Numerical modeling of physical vapor transport under microgravity conditions: Effect of thermal creep and stress

NASA Technical Reports Server (NTRS)

Mackowski, Daniel W.; Knight, Roy W.

1993-01-01

One of the most promising applications of microgravity (micro-g) environments is the manufacture of exotic and high-quality crystals in closed cylindrical ampoules using physical vapor transport (PVT) processes. The quality enhancements are believed to be due to the absence of buoyant convection in the weightless environment - resulting in diffusion-limited transport of the vapor. In a typical experiment, solid-phase sample material is initially contained at one end of the ampoule. The sample is made to sublime into the vapor phase and deposit onto the opposite end by maintaining the source at an elevated temperature with respect to the deposit. Identification of the physical factors governing both the rates and uniformity of crystal growth, and the optimization of the micro-g technology, will require an accurate modeling of the vapor transport within the ampoule. Previous micro-g modeling efforts have approached the problem from a 'classical' convective/diffusion formulation, in which convection is driven by the action of buoyancy on thermal and solutal density differences. The general conclusion of these works have been that in low gravity environments the effect of buoyancy on vapor transport is negligible, and vapor transport occurs in a diffusion-limited mode. However, it has been recently recognized than in the non-isothermal (and often low total pressure) conditions encountered in ampoules, the commonly-assumed no-slip boundary condition to the differential equations governing fluid motion can be grossly unrepresentative of the actual situation. Specifically, the temperature gradients can give rise to thermal creep flows at the ampoule side walls. In addition, temperature gradients in the vapor itself can, through the action of thermal stress, lead to bulk fluid convection.

Significance of vapor phase chemical reactions on CVD rates predicted by chemically frozen and local thermochemical equilibrium boundary layer theories

NASA Technical Reports Server (NTRS)

Gokoglu, Suleyman A.

1988-01-01

This paper investigates the role played by vapor-phase chemical reactions on CVD rates by comparing the results of two extreme theories developed to predict CVD mass transport rates in the absence of interfacial kinetic barrier: one based on chemically frozen boundary layer and the other based on local thermochemical equilibrium. Both theories consider laminar convective-diffusion boundary layers at high Reynolds numbers and include thermal (Soret) diffusion and variable property effects. As an example, Na2SO4 deposition was studied. It was found that gas phase reactions have no important role on Na2SO4 deposition rates and on the predictions of the theories. The implications of the predictions of the two theories to other CVD systems are discussed.

Enhanced Vapor-Phase Diffusion in Porous Media - LDRD Final Report

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

Ho, C.K.; Webb, S.W.

1999-01-01

As part of the Laboratory-Directed Research and Development (LDRD) Program at Sandia National Laboratories, an investigation into the existence of enhanced vapor-phase diffusion (EVD) in porous media has been conducted. A thorough literature review was initially performed across multiple disciplines (soil science and engineering), and based on this review, the existence of EVD was found to be questionable. As a result, modeling and experiments were initiated to investigate the existence of EVD. In this LDRD, the first mechanistic model of EVD was developed which demonstrated the mechanisms responsible for EVD. The first direct measurements of EVD have also been conductedmore » at multiple scales. Measurements have been made at the pore scale, in a two- dimensional network as represented by a fracture aperture, and in a porous medium. Significant enhancement of vapor-phase transport relative to Fickian diffusion was measured in all cases. The modeling and experimental results provide additional mechanisms for EVD beyond those presented by the generally accepted model of Philip and deVries (1957), which required a thermal gradient for EVD to exist. Modeling and experimental results show significant enhancement under isothermal conditions. Application of EVD to vapor transport in the near-surface vadose zone show a significant variation between no enhancement, the model of Philip and deVries, and the present results. Based on this information, the model of Philip and deVries may need to be modified, and additional studies are recommended.« less

Liquid phase stabilization versus bubble formation at a nanoscale curved interface

NASA Astrophysics Data System (ADS)

Schiffbauer, Jarrod; Luo, Tengfei

2018-03-01

We investigate the nature of vapor bubble formation near a nanoscale-curved convex liquid-solid interface using two models: an equilibrium Gibbs model for homogenous nucleation, and a nonequilibrium dynamic van der Waals-diffuse-interface model for phase change in an initially cool liquid. Vapor bubble formation is shown to occur for sufficiently large radius of curvature and is suppressed for smaller radii. Solid-fluid interactions are accounted for and it is shown that liquid-vapor interfacial energy, and hence Laplace pressure, has limited influence over bubble formation. The dominant factor is the energetic cost of creating the solid-vapor interface from the existing solid-liquid interface, as demonstrated via both equilibrium and nonequilibrium arguments.

Assessment of water droplet evaporation mechanisms on hydrophobic and superhydrophobic substrates.

PubMed

Pan, Zhenhai; Dash, Susmita; Weibel, Justin A; Garimella, Suresh V

2013-12-23

Evaporation rates are predicted and important transport mechanisms identified for evaporation of water droplets on hydrophobic (contact angle ~110°) and superhydrophobic (contact angle ~160°) substrates. Analytical models for droplet evaporation in the literature are usually simplified to include only vapor diffusion in the gas domain, and the system is assumed to be isothermal. In the comprehensive model developed in this study, evaporative cooling of the interface is accounted for, and vapor concentration is coupled to local temperature at the interface. Conjugate heat and mass transfer are solved in the solid substrate, liquid droplet, and surrounding gas. Buoyancy-driven convective flows in the droplet and vapor domains are also simulated. The influences of evaporative cooling and convection on the evaporation characteristics are determined quantitatively. The liquid-vapor interface temperature drop induced by evaporative cooling suppresses evaporation, while gas-phase natural convection acts to enhance evaporation. While the effects of these competing transport mechanisms are observed to counterbalance for evaporation on a hydrophobic surface, the stronger influence of evaporative cooling on a superhydrophobic surface accounts for an overprediction of experimental evaporation rates by ~20% with vapor diffusion-based models. The local evaporation fluxes along the liquid-vapor interface for both hydrophobic and superhydrophobic substrates are investigated. The highest local evaporation flux occurs at the three-phase contact line region due to proximity to the higher temperature substrate, rather than at the relatively colder droplet top; vapor diffusion-based models predict the opposite. The numerically calculated evaporation rates agree with experimental results to within 2% for superhydrophobic substrates and 3% for hydrophobic substrates. The large deviations between past analytical models and the experimental data are therefore reconciled with the comprehensive model developed here.

Biodegradation of vapor-phase toluene in unsaturated porous media: Column experiments.

PubMed

Khan, Ali M; Wick, Lukas Y; Harms, Hauke; Thullner, Martin

2016-04-01

Biodegradation of organic chemicals in the vapor phase of soils and vertical flow filters has gained attention as promising approach to clean up volatile organic compounds (VOC). The drivers of VOC biodegradation in unsaturated systems however still remain poorly understood. Here, we analyzed the processes controlling aerobic VOC biodegradation in a laboratory setup mimicking the unsaturated zone above a shallow aquifer. The setup allowed for diffusive vapor-phase transport and biodegradation of three VOC: non-deuterated and deuterated toluene as two compounds of highly differing biodegradability but (nearly) identical physical and chemical properties, and MTBE as (at the applied experimental conditions) non-biodegradable tracer and internal control. Our results showed for toluene an effective microbial degradation within centimeter VOC transport distances despite high gas-phase diffusivity. Degradation rates were controlled by the reactivity of the compounds while oxic conditions were found everywhere in the system. This confirms hypotheses that vadose zone biodegradation rates can be extremely high and are able to prevent the outgassing of VOC to the atmosphere within a centimeter range if compound properties and site conditions allow for sufficiently high degradation rates. Copyright © 2016 Elsevier Ltd. All rights reserved.

Growth kinetics and mass transport mechanisms of GaN columns by selective area metal organic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Wang, Xue; Hartmann, Jana; Mandl, Martin; Sadat Mohajerani, Matin; Wehmann, Hergo-H.; Strassburg, Martin; Waag, Andreas

2014-04-01

Three-dimensional GaN columns recently have attracted a lot of attention as the potential basis for core-shell light emitting diodes for future solid state lighting. In this study, the fundamental insights into growth kinetics and mass transport mechanisms of N-polar GaN columns during selective area metal organic vapor phase epitaxy on patterned SiOx/sapphire templates are systematically investigated using various pitch of apertures, growth time, and silane flow. Species impingement fluxes on the top surface of columns Jtop and on their sidewall Jsw, as well as, the diffusion flux from the substrate Jsub contribute to the growth of the GaN columns. The vertical and lateral growth rates devoted by Jtop, Jsw and Jsub are estimated quantitatively. The diffusion length of species on the SiOx mask surface λsub as well as on the sidewall surfaces of the 3D columns λsw are determined. The influences of silane on the growth kinetics are discussed. A growth model is developed for this selective area metal organic vapor phase epitaxy processing.

Controlled surface diffusion in plasma-enhanced chemical vapor deposition of GaN nanowires.

PubMed

Hou, Wen Chi; Hong, Franklin Chau-Nan

2009-02-04

This study investigates the growth of GaN nanowires by controlling the surface diffusion of Ga species on sapphire in a plasma-enhanced chemical vapor deposition (CVD) system. Under nitrogen-rich growth conditions, Ga has a tendency to adsorb on the substrate surface diffusing to nanowires to contribute to their growth. The significance of surface diffusion on the growth of nanowires is dependent on the environment of the nanowire on the substrate surface as well as the gas phase species and compositions. Under nitrogen-rich growth conditions, the growth rate is strongly dependent on the surface diffusion of gallium, but the addition of 5% hydrogen in nitrogen plasma instantly diminishes the surface diffusion effect. Gallium desorbs easily from the surface by reaction with hydrogen. On the other hand, under gallium-rich growth conditions, nanowire growth is shown to be dominated by the gas phase deposition, with negligible contribution from surface diffusion. This is the first study reporting the inhibition of surface diffusion effects by hydrogen addition, which can be useful in tailoring the growth and characteristics of nanowires. Without any evidence of direct deposition on the nanowire surface, gallium and nitrogen are shown to dissolve into the catalyst for growing the nanowires at 900 degrees C.

Alternate methods of applying diffusants to silicon solar cells. [screen printing of thick-film paste materials and vapor phase transport from solid sources

NASA Technical Reports Server (NTRS)

Brock, T. W.; Field, M. B.

1979-01-01

Low-melting phosphate and borate glasses were screen printed on silicon wafers and heated to form n and p junctions. Data on surface appearance, sheet resistance and junction depth are presented. Similar data are reported for vapor phase transport from sintered aluminum metaphosphate and boron-containing glass-ceramic solid sources. Simultaneous diffusion of an N(+) layer with screen-printed glass and a p(+) layer with screen-printed Al alloy paste was attempted. No p(+) back surface field formation was achieved. Some good cells were produced but the heating in an endless-belt furnace caused a large scatter in sheet resistance and junction depth for three separate lots of wafers.

A three-dimensional phase field model for nanowire growth by the vapor-liquid-solid mechanism

NASA Astrophysics Data System (ADS)

Wang, Yanming; Ryu, Seunghwa; McIntyre, Paul C.; Cai, Wei

2014-07-01

We present a three-dimensional multi-phase field model for catalyzed nanowire (NW) growth by the vapor-liquid-solid (VLS) mechanism. The equation of motion contains both a Ginzburg-Landau term for deposition and a diffusion (Cahn-Hilliard) term for interface relaxation without deposition. Direct deposition from vapor to solid, which competes with NW crystal growth through the molten catalyst droplet, is suppressed by assigning a very small kinetic coefficient at the solid-vapor interface. The thermodynamic self-consistency of the model is demonstrated by its ability to reproduce the equilibrium contact angles at the VLS junction. The incorporation of orientation dependent gradient energy leads to faceting of the solid-liquid and solid-vapor interfaces. The model successfully captures the curved shape of the NW base and the Gibbs-Thomson effect on growth velocity.

A semi-empirical model for the complete orientation dependence of the growth rate for vapor phase epitaxy - Chloride VPE of GaAs

NASA Technical Reports Server (NTRS)

Seidel-Salinas, L. K.; Jones, S. H.; Duva, J. M.

1992-01-01

A semi-empirical model has been developed to determine the complete crystallographic orientation dependence of the growth rate for vapor phase epitaxy (VPE). Previous researchers have been able to determine this dependence for a limited range of orientations; however, our model yields relative growth rate information for any orientation. This model for diamond and zincblende structure materials is based on experimental growth rate data, gas phase diffusion, and surface reactions. Data for GaAs chloride VPE is used to illustrate the model. The resulting growth rate polar diagrams are used in conjunction with Wulff constructions to simulate epitaxial layer shapes as grown on patterned substrates. In general, this model can be applied to a variety of materials and vapor phase epitaxy systems.

Controlled In Meso Phase Crystallization – A Method for the Structural Investigation of Membrane Proteins

PubMed Central

Kubicek, Jan; Schlesinger, Ramona; Baeken, Christian; Büldt, Georg; Schäfer, Frank; Labahn, Jörg

2012-01-01

We investigated in meso crystallization of membrane proteins to develop a fast screening technology which combines features of the well established classical vapor diffusion experiment with the batch meso phase crystallization, but without premixing of protein and monoolein. It inherits the advantages of both methods, namely (i) the stabilization of membrane proteins in the meso phase, (ii) the control of hydration level and additive concentration by vapor diffusion. The new technology (iii) significantly simplifies in meso crystallization experiments and allows the use of standard liquid handling robots suitable for 96 well formats. CIMP crystallization furthermore allows (iv) direct monitoring of phase transformation and crystallization events. Bacteriorhodopsin (BR) crystals of high quality and diffraction up to 1.3 Å resolution have been obtained in this approach. CIMP and the developed consumables and protocols have been successfully applied to obtain crystals of sensory rhodopsin II (SRII) from Halobacterium salinarum for the first time. PMID:22536388

Vapor-phase exchange of perchloroethene between soil and plants

USGS Publications Warehouse

Struckhoff, G.C.; Burken, J.G.; Schumacher, J.G.

2005-01-01

Tree core concentrations of tetrachloroethylene (perchloroethene, PCE) at the Riverfront Superfund Site in New Haven, MO, were found to mimic the profile of soil phase concentrations. The observed soil-tree core relationship was stronger than that of groundwater PCE to tree core concentrations at the same site. Earlier research has shown a direct, linear relationship between tree core and groundwater concentrations of chlorinated solvents and other organics. Laboratory-scale experiments were performed to elucidate this phenomenon, including determining partitioning coefficients of PCE between plant tissues and air and between plant tissues and water, measured to be 8.1 and 49 L/kg, respectively. The direct relationship of soil to tree core PCE concentrations was hypothesized to be caused by diffusion between tree roots and the soil vapor phase in the subsurface. The central findings of this research are discovering the importance of subsurface vapor-phase transfer for VOCs and uncovering a direct relationship between soil vapor-phase chlorinated solvents and uptake rates that impact contaminant translocation from the subsurface and transfer into the atmosphere. ?? 2005 American Chemical Society.

