fatigue wear, and adhesive wear.

Pulsed plasma polymerization for controlling shrinkage and surface composition of nanopores

NASA Astrophysics Data System (ADS)

Asghar, Waseem; Ilyas, Azhar; Deshmukh, Rajendra R.; Sumitsawan, Sulak; Timmons, Richard B.; Iqbal, Samir M.

2011-07-01

Solid-state nanopores have emerged as sensors for single molecules and these have been employed to examine the biophysical properties of an increasingly large variety of biomolecules. Herein we describe a novel and facile approach to precisely adjust the pore size, while simultaneously controlling the surface chemical composition of the solid-state nanopores. Specifically, nanopores fabricated using standard ion beam technology are shrunk to the requisite molecular dimensions via the deposition of highly conformal pulsed plasma generated thin polymeric films. The plasma treatment process provides accurate control of the pore size as the conformal film deposition depends linearly on the deposition time. Simultaneously, the pore and channel chemical compositions are controlled by appropriate selection of the gaseous monomer and plasma conditions employed in the deposition of the polymer films. The controlled pore shrinkage is characterized with high resolution AFM, and the film chemistry of the plasma generated polymers is analyzed with FTIR and XPS. The stability and practical utility of this new approach is demonstrated by successful single molecule sensing of double-stranded DNA. The process offers a viable new advance in the fabrication of tailored nanopores, in terms of both the pore size and surface composition, for usage in a wide range of emerging applications.

Texture Evolution During Laser Direct Metal Deposition of Ti-6Al-4V

DOE PAGES

Sridharan, Niyanth; Chaudhary, Anil; Nandwana, Peeyush; ...

2016-01-20

Titanium alloys are used in a wide variety of high performance applications and hence the processing of the titanium and the resulting microstructures after additive manufacturing has received significant attention. During additive manufacturing the processing route involves the transition from a liquid to solid state. The addition of successive layers results in a complex microstructure due to solid-state transformations. The current study focuses on understanding the phase transformations and relate it to the transformation texture in Ti-6Al-4V to identify conditions leading to a strong alpha transformation texture. The as deposited builds were characterized using optical microscopy and electron backscattered diffraction.more » The results showed columnar prior β grains with a martensitic structure after the deposition of a single layer. On subsequent depositions the martensitic microstructure decomposes to a colony and basketweave microstructure with a stronger transformation texture. The alpha texture with a colony and basketweave microstructure shows a stronger transformation texture as a result of variant selection. Thus by controlling the cooling rate of the build from the β transus it is possible to control the alpha transformation texture.« less

Texture Evolution During Laser Direct Metal Deposition of Ti-6Al-4V

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

Sridharan, Niyanth; Chaudhary, Anil; Nandwana, Peeyush

Titanium alloys are used in a wide variety of high performance applications and hence the processing of the titanium and the resulting microstructures after additive manufacturing has received significant attention. During additive manufacturing the processing route involves the transition from a liquid to solid state. The addition of successive layers results in a complex microstructure due to solid-state transformations. The current study focuses on understanding the phase transformations and relate it to the transformation texture in Ti-6Al-4V to identify conditions leading to a strong alpha transformation texture. The as deposited builds were characterized using optical microscopy and electron backscattered diffraction.more » The results showed columnar prior β grains with a martensitic structure after the deposition of a single layer. On subsequent depositions the martensitic microstructure decomposes to a colony and basketweave microstructure with a stronger transformation texture. The alpha texture with a colony and basketweave microstructure shows a stronger transformation texture as a result of variant selection. Thus by controlling the cooling rate of the build from the β transus it is possible to control the alpha transformation texture.« less

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.

Structure and corrosion properties of PVD Cr-N coatings

NASA Astrophysics Data System (ADS)

Liu, C.; Bi, Q.; Ziegele, H.; Leyland, A.; Matthews, A.

2002-05-01

PVD Cr-N coatings produced by physical vapor deposition (PVD) are increasingly used for mechanical and tribological applications in various industrial sectors. These coatings are particularly attractive for their excellent corrosion resistance, which further enhances the lifetime and service quality of coated components. PVD Cr-N coated steels in an aqueous solution are usually corroded by galvanic attack via through-coating ``permeable'' defects (e.g., pores). Therefore, the corrosion performance of Cr-N coated steel is determined by a number of variables of the coating properties and corrosive environment. These variables include: (i) surface continuity and uniformity; (ii) through-coating porosity; (iii) film density and chemical stability; (iv) growth stresses; (v) interfacial and intermediate layers; (vi) coating thickness; (vii) coating composition; and (viii) substrate properties. In this article, PVD Cr-N coatings were prepared, by electron-beam PVD and sputter deposition, with different compositions, thicknesses, and surface roughnesses, by changing the N2 flow rate, applying multilayering techniques and changing the substrate finish prior to coating. The microstructure of such coatings is investigated by various analytical techniques such as glancing angle x-ray diffraction and scanning electron microscopy, which are also correlated with the corrosion performance of the coated steel. Both dc polarization and ac impedance spectroscopy were employed to investigate the corrosion resistance of Cr-N coated steel in a 0.5N NaCl solution. It has been found that the N2 flow rate during reactive deposition strongly determines the microstructure of Cr-N coatings (due to the changing nitrogen content in the film) and can thus affect the corrosion resistance of coated systems. The surface finish of the steel substrate also affects the uniformity and coverage of PVD coatings; grooves and inclusions on the original substrate can raise the susceptibility of coated systems to crevice corrosion. Increased coating thickness can also greatly reduce the incidence of through-coating porosity such that the improvement in corrosion performance of thicker Cr-N coatings is significant.

The influence of sulphate deposition on the seasonal variation of peat pore water methyl Hg in a boreal mire.

PubMed

Bergman, Inger; Bishop, Kevin; Tu, Qiang; Frech, Wolfgang; Åkerblom, Staffan; Nilsson, Mats

2012-01-01

In this paper we investigate the hypothesis that long-term sulphate (SO(4) (2-)) deposition has made peatlands a larger source of methyl mercury (MeHg) to remote boreal lakes. This was done on experimental plots at a boreal, low sedge mire where the effect of long-term addition of SO(4) (2-) on peat pore water MeHg concentrations was observed weekly throughout the snow-free portion of 1999. The additions of SO(4) (2-) started in 1995. The seasonal mean of the pore water MeHg concentrations on the plots with 17 kg ha(-1) yr(-1) of sulphur (S) addition (1.3±0.08 ng L(-1), SE; n = 44) was significantly (p<0.0001) higher than the mean MeHg concentration on the plots with 3 kg ha(-1) yr(-1) of ambient S deposition (0.6±0.02 ng L(-1), SE; n = 44). The temporal variation in pore water MeHg concentrations during the snow free season was larger in the S-addition plots, with an amplitude of >2 ng L(-1) compared to +/-0.5 ng L(-1) in the ambient S deposition plots. The concentrations of pore water MeHg in the S-addition plots were positively correlated (r(2) = 0.21; p = 0.001) to the groundwater level, with the lowest concentrations of MeHg during the period with the lowest groundwater levels. The pore water MeHg concentrations were not correlated to total Hg, DOC concentration or pH. The results from this study indicate that the persistently higher pore water concentrations of MeHg in the S-addition plots are caused by the long-term additions of SO(4) (2-) to the mire surface. Since these waters are an important source of runoff, the results support the hypothesis that SO(4) (2-) deposition has increased the contribution of peatlands to MeHg in downstream aquatic systems. This would mean that the increased deposition of SO(4) (2-) in acid rain has contributed to the modern increase in the MeHg burdens of remote lakes hydrologically connected to peatlands.

Atomic layer deposition as pore diameter adjustment tool for nanoporous aluminum oxide injection molding masks.

PubMed

Miikkulainen, Ville; Rasilainen, Tiina; Puukilainen, Esa; Suvanto, Mika; Pakkanen, Tapani A

2008-05-06

The wetting properties of polypropylene (PP) surfaces were modified by adjusting the dimensions of the surface nanostructure. The nanostructures were generated by injection molding with nanoporous anodized aluminum oxide (AAO) as the mold insert. Atomic layer deposition (ALD) of molybdenum nitride film was used to control the pore diameters of the AAO inserts. The original 50-nm pore diameter of AAO was adjusted by depositing films of thickness 5, 10, and 15 nm on AAO. Bis(tert-butylimido)-bis(dimethylamido)molybdenum and ammonia were used as precursors in deposition. The resulting pore diameters in the nitride-coated AAO inserts were 40, 30, and 20 nm, respectively. Injection molding of PP was conducted with the coated inserts, as well as with the non-coated insert. Besides the pore diameter, the injection mold temperature was varied with temperatures of 50, 70, and 90 degrees C tested. Water contact angles of PP casts were measured and compared with theoretical contact angles calculated from Wenzel and Cassie-Baxter theories. The highest contact angle, 140 degrees , was observed for PP molded with the AAO mold insert with 30-nm pore diameter. The Cassie-Baxter theory showed better fit than the Wenzel theory to the experimental values. With the optimal AAO mask, the nanofeatures in the molded PP pieces were 100 nm high. In explanation of this finding, it is suggested that some sticking and stretching of the nanofeatures occurs during the molding. Increase in the mold temperature increased the contact angle.

Characteristics of ZrC/Ni-UDD coatings for a tungsten carbide cutting tool

NASA Astrophysics Data System (ADS)

Chayeuski, V. V.; Zhylinski, V. V.; Rudak, P. V.; Rusalsky, D. P.; Višniakov, N.; Černašėjus, O.

2018-07-01

This work deals with the features of the structure of combined ZrC/Ni-ultradisperse diamonds (UDD) coating synthesized by electroplating and cathode arc evaporation physical vapor deposition (CAE-PVD) techniques on the tungsten carbide WC - 2 wt% Co on cutting inserts to improve tool life. The microstructure, phase composition, and micro-scratch test analysis of the ZrC/Ni-UDD coating were studied. The ZrC/Ni-UDD coating consists of separate phases of zirconium carbide ZrC, α-Ni, and Ni-UDD phase. The surface morphology of the coating shows a pattern with pits, pores, and particles. Separated nanodiamond particles are present in the pores of the combined coating. Therefore, the structure of the bottom layer of Ni-UDD affects the morphology of the surface of the ZrC/Ni-UDD coating. The obtained value of the critical loads on the scratch track of the coating in 26 N proves a sufficiently high value of the adhesion strength of the intermediate Ni-UDD-layer with hard alloy of WC-Co substrate. Due to their unique structure ZrC/Ni-UDD-coatings can be used to increase the durability period of a wood-cutting milling tool for cutting chipboard by CNC machines.

a Facile Synthesis of Fully Porous Tazo Composite and its Remarkable Gas Sensitive Performance

NASA Astrophysics Data System (ADS)

Liang, Dongdong; Liu, Shimin; Wang, Zhinuo; Guo, Yu; Jiang, Weiwei; Liu, Chaoqian; Ding, Wanyu; Wang, Hualin; Wang, Nan; Zhang, Zhihua

The composite of a nanocrystalline SnO2 thick film deposited on an Al-doped ZnO ceramic substrate was firstly proposed. This study also provided a simple, fast and cost effective method to prepare SnO2 thick film and Al-doped ZnO ceramic as well as the final composite. The crystal structure, morphology, composition, pore size distribution and gas sensitivity of the composite were investigated by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, Barrett-Joyner-Halenda analysis and gas sensitive measurement system. Results indicated that the composite was fully porous consisted of SnO2, ZnO and ZnAl2O4 crystal phases. The macrosized pores generated in the composite could enhance the gas infiltration into the sensing layers effectively. In this way, combining a high gas-transporting-capability and a nanocrystalline SnO2 thick film, the composite showed very impressive performance. The gas sensitivity of the composite was high enough for ethanol vapor with different concentrations, which was comparable to other kinds of reported SnO2 gas sensors, while showing two straight lines with a turning point at 1000ppm. Finally, the gas sensitive mechanism was proposed based on the microstructure and composition of the composite.

A semi-empirical model relating micro structure to acoustic properties of bimodal porous material

NASA Astrophysics Data System (ADS)

Mosanenzadeh, Shahrzad Ghaffari; Doutres, Olivier; Naguib, Hani E.; Park, Chul B.; Atalla, Noureddine

2015-01-01

Complex morphology of open cell porous media makes it difficult to link microstructural parameters and acoustic behavior of these materials. While morphology determines the overall sound absorption and noise damping effectiveness of a porous structure, little is known on the influence of microstructural configuration on the macroscopic properties. In the present research, a novel bimodal porous structure was designed and developed solely for modeling purposes. For the developed porous structure, it is possible to have direct control on morphological parameters and avoid complications raised by intricate pore geometries. A semi-empirical model is developed to relate microstructural parameters to macroscopic characteristics of porous material using precise characterization results based on the designed bimodal porous structures. This model specifically links macroscopic parameters including static airflow resistivity ( σ ) , thermal characteristic length ( Λ ' ) , viscous characteristic length ( Λ ) , and dynamic tortuosity ( α ∞ ) to microstructural factors such as cell wall thickness ( 2 t ) and reticulation rate ( R w ) . The developed model makes it possible to design the morphology of porous media to achieve optimum sound absorption performance based on the application in hand. This study makes the base for understanding the role of microstructural geometry and morphological factors on the overall macroscopic parameters of porous materials specifically for acoustic capabilities. The next step is to include other microstructural parameters as well to generalize the developed model. In the present paper, pore size was kept constant for eight categories of bimodal foams to study the effect of secondary porous structure on macroscopic properties and overall acoustic behavior of porous media.

Exopolymer alteration of physical properties of sea ice and implications for ice habitability and biogeochemistry in a warmer Arctic

PubMed Central

Krembs, Christopher; Eicken, Hajo; Deming, Jody W.

2011-01-01

The physical properties of Arctic sea ice determine its habitability. Whether ice-dwelling organisms can change those properties has rarely been addressed. Following discovery that sea ice contains an abundance of gelatinous extracellular polymeric substances (EPS), we examined the effects of algal EPS on the microstructure and salt retention of ice grown from saline solutions containing EPS from a culture of the sea-ice diatom, Melosira arctica. We also experimented with xanthan gum and with EPS from a culture of the cold-adapted bacterium Colwellia psychrerythraea strain 34H. Quantitative microscopic analyses of the artificial ice containing Melosira EPS revealed convoluted ice-pore morphologies of high fractal dimension, mimicking features found in EPS-rich coastal sea ice, whereas EPS-free (control) ice featured much simpler pore geometries. A heat-sensitive glycoprotein fraction of Melosira EPS accounted for complex pore morphologies. Although all tested forms of EPS increased bulk ice salinity (by 11–59%) above the controls, ice containing native Melosira EPS retained the most salt. EPS effects on ice and pore microstructure improve sea ice habitability, survivability, and potential for increased primary productivity, even as they may alter the persistence and biogeochemical imprint of sea ice on the surface ocean in a warming climate. PMID:21368216

Exopolymer alteration of physical properties of sea ice and implications for ice habitability and biogeochemistry in a warmer Arctic.

PubMed

Krembs, Christopher; Eicken, Hajo; Deming, Jody W

2011-03-01

The physical properties of Arctic sea ice determine its habitability. Whether ice-dwelling organisms can change those properties has rarely been addressed. Following discovery that sea ice contains an abundance of gelatinous extracellular polymeric substances (EPS), we examined the effects of algal EPS on the microstructure and salt retention of ice grown from saline solutions containing EPS from a culture of the sea-ice diatom, Melosira arctica. We also experimented with xanthan gum and with EPS from a culture of the cold-adapted bacterium Colwellia psychrerythraea strain 34H. Quantitative microscopic analyses of the artificial ice containing Melosira EPS revealed convoluted ice-pore morphologies of high fractal dimension, mimicking features found in EPS-rich coastal sea ice, whereas EPS-free (control) ice featured much simpler pore geometries. A heat-sensitive glycoprotein fraction of Melosira EPS accounted for complex pore morphologies. Although all tested forms of EPS increased bulk ice salinity (by 11-59%) above the controls, ice containing native Melosira EPS retained the most salt. EPS effects on ice and pore microstructure improve sea ice habitability, survivability, and potential for increased primary productivity, even as they may alter the persistence and biogeochemical imprint of sea ice on the surface ocean in a warming climate.

Membrane-on-a-chip: microstructured silicon/silicon-dioxide chips for high-throughput screening of membrane transport and viral membrane fusion.

PubMed

Kusters, Ilja; van Oijen, Antoine M; Driessen, Arnold J M

2014-04-22

Screening of transport processes across biological membranes is hindered by the challenge to establish fragile supported lipid bilayers and the difficulty to determine at which side of the membrane reactants reside. Here, we present a method for the generation of suspended lipid bilayers with physiological relevant lipid compositions on microstructured Si/SiO2 chips that allow for high-throughput screening of both membrane transport and viral membrane fusion. Simultaneous observation of hundreds of single-membrane channels yields statistical information revealing population heterogeneities of the pore assembly and conductance of the bacterial toxin α-hemolysin (αHL). The influence of lipid composition and ionic strength on αHL pore formation was investigated at the single-channel level, resolving features of the pore-assembly pathway. Pore formation is inhibited by a specific antibody, demonstrating the applicability of the platform for drug screening of bacterial toxins and cell-penetrating agents. Furthermore, fusion of H3N2 influenza viruses with suspended lipid bilayers can be observed directly using a specialized chip architecture. The presented micropore arrays are compatible with fluorescence readout from below using an air objective, thus allowing high-throughput screening of membrane transport in multiwell formats in analogy to plate readers.

Bioaccessible Porosity: A new approach to assess residual contamination after bioremediation of hydrophobic organic compounds in sub-surface microporous environments

NASA Astrophysics Data System (ADS)

Akbari, A.; Ghoshal, S.

2016-12-01

We define a new parameter, "bioaccessible porosity", the fraction of aggregate volume accessible to soil bacteria, towards a priori assessment of hydrocarbon bioremediation end points. Microbial uptake of poorly soluble hydrocarbons occurs through direct uptake or micellar solubilzation/emulsification associated with biosurfactant production, and requires close proximity of bacteria and hydrocarbon phase. In subsurface microporous environments, bioremediation rates are attenuated when residual hydrophobic contamination is entrapped in sterically restrictive environments which is not accessible to soil bacteria. This study presents new approaches for characterization of the microstructure of porous media and as well, the ability of indigenous hydrocarbon degraders to access to a range of pore sizes. Bacterial access to poorly soluble hydrocarbons in soil micro pores were simulated with bioreactors with membranes with different pore sizes containing the hydrocarbon degrading bacteria, Dietzia maris. D. maris is Gram-positive, and nonmotile that we isolated as the major hydrocarbon degrader from a fine-grained, weathered, hydrocarbon-contaminated site soil. Under nutritional stress, planktonic D. maris cells were aggregated and accessed 5 µm but not 3 µm and smaller pores. However, when hexadecane was available at the pore mouth, D. maris colonized the pore mouth, and accessed pores as small as 0.4 µm. This suggests bacterial accessibility to different pore sizes is regulated by nutritional conditions. A combination of X-ray micro-CT scanning, gas adsorption and mercury intrusion porosimetry was used to characterize the range of pore sizes of soil aggregates. In case of the studied contaminated soil, the bioaccessible porosity were determined as 25% , 27% and 29% (assuming 4, 1, 0.4 µm respectively as accessibility criteria), and about 2.7% of aggregate volume was attributed to 0.006-0.4 µm pores. The 2% aggregate volume at an assumed saturation of 10% could accommodate 1000 mg/ kg soil of oil. The remediation endpoint after extended biotreatment was at similar order of magnitude of 600 mg/kg. The approach introduced here could be used for qualitative assessment of attainable bioremediation endpoint in soils with different microstructure and hydrocarbon degrading bacterial community.

Porous Nb-Ti based alloy produced from plasma spheroidized powder

NASA Astrophysics Data System (ADS)

Li, Qijun; Zhang, Lin; Wei, Dongbin; Ren, Shubin; Qu, Xuanhui

Spherical Nb-Ti based alloy powder was prepared by the combination of plasma spheroidization and mechanical alloying. Phase constituents, microstructure and surface state of the powder, and pore characteristics of the resulting porous alloy were investigated. The results show that the undissolved W and V in the mechanically alloyed powder is fully alloyed after spheroidization, and single β phase is achieved. Particle size of the spheroidized powder is in the range of 20-110 μm. With the decrease of particle size, a transformation from typical dendrite solidification structure to fine cell microstructure occurs. The surface of the spheroidized powder is coated by a layer of oxides consisting mainly of TiO2 and Nb2O5. Probabilities of sinter-neck formation and particle coalescence increases with increasing sintering temperature. Porous skeleton with relatively homogeneous pore distribution and open pore channel is formed after vacuum sintering at 1700 °C, and the porosity is 32%. The sintering kinetic analysis indicates that grain boundary diffusion is the primary mass transport mechanism during sintering process.

The Effect of Boron on the Low Cycle Fatigue Behavior of Disk Alloy KM4

NASA Technical Reports Server (NTRS)

Gabb, Timothy; Gayda, John; Sweeney, Joseph

2000-01-01

The durability of powder metallurgy nickel base superalloys employed as compressor and turbine disks is often limited by low cycle fatigue (LCF) crack initiation and crack growth from highly stressed surface locations (corners, holes, etc.). Crack growth induced by dwells at high stresses during aerospace engine operation can be particularly severe. Supersolvus solution heat treatments can be used to produce coarse grain sizes approaching ASTM 6 for improved resistance to dwell fatigue crack growth. However, the coarse grain sizes reduce yield strength, which can lower LCF initiation life. These high temperature heat treatments also can encourage pores to form. In the advanced General Electric disk superalloy KM4, such pores can initiate fatigue cracks that limit LCF initiation life. Hot isostatic pressing (HIP) during the supersolvus solution heat treatment has been shown to improve LCF initiation life in KM4, as the HIP pressure minimizes formation of the pores. Reduction of boron levels in KM4 has also been shown to increase LCF initiation life after a conventional supersolvus heat treatment, again possibly due to effects on the formation tendencies of these pores. However, the effects of reduced boron levels on microstructure, pore characteristics, and LCF failure modes in KM4 still need to be fully quantified. The objective of this study was to determine the effect of boron level on the microstructure, porosity, LCF behavior, and failure modes of supersolvus heat treated KM4.

New ceramics incorporated with industrial by-products as pore formers for sorption of toxic chromium from aqueous media

NASA Astrophysics Data System (ADS)

Domopoulou, Artemi

2015-04-01

The incorporation of secondary resources including various industrial wastes as pore-forming agents into clayey raw material mixtures for the development of tailored porous ceramic microstructures is currently of increasing interest. In the present research, sintered ceramic compacts were developed incorporated with industrial solid by-products as pore formers, and then used as new sorbents for chromium removal from aqueous media. The microstructures obtained were characterized through X-ray diffraction (XRD) analysis as well as scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectrometry (EDX). Sorption potential of chromium from synthetic solutions on the porous ceramics was studied by static adsorption experiments as a function of the pore-former percentage in the ceramic matrix as well as the initial heavy metal (chromium) concentration, solution pH and temperature. Kinetic studies were conducted and adsorption isotherms of chromium were determined using the Langmuir equation. Preliminary experimental results concerning the adsorption characteristics of chromium on the ceramic materials produced appear encouraging for their possible beneficial use as new sorbents for the removal of toxic chromium from aqueous media. Keywords: sorbents, ceramics, industrial solid by-products, pore-former, chromium. Acknowledgements: This research has been co-financed by the European Union (European Social Fund - ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) - Research Funding Program ARCHIMEDES III: Investing in knowledge society through the European Social Fund.

New ceramics incorporated with industrial by-products as pore formers for sorption of toxic chromium from aqueous media

NASA Astrophysics Data System (ADS)

Domopoulou, Asimina; Spiliotis, Xenofon; Baklavaridis, Apostolos; Papapolymerou, George; Karayannis, Vayos

2015-04-01

The incorporation of secondary resources including various industrial wastes as pore-forming agents into clayey raw material mixtures for the development of tailored porous ceramic microstructures is currently of increasing interest. In the present research, sintered ceramic compacts were developed incorporated with industrial solid by-products as pore formers, and then used as new sorbents for chromium removal from aqueous media. The microstructures obtained were characterized through X-ray diffraction (XRD) analysis as well as scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectrometry (EDX). Sorption potential of chromium from synthetic solutions on the porous ceramics was studied by static adsorption experiments as a function of the pore-former percentage in the ceramic matrix as well as the initial heavy metal (chromium) concentration, solution pH and temperature. Kinetic studies were conducted and adsorption isotherms of chromium were determined using the Langmuir equation. Preliminary experimental results concerning the adsorption characteristics of chromium on the ceramic materials produced appear encouraging for their possible beneficial use as new sorbents for the removal of toxic chromium from aqueous media. Keywords: sorbents, ceramics, industrial solid by-products, pore former, chromium. Acknowledgements: This research has been co-financed by the European Union (European Social Fund - ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) - Research Funding Program ARCHIMEDES III: Investing in knowledge society through the European Social Fund.

Towards realistic flow modelling. Creation and evaluation of two-dimensional simulated porous media: An image analysis approach

NASA Astrophysics Data System (ADS)

Anguy, Yannick; Bernard, Dominique; Ehrlich, Robert

1996-05-01

This work is part of an attempt to quantify the relationship between the permeability tensor ( K) and the micro-structure of natural porous media. A brief account is first provided of popular theories used to relate the micro-structure to K. Reasons for the lack of predictive power and restricted generality of current models are discussed. An alternative is an empirically based implicit model wherein K is expressed as a consequence of a few “pore-types” arising from the dynamics of depositional processes. The analytical form of that implicit model arises from evidence of universal association between pore-type and throat size in sandstones and carbonates. An explicit model, relying on the local change of scale technique is then addressed. That explicit model allows, from knowledge of the three-dimensional micro-geometry to calculate K explicitly without having recourse to any constitutive assumptions. The predictive and general character of the explicit model is underlined. The relevance of the change of scale technique is recalled to be contingent on the availability of rock-like three-dimensional synthetic media. A random stationary ergodic process is developed, that allows us to generate three-dimensional synthetic media from a two-dimensional autocorrelation function r(λ x ,λ y ) and associated probability density function ∈ β measured on a single binary image. The focus of this work is to ensure the rock-like character of those synthetic media. This is done first through a direct approach: n two-dimensional synthetic media, derived from single set ( ∈ β , r(λ x ,λ y )) yield n permeability tensors K {/i-1,n i} (calculated by the local change of scale) of the same order. This is a necessary condition to ensure that r(λ x ,λ y ) and ∈ β carry all structural information relevant to K. The limits of this direct approach, in terms of required Central Process Unit time and Memory is underlined, raising the need for an alternative. This is done by comparing the pore-type content of a sandstone sample and n synthetic media derived from r(λ x ,λ y ) and ∈ β measured on that sandstone-sample. Achievement of a good match ensures that the synthetic media comprise the fundamental structural level of all natural sandstones, that is a domainal structure of well-packed clusters of grains bounded by loose-packed pores.

Low Cost Fabrication of Silicon Carbide Based Ceramics and Fiber Reinforced Composites

NASA Technical Reports Server (NTRS)

Singh, M.; Levine, S. R.

1995-01-01

A low cost processing technique called reaction forming for the fabrication of near-net and complex shaped components of silicon carbide based ceramics and composites is presented. This process consists of the production of a microporous carbon preform and subsequent infiltration with liquid silicon or silicon-refractory metal alloys. The microporous preforms are made by the pyrolysis of a polymerized resin mixture with very good control of pore volume and pore size thereby yielding materials with tailorable microstructure and composition. Mechanical properties (elastic modulus, flexural strength, and fracture toughness) of reaction-formed silicon carbide ceramics are presented. This processing approach is suitable for various kinds of reinforcements such as whiskers, particulates, fibers (tows, weaves, and filaments), and 3-D architectures. This approach has also been used to fabricate continuous silicon carbide fiber reinforced ceramic composites (CFCC's) with silicon carbide based matrices. Strong and tough composites with tailorable matrix microstructure and composition have been obtained. Microstructure and thermomechanical properties of a silicon carbide (SCS-6) fiber reinforced reaction-formed silicon carbide matrix composites are discussed.

Effect of casein to whey protein ratios on the protein interactions and coagulation properties of low-fat yogurt.

PubMed

Zhao, L L; Wang, X L; Tian, Q; Mao, X Y

2016-10-01

In this study, we investigated the effect of casein (CN) to whey protein (WP) ratios (4:1, 3:1, 2:1, and 1:1) on gelation properties and microstructure of low-fat yogurt made with reconstituted skim milk with or without addition of whey protein concentrate. The rheological properties (storage modulus, G'; yield stress; and yield strain) of the obtained low-fat yogurt were greatly enhanced, the fermentation period was shortened, and the microstructure became more compact with smaller pores as the CN:WP ratio decreased. When CN:WP was 2:1 or 1:1, the obtained yogurt coagulum showed higher G' and greater yield stress, with more compact crosslinking and smaller pores. In addition, the more of skim milk powder was replaced by whey protein concentrate, the more disulfide bonds were formed and the greater the occurrence of hydrophobic interactions during heat treatment, which can improve the rheological properties and microstructure of low-fat yogurt. Copyright © 2016 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

FAST TRACK COMMUNICATION: Poly(methyl methacrylate)-palladium clusters nanocomposite formation by supersonic cluster beam deposition: a method for microstructured metallization of polymer surfaces

NASA Astrophysics Data System (ADS)

Ravagnan, Luca; Divitini, Giorgio; Rebasti, Sara; Marelli, Mattia; Piseri, Paolo; Milani, Paolo

2009-04-01

Nanocomposite films were fabricated by supersonic cluster beam deposition (SCBD) of palladium clusters on poly(methyl methacrylate) (PMMA) surfaces. The evolution of the electrical conductance with cluster coverage and microscopy analysis show that Pd clusters are implanted in the polymer and form a continuous layer extending for several tens of nanometres beneath the polymer surface. This allows the deposition, using stencil masks, of cluster-assembled Pd microstructures on PMMA showing a remarkably high adhesion compared with metallic films obtained by thermal evaporation. These results suggest that SCBD is a promising tool for the fabrication of metallic microstructures on flexible polymeric substrates.

Sol-gel derived ceramic electrolyte films on porous substrates

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

Kueper, T.W.

1992-05-01

A process for the deposition of sol-gel derived thin films on porous substrates has been developed; such films should be useful for solid oxide fuel cells and related applications. Yttria-stabilized zirconia films have been formed from metal alkoxide starting solutions. Dense films have been deposited on metal substrates and ceramic substrates, both dense and porous, through dip-coating and spin-coating techniques, followed by a heat treatment in air. X-ray diffraction has been used to determine the crystalline phases formed and the extent of reactions with various substrates which may be encountered in gas/gas devices. Surface coatings have been successfully applied tomore » porous substrates through the control of substrate pore size and deposition parameters. Wetting of the substrate pores by the coating solution is discussed, and conditions are defined for which films can be deposited over the pores without filling the interiors of the pores. Shrinkage cracking was encountered in films thicker than a critical value, which depended on the sol-gel process parameters and on the substrate characteristics. Local discontinuities were also observed in films which were thinner than a critical value which depended on the substrate pore size. A theoretical discussion of cracking mechanisms is presented for both types of cracking, and the conditions necessary for successful thin formation are defined. The applicability of these film gas/gas devices is discussed.« less

Using Shock Waves to Improve the Acoustic Properties of Closed-Cell Foams

NASA Astrophysics Data System (ADS)

Brouillette, M.; Hébert, C.; Atalla, N.; Doutres, O.

Foam microstructure can be seen as a collection of interlinked struts forming a packing of cells interconnected to others through pores. Materials with a totality of pores closed by thin membranes are called closed-cell foams. The filtration and acoustic efficiency of closed-cell foams is poor compared to open-cell foams since it is very difficult for the fluid or the acoustic waves to penetrate inside the material.

Sphagnum can 'filter' N deposition, but effects on the plant and pore water depend on the N form.

PubMed

Chiwa, Masaaki; Sheppard, Lucy J; Leith, Ian D; Leeson, Sarah R; Tang, Y Sim; Cape, J Neil

2016-07-15

The ability of Sphagnum moss to efficiently intercept atmospheric nitrogen (N) has been assumed to be vulnerable to increased N deposition. However, the proposed critical load (20kgNha(-1)yr(-1)) to exceed the capacity of the Sphagnum N filter has not been confirmed. A long-term (11years) and realistic N manipulation on Whim bog was used to study the N filter function of Sphagnum (Sphagnum capillifolium) in response to increased wet N deposition. On this ombrotrophic peatland where ambient deposition was 8kgNha(-1)yr(-1), an additional 8, 24, and 56kgNha(-1)yr(-1) of either ammonium (NH4(+)) or nitrate (NO3(-)) has been applied for 11years. Nutrient status of Sphagnum and pore water quality from the Sphagnum layer were assessed. The N filter function of Sphagnum was still active up to 32kgNha(-1)yr(-1) even after 11years. N saturation of Sphagnum and subsequent increases in dissolved inorganic N (DIN) concentration in pore water occurred only for 56kgNha(-1)yr(-1) of NH4(+) addition. These results indicate that the Sphagnum N filter is more resilient to wet N deposition than previously inferred. However, functionality will be more compromised when NH4(+) dominates wet deposition for high inputs (56kgNha(-1)yr(-1)). The N filter function in response to NO3(-) uptake increased the concentration of dissolved organic N (DON) and associated organic anions in pore water. NH4(+) uptake increased the concentration of base cations and hydrogen ions in pore water though ion exchange. The resilience of the Sphagnum N filter can explain the reported small magnitude of species change in the Whim bog ecosystem exposed to wet N deposition. However, changes in the leaching substances, arising from the assimilation of NO3(-) and NH4(+), may lead to species change. Copyright © 2016 Elsevier B.V. All rights reserved.

Life and death of a single catalytic cracking particle

PubMed Central

Meirer, Florian; Kalirai, Sam; Morris, Darius; Soparawalla, Santosh; Liu, Yijin; Mesu, Gerbrand; Andrews, Joy C.; Weckhuysen, Bert M.

2015-01-01

Fluid catalytic cracking (FCC) particles account for 40 to 45% of worldwide gasoline production. The hierarchical complex particle pore structure allows access of long-chain feedstock molecules into active catalyst domains where they are cracked into smaller, more valuable hydrocarbon products (for example, gasoline). In this process, metal deposition and intrusion is a major cause for irreversible catalyst deactivation and shifts in product distribution. We used x-ray nanotomography of industrial FCC particles at differing degrees of deactivation to quantify changes in single-particle macroporosity and pore connectivity, correlated to iron and nickel deposition. Our study reveals that these metals are incorporated almost exclusively in near-surface regions, severely limiting macropore accessibility as metal concentrations increase. Because macropore channels are “highways” of the pore network, blocking them prevents feedstock molecules from reaching the catalytically active domains. Consequently, metal deposition reduces conversion with time on stream because the internal pore volume, although itself unobstructed, becomes largely inaccessible. PMID:26601160

Hydraulic and field water-chemistry characteristics of piedmont alluvial deposits in the Middle Tyger River near Lyman, Spartanburg County, South Carolina, 2005

USGS Publications Warehouse

Harrelson, Larry G.; Addison, Adrian D.

2006-01-01

This study explores the possibility of developing a bank-filtration process to improve water quality in which alluvial deposits serve as a natural sand filter to pretreat water to be used as a secondary drinking-water source in a small piedmont reservoir along the Middle Tyger River near Lyman in Spartanburg County, South Carolina. From January 2004 to September 2005, data from 10 auger borings, 2 sediment cores, 29 ground-penetrating radar transects, and 3 temporary observation wells, and field water-chemistry data were collected and analyzed. These data were collected and used to characterize the lithology, geometry, hydraulic properties, yield potential, and water-chemistry characteristics of the alluvial deposits in the channel and on the right bank of the reservoir. The assessment was undertaken to determine if an adequate amount of water could be withdrawn from the alluvial deposits to sustain a bank-filtration process and to characterize the water chemistry of the surface water and pore water. The heterogeneous alluvial and fill material at the study site--clay, silty clay, clayey sand, fine- to coarse-grained sand, and mica--on the right bank of the Middle Tyger River ranges in thickness from 0.6 to 7 meters, has a calculated horizontal hydraulic conductivity of 1 meter per day, and yields approximately 0.07 liter per second of water. The small calculated horizontal hydraulic conductivity and water yield for these deposits restrict the use of the right bank as a potential bank-filtration site. The coarse-grained alluvial sand deposit in the channel of the Middle Tyger River, however, may be used for a limited bank-filtration process. The discharge during pumping of the channel deposit yielded water at the rate of 1.9 liters per second. The coarse-grained channel deposit is approximately 49 meters wide and 3 meters thick near the dam. At approximately 183 meters upstream from the dam, the channel narrows to roughly 9 meters and the channel deposits thin to approximately 0.1 meter. Slug tests conducted in the channel deposits near the dam produced a calculated horizontal hydraulic conductivity of 60 meters per day. The limited thickness and aerial extent of the coarse-grained channel deposits coupled with large horizontal hydraulic conductivity likely would allow rapid transmission of water and may degrade the effectiveness of some water-chemistry improvements typical of a bank-filtration process. Field water-chemistry data were collected for approximately 1 hour and 45 minutes at 10 to 15 minute intervals to compare the surface-water and pore-water quality in and beneath the channel of the Middle Tyger River. The waterchemistry data indicate that (1) the mean water temperature was higher in surface water (22.5 degrees Celsius) than in pore water (18.5 degrees Celsius), (2) the mean specific conductance was less in surface water (56.9 microsiemens per centimeter at 25 degrees Celsius) than in pore water (125.7 microsiemens per centimeter at 25 degrees Celsius), (3) alkalinity was lower in surface water (22.5 milligrams per liter) than in pore water (44.6 milligrams per liter), and (4) recorded pH values ranged between 6.2 and 6.3 in the surface water and pore water during the sampling period. The flow velocity was orders of magnitude slower in the pore water than in the surface water; therefore, the pore water interacts with the alluvial sediment for a longer period of time producing the variation in water-chemistry data between the two waters.

Studies on the reactive melt infiltration of silicon and silicon-molybdenum alloys in porous carbon

NASA Technical Reports Server (NTRS)

Singh, M.; Behrendt, D. R.

1992-01-01

Investigations on the reactive melt infiltration of silicon and silicon-1.7 and 3.2 at percent molybdenum alloys into porous carbon preforms have been carried out by process modeling, differential thermal analysis (DTA) and melt infiltration experiments. These results indicate that the initial pore volume fraction of the porous carbon preform is a critical parameter in determining the final composition of the raction-formed silicon carbide and other residual phases. The pore size of the carbon preform is very detrimental to the exotherm temperatures due to liquid silicon-carbon reactions encountered during the reactive melt infiltration process. A possible mechanism for the liquid silicon-porous (glassy) carbon reaction has been proposed. The composition and microstructure of the reaction-formed silicon carbide has been discussed in terms of carbon preform microstructures, infiltration materials, and temperatures.

A design-centered approach in developing Al-Si-based light-weight alloys with enhanced fatigue life and strength

NASA Astrophysics Data System (ADS)

Fan, Jinghong; Hao, Su

2004-01-01

Material heterogeneities and discontinuities such as porosity, second phase particles, and other defects at meso/micro/nano scales, determine fatigue life, strength, and fracture behavior of aluminum castings. In order to achieve better performance of these alloys, a design-centered computer-aided renovative approach is proposed. Here, the term “design-centered” is used to distinguish the new approach from the traditional trial-and-error design approach by formulating a clear objective, offering a scientific foundation, and developing a computer-aided effective tool for the alloy development. A criterion for tailoring “child” microstructure, obtained by “parent” microstructure through statistical correlation, is proposed for the fatigue design at the initial stage. A dislocations pileup model has been developed. This dislocation model, combined with an optimization analysis, provides an analytical-based solution on a small scale for silicon particles and dendrite cells to enhance both fatigue performance and strength for pore-controlled castings. It can also be used to further tailor microstructures. In addition, a conceptual damage sensitivity map for fatigue life design is proposed. In this map there are critical pore sizes, above which fatigue life is controlled by pores; otherwise it is controlled by other mechanisms such as silicon particles and dendrite cells. In the latter case, the proposed criteria and the dislocation model are the foundations of a guideline in the design-centered approach to maximize both the fatigue life and strength of Al-Si-based light-weight alloy.

Polyelectrolyte layer-by-layer deposition in cylindrical nanopores.

PubMed

Lazzara, Thomas D; Lau, K H Aaron; Abou-Kandil, Ahmed I; Caminade, Anne-Marie; Majoral, Jean-Pierre; Knoll, Wolfgang

2010-07-27

Layer-by-layer (LbL) deposition of polyelectrolytes within nanopores in terms of the pore size and the ionic strength was experimentally studied. Anodic aluminum oxide (AAO) membranes, which have aligned, cylindrical, nonintersecting pores, were used as a model nanoporous system. Furthermore, the AAO membranes were also employed as planar optical waveguides to enable in situ monitoring of the LbL process within the nanopores by optical waveguide spectroscopy (OWS). Structurally well-defined N,N-disubstituted hydrazine phosphorus-containing dendrimers of the fourth generation, with peripherally charged groups and diameters of approximately 7 nm, were used as the model polyelectrolytes. The pore diameter of the AAO was varied between 30-116 nm and the ionic strength was varied over 3 orders of magnitude. The dependence of the deposited layer thickness on ionic strength within the nanopores is found to be significantly stronger than LbL deposition on a planar surface. Furthermore, deposition within the nanopores can become inhibited even if the pore diameter is much larger than the diameter of the G4-polyelectrolyte, or if the screening length is insignificant relative to the dendrimer diameter at high ionic strengths. Our results will aid in the template preparation of polyelectrolyte multilayer nanotubes, and our experimental approach may be useful for investigating theories regarding the partitioning of nano-objects within nanopores where electrostatic interactions are dominant. Furthermore, we show that the enhanced ionic strength dependence of polyelectrolyte transport within the nanopores can be used to selectively deposit a LbL multilayer atop a nanoporous substrate.

Materials Research for Advanced Inertial Instrumentation. Task 3. Rare Earth Magnetic Material Technology as Related to Gyro Torquers and Motors.

DTIC Science & Technology

1980-12-01

spray process ...... ............... .. 40 9 Etched microstructures of as-received alloys ................ 42 10 Microstructures of as...Figure 8. Schematic sketch of spray process . 40 4.5 Results and Discussion 4.5.1 Alloy Procurement The desired compositions of the deposits (after... deposited samples...................... 44 11 As- Sprayed x-ray patterns obtained on two deposits made with 34 wt % Sm and one with 30 wt % Sm powders

Evolution of microstructural disorder in annealed bismuth telluride nanowires

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

Erickson, Kristopher J.; Limmer, Steven J.; Yelton, W. Graham

Controlling the distribution of structural defects in nanostructures is important since such defects can strongly affect critical properties, including thermal and electronic transport. However, characterizing the defect arrangements in individual nanostructures is difficult because of the small length scales involved. Here, we investigate the evolution of microstructural disorder with annealing in electrochemically deposited Bi2Te3 nanowires, which are of interest for thermoelectrics. We combine Convergent Beam Electron Diffraction (CBED) and Scanning Transmission Electron Microscopy (STEM) to provide the necessary spatial and orientational resolution. We find that despite their large initial grain sizes and strong Formula crystallographic texturing, the as-deposited nanowires stillmore » exhibit significant intragranular orientational disorder. Annealing drives both grain growth and a significant reduction in the intragranular disorder. The results are discussed in the context of the existing understanding of the initial microstructure of electrodeposited materials and the understanding of annealing microstructures in both electrochemically deposited and bulk-deformed materials. Finally, this analysis highlights the importance of assessing both the grain size and intragranular disorder in understanding the microstructural evolution of individual nanostructures.« less

Evolution of microstructural disorder in annealed bismuth telluride nanowires

DOE PAGES

Erickson, Kristopher J.; Limmer, Steven J.; Yelton, W. Graham; ...

2017-03-01

Controlling the distribution of structural defects in nanostructures is important since such defects can strongly affect critical properties, including thermal and electronic transport. However, characterizing the defect arrangements in individual nanostructures is difficult because of the small length scales involved. Here, we investigate the evolution of microstructural disorder with annealing in electrochemically deposited Bi2Te3 nanowires, which are of interest for thermoelectrics. We combine Convergent Beam Electron Diffraction (CBED) and Scanning Transmission Electron Microscopy (STEM) to provide the necessary spatial and orientational resolution. We find that despite their large initial grain sizes and strong Formula crystallographic texturing, the as-deposited nanowires stillmore » exhibit significant intragranular orientational disorder. Annealing drives both grain growth and a significant reduction in the intragranular disorder. The results are discussed in the context of the existing understanding of the initial microstructure of electrodeposited materials and the understanding of annealing microstructures in both electrochemically deposited and bulk-deformed materials. Finally, this analysis highlights the importance of assessing both the grain size and intragranular disorder in understanding the microstructural evolution of individual nanostructures.« less

Methods for making deposited films with improved microstructures

DOEpatents

Patten, James W.; Moss, Ronald W.; McClanahan, Edwin D.

1982-01-01

Methods for improving microstructures of line-of-sight deposited films are described. Columnar growth defects ordinarily produced by geometrical shadowing during deposition of such films are eliminated without resorting to post-deposition thermal or mechanical treatments. The native, as-deposited coating qualities, including homogeneity, fine grain size, and high coating-to-substrate adherence, can thus be retained. The preferred method includes the steps of emitting material from a source toward a substrate to deposit a coating non-uniformly on the substrate surface, removing a portion of the coating uniformly over the surface, again depositing material onto the surface, but from a different direction, and repeating the foregoing steps. The quality of line-of-sight deposited films such as those produced by sputtering, progressively deteriorates as the angle of incidence between the flux and the surface becomes increasingly acute. Depositing non-uniformly, so that the coating becomes progressively thinner as quality deteriorates, followed by uniformly removing some of the coating, such as by resputtering, eliminates the poor quality portions, leaving only high quality portions of the coating. Subsequently sputtering from a different direction applies a high quality coating to other regions of the surface. Such steps can be performed either simultaneously or sequentially to apply coatings of a uniformly high quality, closed microstructure to three-dimensional or larger planar surfaces.

Deposited films with improved microstructures

DOEpatents

Patten, James W.; Moss, Ronald W.; McClanahan, Edwin D.