Liquid- and Gas-Phase Diffusion of Ferrocene in Thin Films of Metal-Organic Frameworks

PubMed Central

Zhou, Wencai; Wöll, Christof; Heinke, Lars

2015-01-01

The mass transfer of the guest molecules in nanoporous host materials, in particular in metal-organic frameworks (MOFs), is among the crucial features of their applications. By using thin surface-mounted MOF films in combination with a quartz crystal microbalance (QCM), the diffusion of ferrocene vapor and of ethanolic and hexanic ferrocene solution in HKUST-1 was investigated. For the first time, liquid- and gas-phase diffusion in MOFs was compared directly in the identical sample. The diffusion coefficients are in the same order of magnitude (~10−16 m2·s−1), whereas the diffusion coefficient of ferrocene in the empty framework is roughly 3-times smaller than in the MOF which is filled with ethanol or n-hexane.

Lithium-ions diffusion kinetic in LiFePO4/carbon nanoparticles synthesized by microwave plasma chemical vapor deposition for lithium-ion batteries

NASA Astrophysics Data System (ADS)

Gao, Chao; Zhou, Jian; Liu, Guizhen; Wang, Lin

2018-03-01

Olivine structure LiFePO4/carbon nanoparticles are synthesized successfully using a microwave plasma chemical vapor deposition (MPCVD) method. Microwave is an effective method to synthesize nanomaterials, the LiFePO4/carbon nanoparticles with high crystallinity can shorten diffusion routes for ionic transfer and electron tunneling. Meanwhile, a high quality, complete and homogenous carbon layer with appropriate thickness coating on the surface of LiFePO4 particles during in situ chemical vapor deposition process, which can ensure that electrons are able to transfer fast enough from all sides. Electrochemical impedance spectroscopy (EIS) is carried out to collect information about the kinetic behavior of lithium diffusion in LiFePO4/carbon nanoparticles during the charging and discharging processes. The chemical diffusion coefficients of lithium ions, DLi, are calculated in the range of 10-15-10-9 cm2s-1. Nanoscale LiFePO4/carbon particles show the longer regions of the faster solid-solution diffusion, and corresponding to the narrower region of the slower two-phase diffusion during the insertion/exaction of lithium ions. The CV and galvanostatic charge-discharge measurements show that the LiFePO4/carbon nanoparticles perform an excellent electrochemical performance, especially the high rate capacity and cycle life.

Development of vapor phase hydrogen peroxide sterilization process for spacecraft applications

NASA Technical Reports Server (NTRS)

Rohatgi, N.; Schubert, W.; Knight, J.; Quigley, M.; Forsberg, G.; Ganapathi, G.; Yarbrough, C.; Koukol, R.

2001-01-01

This paper will present test data and discussion on the work we are conducting at JPL to address the following issues: 1) efficacy of sterilization process; 2) diffusion of hydrogen peroxide under sterilization process conditions into hard to reach places; 3) materials and components compatibility with the sterilization process and 4) development of methodology to protect sensitive components from hydrogen peroxide vapor.

Diffusion Bonding of Silicon Carbide for MEMS-LDI Applications

NASA Technical Reports Server (NTRS)

Halbig, Michael C.; Singh, Mrityunjay; Shpargel, Tarah P.; Kiser, J. Douglas

2007-01-01

A robust joining approach is critically needed for a Micro-Electro-Mechanical Systems-Lean Direct Injector (MEMS-LDI) application which requires leak free joints with high temperature mechanical capability. Diffusion bonding is well suited for the MEMS-LDI application. Diffusion bonds were fabricated using titanium interlayers between silicon carbide substrates during hot pressing. The interlayers consisted of either alloyed titanium foil or physically vapor deposited (PVD) titanium coatings. Microscopy shows that well adhered, crack free diffusion bonds are formed under optimal conditions. Under less than optimal conditions, microcracks are present in the bond layer due to the formation of intermetallic phases. Electron microprobe analysis was used to identify the reaction formed phases in the diffusion bond. Various compatibility issues among the phases in the interlayer and substrate are discussed. Also, the effects of temperature, pressure, time, silicon carbide substrate type, and type of titanium interlayer and thickness on the microstructure and composition of joints are discussed.

Bulk Growth of Wide Band Gap II-VI Compound Semiconductors by Physical Vapor Transport

NASA Technical Reports Server (NTRS)

Su, Ching-Hua

1997-01-01

The mechanism of physical vapor transport of II-VI semiconducting compounds was studied both theoretically, using a one-dimensional diffusion model, as well as experimentally. It was found that the vapor phase stoichiometry is critical in determining the vapor transport rate. The experimental heat treatment methods to control the vapor composition over the starting materials were investigated and the effectiveness of the heat treatments was confirmed by partial pressure measurements using an optical absorption technique. The effect of residual (foreign) gas on the transport rate was also studies theoretically by the diffusion model and confirmed experimentally by the measurements of total pressure and compositions of the residual gas. An in-situ dynamic technique for the transport rate measurements and a further extension of the technique that simultaneously measured the partial pressures and transport rates were performed and, for the first time, the experimentally determined mass fluxes were compared with those calculated, without any adjustable parameters, from the diffusion model. Using the information obtained from the experimental transport rate measurements as guideline high quality bulk crystal of wide band gap II-VI semiconductor were grown from the source materials which undergone the same heat treatment methods. The grown crystals were then extensively characterized with emphasis on the analysis of the crystalline structural defects.

Monitoring water phase dynamics in winter clouds

NASA Astrophysics Data System (ADS)

Campos, Edwin F.; Ware, Randolph; Joe, Paul; Hudak, David

2014-10-01

This work presents observations of water phase dynamics that demonstrate the theoretical Wegener-Bergeron-Findeisen concepts in mixed-phase winter storms. The work analyzes vertical profiles of air vapor pressure, and equilibrium vapor pressure over liquid water and ice. Based only on the magnitude ranking of these vapor pressures, we identified conditions where liquid droplets and ice particles grow or deplete simultaneously, as well as the conditions where droplets evaporate and ice particles grow by vapor diffusion. The method is applied to ground-based remote-sensing observations during two snowstorms, using two distinct microwave profiling radiometers operating in different climatic regions (North American Central High Plains and Great Lakes). The results are compared with independent microwave radiometer retrievals of vertically integrated liquid water, cloud-base estimates from a co-located ceilometer, reflectivity factor and Doppler velocity observations by nearby vertically pointing radars, and radiometer estimates of liquid water layers aloft. This work thus makes a positive contribution toward monitoring and nowcasting the evolution of supercooled droplets in winter clouds.

Monitoring water phase dynamics in winter clouds

DOE PAGES

Campos, Edwin F.; Ware, Randolph; Joe, Paul; ...

2014-10-01

This work presents observations of water phase dynamics that demonstrate the theoretical Wegener–Bergeron–Findeisen concepts in mixed-phase winter storms. The work analyzes vertical profiles of air vapor pressure, and equilibrium vapor pressure over liquid water and ice. Based only on the magnitude ranking of these vapor pressures, we identified conditions where liquid droplets and ice particles grow or deplete simultaneously, as well as the conditions where droplets evaporate and ice particles grow by vapor diffusion. The method is applied to ground-based remote-sensing observations during two snowstorms, using two distinct microwave profiling radiometers operating in different climatic regions (North American Central Highmore » Plains and Great Lakes). The results are compared with independent microwave radiometer retrievals of vertically integrated liquid water, cloud-base estimates from a co-located ceilometer, reflectivity factor and Doppler velocity observations by nearby vertically pointing radars, and radiometer estimates of liquid water layers aloft. This work thus makes a positive contribution toward monitoring and now casting the evolution of supercooled droplets in winter clouds.« less

Analysis of pulsating spray flames propagating in lean two-phase mixtures with unity Lewis number

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

Nicoli, C.; Haldenwang, P.; Suard, S.

2005-11-01

Pulsating (or oscillatory) spray flames have recently been observed in experiments on two-phase combustion. Numerical studies have pointed out that such front oscillations can be obtained even with very simple models of homogeneous two-phase mixtures, including elementary vaporization schemes. The paper presents an analytical approach within the simple framework of the thermal-diffusive model, which is complemented by a vaporization rate independent of gas temperature, as soon as the latter reaches a certain thermal threshold ({theta}{sub v} in reduced form). The study involves the Damkoehler number (Da), the ratio of chemical reaction rate to vaporization rate, and the Zeldovich number (Ze)more » as essential parameters. We use the standard asymptotic method based on matched expansions in terms of 1/Ze. Linear analysis of two-phase flame stability is performed by studying, in the absence of differential diffusive effects (unity Lewis number), the linear growth rate of 2-D perturbations added to steady plane solutions and characterized by wavenumber k in the direction transverse to spreading. A domain of existence is found for the pulsating regime. It corresponds to mixture characteristics often met in air-fuel two-phase systems: low boiling temperature ({theta}{sub v} << 1), reaction rate not higher than vaporization rate (Da < 1, i.e., small droplets), and activation temperature assumed to be high compared with flame temperature (Ze {>=} 10). Satisfactory comparison with numerical simulations confirms the validity of the analytical approach; in particular, positive growth rates have been found for planar perturbations (k = 0) and for wrinkled fronts (k {ne} 0). Finally, comparison between predicted frequencies and experimental measurements is discussed.« less

Volatile transport on Venus and implications for surface geochemistry and geology

NASA Technical Reports Server (NTRS)

Brackett, Robert A.; Fegley, Bruce; Arvidson, Raymond E.

1995-01-01

The high vapor pressure of volatile metal halides and chalcogenides (e.g., of Cu, Zn, Sn, Pb, As, Sb, Bi) at typical Venus surface temperatures, coupled with the altitude-dependent temperature gradient of approximately 8.5 K/km, is calculated to transport volatile metal vapors to the highlands of Venus, where condensation and accumulation will occur. The predicted geochemistry of volatile metals on Venus is supported by observations of CuCl in volcanic gases at Kilauea and Nyiragongo, and large enrichments of these and other volatile elements in terrestrial volcanic aerosols. A one-dimensional finite difference vapor transport model shows the diffusive migration of a thickness of 0.01 to greater than 10 microns/yr of moderately to highly volatile phases (e.g., metal halides and chalcogenides) from the hot lowlands (740 K) to the cold highlands (660 K) on Venus. The diffusive transport of volatile phases on Venus may explain the observed low emissivity of the Venusian highlands, hazes at 6-km altitude observed by two Pioneer Venus entry probes, and the Pioneer Venus entry probe anomalies at 12.5 km.

Sound, infrasound, and sonic boom absorption by atmospheric clouds.

PubMed

Baudoin, Michaël; Coulouvrat, François; Thomas, Jean-Louis

2011-09-01

This study quantifies the influence of atmospheric clouds on propagation of sound and infrasound, based on an existing model [Gubaidulin and Nigmatulin, Int. J. Multiphase Flow 26, 207-228 (2000)]. Clouds are considered as a dilute and polydisperse suspension of liquid water droplets within a mixture of dry air and water vapor, both considered as perfect gases. The model is limited to low and medium altitude clouds, with a small ice content. Four physical mechanisms are taken into account: viscoinertial effects, heat transfer, water phase changes (evaporation and condensation), and vapor diffusion. Physical properties of atmospheric clouds (altitude, thickness, water content and droplet size distribution) are collected, along with values of the thermodynamical coefficients. Different types of clouds have been selected. Quantitative evaluation shows that, for low audible and infrasound frequencies, absorption within clouds is several orders of magnitude larger than classical absorption. The importance of phase changes and vapor diffusion is outlined. Finally, numerical simulations for nonlinear propagation of sonic booms indicate that, for thick clouds, attenuation can lead to a very large decay of the boom at the ground level. © 2011 Acoustical Society of America

Synthesis of alloys with controlled phase structure

DOEpatents

Guthrie, Stephen Everett; Thomas, George John; Bauer, Walter; Yang, Nancy Yuan Chi

1999-04-20

A method for preparing controlled phase alloys useful for engineering and hydrogen storage applications. This novel method avoids melting the constituents by employing vapor transport, in a hydrogen atmosphere, of an active metal constituent, having a high vapor pressure at temperatures .apprxeq.300 C. and its subsequent condensation on and reaction with the other constituent (substrate) of an alloy thereby forming a controlled phase alloy and preferably a single phase alloy. It is preferred that the substrate material be a metal powder such that diffusion of the active metal constituent, preferably magnesium, and reaction therewith can be completed within a reasonable time and at temperatures .apprxeq.300 C. thereby avoiding undesirable effects such as sintering, local compositional inhomogeneities, segregation, and formation of unwanted second phases such as intermetallic compounds.

Synthesis of alloys with controlled phase structure

DOEpatents

Guthrie, S.E.; Thomas, G.J.; Bauer, W.; Yang, N.Y.C.

1999-04-20

A method is described for preparing controlled phase alloys useful for engineering and hydrogen storage applications. This novel method avoids melting the constituents by employing vapor transport, in a hydrogen atmosphere, of an active metal constituent, having a high vapor pressure at temperatures {approx_equal}300 C and its subsequent condensation on and reaction with the other constituent (substrate) of an alloy thereby forming a controlled phase alloy and preferably a single phase alloy. It is preferred that the substrate material be a metal powder such that diffusion of the active metal constituent, preferably magnesium, and reaction therewith can be completed within a reasonable time and at temperatures {approx_equal}300 C thereby avoiding undesirable effects such as sintering, local compositional inhomogeneities, segregation, and formation of unwanted second phases such as intermetallic compounds. 4 figs.

Island dynamics and anisotropy during vapor phase epitaxy of m-plane GaN

DOE PAGES

Perret, Edith; Xu, Dongwei; Highland, M. J.; ...

2017-12-04

Using in situ grazing-incidence x-ray scattering, we have measured the diffuse scattering from islands that form during layer-by-layer growth of GaN by metal-organic vapor phase epitaxy on the (10more » $$\\bar{1}$$0) m-plane surface. The diffuse scattering is extended in the (0001) in-plane direction in reciprocal space, indicating a strong anisotropy with islands elongated along [1$$\\bar{2}$$10] and closely spaced along [0001]. This is confirmed by atomic force microscopy of a quenched sample. Islands were characterized as a function of growth rate F and temperature. Furthermore, the island spacing along [0001] observed during the growth of the first monolayer obeys a power-law dependence on growth rate F -n, with an exponent n=0.25±0.02. Our results are in agreement with recent kinetic Monte Carlo simulations, indicating that elongated islands result from the dominant anisotropy in step edge energy and not from surface diffusion anisotropy. The observed power-law exponent can be explained using a simple steady-state model, which gives n = 1/4.« less

Island dynamics and anisotropy during vapor phase epitaxy of m-plane GaN

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

Perret, Edith; Xu, Dongwei; Highland, M. J.

Using in situ grazing-incidence x-ray scattering, we have measured the diffuse scattering from islands that form during layer-by-layer growth of GaN by metal-organic vapor phase epitaxy on the (1010) m-plane surface. The diffuse scattering is extended in the (0001) in-plane direction in reciprocal space, indicating a strong anisotropy with islands elongated along [1210] and closely spaced along [0001]. This is confirmed by atomic force microscopy of a quenched sample. Islands were characterized as a function of growth rate F and temperature. The island spacing along [0001] observed during the growth of the first monolayer obeys a power-law dependence on growthmore » rate F-n, with an exponent n = 0:25 + 0.02. The results are in agreement with recent kinetic Monte Carlo simulations, indicating that elongated islands result from the dominant anisotropy in step edge energy and not from surface diffusion anisotropy. The observed power-law exponent can be explained using a simple steady-state model, which gives n = 1/4.« less

Island dynamics and anisotropy during vapor phase epitaxy of m-plane GaN

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

Perret, Edith; Xu, Dongwei; Highland, M. J.

Using in situ grazing-incidence x-ray scattering, we have measured the diffuse scattering from islands that form during layer-by-layer growth of GaN by metal-organic vapor phase epitaxy on the (10more » $$\\bar{1}$$0) m-plane surface. The diffuse scattering is extended in the (0001) in-plane direction in reciprocal space, indicating a strong anisotropy with islands elongated along [1$$\\bar{2}$$10] and closely spaced along [0001]. This is confirmed by atomic force microscopy of a quenched sample. Islands were characterized as a function of growth rate F and temperature. Furthermore, the island spacing along [0001] observed during the growth of the first monolayer obeys a power-law dependence on growth rate F -n, with an exponent n=0.25±0.02. Our results are in agreement with recent kinetic Monte Carlo simulations, indicating that elongated islands result from the dominant anisotropy in step edge energy and not from surface diffusion anisotropy. The observed power-law exponent can be explained using a simple steady-state model, which gives n = 1/4.« less

Microfabricated diffusion source

DOEpatents

Oborny, Michael C [Albuquerque, NM; Frye-Mason, Gregory C [Cedar Crest, NM; Manginell, Ronald P [Albuquerque, NM

2008-07-15

A microfabricated diffusion source to provide for a controlled diffusion rate of a vapor comprises a porous reservoir formed in a substrate that can be filled with a liquid, a headspace cavity for evaporation of the vapor therein, a diffusion channel to provide a controlled diffusion of the vapor, and an outlet to release the vapor into a gas stream. The microfabricated diffusion source can provide a calibration standard for a microanalytical system. The microanalytical system with an integral diffusion source can be fabricated with microelectromechanical systems technologies.

Preparation of cerium halide solvate complexes

DOEpatents

Vasudevan, Kalyan V; Smith, Nickolaus A; Gordon, John C; McKigney, Edward A; Muenchaussen, Ross E

2013-08-06

Crystals of a solvated cerium(III) halide solvate complex resulted from a process of forming a paste of a cerium(III) halide in an ionic liquid, adding a solvent to the paste, removing any undissolved solid, and then cooling the liquid phase. Diffusing a solvent vapor into the liquid phase also resulted in crystals of a solvated cerium(III) halide complex.

Pore-scale modeling of phase change in porous media

NASA Astrophysics Data System (ADS)

Juanes, Ruben; Cueto-Felgueroso, Luis; Fu, Xiaojing

2017-11-01

One of the main open challenges in pore-scale modeling is the direct simulation of flows involving multicomponent mixtures with complex phase behavior. Reservoir fluid mixtures are often described through cubic equations of state, which makes diffuse interface, or phase field theories, particularly appealing as a modeling framework. What is still unclear is whether equation-of-state-driven diffuse-interface models can adequately describe processes where surface tension and wetting phenomena play an important role. Here we present a diffuse interface model of single-component, two-phase flow (a van der Waals fluid) in a porous medium under different wetting conditions. We propose a simplified Darcy-Korteweg model that is appropriate to describe flow in a Hele-Shaw cell or a micromodel, with a gap-averaged velocity. We study the ability of the diffuse-interface model to capture capillary pressure and the dynamics of vaporization/condensation fronts, and show that the model reproduces pressure fluctuations that emerge from abrupt interface displacements (Haines jumps) and from the break-up of wetting films.

Dissolution kinetics of volatile organic compound vapors in water: An integrated experimental and computational study

NASA Astrophysics Data System (ADS)

Mahmoodlu, Mojtaba G.; Pontedeiro, Elizabeth M.; Pérez Guerrero, Jesús S.; Raoof, Amir; Majid Hassanizadeh, S.; van Genuchten, Martinus Th.

2017-01-01

In this study we performed batch experiments to investigate the dissolution kinetics of trichloroethylene (TCE) and toluene vapors in water at room temperature and atmospheric pressure. The batch systems consisted of a water reservoir and a connected headspace, the latter containing a small glass cylinder filled with pure volatile organic compound (VOC). Results showed that air phase concentrations of both TCE and toluene increased relatively quickly to their maximum values and then became constant. We considered subsequent dissolution into both stirred and unstirred water reservoirs. Results of the stirred experiments showed a quick increase in the VOC concentrations with time up to their solubility limit in water. VOC vapor dissolution was found to be independent of pH. In contrast, salinity had a significant effect on the solubility of TCE and toluene vapors. VOC evaporation and vapor dissolution in the stirred water reservoirs followed first-order rate processes. Observed data could be described well using both simplified analytical solutions, which decoupled the VOC dynamics in the air and water phases, as well as using more complete coupled solutions. However, the estimated evaporation (ke) and dissolution (kd) rate constants differed by up to 70% between the coupled and uncoupled formulations. We also numerically investigated the effects of fluid withdrawal from the small water reservoir due to sampling. While decoupling the VOC air and water phase mass transfer processes produced unreliable estimates of kd, the effects of fluid withdrawal on the estimated rate constants were found to be less important. The unstirred experiments showed a much slower increase in the dissolved VOC concentrations versus time. Molecular diffusion of the VOCs within the aqueous phase became then the limiting factor for mass transfer from air to water. Fluid withdrawal during sampling likely caused some minor convection within the reservoir, which was simulated by increasing the apparent liquid diffusion coefficient.

Substrate-mediated diffusion-induced growth of single-crystal nanowires.

PubMed

Mohammad, S Noor

2009-11-28

Theoretical investigations of the growth and growth rates of single-crystal nanowires (NWs) by vapor phase mechanisms have been carried out. Substrate-induced processes are assumed to dominate this growth. The modeling for growth takes adsorption, desorption, surface scattering, and diffusion into account. It takes into consideration also the retarding electric field arising from the scattering of the NW vapor species by both the substrate and the NW sidewalls. Growth characteristics under the influence of the retarding electric field have been studied. Competitive roles of adatom diffusivity and the electric field in the NW growth are elucidated. Influence of the growing NW length and the adatom impingement rate on the NW growth rate has been described. The effect of adatom collection area around each NW has been examined. The NW tapering and kinking have been explained. The fundamentals of the substrate induction and details of the growth parameters have been analyzed. The influence of foreign element catalytic agents in the vapor-liquid-solid mechanism has been presented. All these have led to the understanding and resolution of problems, controversies, and contradictions involving substrate-induced NW growths.

Analytical modeling of operating characteristics of premixing-prevaporizing fuel-air mixing passages. Volume 1: Analysis and results

NASA Technical Reports Server (NTRS)

Anderson, O. L.; Chiappetta, L. M.; Edwards, D. E.; Mcvey, J. B.

1982-01-01

A model for predicting the distribution of liquid fuel droplets and fuel vapor in premixing-prevaporizing fuel-air mixing passages of the direct injection type is reported. This model consists of three computer programs; a calculation of the two dimensional or axisymmetric air flow field neglecting the effects of fuel; a calculation of the three dimensional fuel droplet trajectories and evaporation rates in a known, moving air flow; a calculation of fuel vapor diffusing into a moving three dimensional air flow with source terms dependent on the droplet evaporation rates. The fuel droplets are treated as individual particle classes each satisfying Newton's law, a heat transfer, and a mass transfer equation. This fuel droplet model treats multicomponent fuels and incorporates the physics required for the treatment of elastic droplet collisions, droplet shattering, droplet coalescence and droplet wall interactions. The vapor diffusion calculation treats three dimensional, gas phase, turbulent diffusion processes. The analysis includes a model for the autoignition of the fuel air mixture based upon the rate of formation of an important intermediate chemical species during the preignition period.

Local Interactions of Hydrometeors by Diffusion in Mixed-Phase Clouds

NASA Astrophysics Data System (ADS)

Baumgartner, Manuel; Spichtinger, Peter

2017-04-01

Mixed-phase clouds, containing both ice particles and liquid droplets, are important for the Earth-Atmosphere system. They modulate the radiation budget by a combination of albedo effect and greenhouse effect. In contrast to liquid water clouds, the radiative impact of clouds containing ice particles is still uncertain. Scattering and absorption highly depends in microphysical properties of ice crystals, e.g. size and shape. In addition, most precipitation on Earth forms via the ice phase. Thus, better understanding of ice processes as well as their representation in models is required. A key process for determining shape and size of ice crystals is diffusional growth. Diffusion processes in mixed-phase clouds are highly uncertain; in addition they are usually highly simplified in cloud models, especially in bulk microphysics parameterizations. The direct interaction between cloud droplets and ice particles, due to spatial inhomogeneities, is ignored; the particles can only interact via their environmental conditions. Local effects as supply of supersaturation due to clusters of droplets around ice particles are usually not represented, although they form the physical basis of the Wegener-Bergeron-Findeisen process. We present direct numerical simulations of the interaction of single ice particles and droplets, especially their local competition for the available water vapor. In addition, we show an approach to parameterize local interactions by diffusion. The suggested parameterization uses local steady-state solutions of the diffusion equations for water vapor for an ice particle as well as a droplet. The individual solutions are coupled together to obtain the desired interaction. We show some results of the scheme as implemented in a parcel model.

Improved thermal lattice Boltzmann model for simulation of liquid-vapor phase change

NASA Astrophysics Data System (ADS)

Li, Qing; Zhou, P.; Yan, H. J.

2017-12-01

In this paper, an improved thermal lattice Boltzmann (LB) model is proposed for simulating liquid-vapor phase change, which is aimed at improving an existing thermal LB model for liquid-vapor phase change [S. Gong and P. Cheng, Int. J. Heat Mass Transfer 55, 4923 (2012), 10.1016/j.ijheatmasstransfer.2012.04.037]. First, we emphasize that the replacement of ∇ .(λ ∇ T ) /∇.(λ ∇ T ) ρ cV ρ cV with ∇ .(χ ∇ T ) is an inappropriate treatment for diffuse interface modeling of liquid-vapor phase change. Furthermore, the error terms ∂t 0(T v ) +∇ .(T vv ) , which exist in the macroscopic temperature equation recovered from the previous model, are eliminated in the present model through a way that is consistent with the philosophy of the LB method. Moreover, the discrete effect of the source term is also eliminated in the present model. Numerical simulations are performed for droplet evaporation and bubble nucleation to validate the capability of the model for simulating liquid-vapor phase change. It is shown that the numerical results of the improved model agree well with those of a finite-difference scheme. Meanwhile, it is found that the replacement of ∇ .(λ ∇ T ) /∇ .(λ ∇ T ) ρ cV ρ cV with ∇ .(χ ∇ T ) leads to significant numerical errors and the error terms in the recovered macroscopic temperature equation also result in considerable errors.

Demonstration of the AGI Universal Samplers (F.K.A. the GORE Modules) for Passive Sampling of Groundwater

DTIC Science & Technology

2014-03-27

Coefficient from Water into the Sorbent KOW Octanol-Water Partition Coefficient LF Low Flow LNAPL Light Non-aqueous Phase Liquid LTM Long-Term...Once in the vapor phase, the molecule can then diffuse through the mem- ERDC/CRREL TR-14-4 5 brane while liquid water is prevented from passing...remediation at this site was conducted in two phases. Phase I consisted of vertical contamina- tion profiling followed by the in situ injection of an

Demonstration of the AGI Universal Samplers (F.K.A. the GORE (registered trademark) Modules) for Passive Sampling of Groundwater

DTIC Science & Technology

2014-03-01

Coefficient from Water into the Sorbent KOW Octanol-Water Partition Coefficient LF Low Flow LNAPL Light Non-aqueous Phase Liquid LTM Long-Term...Once in the vapor phase, the molecule can then diffuse through the mem- ERDC/CRREL TR-14-4 5 brane while liquid water is prevented from passing...remediation at this site was conducted in two phases. Phase I consisted of vertical contamina- tion profiling followed by the in situ injection of an

Diffusion of vaporous guests into a seemingly non-porous organic crystal

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

Herbert, Simon A.; Janiak, Agnieszka; Thallapally, Praveen K.

2014-10-07

In this research, the tetragonal apohost phase of p-tert-butyltetramethoxythiacalix[4]arene absorbs hydrochloric acid and iodine. These guest molecules occupy different sites in the solid-state structure -- either within the small intrinsic voids of the macrocycle or within the interstitial spaces between the host molecules. This study illustrates the dynamic deformation of the host, providing strong mechanistic insight into the diffusion of guests into this seemingly non-porous material.

Liquid phase evaporation on the normal shock wave in moist air transonic flows in nozzles

NASA Astrophysics Data System (ADS)

Dykas, Sławomir; Szymański, Artur; Majkut, Mirosław

2017-06-01

This paper presents a numerical analysis of the atmospheric air transonic flow through de Laval nozzles. By nature, atmospheric air always contains a certain amount of water vapor. The calculations were made using a Laval nozzle with a high expansion rate and a convergent-divergent (CD) "half-nozzle", referred to as a transonic diffuser, with a much slower expansion rate. The calculations were performed using an in-house CFD code. The computational model made it possible to simulate the formation of the liquid phase due to spontaneous condensation of water vapor contained in moist air. The transonic flow calculations also take account of the presence of a normal shock wave in the nozzle supersonic part to analyze the effect of the liquid phase evaporation.

Under What Conditions Can Equilibrium Gas-Particle Partitioning Be Expected to Hold in the Atmosphere?

PubMed

Mai, Huajun; Shiraiwa, Manabu; Flagan, Richard C; Seinfeld, John H

2015-10-06

The prevailing treatment of secondary organic aerosol formation in atmospheric models is based on the assumption of instantaneous gas-particle equilibrium for the condensing species, yet compelling experimental evidence indicates that organic aerosols can exhibit the properties of highly viscous, semisolid particles, for which gas-particle equilibrium may be achieved slowly. The approach to gas-particle equilibrium partitioning is controlled by gas-phase diffusion, interfacial transport, and particle-phase diffusion. Here we evaluate the controlling processes and the time scale to achieve gas-particle equilibrium as a function of the volatility of the condensing species, its surface accommodation coefficient, and its particle-phase diffusivity. For particles in the size range of typical atmospheric organic aerosols (∼50-500 nm), the time scale to establish gas-particle equilibrium is generally governed either by interfacial accommodation or particle-phase diffusion. The rate of approach to equilibrium varies, depending on whether the bulk vapor concentration is constant, typical of an open system, or decreasing as a result of condensation into the particles, typical of a closed system.

Diffusion of Mg dopant in metal-organic vapor-phase epitaxy grown GaN and AlxGa1-xN

NASA Astrophysics Data System (ADS)

Köhler, K.; Gutt, R.; Wiegert, J.; Kirste, L.