1984-01-01

Methods for improving microstructures of line-of-sight deposited films are described. Columnar growth defects ordinarily produced by geometrical shadowing during deposition of such films are eliminated without resorting to post-deposition thermal or mechanical treatments. The native, as-deposited coating qualities, including homogeneity, fine grain size, and high coating-to-substrate adherence, can thus be retained. The preferred method includes the steps of emitting material from a source toward a substrate to deposit a coating non-uniformly on the substrate surface, removing a portion of the coating uniformly over the surface, again depositing material onto the surface, but from a different direction, and repeating the foregoing steps. The quality of line-of-sight deposited films such as those produced by sputtering, progressively deteriorates as the angle of incidence between the flux and the surface becomes increasingly acute. Depositing non-uniformly, so that the coating becomes progressively thinner as quality deteriorates, followed by uniformly removing some of the coating, such as by resputtering, eliminates the poor quality portions, leaving only high quality portions of the coating. Subsequently sputtering from a different direction applies a high quality coating to other regions of the surface. Such steps can be performed either simultaneously or sequentially to apply coatings of a uniformly high quality, closed microstructure to three-dimensional or large planar surfaces.

Experimental determination of pore shapes using phase retrieval from q -space NMR diffraction

NASA Astrophysics Data System (ADS)

Demberg, Kerstin; Laun, Frederik Bernd; Bertleff, Marco; Bachert, Peter; Kuder, Tristan Anselm

2018-05-01

This paper presents an approach to solving the phase problem in nuclear magnetic resonance (NMR) diffusion pore imaging, a method that allows imaging the shape of arbitrary closed pores filled with an NMR-detectable medium for investigation of the microstructure of biological tissue and porous materials. Classical q -space imaging composed of two short diffusion-encoding gradient pulses yields, analogously to diffraction experiments, the modulus squared of the Fourier transform of the pore image which entails an inversion problem: An unambiguous reconstruction of the pore image requires both magnitude and phase. Here the phase information is recovered from the Fourier modulus by applying a phase retrieval algorithm. This allows omitting experimentally challenging phase measurements using specialized temporal gradient profiles. A combination of the hybrid input-output algorithm and the error reduction algorithm was used with dynamically adapting support (shrinkwrap extension). No a priori knowledge on the pore shape was fed to the algorithm except for a finite pore extent. The phase retrieval approach proved successful for simulated data with and without noise and was validated in phantom experiments with well-defined pores using hyperpolarized xenon gas.

Experimental determination of pore shapes using phase retrieval from q-space NMR diffraction.

PubMed

Demberg, Kerstin; Laun, Frederik Bernd; Bertleff, Marco; Bachert, Peter; Kuder, Tristan Anselm

2018-05-01

This paper presents an approach to solving the phase problem in nuclear magnetic resonance (NMR) diffusion pore imaging, a method that allows imaging the shape of arbitrary closed pores filled with an NMR-detectable medium for investigation of the microstructure of biological tissue and porous materials. Classical q-space imaging composed of two short diffusion-encoding gradient pulses yields, analogously to diffraction experiments, the modulus squared of the Fourier transform of the pore image which entails an inversion problem: An unambiguous reconstruction of the pore image requires both magnitude and phase. Here the phase information is recovered from the Fourier modulus by applying a phase retrieval algorithm. This allows omitting experimentally challenging phase measurements using specialized temporal gradient profiles. A combination of the hybrid input-output algorithm and the error reduction algorithm was used with dynamically adapting support (shrinkwrap extension). No a priori knowledge on the pore shape was fed to the algorithm except for a finite pore extent. The phase retrieval approach proved successful for simulated data with and without noise and was validated in phantom experiments with well-defined pores using hyperpolarized xenon gas.

Velocity-porosity relationships for slope apron and accreted sediments in the Nankai Trough Seismogenic Zone Experiment, Integrated Ocean Drilling Program Expedition 315 Site C0001

NASA Astrophysics Data System (ADS)

Hashimoto, Y.; Tobin, H. J.; Knuth, M.

2010-12-01

In this study, we focused on the porosity and compressional wave velocity of marine sediments to examine the physical properties of the slope apron and the accreted sediments. This approach allows us to identify characteristic variations between sediments being deposited onto the active prism and those deposited on the oceanic plate and then carried into the prism during subduction. For this purpose we conducted ultrasonic compressional wave velocity measurements on the obtained core samples with pore pressure control. Site C0001 in the Nankai Trough Seismogenic Zone Experiment transect of the Integrated Ocean Drilling Program is located in the hanging wall of the midslope megasplay thrust fault in the Nankai subduction zone offshore of the Kii peninsula (SW Japan), penetrating an unconformity at ˜200 m depth between slope apron sediments and the underlying accreted sediments. We used samples from Site C0001. Compressional wave velocity from laboratory measurements ranges from ˜1.6 to ˜2.0 km/s at hydrostatic pore pressure conditions estimated from sample depth. The compressional wave velocity-porosity relationship for the slope apron sediments shows a slope almost parallel to the slope for global empirical relationships. In contrast, the velocity-porosity relationship for the accreted sediments shows a slightly steeper slope than that of the slope apron sediments at 0.55 of porosity. This higher slope in the velocity-porosity relationship is found to be characteristic of the accreted sediments. Textural analysis was also conducted to examine the relationship between microstructural texture and acoustic properties. Images from micro-X-ray CT indicated a homogeneous and well-sorted distribution of small pores both in shallow and in deeper sections. Other mechanisms such as lithology, clay fraction, and abnormal fluid pressure were found to be insufficient to explain the higher velocity for accreted sediments. The higher slope in velocity-porosity relationship for accreted sediments can be explained by weak cementation, critical porosity or differences in loading history.

The Influence of Sulphate Deposition on the Seasonal Variation of Peat Pore Water Methyl Hg in a Boreal Mire

PubMed Central

Bergman, Inger; Bishop, Kevin; Tu, Qiang; Frech, Wolfgang; Åkerblom, Staffan; Nilsson, Mats

2012-01-01

In this paper we investigate the hypothesis that long-term sulphate (SO4 2−) deposition has made peatlands a larger source of methyl mercury (MeHg) to remote boreal lakes. This was done on experimental plots at a boreal, low sedge mire where the effect of long-term addition of SO4 2− on peat pore water MeHg concentrations was observed weekly throughout the snow-free portion of 1999. The additions of SO4 2− started in 1995. The seasonal mean of the pore water MeHg concentrations on the plots with 17 kg ha−1 yr−1 of sulphur (S) addition (1.3±0.08 ng L−1, SE; n = 44) was significantly (p<0.0001) higher than the mean MeHg concentration on the plots with 3 kg ha−1 yr−1 of ambient S deposition (0.6±0.02 ng L−1, SE; n = 44). The temporal variation in pore water MeHg concentrations during the snow free season was larger in the S-addition plots, with an amplitude of >2 ng L−1 compared to +/−0.5 ng L−1 in the ambient S deposition plots. The concentrations of pore water MeHg in the S-addition plots were positively correlated (r2 = 0.21; p = 0.001) to the groundwater level, with the lowest concentrations of MeHg during the period with the lowest groundwater levels. The pore water MeHg concentrations were not correlated to total Hg, DOC concentration or pH. The results from this study indicate that the persistently higher pore water concentrations of MeHg in the S-addition plots are caused by the long-term additions of SO4 2− to the mire surface. Since these waters are an important source of runoff, the results support the hypothesis that SO4 2− deposition has increased the contribution of peatlands to MeHg in downstream aquatic systems. This would mean that the increased deposition of SO4 2− in acid rain has contributed to the modern increase in the MeHg burdens of remote lakes hydrologically connected to peatlands. PMID:23029086

Effective removal of calcified deposits on microstructured titanium fixture surfaces of dental implants with erbium lasers.

PubMed

Takagi, Toru; Aoki, Akira; Ichinose, Shizuko; Taniguchi, Yoichi; Tachikawa, Noriko; Shinoki, Takeshi; Meinzer, Walter; Sculean, Anton; Izumi, Yuichi

2018-03-13

Recently, the occurrence of peri-implantitis has been increasing. However, a suitable method to debride the contaminated surface of titanium implants has not been established. The aim of this study was to investigate the morphological changes of the microstructured fixture surface after erbium laser irradiation, and to clarify the effects of the erbium lasers when used to remove calcified deposits from implant fixture surfaces. In experiment 1, sandblasted, large grit, acid etched surface implants were treated with Er:YAG laser or Er,Cr:YSGG laser at 30-60 mJ/pulse and 20 Hz with water spray. In experiments 2 and 3, the effects of erbium lasers used to remove calcified deposits (artificially prepared deposits on virgin implants and natural calculus on failed implants) were investigated and compared with mechanical debridement using either a titanium curette or cotton pellets. After the various debridement methods, all specimens were analyzed by stereomicroscopy (SM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Stereomicroscopy and SEM showed that erbium lasers with optimal irradiation parameters did not have an effect on titanium microstructures. Compared to mechanical debridement, erbium lasers were more capable of removing calcified deposits on the microstructured surface without surface alteration using a non-contact sweeping irradiation at 40 mJ/pulse (ED 14.2 J/cm 2 /pulse) and 20 Hz with water spray. These results indicate that Er:YAG and Er,Cr:YSGG lasers are more advantageous in removing calcified deposits on the microstructured surface of titanium implants without inducing damage, compared to mechanical therapy by cotton pellet or titanium curette. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

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

Peter, William H.; Nandwana, Peeyush; Kirka, Michael M.

In this project, Avure and ORNL evaluated the influence of hot isostatic pressing (HIP) and thermal cycling as standalone post processing techniques on the microstructure of electron beam powder bed deposited Ti-6Al-4V and Inconel 718 alloys. Electron beam powder bed deposition is an effective technology for fabricating complex net shape components that cannot be manufactured with conventional processes. However, material deposited by this technology results in columnar grain growth which is detrimental for many applications. For Ti-6Al-4V, it has been found that thermal cycling alone is not sufficient to breakdown the columnar microstructure that is typical of electron beam powdermore » bed technology. HIP, on the other hand, has the potential to be an effective technique to break down the columnar microstructure of Ti-6Al-4V into a more equiaxed and refined β grain structure, and provide a more homogeneous microstructure compared to the thermally cycled samples. Overall, the project showed that hot isostatic pressing reduced/eliminated porosity in both Ti-6Al-4V and Inconel 718 However, based on the unique thermal cycle and the application of pressure in the HIP vessel, Ti-6Al-4V e-beam deposited microstructures were modified from columnar grain growth to equiaxed microstructures; a significant outcome to this collaboration. Inconel 718, on the other hand, shows no change in the macrostructure as a result of the current HIP cycle based on the thermal history, and would require further investigation. Though the results of HIP cycle were very good at changing the microstructure, further development in optimizing the post heat treatments and HIP cycles is required to improve mechanical properties.« less

Selective hierarchical patterning of silicon nanostructures via soft nanostencil lithography

NASA Astrophysics Data System (ADS)

Du, Ke; Ding, Junjun; Wathuthanthri, Ishan; Choi, Chang-Hwan

2017-11-01

It is challenging to hierarchically pattern high-aspect-ratio nanostructures on microstructures using conventional lithographic techniques, where photoresist (PR) film is not able to uniformly cover on the microstructures as the aspect ratio increases. Such non-uniformity causes poor definition of nanopatterns over the microstructures. Nanostencil lithography can provide an alternative means to hierarchically construct nanostructures on microstructures via direct deposition or plasma etching through a free-standing nanoporous membrane. In this work, we demonstrate the multiscale hierarchical fabrication of high-aspect-ratio nanostructures on microstructures of silicon using a free-standing nanostencil, which is a nanoporous membrane consisting of metal (Cr), PR, and anti-reflective coating. The nanostencil membrane is used as a deposition mask to define Cr nanodot patterns on the predefined silicon microstructures. Then, deep reactive ion etching is used to hierarchically create nanostructures on the microstructures using the Cr nanodots as an etch mask. With simple modification of the main fabrication processes, high-aspect-ratio nanopillars are selectively defined only on top of the microstructures, on bottom, or on both top and bottom.

Selective hierarchical patterning of silicon nanostructures via soft nanostencil lithography.

PubMed

Du, Ke; Ding, Junjun; Wathuthanthri, Ishan; Choi, Chang-Hwan

2017-11-17

It is challenging to hierarchically pattern high-aspect-ratio nanostructures on microstructures using conventional lithographic techniques, where photoresist (PR) film is not able to uniformly cover on the microstructures as the aspect ratio increases. Such non-uniformity causes poor definition of nanopatterns over the microstructures. Nanostencil lithography can provide an alternative means to hierarchically construct nanostructures on microstructures via direct deposition or plasma etching through a free-standing nanoporous membrane. In this work, we demonstrate the multiscale hierarchical fabrication of high-aspect-ratio nanostructures on microstructures of silicon using a free-standing nanostencil, which is a nanoporous membrane consisting of metal (Cr), PR, and anti-reflective coating. The nanostencil membrane is used as a deposition mask to define Cr nanodot patterns on the predefined silicon microstructures. Then, deep reactive ion etching is used to hierarchically create nanostructures on the microstructures using the Cr nanodots as an etch mask. With simple modification of the main fabrication processes, high-aspect-ratio nanopillars are selectively defined only on top of the microstructures, on bottom, or on both top and bottom.

Research on laser direct metal deposition

NASA Astrophysics Data System (ADS)

Zhang, Yongzhong; Shi, Likai

2003-03-01

Laser direct deposition of metallic parts is a new manufacturing technology, which combines with computer-aided design, laser cladding and rapid prototyping. Fully dense metallic parts can be directly obtained through melting the coaxially fed powders with a high-power laser in a layer-by-layer manner. The process characteristics, system composition as well as some research and advancement on laser direct deposition are presented here. The microstructure and properties observation of laser direct formed 663 copper alloy, 316L stainless steel and Rene'95 nickel super alloy samples indicate that, the as-deposited microstructure is similar to rapidly solidified materials, with homogenous composition and free of defects. Under certain conditions, directionally solidified microstructure can be obtained. The as-formed mechanical properties are equal to or exceed those for casting and wrought annealed materials. At the same time, some sample parts with complicate shape are presented for technology demonstration. The formed parts show good surface quality and dimensional accuracy.

Effect of Laser Power on Metallurgical, Mechanical and Tribological Characteristics of Hardfaced Surfaces of Nickel-Based Alloy

NASA Astrophysics Data System (ADS)

Gnanasekaran, S.; Padmanaban, G.; Balasubramanian, V.

2017-12-01

In this present work, nickel based alloy was deposited on 316 LN austenitic stainless steel (ASS) by a laser hardfacing technique to investigate the influence of laser power on macrostructure, microstructure, microhardness, dilution and wear characteristics. The laser power varied from 1.1 to 1.9 kW. The phase constitution, microstructure and microhardness were examined by optical microscope, scanning electron microscopy, energy dispersion spectroscopy and Vickers microhardness tester. The wear characteristics of the hardfaced surfaces and substrate were evaluated at room temperature (RT) under dry sliding wear condition (pin-on-disc). The outcome demonstrates that as the laser power increases, dilution increases and hardness of the deposit decreases. This is because excess heat melts more volume of substrate material and increases the dilution; subsequently it decreases the hardness of the deposit. The microstructure of the deposit is characterized by Ni-rich carbide, boride and silicide.

Microstructure of ceramics fabricated by unidirectional solidification

NASA Technical Reports Server (NTRS)

Kokubo, T.

1984-01-01

The unidirectional solidification methods are zone melting, crystal pulling, Bridgemen, and slow cooling. In order to obtain excellent properties (such as transparency), pores, voids and cracks must be avoided, and elimination of such defects is described.

Initial Assessment of X-Ray Computer Tomography image analysis for material defect microstructure

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

Kane, Joshua James; Windes, William Enoch

2016-06-01

The original development work leading to this report was focused on the non destructive three-dimensional (3-D) characterization of nuclear graphite as a means to better understand the nature of the inherent pore structure. The pore structure of graphite and its evolution under various environmental factors such as irradiation, mechanical stress, and oxidation plays an important role in their observed properties and characteristics. If we are to transition from an empirical understanding of graphite behavior to a truly predictive mechanistic understanding the pore structure must be well characterized and understood. As the pore structure within nuclear graphite is highly interconnected andmore » truly 3-D in nature, 3-D characterization techniques are critical. While 3-D characterization has been an excellent tool for graphite pore characterization, it is applicable to a broad number of materials systems over many length scales. Given the wide range of applications and the highly quantitative nature of the tool, it is quite surprising to discover how few materials researchers understand and how valuable of a tool 3-D image processing and analysis can be. Ultimately, this report is intended to encourage broader use of 3 D image processing and analysis in materials science and engineering applications, more specifically nuclear-related materials applications, by providing interested readers with enough familiarity to explore its vast potential in identifying microstructure changes. To encourage this broader use, the report is divided into two main sections. Section 2 provides an overview of some of the key principals and concepts needed to extract a wide variety of quantitative metrics from a 3-D representation of a material microstructure. The discussion includes a brief overview of segmentation methods, connective components, morphological operations, distance transforms, and skeletonization. Section 3 focuses on the application of concepts from Section 2 to relevant materials at Idaho National Laboratory. In this section, image analysis examples featuring nuclear graphite will be discussed in detail. Additionally, example analyses from Transient Reactor Test Facility low-enriched uranium conversion, Advanced Gas Reactor like compacts, and tristructural isotopic particles are shown to give a broader perspective of the applicability to relevant materials of interest.« less

Osteal integration of porous implants from titanium nickelide.

PubMed

Kelmakov, V P; Itin, V I; Epifancev, A G; Lepakova, O K; Kitler, V D; Bulgakov, V N

2009-10-01

The microstructure of preparations from porous titanium nickelide was studied 4.5 months and 1.5 years after operations on the anterior compartments of the spine. Organic tissues of different morphology, compactness, and thickness occupied 100% of analyzed surface 1.5 years after implantation, while after 4.5 months the pores were filled by 60%. The content of calcium and phosphorus elements in surface pores after 1.5 years was close to their concentrations in human bones.

Study of the deposition features of the organic dye Rhodamine B on the porous surface of silicon with different pore sizes

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

Lenshin, A. S., E-mail: lenshinas@phys.vsu.ru; Seredin, P. V.; Kavetskaya, I. V.

2017-02-15

The deposition features of the organic dye Rhodamine B on the porous surface of silicon with average pore sizes of 50–100 and 100–250 nm are studied. Features of the composition and optical properties of the obtained systems are studied using infrared and photoluminescence spectroscopy. It is found that Rhodamine-B adsorption on the surface of por-Si with various porosities is preferentially physical. The optimal technological parameters of its deposition are determined.

Analysis of microstructures and macrotextures for different apple cultivars based on parenchyma morphology.

PubMed

Hou, Jumin; Sun, Yonghai; Chen, Fangyuan; Yu, Libo; Mao, Qian; Wang, Lu; Guo, Xiaolei; Liu, Chao

2016-04-01

Fuji, Golden Delicious, and Jonagold parenchyma were imaged by confocal laser scanning microscopy to be extracted morphology characteristics, which were used to analyze the relationship with macrotexture of apples tested by penetration and compression. Before analyzing the relationship, the significantly different morphology parameters were reduced in dimensions by principal component analysis and were proved to be availably used for distinguishing the different apple cultivars. For compression results, cell did not absolutely determine the hardness in different apple cultivars, and the pore should also be taken into consideration. With the same size in cell feret diameter, the bigger the pore feret diameter was, the softer the apple became. If no difference existed in pore feret diameter size, the cultivar became harder with a narrower distribution in cell feret diameter. The texture parameters were compared with the roundness parameters in the same or inverse changing trends to explore the relationship. High correlations were found between the texture parameters (energy required in whole penetration (Wt), fracture force (Fp), crispness) and pore solidity (R(2)  > 0.924, P < 0.001). Compactness of parenchyma played an important role in fruit texture. This research could provide the comprehension about relationship between microstructure and macrotexture of apple cultivars and morphological values for modeling apple parenchyma, contributing to numerical simulation for constitutive relation of fruit. © 2016 Wiley Periodicals, Inc.

Fabrication and electrochemical properties of carbon nanotube/polypyrrole composite film electrodes with controlled pore size

NASA Astrophysics Data System (ADS)

Kim, Ji-Young; Kim, Kwang Heon; Kim, Kwang Bum

Carbon nanotube (CNT)/polypyrrole (PPy) composites with controlled pore size in a three-dimensional entangled structure of a CNT film are prepared as electrode materials for a pseudocapacitor. A CNT film electrode containing nanosize silica between the CNTs is first fabricated using an electrostatic spray deposition of a mixed suspension of CNTs and nanosize silica on to a platinium-coated silicon wafer. Later, nanosize silica is removed leaving a three-dimensional entangled structure of a CNT film. Before removal of the silica from the CNT/silica film electrode, PPy is electrochemically deposited on to the CNTs to anchor them in their entangled structure. Control of the pore size of the final CNT/PPy composite film can be achieved by changing the amount of silica in the mixed suspension of CNTs and nanosize silica. Nanosize silica acts as a sacrificial filler to change the pore size of the entangled CNT film. Scanning electron microscopy of the electrochemically prepared PPy on the CNT film substrate shows that the PPy nucleated heterogeneously and deposited on the surface of the CNTs. The specific capacitance and rate capability of the CNT/PPy composite electrode with a heavy loading of PPy of around 80 wt.% can be improved when it is made to have a three-dimensional network of entangled CNTs with interconnected pores through pore size control.

Comparison of Effective Medium Schemes For Seismic Velocities in Cracked Anisotropic Rock

NASA Astrophysics Data System (ADS)

Morshed, S.; Chesnokov, E.

2017-12-01

Understanding of elastic properties of reservoir rock is necessary for meaningful interpretation and analysis of seismic measurements. The elastic properties of a rock are controlled by the microstructural properties such as mineralogical composition, pore and crack distribution, texture and pore connectivity. However, seismic scale is much larger than microstructure scale. Understanding of macroscopic properties at relevant seismic scale (e.g. borehole sonic data) comes from effective medium theory (EMT). However, most of the effective medium theories fail at high crack density as the interactions of strain fields of the cracks can't be ignored. We compare major EMT schemes from low to high crack density. While at low crack density all method gives similar results, at high crack density they differ significantly. Then, we focus on generalized singular approximation (GSA) and effective field (EF) method as they allow cracks beyond the limit of dilute concentrations. Additionally, we use grain contact (GC) method to examine the stiffness constants of the rock matrix. We prepare simple models of a multiphase media containing low to high concentrations of isolated pores. Randomly oriented spherical pores and horizontally oriented ellipsoidal (aspect ratio =0.1) pores have been considered. For isolated spherical pores, all the three methods show exactly same or similar results. However, inclusion interactions are different in different directions in case of horizontal ellipsoidal pores and individual stiffness constants differ greatly from one method to another at different crack density. Stiffness constants remain consistent in GSA method whereas some components become unusual in EF method at a higher crack density (>0.15). Finally, we applied GSA method to interpret ultrasonic velocities of core samples. Mineralogical composition from X-ray diffraction (XRD) data and lab measured porosity data have been utilized. Both compressional and shear wave velocities from GSA method show good fit with the lab measured velocities.

Validation of pore network simulations of ex-situ water distributions in a gas diffusion layer of proton exchange membrane fuel cells with X-ray tomographic images

NASA Astrophysics Data System (ADS)

Agaesse, Tristan; Lamibrac, Adrien; Büchi, Felix N.; Pauchet, Joel; Prat, Marc

2016-11-01

Understanding and modeling two-phase flows in the gas diffusion layer (GDL) of proton exchange membrane fuel cells are important in order to improve fuel cells performance. They are scientifically challenging because of the peculiarities of GDLs microstructures. In the present work, simulations on a pore network model are compared to X-ray tomographic images of water distributions during an ex-situ water invasion experiment. A method based on watershed segmentation was developed to extract a pore network from the 3D segmented image of the dry GDL. Pore network modeling and a full morphology model were then used to perform two-phase simulations and compared to the experimental data. The results show good agreement between experimental and simulated microscopic water distributions. Pore network extraction parameters were also benchmarked using the experimental data and results from full morphology simulations.

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.

Modeling for stress-strain curve of a porous NiTi under compressive loading

NASA Astrophysics Data System (ADS)

Zhao, Ying; Taya, Minoru

2005-05-01

Two models for predicting the stress-strain curve of porous NiTi under compressive loading are presented in this paper. Porous NiTi shape memory alloy is investigated as a composite composed of solid NiTi as matrix and pores as inclusions. Eshelby"s equivalent inclusion method and Mori-Tanaka"s mean-field theory are employed in both models. In the first model, the geometry of the pores is assumed as sphere. The composite is with close-cells. While in the second model, two geometries of the pores, sphere and ellipsoid, are investigated. The pores are interconnected to each other forming an open-cell microstructure. The two adjacent pores connected along equator ring are investigated as a unit. Two pores interact with each other as they are connected. The average eigenstrain of each unit is obtained by taking the average of each pore"s eigenstrain. The stress-strain curves of porous shape memory alloy with spherical pores and ellipsoidal pores are compared, it is found that the shape of the pores has a nonignorable influence on the mechanical property of the porous NiTi. Comparison of the stress-strain curves of the two models shows that introducing of the average eigenstrains in the second model makes the predictions more agreeable to the experimental results.

Impact of the De-Alloying Kinetics and Alloy Microstructure on the Final Morphology of De-Alloyed Meso-Porous Metal Films

PubMed Central

Lin, Bao; Kong, Lingxue; Hodgson, Peter D.; Dumée, Ludovic F.

2014-01-01

Nano-textured porous metal materials present unique surface properties due to their enhanced surface energy with potential applications in sensing, molecular separation and catalysis. In this paper, commercial alloy foils, including brass (Cu85Zn15 and Cu70Zn30) and white gold (Au50Ag50) foils have been chemically de-alloyed to form nano-porous thin films. The impact of the initial alloy micro-structure and number of phases, as well as chemical de-alloying (DA) parameters, including etchant concentration, time and solution temperature on the final nano-porous thin film morphology and properties were investigated by electron microscopy (EM). Furthermore, the penetration depth of the pores across the alloys were evaluated through the preparation of cross sections by focus ion beam (FIB) milling. It is demonstrated that ordered pores ranging between 100 nm and 600 nm in diameter and 2–5 μm in depth can be successfully formed for the range of materials tested. The microstructure of the foils were obtained by electron back-scattered diffraction (EBSD) and linked to development of pits across the material thickness and surface during DA. The role of selective etching of both noble and sacrificial metal phases of the alloy were discussed in light of the competitive surface etching across the range of microstructures and materials tested. PMID:28344253

Effect of different types of surfactants on the microstructure of methyltrimethoxysilane-derived silica aerogels: A combined experimental and computational approach.

PubMed

Vareda, João P; Maximiano, Pedro; Cunha, Luís P; Ferreira, André F; Simões, Pedro N; Durães, Luísa

2018-02-15

Surfactants interfere with sol-gel particle/pore growth, influencing the structure and properties of silica aerogels. Their ability to induce microscopic changes in the aerogel's structure may be useful to improve/control the thermal insulation performance of aerogels. The influence of different types of surfactants (anionic, cationic and non-ionic) on the microstructural arrangement and macroscopic properties of methyltrimethoxysilane (MTMS)-based aerogels was evaluated for the first time, using an experimental and computational comparative approach. Molecular dynamics simulations were performed based on two representative silica molecular structures derived from MTMS, while the experimentally-obtained silica aerogels were characterized in terms of chemical/structural/mechanical/thermal insulation properties. The use of both hexadecyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS) led to a decrease in bulk density, thermal conductivity and average pore size of the aerogels, with notorious increase of their flexibility. The observed changes were due to microstructural arrangements, as evidenced by scanning electron microscopy (SEM). However, the non-ionic surfactant, Pluronic F-127, did not have a positive impact on the desired properties. Globally, the simulation results support the experimental findings, suggesting differentiated microstructural changes induced by the use of cationic or anionic surfactants. The addition of CTAB and SDS generally resulted in smaller or larger silica aggregates, respectively. Copyright © 2017 Elsevier Inc. All rights reserved.

Hydroxyapatite scaffolds processed using a TBA-based freeze-gel casting/polymer sponge technique.

PubMed

Yang, Tae Young; Lee, Jung Min; Yoon, Seog Young; Park, Hong Chae

2010-05-01

A novel freeze-gel casting/polymer sponge technique has been introduced to fabricate porous hydroxyapatite scaffolds with controlled "designer" pore structures and improved compressive strength for bone tissue engineering applications. Tertiary-butyl alcohol (TBA) was used as a solvent in this work. The merits of each production process, freeze casting, gel casting, and polymer sponge route were characterized by the sintered microstructure and mechanical strength. A reticulated structure with large pore size of 180-360 microm, which formed on burn-out of polyurethane foam, consisted of the strut with highly interconnected, unidirectional, long pore channels (approximately 4.5 microm in dia.) by evaporation of frozen TBA produced in freeze casting together with the dense inner walls with a few, isolated fine pores (<2 microm) by gel casting. The sintered porosity and pore size generally behaved in an opposite manner to the solid loading, i.e., a high solid loading gave low porosity and small pore size, and a thickening of the strut cross section, thus leading to higher compressive strengths.

Pore size and LbL chitosan coating influence mesenchymal stem cell in vitro fibrosis and biomineralization in 3D porous poly(epsilon-caprolactone) scaffolds.

PubMed

Mehr, Nima Ghavidel; Li, Xian; Chen, Gaoping; Favis, Basil D; Hoemann, Caroline D

2015-07-01

Poly(epsilon-caprolactone) (PCL) is a hydrophobic bioplastic under development for bone tissue engineering applications. Limited information is available on the role of internal geometry and cell-surface attachment on osseous integration potential. We tested the hypothesis that human bone marrow mesenchymal stem cells (MSCs) deposit more mineral inside porous 3D PCL scaffolds with fully interconnected 84 or 141 µm pores, when the surfaces are coated with chitosan via Layer-by-Layer (LbL)-deposited polyelectrolytes. Freshly trypsinized MSCs were seeded on PCL 3D cylinders using a novel static cold seeding method in 2% serum to optimally populate all depths of the scaffold discs, followed by 10 days of culture in proliferation medium and 21 additional days in osteogenic medium. MSCs were observed by SEM and histology to spread faster and to proliferate more on chitosan-coated pore surfaces. Most pores, with or without chitosan, became filled by collagen networks sparsely populated with fibroblast-like cells. After 21 days of culture in osteogenic medium, sporadic matrix mineralization was detected histologically and by micro-CT in highly cellular surface layers that enveloped all scaffolds and in cell aggregates in 141 µm pores near the edges. LbL-chitosan promoted punctate mineral deposition on the surfaces of 84 µm pores (p < 0.05 vs. PCL-only) but not the 141 µm pores. This study revealed that LbL-chitosan coatings are sufficient to promote MSC attachment to PCL but only enhance mineral formation in 84 µm pores, suggesting a potential inhibitory role for MSC-derived fibroblasts in osteoblast terminal differentiation. © 2014 Wiley Periodicals, Inc.

Effect of Heat Treatment on Microstructure and Mechanical Properties of Inconel 625 Alloy Fabricated by Pulsed Plasma Arc Deposition

NASA Astrophysics Data System (ADS)

Xu, Fujia; Lv, Yaohui; Liu, Yuxin; Xu, Binshi; He, Peng

Pulsed plasma arc deposition (PPAD) was successfully used to fabricate the Ni-based superalloy Inconel 625 samples. The effects of three heat treatment technologies on microstructure and mechanical properties of the as-deposited material were investigated. It was found that the as-deposited structure exhibited homogenous cellular dendrite structure, which grew epitaxially along the deposition direction. Moreover, some intermetallic phases including Laves phase and MC carbides were precipitated in the interdendritic region as a result of Nb segregation. Compared with the as-deposited microstructure, the direct aged (DA) microstructure changed little except the precipitation of hardening phases γ' and γ" (Ni3Nb), which enhanced the hardness and tensile strength. But the plastic property was inferior due to the existence of brittle Laves phase. After solution and aging heat treatment (STA), a large amount of Laves particles in the interdendritic regions were dissolved, resulting in the reduction of Nb segregation and the precipitation of needle-like δ (Ni3Nb) in the interdendritic regions and grain boundaries. The hardness and tensile strength were improved without sacrificing the ductility. By homogenization and STA heat treatment (HSTA), Laves particles were dissolved into the matrix completely and resulted in recrystallized large grains with bands of annealing twins. The primary MC particles and remaining phase still appeared in the matrix and grain boundaries. Compared with the as-deposited sample, the mechanical properties decreased severely as a result of the grain growth coarsening. The failure modes of all the tensile specimens were analyzed with fractography.

In Situ Foaming of Porous (La 0.6 Sr 0.4 ) 0.98 (Co 0.2 Fe 0.8 ) O 3-δ (LSCF) Cathodes for Solid Oxide Fuel Cell Applications

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

Gandavarapu, Sodith; Sabolsky, Edward; Sabolsky, Katarzyna

2013-07-18

A binder system containing polyurethane precursors was used to in situ foam (direct foam) a (La{sub 0.6}Sr{sub 0.4}){sub 0.98} (Co{sub 0.2} Fe{sub 0.8}) O{sub 3-{ delta}} (LSCF) composition for solid oxide fuel cell (SOFC) cathode applications. The relation between in situ foaming parameters on the final microstructure and electrochemical properties was characterized by microscopy and electrochemical impedance spectroscopy (EIS), respectively. The optimal porous cathode architecture was formed with a 70 vol% solids loading within a polymer precursor composition with a volume ratio of 8:4:1 (isocyanate: PEG: surfactant) in a terpineol-based ink vehicle. The resultant microstructure displayed a broad pore sizemore » distribution with highly elongated pore structure.« less

Development of low-pH cementitious materials for HLRW repositories

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

Garcia Calvo, J.L., E-mail: jolgac@ietcc.csic.e; Hidalgo, A.; Alonso, C.

One of the most accepted engineering construction concepts of underground repositories for high radioactive waste considers the use of low-pH cementitious materials. This paper deals with the design of those based on Ordinary Portland Cements with high contents of silica fume and/or fly ashes that modify most of the concrete 'standard' properties, the pore fluid composition and the microstructure of the hydrated products. Their resistance to long-term groundwater aggression is also evaluated. The results show that the use of OPC cement binders with high silica content produces low-pH pore waters and the microstructure of these cement pastes is different frommore » the conventional OPC ones, generating C-S-H gels with lower CaO/SiO{sub 2} ratios that possibly bind alkali ions. Leaching tests show a good resistance of low-pH concretes against groundwater aggression although an altered front can be observed.« less

Mechanical instabilities in periodic porous elasto-plastic solids.

NASA Astrophysics Data System (ADS)

Singamaneni, Srikanth; Bertoldi, Katia; Chang, Sehoon; Jang, Ji-Hyun; Young, Seth; Thomas, Edwin; Boyce, Mary; Tsukruk, Vladimir

2009-03-01

We describe the transformation of the periodic microporous structures fabricated by interference lithography followed by their freezing below glass transition. Periodic porous microstructures subjected to internal compressive stresses can undergo sudden structural transformation at a critical strain. The pattern transformation of collapsed pores is caused by the stresses originated during the polymerization of acrylic acid (rubbery component) inside of cylindrical pores and the subsequent solvent evaporation in the organized microporous structure. The results of a non-linear numerical investigation confirm the critical role of the bifurcation of the periodic solid under compressive stresses. In striking contrast to the earlier observations of elastic instabilities in porous elastomeric solids, the elastic-plastic nature of the crosslinked periodic microstructure studied here provides for the ability to lock in the transformed pattern with complete relaxation of the internal stresses. By confining the polymerization of acrylic acid to localized porous areas complex microscopic periodic structures are obtained.

Characterising the structural properties of polymer separators for lithium-ion batteries in 3D using phase contrast X-ray microscopy

NASA Astrophysics Data System (ADS)

Finegan, Donal P.; Cooper, Samuel J.; Tjaden, Bernhard; Taiwo, Oluwadamilola O.; Gelb, Jeff; Hinds, Gareth; Brett, Dan J. L.; Shearing, Paul R.

2016-11-01

Separators are an integral component for optimising performance and safety of lithium-ion batteries; therefore, a clear understanding of how their microstructure affects cell performance and safety is crucial. Phase contrast X-ray microscopy is used here to capture the microstructures of commercial monolayer, tri-layer, and ceramic-coated lithium-ion battery polymer separators. Spatial variations in key structural parameters, including porosity, tortuosity factor and pore size distribution, are determined through the application of 3D quantification techniques and stereology. The architectures of individual layers in multi-layer membranes are characterised, revealing anisotropy in porosity, tortuosity factor and mean pore size of the three types of separator. Detailed structural properties of the individual layers of multi-layered membranes are then related with their expected effect on safety and rate capability of cells.

Microstructure and corrosion resistance of sputter-deposited titanium-chromium alloy coatings

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

Landolt, D.; Robyr, C.; Mettraux, P.

1998-10-01

Titanium, chromium, and titanium-chromium alloy coatings were sputter-deposited to study their corrosion behaviors in relation to microstructure and composition. Silicon substrates were used to study the effect of alloying on intrinsic corrosion resistance of the coating materials, and brass substrates were used to study the effect of alloying on the penetrating porosity of the coatings. Corrosion behavior was characterized using linear sweep voltammetry. The crystal structure of the coatings was examined by x-ray diffraction (XRD) and the microstructure by scanning electron microscopy (SEM). Electrochemical impedance spectroscopy (EIS) was used to estimate the real surface area of the coatings. Results showedmore » alloying of titanium with chromium greatly influenced microstructure of the coatings. Alloying led to deposits of higher apparent density and, in some cases, to an x-ray amorphous structure. Alloy coatings showed significantly lower corrosion currents than the constituting metals. The effect was attributed to a smoother surface topography. When corrected of differences in real surface area, the intrinsic corrosion rate of the alloy coatings did not differ significantly from that of the constituting metals. Alloy coatings deposited on brass exhibited a lower porosity than titanium or chromium metal coatings produced under identical conditions.« less

Processing conditions and microstructural features of porous 316L stainless steel components by DMLS

NASA Astrophysics Data System (ADS)

Gu, Dongdong; Shen, Yifu

2008-12-01

Direct metal laser sintering (DMLS), due to its flexibility in materials and shapes, would be especially interesting to produce complex shaped porous metallic components. In the present work, processing conditions and microstructural characteristics of direct laser sintered porous 316L stainless steel components were studied. It was found that a partial melting mechanism of powders gave a high feasibility in obtaining porous sintered structures possessing porosities of ˜21-˜55%. Linear energy density (LED), which was defined by the ratio of laser power to scan speed, was used to tailor the laser sintering mechanism. A moderate LED of ˜3400-˜6000 J/m and a lower scan speed less than 0.06 m/s proved to be feasible. With the favorable sintering mechanism prevailed, lowering laser power or increasing scan speed, scan line spacing, and powder layer thickness generally led to a higher porosity. Metallurgical mechanisms of pore formation during DMLS were addressed. It showed that the presence of pores was through: (i) the formation of liquid bridges between partially melted particles during laser irradiation; and (ii) the growth of sintering necks during solidification, leaving residual pores between solidified metallic agglomerates.

Texture and microstructure evolution in single-phase Ti{sub x}Ta{sub 1-x}N alloys of rocksalt structure

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

Koutsokeras, L. E.; Department of Materials Science and Engineering, University of Ioannina, GR-45100 Ioannina; Abadias, G.

2011-08-15

The mechanisms controlling the structural and morphological features (texture and microstructure) of ternary transition metal nitride thin films of the Ti{sub x}Ta{sub 1-x}N system, grown by various physical vapor deposition techniques, are reported. Films deposited by pulsed laser deposition, dual cathode magnetron sputtering, and dual ion beam sputtering have been investigated by means of x-ray diffraction in various geometries and scanning electron microscopy. We studied the effects of composition, energetic, and kinetics in the evolution of the microstructure and texture of the films. We obtain films with single and mixed texture as well as films with columnar ''zone-T'' and globularmore » type morphology. The results have shown that the texture evolution of ternary transition metal nitrides as well as the microstructural features of such films can be well understood in the framework of the kinetic mechanisms proposed for their binary counterparts, thus giving these mechanisms a global application.« less

Distribution of long-lived radioactive iodine isotope (I-129) in pore waters from the gas hydrate fields on the continental margins: Indication for methane source of gas hydrate deposits

NASA Astrophysics Data System (ADS)

Tomaru, H.; Lu, Z.; Fehn, U.

2011-12-01

Because iodine has a strong association with organic matters in marine environments, pore waters in high methane potential region, in particular gas hydrate occurrences on the continental margins, are enriched significantly in iodine compared with seawater. Natural iodine system is composed of stable and radioactive species, I-129 (half-life of 15.7 Myr) has been used for estimating the age of source formations both for methane and iodine, because iodine can be liberated into pore water during the degradation of organic matter to methane in deep sediments. Here we present I-129 age data in pore waters collected from variety of gas hydrate occurrences on the continental margins. The I-129 ages in pore waters from these locations are significantly older than those of host sediments, indicating long-term transport and accumulation from deep/old sediments. The I-129 ages in the Japan Sea and Okhotsk Sea along the plate boundary between the North American and Amurian Plates correspond to the ages of initial spreading of these marginal seas, pointing to the massive deposition of organic matter for methane generation in deep sediments within limited periods. On the Pacific side of these areas, organic matter-rich back stop is responsible for methane in deep-seated gas hydrate deposits along the Nankai Trough. Deep coaly sequences responsible for deep conventional natural gas deposits are also responsible for overlying gas hydrate deposits off Shimokita Peninsula, NE Japan. Those in the Gulf of Mexico are correlative to the ages of sediments where the top of salt diapirs intrude. Marine sediments on the Pacific Plate subducting beneath the Australian Plate are likely responsible for the methane and iodine in the Hikurangi Trough, New Zealand. These ages reflect well the regional geological settings responsible for generation, transport, and accumulation of methane, I-129 is a key to understand the geological history of gas hydrate deposition.

Examining the effects of microstructure and loading on the shock initiation of HMX with mesoscale simulations

NASA Astrophysics Data System (ADS)

Springer, H. Keo; Tarver, Craig; Bastea, Sorin

2015-06-01

We perform reactive mesoscale simulations to study shock initiation in HMX over a range of pore morphologies and sizes, porosities, and loading conditions in order to improve our understanding of structure-performance relationships. These relationships are important because they guide the development of advanced macroscale models incorporating hot spot mechanisms and the optimization of novel energetic material microstructures. Mesoscale simulations are performed using the multiphysics hydrocode, ALE3D. Spherical, elliptical, polygonal, and crack-like pore geometries 0.1, 1, 10, and 100 microns in size and 2, 5, 10, and 14% porosity are explored. Loading conditions are realized with shock pressures of 6, 10, 20, 38, and 50 GPa. A Cheetah-based tabular model, including temperature-dependent heat capacity, is used for the unreacted and the product equation-of-state. Also, in-line Cheetah is used to probe chemical species evolution. The influence of microstructure and shock loading on shock-to-detonation-transition run distance, reaction rate and product gas species evolution are discussed. This work performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344. This work is funded by the Joint DoD-DOE Munitions Program.

Influence of the heat treatment condition of alloy AlCu4Mg1 on the microstructure and properties of anodic oxide layers

NASA Astrophysics Data System (ADS)

Morgenstern, R.; Dietrich, D.; Sieber, M.; Lampke, T.

2017-03-01

Due to their outstanding specific mechanical properties, high-strength, age-hardenable aluminum alloys offer a high potential for lightweight security-related applications. However, the use of copper-alloyed aluminum is limited because of their susceptibility to selective corrosion and their low wear resistance. These restrictions can be overcome and new applications can be opened up by the generation of protective anodic aluminum oxide layers. In contrast to the anodic oxidation of unalloyed aluminum, oxide layers produced on copper-rich alloys exhibit a significantly more complex pore structure. It is the aim of the investigation to identify the influence of microstructural parameters such as size and distribution of the strengthening precipitations on the coating microstructure. The aluminum alloy EN AW-2024 (AlCu4Mg1) in different heat treatment conditions serves as substrate material. The influence of the strengthening precipitations’ size and distribution on the development of the pore structure is investigated by the use of high-resolution scanning electron microscopy. Integral coating properties are characterized by non-destructive and light-microscopic thickness measurements and instrumented indentation tests.

Pore-structure and microstructural investigation of organomodified/Inorganic nano-montmorillonite cementitious nanocomposites

NASA Astrophysics Data System (ADS)

Papatzani, Styliani; Grammatikos, Sotirios; Adl-Zarrabi, Bijan; Paine, Kevin

2018-04-01

In the present paper, the effect of three different types of nano-montmorillonite dispersions (nMt) on the (i) microstructure as witnessed by Scanning Electron Microscopy, (ii) long term density measurements and (iii) pore structure as determined via Mercury Intrusion Porosimetry of Portland - limestone cement formulations have been compared, in an effort to determine the upper and lower bound of nMt addition in cementitious nanocomposites. The reference formulation, contained 60% PC and 40% LS by mass of binder aiming at the minimization of clinker and maximization of other constituents. Two aqueous organomodified NMt dispersions (one dispersed with non-ionic fatty alcohol and the other with anionic alkyl aryl sulphonate) and one aqueous inorganic NMt dispersion (dispersed with sodium tripolyphosphate) were added at 0.5, 1, 2, 4 and 5.5% by mass of solids as replacement of Portland cement. The water to solids ratio was kept constant at 0.3. The inorganic nMt showed the greatest potentials for microstructural enhancement. The way in which the level of the nMt platelet separation affected the pastes was discussed. The research reported was part of a much broader project supported by the EU.

Investigation of GDL compression effects on the performance of a PEM fuel cell cathode by lattice Boltzmann method

NASA Astrophysics Data System (ADS)

Molaeimanesh, G. R.; Nazemian, M.

2017-08-01

Proton exchange membrane (PEM) fuel cells with a great potential for application in vehicle propulsion systems will have a promising future. However, to overcome the exiting challenges against their wider commercialization further fundamental research is inevitable. The effects of gas diffusion layer (GDL) compression on the performance of a PEM fuel cell is not well-recognized; especially, via pore-scale simulation technique capturing the fibrous microstructure of the GDL. In the current investigation, a stochastic microstructure reconstruction method is proposed which can capture GDL microstructure changes by compression. Afterwards, lattice Boltzmann pore-scale simulation technique is adopted to simulate the reactive gas flow through 10 different cathode electrodes with dissimilar carbon paper GDLs produced from five different compression levels and two different carbon fiber diameters. The distributions of oxygen mole fraction, water vapor mole fraction and current density for the simulated cases are presented and analyzed. The results of simulations demonstrate that when the fiber diameter is 9 μm adding compression leads to lower average current density while when the fiber diameter is 7 μm the compression effect is not monotonic.