2013-02-01

Diffusion of the p-type dopant Mg in GaN and AlxGa1-xN which is accompanied by segregation and affected by transient effects in metal-organic vapor-phase epitaxy reactors is investigated. We have grown 110 nm thick Mg doped GaN and Al0.1Ga0.9N layers on top of undoped GaN and Al0.1Ga0.9N layers, respectively, in a temperature range between 925 °C and 1050 °C where we placed special emphasis on the lower temperature limit without diffusion to allow separation of Mg transients, diffusion, and segregation. Hereby, AlxGa1-xN layers enable monitoring of the resolution limit by secondary ion mass spectrometry analyses for the respective samples; therefore, thin AlxGa1-xN marker layers are incorporated in the thick GaN layers. We found an upper limit of 1.25 × 1019 cm-3 for diffusing Mg atoms in both sample types. Owing to the marked influence of Mg segregation in Al0.1Ga0.9N, diffusion is only seen by using a GaN cap on top of the Al0.1Ga0.9N layer sequence. Diffusion in Al0.1Ga0.9N is shown to be increased by about 25%-30% compared to GaN. Post growth annealing experiments under conditions equivalent to those used for growth of the Mg doped samples showed negligible diffusion. Comparing the results to well established findings on other doped III-V compounds, diffusion is explained by an interstitial-substitutional mechanism with a diffusion coefficient, which is concentration dependent. Analysis of the temperature dependent diffusivity revealed an activation energy of 5.0 eV for GaN:Mg and 5.2 eV for Al0.1Ga0.9N:Mg.

Transport of Carbon Tetrachloride in a Fractured Vadose Zone due to Atmospheric Pressure Fluctuations, Diffusion, and Vapor Density

NASA Astrophysics Data System (ADS)

McCray, J. E.; Downs, W.; Falta, R. W.; Housley, T.

2005-12-01

DNAPL sources of carbon tetrachloride (CT) vapors are of interest at the Radioactive Waste Management Complex (RWMC) at the Idaho National Engineering and Environmental Laboratory (INEEL). The site is underlain by thick fractured basalt that includes sedimentary interbeds, each are a few meters thick. Daily atmospheric pressure fluctuations serve as driving forces for CT vapor transport in the subsurface. Other important transport processes for vapor movement include gas-phase diffusion and density-driven transport. The objective of this research is to investigate the influence and relative importance of these processes on gaseous transport of CT. Gas pressure and vapor concentration measurements were conducted at various depths in two wells. A numerical multiphase flow model (TOUGH2), calibrated to field pressure data, is used to conduct sensitivity analyses to elucidate the importance of the different transport mechanisms. Results show that the basalt is highly permeable to vertical air flow. The pressure dampening occurs mainly in the sedimentary interbeds. Model-calibrated permeability values for the interbeds are similar to those obtained in a study by the U.S. Geological Survey for shallow sediments, and an order of magnitude higher than column-scale values obtained by previous studies conducted by INEEL scientists. The transport simulations indicate that considering the effect of barometric pressure changes is critical to simulating transport of pollutants in the vadose zone above the DNAPL source. Predicted concentrations can be orders of magnitude smaller than actual concentrations if the effect is not considered. Below the DNAPL vapor source, accounting for density and diffusion alone would yield acceptable results provided that a 20% error in concentrations are acceptable, and that simulating concentrations trends (and not actual concentrations) is the primary goal.

Cooling of a microchannel with thin evaporating liquid film sheared by dry gas flow

NASA Astrophysics Data System (ADS)

Kabova, Yu O.; Kuznetsov, V. V.

2017-11-01

A joint motion of thin liquid film and dry gas in a microchannel is investigated numerically at different values of initial concentration of the liquid vapor in the gas phase, taking into account the evaporation process. Major factors affecting the temperature distribution in the liquid and the gas phases are as follows: transfer of heat by liquid and gas flows, heat loses due to evaporation, diffusion heat exchange. Comparisons of the numerical results for the case of the dry gas and for the case of equilibrium concentration of vapor in the gas have been carried out. It is shown that use of dry gas enhances the heat dissipation from the heater. It is found out that not only intense evaporation occurs near the heating areas, but also in both cases vapor condensation takes place below the heater in streamwise direction.

Uptake of aromatic hydrocarbon vapors (benzene and phenanthrene) at the air-water interface of micron-size water droplets.

PubMed

Raja, Suresh; Valsaraj, Kalliat T

2004-12-01

Uptake of aromatic hydrocarbon vapors (benzene and phenanthrene) by typical micrometer-sized fog-water droplets was studied using a falling droplet reactor at temperatures between 296 and 316 K. Uptake of phenanthrene vapor greater than that predicted by bulk (air-water)-phase equilibrium was observed for diameters less than 200 microm, and this was attributed to surface adsorption. The experimental values of the droplet-vapor partition constant were used to obtain the overall mass transfer coefficient and the mass accommodation coefficient for both benzene and phenanthrene. Mass transfer of phenanthrene was dependent only on gas-phase diffusion and mass accommodation at the interface. However, for benzene, the mass transfer was limited by liquid-phase diffusion and mass accommodation. A large value of the mass accommodation coefficient, alpha = (1.4 +/- 0.4) x 10(-2) was observed for the highly surface-active (hydrophobic) phenanthrene, whereas a small alpha = (9.7 +/- 1.8) x 10(-5) was observed for the less hydrophobic benzene. Critical cluster numbers ranging from 2 for benzene to 5.7 for phenanthrene were deduced using the critical cluster nucleation theory for mass accommodation. The enthalpy of mass accommodation was more negative for phenanthrene than it was for benzene. Consequently, the temperature effect was more pronounced for phenanthrene. A linear correlation was observed for the enthalpy of accommodation with the excess enthalpy of solution. A natural organic carbon surrogate (Suwannee Fulvic acid) in the water droplet increased the uptake for phenanthrene and benzene, the effect being more marked for phenanthrene. A characteristic time constant analysis showed that uptake and droplet scavenging would compete for the fog deposition of phenanthrene, whereas deposition would be unimpeded by the uptake rate for benzene vapor. For both compounds, the characteristic atmospheric reaction times were much larger and would not impact fog deposition.

Germanium diffusion with vapor-phase GeAs and oxygen co-incorporation in GaAs

NASA Astrophysics Data System (ADS)

Wang, Wei-Fu; Cheng, Kai-Yuan; Hsieh, Kuang-Chien

2018-01-01

Vapor-phase germanium diffusion has been demonstrated in Zn-doped and semi-insulating GaAs in sealed ampoules with GeAs powders and excess arsenic. Secondary-ion-mass spectroscopy (SIMS) profiles indicate the presence of unintentional co-incorporation of oxygen in high densities (>1017/cm3) along with diffused germanium donors whose concentration (>>1018/cm3) determined by electro-chemical capacitance-voltage (ECV) profiler shows significant compensation near the surface. The source of oxygen mainly originates from the GeAs powder which contains Ge-O surface oxides. Variable-temperature photoluminescence (PL) shows that in GeAs-diffused samples, a broad peak ranging from 0.86-1.38 eV with the peak position around 1.1 eV predominates at low temperatures while the near band-edge luminescence quenches. The broad band is attributed to the GeGa-VGa self-activated (SA) centers possibly associated with nearby oxygen-related defect complex, and its luminescence persists up to 400 K. The configurational-coordinate modeling finds that the SA defect complex has a thermal activation energy of 150-180 meV and a vibrational energy 26.8 meV. The presence of oxygen does not much affect the SA emission intensity but may have influenced the peak position, vibration frequency and activation energy as compared to other common donor-VGa defects in GaAs.

Two reference time scales for studying the dynamic cavitation of liquid films

NASA Technical Reports Server (NTRS)

Sun, D. C.; Brewe, D. E.

1992-01-01

Two formulas, one for the characteristic time of filling a void with the vapor of the surrounding liquid, and one of filling the void by diffusion of the dissolved gas in the liquid, are derived. By comparing these time scales with that of the dynamic operation of oil film bearings, it is concluded that the evaporation process is usually fast enough to fill the cavitation bubble with oil vapor; whereas the diffusion process is much too slow for the dissolved air to liberate itself and enter the cavitation bubble. These results imply that the formation of a two phase fluid in dynamically loaded bearings, as often reported in the literature, is caused by air entrainment. They further indicate a way to simplify the treatment of the dynamic problem of bubble evolution.

Carbon dioxide diffuse emission and thermal energy release from hydrothermal systems at Copahue-Caviahue Volcanic Complex (Argentina)

NASA Astrophysics Data System (ADS)

Chiodini, Giovanni; Cardellini, Carlo; Lamberti, María Clara; Agusto, Mariano; Caselli, Alberto; Liccioli, Caterina; Tamburello, Giancarlo; Tassi, Franco; Vaselli, Orlando; Caliro, Stefano

2015-10-01

The north-western sector of Caviahue caldera (Argentina), close to the active volcanic system of Copahue, is characterized by the presence of several hydrothermal sites that host numerous fumarolic emissions, anomalous soil diffuse degassing of CO2 and hot soils. In March 2014, measurements of soil CO2 fluxes in 5 of these sites (namely, Las Máquinas, Las Maquinitas I, Las Maquinitas II, Anfiteatro, and Termas de Copahue) allowed an estimation that 165 t of deeply derived CO2 is daily released. The gas source is likely related to a relatively shallow geothermal reservoir containing a single vapor phase as also suggested by both the geochemical data from the 3 deep wells drilled in the 1980s and gas geoindicators applied to the fumarolic discharges. Gas equilibria within the H-C-O gas system indicate the presence of a large, probably unique, single phase vapor zone at 200-210 °C feeding the hydrothermal manifestations of Las Máquinas, Las Maquinitas I and II and Termas de Copahue. A natural thermal release of 107 MW was computed by using CO2 as a tracer of the original vapor phase. The magmatic signature of the incondensable fumarolic gases, the wide expanse of the hydrothermal areas and the remarkable high amount of gas and heat released by fluid expulsion seem to be compatible with an active magmatic intrusion beneath this portion of the Caviahue caldera.

Critical fluid thermal equilibration experiment (19-IML-1)

NASA Technical Reports Server (NTRS)

Wilkinson, R. Allen

1992-01-01

Gravity sometimes blocks all experimental techniques of making a desired measurement. Any pure fluid possesses a liquid-vapor critical point. It is defined by a temperature, pressure, and density state in thermodynamics. The critical issue that this experiment attempts to understand is the time it takes for a sample to reach temperature and density equilibrium as the critical point is approached; is it infinity due to mass and thermal diffusion, or do pressure waves speed up energy transport while mass is still under diffusion control. The objectives are to observe: (1) large phase domain homogenization without and with stirring; (2) time evolution of heat and mass after temperature step is applied to a one phase equilibrium sample; (3) phase evolution and configuration upon going two phase from a one phase equilibrium state; (4) effects of stirring on a low g two phase configuration; (5) two phase to one phase healing dynamics starting from a two phase low g configuration; and (6) effects of shuttle acceleration events on spatially and temporally varying compressible critical fluid dynamics.

Investigation of aluminosilicate as a solid oxide fuel cell refractory

NASA Astrophysics Data System (ADS)

Gentile, Paul S.; Sofie, Stephen W.

2011-05-01

Aluminosilicate represents a potential low cost alternative to alumina for solid oxide fuel cell (SOFC) refractory applications. The objectives of this investigation are to study: (1) changes of aluminosilicate chemistry and morphology under SOFC conditions, (2) deposition of aluminosilicate vapors on yttria stabilized zirconia (YSZ) and nickel, and (3) effects of aluminosilicate vapors on SOFC electrochemical performance. Thermal treatment of aluminosilicate under high temperature SOFC conditions is shown to result in increased mullite concentrations at the surface due to diffusion of silicon from the bulk. Water vapor accelerates the rate of surface diffusion resulting in a more uniform distribution of silicon. The high temperature condensation of volatile gases released from aluminosilicate preferentially deposit on YSZ rather than nickel. Silicon vapor deposited on YSZ consists primarily of aluminum rich clusters enclosed in an amorphous siliceous layer. Increased concentrations of silicon are observed in enlarged grain boundaries indicating separation of YSZ grains by insulating glassy phase. The presence of aluminosilicate powder in the hot zone of a fuel line supplying humidified hydrogen to an SOFC anode impeded peak performance and accelerated degradation. Energy dispersive X-ray spectroscopy detected concentrations of silicon at the interface between the electrolyte and anode interlayer above impurity levels.

Water-Vapor-Mediated Close-Spaced Vapor Transport Growth of Epitaxial Gallium Indium Phosphide Films on Gallium Arsenide Substrates

DOE PAGES

Greenaway, Ann L.; Bachman, Benjamin F.; Boucher, Jason W.; ...

2018-01-12

Ga 1–xIn xP is a technologically important III–V ternary semiconductor widely utilized in commercial and record-efficiency solar cells. We report the growth of Ga 1–xIn xP by water-vapor-mediated close-spaced vapor transport. Because growth of III–V semiconductors in this system is controlled by diffusion of metal oxide species, we find that congruent transport from the mixed powder source requires complete annealing to form a single alloy phase. Growth from a fully alloyed source at water vapor concentrations of ~7000 ppm in H 2 at 850 °C affords smooth films with electron mobility of 1070 cm 2 V –1 s –1 andmore » peak internal quantum efficiency of ~90% for carrier collection in a nonaqueous photoelectrochemical test cell.« less

Water-Vapor-Mediated Close-Spaced Vapor Transport Growth of Epitaxial Gallium Indium Phosphide Films on Gallium Arsenide Substrates

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

Greenaway, Ann L.; Bachman, Benjamin F.; Boucher, Jason W.

Ga 1–xIn xP is a technologically important III–V ternary semiconductor widely utilized in commercial and record-efficiency solar cells. We report the growth of Ga 1–xIn xP by water-vapor-mediated close-spaced vapor transport. Because growth of III–V semiconductors in this system is controlled by diffusion of metal oxide species, we find that congruent transport from the mixed powder source requires complete annealing to form a single alloy phase. Growth from a fully alloyed source at water vapor concentrations of ~7000 ppm in H 2 at 850 °C affords smooth films with electron mobility of 1070 cm 2 V –1 s –1 andmore » peak internal quantum efficiency of ~90% for carrier collection in a nonaqueous photoelectrochemical test cell.« less

TEM Observation of the Ti Interlayer Between SiC Substrates During Diffusion Bonding

NASA Technical Reports Server (NTRS)

Tsuda, Hiroshi; Mori, Shigeo; Halbig, Michael C.; Singh, Mori

2012-01-01

Diffusion bonding was carried out to join SiC to SiC substrates using titanium interlayers. In this study, 10 m and 20 m thick physical vapor deposited (PVD) Ti surface coatings, and 10 and 20 m thick Ti foils were used. Diffusion bonding was performed at 1250 C for PVD Ti coatings and 1200 C for Ti foil. This study investigates the microstructures of the phases formed during diffusion bonding through TEM and selected-area diffraction analysis of a sample prepared with an FIB, which allows samples to be taken from the reacted area. In all samples, Ti3SiC2, Ti5Si3Cx and TiSi2 phases were identified. In addition, TiC and unknown phases also appeared in the samples in which Ti foils were used as interlayers. Furthermore, Ti3SiC2 phases show high concentration and Ti5Si3Cx formed less when samples were processed at a higher temperature and thinner interlayer samples were used. It appears that the formation of microcracks is caused by the presence of intermediate phase Ti5Si3Cx, which has anisotropic thermal expansion, and by the presence of an unidentified Ti-Si-C ternary phase with relatively low Si content.