Tuning the pore composition by two simultaneous interfacial self-assembly processes: breath figures and coffee stain.

PubMed

de León, Alberto S; del Campo, Adolfo; Fernández-García, Marta; Rodríguez-Hernández, Juan; Muñoz-Bonilla, Alexandra

2014-06-03

In the current paper, we prepared microstructured porous films by the breath figures approach using polymer blends consisting of polystyrene as the major component and an amphiphilic additive, either a synthetic block copolymer {two different polystyrene-b-poly[poly(ethylene glycol) methyl ether methacrylate] copolymers} or a series of commercial surfactants. Tetrahydrofuran was employed as the solvent. Confocal micro-Raman spectroscopy demonstrated the preferential location of the amphiphilic additives in the cavities of the film as a consequence of the breath figures mechanism. However, the distribution of the copolymer within the cavities varies depending upon the structure and, more precisely, the surface properties of the additives, leading to three different situations. First of all, the copolymer with a larger polystyrene segment, insoluble in the condensed water droplets, is homogeneously distributed along the whole surface of the cavities. On the contrary, when the copolymer is soluble in water (shorter polystyrene segment), it migrates inside the droplet and a coffee-stain phenomenon takes place during the water droplet evaporation, conducting to a ring-like deposition on the top edge of the cavities. Finally, when a water-soluble surfactant with high surface activity is used, the surfactant is solubilized inside the water droplets, which provokes a decrease on the surface tension and the coffee-ring effect is modified. In this situation, the copolymer covers the bottom of the pore.

Thermal expansion coefficients of obliquely deposited MgF2 thin films and their intrinsic stress.

PubMed

Jaing, Cheng-Chung

2011-03-20

This study elucidates the effects of columnar angles and deposition angles on the thermal expansion coefficients and intrinsic stress behaviors of MgF2 films with columnar microstructures. The behaviors associated with temperature-dependent stresses in the MgF2 films are measured using a phase-shifting Twyman-Green interferometer with a heating stage and the application of a phase reduction algorithm. The thermal expansion coefficients of MgF2 films at various columnar angles were larger than those of glass substrates. The intrinsic stress in the MgF2 films with columnar microstructures was compressive, while the thermal stress was tensile. The thermal expansion coefficients of MgF2 films with columnar microstructures and their intrinsic stress evidently depended on the deposition angle and the columnar angle.

Direct metal writing: Controlling the rheology through microstructure

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

Chen, Wen; Thornley, Luke; Coe, Hannah G.

Most metal additive manufacturing approaches are based on powder-bed melting techniques such as laser selective melting or electron beam melting, which often yield uncontrolled microstructures with defects (e.g., pores or microcracks) and residual stresses. Here, we introduce a proof-of-concept prototype of a 3D metal freeform fabrication process by direct writing of metallic alloys in the semi-solid regime. This process is achieved through controlling the particular microstructure and the rheological behavior of semi-solid alloy slurries, which demonstrate a well suited viscosity and a shear thinning property to retain the shape upon printing. Furthermore, the ability to control the microstructure through thismore » method yields a flexible manufacturing route to fabricating 3D metal parts with full density and complex geometries.« less

Direct metal writing: Controlling the rheology through microstructure

DOE PAGES

Chen, Wen; Thornley, Luke; Coe, Hannah G.; ...

2017-02-27

Most metal additive manufacturing approaches are based on powder-bed melting techniques such as laser selective melting or electron beam melting, which often yield uncontrolled microstructures with defects (e.g., pores or microcracks) and residual stresses. Here, we introduce a proof-of-concept prototype of a 3D metal freeform fabrication process by direct writing of metallic alloys in the semi-solid regime. This process is achieved through controlling the particular microstructure and the rheological behavior of semi-solid alloy slurries, which demonstrate a well suited viscosity and a shear thinning property to retain the shape upon printing. Furthermore, the ability to control the microstructure through thismore » method yields a flexible manufacturing route to fabricating 3D metal parts with full density and complex geometries.« less

Early cements versus pore-water chemical composition in the subsurface of the sabkha of Abu Dhabi

NASA Astrophysics Data System (ADS)

Paul, Andreas; Yuan, Peng; Court, Wesley M.; Lokier, Stephen W.; Dutton, Kirsten E.; Van der Land, Cees; Lessa Andrade, Luiza; Sherry, Angela; Head, Ian M.

2017-04-01

The coastal sabkha of Abu Dhabi is a complex depositional system in an extremely arid climate. This depositional system is marked by the formation of primary carbonate and microbial deposits, and by the development of secondary evaporite and cement phases. A number of earlier studies have assessed the formation of these secondary phases, yet no research has established a relationship between lateral and vertical variations in the chemical composition of pore water and the nature of, in particular, the precipitating pore-filling cements, re-crystallisation features and dissolution. This study aims to establish an understanding of the environmental and sedimentary factors that control early post-depositional changes to sediment composition as a result of sediment - pore water interactions. A particular focus is to characterise changes in the chemistry of the pore water throughout a tidal cycle, aiming at understanding how the influx of 'fresh' lagoonal sea water influences the chemistry of the pore water, and which elements are replenished on a daily basis. The initial data presented here is based upon the relationship between the petrographic analysis of sediment samples and lateral and vertical variations in the chemistry of in-situ sampled pore water. The pore water is characterised with respect to pH, salinity, alkalinity, dissolved organic carbon, and the concentrations of a variety of common metallic and non-metallic elements, including (but not limited to) Ca, Fe, Mg, P, S and Sr. Initial results show that concentrations of Mg, P, and V, and the ratios Mg/Ca and Sr/Ca are highest at the seaward sampling locations. Contrastingly, individual concentrations for Ca, Sr, Fe, Si, and Cu are highest at the most landward locality. In particular the higher concentrations for Ca and Sr might indicate diagenetic processes and are thus enriched as a result of e.g. aragonite dissolution. A striking pattern in Mg concentrations show the highest values for this element within a buried microbial mat. This might point to an enrichment process within this organo-sedimentary layer, that might ultimately contribute to bacterially controlled and/or mediated dolomite formation.

Microstructure Evolution and Composition Control During the Processing of Thin-Gage Metallic Foil

NASA Astrophysics Data System (ADS)

Semiatin, S. L.; Gross, M. E.; Matson, D. W.; Bennett, W. D.; Bonham, C. C.; Ustinov, A. I.; Ballard, D. L.

2012-12-01

The manufacture of thin-gage superalloy and gamma-titanium-aluminide foil products via near-conventional thermomechanical processing and two different vapor-deposition methods was investigated. Thermomechanical processing was based on hot-pack rolling of plate and sheet. Foils of the superalloy LSHR and the near-gamma titanium aluminide Ti-45.5Al-2Cr-2Nb made by this approach exhibited excellent gage control and fine two-phase microstructures. The vapor-phase techniques used magnetron sputtering (MS) of a target of the desired product composition or electron-beam physical vapor deposition (EBPVD) of separate targets of the specific alloying elements. Thin deposits of LSHR and Ti-48Al-2Cr-2Nb made by MS showed uniform thickness/composition and an ultrafine microstructure. However, systematic deviations from the specific target composition were found. During subsequent heat treatment, the microstructure of the MS samples showed various degrees of grain growth and coarsening. Foils of Ti-43Al and Ti-51Al-1V fabricated by EBPVD were fully dense. The microstructures developed during EBPVD were interpreted in terms of measured phase equilibria and the dependence of evaporant flux on temperature.

Effect of Heat-Pressing Temperature and Holding Time on the Microstructure and Flexural Strength of Lithium Disilicate Glass-Ceramics

PubMed Central

Gao, Jing; Wang, Hui; Chen, Jihua

2015-01-01

The present study aimed to evaluate the influence of various heat-pressing procedures (different holding time and heat pressing temperature) on the microstructure and flexural strength of lithium disilicate glass ceramic. An experimental lithium silicate glass ceramic (ELDC) was prepared from the SiO2-Li2O-K2O-Al2O3-ZrO2-P2O5 system and heat-pressed following different procedures by varying temperature and holding time. The flexural strength was tested and microstructure was analyzed. The relationships between the microstructure, mechanical properties and heat-pressing procedures were discussed in-depth. Results verified the feasibility of the application of dental heat-pressing technique in processing the experimental lithium disilicate glass ceramic. Different heat-pressing procedures showed significant influence on microstructure and flexural strength. ELDC heat-pressed at 950℃ with holding time of 15 min achieved an almost pore-free microstructure and the highest flexural strength, which was suitable for dental restorative application. PMID:25985206

Pore network extraction from pore space images of various porous media systems

NASA Astrophysics Data System (ADS)

Yi, Zhixing; Lin, Mian; Jiang, Wenbin; Zhang, Zhaobin; Li, Haishan; Gao, Jian

2017-04-01

Pore network extraction, which is defined as the transformation from irregular pore space to a simplified network in the form of pores connected by throats, is significant to microstructure analysis and network modeling. A physically realistic pore network is not only a representation of the pore space in the sense of topology and morphology, but also a good tool for predicting transport properties accurately. We present a method to extract pore network by employing the centrally located medial axis to guide the construction of maximal-balls-like skeleton where the pores and throats are defined and parameterized. To validate our method, various rock samples including sand pack, sandstones, and carbonates were used to extract pore networks. The pore structures were compared quantitatively with the structures extracted by medial axis method or maximal ball method. The predicted absolute permeability and formation factor were verified against the theoretical solutions obtained by lattice Boltzmann method and finite volume method, respectively. The two-phase flow was simulated through the networks extracted from homogeneous sandstones, and the generated relative permeability curves were compared with the data obtained from experimental method and other numerical models. The results show that the accuracy of our network is higher than that of other networks for predicting transport properties, so the presented method is more reliable for extracting physically realistic pore network.

Microstructure, Fatigue Behavior, and Failure Mechanisms of Direct Laser-Deposited Inconel 718

NASA Astrophysics Data System (ADS)

Johnson, Alex S.; Shao, Shuai; Shamsaei, Nima; Thompson, Scott M.; Bian, Linkan

2017-03-01

Inconel 718 is considered to be a superalloy with a series of superior properties such as high strength, creep resistance, and corrosion resistance at room and elevated temperatures. Additive manufacturing (AM) is particularly appealing to Inconel 718 because of its near-net-shape production capability for circumventing the poor machinability of this superalloy. Nevertheless, AM parts are prone to porosity, which is detrimental to their fatigue resistance. Thus, further understanding of their fatigue behavior is required before their widespread use in load-bearing applications. In this work, the microstructure and fatigue properties of AM Inconel 718, produced in a Laser Engineered Net Shaping (LENS™) system and heat treated with a standard heat treatment schedule, are evaluated at room temperature. Fully reversed strain controlled fatigue tests were performed on cylindrical specimens with straight gage sections at strain amplitudes ranging from 0.001 mm/mm to 0.01 mm/mm. The fracture surfaces of fatigue specimens were inspected with a scanning electron microscope. The results indicate that the employed heat treatment allowed the large, elongated grains and dendritic structure of the as-built material to break down into smaller, equiaxed grains, with some dendritic structures remaining between layers. The AM specimens were found to possess lower fatigue resistance than wrought Inconel 718, and this is primarily attributed to the presence of brittle metal-carbide/oxide inclusions or pores near their surface.

Microstructural investigation of hardfacing weld deposit obtained from CrB paste

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

Kr. Ray, S.; Sarker, B.; Kr. Bhattacharya, S.

Hardfacing weld deposits are used as a protective layer on engineering components and tools subjected to different modes of wear. Cheaper iron-based alloys with chromium and carbon or relatively expensive alloys with some niobium or titanium have long been used as standard hardfacing materials. In recent years boron has substituted the costlier alloying elements and the newly developed Fe-B-C alloys have shown encouraging results. The microstructure of the welded hardfacing deposit is one of the most important factors that determine its performance. The amount, size, distribution and hardness of the individual constituents play important roles in imparting the desired properties.more » Recently Colomonoy sweat on paste containing fine CrB particles (of about 12 {mu}m average size) suspended in an organic binder has been marketed as the new generation hardfacing material. A thin coating of the paste is applied on the component surface, allowed to dry and welded. The welded deposit has been found to offer good wear resistance in many industrial applications. This paper reports the microstructural investigation of the welded deposit obtained from this paste.« less

Microstructure, Mechanical Properties, and Age-Hardening Behavior of an Al-Si-Fe-Mn-Cu-Mg Alloy Produced by Spray Deposition

NASA Astrophysics Data System (ADS)

Feng, Wang; Jishan, Zhang; Baiqing, Xiong; Yongan, Zhang

2011-02-01

It has been recognized generally that the spray-deposited process is an innovative technique of rapid solidification. In this paper, Al-20Si-5Fe-3Mn-3Cu-1Mg alloy was synthesized by the spray atomization and deposition technique. The microstructure and mechanical properties of the spray-deposited alloy were studied using x-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), and tensile tests. It is observed that the microstructure of spray-deposited Al-20Si-5Fe-3Mn-3Cu-1Mg alloy is composed of the α-Al,Si and the particle-like Al15(FeMn)3Si2 compounds. The aging process of the alloy was investigated by microhardness measurement, differential scanning calorimetry analysis, and TEM observations. The results indicate that the two types of precipitates, S-Al2CuMg and σ-Al5Cu6Mg2 precipitate from matrix and improve the tensile strength of the alloy efficiently at both the ambient and elevated temperatures (300 °C).

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.

Template-assisted electrostatic spray deposition as a new route to mesoporous, macroporous, and hierarchically porous oxide films.

PubMed

Sokolov, S; Paul, B; Ortel, E; Fischer, A; Kraehnert, R

2011-03-01

A novel film coating technique, template-assisted electrostatic spray deposition (TAESD), was developed for the synthesis of porous metal oxide films and tested on TiO(2). Organic templates are codeposited with the titania precursor by electrostatic spray deposition and then removed during calcination. Resultant films are highly porous with pores casted by uniformly sized templates, which introduced a new level of control over the pore morphology for the ESD method. Employing the amphiphilic block copolymer Pluronic P123, PMMA latex spheres, or a combination of the two, mesoporous, macroporous, and hierarchically porous TiO(2) films are obtained. Decoupled from other coating parameters, film thickness can be controlled by deposition time or depositing multiple layers while maintaining the coating's structure and integrity.

Highly Porous NiTi with Isotropic Pore Morphology Fabricated by Self-Propagated High-Temperature Synthesis

NASA Astrophysics Data System (ADS)

Hosseini, S. A.; Alizadeh, M.; Ghasemi, A.; Meshkot, M. A.

2013-02-01

Highly porous NiTi with isotropic pore morphology has been successfully produced by self-propagating high-temperature synthesis of elemental Ni/Ti metallic powders. The effects of adding urea and NaCl as temporary pore fillers were investigated on pore morphology, microstructure, chemical composition, and the phase transformation temperatures of specimens. These parameters were studied by optical microscopy, scanning electron microscopy, x-ray diffraction, and differential scanning calorimetry (DSC). Highly porous specimens were obtained with up to 83% total porosity and pore sizes between 300 and 500 μm in diameter. Results show pore characteristics were improved from anisotropic to isotropic and pore morphology was changed from channel-like to irregular by adding pore filler powders. Furthermore, the highly porous specimens produced when using urea as a space holder, were of more uniform composition in comparison to NaCl. DSC results showed that a two-step martensitic phase transformation takes place during the cooling cycles and the austenite finish temperature ( A f) is close to human body temperature. Compression test results reveal that the compressive strength of highly porous NiTi is about 155 MPa and recoverable strain about 6% in superelasticity regime.

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.

A Study on the Effect of Electrodeposition Parameters on the Morphology of Porous Nickel Electrodeposits

NASA Astrophysics Data System (ADS)

Sengupta, Srijan; Patra, Arghya; Jena, Sambedan; Das, Karabi; Das, Siddhartha

2018-03-01

In this study, the electrodeposition of nickel foam by dynamic hydrogen bubble-template method is optimized, and the effects of key deposition parameters (applied voltage and deposition time) and bath composition (concentration of Ni2+, pH of the bath, and roles of Cl- and SO4 2- ions) on pore size, distribution, and morphology and crystal structure are studied. Nickel deposit from 0.1 M NiCl2 bath concentration is able to produce the honeycomb-like structure with regular-sized holes. Honeycomb-like structure with cauliflower morphology is deposited at higher applied voltages of 7, 8, and 9 V; and a critical time (>3 minutes) is required for the development of the foamy structure. Compressive residual stresses are developed in the porous electrodeposits after 30 seconds of deposition time (-189.0 MPa), and the nature of the residual stress remains compressive upto 10 minutes of deposition time (-1098.6 MPa). Effect of pH is more pronounced in a chloride bath compared with a sulfate bath. The increasing nature of pore size in nickel electrodeposits plated from a chloride bath (varying from 21 to 48 μm), and the constant pore size (in the range of 22 to 24 μm) in deposits plated from a sulfate bath, can be ascribed to the striking difference in the magnitude of the corresponding current-time profiles.

Fused-filament 3D printing of drug products: Microstructure analysis and drug release characteristics of PVA-based caplets.

PubMed

Goyanes, Alvaro; Kobayashi, Masanori; Martínez-Pacheco, Ramón; Gaisford, Simon; Basit, Abdul W

2016-11-30

Fused deposition modeling (FDM) 3-Dimensional (3D) printing is becoming an increasingly important technology in the pharmaceutical sciences, since it allows the manufacture of personalized oral dosage forms by deposition of thin layers of material. Here, a filament extruder was used to obtain filaments of polyvinyl alcohol (PVA) containing paracetamol or caffeine appropriate for 3D printing. The filaments were used to manufacture caplets for oral administration by FDM 3D printing, with the aim of evaluating the effect of the internal structure (micropore volume), drug loading and composition on drug dissolution behaviour. Micropore volume of the caplets was primarily determined by the presence of large pores due to gaps in the printed layers/net while printing, and the porosity of the caplets was 10 fold higher than the porosity of the extruded filament. Dynamic dissolution drug release tests on the caplets in biorelevant bicarbonate media revealed distinctive release profiles, which were dependent on drug solubility and drug loading. Porosity of the caplets did not help to predict the different drug release profiles. This study confirms the potential of 3D printing to fabricate caplets and helps to elucidate which factors influence drug release from this type of new dosage form. Copyright © 2016 Elsevier B.V. All rights reserved.

TiO2 activation using acid-treated vermiculite as a support: Characteristics and photoreactivity

NASA Astrophysics Data System (ADS)

Jin, Ling; Dai, Bin

2012-02-01

Vermiculite was treated by sulfuric or nitric acid aqueous solutions with different concentration. These modified materials as the promising supports, were used to immobilize TiO2. TiO2 was prepared by the precursor, which was obtained by substituting partly isopropyl alcohol with Cl- in titanium chloride {[Ti(IV)(OR)nClm] (n = 2-3, m = 4 - n)}. The TiO2/vermiculite composites were characterized by X-ray diffraction, scanning electron microscopy, and the nitrogen absorption. Their photocatalytic activity was evaluated by removal of methylene blue (MB). The pure anatase type crystalline phase was well deposited on the supports. The concentrations of acid for treatment had a significant influence on pore sizes and surface area of vermiculite. The treatment process changed microstructure of vermiculite, modified its characteristics, and farther improved the catalytic activity and absorption capacity of TiO2/vermiculite composites. The treatment effect of nitric acid was superior to that of sulfuric acid.

Effects of Ti and TiC ceramic powder on laser-cladded Ti-6Al-4V in situ intermetallic composite

NASA Astrophysics Data System (ADS)

Ochonogor, O. F.; Meacock, C.; Abdulwahab, M.; Pityana, S.; Popoola, A. P. I.

2012-12-01

Titanium metal matrix composite (MMCs) was developed on titanium alloy (Ti-6Al-4V) substrate with the aim of improving the hardness and wear properties by laser cladding technique using a Rofin Sinar 4 kW Nd: YAG laser. Wear investigations were carried out with the aid of three body abrasion tester. The resultant microstructure show homogeneous distribution of TiC particles free from cracks and pores. Multiple track deposited systems with 50% overlap revealed micro-hardness increase from 357.3 HV0.1for the substrate reaching a peak as high as 922.2 HV0.1 for 60%Ti + 40%TiC and the least 665.3 HV0.1 for 80%Ti + 20%TiC MMCs. The wear resistance of the materials improved significantly, indicating a fifteen-fold wear rate reduction due to the proper distribution of ceramic particles thereby forming interstitial carbides as revealed by the X-ray diffraction spectrum.

Evolution of Mudstone Porosity, Permeability, and Microstructure in the Presence of Microorganisms During Vertical Compression

NASA Astrophysics Data System (ADS)

Mills, T.; Reece, J. S.

2016-12-01

Here we investigate the influence of microbial activity on the mechanical and transport properties of mudstones during early diagenesis. Despite the proven presence of microbial communities in marine sediments to depths of >500 meters below sea floor (mbsf), little is known about the interactions between microorganisms and sediments, especially during the early stages of burial and compression. To characterize and quantify the impact of microbial activity on mudstone properties, we compare natural mudstone samples treated with iron reducing bacteria Shewanella Oneidensis MR-1 and those without bacteria. Two bulk mudstones are experimentally prepared using sediments from Integrated Ocean Drilling Program Sites U1319 and U1324 in the Gulf of Mexico. The sediments originated from 4-13 mbsf in the Brazos-Trinity Basin and from three depth intervals (3-14 mbsf, 23-32 mbsf, and 493-502 mbsf) in the Ursa Basin. The sediments are dried and ground to clay- and silt-sized particles and homogenized into two natural mudstone powders. These powders are then used to make reproducible mudstone samples through a process called resedimentation, which replicates natural deposition and burial. Changes in microstructure, porosity, compressibility, and permeability are measured while the biotic (with bacteria) and abiotic (without bacteria) mudstones are being uniaxially compressed over several weeks to a maximum stress of 100 kPa. We anticipate that biofilm growth in pore spaces will decrease porosity, compressibility, and permeability, and the resultant microstructural changes created by microorganisms will be evident in high-resolution scanning electron microscope (SEM) images. Recognition of the micro-scale processes that take place during the early stages of mudstone diagenesis, especially those mediated by microbial activity, and their long-term effects on mudstone properties can lead to better identification and more effective production of unconventional hydrocarbon reservoirs.

Electrophoretic and Electrolytic Deposition of Ceramic Particles on Porous Substrates

DTIC Science & Technology

1990-08-30

hydrodynamic drag force exerted on the particle due to the electroosmotic flow of the solvent inside the pore, the electrophoretic force exerted on the...8217 - electrophoretic velocity UN - electroosmotic velocity b - pore mean radius D - diffusion coefficient k - local deposition rate Large Peclet numbers and small...experimentally as the charge is acquired spontaneously on mixing the particles with the solvent and it may be reversed upon addition ot ionic compounds. The

Understanding the solidification and microstructure evolution during CSC-MIG welding of Fe–Cr–B-based alloy

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

Sorour, A.A., E-mail: ahmad.sorour@mail.mcgill.ca; Chromik, R.R., E-mail: richard.chromik@mcgill.ca; Gauvin, R., E-mail: raynald.gauvin@mcgill.ca

2013-12-15

The present is a study of the solidification and microstructure of Fe–28.2%Cr–3.8%B–1.5%Si–1.5%Mn (wt.%) alloy deposited onto a 1020 plain carbon steel substrate using the controlled short-circuit metal inert gas welding process. The as-solidified alloy was a metal matrix composite with a hypereutectic microstructure. Thermodynamic calculation based on the Scheil–Gulliver model showed that a primary (Cr,Fe){sub 2}B phase formed first during solidification, followed by an eutectic formation of the (Cr,Fe){sub 2}B phase and a body-centered cubic Fe-based solid solution matrix, which contained Cr, Mn and Si. Microstructure analysis confirmed the formation of these phases and showed that the shape of themore » (Cr,Fe){sub 2}B phase was irregular plate. As the welding heat input increased, the weld dilution increased and thus the volume fraction of the (Cr,Fe){sub 2}B plates decreased while other microstructural characteristics were similar. - Highlights: • We deposit Fe–Cr–B-based alloy onto plain carbon steel using the CSC-MIG process. • We model the solidification behavior using thermodynamic calculation. • As deposited alloy consists of (Cr,Fe){sub 2}B plates embedded in Fe-based matrix. • We study the effect of the welding heat input on the microstructure.« less

The nanostructure and microstructure of SiC surface layers deposited by MWCVD and ECRCVD

NASA Astrophysics Data System (ADS)

Dul, K.; Jonas, S.; Handke, B.

2017-12-01

Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) have been used to investigate ex-situ the surface topography of SiC layers deposited on Si(100) by Microwave Chemical Vapour Deposition (MWCVD) -S1,S2 layers and Electron Cyclotron Resonance Chemical Vapor Deposition (ECRCVD) - layers S3,S4, using silane, methane, and hydrogen. The effects of sample temperature and gas flow on the nanostructure and microstructure have been investigated. The nanostructure was described by three-dimensional surface roughness analysis based on digital image processing, which gives a tool to quantify different aspects of surface features. A total of 13 different numerical parameters used to describe the surface topography were used. The scanning electron image (SEM) of the microstructure of layers S1, S2, and S4 was similar, however, layer S3 was completely different; appearing like grains. Nonetheless, it can be seen that no grain boundary structure is present in the AFM images.

Microstructural Effects and Properties of Non-line-of-Sight Coating Processing via Plasma Spray-Physical Vapor Deposition

NASA Astrophysics Data System (ADS)

Harder, Bryan J.; Zhu, Dongming; Schmitt, Michael P.; Wolfe, Douglas E.

2017-08-01

Plasma spray-physical vapor deposition (PS-PVD) is a unique processing method that bridges the gap between conventional thermal spray and vapor phase methods, and enables highly tailorable coatings composed of a variety of materials in thin, dense layers or columnar microstructures with modification of the processing conditions. The strengths of this processing technique are material and microstructural flexibility, deposition speed, and potential for non-line-of-sight (NLOS) capability by vaporization of the feedstock material. The NLOS capability of PS-PVD is investigated here using yttria-stabilized zirconia and gadolinium zirconate, which are materials of interest for turbine engine applications. PS-PVD coatings were applied to static cylindrical substrates approximately 6-19 mm in diameter to study the coating morphology as a function of angle. In addition, coatings were deposited on flat substrates under various impingement configurations. Impingement angle had significant effects on the deposition mode, and microscopy of coatings indicated that there was a shift in the deposition mode at approximately 90° from incidence on the cylindrical samples, which may indicate the onset of more turbulent flow and PVD-like growth. Coatings deposited at non-perpendicular angles exhibited a higher density and nearly a 2× improvement in erosion performance when compared to coatings deposited with the torch normal to the surface.

Effect of Microstructure on Spontaneous Polarization in Amorphous Solid Water (ASW) Films C. Bu[a], J. Shi[b] and R. A. Baragiola[a] [a]University of Virginia, Charlottesville, VA 22904[b]Syracuse University, Syracuse, NY 13244

NASA Astrophysics Data System (ADS)

Bu, Caixia; Shi, Jianming; Baragiola, Raul A.

2014-11-01

Introduction: Water ice is abundant on many planetary bodies within the outer solar system. We report on the spontaneous polarization and thermal relaxation of ASW films formed at 10 - 110 K and provide evidence for the essential role of porosity [1].Experiments: Experiments were performed in an ultra-high vacuum system. ASW films were deposited from a collimated vapor beam or from a diffuse background water vapor onto a liquid-He cooled, gold-coated quartz crystal microbalance (QCM). The porosity was calculated by combining the measurements obtained from the QCM and UV reflectance [2]. The surface potential was determined using a Kelvin probe.Results: We focused on observations pertaining to the porosity: 1) the surface potential experiences an abrupt change of -0.25 V relative to the substrate during deposition of the first ~5 monolayers and subsequently increases linearly with thickness; 2) the surface potential magnitude decreases with the incidence angle; 3) the surface potential decreases with temperature after a lag of ~4 K above the deposition temperature; it decreases more slowly in films with larger incidence angle; 4) for charged films with different pre-annealing temperatures, the ratios of surface potential to fluence remain roughly constant with temperature before discharged; 5) the surface potential decreases with time at a constant annealing temperature.Conclusions: These observations suggest that the polarization is governed by the relaxation of the micropore structure rather than changes in intrinsic dielectric behavior of the water network [3]. We propose that the observed surface potential results from a fraction of aligned water dipoles on the internal surface area of the pores. Depolarization occurs during the collapse of the pores, resulting in the decrease of the surface potential. References: [1] E. Mayer et al. (1986) Nature (London) 319, 298 (1986); [2] U. Raut et al. (2007) J. Chem. Phys. 127, 204713. [3] M. J. Iedema et al. (1998) J. Chem. Phys. B 102, 9203.

Additive Manufacturing of IN100 Superalloy Through Scanning Laser Epitaxy for Turbine Engine Hot-Section Component Repair: Process Development, Modeling, Microstructural Characterization, and Process Control

NASA Astrophysics Data System (ADS)

Acharya, Ranadip; Das, Suman

2015-09-01

This article describes additive manufacturing (AM) of IN100, a high gamma-prime nickel-based superalloy, through scanning laser epitaxy (SLE), aimed at the creation of thick deposits onto like-chemistry substrates for enabling repair of turbine engine hot-section components. SLE is a metal powder bed-based laser AM technology developed for nickel-base superalloys with equiaxed, directionally solidified, and single-crystal microstructural morphologies. Here, we combine process modeling, statistical design-of-experiments (DoE), and microstructural characterization to demonstrate fully metallurgically bonded, crack-free and dense deposits exceeding 1000 μm of SLE-processed IN100 powder onto IN100 cast substrates produced in a single pass. A combined thermal-fluid flow-solidification model of the SLE process compliments DoE-based process development. A customized quantitative metallography technique analyzes digital cross-sectional micrographs and extracts various microstructural parameters, enabling process model validation and process parameter optimization. Microindentation measurements show an increase in the hardness by 10 pct in the deposit region compared to the cast substrate due to microstructural refinement. The results illustrate one of the very few successes reported for the crack-free deposition of IN100, a notoriously "non-weldable" hot-section alloy, thus establishing the potential of SLE as an AM method suitable for hot-section component repair and for future new-make components in high gamma-prime containing crack-prone nickel-based superalloys.

Deposition of phosphate coatings on titanium within scaffold structure.

PubMed

Trybuś, Bartłomiej; Zieliński, Andrzej; Beutner, Rene; Seramak, Tomasz; Scharnweber, Dieter

2017-01-01

Existing knowledge about the appearance, thickness, and chemical composition of phosphate coatings on titanium inside porous structures is insufficient. Such knowledge is important for the design and fabrication of porous implants. Metallic scaffolds were fabricated by selective laser melting of 316L stainless steel powder. Phosphate coatings were deposited on Ti sensors placed either outside the scaffolds or in the holes in the scaffolds. The electrochemically-assisted cathodic deposition of phosphate coatings was performed under galvanostatic conditions in an electrolyte containing the calcium and phosphate ions. The phosphate deposits were microscopically investigated; this included the performance of mass weight measurements and chemical analyses of the content of Ca2+ and  24 PO ions after the dissolution of deposits. The thicknesses of the calcium phosphate coatings were about 140 and 200 nm for isolated titanium sensors and 170 and 300 nm for titanium sensors placed inside pores. Deposition of calcium phosphate occurred inside the pores up to 150 mm below the scaffold surface. The deposits were rich in Ca, with a Ca/P ratio ranging from 2 to 2.5. Calcium phosphate coatings can be successfully deposited on a Ti surface inside a model scaffold. An increase in cathodic current results in an increase in coating thickness. Any decrease in the cathodic current inside the porous structure is slight. The calcium phosphate inside the pores has a much higher Ca/P ratio than that of stoichiometric HAp, likely due to a gradual increase in Ca fraction with distance from the surface.

Growth Assisted by Glancing Angle Deposition: A New Technique to Fabricate Highly Porous Anisotropic Thin Films.

PubMed

Sanchez-Valencia, Juan Ramon; Longtin, Remi; Rossell, Marta D; Gröning, Pierangelo

2016-04-06

We report a new methodology based on glancing angle deposition (GLAD) of an organic molecule in combination with perpendicular growth of a second inorganic material. The resulting thin films retain a very well-defined tilted columnar microstructure characteristic of GLAD with the inorganic material embedded inside the columns. We refer to this new methodology as growth assisted by glancing angle deposition or GAGLAD, since the material of interest (here, the inorganic) grows in the form of tilted columns, though it is deposited under a nonglancing configuration. As a "proof of concept", we have used silver and zinc oxide as the perpendicularly deposited material since they usually form ill-defined columnar microstructures at room temperature by GLAD. By means of our GAGLAD methodology, the typical tilted columnar microstructure can be developed for materials that otherwise do not form ordered structures under conventional GLAD. This simple methodology broadens significantly the range of materials where control of the microstructure can be achieved by tuning the geometrical deposition parameters. The two examples presented here, Ag/Alq3 and ZnO/Alq3, have been deposited by physical vapor deposition (PVD) and plasma enhanced chemical vapor deposition (PECVD), respectively: two different vacuum techniques that illustrate the generality of the proposed technique. The two type of hybrid samples present very interesting properties that demonstrate the potentiality of GAGLAD. On one hand, the Ag/Alq3 samples present highly optical anisotropic properties when they are analyzed with linearly polarized light. To our knowledge, these Ag/Alq3 samples present the highest angular selectivity reported in the visible range. On the other hand, ZnO/Alq3 samples are used to develop highly porous ZnO thin films by using Alq3 as sacrificial material. In this way, antireflective ZnO samples with very low refractive index and extinction coefficient have been obtained.

Fast and non-destructive pore structure analysis using terahertz time-domain spectroscopy.

PubMed

Markl, Daniel; Bawuah, Prince; Ridgway, Cathy; van den Ban, Sander; Goodwin, Daniel J; Ketolainen, Jarkko; Gane, Patrick; Peiponen, Kai-Erik; Zeitler, J Axel

2018-02-15

Pharmaceutical tablets are typically manufactured by the uni-axial compaction of powder that is confined radially by a rigid die. The directional nature of the compaction process yields not only anisotropic mechanical properties (e.g. tensile strength) but also directional properties of the pore structure in the porous compact. This study derives a new quantitative parameter, S a , to describe the anisotropy in pore structure of pharmaceutical tablets based on terahertz time-domain spectroscopy measurements. The S a parameter analysis was applied to three different data sets including tablets with only one excipient (functionalised calcium carbonate), samples with one excipient (microcrystalline cellulose) and one drug (indomethacin), and a complex formulation (granulated product comprising several excipients and one drug). The overall porosity, tablet thickness, initial particle size distribution as well as the granule density were all found to affect the significant structural anisotropies that were observed in all investigated tablets. The S a parameter provides new insights into the microstructure of a tablet and its potential was particularly demonstrated for the analysis of formulations comprising several components. The results clearly indicate that material attributes, such as particle size and granule density, cause a change of the pore structure, which, therefore, directly impacts the liquid imbibition that is part of the disintegration process. We show, for the first time, how the granule density impacts the pore structure, which will also affect the performance of the tablet. It is thus of great importance to gain a better understanding of the relationship of the physical properties of material attributes (e.g. intragranular porosity, particle shape), the compaction process and the microstructure of the finished product. Copyright © 2017 Elsevier B.V. All rights reserved.

A Fractal Permeability Model for Shale Oil Reservoir

NASA Astrophysics Data System (ADS)

Zhang, Tao; Dong, Mingzhe; Li, Yajun

2018-01-01

In this work, a fractal analytical model is proposed to predict the permeability of shale reservoir. The proposed model explicitly relates the permeability to the micro-structural parameters (tortuosity, pore area fractal dimensions, porosity and slip velocity coefficient) of shale.

Influences of Au ion radiation on microstructure and surface-enhanced Raman scattering of nanoporous copper

NASA Astrophysics Data System (ADS)

Wang, Jing; Hu, Zhaoyi; Li, Rui; Liu, Xiongjun; Xu, Chuan; Wang, Hui; Wu, Yuan; Fu, Engang; Lu, Zhaoping

2018-05-01

In this work, effects of Au ion irradiation on microstructure and surface-enhanced Raman scattering (SERS) performance of nanoporous copper (NPC) were investigated. It is found that the microstructure of NPC could be tailored by the ion irradiation dose, i.e., the pore size decreases while the ligament size significantly coarsens with the increase of the irradiation dose. In addition, the SERS enhancement for rhodamine 6G molecules was improved by Au ions irradiation at an appropriate dose. The underlying mechanism of the increase of SERS enhancement resulted from ion irradiation was discussed. Our findings could provide a new way to tune nanoporosity of nanoporous metals and improve their SERS performance.

Dynamic Crushing Response of Closed-cell Aluminium Foam at Variable Strain Rates

NASA Astrophysics Data System (ADS)

Islam, M. A.; Kader, M. A.; Escobedo, J. P.; Hazell, P. J.; Appleby-Thomas, G. J.; Quadir, M. Z.

2015-06-01

The impact response of aluminium foams is essential for assessing their crashworthiness and energy absorption capacity for potential applications. The dynamic compactions of closed-cell aluminium foams (CYMAT) have been tested at variable strain rates. Microstructural characterization has also been carried out. The low strain rate impact test has been carried out using drop weight experiments while the high strain compaction test has been carried out via plate impact experiments. The post impacted samples have been examined using optical and electron microscopy to observe the microstructural changes during dynamic loading. This combination of dynamic deformation during impact and post impact microstructural analysis helped to evaluate the pore collapse mechanism and impact energy absorption characteristics.

Influences of Au ion radiation on microstructure and surface-enhanced Raman scattering of nanoporous copper.

PubMed

Wang, Jing; Hu, Zhaoyi; Li, Rui; Liu, Xiongjun; Xu, Chuan; Wang, Hui; Wu, Yuan; Fu, Engang; Lu, Zhaoping

2018-05-04

In this work, effects of Au ion irradiation on microstructure and surface-enhanced Raman scattering (SERS) performance of nanoporous copper (NPC) were investigated. It is found that the microstructure of NPC could be tailored by the ion irradiation dose, i.e., the pore size decreases while the ligament size significantly coarsens with the increase of the irradiation dose. In addition, the SERS enhancement for rhodamine 6G molecules was improved by Au ions irradiation at an appropriate dose. The underlying mechanism of the increase of SERS enhancement resulted from ion irradiation was discussed. Our findings could provide a new way to tune nanoporosity of nanoporous metals and improve their SERS performance.

X-ray Computed Tomography Imaging of the Microstructure of Sand Particles Subjected to High Pressure One-Dimensional Compression

PubMed Central

al Mahbub, Asheque; Haque, Asadul

2016-01-01

This paper presents the results of X-ray CT imaging of the microstructure of sand particles subjected to high pressure one-dimensional compression leading to particle crushing. A high resolution X-ray CT machine capable of in situ imaging was employed to capture images of the whole volume of a sand sample subjected to compressive stresses up to 79.3 MPa. Images of the whole sample obtained at different load stages were analysed using a commercial image processing software (Avizo) to reveal various microstructural properties, such as pore and particle volume distributions, spatial distribution of void ratios, relative breakage, and anisotropy of particles. PMID:28774011

X-ray Computed Tomography Imaging of the Microstructure of Sand Particles Subjected to High Pressure One-Dimensional Compression.

PubMed

Al Mahbub, Asheque; Haque, Asadul

2016-11-03

This paper presents the results of X-ray CT imaging of the microstructure of sand particles subjected to high pressure one-dimensional compression leading to particle crushing. A high resolution X-ray CT machine capable of in situ imaging was employed to capture images of the whole volume of a sand sample subjected to compressive stresses up to 79.3 MPa. Images of the whole sample obtained at different load stages were analysed using a commercial image processing software (Avizo) to reveal various microstructural properties, such as pore and particle volume distributions, spatial distribution of void ratios, relative breakage, and anisotropy of particles.

Long-term aging of Ag/a-C:H:O nanocomposite coatings in air and in aqueous environment

NASA Astrophysics Data System (ADS)

Drábik, Martin; Pešička, Josef; Biederman, Hynek; Hegemann, Dirk

2015-04-01

Nanocomposite coatings of silver particles embedded in a plasma polymer matrix possess interesting properties depending on their microstructure. The film microstructure is affected among others also by the RF power supplied during the deposition, as shown by transmission electron microscopy. The optical properties are characterized by UV-vis-NIR spectroscopy. An anomalous optical absorption peak from the Ag nanoparticles is observed and related to the microstructure of the nanocomposite films. Furthermore, a long-term aging of the coatings is studied in-depth in ambient air and in aqueous environments. It is shown that the studied films are not entirely stable. The deposition conditions and the microstructure of the films affect the processes taking place during their aging in both environments.

Mechanical characteristics of a tool steel layer deposited by using direct energy deposition

NASA Astrophysics Data System (ADS)

Baek, Gyeong Yun; Shin, Gwang Yong; Lee, Eun Mi; Shim, Do Sik; Lee, Ki Yong; Yoon, Hi-Seak; Kim, Myoung Ho

2017-07-01

This study focuses on the mechanical characteristics of layered tool steel deposited using direct energy deposition (DED) technology. In the DED technique, a laser beam bonds injected metal powder and a thin layer of substrate via melting. In this study, AISI D2 substrate was hardfaced with AISI H13 and M2 metal powders for mechanical testing. The mechanical and metallurgical characteristics of each specimen were investigated via microstructure observation and hardness, wear, and impact tests. The obtained characteristics were compared with those of heat-treated tool steel. The microstructures of the H13- and M2-deposited specimens show fine cellular-dendrite solidification structures due to melting and subsequent rapid cooling. Moreover, the cellular grains of the deposited M2 layer were smaller than those of the H13 structure. The hardness and wear resistance were most improved in the M2-deposited specimen, yet the H13-deposited specimen had higher fracture toughness than the M2-deposited specimen and heat-treated D2.

Deposition of Suspended Clay to Open and Sand-Filled Framework Gravel Beds in a Laboratory Flume

NASA Astrophysics Data System (ADS)

Mooneyham, Christian; Strom, Kyle

2018-01-01

Pulses of fine sediment composed of sand, silt, and clay can be introduced to gravel bed rivers through runoff from burn-impacted hillslopes, landslides, bank failure, or the introduction of reservoir sediment as a result of sluicing or dam decommissioning. Here we present a study aimed at quantifying exchange between suspensions of clay and gravel beds. The questions that motivate the work are: how do bed roughness and pore space characteristics, shear velocity (u∗), and initial concentration (C0) affect clay deposition on or within gravel beds? Where does deposition within these beds occur, and can deposited clay be resuspended while the gravel is immobile? We examine these questions in a laboratory flume using acrylic, open-framework gravel, and armored sand-gravel beds under conditions of varying u∗ and C0. Deposition of clay occurred to all beds (even with Rouse numbers ˜ 0.01). We attribute deposition under full suspension conditions to be an outcome of localized protected zones where clay can settle and available pore space in the bed. For smooth wall cases, protection came from the viscous wall region and the development of bed forms; for the rough beds, protection came from separation zones and low-velocity pore spaces. Bed porosity was the strongest influencer of nondimensional deposition rate; deposition increased with porosity. Deposition was inversely related to u∗ for the acrylic bed runs; no influence of u∗ was found for the porous bed runs. Increases in discharge resulted in resuspension of clay from acrylic beds; no resuspension was observed in the porous bed runs.

Morphological evaluation of heterogeneous oolitic limestone under pressure and fluid flow using X-ray microtomography

NASA Astrophysics Data System (ADS)

Zhang, Yihuai; Lebedev, Maxim; Al-Yaseri, Ahmed; Yu, Hongyan; Nwidee, Lezorgia N.; Sarmadivaleh, Mohammad; Barifcani, Ahmed; Iglauer, Stefan

2018-03-01

Pore-scale analysis of carbonate rock is of great relevance to the oil and gas industry owing to their vast application potentials. Although, efficient fluid flow at pore scale is often disrupted owing to the tight rock matrix and complex heterogeneity of limestone microstructures, factors such as porosity, permeability and effective stress greatly impact the rock microstructures; as such an understanding of the effect of these variables is vital for various natural and engineered processes. In this study, the Savonnières limestone as a carbonate mineral was evaluated at micro scales using X-ray micro-computed tomography at high resolutions (3.43 μm and 1.25 μm voxel size) under different effective stress (0 MPa, 20 MPa) to ascertain limestone microstructure and gas permeability and porosity effect. The waterflooding (5 wt% NaCl) test was conducted using microCT in-situ scanning and nanoindentation test was also performed to evaluate microscale geomechanical heterogeneity of the rock. The nanoindentation test results showed that the nano/micro scale geomechanical properties are quite heterogeneous where the indentation modulus for the weak consolidated area was as low as 1 GPa. We observed that the fluid flow easily broke some less-consolidated areas (low indentation modulus) area, coupled with increase in porosity; and consistent with fines/particles migration and re-sedimentation were identified, although the effective stress showed only a minor effect on the rock microstructure.

Strength-Ductility Property Maps of Powder Metallurgy (PM) Ti-6Al-4V Alloy: A Critical Review of Processing-Structure-Property Relationships

NASA Astrophysics Data System (ADS)

Kumar, P.; Chandran, K. S. Ravi

2017-05-01

A comprehensive assessment of tensile properties of powder metallurgical (PM) processed Ti-6Al-4V alloy, through the mapping of strength-ductility property domains, is performed in this review. Tensile property data of PM Ti-6Al-4V alloys made from blended element (BE) and pre-alloyed powders including that additive manufactured (AM) from powders, as well as that made using titanium hydride powders, have been mapped in the form of strength-ductility domains. Based on this, porosity and microstructure have been identified as the dominant variables controlling both the strength and the tensile ductility of the final consolidated materials. The major finding is that tensile ductility of the PM titanium is most sensitive to the presence of pores. The significance of extreme-sized pores or defects in inducing large variations in ductility is emphasized. The tensile strength, however, has been found to depend only weakly on the porosity. The effect of microstructure on properties is masked by the variations in porosity and to some extent by the oxygen level. It is shown that any meaningful comparison of the microstructure can only be made under a constant porosity or density level. The beneficial effect of a refined microstructure is also brought out by logically organizing the data in terms of microstructure groups. The advantages of new processes, using titanium hydride powder to produce PM titanium alloys, in simultaneously increasing strength and ductility, are also highlighted. The tensile properties of AM Ti-6Al-4V alloys are also brought to light, in comparison with the other PM and wrought alloys, through the strength-ductility maps.

Effects of high shock pressures and pore morphology on hot spot mechanisms in HMX

NASA Astrophysics Data System (ADS)

Springer, H. K.; Tarver, C. M.; Bastea, S.

2017-01-01

The shock initiation and detonation behavior of heterogeneous solid explosives is governed by its microstructure and reactive properties. New additive manufacturing techniques offer unprecedented control of explosive microstructures previously impossible, enabling us to develop novel explosives with tailored shock sensitivity and detonation properties. Since microstructure-performance relationships are not well established for explosives, there is little material design guidance for these manufacturing techniques. In this study, we explore the effects of high shock pressures (15-38 GPa) with long shock durations and different pore morphologies on hot spot mechanisms in HMX. HMX is chosen as the model material because we have experimental data on many of the chemical-thermal-mechanical properties required for pore collapse simulations. Our simulations are performed using the multi-physics arbitrary Lagrangian Eulerian finite element hydrocode, ALE3D, with Cheetah-based models for the unreacted and the product equation-of-states. We use a temperature-dependent specific heat with the unreacted equation-of-state and a temperature-dependent viscosity model to ensure accurate shock temperatures for subsequent chemistry. The Lindemann Law model is used for shock melting in HMX. In contrast to previous pore collapse studies at lower shock pressures (≤10 GPa) in HMX and shorter post-collapse burning times, our calculations show that shock melting occurs above 15 GPa due to higher bulk heating and a prominent elongated ("jet-like") hot spot region forms at later times. The combination of the elongated, post-collapse hot spot region and the higher bulk heating with increasing pressure dramatically increases the growth rate of reaction. Our calculations show that the reaction rate, dF/dt, increases with increasing shock pressure. We decompose the reaction rate into ignition ((dF/dt)ig) and growth ((dF/dt)gr) phases to better analyze our results. We define the ignition phase to primarily include pore collapse and growth phase to primarily include post-collapse grain burning. We are able to track late-time, post-collapse burning due to the unique loading conditions employed in these calculations. We find that (dF/dt)gr > (dF/dt)ig for all pressures considered. (dF/dt)gr changes more significantly from 25 to 38 GPa (from 0.05/µs to >10-100/µs) than from 15 to 25 GPa (from 0.005/µs to 0.05/µs). There is a three order-of-magnitude difference in the reaction from 15 to 38 GPa just after pore collapse. This is qualitatively consistent with fitting the (macroscopic) Ignition and Growth model to high pressure shock initiation data, where much larger reaction fractions are needed to capture the early stages of reaction. Calculated burn rates demonstrate better agreement with data at intermediate times in the growth phase for 15 to 25 GPa and late times for 30 GPa then at any time in the growth phase for 38 GPa. Our calculations are much higher than burn rate data at the earliest times in the growth phase for all pressures, which may reflect the higher localized pressures and temperatures just after pore collapse in the ignition phase. Our calculations with spherical, conical, and elliptical pores show that the influence of morphology on reaction rate is pressure dependent and the most influential pore shapes at lower pressures aren't the same at higher pressures in the regime studied. Altogether these studies provide the basis for developing microstructure-aware models that can be used to design new explosives with optimal performance-safety characteristics. Such models can be used to guide additive manufacturing of explosives and fully exploit their disruptive nature.

CVD of silicon carbide on structural fibers - Microstructure and composition

NASA Technical Reports Server (NTRS)

Veitch, Lisa C.; Terepka, Francis M.; Gokoglu, Suleyman A.

1992-01-01

Structural fibers are currently being considered as reinforcements for intermetallic and ceramic materials. Some of these fibers, however, are easily degraded in a high temperature oxidative environment. Therefore, coatings are needed to protect the fibers from environmental attack. Silicon carbide (SiC) was chemically vapor deposited (CVD) on Textron's SCS6 fibers. Fiber temperatures ranging from 1350 to 1500 C were studied. Silane (SiH4) and propane (C2H8) were used for the source gases and different concentrations of these source gases were studied. Deposition rates were determined for each group of fibers at different temperatures. Less variation in deposition rates were observed for the dilute source gas experiments than the concentrated source gas experiments. A careful analysis was performed on the stoichiometry of the CVD SiC coating using electron microprobe. Microstructures for the different conditions were compared. At 1350 C, the microstructures were similar; however, at higher temperatures, the microstructure for the more concentrated source gas group were porous and columnar in comparison to the cross sections taken from the same area for the dilute source gas group.

CVD of silicon carbide on structural fibers: Microstructure and composition

NASA Technical Reports Server (NTRS)

Veitch, Lisa C.; Terepka, Francis M.; Gokoglu, Suleyman A.

1992-01-01

Structural fibers are currently being considered as reinforcements for intermetallic and ceramic materials. Some of these fibers, however, are easily degraded in a high temperature oxidative environment. Therefore, coatings are needed to protect the fibers from environmental attack. Silicon carbide (SiC) was chemically vapor deposited (CVD) on Textron's SCS6 fibers. Fiber temperatures ranging from 1350 to 1500 C were studied. Silane (SiH4) and propane (C2H8) were used for the source gases and different concentrations of these source gases were studied. Deposition rates were determined for each group of fibers at different temperatures. Less variation in deposition rates were observed for the dilute source gas experiments than the concentrated source gas experiments. A careful analysis was performed on the stoichiometry of the CVD SiC coating using electron microprobe. Microstructures for the different conditions were compared. At 1350 C, the microstructures were similar; however, at higher temperatures, the microstructure for the more concentrated source gas group were porous and columnar in comparison to the cross sections taken from the same area for the dilute source gas group.

Three-dimensional patterning methods and related devices

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

Putnam, Morgan C.; Kelzenberg, Michael D.; Atwater, Harry A.

2016-12-27

Three-dimensional patterning methods of a three-dimensional microstructure, such as a semiconductor wire array, are described, in conjunction with etching and/or deposition steps to pattern the three-dimensional microstructure.

Additive Manufacturing of Metastable Beta Titanium Alloys

NASA Astrophysics Data System (ADS)

Yannetta, Christopher J.

Additive manufacturing processes of many alloys are known to develop texture during the deposition process due to the rapid reheating and the directionality of the dissipation of heat. Titanium alloys and with respect to this study beta titanium alloys are especially susceptible to these effects. This work examines Ti-20wt%V and Ti-12wt%Mo deposited under normal additive manufacturing process parameters to examine the texture of these beta-stabilized alloys. Both microstructures contained columnar prior beta grains 1-2 mm in length beginning at the substrate with no visible equiaxed grains. This microstructure remained constant in the vanadium system throughout the build. The microstructure of the alloy containing molybdenum changed from a columnar to an equiaxed structure as the build height increased. Eighteen additional samples of the Ti-Mo system were created under different processing parameters to identify what role laser power and travel speed have on the microstructure. There appears to be a correlation in alpha lath size and power density. The two binary alloys were again deposited under the same conditions with the addition of 0.5wt% boron to investigate the effects an insoluble interstitial alloying element would have on the microstructure. The size of the prior beta grains in these two alloys were reduced with the addition of boron by approximately 50 (V) and 100 (Mo) times.

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

Direct printing of microstructures by femtosecond laser excitation of nanocrystals in solution

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

Shou, Wan; Pan, Heng, E-mail: hp5c7@mst.edu

2016-05-23

We report direct printing of micro/sub-micron structures by femtosecond laser excitation of semiconductor nanocrystals (NCs) in solution. Laser excitation with moderate intensity (10{sup 11}–10{sup 12} W/cm{sup 2}) induces 2D and 3D deposition of CdTe nanocrystals in aqueous solution, which can be applied for direct printing of microstructures. It is believed that laser irradiation induces charge formation on nanocrystals leading to deposition. Furthermore, it is demonstrated that the charged nanocrystals can respond to external electrical bias, enabling a printing approach based on selective laser induced electrophoretic deposition. Finally, energy dispersive X-ray analysis of deposited structures shows oxidation occurs and deposited structure mainlymore » consists of Cd{sub x}O.« less

Catalyst Of A Metal Heteropoly Acid Salt That Is Insoluble In A Polar Solvent On A Non-Metallic Porous Support And Method Of Making

DOEpatents

Wang. Yong; Peden. Charles H. F.; Choi. Saemin

2004-11-09

The present invention includes a catalyst having (a) a non-metallic support having a plurality of pores; (b) a metal heteropoly acid salt that is insoluble in a polar solvent on the non-metallic support; wherein at least a portion of the metal heteropoly acid salt is dispersed within said plurality of pores. The present invention also includes a method of depositing a metal heteropoly acid salt that is insoluble in a polar solvent onto a non-metallic support having a plurality of pores. The method has the steps of: (a) obtaining a first solution containing a first precursor of a metal salt cation; (b) obtaining a second solution containing a second precursor of a heteropoly acid anion in a solvent having a limited dissolution potential for said first precursor; (c) impregnating the non-metallic support with the first precursor forming a first precursor deposit within the plurality of pores, forming a first precursor impregnated support; (d) heating said first precursor impregnated support forming a bonded first precursor impregnated support; (e) impregnating the second precursor that reacts with the precursor deposit and forms the metal heteropoly acid salt.

Catalyst of a metal heteropoly acid salt that is insoluble in a polar solvent on a non-metallic porous support and method of making

DOEpatents

Wang, Yong [Richland, WA; Peden, Charles H. F. [West Richland, WA; Choi, Saemin [Richland, WA

2002-10-29

The present invention includes a catalyst having (a) a non-metallic support having a plurality of pores; (b) a metal heteropoly acid salt that is insoluble in a polar solvent on the non-metallic support; wherein at least a portion of the metal heteropoly acid salt is dispersed within said plurality of pores. The present invention also includes a method of depositing a metal heteropoly acid salt that is insoluble in a polar solvent onto a non-metallic support having a plurality of pores. The method has the steps of: (a) obtaining a first solution containing a first precursor of a metal salt cation; (b) obtaining a second solution containing a second precursor of a heteropoly acid anion in a solvent having a limited dissolution potential for said first precursor; (c) impregnating the non-metallic support with the first precursor forming a first precursor deposit within the plurality of pores, forming a first precursor impregnated support; (d) heating said first precursor impregnated support forming a bonded first precursor impregnated support; (e) impregnating the second precursor that reacts with the precursor deposit and forms the metal heteropoly acid salt.

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.

Near-failure detonation behavior of vapor-deposited hexanitrostilbene (HNS) films

NASA Astrophysics Data System (ADS)

Knepper, Robert; Wixom, Ryan R.; Marquez, Michael P.; Tappan, Alexander S.

2017-01-01

Hexanitrostilbene (HNS) films were deposited onto polycarbonate substrates using vacuum thermal sublimation. The deposition conditions were varied in order to alter porosity in the films, and the resulting microstructures were quantified by analyzing ion-polished cross-sections using scanning electron microscopy. The effects of these changes in microstructure on detonation velocity and the critical thickness needed to sustain detonation were determined. The polycarbonate substrates also acted as recording plates for detonation experiments, and films near the critical thickness displayed distinct patterns in the dent tracks that indicate instabilities in the detonation front when approaching failure conditions.

Controlling Microstructure of Yttria-Stabilized Zirconia Prepared from Suspensions and Solutions by Plasma Spraying with High Feed Rates

NASA Astrophysics Data System (ADS)

Musalek, Radek; Medricky, Jan; Tesar, Tomas; Kotlan, Jiri; Pala, Zdenek; Lukac, Frantisek; Illkova, Ksenia; Hlina, Michal; Chraska, Tomas; Sokolowski, Pawel; Curry, Nicholas

2017-12-01

Introduction of suspension and solution plasma spraying led to a breakthrough in the deposition of yttria-stabilized zirconia (YSZ) coatings and enabled preparation of new types of layers. However, their deposition with high feed rates needed, for example, for the deposition of thermal barrier coatings (TBCs) on large-scale components, is still challenging. In this study, possibility of high-throughput plasma spraying of YSZ coatings is demonstrated for the latest generation of high-enthalpy hybrid water-stabilized plasma (WSP-H) torch technology. The results show that microstructure of the coatings prepared by WSP-H may be tailored for specific applications by the choice of deposition conditions, in particular formulation of the liquid feedstock. Porous and columnar coatings with low thermal conductivity (0.5-0.6 W/mK) were prepared from commercial ethanol-based suspension. Dense vertically cracked coatings with higher thermal conductivity but also higher internal cohesion were deposited from suspension containing ethanol/water mixture and coarser YSZ particles. Spraying of solution formulated from diluted zirconium acetate and yttrium nitrate hexahydrate led also to the successful deposition of YSZ coating combining regions of porous and denser microstructure and providing both low thermal conductivity and improved cohesion of the coating. Enthalpy content, liquid-plasma interaction and coating buildup mechanisms are also discussed.

Statistical scaling of geometric characteristics in stochastically generated pore microstructures

DOE PAGES

Hyman, Jeffrey D.; Guadagnini, Alberto; Winter, C. Larrabee

2015-05-21

In this study, we analyze the statistical scaling of structural attributes of virtual porous microstructures that are stochastically generated by thresholding Gaussian random fields. Characterization of the extent at which randomly generated pore spaces can be considered as representative of a particular rock sample depends on the metrics employed to compare the virtual sample against its physical counterpart. Typically, comparisons against features and/patterns of geometric observables, e.g., porosity and specific surface area, flow-related macroscopic parameters, e.g., permeability, or autocorrelation functions are used to assess the representativeness of a virtual sample, and thereby the quality of the generation method. Here, wemore » rely on manifestations of statistical scaling of geometric observables which were recently observed in real millimeter scale rock samples [13] as additional relevant metrics by which to characterize a virtual sample. We explore the statistical scaling of two geometric observables, namely porosity (Φ) and specific surface area (SSA), of porous microstructures generated using the method of Smolarkiewicz and Winter [42] and Hyman and Winter [22]. Our results suggest that the method can produce virtual pore space samples displaying the symptoms of statistical scaling observed in real rock samples. Order q sample structure functions (statistical moments of absolute increments) of Φ and SSA scale as a power of the separation distance (lag) over a range of lags, and extended self-similarity (linear relationship between log structure functions of successive orders) appears to be an intrinsic property of the generated media. The width of the range of lags where power-law scaling is observed and the Hurst coefficient associated with the variables we consider can be controlled by the generation parameters of the method.« less

The effects of ageing time on the microstructure and properties of mesoporous silica-hydroxyapatite nanocomposite

NASA Astrophysics Data System (ADS)

Yousefpour, Mardali; Taherian, Zahra

2013-02-01

In this study, a mesoporous silica-hydroxyapatite nanocomposite (MCM-41/HA) was synthesized via sol-gel technique as a drug delivery system. The synthesis of MCM-41/hydroxyapatite nanocomposite was carried out at room temperature. The effect of various ageing time on the nanocomposite properties was studied during synthesis process. 0, 24, 36, and 48 h aging times were chosen. Textural properties and microstructure of the nanocomposites were characterized by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Spectroscopy (EDS), Electron Diffraction pattern (ED), and N2 adsorption-desorption. Results showed that ageing process led to HA crystals nucleation and growth on the surface of mesoporous silica. At 48 h of aging time, the surface area and total pore volume increased from 36.2 to 334 m2/g and 0.14-0.7 cm3/g, respectively. In contrast, the average pore diameter considerably decreased from 20.1 nm for (MCM-41/HA)24 to 8.39 nm for (MCM-41/HA)48. Furthermore, it was observed more homogeneous pore distribution with increasing the ageing time. In conclusion, the ageing time play an important role on textural properties of MCM-41/HA nanocomposite which could have a major effect on drug delivery properties such as molecular loading and release kinetics.

The Influence of Heat Treatments on the Porosity of Suspension Plasma-Sprayed Yttria-Stabilized Zirconia Coatings

NASA Astrophysics Data System (ADS)

Ekberg, Johanna; Ganvir, Ashish; Klement, Uta; Creci, Simone; Nordstierna, Lars

2018-02-01

Suspension plasma-sprayed coatings are produced using fine-grained feedstock. This allows to control the porosity and to achieve low thermal conductivity which makes the coatings attractive as topcoats in thermal barrier coatings (TBCs). Used in gas turbine applications, TBCs are exposed to high temperature exhaust gases which lead to microstructure alterations. In order to obtain coatings with optimized thermomechanical properties, microstructure alterations like closing of pores and opening of cracks have to be taken into account. Hence, in this study, TBC topcoats consisting of 4 mol.% yttria-stabilized zirconia were heat-treated in air at 1150 °C and thereafter the coating porosity was investigated using image analysis (IA) and nuclear magnetic resonance (NMR) cryoporometry. Both IA and NMR cryoporometry showed that the porosity changed as a result of the heat treatment for all investigated coatings. In fact, both techniques showed that the fine porosity decreased as a result of the heat treatment, while IA also showed an increase in the coarse porosity. When studying the coatings using scanning electron microscopy, it was noticed that finer pores and cracks disappeared and larger pores grew slightly and achieved a more distinct shape as the material seemed to become more compact.

Challenge for lowering concentration polarization in solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Shimada, Hiroyuki; Suzuki, Toshio; Yamaguchi, Toshiaki; Sumi, Hirofumi; Hamamoto, Koichi; Fujishiro, Yoshinobu

2016-01-01

In the scope of electrochemical phenomena, concentration polarization at electrodes is theoretically inevitable, and lowering the concentration overpotential to improve the performance of electrochemical cells has been a continuing challenge. Electrodes with highly controlled microstructure, i.e., high porosity and uniform large pores are therefore essential to achieve high performance electrochemical cells. In this study, state-of-the-art technology for controlling the microstructure of electrodes has been developed for realizing high performance support electrodes of solid oxide fuel cells (SOFCs). The key is controlling the porosity and pore size distribution to improve gas diffusion, while maintaining the integrity of the electrolyte and the structural strength of actual sized electrode supports needed for the target application. Planar anode-supported SOFCs developed in this study realize 5 μm thick dense electrolyte (yttria-stabilized zirconia: YSZ) and the anode substrate (Ni-YSZ) of 53.6 vol.% porosity with a large median pore diameter of 0.911 μm. Electrochemical measurements reveal that the performance of the anode-supported SOFCs improves with increasing anode porosity. This Ni-YSZ anode minimizes the concentration polarization, resulting in a maximum power density of 3.09 W cm-2 at 800 °C using humidified hydrogen fuel without any electrode functional layers.

Environment-oriented low-cost porous mullite ceramic membrane supports fabricated from coal gangue and bauxite.

PubMed

Lü, Qikai; Dong, Xinfa; Zhu, Zhiwen; Dong, Yingchao

2014-05-30

Porous mullite ceramic supports for filtration membrane were successfully fabricated via recycling of coal gangue and bauxite at sintering temperatures from 1100 to 1500°C with corn starch as pore-forming agent. The dynamic sintering behaviors, phase evolution, shrinkage, porosity and pore size, gas permeation flux, microstructure and mechanical property were systematically studied. A unique volume-expansion stage was observed at increased temperatures from 1276 to 1481°C caused by a mullitization-crystal-growth process. During this stage, open porosity increases and pore size distributions broaden, which result in a maximum of nitrogen gas flux at 1400°C. The X-ray diffraction results reveal that secondary mullitization took place from 1100°C and the major phase is mullite with a content of ∼84.7wt.% at 1400°C. SEM images show that the as-fabricated mullite supports have a porous microstructure composed of sintered glassy particles embedded with inter-locked mullite crystals, which grew gradually with increasing temperature from rod-like into blocky-like morphologies. To obtain mullite membrane supports with sufficient porosity and acceptable mechanical strength, the relationship between porosity and mechanical strength was investigated, which was fitted using a parabolic equation. Copyright © 2014 Elsevier B.V. All rights reserved.

Sintering and microstructure property relationships of porous hydroxyapatite

NASA Astrophysics Data System (ADS)

Zakaria, Fadzil Ayad

2000-09-01

The use of ceramics inside the body, as implant materials, is a relatively new technology, the first instance having been reported just 20 years ago. The ceramics used for the repair and reconstruction of diseased, damaged or 'worn out' parts of the body are referred to as bioceramics, and such a material is hydroxyapatite. The use of calcium phosphate to repair bone defects has been based on the rationale that calcium phosphate resembles vertebrate tooth and bone mineral, and is biologically compatible with these and surrounding tissues. The concept of preparing porous hydroxyapatite was developed to prevent loosening of implants by enhancing the ingrowth of tissue into the pores (biological fixation). A structural limitation of this type of implant is the requirement to have a minimal pore size between 80- 100 m in diameter to allow bone to grow into the pores. The presence of such porosity would lead to a lower strength of the bioceramic component, but this is offset by the advantages of biocompatibility. It is well known that hydroxyapatite is a brittle material and making it porous would reduce the existing mechanical properties. This study was carried out to optimise the mechanical properties by investigating the processing conditions and methods of preparation. The effect of forming method, pore geometry, pore size, sintering cycle, sintering atmosphere and types of spherical polymers on the microstructure and mechanical properties were studied. As a consequence of the experiments, it was observed that porous hydroxyapatite is formed using an isostatic pressing technique, with 53 vol. % of HMWPVC as the porosifier. Sintering in air, with a heating rate of 50C/h, held for 1h at 600C in the first stage, and a heating rate of 100C/h, held for 4h at between 1200 and 1250C, generated a spherical pore geometry which gave the best combination of properties. This fabrication route resulted in an interconnected porous hydroxyapatite with a pore size ~90 m, the volume fraction of porosity ~35%, relative density of ~60%, a grain size ~1.7-2 m, a compressive strength between 14-18 MPa and a tensile strength of 4-5 MPa.

Micro-structure and Mechanical Properties of Nano-TiC Reinforced Inconel 625 Deposited using LAAM

NASA Astrophysics Data System (ADS)

Bi, G.; Sun, C. N.; Nai, M. L.; Wei, J.

In this paper, deposition of Ni-base Inconel 625 mixed with nano-TiC powders using laser aided additive manufacturing (LAAM) was studied. Micro-structure and mechanical properties were intensively investigated. The results showed that nano-size TiC distributed uniformly throughout the Ni- matrix. Inconel 625 can be reinforced by the strengthened grain boundaries with nano-size TiC. Improved micro-hardness and tensile properties were observed.

Wettability control of micropore-array films by altering the surface nanostructures.

PubMed

Chang, Chi-Jung; Hung, Shao-Tsu

2010-07-01

By controlling the surface nanostructure, the wettability of films with similar pore-array microstructure can be tuned from hydrophilic to nearly superhydrophobic without variation of the chemical composition. PA1 pore-array film consisting of the horizontal ZnO nanosheets was nearly superhydrophobic. PA2 pore-array film consisting of growth-hindered vertically-aligned ZnO nanorods was hydrophilic. The influences of the nanostructure shape, orientation and the micropore size on the contact angle of the PA1 films were studied. This study provides a new approach to control the wettability of films with similar pore-array structure at the micro-scale by changing their surface nanostructure. PA1 films exhibited irradiation induced reversible wettability transition. The feasibility of creating a wetted radial pattern by selective UV irradiation of PA1 film through a mask with radial pattern and water vapor condensation was also evaluated.

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.

Mechanical properties and failure behavior of unidirectional porous ceramics

NASA Astrophysics Data System (ADS)

Seuba, Jordi; Deville, Sylvain; Guizard, Christian; Stevenson, Adam J.

2016-04-01

We show that the honeycomb out-of-plane model derived by Gibson and Ashby can be applied to describe the compressive behavior of unidirectional porous materials. Ice-templating allowed us to process samples with accurate control over pore volume, size, and morphology. These samples allowed us to evaluate the effect of this microstructural variations on the compressive strength in a porosity range of 45-80%. The maximum strength of 286 MPa was achieved in the least porous ice-templated sample (P(%) = 49.9), with the smallest pore size (3 μm). We found that the out-of-plane model only holds when buckling is the dominant failure mode, as should be expected. Furthermore, we controlled total pore volume by adjusting solids loading and sintering temperature. This strategy allows us to independently control macroporosity and densification of walls, and the compressive strength of ice-templated materials is exclusively dependent on total pore volume.

Mechanical properties and failure behavior of unidirectional porous ceramics.

PubMed

Seuba, Jordi; Deville, Sylvain; Guizard, Christian; Stevenson, Adam J

2016-04-14

We show that the honeycomb out-of-plane model derived by Gibson and Ashby can be applied to describe the compressive behavior of unidirectional porous materials. Ice-templating allowed us to process samples with accurate control over pore volume, size, and morphology. These samples allowed us to evaluate the effect of this microstructural variations on the compressive strength in a porosity range of 45-80%. The maximum strength of 286 MPa was achieved in the least porous ice-templated sample (P(%) = 49.9), with the smallest pore size (3 μm). We found that the out-of-plane model only holds when buckling is the dominant failure mode, as should be expected. Furthermore, we controlled total pore volume by adjusting solids loading and sintering temperature. This strategy allows us to independently control macroporosity and densification of walls, and the compressive strength of ice-templated materials is exclusively dependent on total pore volume.

Evolution of the Thermal Conductivity of Sintered Silver Joints with their Porosity Predicted by the Finite Element Analysis of Real 3D Microstructures

NASA Astrophysics Data System (ADS)

Signor, L.; Kumar, P.; Tressou, B.; Nadot-Martin, C.; Miranda-Ordonez, José; Carr, J.; Joulain, K.; Milhet, X.

2018-07-01

Silver paste sintering is a very promising technology for chip bonding in future power electronics modules owing to its high melting temperature and the good electrical and thermal properties among other classic solder alloys. However, in its sintered form, these joints contain nanometric/submicrometric pores that affect their thermal performance. The present study gives insight into the relationship between the material thermal conductivity and the real three-dimensional porous structure using finite element modelling. It is shown that over a certain pore fraction threshold (˜ 13%), the pore morphology has a non-negligible influence on the thermal conductivity. Results are also compared to predictions obtained by analytical models available in the literature.

Evolution of the Thermal Conductivity of Sintered Silver Joints with their Porosity Predicted by the Finite Element Analysis of Real 3D Microstructures

NASA Astrophysics Data System (ADS)

Signor, L.; Kumar, P.; Tressou, B.; Nadot-Martin, C.; Miranda-Ordonez, José; Carr, J.; Joulain, K.; Milhet, X.

2018-03-01

Silver paste sintering is a very promising technology for chip bonding in future power electronics modules owing to its high melting temperature and the good electrical and thermal properties among other classic solder alloys. However, in its sintered form, these joints contain nanometric/submicrometric pores that affect their thermal performance. The present study gives insight into the relationship between the material thermal conductivity and the real three-dimensional porous structure using finite element modelling. It is shown that over a certain pore fraction threshold (˜ 13%), the pore morphology has a non-negligible influence on the thermal conductivity. Results are also compared to predictions obtained by analytical models available in the literature.

Low Conductive Thermal Barrier Coatings Produced by Ion Beam Assisted EB-PVD with Controlled Porosity, Microstructure Refinement and Alloying Additions for High Temperature Applications

NASA Technical Reports Server (NTRS)

Wolfe, Douglas E.; Singh, Jogender

2005-01-01

Various advanced Hafnia-based thermal barrier coatings (TBC) were applied on nickel-based superalloy coupons by electron beam physical vapor deposition. In addition, microstructural modifications to the coating material were made in an effort to reduce the thermal conductivity of the coating materials. Various processing parameters and coating system modifications were made in order to deposit the alloyed TBC with the desired microstructure and thus coating performance, some of which include applying coatings at substrate temperatures of 1150 C on both PtAl and CoNiCrAlY bond coated samples, as well as using 8YSZ as a bond layer. In addition, various characterization techniques including thermal cyclic tests, scanning electron microscopy, x-ray diffraction, thermal conductivity, and reflectivity measurements were performed. Although the coating microstructure was never fully optimized due to funding being cut short, significant reductions in thermal conductivity were accomplished through both chemistry changes (composition) and microstructural modifications.

Texture-Induced Anisotropy in an Inconel 718 Alloy Deposited Using Electron Beam Freeform Fabrication

NASA Technical Reports Server (NTRS)

Tayon, W.; Shenoy, R.; Bird, R.; Hafley, R.; Redding, M.

2014-01-01

A test block of Inconel (IN) 718 was fabricated using electron beam freeform fabrication (EBF(sup 3)) to examine how the EBF(sup 3) deposition process affects the microstructure, crystallographic texture, and mechanical properties of IN 718. Tests revealed significant anisotropy in the elastic modulus for the as-deposited IN 718. Subsequent tests were conducted on specimens subjected to a heat treatment designed to decrease the level of anisotropy. Electron backscatter diffraction (EBSD) was used to characterize crystallographic texture in the as-deposited and heat treated conditions. The anisotropy in the as-deposited condition was strongly affected by texture as evidenced by its dependence on orientation relative to the deposition direction. Heat treatment resulted in a significant improvement in modulus of the EBF(sup 3) product to a level nearly equivalent to that for wrought IN 718 with reduced anisotropy; reduction in texture through recrystallization; and production of a more homogeneous microstructure.

Deposition and micro electrical discharge machining of CVD-diamond layers incorporated with silicon

NASA Astrophysics Data System (ADS)

Kühn, R.; Berger, T.; Prieske, M.; Börner, R.; Hackert-Oschätzchen, M.; Zeidler, H.; Schubert, A.

2017-10-01

In metal forming, lubricants have to be used to prevent corrosion or to reduce friction and tool wear. From an economical and ecological point of view, the aim is to avoid the usage of lubricants. For dry deep drawing of aluminum sheets it is intended to apply locally micro-structured wear-resistant carbon based coatings onto steel tools. One type of these coatings are diamond layers prepared by chemical vapor deposition (CVD). Due to the high strength of diamond, milling processes are unsuitable for micro-structuring of these layers. In contrast to this, micro electrical discharge machining (micro EDM) is a suitable process for micro-structuring CVD-diamond layers. Due to its non-contact nature and its process principle of ablating material by melting and evaporating, it is independent of the hardness, brittleness or toughness of the workpiece material. In this study the deposition and micro electrical discharge machining of silicon incorporated CVD-diamond (Si-CVD-diamond) layers were presented. For this, 10 µm thick layers were deposited on molybdenum plates by a laser-induced plasma CVD process (LaPlas-CVD). For the characterization of the coatings RAMAN- and EDX-analyses were conducted. Experiments in EDM were carried out with a tungsten carbide tool electrode with a diameter of 90 µm to investigate the micro-structuring of Si-CVD-diamond. The impact of voltage, discharge energy and tool polarity on process speed and resulting erosion geometry were analyzed. The results show that micro EDM is a suitable technology for micro-structuring of silicon incorporated CVD-diamond layers.

Effect of Microstructural Parameters on the Relative Densities of Metal Foams

NASA Technical Reports Server (NTRS)

Raj, S. V.; Kerr, Jacob A.

2010-01-01

A detailed quantitative microstructural analyses of primarily open cell FeCrAlY and 314 stainless steel metal foams with different relative densities and pores per inch (p.p.i.) were undertaken in the present investigation to determine the effect of microstructural parameters on the relative densities of metal foams. Several elements of the microstructure, such as longitudinal and transverse cell sizes, cell areas and perimeters, ligament dimensions, cell shapes and volume fractions of closed and open cells, were measured. The cross-sections of the foam ligaments showed a large number of shrinkage cavities, and their circularity factors and average sizes were determined. The volume fractions of closed cells increased linearly with increasing relative density. In contrast, the volume fractions of the open cells and ligaments decreased with increasing relative density. The relative densities and p.p.i. were not significantly dependent on cell size, cell perimeter and ligament dimensions within the limits of experimental scatter. A phenomenological model is proposed to rationalize the present microstructural observations.

Impact load-induced micro-structural damage and micro-structure associated mechanical response of concrete made with different surface roughness and porosity aggregates

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

Erdem, Savas, E-mail: evxse1@nottingham.ac.uk; Dawson, Andrew Robert; Thom, Nicholas Howard

2012-02-15

The relationship between the nature of micro damage under impact loading and changes in mechanical behavior associated with different microstructures is studied for concretes made with two different coarse aggregates having significant differences mainly in roughness and porosity - sintered fly ash and uncrushed gravel. A range of techniques including X-ray diffraction, digital image analysis, mercury porosimetry, X-ray computed tomography, laser surface profilometry and scanning electron microscopy were used to characterize the aggregates and micro-structures. The concrete prepared with lightweight aggregates was stronger in compression than the gravel aggregate concrete due to enhanced hydration as a result of internal curing.more » In the lightweight concrete, it was deduced that an inhomogeneous micro-structure led to strain incompatibilities and consequent localized stress concentrations in the mix, leading to accelerated failure. The pore structure, compressibility, and surface texture of the aggregates are of paramount importance for the micro-cracking growth.« less

Micromechanics of cataclastic pore collapse in limestone

NASA Astrophysics Data System (ADS)

Zhu, Wei; Baud, Patrick; Wong, Teng-Fong

2010-04-01

The analysis of compactant failure in carbonate formations hinges upon a fundamental understanding of the mechanics of inelastic compaction. Microstructural observations indicate that pore collapse in a limestone initiates at the larger pores, and microcracking dominates the deformation in the periphery of a collapsed pore. To capture these micromechanical processes, we developed a model treating the limestone as a dual porosity medium, with the total porosity partitioned between macroporosity and microporosity. The representative volume element is made up of a large pore which is surrounded by an effective medium containing the microporosity. Cataclastic yielding of this effective medium obeys the Mohr-Coulomb or Drucker-Prager criterion, with failure parameters dependent on porosity and pore size. An analytic approximation was derived for the unconfined compressive strength associated with failure due to the propagation and coalescence of pore-emanated cracks. For hydrostatic loading, identical theoretical results for the pore collapse pressure were obtained using the Mohr-Coulomb or Drucker-Prager criterion. For nonhydrostatic loading, the stress state at the onset of shear-enhanced compaction was predicted to fall on a linear cap according to the Mohr-Coulomb criterion. In contrast, nonlinear caps in qualitative agreement with laboratory data were predicted using the Drucker-Prager criterion. Our micromechanical model implies that the effective medium is significantly stronger and relatively pressure-insensitive in comparison to the bulk sample.

Modeling failure in brittle porous ceramics

NASA Astrophysics Data System (ADS)

Keles, Ozgur

Brittle porous materials (BPMs) are used for battery, fuel cell, catalyst, membrane, filter, bone graft, and pharmacy applications due to the multi-functionality of their underlying porosity. However, in spite of its technological benefits the effects of porosity on BPM fracture strength and Weibull statistics are not fully understood--limiting a wider use. In this context, classical fracture mechanics was combined with two-dimensional finite element simulations not only to account for pore-pore stress interactions, but also to numerically quantify the relationship between the local pore volume fraction and fracture statistics. Simulations show that even the microstructures with the same porosity level and size of pores differ substantially in fracture strength. The maximum reliability of BPMs was shown to be limited by the underlying pore--pore interactions. Fracture strength of BMPs decreases at a faster rate under biaxial loading than under uniaxial loading. Three different types of deviation from classic Weibull behavior are identified: P-type corresponding to a positive lower tail deviation, N-type corresponding to a negative lower tail deviation, and S-type corresponding to both positive upper and lower tail deviations. Pore-pore interactions result in either P-type or N-type deviation in the limit of low porosity, whereas S-type behavior occurs when clusters of low and high fracture strengths coexist in a fracture data.

Crystalline mesoporous zirconia catalysts having stable tetragonal pore wall structure

DOEpatents

Sachtler, W.M.H.; Huang, Y.Y.

1998-07-28

Methods are disclosed for the preparation of new sulfated mesoporous zirconia materials/catalysts with crystalline pore walls of predominantly tetragonal crystal structure, characterized by nitrogen physical sorption measurement, X-ray diffraction, transmission electron microscopy and catalytic tests using n-butane isomerization to iso-butane and alkylation of 1-naphthol with 4-tert-butylstyrene as probe reactions. Sulfate deposition is preferred for the transformation of a mesoporous precursor with amorphous pore walls into a material with crystalline pore walls maintaining the mesoporous characteristics. 17 figs.

Crystalline mesoporous zirconia catalysts having stable tetragonal pore wall structure

DOEpatents

Sachtler, Wolfgang M. H.; Huang, Yin-Yan

1998-01-01

Methods for the preparation of new sulfated mesoporous zirconia materials/catalysts with crystalline pore walls of predominantly tetragonal crystal structure, characterized by nitrogen physisorption measurement, X-ray diffraction, transmission electron microscopy and catalytic tests using n-butane isomerization to iso-butane and alkylation of 1-naphthol with 4-tert-butylstyrene as probe reactions. Sulfate deposition is preferred for the transformation of a mesoporous precursor with amorphous pore walls into a material with crystalline pore walls maintaining the mesoporous characteristics.

Microstructural Effects on Initiation Behavior in HMX

NASA Astrophysics Data System (ADS)

Molek, Christopher; Welle, Eric; Hardin, Barrett; Vitarelli, Jim; Wixom, Ryan; Samuels, Philip

Understanding the role microstructure plays on ignition and growth behavior has been the subject of a significant body of research within the detonation physics community. The pursuit of this understanding is important because safety and performance characteristics have been shown to strongly correlate to particle morphology. Historical studies have often correlated bulk powder characteristics to the performance or safety characteristics of pressed materials. We believe that a clearer and more relevant correlation is made between the pressed microstructure and the observed detonation behavior. This type of assessment is possible, as techniques now exist for the quantification of the pressed microstructures. Our talk will report on experimental efforts that correlate directly measured microstructural characteristics to initiation threshold behavior of HMX based materials. The internal microstructures were revealed using an argon ion cross-sectioning technique. This technique enabled the quantification of density and interface area of the pores within the pressed bed using methods of stereology. These bed characteristics are compared to the initiation threshold behavior of three HMX based materials using an electric gun based test method. Finally, a comparison of experimental threshold data to supporting theoretical efforts will be made.

Changes in the microstructure and properties of aspen chemithermomechanical pulp fibres during recycling.

PubMed

Fu, Yingjuan; Wang, Rongrong; Li, Dejuan; Wang, Zhaojiang; Zhang, Fengshan; Meng, Qinglin; Qin, Menghua

2015-03-06

The effects of recycling on the microstructure and properties of bleached aspen chemithermomechanical pulp (CTMP) fibres were systematically investigated. The low-temperature nitrogen adsorption and atomic force microscopy results showed that a substantial amount of large pores and most of the very small pores in the fibre wall closed and the fibre surface became less coarse and porous during recycling. The partial cocrystallisation of cellulose microfibrils took place, as reflected in the increment of the cellulose crystallinity and the width of the crystallite in the 0 0 2 lattice plane. These irreversible structural changes caused significant hornification of the recycled fibres, leading to the loss of swelling and bonding capability. The decrease of the tensile index, burst index, and tear index further demonstrated the deterioration of the fibre properties. However, the single-fibre strength considerably increased after recycling, which was mainly due to the enlarged cellulose aggregates in the fibre wall. Copyright © 2014 Elsevier Ltd. All rights reserved.

Regioselective atomic layer deposition in metal–organic frameworks directed by dispersion interactions

DOE PAGES

Gallington, Leighanne C.; Kim, In Soo; Liu, Wei-Guang; ...

2016-10-03

The application of atomic layer deposition (ALD) to metal–organic frameworks (MOFs) offers a promising new approach to synthesize designer functional materials with atomic precision. While ALD on flat substrates is well established, the complexity of the pore architecture and surface chemistry in MOFs present new challenges. Through in situ synchrotron X-ray powder diffraction, we visualize how the deposited atoms are localized and redistribute within the MOF during ALD. We demonstrate that the ALD is regioselective, with preferential deposition of oxy-Zn(II) species within the small pores of NU-1000. As a result, complementary density functional calculations indicate that this startling regioselectivity ismore » driven by dispersion interactions associated with the preferential adsorption sites for the organometallic precursors prior to reaction.« less

Regioselective atomic layer deposition in metal–organic frameworks directed by dispersion interactions

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

Gallington, Leighanne C.; Kim, In Soo; Liu, Wei-Guang

The application of atomic layer deposition (ALD) to metal–organic frameworks (MOFs) offers a promising new approach to synthesize designer functional materials with atomic precision. While ALD on flat substrates is well established, the complexity of the pore architecture and surface chemistry in MOFs present new challenges. Through in situ synchrotron X-ray powder diffraction, we visualize how the deposited atoms are localized and redistribute within the MOF during ALD. We demonstrate that the ALD is regioselective, with preferential deposition of oxy-Zn(II) species within the small pores of NU-1000. As a result, complementary density functional calculations indicate that this startling regioselectivity ismore » driven by dispersion interactions associated with the preferential adsorption sites for the organometallic precursors prior to reaction.« less

Laser powder-bed fusion additive manufacturing: Physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones

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

Khairallah, Saad A.; Anderson, Andrew T.; Rubenchik, Alexander

Our study demonstrates the significant effect of the recoil pressure and Marangoni convection in laser powder bed fusion (L-PBF) of 316L stainless steel. A three-dimensional high fidelity powder-scale model reveals how the strong dynamical melt flow generates pore defects, material spattering (sparking), and denudation zones. The melt track is divided into three sections: a topological depression, a transition and a tail region, each being the location of specific physical effects. The inclusion of laser ray-tracing energy deposition in the powder-scale model improves over traditional volumetric energy deposition. It enables partial particle melting, which impacts pore defects in the denudation zone.more » Different pore formation mechanisms are observed at the edge of a scan track, at the melt pool bottom (during collapse of the pool depression), and at the end of the melt track (during laser power ramp down). Finally, we discuss remedies to these undesirable pores are discussed. The results are validated against the experiments and the sensitivity to laser absorptivity.« less

Laser powder-bed fusion additive manufacturing: Physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones

DOE PAGES

Khairallah, Saad A.; Anderson, Andrew T.; Rubenchik, Alexander; ...

2016-02-23

Our study demonstrates the significant effect of the recoil pressure and Marangoni convection in laser powder bed fusion (L-PBF) of 316L stainless steel. A three-dimensional high fidelity powder-scale model reveals how the strong dynamical melt flow generates pore defects, material spattering (sparking), and denudation zones. The melt track is divided into three sections: a topological depression, a transition and a tail region, each being the location of specific physical effects. The inclusion of laser ray-tracing energy deposition in the powder-scale model improves over traditional volumetric energy deposition. It enables partial particle melting, which impacts pore defects in the denudation zone.more » Different pore formation mechanisms are observed at the edge of a scan track, at the melt pool bottom (during collapse of the pool depression), and at the end of the melt track (during laser power ramp down). Finally, we discuss remedies to these undesirable pores are discussed. The results are validated against the experiments and the sensitivity to laser absorptivity.« less

Highly ordered, accessible and nanocrystalline mesoporous TiO₂ thin films on transparent conductive substrates.

PubMed

Violi, Ianina L; Perez, M Dolores; Fuertes, M Cecilia; Soler-Illia, Galo J A A

2012-08-01

Highly porous (V(mesopore) = 25-50%) and ordered mesoporous titania thin films (MTTF) were prepared on ITO (indium tin oxide)-covered glass by a fast two-step method. The effects of substrate surface modification and thermal treatment on pore order, accessibility and crystallinity of the MTTF were systematically studied for MTTF deposited onto bare and titania-modified ITO. MTTF exposed briefly to 550 °C resulted in highly ordered films with grid-like structures, enlarged pore size, and increased accessible pore volume when prepared onto the modified ITO substrate. Mesostructure collapse and no significant change in pore volume were observed for MTTF deposited on bare ITO substrates. Highly crystalline anatase was obtained for MTTF prepared on the modified-ITO treated at high temperatures, establishing the relationship between grid-like structures and titania crystallization. Photocatalytic activity was maximized for samples with increased crystallization and high accessible pore volume. In this manner, a simple way of designing materials with optimized characteristics for optoelectronic applications was achieved through the modification of the ITO surface and a controlled thermal treatment.

Internal Stress and Microstructure of Zinc Oxide Films Sputter-Deposited with Carbon Dioxide Gas

NASA Astrophysics Data System (ADS)

Toru Ashida,; Kazuhiro Kato,; Hideo Omoto,; Atsushi Takamatsu,

2010-06-01

The internal stress and microstructure of ZnO films were investigated as a function of carbon dioxide (CO2) gas flow ratio [CO2/(O2+CO2)] during sputter deposition. The internal stress of the ZnO films decreased with increasing CO2 gas flow ratio. The carbon concentration in the films deposited using CO2 gas increased by up to 4.0 at. %. Furthermore, the ZnO films deposited without CO2 gas exhibited a preferred orientation of (002); however, the C-doped ZnO films exhibited random orientations. These findings suggest that the C atoms incorporated in the ZnO crystal lattice induce this random orientation, thereby relaxing the internal stress of C-doped ZnO films.

The Manufacturing of High Porosity Iron with an Ultra-Fine Microstructure via Free Pressureless Spark Plasma Sintering

PubMed Central

Cui, Guodong; Wei, Xialu; Olevsky, Eugene A.; German, Randall M.; Chen, Junying

2016-01-01

High porosity (>40 vol %) iron specimens with micro- and nanoscale isotropic pores were fabricated by carrying out free pressureless spark plasma sintering (FPSPS) of submicron hollow Fe–N powders at 750 °C. Ultra-fine porous microstructures are obtained by imposing high heating rates during the preparation process. This specially designed approach not only avoids the extra procedures of adding and removing space holders during the formation of porous structures, but also triggers the continued phase transitions of the Fe–N system at relatively lower processing temperatures. The compressive strength and energy absorption characteristics of the FPSPS processed specimens are examined here to be correspondingly improved as a result of the refined microstructure. PMID:28773617

Tensile Properties and Microstructure of Inconel 718 Fabricated with Electron Beam Freeform Fabrication (EBF(sup 3))

NASA Technical Reports Server (NTRS)

Bird, R. Keith; Hibberd, Joshua

2009-01-01

Electron beam freeform fabrication (EBF3) direct metal deposition processing was used to fabricate two Inconel 718 single-bead-width wall builds and one multiple-bead-width block build. Specimens were machined to evaluate microstructure and room temperature tensile properties. The tensile strength and yield strength of the as-deposited material from the wall and block builds were greater than those for conventional Inconel 718 castings but were less than those for conventional cold-rolled sheet. Ductility levels for the EBF3 material were similar to those for conventionally-processed sheet and castings. An unexpected result was that the modulus of the EBF3-deposited Inconel 718 was significantly lower than that of the conventional material. This low modulus may be associated with a preferred crystallographic orientation resultant from the deposition and rapid solidification process. A heat treatment with a high solution treatment temperature resulted in a recrystallized microstructure and an increased modulus. However, the modulus was not increased to the level that is expected for Inconel 718.

Characterization and Quantification of the Pore Structures of the Shale Oil Reservoir Formations in Multiscale

NASA Astrophysics Data System (ADS)

Liu, K.; Ostadhassan, M.