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

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

Webb, S.W.

1999-07-01

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

Phosphate Reactions as Mechanisms of High-Temperature Lubrication

NASA Technical Reports Server (NTRS)

Nagarajan, Anitha; Garrido, Carolina; Gatica, Jorge E.; Morales, Wilfredo

2006-01-01

One of the major problems preventing the operation of advanced gas turbine engines at higher temperatures is the inability of currently used liquid lubricants to survive at these higher temperatures under friction and wear conditions. Current state-of-the-art organic liquid lubricants rapidly degrade at temperatures above 300 C; hence some other form of lubrication is necessary. Vapor-phase lubrication is a promising new technology for high-temperature lubrication. This lubrication method employs a liquid phosphate ester that is vaporized and delivered to bearings or gears; the vapor reacts with the metal surfaces, generating a solid lubricious film that has proven very stable at high temperatures. In this study, solid lubricious films were grown on cast-iron foils in order to obtain reaction and diffusion rate data to help characterize the growth mechanism. A phenomenological mathematical model of the film deposition process was derived incorporating transport and kinetic parameters that were coupled to the experimental data. This phenomenological model can now be reliably used as a predictive and scale-up tool for future vapor-phase lubrication studies.

Cluster growth mechanisms in Lennard-Jones fluids: A comparison between molecular dynamics and Brownian dynamics simulations

NASA Astrophysics Data System (ADS)

Jung, Jiyun; Lee, Jumin; Kim, Jun Soo

2015-03-01

We present a simulation study on the mechanisms of a phase separation in dilute fluids of Lennard-Jones (LJ) particles as a model of self-interacting molecules. Molecular dynamics (MD) and Brownian dynamics (BD) simulations of the LJ fluids are employed to model the condensation of a liquid droplet in the vapor phase and the mesoscopic aggregation in the solution phase, respectively. With emphasis on the cluster growth at late times well beyond the nucleation stage, we find that the growth mechanisms can be qualitatively different: cluster diffusion and coalescence in the MD simulations and Ostwald ripening in the BD simulations. We also show that the rates of the cluster growth have distinct scaling behaviors during cluster growth. This work suggests that in the solution phase the random Brownian nature of the solute dynamics may lead to the Ostwald ripening that is qualitatively different from the cluster coalescence in the vapor phase.

Vapor Phase Synthesis of Organometal Halide Perovskite Nanowires for Tunable Room-Temperature Nanolasers.

PubMed

Xing, Jun; Liu, Xin Feng; Zhang, Qing; Ha, Son Tung; Yuan, Yan Wen; Shen, Chao; Sum, Tze Chien; Xiong, Qihua

2015-07-08

Semiconductor nanowires have received considerable attention in the past decade driven by both unprecedented physics derived from the quantum size effect and strong isotropy and advanced applications as potential building blocks for nanoscale electronics and optoelectronic devices. Recently, organic-inorganic hybrid perovskites have been shown to exhibit high optical absorption coefficient, optimal direct band gap, and long electron/hole diffusion lengths, leading to high-performance photovoltaic devices. Herein, we present the vapor phase synthesis free-standing CH3NH3PbI3, CH3NH3PbBr3, and CH3NH3PbIxCl3(-x) perovskite nanowires with high crystallinity. These rectangular cross-sectional perovskite nanowires have good optical properties and long electron hole diffusion length, which ensure adequate gain and efficient optical feedback. Indeed, we have demonstrated optical-pumped room-temperature CH3NH3PbI3 nanowire lasers with near-infrared wavelength of 777 nm, low threshold of 11 μJ/cm(2), and a quality factor as high as 405. Our research advocates the promise of optoelectronic devices based on organic-inorganic perovskite nanowires.

Water vapor diffusion membrane development. [for water recovery purposes onboard manned spacecraft

NASA Technical Reports Server (NTRS)

Tan, M. K.

1974-01-01

The phase separator component used as a membrane in the vapor diffusion process (VRD) for the recovery of potable water from urine on manned space missions of extended duration was investigated, with particular emphasis on cation-selective membranes because of their noted mechanical strength, superior resistance to acids, oxidants, and germicides, and their potential resistance to organic foulants. Two of the membranes were tested for 700 hours continuously, and were selected on the basis of criteria deemed important to an effective water reclamation system onboard spacecraft. The samples of urine were successfully processed by removing 93 percent of their water content in 70 hours using the selected membranes. Pretreatment with an acid-oxidant formulation improved product quality. Cation exchange membranes were shown to possess superior mechanical strength and chemical resistance, as compared to cellulosic membranes.

Evaluating BTEX concentration in soil using a simple one-dimensional vado zone model: application to a new fuel station in Valencia (Spain)

NASA Astrophysics Data System (ADS)

Rodrigo-Ilarri, Javier; Rodrigo-Clavero, María-Elena

2017-04-01

Specific studies of the impact of fuel spills on the vadose zone are currently required when trying to obtain the environmental permits for new fuel stations. The development of One-Dimensional mathematical models of fate and transport of BTEX on the vadose zone can therefore be used to understand the behavior of the pollutants under different scenarios. VLEACH - a simple One-Dimensional Finite Different Vadose Zone Leaching Model - uses an numerical approximation of the Millington Equation, a theoretical based model for gaseous diffusion in porous media. This equation has been widely used in the fields of soil physics and hydrology to calculate the gaseous or vapor diffusion in porous media. The model describes the movement of organic contaminants within and between three different phases: (1) as a solute dissolved in water, (2) as a gas in the vapor phase, and (3) as an absorbed compound in the soil phase. Initially, the equilibrium distribution of contaminant mass between liquid, gas and sorbed phases is calculated. Transport processes are then simulated. Liquid advective transport is calculated based on values defined by the user for infiltration and soil water content. The contaminant in the vapor phase migrates into or out of adjacent cells based on the calculated concentration gradients that exist between adjacent cells. After the mass is exchanged between the cells, the total mass in each cell is recalculated and re-equilibrated between the different phases. At the end of the simulation, (1) an overall area-weighted groundwater impact for the entire modeled area and (2) the concentration profile of BTEX on the vadose zone are calculated. This work shows the results obtained when applying VLEACH to analyze the contamination scenario caused by a BTEX spill coming from a set of future underground storage tanks located on a new fuel station in Aldaia (Valencia region - Spain).

Fabrication and Characterization of Diffusion Bonds for Silicon Carbide

NASA Technical Reports Server (NTRS)

Halbig, Michael; Singh, Mrityunjay; Martin, Richard E.; Cosgriff, Laura M.

2007-01-01

Diffusion bonds of silicon carbide (SiC) were fabricated using several different types of titanium (Ti) based interlayers between the SiC substrates. The interlayers were an alloyed Ti foil, a pure Ti foil, and a physically vapor deposited (PVD) Ti coating. Microscopy was conducted to evaluate the cross-sections of the resulting bonds. Microprobe analysis identified reaction formed phases in the diffusion bonded region. Uniform and well adhered bonds were formed between the SiC substrates. In the case where the alloyed Ti foil or a thick Ti coating (i.e. 20 micron) was used as the interlayer, microcracks and several phases were present in the diffusion bonds. When a thinner interlayer was used (i.e. 10 micron PVD Ti), no microcracks were observed and only two reaction formed phases were present. The two phases were preferred and fully reacted phases that did not introduce thermal stresses or microcracks during the cool-down stage after processing. Diffusion bonded samples were evaluated with the non-destructive evaluation (NDE) methods of pulsed thermography and immersion ultrasonic testing. Joined SiC substrates that were fully bonded and that had simulated bond flaws in the interlayer were also evaluated using immersion ultrasound. Pull testing was conducted on the bonds to determine the tensile strength. To demonstrate the joining approach for a complex multilayered component for a low NOx injector application, the diffusion bonding approach was used to join three 4" diameter SiC discs that contained complex fuel and air flow channels.

Lattice Boltzmann Simulation of Kinetic Isotope Effect During Snow Crystal Formation

NASA Astrophysics Data System (ADS)

Lu, G.; Depaolo, D. J.; Kang, Q.; Zhang, D.

2007-12-01

The isotopic composition of precipitation, especially that of snow, plays a special role in the global hydrological cycle and in reconstruction of past climates using polar ice cores. The fractionation of the major water isotope species (HHO, HDO, HHO-18) during ice crystal formation is critical to understanding the global distribution of isotopes in precipitation. Ice crystal growth in clouds is traditionally treated with a spherically-symmetric steady state diffusion model, with semi-empirical modifications added to account for ventilation and for complex crystal morphology. Although it is known that crystal growth rate, which depends largely on the degree of vapor over- saturation, determines crystal morphology, there are no quantitative models that relate morphology to the vapor saturation factor. Since kinetic (vapor phase diffusion-controlled) isotopic fractionation also depends on growth rate, there should be direct relationships between vapor saturation, crystal morphology, and crystal isotopic composition. We use a 2D lattice Boltzmann model to simulate diffusion-controlled ice crystal growth from vapor- oversaturated air. In the model, crystals grow solely according to the diffusive fluxes just above the crystal surfaces, and hence crystal morphology arises from the initial and boundary conditions in the model and does not need to be specified a priori. Crystal growth patterns can be varied between random growth and deterministic growth (along the maximum concentration gradient for example). The input parameters needed are the isotope- dependent vapor deposition rate constant (k) and the water vapor diffusivity in air (D). The values of both k and D can be computed from kinetic theory, and there are also experimentally determined values of D. The deduced values of k are uncertain to the extent that the condensation coefficient for ice is uncertain. The ratio D/k is a length (order 1 micron) that determines the minimum scale of dendritic growth features and allows us to scale the numerical calculations to atmospheric conditions. Our calculations confirm that the crystal/vapor isotopic fractionation approaches the equilibrium value, and the crystals are compact (circular in 2D) as the saturation factor approaches unity (S= 1.0). However, few natural crystals form under such conditions. At higher oversaturation (e.g. S = 1.2), dendritic crystals of millimeter size develop on timescales appropriate to cloud processes, and kinetic effects control isotopic fractionation. Fractionation factors for dendritic crystals are similar to those predicted by the spherical diffusion model, but the model also gives estimates of crystal heterogeneity. Dendritic crystals are constrained to be relatively large, with dimension much greater than about 20D/k. The most difficult aspect of the modeling is to account for the large density difference between air and ice, which requires us to use a fictitious higher density for the vapor-oversaturated air and scale the crystal growth time accordingly. An approach using a larger scale simulation and the domain decomposition method can provide a vapor flux for a nested smaller scale calculation. The results clarify the controls on crystal growth, and the relationships between saturation state, growth rate, crystal morphology and isotopic fractionation.

Jet Simulation in a Diesel Engine

NASA Astrophysics Data System (ADS)

Xu, Zhiliang

2005-03-01

We present a numerical study of the jet breakup and spray formation in a diesel engine by the Front Tracking method. The mechanisms of jet breakup and spray formation of a high speed diesel jet injected through a circular nozzle are the key to design a fuel efficient, nonpolluting diesel engine. We conduct the simulations for the jet breakup within a 2D axis-symmetric geometry. Our goal is to model the spray at a micro-physical level, with the creation of individual droplets. The problem is multiscale. The droplets are a few microns in size. The nozzle is about 0.2 mm in diameter and 1 mm in length. To resolve various physical patterns such as vortex, shock waves, vacuum and track droplets and spray, the Burger-Colella adaptive mesh refinement technique is used. To simulate the spray formation, we model mixed vapor-liquid region through a heterogeneous model with dynamic vapor bubble insertion. The formation of the cavitation is represented by the dynamic creation of vapor bubbles. On the liquid/vapor interface, a phase transition problem is solved numerically. The phase transition is governed by the compressible Euler equations with heat diffusion. Our solution is a new description for the Riemann problem associated with a phase transition in a fully compressible fluid.

Tritium plume dynamics in the shallow unsaturated zone in an arid environment

USGS Publications Warehouse

Maples, S.R.; Andraski, Brian J.; Stonestrom, David A.; Cooper, C.A.; Pohll, G.; Michel, R.L.

2014-01-01

The spatiotemporal variability of a tritium plume in the shallow unsaturated zone and the mechanisms controlling its transport were evaluated during a 10-yr study. Plume movement was minimal and its mass declined by 68%. Upward-directed diffusive-vapor tritium fluxes and radioactive decay accounted for most of the observed plume-mass declines.Effective isolation of tritium (3H) and other contaminants at waste-burial facilities requires improved understanding of transport processes and pathways. Previous studies documented an anomalously widespread (i.e., theoretically unexpected) distribution of 3H (>400 m from burial trenches) in a dry, sub-root-zone gravelly layer (1–2-m depth) adjacent to a low-level radioactive waste (LLRW) burial facility in the Amargosa Desert, Nevada, that closed in 1992. The objectives of this study were to: (i) characterize long-term, spatiotemporal variability of 3H plumes; and (ii) quantify the processes controlling 3H behavior in the sub-root-zone gravelly layer beneath native vegetation adjacent to the facility. Geostatistical methods, spatial moment analyses, and mass flux calculations were applied to a spatiotemporally comprehensive, 10-yr data set (2001–2011). Results showed minimal bulk-plume advancement during the study period and limited Fickian spreading of mass. Observed spreading rates were generally consistent with theoretical vapor-phase dispersion. The plume mass diminished more rapidly than would be expected from radioactive decay alone, indicating net efflux from the plume. Estimates of upward 3H efflux via diffusive-vapor movement were >10× greater than by dispersive-vapor or total-liquid movement. Total vertical fluxes were >20× greater than lateral diffusive-vapor fluxes, highlighting the importance of upward migration toward the land surface. Mass-balance calculations showed that radioactive decay and upward diffusive-vapor fluxes contributed the majority of plume loss. Results indicate that plume losses substantially exceeded any continuing 3H contribution to the plume from the LLRW facility during 2001 to 2011 and suggest that the widespread 3H distribution resulted from transport before 2001.

Growth of NH4Cl Single Crystal from Vapor Phase in Vertical Furnace

NASA Astrophysics Data System (ADS)

Nigara, Yutaka; Yoshizawa, Masahito; Fujimura, Tadao

1983-02-01

A pure and internally stress-free single crystal of NH4Cl was grown successfully from the vapor phase. The crystal measured 1.6 cmφ× 2 cm and had the disordered CsCl structure, which was stable below 184°C. The crystal was grown in an ampoule in a vertical furnace, in which the vapor was efficiently transported both by diffusion and convection. In line with the growth mechanism of a single crystal, the temperature fluctuation (°C/min) on the growth interface was kept smaller than the product of the temperature gradient (°C/cm) and the growth rate (cm/min). The specific heat of the crystal was measured around -31°C (242 K) during cooling and heating cycles by AC calorimetry. The thermal hysteresis (0.4 K) obtained here was smaller than that (0.89 K) of an NH4Cl crystal grown from its aqueous solution with urea added as a habit modifier.