2016-12-01

Due to the fast development of hydraulic fracturing and horizontal drilling, shale formations now are one important resource of energy in North America. Characterizing the pore structure of these shale formations is of critical importance in understanding the original oil/gas in place and also the flow properties of the rock matrix. Pore with different properties such as pore size and pore shape can impact the physical, mechanical and chemical properties including strength, elastic modulus, permeability and conductivity. Nowadays, image analysis has been a robust method to quantify the pore information from the porous medium.SEM has been one of the most useful tools to study the pore microstructures due to its high depth of focus which can provide detailed topographical information about the surface. The suitable difference between solid matrix and pores due to the different gray level pixels can be used to study the pore structures.In this paper, we characterized and quantified the pore structures of rock samples from Middle Bakken Formation which is a typical unconventional reservoir in North America. High resolution SEM images of five samples we chose based on the gamma logs were derived after sample preparation. After determining the threshold of the images, we extracted the pore spaces. Then we analyzed the pore structures properties such as pore size distributions and pore shape distributions of the five samples and compared based on their mineral compositions. After that, we analyzed their heterogeneity and isotropy properties which have been identified as an important factor affecting reservoir productivity. Finally, we studied the impact of scale effect on the pore structures characterization.

Effect of microstructure on the detonation initiation in energetic materials

NASA Astrophysics Data System (ADS)

Zhang, J.; Jackson, T. L.

2017-12-01

In this work we examine the role of the microstructure on detonation initiation of energetic materials. We solve the reactive Euler equations, with the energy equation augmented by a power deposition term. The deposition term is based on simulations of void collapse at the microscale, modeled at the mesoscale as hot-spots, while the reaction rate at the mesoscale is modeled using density-based kinetics. We carry out two-dimensional simulations of random packs of HMX crystals in a binder. We show that mean particle size, size distribution, and particle shape have a major effect on the transition between detonation and no-detonation, thus highlighting the importance of the microstructure for shock-induced initiation.

The beneficial effects of straight open large pores in the support on steam electrolysis performance of electrode-supported solid oxide electrolysis cell

NASA Astrophysics Data System (ADS)

Lin, Jie; Chen, Long; Liu, Tong; Xia, Changrong; Chen, Chusheng; Zhan, Zhongliang

2018-01-01

This study is aimed at improving the electrochemical performance of electrode-supported solid oxide electrolysis cells (SOECs) by optimizing the pore structure of the supports. Two planar NiO-8 mol% yttria-stabilized zirconia supports are prepared, one by the phase-inversion tape casting, and the other by conventional tape casting method using graphite as the pore former. The former contains finger-like straight open large pores, while the latter contains randomly distributed and tortuous pores. The steam electrolysis of the cells with different microstructure cathode supports is measured. The cell supported on the cathode with straight pores shows a high current density of 1.42 A cm-2 and a H2 production rate of 9.89 mL (STP) cm-2 min-1 at 1.3 V and 50 vol % humidity and 750 °C, while the cell supported on the cathode with tortuous pores shows a current density of only 0.91 A cm-2 and a H2 production rate of 6.34 mL cm-2min-1. It is concluded that the introduction of large straight open pores into the cathode support allows fast gas phase transport and thus minimizes the concentration polarization. Furthermore, the straight pores could provide better access to the reaction site (the electrode functional layer), thereby reducing the activation polarization as well.

Bioaccessible Porosity in Soil Aggregates and Implications for Biodegradation of High Molecular Weight Petroleum Compounds.

PubMed

Akbari, Ali; Ghoshal, Subhasis

2015-12-15

We evaluated the role of soil aggregate pore size on biodegradation of essentially insoluble petroleum hydrocarbons that are biodegraded primarily at the oil-water interface. The size and spatial distribution of pores in aggregates sampled from biodegradation experiments of a clayey, aggregated, hydrocarbon-contaminated soil with relatively high bioremediation end point were characterized by image analyses of X-ray micro-CT scans and N2 adsorption. To determine the bioaccessible pore sizes, we performed separate experiments to assess the ability of hydrocarbon degrading bacteria isolated from the soil to pass through membranes with specific sized pores and to access hexadecane (model insoluble hydrocarbon). Hexadecane biodegradation occurred only when pores were 5 μm or larger, and did not occur when pores were 3 μm and smaller. In clayey aggregates, ∼ 25% of the aggregate volume was attributed to pores larger than 4 μm, which was comparable to that in aggregates from a sandy, hydrocarbon-contaminated soil (~23%) scanned for comparison. The ratio of volumes of inaccessible pores (<4 μm) to bioaccessible pores (>4 μm) in the clayey aggregates was 0.32, whereas in the sandy aggregates it was approximately 10 times lower. The role of soil microstructure on attainable bioremediation end points could be qualitatively assessed in various soils by the aggregate characterization approach outlined herein.

Bioactive glass-reinforced bioceramic ink writing scaffolds: sintering, microstructure and mechanical behavior.

PubMed

Shao, Huifeng; Yang, Xianyan; He, Yong; Fu, Jianzhong; Liu, Limin; Ma, Liang; Zhang, Lei; Yang, Guojing; Gao, Changyou; Gou, Zhongru

2015-09-10

The densification of pore struts in bioceramic scaffolds is important for structure stability and strength reliability. An advantage of ceramic ink writing is the precise control over the microstructure and macroarchitecture. However, the use of organic binder in such ink writing process would heavily affect the densification of ceramic struts and sacrifice the mechanical strength of porous scaffolds after sintering. This study presents a low-melt-point bioactive glass (BG)-assisted sintering strategy to overcome the main limitations of direct ink writing (extrusion-based three-dimensional printing) and to produce high-strength calcium silicate (CSi) bioceramic scaffolds. The 1% BG-added CSi (CSi-BG1) scaffolds with rectangular pore morphology sintered at 1080 °C have a very small BG content, readily induce apatite formation, and show appreciable linear shrinkage (∼21%), which is consistent with the composite scaffolds with less or more BG contents sintered at either the same or a higher temperature. These CSi-BG1 scaffolds also possess a high elastic modulus (∼350 MPa) and appreciable compressive strength (∼48 MPa), and show significant strength enhancement after exposure to simulated body fluid-a performance markedly superior to those of pure CSi scaffolds. Particularly, the honeycomb-pore CSi-BG1 scaffolds show markedly higher compressive strength (∼88 MPa) than the scaffolds with rectangular, parallelogram, and Archimedean chord pore structures. It is suggested that this approach can potentially facilitate the translation of ceramic ink writing and BG-assisted sintering of bioceramic scaffold technologies to the in situ bone repair.

Fabrication and Characterization of 3D-Printed Highly-Porous 3D LiFePO4 Electrodes by Low Temperature Direct Writing Process

PubMed Central

Cheng, Xingxing; Li, Bohan; Chen, Zhangwei; Mi, Shengli; Lao, Changshi

2017-01-01

LiFePO4 (LFP) is a promising cathode material for lithium-ion batteries. In this study, low temperature direct writing (LTDW)-based 3D printing was used to fabricate three-dimensional (3D) LFP electrodes for the first time. LFP inks were deposited into a low temperature chamber and solidified to maintain the shape and mechanical integrity of the printed features. The printed LFP electrodes were then freeze-dried to remove the solvents so that highly-porous architectures in the electrodes were obtained. LFP inks capable of freezing at low temperature was developed by adding 1,4 dioxane as a freezing agent. The rheological behavior of the prepared LFP inks was measured and appropriate compositions and ratios were selected. A LTDW machine was developed to print the electrodes. The printing parameters were optimized and the printing accuracy was characterized. Results showed that LTDW can effectively maintain the shape and mechanical integrity during the printing process. The microstructure, pore size and distribution of the printed LFP electrodes was characterized. In comparison with conventional room temperature direct ink writing process, improved pore volume and porosity can be obtained using the LTDW process. The electrochemical performance of LTDW-fabricated LFP electrodes and conventional roller-coated electrodes were conducted and compared. Results showed that the porous structure that existed in the printed electrodes can greatly improve the rate performance of LFP electrodes. PMID:28796182

Fabrication and Characterization of 3D-Printed Highly-Porous 3D LiFePO₄ Electrodes by Low Temperature Direct Writing Process.

PubMed

Liu, Changyong; Cheng, Xingxing; Li, Bohan; Chen, Zhangwei; Mi, Shengli; Lao, Changshi

2017-08-10

LiFePO₄ (LFP) is a promising cathode material for lithium-ion batteries. In this study, low temperature direct writing (LTDW)-based 3D printing was used to fabricate three-dimensional (3D) LFP electrodes for the first time. LFP inks were deposited into a low temperature chamber and solidified to maintain the shape and mechanical integrity of the printed features. The printed LFP electrodes were then freeze-dried to remove the solvents so that highly-porous architectures in the electrodes were obtained. LFP inks capable of freezing at low temperature was developed by adding 1,4 dioxane as a freezing agent. The rheological behavior of the prepared LFP inks was measured and appropriate compositions and ratios were selected. A LTDW machine was developed to print the electrodes. The printing parameters were optimized and the printing accuracy was characterized. Results showed that LTDW can effectively maintain the shape and mechanical integrity during the printing process. The microstructure, pore size and distribution of the printed LFP electrodes was characterized. In comparison with conventional room temperature direct ink writing process, improved pore volume and porosity can be obtained using the LTDW process. The electrochemical performance of LTDW-fabricated LFP electrodes and conventional roller-coated electrodes were conducted and compared. Results showed that the porous structure that existed in the printed electrodes can greatly improve the rate performance of LFP electrodes.

Porous Silicon—A Versatile Host Material

PubMed Central

Granitzer, Petra; Rumpf, Klemens

2010-01-01

This work reviews the use of porous silicon (PS) as a nanomaterial which is extensively investigated and utilized for various applications, e.g., in the fields of optics, sensor technology and biomedicine. Furthermore the combination of PS with one or more materials which are also nanostructured due to their deposition within the porous matrix is discussed. Such nanocompounds offer a broad avenue of new and interesting properties depending on the kind of involved materials as well as on their morphology. The filling of the pores performed by electroless or electrochemical deposition is described, whereas different morphologies, reaching from micro- to macro pores are utilized as host material which can be self-organized or fabricated by prestructuring. For metal-deposition within the porous structures, both ferromagnetic and non-magnetic metals are used. Emphasis will be put on self-arranged mesoporous silicon, offering a quasi-regular pore arrangement, employed as template for filling with ferromagnetic metals. By varying the deposition parameters the precipitation of the metal structures within the pores can be tuned in geometry and spatial distribution leading to samples with desired magnetic properties. The correlation between morphology and magnetic behaviour of such semiconducting/magnetic systems will be determined. Porous silicon and its combination with a variety of filling materials leads to nanocomposites with specific physical properties caused by the nanometric size and give rise to a multiplicity of potential applications in spintronics, magnetic and magneto-optic devices, nutritional food additives as well as drug delivery.

Formation and stability of dense arrays of Au nanoclusters on hexagonal boron nitride/Rh(111)

NASA Astrophysics Data System (ADS)

Patterson, Matthew C.; Habenicht, Bradley F.; Kurtz, Richard L.; Liu, Li; Xu, Ye; Sprunger, Phillip T.

2014-05-01

We have studied the nucleation and growth of Au clusters at submonolayer and greater coverages on the h-BN nanomesh grown on Rh(111) by means of scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT). STM reveals that submonolayer Au deposited at 115 K nucleates within the nanomesh pores and remains confined to the pores even after warming to room temperature. Whereas there is a propensity of monoatomic high islands at low temperature, upon annealing, bi- and multilayer Au clusters emerge. Deposition of higher coverages of Au similarly results in Au clusters primarily confined to the nanomesh pores at room temperature. XPS analysis of core-level electronic states in the deposited Au shows strong final-state effects induced by restricted particle size dominating for low Au coverage, with indications that larger Au clusters are negatively charged by interaction through the h-BN monolayer. DFT calculations suggest that the structure of the Au clusters transitions from monolayer to bilayer at a size between 30 and 37 atoms per cluster, in line with our experiment. Bader charge analysis supports the negative charge state of deposited Au.

Effect of Target Density on Microstructural, Electrical, and Optical Properties of Indium Tin Oxide Thin Films

NASA Astrophysics Data System (ADS)

Zhu, Guisheng; Zhi, Li; Yang, Huijuan; Xu, Huarui; Yu, Aibing

2012-09-01

In this paper, indium tin oxide (ITO) targets with different densities were used to deposit ITO thin films. The thin films were deposited from these targets at room temperature and annealed at 750°C. Microstructural, electrical, and optical properties of the as-prepared films were studied. It was found that the target density had no effect on the properties or deposition rate of radiofrequency (RF)-sputtered ITO thin films, different from the findings for direct current (DC)-sputtered films. Therefore, when using RF sputtering, the target does not require a high density and may be reused.

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.

In situ monitoring of atomic layer controlled pore reduction in alumina tubular membranes using sequential surface reactions

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

Berland, B.S.; Gartland, I.P.; Ott, A.W.

1998-12-01

The pore diameter in alumina tubular membranes with an initial diameter of 50 {angstrom} was systematically reduced using the atomic layer controlled deposition of Al{sub 2}O{sub 3}. The Al{sub 2}O{sub 3} was deposited using sequential exposures of Al(CH{sub 3}){sub 3} (trimethylaluminum, TMA) and H{sub 2}O in an ABAB... binary reaction sequence. The pore diameter reduction was monitored using in situ N{sub 2} and Ar conductance measurements. The conductance, C = Q/{Delta}P, was measured using a mass flow controller to define a constant gas throughput, Q, and a pair of capacitance manometers to monitor the transmembrane pressure drop, {Delta}P. Conductance measurementsmore » were periodically obtained at 298 K as a function of AB binary reaction cycles. These conductance measurements were consistent with a pore diameter reduction from 50 {angstrom} to {approximately}5--10 {angstrom} at a rate of {approximately}2.5 {angstrom} for each AB cycle. Conductance measurements were also performed during the Al{sub 2}O{sub 3} deposition at 500 K after each half-reaction in the binary reaction sequence. These in situ conductance measurements demonstrate that the pore diameters in mesoporous membranes can be reduced to molecular dimensions with atomic layer control using sequential surface reactions. Poe diameters can be tailored for specific applications by varying the number of AB cycles and changing the nature of the terminating surface functional groups.« less

Investigating microstructural evolution during the electroreduction of UO2 to U in LiCl-KCl eutectic using focused ion beam tomography

NASA Astrophysics Data System (ADS)

Brown, L. D.; Abdulaziz, R.; Tjaden, B.; Inman, D.; Brett, D. J. L.; Shearing, P. R.

2016-11-01

Reprocessing of spent nuclear fuels using molten salt media is an attractive alternative to liquid-liquid extraction techniques. Pyroelectrochemical processing utilizes direct, selective, electrochemical reduction of uranium dioxide, followed by selective electroplating of a uranium metal. Thermodynamic prediction of the electrochemical reduction of UO2 to U in LiCl-KCl eutectic has shown to be a function of the oxide ion activity. The pO2- of the salt may be affected by the microstructure of the UO2 electrode. A uranium dioxide filled "micro-bucket" electrode has been partially electroreduced to uranium metal in molten lithium chloride-potassium chloride eutectic. This partial electroreduction resulted in two distinct microstructures: a dense UO2 and a porous U metal structure were characterised by energy dispersive X-ray spectroscopy. Focused ion beam tomography was performed on five regions of this electrode which revealed an overall porosity ranging from 17.36% at the outer edge to 3.91% towards the centre, commensurate with the expected extent of reaction in each location. The pore connectivity was also seen to reduce from 88.32% to 17.86% in the same regions and the tortuosity through the sample was modelled along the axis of propagation of the electroreduction, which was seen to increase from a value of 4.42 to a value of infinity (disconnected pores). These microstructural characteristics could impede the transport of O2- ions resulting in a change in the local pO2- which could result in the inability to perform the electroreduction.

Fatigue Performance of Powder Metallurgy (PM) Ti-6Al-4V Alloy: A Critical Analysis of Current Fatigue Data and Metallurgical Approaches for Improving Fatigue Strength

NASA Astrophysics Data System (ADS)

Cao, Fei; Ravi Chandran, K. S.

2016-03-01

A comprehensive assessment of fatigue performance of powder metallurgy (PM) Ti-6Al-4V alloy, manufactured using various powder-based processing approaches to-date, is performed in this work. The focus is on PM processes that use either blended element (BE) or pre-alloyed (PA) powder as feedstock. Porosity and the microstructure condition have been found to be the two most dominant material variables that control the fatigue strength. The evaluation reveals that the fatigue performance of PM Ti-6Al-4V, in the as-sintered state, is far lower than that in the wrought condition. This is largely caused by residual porosity, even if it is present in small amounts, or, by the coarse lamellar colony microstructure. The fatigue strength is significantly improved by the closure of pores, and it approaches the levels of wrought Ti-6Al-4V alloys, after hot-isostatic-pressing (HIPing). Further thermo-mechanical and heat treatments lead to additional increases in fatigue strength-in one case, a high fatigue strength level, exceeding that of the mill-annealed condition, was achieved. The work identifies the powder, process and microstructure improvements that are necessary for achieving high fatigue strength in powder metallurgical Ti-6Al-4V alloys in order for them to effectively compete with wrought forms. The present findings, gathered from the traditional titanium powder metallurgy, are also directly applicable to additively manufactured titanium, because of the similarities in pores, defects, and microstructures between the two manufacturing processes.

Enhanced Performance and Flexibility of Perovskite Solar Cells Based on Microstructured Multilayer Transparent Electrodes.

PubMed

Liu, Xue; Guo, Xiaoyang; Lv, Ying; Hu, Yongsheng; Lin, Jie; Fan, Yi; Zhang, Nan; Liu, Xingyuan

2018-05-30

The performance and flexibility of perovskite solar cells (PSCs) have been enhanced by introducing microstructured WO 3 /Ag/WO 3 (WAW) multilayer transparent electrodes, which can be fabricated through glancing angle deposition (GLAD) method. The structure and morphology of the second WO 3 layers in WAW films can be altered significantly by changing the deposition angles. A film with porous, oriented WO 3 nanocolumns was obtained at the deposition angle of 75°. The rigid and flexible devices based on this microstructured electrodes show enhanced power conversion efficiencies (PCEs) of 14.91 and 13.79%, respectively, which are increasing by 10.36 and 10.14% in comparison with the devices based on the WAW electrodes with planar structure, respectively. Simultaneously, the bending stability of the flexible PSCs based on the microstructured WAW electrode has been improved significantly, which retains 90.97% of its initial PCE after 1000 times bending under the maximum strain of 1.3%, compared with the 78.39% of the reference device with the planar WAW electrode. This can be attributed to the unique microstructure of WAW electrodes fabricated by GLAD methods, releasing the mechanical stresses under repeated bending; moreover, the smaller grains induced by this electrode can disperse the stress, which decrease the damage on the perovskite layer; we believe that this work will pave for the way to improve the performance and flexibility of PSCs.

Microbes and Microstructure: Dust's Role in the Snowpack Evolution

NASA Astrophysics Data System (ADS)

Lieblappen, R.; Courville, Z.; Fegyveresi, J. M.; Barbato, R.; Thurston, A.

2017-12-01

Dust is a primary vehicle for transporting microbial communities to polar and alpine snowpacks both through wind distribution (dry deposition) and snowfall events (wet deposition). The resulting microbial community diversity in the snowpack may then resemble the source material properties rather than its new habitat. Dust also has a strong influence on the microstructural properties of snow, resulting in changes to radiative and mechanical properties. As local reductions in snowpack albedo lead to enhanced melting and a heterogeneous snow surface, the microbial communities are also impacted. Here we study the impact of the changing microstructure in the snowpack, its influence on microbial function, and the fate of dust particles within the snow matrix. We seek to quantify the changes in respiration and water availability with the onset of melt. Polar samples were collected from the McMurdo Ice Shelf, Antarctica in February, 2017, while alpine samples were collected from Silverton, CO from October to May, 2017 as part of the Colorado Dust on Snow (CDOS) network. At each site, coincident meteorological data provides temperature, wind, and radiative measurements. Samples were collected immediately following dust deposition events and after subsequent snowpack evolution. We used x-ray micro-computed tomography to quantify the microstructural evolution of the snow, while also imaging the microstructural distribution of the dust within the snow. The dust was then collected and analyzed for chemical and microbial activity.

Influence of Powder Morphology and Microstructure on the Cold Spray and Mechanical Properties of Ti6Al4V Coatings

NASA Astrophysics Data System (ADS)

Munagala, Venkata Naga Vamsi; Akinyi, Valary; Vo, Phuong; Chromik, Richard R.

2018-06-01

The powder microstructure and morphology has significant influence on the cold sprayability of Ti6Al4V coatings. Here, we compare the cold sprayability and properties of coatings obtained from Ti6Al4V powders of spherical morphology (SM) manufactured using plasma gas atomization and irregular morphology (IM) manufactured using the Armstrong process. Coatings deposited using IM powders had negligible porosity and better properties compared to coatings deposited using SM powders due to higher particle impact velocities, porous surface morphology and more deformable microstructure. To evaluate the cohesive strength, multi-scale indentation was performed and hardness loss parameter was calculated. Coatings deposited using SM powders exhibited poor cohesive strength compared to coatings deposited using IM powders. Images of the residual indents showed de-bonding and sliding of adjacent splats in the coatings deposited using SM powders irrespective of the load. Coatings deposited using IM powders showed no evidence of de-bonding at low loads. At high loads, splat de-bonding was observed resulting in hardness loss despite negligible porosity. Thus, while the powders from Armstrong process lead to a significant improvement in sprayability and coating properties, further optimization of powder and cold spray process will be required as well as consideration of post-annealing treatments to obtain acceptable cohesive strength.

Microstructure, Tensile Adhesion Strength and Thermal Shock Resistance of TBCs with Different Flame-Sprayed Bond Coat Materials Onto BMI Polyimide Matrix Composite

NASA Astrophysics Data System (ADS)

Abedi, H. R.; Salehi, M.; Shafyei, A.

2017-10-01

In this study, thermal barrier coatings (TBCs) composed of different bond coats (Zn, Al, Cu-8Al and Cu-6Sn) with mullite top coats were flame-sprayed and air-plasma-sprayed, respectively, onto bismaleimide matrix composites. These polyimide matrix composites are of interest to replace PMR-15, due to concerns about the toxicity of the MDA monomer from which PMR-15 is made. The results showed that pores and cracks appeared at the bond coat/substrate interface for the Al-bonded TBC because of its high thermal conductivity and diffusivity resulting in transferring of high heat flux and temperature to the polymeric substrate during top coat deposition. The other TBC systems due to the lower conductivity and diffusivity of bonding layers could decrease the adverse thermal effect on the polymer substrate during top coat deposition and exhibited adhesive bond coat/substrate interfaces. The tensile adhesion test showed that the adhesion strength of the coatings to the substrate is inversely proportional to the level of residual stress in the coatings. However, the adhesion strength of Al bond-coated sample decreased strongly after mullite top coat deposition due to thermal damage at the bond coat/substrate interface. TBC system with the Cu-6Sn bond coat exhibited the best thermal shock resistance, while Al-bonded TBC showed the lowest. It was inferred that thermal mismatch stresses and oxidation of the bond coats were the main factors causing failure in the thermal shock test.

The microstructure, mechanical stress, texture, and electromigration behavior of Al-Pd alloys

NASA Astrophysics Data System (ADS)

Rodbell, K. P.; Knorr, D. B.; Mis, J. D.

1993-06-01

As the minimum feature size of interconnect lines decreases below 0.5 urn, the need to control the line microstructure becomes increasingly important. The alloy content, deposition process, fabrication method, and thermal history all determine the microstructure of an interconnect, which, in turn, affects its performance and reliability. The motivation for this work was to characterize the microstructure of various sputtered Al-Pd alloys (Al-0.3wt.%Pd, Al-2Cu-0.3Pd, and Al-0.3Nb-0.3Pd) vs sputtered Al-Cu control samples (Al-0.5Cu and Al-2Cu) and to assess the role of grain size, mechanical stress, and crystallographic texture on the electromigration behavior of submicrometer wide lines. The grain size, mechanical stress, and texture of blanket films were measured as a function of annealing. The as-deposited film stress was tensile and followed a similar stress history on heating for all of the films; on cooling, however, significant differences were observed between the Al-Pd and Al-Cu films in the shape of their stress-temperature-curves. A strong (111) crystallographic texture was typically found for Al-Cu films deposited on SiO2. A stronger (111) texture resulted when Al-Cu was deposited on 25 nm titanium. Al-0.3Pd films, however, exhibited either a weak (111) or (220) texture when deposited on SiO2, which reverted to a strong (111) texture when deposited on 25 nm titanium. The electromigration lifetimes of passivated, ≈0.7 μm wide lines at 250°C and 2.5 × 106 A/cm2 for both single and multi-level samples (separated with W studs) are reported. The electromigration behavior of Al-0.3Pd was found to be less dependent on film microstructure than on the annealing atmosphere used, i.e. forming gas (90% N2-10%H2) annealed Al-0.3Pd films were superior to all of the alloys investigated, while annealing in only N2 resulted in poor lifetimes.

Reactive Infiltration of Silicon Melt Through Microporous Amorphous Carbon Preforms

NASA Technical Reports Server (NTRS)

Sangsuwan, P.; Tewari, S. N.; Gatica, J. E.; Singh, M.; Dickerson, R.

1999-01-01

The kinetics of unidirectional capillary infiltration of silicon melt into microporous carbon preforms have been investigated as a function of the pore morphology and melt temperature. The infiltrated specimens showed alternating bands of dark and bright regions, which corresponded to the unreacted free carbon and free silicon regions, respectively. The decrease in the infiltration front velocity for increasing infiltration distances, is in qualitative agreement with the closed-form solution of capillarity driven fluid flow through constant cross section cylindrical pores. However, drastic changes in the thermal response and infiltration front morphologies were observed for minute differences in the preforms microstructure. This suggests the need for a dynamic percolation model that would account for the exothermic nature of the silicon-carbon chemical reaction and the associated pore closing phenomenon.

Compressive Deformation Behavior of Closed-Cell Micro-Pore Magnesium Composite Foam.

PubMed

Wang, Jing; Wang, Nannan; Liu, Xin; Ding, Jian; Xia, Xingchuan; Chen, Xueguang; Zhao, Weimin

2018-05-04

The closed-cell micro-pore magnesium composite foam with hollow ceramic microspheres (CMs) was fabricated by a modified melt foaming method. The effect of CMs on the compressive deformation behavior of CM-containing magnesium composite foam was investigated. Optical microscopy and scanning electron microscopy were used for observation of the microstructure. Finite element modeling of the magnesium composite foam was established to predict localized stress, fracture of CMs, and the compressive deformation behavior of the foam. The results showed that CMs and pores directly affected the compressive deformation behavior of the magnesium composite foam by sharing a part of load applied on the foam. Meanwhile, the presence of Mg₂Si phase influenced the mechanical properties of the foam by acting as the crack source during the compression process.

Compressive Deformation Behavior of Closed-Cell Micro-Pore Magnesium Composite Foam

PubMed Central

Wang, Jing; Wang, Nannan; Liu, Xin; Ding, Jian; Xia, Xingchuan; Chen, Xueguang; Zhao, Weimin

2018-01-01

The closed-cell micro-pore magnesium composite foam with hollow ceramic microspheres (CMs) was fabricated by a modified melt foaming method. The effect of CMs on the compressive deformation behavior of CM-containing magnesium composite foam was investigated. Optical microscopy and scanning electron microscopy were used for observation of the microstructure. Finite element modeling of the magnesium composite foam was established to predict localized stress, fracture of CMs, and the compressive deformation behavior of the foam. The results showed that CMs and pores directly affected the compressive deformation behavior of the magnesium composite foam by sharing a part of load applied on the foam. Meanwhile, the presence of Mg2Si phase influenced the mechanical properties of the foam by acting as the crack source during the compression process. PMID:29734700

Silicon macroporous arrays with high aspect ratio prepared by ICP etching

NASA Astrophysics Data System (ADS)

Wang, Guozheng; Yang, Bingchen; Wang, Ji; Yang, Jikai; Duanmu, Qingduo

2018-02-01

This paper reports on a macroporous silicon arrays with high aspect ratio, the pores of which are of 162, 205, 252, 276μm depths with 6, 10, 15 and 20 μm diameters respectively, prepared by Multiplex Inductively Coupled Plasma (ICP) etching. It was shown that there are very differences in process of high aspect ratio microstructures between the deep pores, a closed structure, and deep trenches, a open structure. The morphology and the aspect ratio dependent etching were analyzed and discussed. The macroporous silicon etched by ICP process yield an uneven, re-entrant, notched and ripples surface within the pores. The main factors effecting on the RIE lag of HARP etching are the passivation cycle time, the pressure of reactive chamber, and the platen power of ICP system.

Characterizing the Effect of Laser Power on Laser Metal Deposited Titanium Alloy and Boron Carbide

NASA Astrophysics Data System (ADS)

Akinlabi, E. T.; Erinosho, M. F.

2017-11-01

Titanium alloy has gained acceptance in the aerospace, marine, chemical, and other related industries due to its excellent combination of mechanical and corrosion properties. In order to augment its properties, a hard ceramic, boron carbide has been laser cladded with it at varying laser powers between 0.8 and 2.4 kW. This paper presents the effect of laser power on the laser deposited Ti6Al4V-B4C composites through the evolving microstructures and microhardness. The microstructures of the composites exhibit the formation of α-Ti phase and β-Ti phase and were elongated towards the heat affected zone. These phases were terminated at the fusion zone and globular microstructures were found growing epitaxially just immediately after the fusion zone. Good bondings were formed in all the deposited composites. Sample A1 deposited at a laser power of 0.8 kW and scanning speed of 1 m/min exhibits the highest hardness of HV 432 ± 27, while sample A4 deposited at a laser power of 2.0 kW and scanning speed of 1 m/min displays the lowest hardness of HV 360 ± 18. From the hardness results obtained, ceramic B4C has improved the mechanical properties of the primary alloy.

Template assisted synthesis and optical properties of gold nanoparticles.

NASA Astrophysics Data System (ADS)

Fodor, Petru; Lasalvia, Vincenzo

2009-03-01

A hybrid nanofabrication method (interference lithography + self assembly) was explored for the fabrication of arrays of gold nanoparticles. To ensure the uniformity of the nanoparticles, a template assisted synthesis was used in which the gold is electrodeposited in the pores of anodized aluminum membranes. The spacing between the pores and their ordering is controlled in the first fabrication step of the template in which laser lithography and metal deposition are used to produce aluminum films with controlled strain profiles. The diameter of the pores produced after anodizing the aluminum film in acidic solution determines the diameter of the gold particles, while their aspect ratio is controlled through the deposition time. Optical absorbance spectroscopy is used to evaluate the ability to tune the nanoparticles plasmon resonance spectra through control over their size and aspect ratio.

High resolution masks for ion milling pores through substrates of biological interest

NASA Technical Reports Server (NTRS)

Donovan, S. S.

1978-01-01

The feasibility was investigated of electrochemically oxidizing vapor deposited aluminum coatings to produce porous aluminum oxide coatings with submicron pore diameters and with straight channels normal to the substrate surface. Porous aluminum oxide coatings were produced from vapor deposited aluminum coatings on thin stainless steel (304), copper, Teflon (FEP) and Kapton substrates and also on pure aluminum substrates. Scanning electron microscope examination indicated that porous oxide coatings can be produced with straight channels, appropriate pore diameters and none or minimal intervening residual aluminum. The oxide coatings on the copper and Kapton substrates had the straightest channels and in general were superior to those fabricated on the other substrate materials. For oxide coatings fabricated at 600 V and 300 V, pore diameters were 0.4-0.6, and 0.3 micron with center-to-center spacing of 0.7-0.8, and 0.4 micron, respectively. Estimated direct labor and materials costs to prepare an oxide mask is anticipated to be about $4-$6 per square foot.

High capacity hard carbon derived from lotus stem as anode for sodium ion batteries

NASA Astrophysics Data System (ADS)

Zhang, Nan; Liu, Qing; Chen, Weilun; Wan, Min; Li, Xiaocheng; Wang, Lili; Xue, Lihong; Zhang, Wuxing

2018-02-01

Porous hard carbons are synthesized via carbonizing lotus stems with naturally hierarchical structures. The hard carbon carbonized at 1400 °C (LS1400) delivers a total capacity 350 mAh g-1 in the current density of 100 mA g-1 and a plateau capacity of 250 mAh g-1. Even cycled at 100 mA g-1 after 450 cycles, the capacity still retains 94%. Further investigation shows that the sodium storage of LS carbons involves Na+ adsorption in the defect sites, Na+ insertion and Na metal deposition in the closed pores. However, the Na metal deposition in closed pores mainly contribute to the plateau capacity, leading to the excellent sodium storage performance of LS1400 with a large closed pore ratio of 66%. The results show that the intrinsic structure of natural biomass can inspire us to design hard carbon with large closed pore ratio as excellent anode for sodium ion batteries.

Effect of field deposition and pore size on Co/Cu barcode nanowires by electrodeposition

NASA Astrophysics Data System (ADS)

Cho, Ji Ung; Wu, Jun-Hua; Min, Ji Hyun; Lee, Ju Hun; Liu, Hong-Ling; Kim, Young Keun

2007-03-01

We have studied the effect of an external magnetic field applied during electrodeposition of Co/Cu barcode nanowires in anodic aluminum oxide nanotemplates. The magnetic properties of the barcode nanowires were greatly enhanced for 50 nm pore diameter regardless of segment aspect ratio, but field deposition has little effect on the 200 nm nanowires. The magnetic improvement is correlated with a structural change, attributed to field modification of the growth habit of the barcode nanowires. A mechanism of growth subject to geometric confinement is proposed.

Experimental Investigation on Pore Structure Characterization of Concrete Exposed to Water and Chlorides

PubMed Central

Liu, Jun; Tang, Kaifeng; Qiu, Qiwen; Pan, Dong; Lei, Zongru; Xing, Feng

2014-01-01

In this paper, the pore structure characterization of concrete exposed to deionised water and 5% NaCl solution was evaluated using mercury intrusion porosity (MIP), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The effects of calcium leaching, fly ash incorporation, and chloride ions on the evolution of pore structure characteristics were investigated. The results demonstrate that: (i) in ordinary concrete without any fly ash, the leaching effect of the cement products is more evident than the cement hydration effect. From the experimental data, Ca(OH)2 is leached considerably with the increase in immersion time. The pore structure of concrete can also be affected by the formation of an oriented structure of water in concrete materials; (ii) incorporation of fly ash makes a difference for the performance of concrete submersed in solutions as the total porosity and the pore connectivity can be lower. Especially when the dosage of fly ash is up to 30%, the pores with the diameter of larger than 100 nm show significant decrease. It demonstrates that the pore properties are improved by fly ash, which enhances the resistance against the calcium leaching; (iii) chlorides have a significant impact on microstructure of concrete materials because of the chemical interactions between the chlorides and cement hydrates. PMID:28788204

Highly structured and surface modified poly(epsilon-caprolactone) scaffolds derived from co-continuous polymer blends for bone tissue engineering

NASA Astrophysics Data System (ADS)

Mehr, Nima Ghavidel

Chitosan, an important member of the polysaccharide family was used to alter the chemistry of PCL scaffolds and bring hydrophilicity to the surface. The deposition of a homogeneous chitosan layer on the surface of the PCL scaffolds was carried out using a Layer-by-Layer (LbL) selfassembly of poly(dialyldemethylammunium chloride) (PDADMAC) as cationic and poly(sodium 4-styrenesulfonate) (PSS) as anionic polyelectrolytes. The final negatively charged PSS layer allows for the addition of the positively charged chitosan as the outermost layer. Gravimetric measurements revealed that the addition of up to 3 layers leads to the formation of interdiffusing polyelectrolyte layers which do not allow for the formation of defined positive or negative charges. By increasing the number of polyelectrolyte layers with alternating charges, more welldefined layers are formed. Detailed analyses of O/C, N/C and S/C ratios by X-ray photoelectron spectroscopy (XPS) show that the PSS molecule dominates the surface as the last deposited polyelectrolyte layer at higher number of depositions (n=8), which can later be the surface for the deposition of chitosan. The LbL deposition of the chitosan layer on the LbL coating was then shown to be locally homogeneous at different depths within the scaffolds which also clarified that the LbL method is superior to the dip coating strategy. SEM analysis showed that there is a rough chitosan surface on the 2D solid PCL constructs whose thickness ranges from 550-700 nanometers. These results demonstrate that the application of LbL self-assembly of polyelectrolytes followed by the addition of chitosan as the outermost layer provides a route towards stable and homogeneous surface modification and has the potential to transform a classic fully interconnected porous synthetic polymer material to one with essentially complete chitosanlike surface characteristics. The osteogenic potential of PCL scaffolds with a chitosan coating using Layer-by-Layer (LbL) surface modification has never been evaluated before. This part of the study tests the hypothesis that in vitro osteogenesis can be achieved in 3D PCL scaffolds with fully interconnected pores of 84 im or 141 im average diameter and biomineralization can be enhanced when pore surfaces are coated with chitosan adsorbed to LbL deposited polyelectrolytes. In order to reduce the errors originating from cell infiltration inefficiencies, the most competent cell seeding protocol has to be defined. Among classical cell seeding at 37°C, 2-step seeding at 37°C and cold seeding at 4°C in a medium containing 2% FBS, the last strategy proved to yield the best population of freshly trypsinized hBMSCs at all depths of the 1mm-thick scaffolds. hBMSCs cold-seeded in PCL scaffolds with or without an LbL-chitosan coating were cultured for 10 days in proliferation medium, followed by 21 days in osteogenic medium. At day 2, MSCs formed sparse monolayers with rounded cell morphologies with thin filopodia anchored to the unmodified PCL, as compared to more spread cells on chitosan-coated pore surfaces. At day 10, cells proliferated as an external layer, and migrated onto secreted collagen networks that filled the interpore spaces of all scaffolds, but only adhered to chitosan-coated pore surfaces. At day 31, similar levels of tissue formed in scaffolds with and without chitosan, but more tissue was deposited in the outer pores than the inner pores. Furthermore, more biomineralized matrix was observed in the inner 84 im chitosan-coated pores (p<0.05). In the PCL-only samples, haphazard mineral deposits were observed in highly colonized outer layers and in the inner 141 im pores. MSCs cultured on chitosan-coated 2D control surfaces show higher alkaline phosphatase staining but negligible mineralization. This study showed that hBMSCs survive, proliferate, and attach to fibrotic matrix rather than the PCL-only scaffold pore surfaces. LbL-chitosan-coated scaffolds showed more biomineralization in 3D inner 84 im pores, a cell response that may be related to surface curvature in addition to improved surface hydrophilicity. (Abstract shortened by UMI.).

Effect of carbon and manganese on the microstructure and mechanical properties of 9Cr2WVTa deposited metals

NASA Astrophysics Data System (ADS)

Wang, Jian; Rong, Lijian; Li, Dianzhong; Lu, Shanping

2017-03-01

Six 9Cr2WVTa deposited metals with different carbon and manganese contents have been studied to reveal the role of major elements, which guide for the design of welding consumables for reduced activation ferritic/martensitic steel and meet for the requirements of accelerator driven systems-lead fusion reactors. The typical microstructure for the 9Cr2WVTa deposited metals is the lath martensite along with the fine stripe δ-ferrite. The chemical compositions influence the solidification sequence and therefore, change the δ-ferrite content in the deposited metal. The impact toughness for the 9Cr2WVTa deposited metals decreases remarkably when the δ-ferrite content is more than 5.2 vol%, also the impact toughness decreases owing to the high quenching martensite formation. Increasing the level of manganese addition, α phase of each alloy shifts to the bottom right according to the CCT diagram.

In Vitro Cell Proliferation and Mechanical Behaviors Observed in Porous Zirconia Ceramics

PubMed Central

Li, Jing; Wang, Xiaobei; Lin, Yuanhua; Deng, Xuliang; Li, Ming; Nan, Cewen

2016-01-01

Zirconia ceramics with porous structure have been prepared by solid-state reaction using yttria-stabilized zirconia and stearic acid powders. Analysis of its microstructure and phase composition revealed that a pure zirconia phase can be obtained. Our results indicated that its porosity and pore size as well as the mechanical characteristics can be tuned by changing the content of stearic acid powder. The optimal porosity and pore size of zirconia ceramic samples can be effective for the increase of surface roughness, which results in higher cell proliferation values without destroying the mechanical properties. PMID:28773341

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.

Analysis of microstructure in electro-spark deposited IN718 superalloy

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

Anisimov, E.; Khan, A.K.; Ojo, O.A., E-mail: olanr

2016-09-15

The microstructure of electro-spark deposited (ESD) superalloy IN718 was studied by the use of scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) techniques. In converse to general assumption, the extremely high cooling rate involved in the ESD process did not produce partitionless solidification that is devoid of second phase microconstituents in the material, nano-sized Laves phase and MC carbide particles were observed within the deposited layer. Notwithstanding the several thermal cycles involved in the process, the extremely low heat input of the process produced a deposited region that is free ofmore » the main strengthening phase of the alloy, γ″ phase precipitates, which is in contrast to what have been reported on laser deposition. Nevertheless, application of the standard full heat treatment of the alloy resulted in extensive formation of the γ″ phase precipitates and δ phase precipitates, the most stable secondary phase of the alloy, with nearly, if not complete, dissolution of the Laves phase particles. Furthermore, the XPS analysis done in the study revealed the formation of nano-oxides within the deposited layer, which increased the microhardness of the superalloy in the as-deposited condition and inhibited its grain growth during post-process heat treatment. The microstructure analysis done in this work is crucial to the understanding of properties of the superalloy processed by the ESD technique. - Highlights: •Electron microscopy analyses of electro-spark deposited IN 718 superalloy were performed. •Nano-sized secondary phase particles were observed within the deposited layer. •The study shows that the ESD did not produce partitionless solidification of the alloy.« less

Three-dimensional printing of freeform helical microstructures: a review.

PubMed

Farahani, R D; Chizari, K; Therriault, D

2014-09-21

Three-dimensional (3D) printing is a fabrication method that enables creation of structures from digital models. Among the different structures fabricated by 3D printing methods, helical microstructures attracted the attention of the researchers due to their potential in different fields such as MEMS, lab-on-a-chip systems, microelectronics and telecommunications. Here we review different types of 3D printing methods capable of fabricating 3D freeform helical microstructures. The techniques including two more common microfabrication methods (i.e., focused ion beam chemical vapour deposition and microstereolithography) and also five methods based on computer-controlled robotic direct deposition of ink filament (i.e., fused deposition modeling, meniscus-confined electrodeposition, conformal printing on a rotating mandrel, UV-assisted and solvent-cast 3D printings) and their advantages and disadvantages regarding their utilization for the fabrication of helical microstructures are discussed. Focused ion beam chemical vapour deposition and microstereolithography techniques enable the fabrication of very precise shapes with a resolution down to ∼100 nm. However, these techniques may have material constraints (e.g., low viscosity) and/or may need special process conditions (e.g., vacuum chamber) and expensive equipment. The five other techniques based on robotic extrusion of materials through a nozzle are relatively cost-effective, however show lower resolution and less precise features. The popular fused deposition modeling method offers a wide variety of printable materials but the helical microstructures manufactured featured a less precise geometry compared to the other printing methods discussed in this review. The UV-assisted and the solvent-cast 3D printing methods both demonstrated high performance for the printing of 3D freeform structures such as the helix shape. However, the compatible materials used in these methods were limited to UV-curable polymers and polylactic acid (PLA), respectively. Meniscus-confined electrodeposition is a flexible, low cost technique that is capable of fabricating 3D structures both in nano- and microscales including freeform helical microstructures (down to few microns) under room conditions using metals. However, the metals suitable for this technique are limited to those that can be electrochemically deposited with the use of an electrolyte solution. The highest precision on the helix geometry was achieved using the conformal printing on a rotating mandrel. This method offers the lowest shape deformation after printing but requires more tools (e.g., mandrel, motor) and the printed structure must be separated from the mandrel. Helical microstructures made of multifunctional materials (e.g., carbon nanotube nanocomposites, metallic coated polymer template) were used in different technological applications such as strain/load sensors, cell separators and micro-antennas. These innovative 3D microsystems exploiting the unique helix shape demonstrated their potential for better performance and more compact microsystems.

Evolution and Control of 2219 Aluminum Microstructural Features Through Electron Beam Freeform Fabrication

NASA Technical Reports Server (NTRS)

Taminger, Karen M.; Hafley, Robert A.; Domack, Marcia S.

2006-01-01

The layer-additive nature of the electron beam freeform fabrication (EBF3) process results in a tortuous thermal path producing complex microstructures including: small homogeneous equiaxed grains; dendritic growth contained within larger grains; and/or pervasive dendritic formation in the interpass regions of the deposits. Several process control variables contribute to the formation of these different microstructures, including translation speed, wire feed rate, beam current and accelerating voltage. In electron beam processing, higher accelerating voltages embed the energy deeper below the surface of the substrate. Two EBF3 systems have been established at NASA Langley, one with a low-voltage (10-30kV) and the other a high-voltage (30-60 kV) electron beam gun. Aluminum alloy 2219 was processed over a range of different variables to explore the design space and correlate the resultant microstructures with the processing parameters. This report is specifically exploring the impact of accelerating voltage. Of particular interest is correlating energy to the resultant material characteristics to determine the potential of achieving microstructural control through precise management of the heat flux and cooling rates during deposition.

Modeling physical vapor deposition of energetic materials

DOE PAGES

Shirvan, Koroush; Forrest, Eric C.

2018-03-28

Morphology and microstructure of organic explosive films formed using physical vapor deposition (PVD) processes strongly depends on local surface temperature during deposition. Currently, there is no accurate means of quantifying the local surface temperature during PVD processes in the deposition chambers. This study focuses on using a multiphysics computational fluid dynamics tool, STARCCM+, to simulate pentaerythritol tetranitrate (PETN) deposition. The PETN vapor and solid phase were simulated using the volume of fluid method and its deposition in the vacuum chamber on spinning silicon wafers was modeled. The model also included the spinning copper cooling block where the wafers are placedmore » along with the chiller operating with forced convection refrigerant. Implicit time-dependent simulations in two- and three-dimensional were performed to derive insights in the governing physics for PETN thin film formation. PETN is deposited at the rate of 14 nm/s at 142.9 °C on a wafer with an initial temperature of 22 °C. The deposition of PETN on the wafers was calculated at an assumed heat transfer coefficient (HTC) of 400 W/m 2 K. This HTC proved to be the most sensitive parameter in determining the local surface temperature during deposition. Previous experimental work found noticeable microstructural changes with 0.5 mm fused silica wafers in place of silicon during the PETN deposition. This work showed that fused silica slows initial wafer cool down and results in ~10 °C difference for the surface temperature at 500 μm PETN film thickness. It was also found that the deposition surface temperature is insensitive to the cooling power of the copper block due to the copper block's very large heat capacity and thermal conductivity relative to the heat input from the PVD process. Future work should incorporate the addition of local stress during PETN deposition. Lastly, based on simulation results, it is also recommended to investigate the impact of wafer surface energy on the PETN microstructure and morphology formation.« less

Modeling physical vapor deposition of energetic materials

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

Shirvan, Koroush; Forrest, Eric C.

Morphology and microstructure of organic explosive films formed using physical vapor deposition (PVD) processes strongly depends on local surface temperature during deposition. Currently, there is no accurate means of quantifying the local surface temperature during PVD processes in the deposition chambers. This study focuses on using a multiphysics computational fluid dynamics tool, STARCCM+, to simulate pentaerythritol tetranitrate (PETN) deposition. The PETN vapor and solid phase were simulated using the volume of fluid method and its deposition in the vacuum chamber on spinning silicon wafers was modeled. The model also included the spinning copper cooling block where the wafers are placedmore » along with the chiller operating with forced convection refrigerant. Implicit time-dependent simulations in two- and three-dimensional were performed to derive insights in the governing physics for PETN thin film formation. PETN is deposited at the rate of 14 nm/s at 142.9 °C on a wafer with an initial temperature of 22 °C. The deposition of PETN on the wafers was calculated at an assumed heat transfer coefficient (HTC) of 400 W/m 2 K. This HTC proved to be the most sensitive parameter in determining the local surface temperature during deposition. Previous experimental work found noticeable microstructural changes with 0.5 mm fused silica wafers in place of silicon during the PETN deposition. This work showed that fused silica slows initial wafer cool down and results in ~10 °C difference for the surface temperature at 500 μm PETN film thickness. It was also found that the deposition surface temperature is insensitive to the cooling power of the copper block due to the copper block's very large heat capacity and thermal conductivity relative to the heat input from the PVD process. Future work should incorporate the addition of local stress during PETN deposition. Lastly, based on simulation results, it is also recommended to investigate the impact of wafer surface energy on the PETN microstructure and morphology formation.« less

The Manufacturing of High Porosity Iron with an Ultra-Fine Microstructure via Free Pressureless Spark Plasma Sintering

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

Cui, Guodong; Wei, Xialu; Olevsky, Eugene

2016-06-01

High porosity (>40 vol %) iron specimens with micro- and nanoscale isotropic pores were fabricated by carrying out free pressureless spark plasma sintering (FPSPS) of submicron hollow Fe–N powders at 750 °C. Ultra-fine porous microstructures are obtained by imposing high heating rates during the preparation process. This specially designed approach not only avoids the extra procedures of adding and removing space holders during the formation of porous structures, but also triggers the continued phase transitions of the Fe–N system at relatively lower processing temperatures. In conclusion, the compressive strength and energy absorption characteristics of the FPSPS processed specimens are examinedmore » here to be correspondingly improved as a result of the refined microstructure.« less

The effect of surface treatment on the microstructure of the skin of concrete

NASA Astrophysics Data System (ADS)

Sadowski, Łukasz; Stefaniuk, Damian

2018-01-01

The aim of this study is to better understand the heterogeneity and microstructural properties of the skin of concrete. The microstructural evaluation of the skin of concrete was performed using X-ray micro computed tomography (micro-CT). The concrete surface was treated using four methods, due to which different surfaces were obtained, i.e. a raw surface, a surface formed after contact with formwork, a grinded surface and also a shotblasted surface. The results of the pore structure obtained from the micro-CT images were used to assess the influence of selected surface treatment method on the nature of the skin of concrete. It was shown that the thickness and unique nature of the skin of concrete differ for various surface treatment methods.

Improving Ionic Conductivity and Lithium-Ion Transference Number in Lithium-Ion Battery Separators.

PubMed

Zahn, Raphael; Lagadec, Marie Francine; Hess, Michael; Wood, Vanessa

2016-12-07

The microstructure of lithium-ion battery separators plays an important role in separator performance; however, here we show that a geometrical analysis falls short in predicting the lithium-ion transport in the electrolyte-filled pore space. By systematically modifying the surface chemistry of a commercial polyethylene separator while keeping its microstructure unchanged, we demonstrate that surface chemistry, which alters separator-electrolyte interactions, influences ionic conductivity and lithium-ion transference number. Changes in separator surface chemistry, particularly those that increase lithium-ion transference numbers can reduce voltage drops across the separator and improve C-rate capability.

X-ray Computed Microtomography technique applied for cementitious materials: A review.

PubMed

da Silva, Ítalo Batista

2018-04-01

The main objective of this article is to present a bibliographical review about the use of the X-ray microtomography method in 3D images processing of cementitious materials microstructure, analyzing the pores microstructure and connectivity network, enabling tthe possibility of building a relationship between permeability and porosity. The use of this technique enables the understanding of physical, chemical and mechanical properties of cementitious materials by publishing good results, considering that the quality and quantity of accessible information were significant and may contribute to the study of cementitious materials development. Copyright © 2018 Elsevier Ltd. All rights reserved.

Comparison between PCL/hydroxyapatite (HA) and PCL/halloysite nanotube (HNT) composite scaffolds prepared by co-extrusion and gas foaming.

PubMed

Jing, Xin; Mi, Hao-Yang; Turng, Lih-Sheng

2017-03-01

In this work, three-dimensional poly(caprolactone) (PCL) tissue engineering scaffolds were prepared by co-extrusion and gas foaming. Biocompatible hydroxyapatite (HA) and halloysite nanotubes (HNT) were added to the polymer matrix to enhance the mechanical properties and bioactivity of the composite scaffolds. The effects of HA and HNT on the rheological behavior, microstructure, and mechanical properties of the composite scaffolds were systematically compared. It was found that the HNT improved viscosity more significantly than HA, and reduced the pore size of scaffolds, while the mechanical performance of PCL/HNT scaffolds was higher than PCL/HA scaffolds with the same filler content. Human mesenchymal stem cells (hMSCs) were used as the cell model to compare the biological properties of two composite scaffolds. The results demonstrated that cells could survive on all scaffolds, and showed a more flourishing living state on the composite scaffolds. The cell differentiation for 5% HA and 1% HNT scaffolds were significantly higher than other scaffolds, while the differentiation of 5% HNT scaffolds was lower than that of 1% HNT scaffolds mainly because of the reduced pore size and pore interconnectivity. Therefore, this study suggested that, with proper filler content and control of microstructure through processing, HNT could be a suitable substitute for HA for bone tissue engineering to reduce the cost and improve mechanical performance. Copyright © 2016. Published by Elsevier B.V.

Analysis of 3D Prints by X-ray Computed Microtomography and Terahertz Pulsed Imaging.

PubMed

Markl, Daniel; Zeitler, J Axel; Rasch, Cecilie; Michaelsen, Maria Høtoft; Müllertz, Anette; Rantanen, Jukka; Rades, Thomas; Bøtker, Johan

2017-05-01

A 3D printer was used to realise compartmental dosage forms containing multiple active pharmaceutical ingredient (API) formulations. This work demonstrates the microstructural characterisation of 3D printed solid dosage forms using X-ray computed microtomography (XμCT) and terahertz pulsed imaging (TPI). Printing was performed with either polyvinyl alcohol (PVA) or polylactic acid (PLA). The structures were examined by XμCT and TPI. Liquid self-nanoemulsifying drug delivery system (SNEDDS) formulations containing saquinavir and halofantrine were incorporated into the 3D printed compartmentalised structures and in vitro drug release determined. A clear difference in terms of pore structure between PVA and PLA prints was observed by extracting the porosity (5.5% for PVA and 0.2% for PLA prints), pore length and pore volume from the XμCT data. The print resolution and accuracy was characterised by XμCT and TPI on the basis of the computer-aided design (CAD) models of the dosage form (compartmentalised PVA structures were 7.5 ± 0.75% larger than designed; n = 3). The 3D printer can reproduce specific structures very accurately, whereas the 3D prints can deviate from the designed model. The microstructural information extracted by XμCT and TPI will assist to gain a better understanding about the performance of 3D printed dosage forms.

Deposition of Composite LSCF-SDC and SSC-SDC Cathodes by Axial-Injection Plasma Spraying

NASA Astrophysics Data System (ADS)

Harris, Jeffrey; Qureshi, Musab; Kesler, Olivera

2012-06-01

The performance of solid oxide fuel cell cathodes can be improved by increasing the number of electrochemical reaction sites, by controlling microstructures, or by using composite materials that consist of an ionic conductor and a mixed ionic and electronic conductor. LSCF (La0.6Sr0.4Co0.2Fe0.8O3-δ) and SSC (Sm0.5Sr0.5CoO3) cathodes were manufactured by axial-injection atmospheric plasma spraying, and composite cathodes were fabricated by mixing SDC (Ce0.8Sm0.2O1.9) into the feedstock powders. The plasma power was varied by changing the proportion of nitrogen in the plasma gas. The microstructures of cathodes produced with different plasma powers were characterized by scanning electron microscopy and gas permeation measurements. The deposition efficiencies of these cathodes were calculated based on the mass of the sprayed cathode. Particle surface temperatures were measured in-flight to enhance understanding of the relationship between spray parameters, microstructure, and deposition efficiency.

Effective Parameters in Axial Injection Suspension Plasma Spray Process of Alumina-Zirconia Ceramics

NASA Astrophysics Data System (ADS)

Tarasi, F.; Medraj, M.; Dolatabadi, A.; Oberste-Berghaus, J.; Moreau, C.

2008-12-01

Suspension plasma spray (SPS) is a novel process for producing nano-structured coatings with metastable phases using significantly smaller particles as compared to conventional thermal spraying. Considering the complexity of the system there is an extensive need to better understand the relationship between plasma spray conditions and resulting coating microstructure and defects. In this study, an alumina/8 wt.% yttria-stabilized zirconia was deposited by axial injection SPS process. The effects of principal deposition parameters on the microstructural features are evaluated using the Taguchi design of experiment. The microstructural features include microcracks, porosities, and deposition rate. To better understand the role of the spray parameters, in-flight particle characteristics, i.e., temperature and velocity were also measured. The role of the porosity in this multicomponent structure is studied as well. The results indicate that thermal diffusivity of the coatings, an important property for potential thermal barrier applications, is barely affected by the changes in porosity content.

Porous substrates filled with nanomaterials

DOEpatents

Worsley, Marcus A.; Baumann, Theodore F.; Satcher, Jr., Joe H.; Stadermann, Michael

2018-04-03

A composition comprising: at least one porous carbon monolith, such as a carbon aerogel, comprising internal pores, and at least one nanomaterial, such as carbon nanotubes, disposed uniformly throughout the internal pores. The nanomaterial can be disposed in the middle of the monolith. In addition, a method for making a monolithic solid with both high surface area and good bulk electrical conductivity is provided. A porous substrate having a thickness of 100 microns or more and comprising macropores throughout its thickness is prepared. At least one catalyst is deposited inside the porous substrate. Subsequently, chemical vapor deposition is used to uniformly deposit a nanomaterial in the macropores throughout the thickness of the porous substrate. Applications include electrical energy storage, such as batteries and capacitors, and hydrogen storage.

Porous substrates filled with nanomaterials

DOEpatents

Worsley, Marcus A.; Baumann, Theodore F.; Satcher, Jr., Joe H.; Stadermann, Michael

2014-08-19

A composition comprising: at least one porous carbon monolith, such as a carbon aerogel, comprising internal pores, and at least one nanomaterial, such as carbon nanotubes, disposed uniformly throughout the internal pores. The nanomaterial can be disposed in the middle of the monolith. In addition, a method for making a monolithic solid with both high surface area and good bulk electrical conductivity is provided. A porous substrate having a thickness of 100 microns or more and comprising macropores throughout its thickness is prepared. At least one catalyst is deposited inside the porous substrate. Subsequently, chemical vapor deposition is used to uniformly deposit a nanomaterial in the macropores throughout the thickness of the porous substrate. Applications include electrical energy storage, such as batteries and capacitors, and hydrogen storage.

An Analytical Solution and Numerical Modeling Study of Gas Hydrate Saturation Effects on Porosity and Permeability of Porous Media

NASA Astrophysics Data System (ADS)

Zerpa, L.; Gao, F.; Wang, S.

2017-12-01

There are two major types of natural gas hydrate distributions in porous media: pore filling and contact cementing. The difference between these two distribution types is related to hydrate nucleation and growth processes. In the pore filling distribution, hydrate nucleates from a gas-dissolved aqueous phase at the grain boundary and grows away from grain contacts and surfaces into the pore space. In the contact cementing distribution, hydrate nucleates and grows at the gas-water interface and at intergranular contacts. Previous attempts to correlate changes on porosity and permeability during hydrate formation/dissociation were based on the length difference between the pore body and pore throat, and only considered contact cementing hydrate distribution. This work consists of a study of mathematical models of permeability and porosity as a function of gas hydrate saturation during formation and dissociation of gas hydrates in porous media. In this work, first we derive the permeability equation for the pore filling hydrate deposition as a function of hydrate saturation. Then, a more comprehensive model considering both types of gas hydrate deposition is developed to represent changes in permeability and porosity during hydrate formation and dissociation. This resulted in a model that combines pore filling and contact cementing deposition types in the same reservoir. Finally, the TOUGH+Hydrate numerical reservoir simulator was modified to include these models to analyze the response of production and saturation during a depressurization process, considering different combinations of pore filling and contact cementing hydrate distributions. The empirical exponent used in the permeability adjustment factor model influences both production profile and saturation results. This empirical factor describes the permeability dependence to changes in porosity caused by solid phase formation in the porous medium. The use of the permeability exponent decreases the permeability of the system for a given hydrate saturation, which affects the hydraulic performance of the system. However, from published experimental work, there is only a rough estimation of this permeability exponent. This factor could be represented with an empirical equation if more laboratory and field data becomes available.

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

Viani, Alberto, E-mail: viani@itam.cas.cz; Sotiriadis, Konstantinos; Len, Adél

Full characterization of fired-clay bricks is crucial for the improvement of process variables in manufacturing and, in case of old bricks, for restoration/replacement purposes. To this aim, five bricks produced in a plant in Czech Republic in the past have been investigated with a combination of analytical techniques in order to derive information on the firing process. An additional old brick from another brickyard was also used to study the influence of different raw materials on sample microstructure. The potential of X-ray diffraction with the Rietveld method and small angle neutron scattering technique has been exploited to describe the phasemore » transformations taking place during firing and characterize the brick microstructure. Unit-cell parameter of spinel and amount of hematite are proposed as indicators of the maximum firing temperature, although for the latter, limited to bricks produced from the same raw material. The fractal quality of the surface area of pores obtained from small angle neutron scattering is also suggested as a method to distinguish between bricks produced from different raw clays. - Highlights: • Rietveld method helps in describing microstructure and physical properties of bricks. • XRPD derived cell parameter of spinel is proposed as an indicator of firing temperature. • SANS effectively describes brick micro and nanostructure, including closed porosity. • Fractal quality of pore surface is proposed as ‘fingerprint’ of brick manufacturing.« less

Organic pi-stacking Semiconducting Material: Design, Synthesis and the Analysis of Structure and Properties

NASA Astrophysics Data System (ADS)

Wilkinson, Taylor Marie

Oil shales are naturally occurring heterogeneous composites with micro-scale, micro-structural variations. They may be found throughout the world, with large deposits located in the United States; shales are composed of organic matter known as kerogen, clays, calcite, quartz, and other minerals. Typically their microstructure consists of a composite network where the organic matter is housed in open and closed pores between different mineral phases that range in size from sub-micron to several microns. Currently, it is unknown how the micro-scale heterogeneity of the shale will impact hydraulic fracture, which is the key extraction technique used for these materials. In this thesis, high-resolution topographic and modulus maps were collected from oil shales with the use of new nanoindentation techniques in order to characterize the micro-scale, micro-structural variations that are typical for these materials. Dynamic modulus mapping allows for substantially higher spatial resolution of properties across grains and intragranular regions of kerogen than has previously been produced with standard quasistatic indentation methods. For accurate scanning, surface variations were minimized to maintain uniform contact of the tip and appropriate quasi-static and dynamic forces were used to maintain displacement amplitudes that avoid plastic deformation of the sample. Sample preparation to minimize surface roughness was completed with the use of focused ion beam milling, however, some variation was still noted. Due to the large changes in modulus values between the constituents of the shale, there were variations in the recorded displacement amplitude values as well. In order to distinguish biased data due to surface topography or a lack of displacement amplitude, filtering techniques were developed, optimization and implemented. Variations in surface topography, which resulted in the indenter tip not being able to accurately resolve surface features, and inadequate displacement amplitude values that prohibit differentiation between material changes and the noise floor of the machine, were removed. These filters resulted in a more valid interpretation of the micro-scale, micro-structural features and arrangement, as well as the mechanical properties, that are common to oil shales.

Surface modification of nanoporous alumina layers by deposition of Ag nanoparticles. Effect of alumina pore diameter on the morphology of silver deposit and its influence on SERS activity

NASA Astrophysics Data System (ADS)

Pisarek, Marcin; Nowakowski, Robert; Kudelski, Andrzej; Holdynski, Marcin; Roguska, Agata; Janik-Czachor, Maria; Kurowska-Tabor, Elżbieta; Sulka, Grzegorz D.

2015-12-01

Self-organized Al2O3 nanoporous/nanotubular (Al2O3-NP) oxide layers decorated with silver nanoparticles (Ag-NPs) exhibiting specific properties may serve as attractive SERS substrates for investigating the interactions between an adsorbate and adsorbent, or as stable platforms for detecting various organic compounds. This article presents the influence of the size of the alumina nanopores with a deposit of silver nanoparticles obtained by the magnetron sputtering technique on the morphology of silver film. Moreover, the effect of pore diameter on the intensity of SERS spectra in Ag-NPs/Al2O3-NP/Al composites has also been estimated. For such investigations we used pyridine as a probe molecule, since it has a large cross-section for Raman scattering. To characterize the morphology of the composite oxide layer Ag-NPs/Al2O3-NP/Al, before and after deposition of Ag-NPs by PVD methods (Physical Vapor Deposition), we used scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface analytical technique of surface-enhanced Raman spectroscopy (SERS) was used to investigate the surface activity of the composite. The results obtained show that, for a carefully controlled amount of Ag (0.020 mg/cm2 - deposited on the top of alumina nanopores whose average size varies from ∼86 nm up to ∼320 nm) in the composites investigated, pore size significantly affects SERS enhancement. We obtained distinctly higher intensities of SERS spectra for substrates with an Ag-NPs deposit having a larger diameter of the alumina nanopores. AFM results suggest that both the lateral and perpendicular distribution of Ag-NPs within and on the top of the largest pores is responsible for the highest SERS activity of the resulting Ag-NPs/Al2O3-NP/Al composite layer, since it produces a variety of cavities and slits which function as resonators for the adsorbed molecules. The Ag-NPs/MeOx-NP/Me composite layers obtained ensure a good reproducibility of the SERS measurements.

Microstructural control over soluble pentacene deposited by capillary pen printing for organic electronics.

PubMed

Lee, Wi Hyoung; Min, Honggi; Park, Namwoo; Lee, Junghwi; Seo, Eunsuk; Kang, Boseok; Cho, Kilwon; Lee, Hwa Sung

2013-08-28

Research into printing techniques has received special attention for the commercialization of cost-efficient organic electronics. Here, we have developed a capillary pen printing technique to realize a large-area pattern array of organic transistors and systematically investigated self-organization behavior of printed soluble organic semiconductor ink. The capillary pen-printed deposits of organic semiconductor, 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS_PEN), was well-optimized in terms of morphological and microstructural properties by using ink with mixed solvents of chlorobenzene (CB) and 1,2-dichlorobenzene (DCB). Especially, a 1:1 solvent ratio results in the best transistor performances. This result is attributed to the unique evaporation characteristics of the TIPS_PEN deposits where fast evaporation of CB induces a morphological evolution at the initial printed position, and the remaining DCB with slow evaporation rate offers a favorable crystal evolution at the pinned position. Finally, a large-area transistor array was facilely fabricated by drawing organic electrodes and active layers with a versatile capillary pen. Our approach provides an efficient printing technique for fabricating large-area arrays of organic electronics and further suggests a methodology to enhance their performances by microstructural control of the printed organic semiconducting deposits.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Influence of the total gas flow rate on high rate growth microcrystalline silicon films and solar cells

NASA Astrophysics Data System (ADS)

Han, Xiao-Yan; Hou, Guo-Fu; Zhang, Xiao-Dan; Wei, Chang-Chun; Li, Gui-Jun; Zhang, De-Kun; Chen, Xin-Liang; Sun, Jian; Zhang, Jian-Jun; Zhao, Ying; Geng, Xin-Hua

2009-08-01

This paper reports that high-rate-deposition of microcrystalline silicon solar cells was performed by very-high-frequency plasma-enhanced chemical vapor deposition. These solar cells, whose intrinsic μc-Si:H layers were prepared by using a different total gas flow rate (Ftotal), behave much differently in performance, although their intrinsic layers have similar crystalline volume fraction, opto-electronic properties and a deposition rate of ~ 1.0 nm/s. The influence of Ftotal on the micro-structural properties was analyzed by Raman and Fourier transformed infrared measurements. The results showed that the vertical uniformity and the compact degree of μc-Si:H thin films were improved with increasing Ftotal. The variation of the microstructure was regarded as the main reason for the difference of the J-V parameters. Combined with optical emission spectroscopy, we found that the gas temperature plays an important role in determining the microstructure of thin films. With Ftotal of 300 sccm, a conversion efficiency of 8.11% has been obtained for the intrinsic layer deposited at 8.5 Å/s (1 Å = 0.1 nm).

Microstructure based model for sound absorption predictions of perforated closed-cell metallic foams.

PubMed

Chevillotte, Fabien; Perrot, Camille; Panneton, Raymond

2010-10-01

Closed-cell metallic foams are known for their rigidity, lightness, thermal conductivity as well as their low production cost compared to open-cell metallic foams. However, they are also poor sound absorbers. Similarly to a rigid solid, a method to enhance their sound absorption is to perforate them. This method has shown good preliminary results but has not yet been analyzed from a microstructure point of view. The objective of this work is to better understand how perforations interact with closed-cell foam microstructure and how it modifies the sound absorption of the foam. A simple two-dimensional microstructural model of the perforated closed-cell metallic foam is presented and numerically solved. A rough three-dimensional conversion of the two-dimensional results is proposed. The results obtained with the calculation method show that the perforated closed-cell foam behaves similarly to a perforated solid; however, its sound absorption is modulated by the foam microstructure, and most particularly by the diameters of both perforation and pore. A comparison with measurements demonstrates that the proposed calculation method yields realistic trends. Some design guides are also proposed.

In Situ Electrosynthesis of Polymethyl Methacrylate Within Ceramic Launch Pad Materials

NASA Technical Reports Server (NTRS)

Acevedo, Raul; Cardenas, Henry

2012-01-01

Electrokinetic deposition of methylmethacrylate is used to mitigate corrosion in reinforced concrete. The methylmethacrylate (MMA) monomer deposits in the pores in the concrete where it is converted into its polymer, polymethylmethacrylate, thus creating a barrier that also enhances the mechanical properties of the concrete. Previous to the MMA treatment an Electrokinetic deposition is used to transport calcium, sodium and potassium hydroxide particles through the capillary pores of concrete directly to the concrete reinforcement. The intent is to use these compounds as a sacrificial electrode layer during the electrokinetic deposition of methylmethacrylate monomer. Cylindrical reinforced concrete specimens were subjected to electrokinetic treatment and the specimens were tested to characterize porosity reduction and tensile splitting strength showing an increase in the tensile strength. In addition, nine specimens treated electro-kinetically and in long-term atmospheric exposure testing at NASA's Kennedy Space Center, seaside atmospheric exposure test site were tested to determine their corrosion rate.

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.

Effect of the three-dimensional microstructure on the sound absorption of foams: A parametric study.

PubMed

Chevillotte, Fabien; Perrot, Camille

2017-08-01

The purpose of this work is to systematically study the effect of the throat and the pore sizes on the sound absorbing properties of open-cell foams. The three-dimensional idealized unit cell used in this work enables to mimic the acoustical macro-behavior of a large class of cellular solid foams. This study is carried out for a normal incidence and also for a diffuse field excitation, with a relatively large range of sample thicknesses. The transport and sound absorbing properties are numerically studied as a function of the throat size, the pore size, and the sample thickness. The resulting diagrams show the ranges of the specific throat sizes and pore sizes where the sound absorption grading is maximized due to the pore morphology as a function of the sample thickness, and how it correlates with the corresponding transport parameters. These charts demonstrate, together with typical examples, how the morphological characteristics of foam could be modified in order to increase the visco-thermal dissipation effects.

Influence of laser irradiation on deposition characteristics of cold sprayed Stellite-6 coatings

NASA Astrophysics Data System (ADS)

Li, Bo; Jin, Yan; Yao, Jianhua; Li, Zhihong; Zhang, Qunli; Zhang, Xin

2018-03-01

Depositing hard materials such as Stellite-6 solely by cold spray (CS) is challengeable due to limited ability of plastic deformation. In this study, the deposition of Stellite-6 powder was achieved by supersonic laser deposition (SLD) which combines CS with synchronous laser irradiation. The surface morphology, deposition efficiency, track shape of Stellite-6 coatings produced over a range of laser irradiation temperatures were examined so as to reveal the effects of varying laser energy inputting on the deposition process of high strength material. The microstructure, phase composition and wear/corrosion resistant properties of the as-deposited Stellite-6 coatings were also investigated. The experimental results demonstrate that the surface flatness and deposition efficiency increase with laser irradiation temperature due to the softening effect induced by laser heating. The as-deposited Stellite-6 tracks show asymmetric shapes which are influenced by the relative configuration of powder stream and laser beam. The SLD coatings can preserve the original microstructure and phase of the feedstock material due to relatively low laser energy inputting, which result in the superior wear/corrosion resistant properties as compared to the counterpart prepared by laser cladding.

Metal/ceramic composites via infiltration of an interconnected wood-derived ceramic

NASA Astrophysics Data System (ADS)

Wilkes, Thomas E.

The use of composites is increasing as they afford scientists and engineers the ability to combine the advantageous properties of each constituent phase, e.g. metal ductility and ceramic stiffness. With respect to materials design, biomimetics is garnering increasing attention due to the complex, yet efficient, natural microstructures. One such biomimetic, or in this case 'bio-derived,' curiosity is wood-derived ceramic, which is made by either replicating or converting wood into a ceramic. The resulting porous and anisotropic material retains the precursor microstructure. The wide variety of precursors can yield materials with a range of pore sizes and distribution of pores. The purpose of this work was to study the processing, microstructure, and properties of aluminum/silicon carbide composites. The composites were made by infiltrating molten aluminum into porous wood-derived SIC, which was produced by the reactive melt-infiltration of silicon into pyrolyzed wood. The composite microstructure consisted of interconnected SiC surrounding Al-alloy 'fibers.' The strength, modulus, and toughness were measured in both longitudinal and transverse orientations. The Al → SiC load transfer was investigated with high-energy X-ray diffraction in combination with in-situ compressive loading. The properties in flexure were found to decrease with increasing temperature. Despite the complex microstructure, predictions of the composite flexural modulus and longitudinal fracture toughness were obtained using simple models: Halpin-Tsai bounds and the Ashby et al. model of the effect of ductile particle-reinforcements on the toughness of brittle materials (Ashby et al. 1989), respectively. In addition, the Al/SiC research inspired the investigation of carbon-reinforced copper composites. The goal was to explore the feasibility of making a high-thermal conductivity composite by infiltrating copper into wood-derived carbon. Results indicated that Cu/C composites could be made with pressurized infiltration, but the predicted thermal conductivity was low due to the amorphous wood-derived carbon.

Stability of phase transformation models for Ti-6Al-4V under cyclic thermal loading imposed during laser metal deposition

NASA Astrophysics Data System (ADS)

Klusemann, Benjamin; Bambach, Markus

2018-05-01

Processing conditions play a crucial role for the resulting microstructure and properties of the material. In particular, processing materials under non-equilibrium conditions can lead to a remarkable improvement of the final properties [1]. Additive manufacturing represents a specific process example considered in this study. Models for the prediction of residual stresses and microstructure in additive manufacturing processes, such as laser metal deposition, are being developed with huge efforts to support the development of materials and processes as well as to support process design [2-4]. Since the microstructure predicted after each heating and cooling cycle induced by the moving laser source enters the phase transformation kinetics and microstucture evolution of the subsequent heating and cooling cycle, a feed-back loop for the microstructure calculation is created. This calculation loop may become unstable so that the computed microstructure and related properties become very sensitive to small variations in the input parameters, e.g. thermal conductivity. In this paper, a model for phase transformation in Ti-6Al-4V, originally proposed by Charles Murgau et al. [5], is adopted and minimal adjusted concerning the decomposition of the martensite phase are made. This model is subsequently used to study the changes in the predictions of the different phase volume fractions during heating and cooling under the conditions of laser metal deposition with respect to slight variations in the thermal process history.

Physicochemical and microstructural characterisation of green gram and foxtail millet starch gels.

PubMed

Nagaprabha, P; Devisetti, Rajesh; Bhattacharya, Sila

2018-02-01

The starch and starch gels from green gram (GG) and foxtail millet (FM) were characterised for their physicochemical, thermal and microstructural characteristics; the features of shape and size were determined by image analysis. Both GG and FM formed well-set gels at 9% concentration of starch. The fracture strain of the gels was between 78 and 80% indicating non-brittle gels. The peak temperatures of the native flour of GG (74.9 °C) and FM (75.7 °C) were significantly higher than their corresponding starch samples (72.2 and 75.0 °C). The conclusion temperatures of the FM native flour (81.2 °C) and starch (79.4 °C) samples were higher than the native GG flour (79.9 °C) and GG starch (77.1 °C) samples. Starches were nearly spherical as the roundness values were between 0.88 and 0.95. Green gram starch was pentagonal having an average diameter of 3.9-9.2 µm while foxtail millet starch was spherical with a diameter of 4.9-10.1 µm. The freeze-dried GG and FM starch gels showed cellular structure containing organised hexagonal pores, bound by thin pore walls; the GG starch gels deviated from the circular shape as they had the highest elongation value of 4.21. The thicker pore walls were observed for GG starch gels (0.88 μm) compared to that of FM samples (0.57 μm). The higher pore wall thickness in the case of GG gel showed the formation of junction zones.

Synthesis of functional ceramic supports by ice templating and atomic layer deposition

NASA Astrophysics Data System (ADS)

Klotz, Michaela; Weber, Matthieu; Deville, Sylvain; Oison, Didier; Iatsunskyi, Igor; Coy, Emerson; Bechelany, Mikhael

2018-05-01

In this work, we report an innovative route for the manufacturing of functional ceramic supports, by combining ice templating of yttria stabilized zirconia (YSZ) and atomic layer deposition (ALD) of Al2O3 processes. Ceramic YSZ monoliths are prepared using the ice-templating process, which is based on the controlled crystallization of water following a thermal gradient. Sublimation of the ice and the sintering of the material reveal the straight micrometer sized pores shaped by the ice crystal growth. The high temperature sintering allows for the ceramic materials to present excellent mechanical strength and porosities of 67%. Next, the conformality benefit of ALD is used to deposit an alumina coating at the surface of the YSZ pores, in order to obtain a functional material. The Al2O3 thin films obtained by ALD are 100 nm thick and conformally deposited within the macroporous ceramic supports, as shown by SEM and EDS analysis. Mercury intrusion experiments revealed a reduction of the entrance pore diameter, in line with the growth per cycle of 2 Å of the ALD process. In addition to the manufacture of the innovative ceramic nanomaterials, this article also describes the fine characterization of the coatings obtained using mercury intrusion, SEM and XRD analysis.

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

Burnett, W.C.

Hundreds of islands in the tropical Pacific Ocean contain phosphate deposits ranging from inconsequential to economically significant in size. Although many of these deposits clearly have formed by the interaction of avian guano with underlying limestone, some display evidence of having developed within an aqueous environment. Several of the emergent carbonate islands in the southern part of Palau contain phosphate deposits that the authors speculate formed in anoxic marine lakes, similar to those which still occur on a few of these islands. Lake water, sediments, and sediment pore waters from Jellyfish Lake, on the island of Eil Malk in Palau,more » were analyzed during an expedition in 1987. The results of this investigation supported, but did not provide, conclusive evidence of our hypothesis. Pore water profiles of phosphate and fluoride confirmed precipitation of carbonate fluorapatite. However, the extremely high bulk sediment accumulation rate, driven by the high biological productivity of the surface waters of the lake, dilutes authigenic phosphate to low levels. They have refined their original proposal to suggest that phosphate deposits may form either by: (1) subaerial weathering and concentration of phosphatic sediments after these lakes disappear; or (2) interaction of phosphate-enriched sediment pore solutions with limestone at the underlying contact. Another expedition to test these concepts is being planned.« less

An Alternative Cu-Based Bond Layer for Electric Arc Coating Process

NASA Astrophysics Data System (ADS)

Fadragas, Carlos R.; Morales, E. V.; Muñoz, J. A.; Bott, I. S.; Lariot Sánchez, C. A.

2011-12-01

A Cu-Al alloy has been used as bond coat between a carbon steel substrate and a final coating deposit obtained by applying the twin wire electric arc spraying coating technique. The presence of a copper-based material in the composite system can change the overall temperature profile during deposition because copper exhibits a thermal conductivity several times higher than that of the normally recommended bond coat materials (such as nickel-aluminum alloys or nickel-chromium alloys). The microstructures of 420 and 304 stainless steels deposited by the electric arc spray process have been investigated, focusing attention on the deposit homogeneity, porosity, lamellar structure, and microhardness. The nature of the local temperature gradient during deposition can strongly influence the formation of the final coating deposit. This study presents a preliminary study, undertaken to investigate the changes in the temperature profile which occur when a Cu-Al alloy is used as bond coat, and the possible consequences of these changes on the microstructure and adhesion of the final coating deposit. The influence of the thickness of the bond layer on the top coating temperature has also been also evaluated.

Three dimensional rock microstructures: insights from FIB-SEM tomography

NASA Astrophysics Data System (ADS)

Drury, Martyn; Pennock, Gill; de Winter, Matthijs

2016-04-01

Most studies of rock microstructures investigate two-dimensional sections or thin slices of three dimensional grain structures. With advances of X-ray and electron tomography methods the 3-D microstructure can be(relatively) routinely investigated on scales from a few microns to cm. 3D studies are needed to investigate the connectivity of microstructures and to test the assumptions we use to calculate 3D properties from 2D sections. We have used FIB-SEM tomography to study the topology of melts in synthetic olivine rocks, 3D crystal growth microstructures, pore networks and subgrain structures. The technique uses a focused ion beam to make serial sections with a spacing of tens to hundreds of nanometers. Each section is then imaged or mapped using the electron beam. The 3D geometry of grains and subgrains can be investigated using orientation contrast or EBSD mapping. FIB-SEM tomography of rocks and minerals can be limited by charging of the uncoated surfaces exposed by the ion beam. The newest generation of FIB-SEMs have much improved low voltage imaging capability allowing high resolution charge free imaging. Low kV FIB-SEM tomography is now widely used to study the connectivity of pore networks. In-situ fluids can also be studied using cryo-FIB-SEM on frozen samples, although special freezing techniques are needed to avoid artifacts produced by ice crystallization. FIB-SEM tomography is complementary, in terms of spatial resolution and sampled volume, to TEM tomography and X-ray tomography, and the combination of these methods can cover a wide range of scales. Our studies on melt topology in synthetic olivine rocks with a high melt content show that many grain boundaries are wetted by nanometre scale melt layers that are too thin to resolve by X-ray tomography. A variety of melt layer geometries occur consistent with several mechanisms of melt layer formation. The nature of melt geometries along triple line junctions and quadruple points can be resolved. Quadruple point junctions between four grains cannot be investigated in 2D studies. 3D microstructural studies suggest that triple lines and quadruple points are important sites for the initiation of recrystallization, reaction and fracture.

Air plasma spray processing and electrochemical characterization of SOFC composite cathodes

NASA Astrophysics Data System (ADS)

White, B. D.; Kesler, O.; Rose, Lars

Air plasma spraying has been used to produce porous composite cathodes containing (La 0.8Sr 0.2) 0.98MnO 3- y (LSM) and yttria-stabilized zirconia (YSZ) for use in solid oxide fuel cells (SOFCs). Preliminary investigations focused on determining the range of plasma conditions under which each of the individual materials could be successfully deposited. A range of conditions was thereby determined that was suitable for the deposition of a composite cathode from pre-mixed LSM and YSZ powders. A number of composite cathodes were produced using different combinations of parameter values within the identified range according to a Uniform Design experimental grid. Coatings were then characterized for composition and microstructure using EDX and SEM. As a result of these tests, combinations of input parameter values were identified that are best suited to the production of coatings with microstructures appropriate for use in SOFC composite cathodes. A selection of coatings representative of the types of observed microstructures were then subjected to electrochemical testing to evaluate the performance of these cathodes. From these tests, it was found that, in general, the coatings that appeared to have the most suitable microstructures also had the highest electrochemical performances, provided that the deposition efficiency of both phases was sufficiently high.

Effect of sintering temperature on the microstructure and properties of foamed glass-ceramics prepared from high-titanium blast furnace slag and waste glass

NASA Astrophysics Data System (ADS)

Chen, Chang-hong; Feng, Ke-qin; Zhou, Yu; Zhou, Hong-ling

2017-08-01

Foamed glass-ceramics were prepared via a single-step sintering method using high-titanium blast furnace slag and waste glass as the main raw materials The influence of sintering temperature (900-1060°C) on the microstructure and properties of foamed glass-ceramics was studied. The results show that the crystal shape changed from grainy to rod-shaped and finally turned to multiple shapes as the sintering temperature was increased from 900 to 1060°C. With increasing sintering temperature, the average pore size of the foamed glass-ceramics increased and subsequently decreased. By contrast, the compressive strength and the bulk density decreased and subsequently increased. An excessively high temperature, however, induced the coalescence of pores and decreased the compressive strength. The optimal properties, including the highest compressive strength (16.64 MPa) among the investigated samples and a relatively low bulk density (0.83 g/cm3), were attained in the case of the foamed glass-ceramics sintered at 1000°C.

Fabrication and Characterization of Porous MgAl₂O₄ Ceramics via a Novel Aqueous Gel-Casting Process.

PubMed

Yuan, Lei; Liu, Zongquan; Liu, Zhenli; He, Xiao; Ma, Beiyue; Zhu, Qiang; Yu, Jingkun

2017-11-30

A novel and aqueous gel-casting process has been successfully developed to fabricate porous MgAl₂O₄ ceramics by using hydratable alumina and MgO powders as raw materials and deionized water as hydration agent. The effects of different amounts of deionized water on the hydration properties, apparent porosity, bulk density, microstructure, pore size distribution and compressive strength of the samples were investigated. The results indicated that the porosity and the microstructure of porous MgAl₂O₄ ceramics were governed by the amounts of deionized water added. The porous structure was formed by the liberation of physisorbed water and the decomposition of hydration products such as bayerite, brucite and boehmite. After determining the addition amounts of deionized water, the fabricated porous MgAl₂O₄ ceramics had a high apparent porosity (52.5-65.8%), a small average pore size structure (around 1-3 μm) and a relatively high compressive strength (12-28 MPa). The novel aqueous gel-casting process with easy access is expected to be a promising candidate for the preparation of Al₂O₃-based porous ceramics.

Microstructure, Mechanical Properties and Corrosion Behavior of Porous Mg-6 wt.% Zn Scaffolds for Bone Tissue Engineering

NASA Astrophysics Data System (ADS)

Yan, Yang; Kang, Yijun; Li, Ding; Yu, Kun; Xiao, Tao; Wang, Qiyuan; Deng, Youwen; Fang, Hongjie; Jiang, Dayue; Zhang, Yu

2018-03-01

Porous Mg-based scaffolds have been extensively researched as biodegradable implants due to their attractive biological and excellent mechanical properties. In this study, porous Mg-6 wt.% Zn scaffolds were prepared by powder metallurgy using ammonium bicarbonate particles as space-holder particles. The effects of space-holder particle content on the microstructure, mechanical properties and corrosion resistance of the Mg-6 wt.% Zn scaffolds were studied. The mean porosity and pore size of the open-cellular scaffolds were within the range 6.7-52.2% and 32.3-384.2 µm, respectively. Slight oxidation was observed at the grain boundaries and on the pore walls. The Mg-6 wt.% Zn scaffolds were shown to possess mechanical properties comparable with those of natural bone and had variable in vitro degradation rates. Increased content of space-holder particles negatively affected the mechanical behavior and corrosion resistance of the Mg-6 wt.% Zn scaffolds, especially when higher than 20%. These results suggest that porous Mg-6 wt.% Zn scaffolds are promising materials for application in bone tissue engineering.

HA/nylon 6,6 porous scaffolds fabricated by salt-leaching/solvent casting technique: effect of nano-sized filler content on scaffold properties

PubMed Central

Mehrabanian, Mehran; Nasr-Esfahani, Mojtaba

2011-01-01

Nanohydroxyapatite (n-HA)/nylon 6,6 composite scaffolds were produced by means of the salt-leaching/solvent casting technique. NaCl with a distinct range size was used with the aim of optimizing the pore network. Composite powders with different n-HA contents (40%, 60%) for scaffold fabrication were synthesized and tested. The composite scaffolds thus obtained were characterized for their microstructure, mechanical stability and strength, and bioactivity. The microstructure of the composite scaffolds possessed a well-developed interconnected porosity with approximate optimal pore size ranging from 200 to 500 μm, ideal for bone regeneration and vascularization. The mechanical properties of the composite scaffolds were evaluated by compressive strength and modulus tests, and the results confirmed their similarity to cortical bone. To characterize bioactivity, the composite scaffolds were immersed in simulated body fluid for different lengths of time and results monitored by scanning electron microscopy and energy dispersive X-ray microanalysis to determine formation of an apatite layer on the scaffold surface. PMID:21904455

Resistance of class C fly ash belite cement to simulated sodium sulphate radioactive liquid waste attack.

PubMed

Guerrero, A; Goñi, S; Allegro, V R

2009-01-30

The resistance of class C fly ash belite cement (FABC-2-W) to concentrated sodium sulphate salts associated with low level wastes (LLW) and medium level wastes (MLW) is discussed. This study was carried out according to the Koch and Steinegger methodology by testing the flexural strength of mortars immersed in simulated radioactive liquid waste rich in sulphate (48,000 ppm) and demineralised water (used as a reference), at 20 degrees C and 40 degrees C over a period of 180 days. The reaction mechanisms of sulphate ion with the mortar was carried out through a microstructure study, which included the use of Scanning electron microscopy (SEM), porosity and pore-size distribution and X-ray diffraction (XRD). The results showed that the FABC mortar was stable against simulated sulphate radioactive liquid waste (SSRLW) attack at the two chosen temperatures. The enhancement of mechanical properties was a result of the formation of non-expansive ettringite inside the pores and an alkaline activation of the hydraulic activity of cement promoted by the ingress of sulphate. Accordingly, the microstructure was strongly refined.

Optimizing Discharge Capacity of Li-O 2 Batteries by Design of Air-Electrode Porous Structure: Multifidelity Modeling and Optimization

DOE PAGES

Pan, Wenxiao; Yang, Xiu; Bao, Jie; ...

2017-01-01

We develop a new mathematical framework to study the optimal design of air electrode microstructures for lithium-oxygen (Li-O2) batteries. It can eectively reduce the number of expensive experiments for testing dierent air-electrodes, thereby minimizing the cost in the design of Li-O2 batteries. The design parameters to characterize an air-electrode microstructure include the porosity, surface-to-volume ratio, and parameters associated with the pore-size distribution. A surrogate model (also known as response surface) for discharge capacity is rst constructed as a function of these design parameters. The surrogate model is accurate and easy to evaluate such that an optimization can be performed basedmore » on it. In particular, a Gaussian process regression method, co-kriging, is employed due to its accuracy and eciency in predicting high-dimensional responses from a combination of multidelity data. Specically, a small amount of data from high-delity simulations are combined with a large number of data obtained from computationally ecient low-delity simulations. The high-delity simulation is based on a multiscale modeling approach that couples the microscale (pore-scale) and macroscale (device-scale) models. Whereas, the low-delity simulation is based on an empirical macroscale model. The constructed response surface provides quantitative understanding and prediction about how air electrode microstructures aect the discharge performance of Li-O2 batteries. The succeeding sensitivity analysis via Sobol indices and optimization via genetic algorithm ultimately oer a reliable guidance on the optimal design of air electrode microstructures. The proposed mathematical framework can be generalized to investigate other new energy storage techniques and materials.« less

Optimizing Discharge Capacity of Li-O 2 Batteries by Design of Air-Electrode Porous Structure: Multifidelity Modeling and Optimization

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

Pan, Wenxiao; Yang, Xiu; Bao, Jie

We develop a new mathematical framework to study the optimal design of air electrode microstructures for lithium-oxygen (Li-O2) batteries. It can eectively reduce the number of expensive experiments for testing dierent air-electrodes, thereby minimizing the cost in the design of Li-O2 batteries. The design parameters to characterize an air-electrode microstructure include the porosity, surface-to-volume ratio, and parameters associated with the pore-size distribution. A surrogate model (also known as response surface) for discharge capacity is rst constructed as a function of these design parameters. The surrogate model is accurate and easy to evaluate such that an optimization can be performed basedmore » on it. In particular, a Gaussian process regression method, co-kriging, is employed due to its accuracy and eciency in predicting high-dimensional responses from a combination of multidelity data. Specically, a small amount of data from high-delity simulations are combined with a large number of data obtained from computationally ecient low-delity simulations. The high-delity simulation is based on a multiscale modeling approach that couples the microscale (pore-scale) and macroscale (device-scale) models. Whereas, the low-delity simulation is based on an empirical macroscale model. The constructed response surface provides quantitative understanding and prediction about how air electrode microstructures aect the discharge performance of Li-O2 batteries. The succeeding sensitivity analysis via Sobol indices and optimization via genetic algorithm ultimately oer a reliable guidance on the optimal design of air electrode microstructures. The proposed mathematical framework can be generalized to investigate other new energy storage techniques and materials.« less

A combined microstructural and petrophysical study to analyse the mechanical behaviour of shales in the Flysch units, Glarus Alps, Switzerland

NASA Astrophysics Data System (ADS)

Akker, Vénice; Kaufmann, Josef; Berger, Alfons; Herwegh, Marco

2017-04-01

Crustal scale deformation is strongly controlled by the rheological behaviour of sheet-silicate-rich rock types. As these rocks have low rock strength, facilitated by the strong crystallographically controlled mechanical anisotropy and interstitial pore fluid in the aggregate, they are able to accommodate considerable amounts of strain. A close relationship is expected between microstructure, porosity and permeability as function of metamorphic conditions and strain gradients. Thereby, fluids set free by compaction, mineral reactions or deformation play an important role. Rising industries in underground storage such as nuclear waste disposal, shale gas exploration or geological carbon sequestration make use of the advantageous properties of such rock types. Therefore, there is a great demand for research on the interaction of these processes. This study uses samples from Flysch-units of the Glarus Alps (Switzerland) collected along a metamorphic gradient (150-400°C) to unravel the link between the mechanical behaviour of these sheet-silicate-rich rocks at geological conditions and their present-day physical parameters. Investigations include two topics: (1) characterization of such rock types in terms of mineralogy, microstructure and petrophysical properties; and (2) possible reconstruction of deformation processes from microstructures. Quantitative information on the porosity, i.e. the pore sizes, distribution and their interconnectivity is crucial for both topics. Porosity is therefore estimated by: (1) image analysis of high resolution SEM images, (2) He-pycnometry, and (3) Hg-porosimetry. In a first step, differences in their present day physical parameters between low and high temperature sampling sites are shown. The variations inside and between the investigated samples is partly due to initial sedimentological heterogeneity and partly to the changes along the metamorphic gradient. This study will demonstrate how the characterized present day porosity evolved owing to these two prerequisites.