Cd(1-x)Zn(x)O [0.05 ≤x≤ 0.26] synthesized by vapor-diffusion induced hydrolysis and co-nucleation from aqueous metal salt solutions.

PubMed

Schwenzer, Birgit; Neilson, James R; Jeffries, Stacie M; Morse, Daniel E

2011-02-14

Nanoparticulate Cd(1-x)Zn(x)O (x = 0, 0.05-0.26, 1) is synthesized in a simple two-step synthesis approach. Vapor-diffusion induced catalytic hydrolysis of two molecular precursors at low temperature induces co-nucleation and polycondensation to produce bimetallic layered hydroxide salts (M = Cd, Zn) as precursor materials which are subsequently converted to Cd(1-x)Zn(x)O at 400 °C. Unlike ternary materials prepared by standard co-precipitation procedures, all products presented here containing < 30 mol% Zn(2+) ions are homogeneous in elemental composition on the micrometre scale. This measured compositional homogeneity within the samples, as determined by energy dispersive spectroscopy and inductively coupled plasma spectroscopy, is a testimony to the kinetic control achieved by employing slow hydrolysis conditions. In agreement with this observation, the optical properties of the materials obey Vegard's Law for a homogeneous solid solution of Cd(1-x)Zn(x)O, where x corresponds to the values determined by inductively coupled plasma analysis, even though powder X-ray diffraction shows phase separation into a cubic mixed metal oxide phase and a hexagonal ZnO phase at all doping levels.

Water vapor diffusion membranes, 2

NASA Technical Reports Server (NTRS)

Holland, F. F.; Klein, E.; Smith, J. K.; Eyer, C.

1976-01-01

Transport mechanisms were investigated for the three different types of water vapor diffusion membranes. Membranes representing porous wetting and porous nonwetting structures as well as dense diffusive membrane structures were investigated for water permeation rate as a function of: (1) temperature, (2) solids composition in solution, and (3) such hydrodynamic parameters as sweep gas flow rate, solution flow rate and cell geometry. These properties were measured using nitrogen sweep gas to collect the effluent. In addition, the chemical stability to chromic acid-stabilized urine was measured for several of each type of membrane. A technology based on the mechanism of vapor transport was developed, whereby the vapor diffusion rates and relative susceptibility of membranes to fouling and failure could be projected for long-term vapor recovery trials using natural chromic acid-stabilized urine.

Lattice Boltzmann Simulation of Water Isotope Fractionation During Growth of Ice Crystals in Clouds

NASA Astrophysics Data System (ADS)

Lu, G.; Depaolo, D.; Kang, Q.; Zhang, D.

2006-12-01

The isotopic composition of precipitation, especially that of snow, plays a special role in the global hydrological cycle and in reconstruction of past climates using polar ice cores. The fractionation of the major water isotope species (HHO, HDO, HHO-18) during ice crystal formation is critical to understanding the global distribution of isotopes in precipitation. Ice crystal growth in clouds is traditionally treated with a spherically- symmetric steady state diffusion model, with semi-empirical modifications added to account for ventilation and for complex crystal morphology. Although it is known that crystal growth rate, which depends largely on the degree of vapor over-saturation, determines crystal morphology, there are no existing quantitative models that directly relate morphology to the vapor saturation factor. Since kinetic (vapor phase diffusion-controlled) isotopic fractionation also depends on growth rate, there should be a direct relationship between vapor saturation, crystal morphology, and crystal isotopic composition. We use a 2D Lattice-Boltzmann model to simulate diffusion-controlled ice crystal growth from vapor- oversaturated air. In the model, crystals grow solely according to the diffusive fluxes just above the crystal surfaces, and hence crystal morphology arises from the initial and boundary conditions in the model and does not need to be specified a priori. The input parameters needed are the isotope-dependent vapor deposition rate constant (k) and the water vapor diffusivity in air (D). The values of both k and D can be computed from kinetic theory, and there are also experimentally determined values of D. The deduced values of k are uncertain to the extent that the sticking coefficient (or accommodation coefficient) for ice is uncertain. The ratio D/k is a length that determines the minimum scale of dendritic growth features and allows us to scale the numerical calculations to atmospheric conditions using a dimensionless Damkohler number: Da = kh/D, where h is the width of the 2D calculation domain. Varying the nondimensional Da in the model is equivalent to varying the scale (h) in the model. Our calculations confirm that the crystal/vapor isotopic fractionation approaches the equilibrium value, and the crystals are compact (circular in 2D) as the saturation factor approaches unity (S= 1.0). At higher oversaturation (e.g. S = 1.2), dendritic crystals of millimeter size develop on timescales appropriate to cloud processes, the isotopic fractionations are dominated by kinetic effects, and similar to those predicted by the spherical diffusion model. Dendritic crystals are constrained to be relatively large, with dimension much greater than D/k. The most difficult aspect of the modeling is to account for the large density difference between air and ice, which requires us to use a fictitious higher density for the vapor-oversaturated air and scale the crystal growth time accordingly. A different approach, using a larger scale simulation to derive boundary conditions for a nested smaller scale calculation is in progress. The results to date clarify the controls on dendritic crystal growth, the relationships between saturation state, growth rate, crystal morphology and isotopic fractionation, and provide limits on the value of the accommodation coefficient.

Effects of Atmospheric Conditions and the Land/Atmospheric Interface on Transport of Chemical Vapors from Subsurface Sources

NASA Astrophysics Data System (ADS)

Rice, A. K.; Smits, K. M.; Cihan, A.; Howington, S. E.; Illangasekare, T. H.

2013-12-01

Understanding the movement of chemical vapors and gas through variably saturated soil subjected to atmospheric thermal and mass flux boundary conditions at the land/atmospheric interface is important to many applications, including landmine detection, methane leakage during natural gas production from shale and CO2 leakage from deep geologic storage. New, advanced technologies exist to sense chemical signatures and gas leakage at the land/atmosphere interface, but interpretation of sensor signals remains a challenge. Chemical vapors are subject to numerous interactions while migrating through the soil environment, masking source conditions. The process governing movement of gases through porous media is often assumed to be Fickian diffusion through the air phase with minimal quantification of other processes, such as convective gas flow and temporal or spatial variation in soil moisture. Vapor migration is affected by atmospheric conditions (e.g. humidity, temperature, wind velocity), soil thermal and hydraulic properties and contaminant properties, all of which are physically and thermodynamically coupled. The complex coupling of two drastically different flow regimes in the subsurface and atmosphere is commonly ignored in modeling efforts, or simplifying assumptions are made to treat the systems as de-coupled. Experimental data under controlled laboratory settings are lacking to refine the theory for proper coupling and complex treatment of vapor migration through porous media in conversation with atmospheric flow and climate variations. Improving fundamental understanding and accurate quantification of these processes is not feasible in field settings due to lack of controlled initial and boundary conditions and inability to fully characterize the subsurface at all relevant scales. The goal of this work is to understand the influence of changes in atmospheric conditions to transport of vapors through variably saturated soil. We have developed a tank apparatus with a network of soil and atmospheric sensors and a head space for air flow to simulate the atmospheric boundary layer. Experiments were performed under varying temperature values at the soil surface bounded by the atmospheric boundary layer. The model of Smits et al. [2011], accounting for non-equilibrium phase change and coupled heat, water vapor and liquid water flux through soil, was amended to include organic vapor in the gas phase and migration mechanisms often overlooked in models (thermal and Knudsen diffusion, density driven advection). Experimental results show increased vapor mass flux across the soil/atmospheric interface due to heat applied from the atmosphere and coupling of heat and mass transfer in the shallow subsurface for both steady and diurnal temperature patterns. Comparison of model results to experimental data shows dynamic interactions between transport in porous media and boundary conditions. Results demonstrate the value of considering interactions of the atmosphere and subsurface to better understand chemical gas transport through unsaturated soils and the land/atmospheric interface.

Numerical Simulation of Permeation from Deposited Droplets: Model Expansion

DTIC Science & Technology

1992-04-01

This is primarily due to the low vapor pressures of chemical agent simulants, which minimize the driving forces for diffusion through the gas-phase...was presented at the November 1990 CRDEC Scientific Conference on Chemical Defense Research (4]. Previous work in this area also includes a substantial...most of the overall chemical poten- tial driving force is dissipated in the gas, not the membrane phase). 1.0 l 0.9-0 A 0 0.8 - 0.7 C 0.6,, 0.00 0.25

Determination of mercury distribution inside spent compact fluorescent lamps by atomic absorption spectrometry.

PubMed

Rey-Raap, Natalia; Gallardo, Antonio

2012-05-01

In this study, spent compact fluorescent lamps were characterized to determine the distribution of mercury. The procedure used in this research allowed mercury to be extracted in the vapor phase, from the phosphor powder, and the glass matrix. Mercury concentration in the three phases was determined by the method known as cold vapor atomic absorption spectrometry. Median values obtained in the study showed that a compact fluorescent lamp contained 24.52±0.4ppb of mercury in the vapor phase, 204.16±8.9ppb of mercury in the phosphor powder, and 18.74±0.5ppb of mercury in the glass matrix. There are differences in mercury concentration between the lamps since the year of manufacture or the hours of operation affect both mercury content and its distribution. The 85.76% of the mercury introduced into a compact fluorescent lamp becomes a component of the phosphor powder, while more than 13.66% is diffused through the glass matrix. By washing and eliminating all phosphor powder attached to the glass surface it is possible to classified the glass as a non-hazardous waste. Copyright © 2011 Elsevier Ltd. All rights reserved.

Composition, diffusion, and antifungal activity of black mustard (Brassica nigra) essential oil when applied by direct addition or vapor phase contact.

PubMed

Mejía-Garibay, Beatriz; Palou, Enrique; López-Malo, Aurelio

2015-04-01

In this study, we characterized the essential oil (EO) of black mustard (Brassica nigra) and quantified its antimicrobial activity, when applied by direct contact into the liquid medium or by exposure in the vapor phase (in laboratory media or in a bread-type product), against the growth of Aspergillus niger, Aspergillus ochraceus, or Penicillium citrinum. Allyl-isothiocyanate (AITC) was identified as the major component of B. nigra EO with a concentration of 378.35 mg/ml. When B. nigra EO was applied by direct contact into the liquid medium, it inhibited the growth of A. ochraceus and P. citrinum when the concentration was 2 μl/ml of liquid medium (MIC), while for A. niger, a MIC of B. nigra EO was 4 μl/ml of liquid medium. Exposure of molds to B. nigra EO in vapor phase showed that 41.1 μl of B. nigra EO per liter of air delayed the growth of P. citrinum and A. niger by 10 days, while A. ochraceus growth was delayed for 20 days. Exposure to concentrations ≥ 47 μl of B. nigra EO per liter of air (MIC) inhibited the growth of tested molds by 30 days, and they were not able to recover after further incubation into an environment free of EO (fungicidal effect). Adsorbed AITC was quantified by exposing potato dextrose agar to B. nigra EO in a vapor phase, exhibiting that AITC was retained at least 5 days when testing EO at its MIC or with higher concentrations. Mustard EO MIC was also effective against the evaluated molds inhibiting their growth for 30 days in a bread-type product when exposed to EO by vapor contact, demonstrating its antifungal activity.

Properties of water along the liquid-vapor coexistence curve via molecular dynamics simulations using the polarizable TIP4P-QDP-LJ water model

PubMed Central

Bauer, Brad A.; Patel, Sandeep

2009-01-01

We present an extension of the TIP4P-QDP model, TIP4P-QDP-LJ, that is designed to couple changes in repulsive and dispersive nonbond interactions to changes in polarizability. Polarizability is intimately related to the dispersion component of classical force field models of interactions, and we explore the effect of incorporating this connection explicitly on properties along the liquid-vapor coexistence curve of pure water. Parametrized to reproduce condensed-phase liquid water properties at 298 K, the TIP4P-QDP-LJ model predicts density, enthalpy of vaporization, self-diffusion constant, and the dielectric constant at ambient conditions to about the same accuracy as TIP4P-QDP but shows remarkable improvement in reproducing the liquid-vapor coexistence curve. TIP4P-QDP-LJ predicts critical constants of Tc=623 K, ρc=0.351 g∕cm3, and Pc=250.9 atm, which are in good agreement with experimental values of Tc=647.1 K, ρc=0.322 g∕cm3, and Pc=218 atm, respectively. Applying a scaling factor correction (obtained by fitting the experimental vapor-liquid equilibrium data to the law of rectilinear diameters using a three-term Wegner expansion) the model predicts critical constants (Tc=631 K and ρc=0.308 g∕cm3). Dependence of enthalpy of vaporization, self-diffusion constant, surface tension, and dielectric constant on temperature are shown to reproduce experimental trends. We also explore the interfacial potential drop across the liquid-vapor interface for the temperatures studied. The interfacial potential demonstrates little temperature dependence at lower temperatures (300–450 K) and significantly enhanced (exponential) dependence at elevated temperatures. Terms arising from the decomposition of the interfacial potential into dipole and quadrupole contributions are shown to monotonically approach zero as the temperature approaches the critical temperature. Results of this study suggest that self-consistently treating the coupling of phase-dependent polarizability with dispersion interactions in classical water force fields may be an important effect for the extension of polarizable water force fields to reproduce properties along the liquid-vapor coexistence envelope as well as near critical conditions. More importantly, the present study demonstrates the rather remarkable transferability of a water model parametrized to a single state point to other thermodynamic states. Further studies are recommended. PMID:19725623

Properties of water along the liquid-vapor coexistence curve via molecular dynamics simulations using the polarizable TIP4P-QDP-LJ water model.

PubMed

Bauer, Brad A; Patel, Sandeep

2009-08-28

We present an extension of the TIP4P-QDP model, TIP4P-QDP-LJ, that is designed to couple changes in repulsive and dispersive nonbond interactions to changes in polarizability. Polarizability is intimately related to the dispersion component of classical force field models of interactions, and we explore the effect of incorporating this connection explicitly on properties along the liquid-vapor coexistence curve of pure water. Parametrized to reproduce condensed-phase liquid water properties at 298 K, the TIP4P-QDP-LJ model predicts density, enthalpy of vaporization, self-diffusion constant, and the dielectric constant at ambient conditions to about the same accuracy as TIP4P-QDP but shows remarkable improvement in reproducing the liquid-vapor coexistence curve. TIP4P-QDP-LJ predicts critical constants of T(c)=623 K, rho(c)=0.351 g/cm(3), and P(c)=250.9 atm, which are in good agreement with experimental values of T(c)=647.1 K, rho(c)=0.322 g/cm(3), and P(c)=218 atm, respectively. Applying a scaling factor correction (obtained by fitting the experimental vapor-liquid equilibrium data to the law of rectilinear diameters using a three-term Wegner expansion) the model predicts critical constants (T(c)=631 K and rho(c)=0.308 g/cm(3)). Dependence of enthalpy of vaporization, self-diffusion constant, surface tension, and dielectric constant on temperature are shown to reproduce experimental trends. We also explore the interfacial potential drop across the liquid-vapor interface for the temperatures studied. The interfacial potential demonstrates little temperature dependence at lower temperatures (300-450 K) and significantly enhanced (exponential) dependence at elevated temperatures. Terms arising from the decomposition of the interfacial potential into dipole and quadrupole contributions are shown to monotonically approach zero as the temperature approaches the critical temperature. Results of this study suggest that self-consistently treating the coupling of phase-dependent polarizability with dispersion interactions in classical water force fields may be an important effect for the extension of polarizable water force fields to reproduce properties along the liquid-vapor coexistence envelope as well as near critical conditions. More importantly, the present study demonstrates the rather remarkable transferability of a water model parametrized to a single state point to other thermodynamic states. Further studies are recommended.