Nitrogen doped RGO-Co3O4 nanograin cookies: highly porous and robust catalyst for removing nitrophenol from waste water

NASA Astrophysics Data System (ADS)

Pervaiz, Erum; Syam Azhar Virk, Muhammad; Bingxue, Zhang; Yin, Conglin; Yang, Minghui

2017-09-01

The fabrication of nanograins with a uniform morphology wrapped with reduced graphene oxide (RGO) in a designed manner is critical for obtaining a large surface, high porosity and efficient catalytic ability at mild conditions. Hybrid structures of metal oxides decorated on two-dimensional (2D) RGO lacked an interface and channels between the individual grains and RGO. The present work focuses on the synthesis of RGO-wrapped Co3O4 nanograin architecture in micron-sized polyhedrons and the ability to reduce aromatic nitro compounds. Doping N in the designed microstructure polyhedrons resulted in very large surface area (1085.6 m2 g-1) and pore density (0.47 m3 g-1) microcages. Binding energies from x-ray photoelectron spectroscopy (XPS) and Raman intensities confirmed the presence of doped N and RGO-wrapped around Co3O4 nanograins. However, the morphology and microstructure was supported by FESEM and HRTEM images revealing the fabrication of high integrity RGO-Co3O4 microstructure hybrids composed of a 10 nm grain size with narrower grain size distribution. Ammonia treatment produced interconnected channels and dumbbell pores that facilitated ion exchange between the catalyst surface and the liquid medium at the grain boundary interfaces, and offered less mass transport resistance providing fast adsorption of reactants and desorption of the product causing surface renewal. Prepared N-RGO-Co3O4 shows the largest percentage reduction (96%) of p-nitrophenol (p-NP) at room temperature as compared to pure Co3O4 and RGO-Co3O4 nanograin microstructures over 10 min. Fabricated architectures can be applied effectively for fast and facile treatment of industrial waste streams with complex organic molecules.

Effect of Starch on Sintering Behavior for Fabricating Porous Cordierite Ceramic

NASA Astrophysics Data System (ADS)

Li, Ye; Cao, Wei; Gong, Lunlun; Zhang, Ruifang; Cheng, Xudong

2016-10-01

Porous cordierite ceramics were prepared with starch as pore-forming agent by solid-state method. The green bodies were sintered at 1,100-1,400 °C for 2 h. The characterization was focused on thermal analysis, phase evolution, sintering behavior, porosity and micro-structural changes. The results show that cordierite becomes the main crystallization phase at 1,200 °C. The shrinkage behavior shows the most obvious dependence on the sintering temperature and starch content, and it can be divided into three stages. Moreover, the open porosity increases with the increase of starch content, but the pore-forming effectivity decreases. Nevertheless, compared with the open porosity curves, the bulk density curves are more in line with the linear rule. The microphotographs show the densification process with the sintering temperature and the variation of pore connectivity with the starch content.

Gravitational Effects on Closed-Cellular-Foam Microstructure

NASA Technical Reports Server (NTRS)

Noever, David A.; Cronise, Raymond J.; Wessling, Francis C.; McMannus, Samuel P.; Mathews, John; Patel, Darayas

1996-01-01

Polyurethane foam has been produced in low gravity for the first time. The cause and distribution of different void or pore sizes are elucidated from direct comparison of unit-gravity and low-gravity samples. Low gravity is found to increase the pore roundness by 17% and reduce the void size by 50%. The standard deviation for pores becomes narrower (a more homogeneous foam is produced) in low gravity. Both a Gaussian and a Weibull model fail to describe the statistical distribution of void areas, and hence the governing dynamics do not combine small voids in either a uniform or a dependent fashion to make larger voids. Instead, the void areas follow an exponential law, which effectively randomizes the production of void sizes in a nondependent fashion consistent more with single nucleation than with multiple or combining events.

Growth control of carbon nanotubes using by anodic aluminum oxide nano templates.

PubMed

Park, Yong Seob; Choi, Won Seek; Yi, Junsin; Lee, Jaehyeong

2014-05-01

Anodic Aluminum Oxide (AAO) template prepared in acid electrolyte possess regular and highly anisotropic porous structure with pore diameter range from five to several hundred nanometers, and with a density of pores ranging from 10(9) to 10(11) cm(-2). AAO can be used as microfilters and templates for the growth of CNTs and metal or semiconductor nanowires. Varying anodizing conditions such as temperature, electrolyte, applied voltage, anodizing and widening time, one can control the diameter, the length, and the density of pores. In this work, we deposited Al thin film by radio frequency magnetron sputtering method to fabricate AAO nano template and synthesized multi-well carbon nanotubes on a glass substrate by microwave plasma-enhanced chemical vapor deposition (MPECVD). AAO nano-porous templates with various pore sizes and depths were introduced to control the dimension and density of CNT arrays. The AAO nano template was synthesize on glass by two-step anodization technique. The average diameter and interpore distance of AAO nano template are about 65 nm and 82 nm. The pore density and AAO nano template thickness are about 2.1 x 10(10) pores/cm2 and 1 microm, respectively. Aligned CNTs on the AAO nano template were synthesized by MPECVD at 650 degrees C with the Ni catalyst layer. The length and diameter of CNTs were grown 2 microm and 50 nm, respectively.

A study on the effects of temperature and substrate structure on the templated two-phase film growth via a hybrid model

NASA Astrophysics Data System (ADS)

Lu, Xiao; Li, Jia; Zhu, Jian-Gang; Laughlin, David E.; Zhu, Jingxi

2018-06-01

Templated growth of two-phase thin films can achieve desirably ordered microstructures. In such cases, the microstructure of the growing films follows the topography of the template. By combining the Potts model Monte Carlo simulation and the "level set" method, an attempt was previously made to understand the physical mechanism behind the templated growth process. In the current work, this model is further used to study the effect of two parameters within the templated growth scenario, namely, the temperature and the geometric features of the template. The microstructure of the thin film grown with different lattice temperatures and domes is analyzed. It is found that within a moderate temperature range, the effect of geometric features took control of the ordering of the microstructure by its influence on the surface energy gradient. Interestingly, within this temperature range, as the temperature is increased, an ordered microstructure forms on a template without the optimal geometric features, which seems to be a result of competition between the kinetics and the thermodynamics during deposition. However, when the temperature was either above or below this temperature range, the template provided no guide to the whole deposition so that no ordered microstructure formed.

An investigation into the effects of pore connectivity on T2 NMR relaxation

NASA Astrophysics Data System (ADS)

Ghomeshi, Shahin; Kryuchkov, Sergey; Kantzas, Apostolos

2018-04-01

Nuclear Magnetic Resonance (NMR) is a powerful technique used to characterize fluids and flow in porous media. The NMR relaxation curves are closely related to pore geometry, and the inversion of the NMR relaxometry data is known to give useful information with regards to pore size distribution (PSD) through the relative amplitudes of the fluids stored in the small and large pores. While this information is crucial, the main challenge for the successful use of the NMR measurements is the proper interpretation of the measured signals. Natural porous media patterns consist of complex pore structures with many interconnected or "coupled" regions, as well as isolated pores. This connectivity along the throats changes the relaxation distribution and in order to properly interpret this data, a thorough understanding of the effects of pore connectivity on the NMR relaxation distribution is warranted. In this paper we address two main points. The first pertains to the fact that there is a discrepancy between the relaxation distribution obtained from experiments, and the ones obtained from solving the mathematical models of diffusion process in the digitized images of the pore space. There are several reasons that may attribute to this such as the lack of a proper incorporation of surface roughness into the model. However, here we are more interested in the effects of pore connectivity and to understand why the typical NMR relaxation distribution obtained from experiments are wider, while the numerical simulations predict that a wider NMR relaxation distribution may indicate poor connectivity. Secondly, by not taking into account the pore coupling effects, from our experience in interpreting the data, we tend to underestimate the pore volume of small pores and overestimate the amplitudes in the large pores. The role of pore coupling becomes even more prominent in rocks with small pore sizes such as for example in shales, clay in sandstones, and in the microstructures of carbonates.

Microstructure characterisation of Ti-6Al-4V from different additive manufacturing processes

NASA Astrophysics Data System (ADS)

Neikter, M.; Åkerfeldt, P.; Pederson, R.; Antti, M.-L.

2017-10-01

The focus of this work has been microstructure characterisation of Ti-6Al-4V manufactured by five different additive manufacturing (AM) processes. The microstructure features being characterised are the prior β size, grain boundary α and α lath thickness. It was found that material manufactured with powder bed fusion processes has smaller prior β grains than the material from directed energy deposition processes. The AM processes with fast cooling rate render in thinner α laths and also thinner, and in some cases discontinuous, grain boundary α. Furthermore, it has been observed that material manufactured with the directed energy deposition processes has parallel bands, except for one condition when the parameters were changed, while the powder bed fusion processes do not have any parallel bands.

Comparative Analysis of the Microstructural Features of 28 wt.% Cr Cast Iron Fabricated by Pulsed Plasma Deposition and Conventional Casting

NASA Astrophysics Data System (ADS)

Chabak, Yu. G.; Efremenko, V. G.; Shimizu, K.; Lekatou, A.; Pastukhova, T. V.; Azarkhov, A. Yu.; Zurnadzhy, V. I.

2018-02-01

The effect of pulsed plasma deposition (by an electrothermal axial plasma accelerator) followed by post-heat treatment on the structure and microhardness of a 28 wt.% Cr white cast iron is analyzed and discussed with respect to the microstructure of the conventionally cast monolithic counterpart. The cast iron (as deposited on a 14 wt.% Cr cast iron substrate) had a microhardness of 630-750 HV0.05; it had layered light contrast/dark contrast structure where dark contrast layers contain fine carbide network. Pulsed plasma deposition followed by heat treatment resulted in a substantial refinement of the microstructure: eutectic M7C3 coarse acicular plates in the conventional cast iron were replaced by fine M7C3, M3C2, M3C particles (Cr depleted in favor of Fe), while the initial carbide particle of 2-3 μm was reduced to 0.6 μm. Secondary dendrite arm spacing decreased from 15 to 1.3 μm, accordingly. The carbide volume fraction in the post-heat-treated coating remarkably increased with respect to the conventional counterpart resulting in a substantial increase in the coating hardness (1300-1750 HV0.05). The heat-treated coating displayed higher resistance to three-body abrasion than the as-deposited coating and similar resistance with that of the conventionally cast iron.

Quantifying microstructural dynamics and electrochemical activity of graphite and silicon-graphite lithium ion battery anodes

NASA Astrophysics Data System (ADS)

Pietsch, Patrick; Westhoff, Daniel; Feinauer, Julian; Eller, Jens; Marone, Federica; Stampanoni, Marco; Schmidt, Volker; Wood, Vanessa

2016-09-01

Despite numerous studies presenting advances in tomographic imaging and analysis of lithium ion batteries, graphite-based anodes have received little attention. Weak X-ray attenuation of graphite and, as a result, poor contrast between graphite and the other carbon-based components in an electrode pore space renders data analysis challenging. Here we demonstrate operando tomography of weakly attenuating electrodes during electrochemical (de)lithiation. We use propagation-based phase contrast tomography to facilitate the differentiation between weakly attenuating materials and apply digital volume correlation to capture the dynamics of the electrodes during operation. After validating that we can quantify the local electrochemical activity and microstructural changes throughout graphite electrodes, we apply our technique to graphite-silicon composite electrodes. We show that microstructural changes that occur during (de)lithiation of a pure graphite electrode are of the same order of magnitude as spatial inhomogeneities within it, while strain in composite electrodes is locally pronounced and introduces significant microstructural changes.

Effects of aging treatment and heat input on the microstructures and mechanical properties of TIG-welded 6061-T6 alloy joints

NASA Astrophysics Data System (ADS)

Peng, Dong; Shen, Jun; Tang, Qin; Wu, Cui-ping; Zhou, Yan-bing

2013-03-01

Aging treatment and various heat input conditions were adopted to investigate the microstructural evolution and mechanical properties of TIG welded 6061-T6 alloy joints by microstructural observations, microhardness tests, and tensile tests. With an increase in heat input, the width of the heat-affected zone (HAZ) increases and grains in the fusion zone (FZ) coarsen. Moreover, the hardness of the HAZ decreases, whereas that of the FZ decreases initially and then increases with an increase in heat input. Low heat input results in the low ultimate tensile strength of the welded joints due to the presence of partial penetrations and pores in the welded joints. After a simple artificial aging treatment at 175°C for 8 h, the microstructure of the welded joints changes slightly. The mechanical properties of the welded joints enhance significantly after the aging process as few precipitates distribute in the welded seam.

Pore Structure Characterization of Sodium Hydroxide Activated Slag Using Mercury Intrusion Porosimetry, Nitrogen Adsorption, and Image Analysis.

PubMed

Zuo, Yibing; Ye, Guang

2018-06-19

The pore structure of alkali-activated slag has a significant influence on its performance. However, the literature shows insufficient studies regarding the suitability of different techniques for characterizing the pore structure and the influences of Na₂O and curing age on pore structure development. In pursuit of a better understanding, the pore structure of sodium hydroxide activated slag paste was characterized by multiple techniques, e.g., mercury intrusion porosimetry (MIP), nitrogen (N₂) adsorption, and scanning electron microscopy (SEM) image analysis. The sodium hydroxide activated slag pastes were prepared with three different contents of Na₂O (Na₂O/slag = 4, 6, and 8%) and cured for different times up to 360 days. The microstructure observation reveals that outer C⁻(N⁻)A⁻S⁻H and inner C⁻(N⁻)A⁻S⁻H grow successively around the reacting slag grains, along with crystalline reaction products which are formed in the empty coarse pore space. The increase of Na₂O content and curing age lead to a finer pore structure. The MIP measurements show that the total porosity drops about 70% within the first day, and that one peak at most, corresponding to gel pores, was identified in the differential curves of all the investigated samples from 1 to 360 days. On the contrary, only one peak, corresponding to capillary pores, was identified by SEM-image analysis. The differential curves derived from N₂ adsorption generally reveal two peaks, and the trend that the pore diameters of those two peaks vary with curing age depends on the content of Na₂O. Compared to Portland cement, sodium hydroxide activated slag has a higher pore space filling capacity ( χ , V products / V slag-reacted ), while the capacity decreases with increasing Na₂O content and curing age.

Mean apparent propagator (MAP) MRI: a novel diffusion imaging method for mapping tissue microstructure.

PubMed

Özarslan, Evren; Koay, Cheng Guan; Shepherd, Timothy M; Komlosh, Michal E; İrfanoğlu, M Okan; Pierpaoli, Carlo; Basser, Peter J

2013-09-01

Diffusion-weighted magnetic resonance (MR) signals reflect information about underlying tissue microstructure and cytoarchitecture. We propose a quantitative, efficient, and robust mathematical and physical framework for representing diffusion-weighted MR imaging (MRI) data obtained in "q-space," and the corresponding "mean apparent propagator (MAP)" describing molecular displacements in "r-space." We also define and map novel quantitative descriptors of diffusion that can be computed robustly using this MAP-MRI framework. We describe efficient analytical representation of the three-dimensional q-space MR signal in a series expansion of basis functions that accurately describes diffusion in many complex geometries. The lowest order term in this expansion contains a diffusion tensor that characterizes the Gaussian displacement distribution, equivalent to diffusion tensor MRI (DTI). Inclusion of higher order terms enables the reconstruction of the true average propagator whose projection onto the unit "displacement" sphere provides an orientational distribution function (ODF) that contains only the orientational dependence of the diffusion process. The representation characterizes novel features of diffusion anisotropy and the non-Gaussian character of the three-dimensional diffusion process. Other important measures this representation provides include the return-to-the-origin probability (RTOP), and its variants for diffusion in one- and two-dimensions-the return-to-the-plane probability (RTPP), and the return-to-the-axis probability (RTAP), respectively. These zero net displacement probabilities measure the mean compartment (pore) volume and cross-sectional area in distributions of isolated pores irrespective of the pore shape. MAP-MRI represents a new comprehensive framework to model the three-dimensional q-space signal and transform it into diffusion propagators. Experiments on an excised marmoset brain specimen demonstrate that MAP-MRI provides several novel, quantifiable parameters that capture previously obscured intrinsic features of nervous tissue microstructure. This should prove helpful for investigating the functional organization of normal and pathologic nervous tissue. Copyright © 2013 Elsevier Inc. All rights reserved.

Effect of Organic Material on Mechanical, Hydrological, and Microstructural Properties of Mudstones

NASA Astrophysics Data System (ADS)

Altobelli, M. A.; Reece, J. S.

2016-12-01

In this research we analyze the influence of organic material on the mechanical and flow properties of mudstones. We uniformly mix peat, milled and harvested by Bord na Móna from the surface of bogs in Ireland, with natural mudstone from Site C0011 in the Nankai Trough, offshore Japan, obtained during Integrated Ocean Drilling Program Expedition 322. The mudstone had previously been disaggregated into a homogeneous dry powder of clay- and silt-sized particles. The peat is ground and dry-sieved to achieve a similar particle size distribution as the mudstone (< 63 micrometers). In order to understand the mechanical and hydrological processes affected by peat, we prepare dry peat-mudstone mixtures with three different peat concentrations: 0 wt%, 5 wt%, and 10 wt%. Then, these peat - mudstone mixtures are saturated with deionized water at a water content of 109%, formed into stable slurries, and uniaxially compressed to an axial stress of 100 kPa using resedimentation, a method that simulates the natural behavior of deposition and burial in the laboratory under controlled conditions. How the organic material interacts with the mudstone matrix and pore fluid under compression influences the physical properties of the mudstones such as porosity, compressibility, and permeability; all of which are measured in the resedimentation experiments. We will also analyze the microstructural changes as a function of peat concentration using a petrographic microscope and scanning electron microscope. Due to the fibrous and absorbent nature of peat, we anticipate the peat to force tightly packed clay particles in the mudstone apart resulting in a looser microstructure and increased porosity, and thus, a higher compressibility and permeability. Understanding the controls on the mechanical and flow properties of hydrocarbon-bearing, fine-grained formations is crucial for exploration and successful production from hydrocarbon reservoirs. Additionally, this study has large implications for soil water storage and soil amendment to improve plant growth and health in clayey soils.

Effects of Pouring Temperature and Electromagnetic Stirring on Porosity and Mechanical Properties of A357 Aluminum Alloy Rheo-Diecasting

NASA Astrophysics Data System (ADS)

Guo, An; Zhao, Junwen; Xu, Chao; Li, Hu; Han, Jing; Zhang, Xu

2018-05-01

Semisolid slurry of A357 aluminum alloy was prepared using a temperature-controllable electromagnetic stirrer and rheo-diecast at different temperatures. The effects of pouring temperature and electromagnetic stirring (EMS) on the porosity in rheo-diecast samples, as well as the relation between porosity and mechanical properties, were investigated. The results show that pouring temperature and EMS had minor influences on rheo-diecast microstructure but marked influence on the porosity. With decreasing slurry pouring temperature, the porosity decreased first and then increased, whereas the maximum pore ratio (ratio of shape factor to diameter of the largest pore) increased first and then decreased. The maximum pore ratio determines the level of tensile strength and elongation, and higher mechanical properties can be obtained with smaller and rounder pores in samples. The mechanical properties of the rheo-diecast samples increased linearly with increasing maximum pore ratio. The maximum pore ratio was 1.43 µm-1, and the minimum porosity level was 0.37% under EMS condition for the rheo-diecast samples obtained at a pouring temperature of 608 °C. With this porosity condition, the maximum tensile strength and elongation were achieved at 274 MPa and 4.9%, respectively. It was also revealed that EMS improves mechanical properties by reduction in porosity and an increase in maximum pore ratio.

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.

The Effect of Hydrofluoric Acid Etching Duration on the Surface Micromorphology, Roughness, and Wettability of Dental Ceramics

PubMed Central

Ramakrishnaiah, Ravikumar; Alkheraif, Abdulaziz A.; Divakar, Darshan Devang; Matinlinna, Jukka P.; Vallittu, Pekka K.

2016-01-01

The current laboratory study is evaluating the effect of hydrofluoric acid etching duration on the surface characteristics of five silica-based glass ceramics. Changes in the pore pattern, crystal structure, roughness, and wettability were compared and evaluated. Seventy-five rectangularly shaped specimens were cut from each material (IPS e-max™, Dentsply Celtra™, Vita Suprinity™, Vita mark II™, and Vita Suprinity FC™); the sectioned samples were finished, polished, and ultrasonically cleaned. Specimens were randomly assigned into study groups: control (no etching) and four experimental groups (20, 40, 80 and 160 s of etching). The etched surfaces’ microstructure including crystal structure, pore pattern, pore depth, and pore width was studied under a scanning electron microscope, and the surface roughness and wettability were analyzed using a non-contact surface profilometer and a contact angle measuring device, respectively. The results were statistically analyzed using one-way analysis of variance (ANOVA) and the post hoc Tukey’s test. The results showed a significant change in the pore number, pore pattern, crystal structure, surface roughness, and wettability with increased etching duration. Etching for a short time resulted in small pores, and etching for longer times resulted in wider, irregular grooves. A significant increase in the surface roughness and wettability was observed with an increase in the etching duration. The findings also suggested a strong association between the surface roughness and wettability. PMID:27240353

Three dimensional X-ray Diffraction Contrast Tomography Reconstruction of Polycrystalline Strontium Titanate during Sintering and Electron Backscatter Diffraction Validation

NASA Astrophysics Data System (ADS)

Syha, M.; Rheinheimer, W.; Loedermann, B.; Graff, A.; Trenkle, A.; Baeurer, M.; Weygand, D.; Ludwig, W.; Gumbsch, P.

The microstructural evolution of polycrystalline strontium titanate was investigated in three dimensions (3D) using X-ray diffraction contrast tomography (DCT) before and after ex-situ annealing at 1600°C. Post-annealing, the specimen was additionally subjected to phase contrast tomography (PCT) in order to finely resolve the porosities. The resulting microstructure reconstructions were studied with special emphasis on morphology and interface orientation during microstructure evolution. Subsequently, cross-sections of the specimen were studied using electron backscatter diffraction (EBSD). Corresponding cross-sections through the 3D reconstruction were identified and the quality of the reconstruction is validated with special emphasis on the spatial resolution at the grain boundaries, the size and location of pores contained in the material and the accuracy of the orientation determination.

Structures and properties of alumina-based ceramic for reconstructive oncology

NASA Astrophysics Data System (ADS)

Grigoriev, M. V.; Kulkov, S. N.

2016-08-01

The microstructure of alumina ceramics based on powders with a varying grain size has been investigated. Both commercial alumina powders and those fabricated by denitration of aluminum salts in high-frequency discharge plasma were used. It is shown that the variation of the sintering temperature and morphology of the initial powders of the particles leads to a change of the pore structure of ceramics from pore isolated clusters to a structure consisting of a ceramic skeleton and a large pore space. Changing the type of pore structure occurs at about 50% of porosity. The ceramic pore size distribution is bimodal. Dependencies final density vs initial density are linear; at the same time with increasing temperature, inclination of changes from positive to negative, indicating the change of sealing mechanisms. Extrapolation of these curves showed that they intersect with the values of density of about 2 g/cm3, which indicates the possibility of producing non-shrink ceramics. It is shown that the strength increases with increasing nanocrystalline alumina content in powder mixture. A change in the character the pore structure is accompanied by a sharp decrease in strength, which corresponds to the percolation transition in ceramics. These results showed that it is possible to obtain ceramic materials with the structure and properties similar to natural bone.

Chemical vapor deposition of Mo tubes for fuel cladding applications

DOE PAGES

Beaux, Miles F.; Vodnik, Douglas R.; Peterson, Reuben J.; ...

2018-01-31

In this study, chemical vapor deposition (CVD) techniques have been evaluated for fabrication of free-standing 0.25 mm thick molybdenum tubes with the end goal of nuclear fuel cladding applications. In order to produce tubes with the wall thickness and microstructures desirable for this application, long deposition durations on the order of 50 h with slow deposition rates were employed. A standard CVD method, involving molybdenum pentachloride reduction by hydrogen, as well as a fluidized-bed CVD (FBCVD) method was applied towards these objectives. Characterization of the tubes produced in this manner revealed regions of material with fine grain microstructure and wallmore » thickness suitable for fuel cladding applications, but lacking necessary uniformity across the length of the tubes. Finally, a path forward for the production of freestanding molybdenum tubes that possess the desired properties across their entire length has been identified and can be accomplished by future optimization of the deposition system.« less

Chemical vapor deposition of Mo tubes for fuel cladding applications

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

Beaux, Miles F.; Vodnik, Douglas R.; Peterson, Reuben J.

In this study, chemical vapor deposition (CVD) techniques have been evaluated for fabrication of free-standing 0.25 mm thick molybdenum tubes with the end goal of nuclear fuel cladding applications. In order to produce tubes with the wall thickness and microstructures desirable for this application, long deposition durations on the order of 50 h with slow deposition rates were employed. A standard CVD method, involving molybdenum pentachloride reduction by hydrogen, as well as a fluidized-bed CVD (FBCVD) method was applied towards these objectives. Characterization of the tubes produced in this manner revealed regions of material with fine grain microstructure and wallmore » thickness suitable for fuel cladding applications, but lacking necessary uniformity across the length of the tubes. Finally, a path forward for the production of freestanding molybdenum tubes that possess the desired properties across their entire length has been identified and can be accomplished by future optimization of the deposition system.« less

Influence of a TiN interlayer on the microstructure and mechanical properties of hydroxyapatite films grown by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Nelea, Valentin D.; Ristoscu, Carmen; Colis, Silviu; Arens, Simona; Pelletier, Herve; Mihailescu, Ion N.; Mille, Pierre

2001-04-01

Crystalline hydroxyapatite (HA) thin films grown on metallic substrates is the best choice for bone restoration. This is due to the good biological compatibility of the hydroxyapatite material combined with the good mechanical characteristics of the substrates. We deposit HA thin films by Pulsed Laser Deposition (PLD) in vacuum at room temperature using a KrF* excimer laser ((lambda) equals 248 nm, (tau) FWHM >= 20 ns). The depositions were performed directly on Ti-5Al-2.5Fe or on substrates previously coated with a TiN buffer layer. The HA deposited structures were characterized by complementary techniques: GIXRD, SEM, TEM, SAED, EDS and nanoindentation. Properties of the HA films grown with and without the TiN buffer were discussed in term of microstructure and mechanical behavior. The films with interlayer preserve the stoichiometry, are completely recrystallized and present better mechanical characteristics as compared with those without buffer.

Thermally Sprayed High Temperature Sandwich Structures: Physical Properties and Mechanical Performance

NASA Astrophysics Data System (ADS)

Salavati, Saeid

Metallic foam core sandwich structures have been of particular interest for engineering applications in recent decades due to their unique physical and mechanical properties. One of the potential applications of open pore metallic foam core sandwich structures is in heat exchangers. An investigation of sandwich structures fabricated from materials suitable for application at high temperatures and in corrosive environments was undertaken in this project. A novel method for fabrication of metallic foam core sandwich structures is thermal spray deposition of the faces on the prepared surfaces of the metallic foam substrate. The objective of the current study was to optimize the twin wire arc spray process parameters for the deposition of alloy 625 faces with controllable porosity content on the nickel foam substrate, and to characterize the physical and mechanical properties of the sandwich structure. The experimental investigations consisted of microstructural evaluation of the skin material and the foam substrate, investigation of the effect of alloying on the mechanical and thermal properties of the nickel foam, optimization of the grit-blasting and arc spray processes, observation of mechanical properties of the alloy 625 deposit by tensile testing and evaluation of the overall mechanical properties of the sandwich structure under flexural loading condition. The optimization of arc spraying process parameters allowed deposition of alloy 625 faces with a porosity of less than 4% for heat exchanger applications. Modification of the arc spraying process by co-deposition of polyester powder enabled 20% porosity to be obtained in the deposited faces for heat shield applications with film cooling. The effects of nickel foam alloying and heat treatment on the flexural rigidity of the sandwich structures were investigated and compared with as-received foam and as-fabricated sandwich structures. Available analytical models were employed to describe the effect of constituents' mechanical properties on the overall mechanical performance of the sandwich structures. Finite element modeling using ANSYS Structural was used to simulate the behaviour of the sandwich structures in four-point bending. The analytical and simulation results were compared with the experimental results obtained from the flexural tests.

Effect of in-situ TiC particulate on the wear resistance of spray-deposited 7075 Al matrix composite

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

Wang Feng; Liu Huimin; Yang Bin

2005-05-15

TiC reinforced 7075 Al matrix composites have been fabricated by a melt in-situ reaction spray deposition. The microstructures of spray-deposited alloys were studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The dry sliding wear behavior of the alloys was investigated using a pin-on-disc machine under four loads, namely 8.9, 17.8, 26.7 and 35.6 N. It has been found that the wear behavior of the alloys was dependent on the TiC content in the microstructure and the applied load. At a lower load (8.9 N), with increasing TiC content, the wear rate of the alloy was decreased. At amore » higher loads (26.7, 35.6 N), a spray-deposited 7075 Al alloy exhibited superior wear resistance to the 7075/TiC composites.« less

Semiconductor gas sensor based on tin oxide nanorods prepared by plasma-enhanced chemical vapor deposition with postplasma treatment

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

Huang Hui; Tan, O.K.; Lee, Y.C.

2005-10-17

SnO{sub 2} thin films were deposited by radio-frequency inductively coupled plasma-enhanced chemical vapor deposition. Postplasma treatments were used to modify the microstructure of the as-deposited SnO{sub 2} thin films. Uniform nanorods with dimension of null-set 7x100 nm were observed in the plasma-treated films. After plasma treatments, the optimal operating temperature of the plasma-treated SnO{sub 2} thin films decreased by 80 deg. C, while the gas sensitivity increased eightfold. The enhanced gas sensing properties of the plasma-treated SnO{sub 2} thin film were believed to result from the large surface-to-volume ratio of the nanorods' tiny grain size in the scale comparable tomore » the space-charge length and its unique microstructure of SnO{sub 2} nanorods rooted in SnO{sub 2} thin films.« less

Metallic coatings on silicon substrates, and methods of forming metallic coatings on silicon substrates

DOEpatents

Branagan, Daniel J [Idaho Falls, ID; Hyde, Timothy A [Idaho Falls, ID; Fincke, James R [Los Alamos, NM

2008-03-11

The invention includes methods of forming a metallic coating on a substrate which contains silicon. A metallic glass layer is formed over a silicon surface of the substrate. The invention includes methods of protecting a silicon substrate. The substrate is provided within a deposition chamber along with a deposition target. Material from the deposition target is deposited over at least a portion of the silicon substrate to form a protective layer or structure which contains metallic glass. The metallic glass comprises iron and one or more of B, Si, P and C. The invention includes structures which have a substrate containing silicon and a metallic layer over the substrate. The metallic layer contains less than or equal to about 2 weight % carbon and has a hardness of at least 9.2 GPa. The metallic layer can have an amorphous microstructure or can be devitrified to have a nanocrystalline microstructure.

Effect of Turning and Ball Burnishing on the Microstructure and Residual Stress Distribution in Stainless Steel Cold Spray Deposits

NASA Astrophysics Data System (ADS)

Sova, A.; Courbon, C.; Valiorgue, F.; Rech, J.; Bertrand, Ph.

2017-12-01

In this paper, an experimental study of influence of machining by turning and ball burnishing on the surface morphology, structure and residual stress distribution of cold spray 17-4 PH stainless steel deposits is provided. It is shown that cold spray deposits could be machined by turning under parameters closed to turning of bulk 17-4 PH stainless steel. Ball burnishing process permits to decrease surface roughness. Cross-sectional observation revealed that the turning and ball burnishing process allowed microstructure changes in the coating near-surface zone. In particular, significant particle deformation and particle boundary fragmentation is observed. Measurements of residual stresses showed that residual stresses in the as-spray deposit are compressive. After machining by turning, tensile residual stresses in the near-surface zone were induced. Further surface finishing of turned coating by ball burnishing allowed the establishment of the compressive residual stresses in the coating.

A computational and cellular solids approach to the stiffness-based design of bone scaffolds.

PubMed

Norato, J A; Wagoner Johnson, A J

2011-09-01

We derive a cellular solids approach to the design of bone scaffolds for stiffness and pore size. Specifically, we focus on scaffolds made of stacked, alternating, orthogonal layers of hydroxyapatite rods, such as those obtained via micro-robotic deposition, and aim to determine the rod diameter, spacing and overlap required to obtain specified elastic moduli and pore size. To validate and calibrate the cellular solids model, we employ a finite element model and determine the effective scaffold moduli via numerical homogenization. In order to perform an efficient, automated execution of the numerical studies, we employ a geometry projection method so that analyses corresponding to different scaffold dimensions can be performed on a fixed, non-conforming mesh. Based on the developed model, we provide design charts to aid in the selection of rod diameter, spacing and overlap to be used in the robotic deposition to attain desired elastic moduli and pore size.

Fabrication of complex free-standing nanostructures with concave and convex curvature via the layer-by-layer approach.

PubMed

Raoufi, Mohammad; Schönherr, Holger

2014-02-18

We report on the fabrication of unprecedented free-standing complex polymeric nanoobjects, which possess both concave and convex curvatures, by exploiting the layer-by-layer (LBL) deposition of polyelectrolytes. In a combined top-down/bottom-up replication approach pore diameter-modulated anodic aluminum oxide (AAO) templates, fabricated by temperature modulation hard anodization (TMHA), were replicated with multilayers of poly(styrene sulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) to yield open nanotubes with diameters in the wide and narrow segments of 210 and 150 nm, respectively. To obtain stable pore diameter-modulated nanopores, which possess segment lengths between 1 and 5 μm and 5 and 10 μm in the narrow and wide pore portion, respectively, conventional hard anodization of aluminum was followed by a subsequent temperature-modulated anodization. After removing the backside aluminum electrode, silanizing the aluminum oxide, and passivating the exposed membrane surface with a thin layer of gold, PSS and PAH were deposited alternatingly to yield LBL multilayers. For optimized LBL multilayer thicknesses and compactness, established in separate experiments on silicon substrates and nanoporous AAO with straight pores, free-standing polymeric nanoobjects with concave and convex curvatures, were obtained. These were stable for wall thickness to pore diameter ratios of ≥0.08.

Pore-scale water dynamics during drying and the impacts of structure and surface wettability

NASA Astrophysics Data System (ADS)

Cruz, Brian C.; Furrer, Jessica M.; Guo, Yi-Syuan; Dougherty, Daniel; Hinestroza, Hector F.; Hernandez, Jhoan S.; Gage, Daniel J.; Cho, Yong Ku; Shor, Leslie M.

2017-07-01

Plants and microbes secrete mucilage into soil during dry conditions, which can alter soil structure and increase contact angle. Structured soils exhibit a broad pore size distribution with many small and many large pores, and strong capillary forces in narrow pores can retain moisture in soil aggregates. Meanwhile, contact angle determines the water repellency of soils, which can result in suppressed evaporation rates. Although they are often studied independently, both structure and contact angle influence water movement, distribution, and retention in soils. Here drying experiments were conducted using soil micromodels patterned to emulate different aggregation states of a sandy loam soil. Micromodels were treated to exhibit contact angles representative of those in bulk soil (8.4° ± 1.9°) and the rhizosphere (65° ± 9.2°). Drying was simulated using a lattice Boltzmann single-component, multiphase model. In our experiments, micromodels with higher contact angle surfaces took 4 times longer to completely dry versus micromodels with lower contact angle surfaces. Microstructure influenced drying rate as a function of saturation and controlled the spatial distribution of moisture within micromodels. Lattice Boltzmann simulations accurately predicted pore-scale moisture retention patterns within micromodels with different structures and contact angles.

TC17 titanium alloy laser melting deposition repair process and properties

NASA Astrophysics Data System (ADS)

Liu, Qi; Wang, Yudai; Zheng, Hang; Tang, Kang; Li, Huaixue; Gong, Shuili

2016-08-01

Due to the high manufacturing cost of titanium compressor blisks, aero engine repairing process research has important engineering significance and economic value. TC17 titanium alloy is a rich β stable element dual α+β phase alloy whose nominal composition is Ti-5Al-2Sn-2Zr-4Mo-4Cr. It has high mechanical strength, good fracture toughness, high hardenability and a wide forging-temperature range. Through a surface response experiment with different laser powers, scanning speeds and powder feeding speeds, the coaxial powder feeding laser melting deposition repair process is studied for the surface circular groove defects. In this paper, the tensile properties, relative density, microhardness, elemental composition, internal defects and microstructure of the laser-repaired TC17 forging plate are analyzed. The results show that the laser melting deposition process could realize the form restoration of groove defect; tensile strength and elongation could reach 1100 MPa and 10%, which could reach 91-98% that of original TC17 wrought material; with the optimal parameters (1000 W-25 V-8 mm/s), the microhardness of the additive zone, the heat-affected zone and base material is evenly distributed at 370-390 HV500. The element content difference between the additive zone and base material is less than ±0.15%. Due to the existence of the pores 10 μm in diameter, the relative density could reach 99%, which is mainly inversely proportional to the powder feeding speed. The repaired zone is typically columnar and dendrite crystal, and the 0.5-1.5 mm-deep heat-affected zone in the groove interface is coarse equiaxial crystal.

Low-temperature (120 °C) growth of nanocrystalline silicon films prepared by plasma enhanced chemical vapor deposition from SiCl 4/H 2 gases: Microstructure characterization

NASA Astrophysics Data System (ADS)

Zhang, L.; Gao, J. H.; Xiao, J. Q.; Wen, L. S.; Gong, J.; Sun, C.

2012-01-01

Hydrogenated nanocrystalline silicon (nc-Si:H) films were prepared using diluted tetrachlorosilane (SiCl4) with various hydrogen flow rates (Hf) by plasma enhanced chemical vapor deposition (PECVD) at a constant substrate temperature (Ts) as low as 120 °C. Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), infrared spectra (IR) and spectroscopic ellipsometry (SE) were employed to investigate the microstructure and hydrogen bonding of the nc-Si:H films. Our results showed that the microstructure and hydrogen content of the films could be effectively tailored by the hydrogen flow rates, and a distinct transition from amorphous to nanocrystalline phase was observed with an increase of Hf. At an optimal preparation condition, a deposition rate was as high as 3.7 nm/min and the crystallinity reached up to 64.1%. In addition, the effect of hydrogen on the low-temperature growth of nc-Si:H film was proposed in relation to the surface reaction of radicals and the hydrogen diffusion in the surface growing region.

Assembly of live micro-organisms on microstructured PDMS stamps by convective/capillary deposition for AFM bio-experiments

NASA Astrophysics Data System (ADS)

Dague, E.; Jauvert, E.; Laplatine, L.; Viallet, B.; Thibault, C.; Ressier, L.

2011-09-01

Immobilization of live micro-organisms on solid substrates is an important prerequisite for atomic force microscopy (AFM) bio-experiments. The method employed must immobilize the cells firmly enough to enable them to withstand the lateral friction forces exerted by the tip during scanning but without denaturing the cell interface. In this work, a generic method for the assembly of living cells on specific areas of substrates is proposed. It consists in assembling the living cells within the patterns of microstructured, functionalized poly-dimethylsiloxane (PDMS) stamps using convective/capillary deposition. This versatile approach is validated by applying it to two systems of foremost importance in biotechnology and medicine: Saccharomyces cerevisiae yeasts and Aspergillus fumigatus fungal spores. We show that this method allows multiplexing AFM nanomechanical measurements by force spectroscopy on S. cerevisiae yeasts and high-resolution AFM imaging of germinated Aspergillus conidia in buffer medium. These two examples clearly demonstrate the immense potential of micro-organism assembly on functionalized, microstructured PDMS stamps by convective/capillary deposition for performing rigorous AFM bio-experiments on living cells.

Electron microscopy characterization of Ni-Cr-B-Si-C laser deposited coatings.

PubMed

Hemmati, I; Rao, J C; Ocelík, V; De Hosson, J Th M

2013-02-01

During laser deposition of Ni-Cr-B-Si-C alloys with high amounts of Cr and B, various microstructures and phases can be generated from the same chemical composition that results in heterogeneous properties in the clad layer. In this study, the microstructure and phase constitution of a high-alloy Ni-Cr-B-Si-C coating deposited by laser cladding were analyzed by a combination of several microscopy characterization techniques including scanning electron microscopy in secondary and backscatter imaging modes, energy dispersive spectroscopy (EDS), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). The combination of EDS and EBSD allowed unequivocal identification of micron-sized precipitates as polycrystalline orthorhombic CrB, single crystal tetragonal Cr5B3, and single crystal hexagonal Cr7C3. In addition, TEM characterization showed various equilibrium and metastable Ni-B, Ni-Si, and Ni-Si-B eutectic products in the alloy matrix. The findings of this study can be used to explain the phase formation reactions and to tune the microstructure of Ni-Cr-B-Si-C coatings to obtain the desired properties.

Effects of process parameters on properties of porous foams formed by laser-assisted melting of steel powder (AISI P21)/foaming agent (ZrH2) mixture

NASA Astrophysics Data System (ADS)

Seo, Ja-Ye; Lee, Ki-Yong; Shim, Do-Sik

2018-01-01

This paper describes the fabrication of lightweight metal foams using the directed energy deposition (DED) method. DED is a highly flexible additive manufacturing process wherein a metal powder mixed with a foaming agent is sprayed while a high-power laser is used to simultaneously melt the powder mixture into layered metal foams. In this study, a mixture of a carbon steel material (P21 powder) and a widely used foaming agent, ZrH2, is used to fabricate metal foams. The effects of various process parameters, such as the laser power, powder feed rate, powder gas flow rate, and scanning speed, on the deposition characteristics (porosity, pore size, and pore distribution) are investigated. The synthesized metal foams exhibit porosities of 10% or lower, and a mean pore area of 7 × 105 μm2. It is observed that the degree of foaming increases in proportion to the laser power to a certain extent. The results also show that the powder feed rate has the most pronounced effect on the porosity of the metal foams, while the powder gas flow rate is the most suitable parameter for adjusting the size of the pores formed within the foams. Further, the scanning speed, which determines the amounts of energy and powder delivered, has a significant effect on the height of the deposits as well as on the properties of the foams. Thus, during the DED process for fabricating metal foams, the pore size and distribution and hence the foam porosity can be tailored by varying the individual process parameters. These findings should be useful as reference data for the design of processes for fabricating porous metallic materials that meet the specific requirements for specialized parts.

Processing and Characterization of Graphene/Polyimide-Nickel Oxide Hybrid Nanocomposites for Advanced Energy Storage in Supercapacitor Applications

NASA Astrophysics Data System (ADS)

Okafor, Patricia A.

This research is focused on enhancing electrochemical properties/energy storage capabilities of graphene-polyimide composites. The composite's dense morphology/structure limits ionic penetration owing to high bulk resistances resulting in poor electrochemical performance. Modification of the composite's morphology by incorporation of facile pores during curing increases total available surface area to electrolyte species. Presence of pores increases adsorption sites for double layer formation and increases overall capacitance. In this work, aromatic polyimide precursors were reacted in the presence of nano-graphene fillers to synthesize graphene-polyimide composite films. The resulting composite was very stiff and dense with a high glass transition temperature (Tg) of 400 °C and storage modulus of 7.20 GPa. Selective decomposition of a thermally labile poly(acrylic ester) resin introduced into the composite during synthesis creates pores of varying size and shapes which increases available surface area of embedded stacked graphene sheets available for ion adsorption and double layer formation. Proper control over pore size and specific surface area of pores was required to ensure good performance in terms of both power delivery rate and energy storage capacity. Dynamic mechanical studies on modified composite showed very good mechanical property while shifts in imide peaks to lower wave numbers in Raman and Fourier transform spectroscopy (FTIR) confirms presence of chemical interaction between graphene filler and polymer matrix confirming uniform dispersion of fillers in the material. Thermogravimetric analysis (TGA) shows thermal stability for the composite systems at temperatures above 700°C. To further optimize material's energy storage capabilities, a hybrid composite was formed by depositing relatively cheap nickel oxide onto the modified porous composite system by a two-step process. A remarkable improvement in electrochemical properties up to an order of magnitude was observed. Electrochemical performance of the hybrid system showed strong dependence on deposition current density, deposition time and substrate pore morphology. Increased NiO particle size (aggregates) was observed with increased deposition time and current density which had a significant impact on charge transfer resistance and specific capacitance. Several correlations were made between composite's morphology and obtained properties. The material's morphology showed direct correlation with double layer capacitance, charge capacity, bulk resistance and sheet conductivity measured using cyclic voltammetry (CV), cyclic charge discharge (CCD), electrochemical impedance spectroscopy (EIS) and four probe measurements respectively. It was observed that smaller well distributed pores showed enhanced properties compared to larger pores. Material's overall performance shows a linear dependence on porosity. The overall electrochemical and electrical behavior of the system is directly linked to the composite's morphology and structure as will be demonstrated in this thesis work.

Effects of Microgravity on the Formation of Aerogels

NASA Technical Reports Server (NTRS)

Hunt, A. J.; Ayers, M. R.; Sibille, L.; Cronise, R. J.; Noever, D. A.

1999-01-01

This paper describes research to investigate fundamental aspects of the effects of microgravity on the formation of the microstructure of metal oxide alcogels and aerogels. We are studying the role of gravity on pore structure and gel uniformity in collaboration with Marshall Space Flight Center (MSFC) on gelling systems under microgravity conditions. While this project was just initiated in May 1998, related research performed earlier is described along with the plans and rationale for the current microgravity investigation to provide background and describe newly developing techniques that should be useful for the current gellation studies. The role of gravity in materials processing must be investigated through the study of well-mastered systems. Sol-gel processed materials are near-perfect candidates to determine the effect of gravity on the formation and growth of random clusters from hierarchies of aggregated units. The processes of hydrolysis, condensation, aggregation and gellation in the formation of alcogels are affected by gravity and therefore provide a rich system to study under microgravity conditions. Supercritical drying of the otherwise unstable wet alcogel preserves the alcogel structure produced during sol-gel processing as aerogel. Supercritically dried aerogel provides for the study of material microstructures without interference from the effects of surface tension, evaporation, and solvent flow. Aerogels are microstructured, low density open-pore solids. They have many unusual properties including: transparency, excellent thermal resistance, high surface area, very low refractive index, a dielectric constant approaching that of air, and extremely low sound velocity. Aerogels are synthesized using sol-gel processing followed by supercritical solvent extraction that leaves the original gel structure virtually intact. These studies will elucidate the effects of microgravity on the homogeneity of the microstructure and porosity of aerogel. The presence of poorly controlled microporosity in aerogel leads to material non-uniformity that gives rise to increased light scattering. Investigation of the effect of gravity driven solute flows within microclusters and their effect on condensation and agglomeration reactions will enable us to improve the preparation and properties of aerogel. Increased clarity of images viewed through aerogel and decreased scattering from the pores of aerogel will significantly improve the prospects for large-scale adoption of aerogel in such applications as transparent insulating windows, high performance thermal insulation, and Cherenkov detectors.

Solid polymer electrolyte composite membrane comprising a porous support and a solid polymer electrolyte including a dispersed reduced noble metal or noble metal oxide

DOEpatents

Liu, Han; Mittelsteadt, Cortney K; Norman, Timothy J; Griffith, Arthur E; LaConti, Anthony B

2015-02-24

A solid polymer electrolyte composite membrane and method of manufacturing the same. According to one embodiment, the composite membrane comprises a thin, rigid, dimensionally-stable, non-electrically-conducting support, the support having a plurality of cylindrical, straight-through pores extending perpendicularly between opposing top and bottom surfaces of the support. The pores are unevenly distributed, with some or no pores located along the periphery and more pores located centrally. The pores are completely filled with a solid polymer electrolyte, the solid polymer electrolyte including a dispersed reduced noble metal or noble metal oxide. The solid polymer electrolyte may also be deposited over the top and/or bottom surfaces of the support.

Deformation modes in an Icelandic basalt: From brittle failure to localized deformation bands

NASA Astrophysics Data System (ADS)

Adelinet, M.; Fortin, J.; Schubnel, A.; Guéguen, Y.

2013-04-01

According to the stress state, deformation mode observed in rocks may be very different. Even in the brittle part of the crust a differential stress can induce shear failure but also localized compacting deformation, such as compaction bands in porous sedimentary rocks. The mode of deformation controls many hydrodynamic factors, such as permeability and porosity. We investigate in this paper two different modes of deformation in an Icelandic basalt by using laboratory seismological tools (elastic waves and acoustic emissions) and microstructural observations. First of all, we show that at low effective confining pressure (Peff = 5 MPa) an axial loading induces a shear failure in the basalt with an angle of about 30° with respect to the main stress direction. On the contrary, at high effective confining pressure (Peff ≥ 75 MPa and more) an increase of the axial stress induces a localization of the deformation in the form of subhorizontal bands again with respect to the main stress direction. In this second regime, focal mechanisms of the acoustic emissions reveal an important number of compression events suggesting pore collapse mechanisms. Microstructural observations confirm this assumption. Similar compaction structures are usually obtained for porous sedimentary rocks (20-25%). However, the investigated basalt has an initial total porosity of only about 10% so that compaction structures were not expected. The pore size and the ratio of pore to grain size are likely to be key factors for the particular observed mechanical behavior.

Carbon spheres-assisted strategy to prepare mesoporous manganese dioxide for supercapacitor applications

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

Li Siheng; Graduate University of Chinese Academy of Sciences, Beijing 100039; Qi Li, E-mail: qil@ciac.jl.cn

Mesoporous MnO{sub 2} microstructures with large specific surface area have been successfully synthesized by an in-situ redox precipitation method in the presence of colloidal carbon spheres. The samples of them had much higher specific surface area, pore size and pore volume than those obtained via routes without carbon spheres. The morphology, chemical compositions and porous nature of products were fully characterized. Electrochemical measurements showed that these mesoporous MnO{sub 2} could function well when used as positive electrode materials for supercapacitor. Ideal electrochemical capacitive performances and cyclic stability after 2000 galvanostatic charge-discharge cycles could be observed in 1 M neutral Na{submore » 2}SO{sub 4} aqueous electrolyte with a working voltage of 1.7 V. - Graphical Abstract: Mesoporous MnO{sub 2} microstructures with large S{sub BET} were successfully synthesized by in-situ redox precipitation method in the presence of colloidal carbon spheres. Electrochemical measurements showed that these mesoporous MnO{sub 2} could be well used as electrode materials for supercapacitor. Highlights: Black-Right-Pointing-Pointer Mesoporous MnO{sub 2} was prepared by in-situ redox method assisted by carbon spheres. Black-Right-Pointing-Pointer S{sub BET}, pore size and volume were higher than MnO{sub 2} obtained without carbon spheres. Black-Right-Pointing-Pointer They could function well when used as electrode materials for supercapacitor. Black-Right-Pointing-Pointer Ideal capacitive behaviors and long cycling life showed after 2000 charge-discharge.« less

Compression fatigue behavior and failure mechanism of porous titanium for biomedical applications.

PubMed

Li, Fuping; Li, Jinshan; Huang, Tingting; Kou, Hongchao; Zhou, Lian

2017-01-01

Porous titanium and its alloys are believed to be one of the most attractive biomaterials for orthopedic implant applications. In the present work, porous pure titanium with 50-70% porosity and different pore size was fabricated by diffusion bonding. Compression fatigue behavior was systematically studied along the out-of-plane direction. It resulted that porous pure titanium has anisotropic pore structure and the microstructure is fine-grained equiaxed α phase with a few twins in some α grains. Porosity and pore size have some effect on the S-N curve but this effect is negligible when the fatigue strength is normalized by the yield stress. The relationship between normalized fatigue strength and fatigue life conforms to a power law. The compression fatigue behavior is characteristic of strain accumulation. Porous titanium experiences uniform deformation throughout the entire sample when fatigue cycle is lower than a critical value (N T ). When fatigue cycles exceed N T , strain accumulates rapidly and a single collapse band forms with a certain angle to the loading direction, leading to the sudden failure of testing sample. Both cyclic ratcheting and fatigue crack growth contribute to the fatigue failure mechanism, while the cyclic ratcheting is the dominant one. Porous titanium possesses higher normalized fatigue strength which is in the range of 0.5-0.55 at 10 6 cycles. The reasons for the higher normalized fatigue strength were analyzed based on the microstructure and fatigue failure mechanism. Copyright © 2016 Elsevier Ltd. All rights reserved.

A unique skeletal microstructure of the deep-sea micrabaciid scleractinian corals

NASA Astrophysics Data System (ADS)

Janiszewska, Katarzyna; Stolarski, Jaroslaw; Benzerara, Karim; Meibom, Anders; Mazur, Maciej; Kitahara, Marcelo; Cairns, Stephen D.

2010-05-01

Structural and biogeochemical properties of the skeleton of many invertebrates rely on organic matrix-mediated biomineralization processes. Organic matrices, composed of complex assemblages of macromolecules (proteins, polysaccharides), may control nucleation, spatial delineation and organization of basic microstructural units. Biologically controlled mineralization is also suggested for the scleractinian corals whose different, molecularly recognized clades are supported by distinct types of skeletal microstructures. Main differences in scleractinian coral skeletal microstructures suggested so far consist in (1) varying spatial relationships between Rapid Accretion Deposits (RAD, 'centers of calcification') and thickening deposits (TD, 'fibers'), and (2) varying arrangements of biomineral fibers into higher order structures (e.g., bundles of fibers perpendicular to skeletal surfaces in some 'caryophylliid' corals vs. scale-like units with fibers parallel to the surface in acroporiids). However, a common feature of biomineral fibers in corals described thus far was their similar crystallographic arrangement within larger meso-scale structures (bundles of fibers) and continuity between successive growth layers. Herein we show that representatives of the deep-sea scleractinian family Micrabaciidae (genera: Letepsammia, Rhombopsammia, Stephanophyllia, Leptopenus) have thickening deposits composed of irregular meshwork of short (1-2 μm) and extremely thin (ca. 100-300 nm) fibers organized into small bundles (ca. 1-2 μm thick). Longer axes of fibers are aligned within individual bundles that, in turn, show rather irregular arrangement on the growing surfaces and within the skeleton (irregular criss-cross pattern). In contrast to other scleractinians (including deep-water 'caryophylliids', fungiacyathids, and anthemiphyllids sympatric with micrabaciids), growth layers are not distinct. Also the regions of rapid accretion and thickening deposits are not clearly separated at the meso-scale. However, AFM and FESEM observations of RAD show nanogranular units (ca. 30-100 nm in diameter) typical of fast growing skeletal regions. Unique microstructural organization of the micrabaciid skeleton supports their monophyletic status (reinforced by macromorphological and molecular data), and points to a diversity of organic matrix-mediated biomineralization strategies in Scleractinia.

Microstructural and associated chemical changes during the composting of a high temperature biochar: Mechanisms for nitrate, phosphate and other nutrient retention and release

USDA-ARS?s Scientific Manuscript database

Recent studies have demonstrated the importance of the nutrient status of biochar and soils prior to its inclusion in particular agricultural systems. Pre-treatment of nutrient-reactive biochar, where nutrients are loaded into pores and onto surfaces, gives improved yield outcomes compared to untrea...

The processing of aluminum gasarites via thermal decomposition of interstitial hydrides

NASA Astrophysics Data System (ADS)

Licavoli, Joseph J.

Gasarite structures are a unique type of metallic foam containing tubular pores. The original methods for their production limited them to laboratory study despite appealing foam properties. Thermal decomposition processing of gasarites holds the potential to increase the application of gasarite foams in engineering design by removing several barriers to their industrial scale production. The following study characterized thermal decomposition gasarite processing both experimentally and theoretically. It was found that significant variation was inherent to this process therefore several modifications were necessary to produce gasarites using this method. Conventional means to increase porosity and enhance pore morphology were studied. Pore morphology was determined to be more easily replicated if pores were stabilized by alumina additions and powders were dispersed evenly. In order to better characterize processing, high temperature and high ramp rate thermal decomposition data were gathered. It was found that the high ramp rate thermal decomposition behavior of several hydrides was more rapid than hydride kinetics at low ramp rates. This data was then used to estimate the contribution of several pore formation mechanisms to the development of pore structure. It was found that gas-metal eutectic growth can only be a viable pore formation mode if non-equilibrium conditions persist. Bubble capture cannot be a dominant pore growth mode due to high bubble terminal velocities. Direct gas evolution appears to be the most likely pore formation mode due to high gas evolution rate from the decomposing particulate and microstructural pore growth trends. The overall process was evaluated for its economic viability. It was found that thermal decomposition has potential for industrialization, but further refinements are necessary in order for the process to be viable.

Effect of Ni content on stainless steel fabricated by laser melting deposition

NASA Astrophysics Data System (ADS)

Zhang, H.; Zhang, C. H.; Wang, Q.; Wu, C. L.; Zhang, S.; Chen, J.; Abdullah, Adil O.

2018-05-01

The novel stainless steel + x wt.% Ni (x = 0, 3.05, 6.10, 9.15) specimens were successfully fabricated by laser melting deposition, aiming at investigating the influence of Ni content on stainless steel structure and property. The effects of Ni content on phase compositions, microstructure, microhardness, wear and electrochemical corrosion resistance of as-deposited stainless steel were studied systematically using XRD, OM, SEM, microhardness tester, friction-wear tester and potentiodynamic polarization measurement, respectively. Experimental results showed that with the increase of Ni content, the constituent phase of the as-deposited specimen changed from ferrite phase (specimen for x = 0) to austenite phase (specimen for x = 9.15). The microstructure growth followed the principle of dendrite growth. However, the dominant microstructure varied from equiaxed dendrite to columnar dendrite with increasing Ni content. Phase transition from ferrite phase to austenite phase with the addition of Ni content resulted in the decrease of microhardness value from 643HV to 289HV. Meanwhile, the wear resistance of as-deposited specimens decreased gradually with the increasing of Ni content, which might be attributed to the fact that the wear resistance is proportional to microhardness according to Archard's law. It was noted that corrosion resistance of as-deposited stainless steel was extremely improved with the increase of Ni content. The higher Ni content specimen (specimen for x = 9.15) exhibited the best corrosion resistance among the tested specimens based on corrosion rate, which was one order of magnitude lower than that of the lower Ni content specimens (specimens for x = 0, 3.05).

Sputtered deposited nanocrystalline ZnO films: A correlation between electrical, optical and microstructural properties

NASA Astrophysics Data System (ADS)

Lee, J.; Gao, W.; Li, Z.; Hodgson, M.; Metson, J.; Gong, H.; Pal, U.

2005-05-01

Zinc oxide thin films were prepared by dc (direct current) and rf (radio frequency) magnetron sputtering on glass substrates. ZnO films produced by dc sputtering have a high resistance, while the films produced using rf sputtering are significantly more conductive. While the conductive films have a compact nodular surface morphology, the resistive films have a relatively porous surface with columnar structures in cross section. Compared to the dc sputtered films, rf sputtered films have a microstructure with smaller d spacing, lower internal stress, higher band gap energy and higher density. Dependence of conductivity on the deposition technique and the resulting d spacing , stress, density, band gap, film thickness and Al doping are discussed. Correlations between the electrical conductivity, microstructural parameters and optical properties of the films have been made.

Synthesis and characterization of bulk metallic glasses prepared by laser direct deposition

NASA Astrophysics Data System (ADS)

Ye, Xiaoyang

Fe-based and Zr-based metallic glasses have attracted extensive interest for structural applications due to their excellent glass forming ability, superior mechanical properties, unique thermal and corrosion properties. In this study, the feasibility of synthesizing metallic glasses with good ductility by laser direct deposition is explored. Both in-situ synthesis with elemental powder mixture and ex-situ synthesis with prealloyed powder are discussed. Microstructure and properties of laser direct deposited metallic glass composites are analyzed. Synthesis of Fe-Cr-Mo-W-Mn-C-Si-B metallic glass composite with a large fraction of amorphous phase was accomplished using laser direct deposition. X-ray diffraction (XRD) and transmission electron microscopy investigations revealed the existence of amorphous structure. Microstructure analyses by optical microscopy and scanning electron microscopy (SEM) indicated the periodically repeated microstructures of amorphous and crystalline phases. Partially crystallized structure brought by laser reheating and remelting during subsequent laser scans aggregated in the overlapping area between each scan. XRD analysis showed that the crystalline particle embedded in the amorphous matrix was Cr 1.07Fe18.93 phase. No significant microstructural differences were found from the first to the last layer. Microhardness of the amorphous phase (HV0.2 1591) showed a much higher value than that of the crystalline phase (HV0.2 947). Macrohardness of the top layer had a value close to the microhardness of the amorphous region. Wear resistance property of deposited layers showed a significant improvement with the increased fraction of amorphous phase. Zr65Al10Ni10Cu15 amorphous composites with a large fraction of amorphous phase were in-situ synthesized by laser direct deposition. X-ray diffraction confirmed the existence of both amorphous and crystalline phases. Laser parameters were optimized in order to increase the fraction of amorphous phase. The microstructure analysis by scanning electron microscopy revealed the deposited structure was composed of periodically repeated amorphous and crystalline phases. Overlapping regions with nanoparticles aggregated were crystallized by laser reheating and remelting processes during subsequent laser scans. Vickers microhardness of the amorphous region showed around 35% higher than that of crystalline region. Average hardness obtained by a Rockwell macrohardness tester was very close to the microhardness of the amorphous region. The compression test showed that the fracture strain of Zr65Al10Ni10Cu15 amorphous composites was enhanced from less than 2% to as high as 5.7%, compared with fully amorphous metallic glass. Differential scanning calorimetry test results further revealed the amorphous structure and glass transition temperature Tg was observed to be around 655K. In 3 mol/L NaCl solution, laser direct deposited amorphous composites exhibited distinctly improved corrosion resistance, compared with fully-crystallized samples.

Influence of nanoporosity on biological response of sol-gel-derived 70S30C bioactive glass monoliths

NASA Astrophysics Data System (ADS)

Thamma, Ukrit

In the field of bioactive glasses for hard tissue regeneration, the bioactivity of a material is measured by its ability to induce the formation of hydroxyapatite (HA), Ca10(PO4)6(OH)2, under physiological conditions. Due to its close chemical crystallographic resemblance to natural bones, the newly formed HA layer has been shown to be critical for the biological interaction and bonding between the surfaces of bioactive glasses and osteoblast (bone) cells. Since the formation mechanism of HA is dependent on the dissolution behavior of the bioactive glass substrate, the characteristics of HA layer are dominated by the glass composition and structure. By introducing nanoporosity into glass structure, the dissolution rate and HA growth rate on nanoporous sol-gel-derived glasses are drastically enhanced compared to that of non-porous melt-quench glasses with the same composition. While enhanced HA growth on nanoporous glass, compared to non-porous glass, was hypothesized to be associated with greater specific surface area (SSA), other studies argued that growth rate of HA layer on nanoporous glass is dominated by nanopore size distribution, and minimally affected by the bulk SSA of the underlying glass. In order to decouple the influence of nanopore size and SSA on HA formation, we have successfully fabricated homogeneous 70S30C bioactive glass monoliths with different nanopore sizes, yet similar SSA via sol-gel process. After 3-day PBS incubation of 70S30C nanoporous glass monoliths, the presence of hydroxyapatite and Type-B carbonated hydroxyapatite (HA/B-CHA) was confirmed by XPS and FTIR. Here, we report the influence of nanopore size on HA/CHA formation pathway, growth rate, and its microstructure. Due to pore-size limited diffusion of PO43-, two HA/CHA formation pathways were observed: HA/CHA surface deposition and/or HA/CHA incorporation into nanopores. HA/CHA growth rate on the surface of a nanoporous glass monolith is dominated by the pore-size limited transport of Ca2+ ions dissolved from nanoporous glass substrates. Furthermore, with rising overall growth rate controlled by nanopore size, HA/CHA microstructures evolved from needle-like, plate-like, and flower-like, respectively. Furthermore, the levels of initial cell attachment and protein adsorption on HA/CHA microstructures formed on different nanopore sizes were investigated. The initial cell attachment was quantified by measuring the density and average size of attached MC3T3-E1 cells after 2-hour seeding period. The amounts and conformation of adsorbed proteins after 2-hour incubation with HA/CHA were characterized by Western blot and FTIR, respectively. It was shown that the amounts of protein adsorption on various HA/CHA microstructures do not correlate with the initial MC3T3-E1 attachment, while the beta-sheet/alpha-helix ratios in Amide I of bovine albumin serum (BSA) adsorbed on HA/CHA microstructures do correlate to the level of initial cell attachment. This result suggests that the beta-sheet structure in BSA interacts with and activates the RGD sequence of adhesion proteins, such as fibronectin, upon adsorption, thus significantly enhancing the initial attachment of MC3T3-E1 cells. These findings provide new insights that can lead to a more detailed fundamental understanding of protein-surface and protein-protein interactions, which are crucial for the further development of bioactive material.

Anisotropic and Hierarchical Porosity in Multifunctional Ceramics

NASA Astrophysics Data System (ADS)

Lichtner, Aaron Zev

The performance of multifunctional porous ceramics is often hindered by the seemingly contradictory effects of porosity on both mechanical and non-structural properties and yet a sufficient body of knowledge linking microstructure to these properties does not exist. Using a combination of tailored anisotropic and hierarchical materials, these disparate effects may be reconciled. In this project, a systematic investigation of the processing, characterization and properties of anisotropic and isotropic hierarchically porous ceramics was conducted. The system chosen was a composite ceramic intended as the cathode for a solid oxide fuel cell (SOFC). Comprehensive processing investigations led to the development of approaches to make hierarchical, anisotropic porous microstructures using directional freeze-casting of well dispersed slurries. The effect of all the important processing parameters was investigated. This resulted in an ability to tailor and control the important microstructural features including the scale of the microstructure, the macropore size and total porosity. Comparable isotropic porous ceramics were also processed using fugitive pore formers. A suite of characterization techniques including x-ray tomography and 3-D sectional scanning electron micrographs (FIB-SEM) was used to characterize and quantify the green and partially sintered microstructures. The effect of sintering temperature on the microstructure was quantified and discrete element simulations (DEM) were used to explain the experimental observations. Finally, the comprehensive mechanical properties, at room temperature, were investigated, experimentally and using DEM, for the different microstructures.

Multiphase imaging of gas flow in a nanoporous material using remote-detection NMR

NASA Astrophysics Data System (ADS)

Harel, Elad; Granwehr, Josef; Seeley, Juliette A.; Pines, Alex

2006-04-01

Pore structure and connectivity determine how microstructured materials perform in applications such as catalysis, fluid storage and transport, filtering or as reactors. We report a model study on silica aerogel using a time-of-flight magnetic resonance imaging technique to characterize the flow field and explain the effects of heterogeneities in the pore structure on gas flow and dispersion with 129Xe as the gas-phase sensor. The observed chemical shift allows the separate visualization of unrestricted xenon and xenon confined in the pores of the aerogel. The asymmetrical nature of the dispersion pattern alludes to the existence of a stationary and a flow regime in the aerogel. An exchange time constant is determined to characterize the gas transfer between them. As a general methodology, this technique provides insights into the dynamics of flow in porous media where several phases or chemical species may be present.

Electrophoretic deposition of multi-walled carbon nanotubes on porous anodic aluminum oxide using ionic liquid as a dispersing agent

NASA Astrophysics Data System (ADS)

Hekmat, F.; Sohrabi, B.; Rahmanifar, M. S.; Jalali, A.

2015-06-01

Multi-wall carbon nanotubes (MW-CNTs) have been arranged in nanochannels of anodic aluminum oxide template (AAO) by electrophoretic deposition (EPD) to make a vertically-aligned carbon nanotube (VA-CNT) based electrode. Well ordered AAO templates were prepared by a two-step anodizing process by applying a constant voltage of 45 V in oxalic acid solution. The stabilized CNTs in a water-soluble room temperature ionic liquid (1-methyl-3-octadecylimidazolium bromide), were deposited in the pores of AAO templates which were conductive by deposition of Ni nanoparticles in the bottom of pores. In order to obtain ideal results, different EPD parameters, such as concentration of MWCNTs and ionic liquid on stability of MWCNT suspensions, deposition time and voltage which are applied in EPD process and also optimal conditions for anodizing of template were investigated. The capacitive performance of prepared electrodes was analyzed by measuring the specific capacitance from cyclic voltammograms and the charge-discharge curves. A maximum value of 50 Fg-1 at the scan rate of 20 mV s-1was achieved for the specific capacitance.

Elongated unique DNA strand deposition on microstructured substrate by receding meniscus assembly and capillary force

PubMed Central

Charlot, B.; Bardin, F.; Sanchez, N.; Roux, P.; Teixeira, S.; Schwob, E.

2014-01-01

Ordered deposition of elongated DNA molecules was achieved by the forced dewetting of a DNA solution droplet over a microstructured substrate. This technique allows trapping, uncoiling, and deposition of DNA fragments without the need of a physicochemical anchoring of the molecule and results in the combing of double stranded DNA from the edge of microwells on a polydimethylsiloxane (PDMS) substrate. The technique involves scanning a droplet of DNA solution caught between a movable blade and a PDMS substrate containing an array of microwells. The deposition and elongation appears when the receding meniscus dewets microwells, the latter acting here as a perturbation in the dewetting line forcing the water film to break locally. Thus, DNA molecules can be deposited in an ordered manner and elongated conformation based solely on a physical phenomenon, allowing uncoiled DNA molecules to be observed in all their length. However, the exact mechanism that governs the deposition of DNA strands is not well understood. This paper is an analysis of the physical phenomenon occurring in the deposition process and is based on observations made with the use of high frame/second rate video microscopy. PMID:24753724

Deposition and characterization of titania-silica optical multilayers by asymmetric bipolar pulsed dc sputtering of oxide targets

NASA Astrophysics Data System (ADS)

Sagdeo, P. R.; Shinde, D. D.; Misal, J. S.; Kamble, N. M.; Tokas, R. B.; Biswas, A.; Poswal, A. K.; Thakur, S.; Bhattacharyya, D.; Sahoo, N. K.; Sabharwal, S. C.

2010-02-01

Titania-silica (TiO2/SiO2) optical multilayer structures have been conventionally deposited by reactive sputtering of metallic targets. In order to overcome the problems of arcing, target poisoning and low deposition rates encountered there, the application of oxide targets was investigated in this work with asymmetric bipolar pulsed dc magnetron sputtering. In order to evaluate the usefulness of this deposition methodology, an electric field optimized Fabry Perot mirror for He-Cd laser (λ = 441.6 nm) spectroscopy was deposited and characterized. For comparison, this mirror was also deposited by the reactive electron beam (EB) evaporation technique. The mirrors developed by the two complementary techniques were investigated for their microstructural and optical reflection properties invoking atomic force microscopy, ellipsometry, grazing incidence reflectometry and spectrophotometry. From these measurements the layer geometry, optical constants, mass density, topography, surface and interface roughness and disorder parameters were evaluated. The microstructural properties and spectral functional characteristics of the pulsed dc sputtered multilayer mirror were found to be distinctively superior to the EB deposited mirror. The knowledge gathered during this study has been utilized to develop a 21-layer high-pass edge filter for radio photoluminescence dosimetry.

3-D Distribution of Retained Colloids in Unsaturated Porous Media

NASA Astrophysics Data System (ADS)

Morales, V. L.; Perez-Reche, F. J.; Holzner, M.; Kinzelbach, W. K.; Otten, W.

2013-12-01

It is well accepted that colloid transport processes in porous media differ substantially between water saturated and unsaturated conditions. Differences are frequently ascribed to colloid immobilization by association with interfaces with the gas, as well as to restrictions of the liquid medium through which colloids are transported. Such factors depend on interfacial conditions provided by the water saturation of the porous medium. Yet, the current understanding of the importance of colloid retention at gas interfaces is based on observations of single pores or two-dimensional pore network representations, leaving open the question of their statistical significance when all pores in the medium are considered. In order to address this question, column experiments were performed using a model porous medium of glass beads through which colloidal silver particles were transported for conditions of varying water content. X-ray microtomography was subsequently employed as a non-destructive imaging technique to obtain pore-scale information of the entire column regarding: i) the presence and distribution of the four main locations where colloids can become retained (interfaces with the liquid-solid, gas-liquid and gas-solid, and the bulk liquid), ii) deposition profiles of colloids along the column classified by the available retention location, iii) morphological characteristics of the deposited colloidal aggregates, and iv) channel widths of 3-dimensional pore-water network representations. The results presented provide, for the first time, a direct statistical evaluation on the significance of colloid retention by attachment to the liquid-solid, gas-liquid, gas-solid interfaces, and by straining in the bulk liquid. Additionally, an effective-pore structure characteristic is proposed to improve predictions of mass removal by straining under various water saturations. A) Unsaturated conditions. B) Saturated conditions. Left: Tomograph slice illustrating with false coloring Regions Of Interest corresponding to retention locations at the gas-liquid (purple), gas-solid (white) and solid-liquid interface (blue), and the bulk liquid (teal). Right: Deposition profiles of silver colloids (Ag) per retention location (T: total, GLI: gas-liquid interface, GSI: gas-solid interface, SLI: solid-liquid interface, L: bulk liquid) (Top). Depth profiles of the volume occupied by each retention location (Middle). Normalized deposition profiles of silver volume retained by its corresponding retention-location volume (Bottom).

Control of microstructure in soldered, brazed, welded, plated, cast or vapor deposited manufactured components

DOEpatents

Ripley, Edward B.; Hallman, Russell L.

2015-11-10

Disclosed are methods and systems for controlling of the microstructures of a soldered, brazed, welded, plated, cast, or vapor deposited manufactured component. The systems typically use relatively weak magnetic fields of either constant or varying flux to affect material properties within a manufactured component, typically without modifying the alloy, or changing the chemical composition of materials or altering the time, temperature, or transformation parameters of a manufacturing process. Such systems and processes may be used with components consisting of only materials that are conventionally characterized as be uninfluenced by magnetic forces.

Do Surface Porosity and Pore Size Influence Mechanical Properties and Cellular Response to PEEK?

PubMed

Torstrick, F Brennan; Evans, Nathan T; Stevens, Hazel Y; Gall, Ken; Guldberg, Robert E

2016-11-01

Despite its widespread use in orthopaedic implants such as soft tissue fasteners and spinal intervertebral implants, polyetheretherketone (PEEK) often suffers from poor osseointegration. Introducing porosity can overcome this limitation by encouraging bone ingrowth; however, the corresponding decrease in implant strength can potentially reduce the implant's ability to bear physiologic loads. We have previously shown, using a single pore size, that limiting porosity to the surface of PEEK implants preserves strength while supporting in vivo osseointegration. However, additional work is needed to investigate the effect of pore size on both the mechanical properties and cellular response to PEEK. (1) Can surface porous PEEK (PEEK-SP) microstructure be reliably controlled? (2) What is the effect of pore size on the mechanical properties of PEEK-SP? (3) Do surface porosity and pore size influence the cellular response to PEEK? PEEK-SP was created by extruding PEEK through NaCl crystals of three controlled ranges: 200 to 312, 312 to 425, and 425 to 508 µm. Micro-CT was used to characterize the microstructure of PEEK-SP. Tensile, fatigue, and interfacial shear tests were performed to compare the mechanical properties of PEEK-SP with injection-molded PEEK (PEEK-IM). The cellular response to PEEK-SP, assessed by proliferation, alkaline phosphatase activity, vascular endothelial growth factor production, and calcium content of osteoblast, mesenchymal stem cell, and preosteoblast (MC3T3-E1) cultures, was compared with that of machined smooth PEEK and Ti6Al4V. Micro-CT analysis showed that PEEK-SP layers possessed pores that were 284 ± 35 µm, 341 ± 49 µm, and 416 ± 54 µm for each pore size group. Porosity and pore layer depth ranged from 61% to 69% and 303 to 391 µm, respectively. Mechanical testing revealed tensile strengths > 67 MPa and interfacial shear strengths > 20 MPa for all three pore size groups. All PEEK-SP groups exhibited > 50% decrease in ductility compared with PEEK-IM and demonstrated fatigue strength > 38 MPa at one million cycles. All PEEK-SP groups also supported greater proliferation and cell-mediated mineralization compared with smooth PEEK and Ti6Al4V. The PEEK-SP formulations evaluated in this study maintained favorable mechanical properties that merit further investigation into their use in load-bearing orthopaedic applications and supported greater in vitro osteogenic differentiation compared with smooth PEEK and Ti6Al4V. These results are independent of pore sizes ranging 200 µm to 508 µm. PEEK-SP may provide enhanced osseointegration compared with current implants while maintaining the structural integrity to be considered for several load-bearing orthopaedic applications such as spinal fusion or soft tissue repair.

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.

Particulate removal processes and hydraulics of porous gravel media filters

NASA Astrophysics Data System (ADS)

Minto, J. M.; Phoenix, V. R.; Dorea, C. C.; Haynes, H.; Sloan, W. T.

2013-12-01

Sustainable urban Drainage Systems (SuDS) are rapidly gaining acceptance as a low-cost tool for treating urban runoff pollutants close to source. Road runoff water in particular requires treatment due to the presence of high levels of suspended particles and heavy metals adsorbed to these particles. The aim of this research is to elucidate the particle removal processes that occur within gravel filters that have so far been considered as 'black-box' systems. Based on these findings, a better understanding will be attained on what influences gravel filter removal efficiency and how this changes throughout their design life; leading to a more rational design of this useful technology. This has been achieved by tying together three disparate research elements: tracer residence time distribution curves of filters during clogging; 3D magnetic resonance imaging (MRI) of clogging filters and computational fluid dynamics (CFD) modelling of complex filter pore networks. This research relates column average changes in particle removal efficiency and tracer residence time distributions (RTDs) due to clogging with non-invasive measurement of the spatial variability in particle deposition. The CFD modelling provides a link between observed deposition patterns, flow velocities and wall shear stresses as well as the explanations for the change in RTD with clogging and the effect on particle transport. Results show that, as a filter clogs, particles take a longer, more tortuous path through the filter. This is offset by a reduction in filter volume resulting in higher flow velocities and more rapid particle transport. Higher velocities result in higher shear stresses and the development of preferential pathways in which the velocity exceeds the deposition threshold and the overall efficiency of the filter decreases. Initial pore geometry is linked to the pattern of deposition and subsequent formation of preferential pathways. These results shed light on the 'black-box' internal clogging processes of gravel filters and are a considerable improvement on the inflow/outflow data most often available to monitor removal efficiency and clogging. Sub-section of the MRI derived geometry showing gravel (grey), pore space (blue), deposited particles (red) for 1) prior to clogging and 2) after clogging. The pore network skeleton (green) provided a reference point for comparing pore diameter change with clogging.

Solid-state 13C NMR studies of dissolved organic matter in pore waters from different depositional environments

USGS Publications Warehouse

Orem, W.H.; Hatcher, P.G.

1987-01-01

Dissolved organic matter (DOM) in pore waters from sediments of a number of different depositional environments was isolated by ultrafiltration using membranes with a nominal molecular weight cutoff of 500. This > 500 molecular weight DOM represents 70-98% of the total DOM in these pore waters. We determined the gross chemical structure of this material using both solid-state 13C nuclear magnetic resonance spectroscopy and elemental analysis. Our results show that the DOM in these pore waters appears to exist as two major types: one type dominated by carbohydrates and paraffinic structures and the second dominated by paraffinic and aromatic structures. We suggest that the dominance of one or the other structural type of DOM in the pore water depends on the relative oxidizing/reducing nature of the sediments as well as the source of the detrital organic matter. Under dominantly anaerobic conditions carbohydrates in the sediments are degraded by bacteria and accumulate in the pore water as DOM. However, little or no degradation of lignin occurs under these conditions. In contrast, sediments thought to be predominantly aerobic in character have DOM with diminished carbohydrate and enhanced aromatic character. The aromatic structures in the DOM from these sediments are thought to arise from the degradation of lignin. The large amounts of paraffinic structures in both types of DOM may be due to the degradation of unidentified paraffinic materials in algal or bacterial remains. ?? 1987.

Effects of sulfate deposition on pore water dissolved organic carbon, nutrients, and microbial enzyme activities in a northern peatland

Treesearch

L.R. Seifert-Monson; B.H. Hill; R.K. Kolka; T.M. Jicha; L.L. Lehto; C.M. Elonen

2014-01-01

Export of dissolved organic carbon from lakes and streams has increased throughout Europe and North America over the past several decades. One possible cause is altered deposition chemistry; specifically, decreasing sulfate inputs leading to changes in ionic strength and dissolved organic carbon solubility. To further investigate the relationship between deposition...

Development of porous metal oxide thin films by co-evaporation

NASA Astrophysics Data System (ADS)

Tesfamichael, T.; Motta, Nunzio; Bostrom, Thor; Bell, J. M.

2007-03-01

This paper focuses on the development of mixed metal oxide thin films and physical characterization of the films. The films were produced by co-evaporation of titanium oxide and tungsten oxide powders. This allowed the development of titanium oxide-tungsten oxide films as analyzed using XPS. Examination in the SEM and AFM showed that the films were nanoporous with the pore size and pore orientation varying as a function of the deposition angle. UV-vis spectra of the films show an increase of transmittance with increasing deposition angle which is attributed to the structure and porosity of the films. Raman analysis indicated that the as-deposited films have broad and weak Raman characteristics, attributed to the nanocrystal nature of the films and the presence of defects, and the peak broadening deceases after annealing the film, as expected.

Structure of anodized Al-Zr sputter deposited coatings and effect on optical appearance

NASA Astrophysics Data System (ADS)

Gudla, Visweswara Chakravarthy; Canulescu, Stela; Shabadi, Rajashekhara; Rechendorff, Kristian; Dirscherl, Kai; Ambat, Rajan

2014-10-01

The mechanism of interaction of light with the microstructure of anodized layer giving specific optical appearance is investigated using Al-Zr sputter deposited coating as a model system on an AA6060 substrate. Differences in the oxidative nature of various microstructural components result in the evolution of typical features in the anodized layer, which are investigated as a function of microstructure and correlated with its optical appearance. The Zr concentration in the coating was varied from 6 wt.% to 23 wt.%. Heat treatment of the coated samples was carried out at 550 °C for 4 h in order to evolve Al-Zr based second phase precipitates in the microstructure. Anodizing was performed using 20 wt.% sulphuric acid at 18 °C with an intention to study the effect of anodizing on the Al-Zr based precipitates in the coating. Detailed microstructural characterization of the coating and anodized layer was carried out using high resolution scanning and transmission electron microscopy, grazing incidence X-ray diffraction analysis, glow discharge optical emission spectroscopy, and optical appearance using spectrophotometry. The evolution of microstructure in the anodized layer as a function of anodizing parameters and their influence on the interaction of light is investigated and the results in general are applicable to discolouration of anodized layer on recycled aluminium alloys due to intermetallics.

A multidisciplinary approach to quantify the permeability of the Whakaari/White Island volcanic hydrothermal system (Taupo Volcanic Zone, New Zealand)

NASA Astrophysics Data System (ADS)

Heap, Michael J.; Kennedy, Ben M.; Farquharson, Jamie I.; Ashworth, James; Mayer, Klaus; Letham-Brake, Mark; Reuschlé, Thierry; Gilg, H. Albert; Scheu, Bettina; Lavallée, Yan; Siratovich, Paul; Cole, Jim; Jolly, Arthur D.; Baud, Patrick; Dingwell, Donald B.

2017-02-01

Our multidisciplinary study aims to better understand the permeability of active volcanic hydrothermal systems, a vital prerequisite for modelling and understanding their behaviour and evolution. Whakaari/White Island volcano (an active stratovolcano at the north-eastern end of the Taupo Volcanic Zone of New Zealand) hosts a highly reactive hydrothermal system and represents an ideal natural laboratory to undertake such a study. We first gained an appreciation of the different lithologies at Whakaari and (where possible) their lateral and vertical extent through reconnaissance by land, sea, and air. The main crater, filled with tephra deposits, is shielded by a volcanic amphitheatre comprising interbedded lavas, lava breccias, and tuffs. We deployed field techniques to measure the permeability and density/porosity of (1) > 100 hand-sized sample blocks and (2) layered unlithified deposits in eight purpose-dug trenches. Our field measurements were then groundtruthed using traditional laboratory techniques on almost 150 samples. Our measurements highlight that the porosity of the materials at Whakaari varies from ∼ 0.01 to ∼ 0.7 and permeability varies by eight orders of magnitude (from ∼ 10-19 to ∼ 10-11 m2). The wide range in physical and hydraulic properties is the result of the numerous lithologies and their varied microstructures and alteration intensities, as exposed by a combination of macroscopic and microscopic (scanning electron microscopy) observations, quantitative mineralogical studies (X-ray powder diffraction), and mercury porosimetry. An understanding of the spatial distribution of lithology and alteration style/intensity is therefore important to decipher fluid flow within the Whakaari volcanic hydrothermal system. We align our field observations and porosity/permeability measurements to construct a schematic cross section of Whakaari that highlights the salient findings of our study. Taken together, the alteration typical of a volcanic hydrothermal system can result in increases (due to alteration-induced dissolution and fracturing) and decreases (due to hydrothermal precipitation) to permeability. Importantly, a decrease in permeability-be it due to fracture sealing in lava, pore-filling alunite precipitation in tuff, near-vent cementation by sulphur, and/or well-sorted layers of fine ash-can result in pore pressure augmentation. An increase in pore pressure could result in ground deformation, seismicity, jeopardise the stability of the volcanic slopes, and/or drive the wide variety of eruptions observed at Whakaari. Our systematic study offers the most complete porosity-permeability dataset for a volcanic hydrothermal system to date. These new data will inform and support modelling, unrest monitoring, and eruption characterisation at Whakaari and other hydrothermally modified volcanic systems worldwide.

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).

Effect of milling time on microstructure and mechanical properties of Cu-Ni-graphite composites

NASA Astrophysics Data System (ADS)

Wang, Yiran; Gao, Yimin; Li, Yefei; Zhang, Chao; Huang, Xiaoyu; Zhai, Wenyan

2017-09-01

Cu-Ni-graphite composites are intended for application in switch slide baseplate materials. The microstructure of the composites depends strongly on the ball milling time, and a suitable time can significantly improve the properties of the Cu-Ni-graphite composites. In this study, a two-step milling method was employed. The morphology evolution and microstructural features of the powder was characterized at different milling times. Afterwards, the Cu-Ni-graphite composites were prepared in the process of cold pressing, sintering, re-pressing and re-sintering as a function of the different milling times. Finally, both the microstructure and mechanical properties of the Cu-Ni-graphite composites are discussed. The results show that no new phase was generated during the milling process. The morphology evolution of the mixture of Cu/Ni powder changed from spherical-like to cubic-like, plate-like and flake-like with an increasing milling time. The microstructure of the composites consisted of α-phase and graphite. The boundary area and quantity of pores changed as the milling time increased. The relative density, hardness and flexural strength reached maximum values at 15 h of milling time.

Altered Sputum Microstructure as a Marker of Airway Obstruction in Cystic Fibrosis Patients

NASA Astrophysics Data System (ADS)

Duncan, Gregg; Jung, James; West, Natalie; Boyle, Michael; Suk, Jung Soo; Hanes, Justin

In the lungs of cystic fibrosis (CF) patients, highly viscoelastic mucus remains stagnant in the lung leading to obstructed airways prone to recurrent infections. Bulk-fluid rheological measurement is primarily used to assess the pathological features of mucus. However, this approach is limited in detecting microscopic properties on the length scale of pathogens and immune cells. We have shown in prior work based on the transport of muco-inert nanoparticles (MIP) in CF sputum that patients can carry significantly different microstructural properties. In this study, we aimed to determine the factors leading to variations between patients in sputum microstructure and their clinical implications. The microrheological properties of CF sputum were measured using multi-particle tracking experiments of MIP. MIP were made by grafting polyethylene glycol onto the surface of polystyrene nanoparticles which prior work has shown prevents adhesion to CF sputum. Biochemical analyses show that sputum microstructure was significantly altered by elevated mucin and DNA content. Reduction in sputum pore size is characteristic of patients with obstructed airways as indicated by measured pulmonary function tests. Our microstructural read-out may serve as a novel biomarker for CF.

Controlling interferometric properties of nanoporous anodic aluminium oxide

PubMed Central

2012-01-01

A study of reflective interference spectroscopy [RIfS] properties of nanoporous anodic aluminium oxide [AAO] with the aim to develop a reliable substrate for label-free optical biosensing is presented. The influence of structural parameters of AAO including pore diameters, inter-pore distance, pore length, and surface modification by deposition of Au, Ag, Cr, Pt, Ni, and TiO2 on the RIfS signal (Fabry-Perot fringe) was explored. AAO with controlled pore dimensions was prepared by electrochemical anodization of aluminium using 0.3 M oxalic acid at different voltages (30 to 70 V) and anodization times (10 to 60 min). Results show the strong influence of pore structures and surface modifications on the interference signal and indicate the importance of optimisation of AAO pore structures for RIfS sensing. The pore length/pore diameter aspect ratio of AAO was identified as a suitable parameter to tune interferometric properties of AAO. Finally, the application of AAO with optimised pore structures for sensing of a surface binding reaction of alkanethiols (mercaptoundecanoic acid) on gold surface is demonstrated. PMID:22280884

Chemical vapor deposition of mullite coatings

DOEpatents

Sarin, Vinod; Mulpuri, Rao

1998-01-01

This invention is directed to the creation of crystalline mullite coatings having uniform microstructure by chemical vapor deposition (CVD). The process comprises the steps of establishing a flow of reactants which will yield mullite in a CVD reactor, and depositing a crystalline coating from the reactant flow. The process will yield crystalline coatings which are dense and of uniform thickness.

An in vitro study of the microstructure, composition and nanoindentation mechanical properties of remineralizing human dental enamel

NASA Astrophysics Data System (ADS)

Arsecularatne, J. A.; Hoffman, M.

2014-08-01

This paper describes the results of an in vitro investigation on the interrelations among microstructure, composition and mechanical properties of remineralizing human dental enamel. Polished enamel samples have been demineralized for 10 min in an acetic acid solution (at pH 3) followed by remineralization in human saliva for 30 and 120 min. Microstructure variations of sound, demineralized and remineralized enamel samples have been analysed using focused ion beam, scanning electron microscopy and transmission electron microscopy, while their compositions have been analysed using energy dispersive x-ray. Variations in the mechanical properties of enamel samples have been assessed using nanoindentation. The results reveal that, under the selected conditions, only partial remineralization of the softened enamel surface layer occurs where some pores remain unrepaired. As a result, while the nanoindentation elastic modulus shows an improvement following remineralization, hardness does not.

Peculiarities of binding composition production in vortex jet mill

NASA Astrophysics Data System (ADS)

Zagorodnyuk, L. Kh; Lesovik, V. S.; Sumskoy, D. A.; Elistratkin, M. Yu; Makhortov, D. S.

2018-03-01

The article investigates the disintegration of perlite production waste in a vortex jet mill; the regularities of milling were established. Binding compositions were obtained at different ratios of cement vs. perlite sand production waste in the vortex jet mill in various milling regimes. The peculiarities of milling processes were studied, and technological and physicomechanical properties of the binding compositions were determined as well. The microstructure of the cement stones made of activated Portland cement and binding compositions in the vortex jet mill was elucidated by electron microscopy. The open pores of the cement-binding compositions prepared using perlite fillers were found to be filled by newgrowths at different stages of collective growth. The microstructure of the binding compositions is dense due to rationally proportioned composition, effective mineral filler— perlite waste — that creates additional substrates for internal composite microstructure formation, mechanochemical activation of raw mixture, which allows obtaining composites with required properties.