Thin film solar cells grown by organic vapor phase deposition

NASA Astrophysics Data System (ADS)

Yang, Fan

Organic solar cells have the potential to provide low-cost photovoltaic devices as a clean and renewable energy resource. In this thesis, we focus on understanding the energy conversion process in organic solar cells, and improving the power conversion efficiencies via controlled growth of organic nanostructures. First, we explain the unique optical and electrical properties of organic materials used for photovoltaics, and the excitonic energy conversion process in donor-acceptor heterojunction solar cells that place several limiting factors of their power conversion efficiency. Then, strategies for improving exciton diffusion and carrier collection are analyzed using dynamical Monte Carlo models for several nanostructure morphologies. Organic vapor phase deposition is used for controlling materials crystallization and film morphology. We improve the exciton diffusion efficiency while maintaining good carrier conduction in a bulk heterojunction solar cell. Further efficiency improvement is obtained in a novel nanocrystalline network structure with a thick absorbing layer, leading to the demonstration of an organic solar cell with 4.6% efficiency. In addition, solar cells using simultaneously active heterojunctions with broad spectral response are presented. We also analyze the efficiency limits of single and multiple junction organic solar cells, and discuss the challenges facing their practical implementations.

Comment on "A centroid molecular dynamics study of liquid para hydrogen and ortho deuterium" [J. Chem. Phys. 121, 6412 (2004)].

PubMed

Miller, Thomas F; Manolopoulos, David E; Madden, Paul A; Konieczny, Martin; Oberhofer, Harald

2005-02-01

We show that the two phase points considered in the recent simulations of liquid para hydrogen by Hone and Voth lie in the liquid-vapor coexistence region of a purely classical molecular dynamics simulation. By contrast, their phase point for ortho deuterium was in the one-phase liquid region for both classical and quantum simulations. These observations are used to account for their report that quantum mechanical effects enhance the diffusion in liquid para hydrogen and decrease it in ortho deuterium.(c) 2005 American Institute of Physics.

Approach to high quality GaN lateral nanowires and planar cavities fabricated by focused ion beam and metal-organic vapor phase epitaxy.

PubMed

Pozina, Galia; Gubaydullin, Azat R; Mitrofanov, Maxim I; Kaliteevski, Mikhail A; Levitskii, Iaroslav V; Voznyuk, Gleb V; Tatarinov, Evgeniy E; Evtikhiev, Vadim P; Rodin, Sergey N; Kaliteevskiy, Vasily N; Chechurin, Leonid S

2018-05-08

We have developed a method to fabricate GaN planar nanowires and cavities by combination of Focused Ion Beam (FIB) patterning of the substrate followed by Metal Organic Vapor Phase Epitaxy (MOVPE). The method includes depositing a silicon nitride mask on a sapphire substrate, etching of the trenches in the mask by FIB with a diameter of 40 nm with subsequent MOVPE growth of GaN within trenches. It was observed that the growth rate of GaN is substantially increased due to enhanced bulk diffusion of the growth precursor therefore the model for analysis of the growth rate was developed. The GaN strips fabricated by this method demonstrate effective luminescence properties. The structures demonstrate enhancement of spontaneous emission via formation of Fabry-Perot modes.

[Lateral diffusion of saturated phosphatidylcholines in cholesterol-containing bilayers].

PubMed

Filippov, A V; Rudakova, M A; Oradd, G; Lindblom, J

2007-01-01

Lateral diffusion in oriented bilayers of saturated cholesterol-containing phosphatidylcholines, dipalmitoylphosphatidylcholine and dimyrilstoylphosphatidylcholine upon their limiting hydration has been studied by NMR with impulse gradient of magnetic field. For both systems, similar dependences of the coefficient of lateral diffusion on temperature and cholesterol concentration were observed, which agree with the phase diagram showing the presence of regions of ordered and unordered liquid-crystalline phases and a two-phase region. Under similar conditions, the coefficient of lateral diffusion for dipalmytoylphosphatidylcholine has lower values, which is in qualitative agreement with its greater molecular mass. A comparison of data for dipalmytoylphosphatidylcholine with the results obtained earlier for dipalmytoylsphyngomyelin/cholesterol under the same conditions shows, despite a similarity in phase diagrams, greater (two- to threefold) differences in the values of the coefficient of lateral diffusion and a different mode of dependence of the coefficient on cholesterol concentration. A comparison of data for dimyrilstoylphosphatidylcholine with the results obtained previously shows that the values of the coefficient of lateral diffusion and the mode of its dependence on cholesterol concentration coincide in the region of higher concentrations (more than 15 mole %) and differ in the region of lower concentrations (below 15 mole %). The discrepancies may be explained by different contents of water in the systems during the measurements. At a limiting hydration (more than 35%) of water, the coefficient of lateral diffusion decreases with increasing cholesterol concentration. If the content of water is about 25% (as a result of equilibrium hydration from vapors), the coefficient of lateral diffusion of phosphatidylcholine is probably independent of cholesterol concentration. This results from a denser packing of molecules in the bilayer at a lower water concentration, an effect that competes with the ordering effect of cholesterol.

Inhibitory effects of terpene alcohols and aldehydes on growth of green alga Chlorella pyrenoidosa

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

Ikawa, Miyoshi; Mosley, S.P.; Barbero, L.J.

1992-10-01

The growth of the green alga Chlorella pyrenoidosa was inhibited by terpene alcohols and the terpene aldehyde citral. The strongest activity was shown by citral. Nerol, geraniol, and citronellol also showed pronounced activity. Strong inhibition was linked to acyclic terpenes containing a primary alcohol or aldehyde function. Inhibition appeared to be taking place through the vapor phase rather than by diffusion through the agar medium from the terpene-treated paper disks used in the system. Inhibition through agar diffusion was shown by certain aged samples of terpene hydrocarbons but not by recently purchased samples.

Chromium Vaporization Reduction by Nickel Coatings For SOEC Interconnect Materials

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

Michael V. Glazoff; Sergey N. Rashkeev; J. Stephen Herring

2014-09-01

The vaporization of Cr-rich volatile species from interconnect materials is a major source of degradation that limits the lifetime of planar solid oxide devices systems with metallic interconnects, including Solid Oxide Electrolysis Cells, or SOECs. Some metallic coatings (Ni, Co, and Cu) significantly reduce the Cr release from interconnects and slow down the oxide scale growth on the steel substrate. To shed additional light upon the mechanisms of such protection and find a suitable coating material for ferritic stainless steel materials, we used a combination of first-principles calculations, thermodynamics, and diffusion modeling to investigate which factors determine the quality ofmore » the Ni metallic coating at stainless steel interconnector. We found that the Cr migration in Ni coating is determined by a delicate combination of the nickel oxidation, Cr diffusion, and phase transformation processes. Although the formation of Cr2O3 oxide is more exothermic than that of NiO, the kinetic rate of the chromia formation in the coating layer and its surface is significantly reduced by the low mobility of Cr in nickel oxide and in NiCr2O4 spinel. These results are in a good agreement with diffusion modeling for Cr diffusion through Ni coating layer on the ferritic 441 steel substrate.« less

Relating adatom emission to improved durability of Pt-Pd diesel oxidation catalysts

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

Johns, Tyne Richele; Goeke, Ronald S.; Ashbacher, Valerie

Sintering of nanoparticles is an important contributor to loss of activity in heterogeneous catalysts, such as those used for controlling harmful emissions from automobiles. But mechanistic details, such as the rates of atom emission or the nature of the mobile species, remain poorly understood. Herein we report a novel approach that allows direct measurement of atom emission from nanoparticles. We use model catalyst samples and a novel reactor that allows the same region of the sample to be observed after short-term heat treatments (seconds) under conditions relevant to diesel oxidation catalysts (DOCs). Monometallic Pd is very stable and does notmore » sinter when heated in air (T ≤ 800 °C). Pt sinters readily in air, and at high temperatures (≥800 °C) mobile Pt species emitted to the vapor phase cause the formation of large, faceted particles. In Pt–Pd nanoparticles, Pd slows the rate of emission of atoms to the vapor phase due to the formation of an alloy. However, the role of Pd in Pt DOCs in air is quite complex: at low temperatures, Pt enhances the rate of Pd sintering (which otherwise would be stable as an oxide), while at higher temperature Pd helps to slow the rate of Pt sintering. DFT calculations show that the barrier for atom emission to the vapor phase is much greater than the barrier for emitting atoms to the support. Thus, vapor-phase transport becomes significant only at high temperatures while diffusion of adatoms on the support dominates at lower temperatures.« less

Relating adatom emission to improved durability of Pt-Pd diesel oxidation catalysts

DOE PAGES

Johns, Tyne Richele; Goeke, Ronald S.; Ashbacher, Valerie; ...

2015-06-05

Sintering of nanoparticles is an important contributor to loss of activity in heterogeneous catalysts, such as those used for controlling harmful emissions from automobiles. But mechanistic details, such as the rates of atom emission or the nature of the mobile species, remain poorly understood. Herein we report a novel approach that allows direct measurement of atom emission from nanoparticles. We use model catalyst samples and a novel reactor that allows the same region of the sample to be observed after short-term heat treatments (seconds) under conditions relevant to diesel oxidation catalysts (DOCs). Monometallic Pd is very stable and does notmore » sinter when heated in air (T ≤ 800 °C). Pt sinters readily in air, and at high temperatures (≥800 °C) mobile Pt species emitted to the vapor phase cause the formation of large, faceted particles. In Pt–Pd nanoparticles, Pd slows the rate of emission of atoms to the vapor phase due to the formation of an alloy. However, the role of Pd in Pt DOCs in air is quite complex: at low temperatures, Pt enhances the rate of Pd sintering (which otherwise would be stable as an oxide), while at higher temperature Pd helps to slow the rate of Pt sintering. DFT calculations show that the barrier for atom emission to the vapor phase is much greater than the barrier for emitting atoms to the support. Thus, vapor-phase transport becomes significant only at high temperatures while diffusion of adatoms on the support dominates at lower temperatures.« less

Semiempirical self-consistent polarization description of bulk water, the liquid-vapor interface, and cubic ice.

PubMed

Murdachaew, Garold; Mundy, Christopher J; Schenter, Gregory K; Laino, Teodoro; Hutter, Jürg

2011-06-16

We have applied an efficient electronic structure approach, the semiempirical self-consistent polarization neglect of diatomic differential overlap (SCP-NDDO) method, previously parametrized to reproduce properties of water clusters by Chang, Schenter, and Garrett [ J. Chem. Phys. 2008 , 128 , 164111 ] and now implemented in the CP2K package, to model ambient liquid water at 300 K (both the bulk and the liquid-vapor interface) and cubic ice at 15 and 250 K. The SCP-NDDO potential retains its transferability and good performance across the full range of conditions encountered in the clusters and the bulk phases of water. In particular, we obtain good results for the density, radial distribution functions, enthalpy of vaporization, self-diffusion coefficient, molecular dipole moment distribution, and hydrogen bond populations, in comparison to experimental measurements. © 2011 American Chemical Society

24 CFR 3280.704 - Fuel supply systems.

Code of Federal Regulations, 2012 CFR

2012-04-01

... be ventilated at top and bottom to facilitate diffusion of vapors. The compartment shall be... to permit diffusion of vapors and shall be insulated from the structural members of the body. Tanks...

24 CFR 3280.704 - Fuel supply systems.

Code of Federal Regulations, 2014 CFR

2014-04-01

... be ventilated at top and bottom to facilitate diffusion of vapors. The compartment shall be... to permit diffusion of vapors and shall be insulated from the structural members of the body. Tanks...

24 CFR 3280.704 - Fuel supply systems.

Code of Federal Regulations, 2013 CFR

2013-04-01

... be ventilated at top and bottom to facilitate diffusion of vapors. The compartment shall be... to permit diffusion of vapors and shall be insulated from the structural members of the body. Tanks...

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

NASA Astrophysics Data System (ADS)

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

2018-02-01

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

Theoretical studies in support of the 3M-vapor transport (PVTOS-) experiments

NASA Technical Reports Server (NTRS)

Rosner, Daniel E.; Keyes, David E.

1989-01-01

Results are reported for a preliminary theoretical study of the coupled mass-, momentum-, and heat-transfer conditions expected within small ampoules used to grow oriented organic solid (OS-) films, by physical vapor transport (PVT) in microgravity environments. It is show that previous studies made restrictive assumptions (e.g., smallness of delta T/T, equality of molecular diffusivities) not valid under PVTOS conditions, whereas the important phenomena of sidewall gas creep, Soret transport of the organic vapor, and large vapor phase supersaturations associated with the large prevailing temperature gradients were not previously considered. Rational estimates are made of the molecular transport properties relevant to copper-phthalocyanine monomeric vapor in a gas mixture containing H2(g) and Xe(g). Efficient numerical methods have been developed and are outlined/illustrated here to making steady axisymmetric gas flow calculations within such ampoules, allowing for realistic realistic delta T/T(sub)w-values, and even corrections to Navier-Stokes-Fourier 'closure' for the governing continuum differential equations. High priority follow-on studies are outlined based on these new results.

Phase-field study on geometry-dependent migration behavior of voids under temperature gradient in UO2 crystal matrix

NASA Astrophysics Data System (ADS)

Chen, Weijin; Peng, Yuyi; Li, Xu'an; Chen, Kelang; Ma, Jun; Wei, Lingfeng; Wang, Biao; Zheng, Yue

2017-10-01

In this work, a phase-field model is established to capture the void migration behavior under a temperature gradient within a crystal matrix, with an appropriate consideration of the surface diffusion mechanism and the vapor transport mechanism. The interfacial energy and the coupling between the vacancy concentration field and the crystal order parameter field are carefully modeled. Simulations are performed on UO2. The result shows that for small voids (with an area ≤ πμm2), the well-known characteristics of void migration, in consistence with the analytical model, can be recovered. The migration is manifested by a constant velocity and a minor change of the void shape. In contrast, for large voids (with an area of ˜10 μm2) initially in circular shapes, significant deformation of the void from a circular to cashew-like shape is observed. After long-time migration, the deformed void would split into smaller voids. The size-dependent behavior of void migration is due to the combined effect of the interfacial energy (which tends to keep the void in circular shape) and the surface diffusion flow (which tends to deform the void due to the nonuniform diffusion along the surface). Moreover, the initial shape of the void modifies the migration velocity and the time point when splitting occurs (for large voids) at the beginning of migration due to the shape relaxation of the void. However, it has a minor effect on the long-time migration. Our work reveals novel void migration behaviors in conditions where the surface-diffusion mechanism is dominant over the vapor transport mechanism; meanwhile, the size of the void lies at a mediate size range.

Diffusion Bonding of Silicon Carbide Ceramics using Titanium Interlayers

NASA Technical Reports Server (NTRS)

Halbig, Michael C.; Singh, Mrityunjay; Shpargel, Tarah P.; Kiser, James D.

2006-01-01

Robust joining approaches for silicon carbide ceramics are critically needed to fabricate leak free joints with high temperature mechanical capability. In this study, titanium foils and physical vapor deposited (PVD) titanium coatings were used to form diffusion bonds between SiC ceramics using hot pressing. Silicon carbide substrate materials used for bonding include sintered SiC and two types of CVD SiC. Microscopy results show the formation of well adhered diffusion bonds. The bond strengths as determined from pull tests are on the order of several ksi, which is much higher than required for a proposed application. Microprobe results show the distribution of silicon, carbon, titanium, and other minor elements across the diffusion bond. Compositions of several phases formed in the joint region were identified. Potential issues of material compatibility and optimal bond formation will also be discussed.

Mass Flux of ZnSe by Physical Vapor Transport

NASA Technical Reports Server (NTRS)

Sha, Yi-Gao; Su, Ching-Hua; Palosz, W.; Volz, M. P.; Gillies, D. C.; Szofran, F. R.; Lehoczky, S. L.; Liu, Hao-Chieh; Brebrick, R. F.

1995-01-01

Mass fluxes of ZnSe by physical vapor transport (PVT) were measured in the temperature range of 1050 to 1160 C using an in-situ dynamic technique. The starting materials were either baked out or distilled under vacuum to obtain near-congruently subliming compositions. Using an optical absorption technique Zn and Se, were found to be the dominant vapor species. Partial pressures of Zn and Se, over the starting materials at temperatures between 960 and 1140 C were obtained by measuring the optical densities of the vapor phase at the wavelengths of 2138, 3405, 3508, 3613, and 3792 A. The amount and composition of the residual gas inside the experimental ampoules were measured after the run using a total pressure gauge. For the first time, the experimentally determined partial pressures of Zn and Se, and the amount and composition of the residual gas were used in a one-dimensional diffusion limited analysis of the mass transport rates for a PVT system. Reasonable agreement between the experimental and theoretical results was observed.

The structure of premixed particle-cloud flames

NASA Technical Reports Server (NTRS)

Seshadri, K.; Berlad, A. L.; Tangirala, V.

1992-01-01

The structure of premixed flames propagating in combustible systems, containing uniformly distributed volatile fuel particles, in an oxidizing gas mixture, is analyzed. It is presumed that the fuel particles vaporize first to yield a gaseous fuel of known chemical structure, which is subsequently oxidized in the gas phase. The analysis is performed in the asymptotic limit, where the value of the characteristic Zeldovich number, based on the gas-phase oxidation of the gaseous fuel is large, and for values of phi(u) greater than or equal to 1.0, where phi(u) is the equivalence ratio based on the fuel available in the fuel particles. The structure of the flame is presumed to consist of a preheat vaporization zone where the rate of the gas-phase chemical reaction is small, a reaction zone where convection and the rate of vaporization of the fuel particles are small and a convection zone where diffusive terms in the conservation equations are small. For given values phi(u) the analysis yields results for the burning velocity and phi(g) where phi(g) is the effective equivalence ratio in the reaction zone. The analysis shows that even though phi(u) greater than or equal to 1.0, for certain cases the calculated value of phi(g) is less than unity. This prediction is in agreement with experimental observations.

Advances in Studies of Electrode Kinetics and Mass Transport in AMTEC Cells (abstract)

NASA Technical Reports Server (NTRS)

Williams, R. M.; Jeffries-Nakamura, B.; Ryan, M. A.; Underwood, M. L.; Kisor, A.; O'Connor, D.; Kikkert, S.

1993-01-01

Previous work reported from JPL has included characterization of electrode kinetics and alkali atom transport from electrodes including Mo, W, WRh(sub x), WPt(sub x)(Mn), in sodium AMTEC cells and vapor exposure cells, and Mo in potassium vapor exposure cells. These studies were generally performed in cells with small area electrodes (about 1 to 5 cm(sup 2)), and device geometry had little effect on transport. Alkali diffusion coefficients through these electrodes have been characterized, and approximate surface diffusion coefficients derived in cases of activated transport. A basic model of electrode kinetic at the alkali metal vapor/porous metal electrode/alkali beta'-alumina solid electrolyte three phase boundary has been proposed which accounts for electrochemical reaction rates with a collision frequency near the three phase boundary and tunneling from the porous electrode partially covered with adsorbed alkali metal atoms. The small electrode effect in AMTEC cells has been discussed in several papers, but quantitative investigations have described only the overall effect and the important contribution of electrolyte resistance. The quantitative characterization of transport losses in cells with large area electrodes has been limited to simulations of large area electrode effects, or characterization of transport losses from large area electrodes with significant longitudinal temperature gradients. This paper describes new investigations of electrochemical kinetics and transport, particularily with WPt(sub 3.5) electrodes, including the influence of electrode size on the mass transport loss in the AMTEC cell. These electrodes possess excellent sodium transport properties making verification of device limitations on transport much more readily attained.

A comparison between protein crystals grown with vapor diffusion methods in microgravity and protein crystals using a gel liquid-liquid diffusion ground-based method

NASA Technical Reports Server (NTRS)

Miller, Teresa Y.; He, Xiao-Min; Carter, Daniel C.

1992-01-01

Crystals of human serum albumin have been successfully grown in a variety of gels using crystallization conditions otherwise equivalent to those utilized in the popular hanging-drop vapor-equilibrium method. Preliminary comparisons of gel grown crystals with crystals grown by the vapor diffusion method via both ground-based and microgravity methods indicate that crystals superior in size and quality may be grown by limiting solutal convection. Preliminary X-ray diffraction statistics are presented.

Spreading of a liquid film on a substrate by the evaporation-adsorption process

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

Wayner, P.C. Jr.; Schonberg, J.

1992-09-01

The importance of evaporation followed by multilayer adsorption in comparison to liquid flow at the leading edge of a volatile spreading film is analyzed. Presuming that both flows are functions of the same chemical potential gradient, a dimensionless group (N) which delineates the relative importance of vapor diffusion flow to viscous flow on the surface is obtained: N = [rho][sub i]D[nu]x/([minus][bar A][pi]). The relative importance of vapor flow increases with the vapor-pressure dependent partial density, [rho][sub i], and diffusivity, D, of the diffusing vapor, the kinematic viscosity of the liquid, [nu], and the distance downstream from the bulk liquid region,more » x, and decreases with the Hamaker constant, 6[pi][bar A]. Using physical properties the modifiers volatile'' and nonvolatile'' can thereby be put in perspective. Changes in the interfacial force field are a function of [bar A]. The spreading velocity due to the vapor diffusion process is obtained and is found to decrease with a decrease in the interfacial force field and the bulk vapor pressure. The infinite stress at the contact line can be easily relieved by evaporation-adsorption in many systems.« less

VQS (vapor-quasiliquid-solid, vapor-quasisolid-solid) mechanism presents a unified foundation for the syntheses of nanotubes, primarily carbon nanotubes

NASA Astrophysics Data System (ADS)

Mohammad, S. Noor

2017-09-01

Nanotubes are synthesized almost entirely by metal-catalyst-free and metal-catalyst-mediated non-eutectic mechanism(s). An investigation has been carried out to understand the basics of this mechanism. Various possible chemical and physical processes involved in nanotube synthesis have been researched. Various components and attributes of nanotube synthesis have been evaluated. Phase transitions, alloy formation, porosity, carrier transport and the fundamentals underlying them have been examined. Nanoparticle surfaces conducive to nanotube synthesis have been examined. The role of surface treatment, which includes oxidation, oxygenation, acid treatment, plasma treatment, water treatment, sputtering, etc in creating such surfaces, has been investigated. The role of surface treatment and phase transitions as functions of temperature, pressure, ambient, contaminants, surface amorphicity, etc in creating diffusion paths for the diffusion of growth species for supersaturation and nucleation has been explored. Interdiffusion of catalyst and source materials, and hence exchange of materials, on the nanoparticle surface, have been elucidated. This exchange of materials on catalyst surface appears to add a new dimension to the synthesis kinetics. Integrated together, they reveal a general mechanism for probably all metal-catalyst-free and metal-catalyst-mediated non-eutectic nanotube synthesis. Available experiments strongly support the proposed mechanism; they suggest that this mechanism has a broad appeal.

Surface effects on exciton diffusion in non polar ZnO/ZnMgO heterostructures

NASA Astrophysics Data System (ADS)

Sakr, G.; Sartel, C.; Sallet, V.; Lusson, A.; Patriarche, G.; Galtier, P.; Barjon, J.

2017-12-01

The diffusion of excitons injected in ZnO/Zn0.92Mg0.08O quantum well heterostructures grown by metal-organic-vapor-phase-epitaxy on non-polar ZnO substrates is investigated at room temperature. Cathodoluminescence linescans in a field-emission-gun scanning-electron-microscope are performed across cleaved cross-sections. A 55 nm diffusion length is assessed for excitons in bulk ZnMgO. When prepared as small angle bevels using focused ion beam (FIB), the effective diffusion length of excitons is shown to decrease down to 8 nm in the thinner part of the slab. This effect is attributed to non-radiative surface recombinations, with a 7  ×  104 cm s-1 recombination velocity estimated at the FIB-machined ZnMgO surface. The strong reduction of the diffusion extent in such thin lamellae usually used for transmission electron microscopy could be use improve the spatial resolution of cathodoluminescence images, often limited by diffusion processes.

Development of a Computational Chemical Vapor Deposition Model: Applications to Indium Nitride and Dicyanovinylaniline

NASA Technical Reports Server (NTRS)

Cardelino, Carlos

1999-01-01

A computational chemical vapor deposition (CVD) model is presented, that couples chemical reaction mechanisms with fluid dynamic simulations for vapor deposition experiments. The chemical properties of the systems under investigation are evaluated using quantum, molecular and statistical mechanics models. The fluid dynamic computations are performed using the CFD-ACE program, which can simulate multispecies transport, heat and mass transfer, gas phase chemistry, chemistry of adsorbed species, pulsed reactant flow and variable gravity conditions. Two experimental setups are being studied, in order to fabricate films of: (a) indium nitride (InN) from the gas or surface phase reaction of trimethylindium and ammonia; and (b) 4-(1,1)dicyanovinyl-dimethylaminoaniline (DCVA) by vapor deposition. Modeling of these setups requires knowledge of three groups of properties: thermodynamic properties (heat capacity), transport properties (diffusion, viscosity, and thermal conductivity), and kinetic properties (rate constants for all possible elementary chemical reactions). These properties are evaluated using computational methods whenever experimental data is not available for the species or for the elementary reactions. The chemical vapor deposition model is applied to InN and DCVA. Several possible InN mechanisms are proposed and analyzed. The CVD model simulations of InN show that the deposition rate of InN is more efficient when pulsing chemistry is used under conditions of high pressure and microgravity. An analysis of the chemical properties of DCVA show that DCVA dimers may form under certain conditions of physical vapor transport. CVD simulations of the DCVA system suggest that deposition of the DCVA dimer may play a small role in the film and crystal growth processes.

Diffusive-convective physical vapor transport of PbTe from a Te-rich solid source

NASA Technical Reports Server (NTRS)

Zoutendyk, J.; Akutagawa, W.

1982-01-01

Crystal growth of PbTe by physical vapor transport (sublimation) in a closed ampoule is governed by the vapor species in thermal equilibrium with the solid compound. Deviations from stoichiometry in the source material cause diffusion limitation of the transport rate, which can be modified by natural (gravity-driven) convection. Mass-transport experiments have been performed using Te-rich material wherein sublimation rates have been measured in order to study the effects of natural convection in diffusion-limited vapor transport. Linear velocities for both crystal growth and evaporation (back sublimation) have been measured for transport in the direction of gravity, horizontally, and opposite to gravity. The experimental results are discussed in terms of both the one-dimensional diffusive-advective model and current, more sophisticated theory which includes natural convection. There is some evidence that convection effects from radial temperature gradients and solutal density gradients have been observed.

Methods for characterizing subsurface volatile contaminants using in-situ sensors

DOEpatents

Ho, Clifford K [Albuquerque, NM

2006-02-21

An inverse analysis method for characterizing diffusion of vapor from an underground source of volatile contaminant using data taken by an in-situ sensor. The method uses one-dimensional solutions to the diffusion equation in Cartesian, cylindrical, or spherical coordinates for isotropic and homogenous media. If the effective vapor diffusion coefficient is known, then the distance from the source to the in-situ sensor can be estimated by comparing the shape of the predicted time-dependent vapor concentration response curve to the measured response curve. Alternatively, if the source distance is known, then the effective vapor diffusion coefficient can be estimated using the same inverse analysis method. A triangulation technique can be used with multiple sensors to locate the source in two or three dimensions. The in-situ sensor can contain one or more chemiresistor elements housed in a waterproof enclosure with a gas permeable membrane.

Lateral gas phase diffusion length of boron atoms over Si/B surfaces during CVD of pure boron layers

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

Mohammadi, V., E-mail: V.Mohammadi@tudelft.nl; Nihtianov, S.

The lateral gas phase diffusion length of boron atoms, L{sub B}, along silicon and boron surfaces during chemical vapor deposition (CVD) using diborane (B{sub 2}H{sub 6}) is reported. The value of L{sub B} is critical for reliable and uniform boron layer coverage. The presented information was obtained experimentally and confirmed analytically in the boron deposition temperature range from 700 °C down to 400 °C. For this temperature range the local loading effect of the boron deposition is investigated on the micro scale. A L{sub B} = 2.2 mm was determined for boron deposition at 700 °C, while a L{sub B}more » of less than 1 mm was observed at temperatures lower than 500 °C.« less

Distribution of selected volatile organic compounds determined with water-to-vapor diffusion samplers at the interface between ground water and surface water, Centredale Manor site, North Providence, Rhode Island, September 1999

USGS Publications Warehouse

Church, Peter E.; Lyford, Forest P.; Clifford, Scott

2000-01-01

Volatile organic compounds are present in soils and ground water at the Centredale Manor Superfund Site in North Providence, Rhode Island. In September 1999, water-to-vapor diffusion samplers were placed in the bottom sediments of waterways adjacent to the site to identify possible contaminated ground-water discharge areas. The approximate12-acre site is a narrow stretch of land between the eastern bank of the Woonasquatucket River, downstream from the U.S. Route 44 bridge and a former mill raceway. The samplers were placed along a 2,250-foot reach of the Woonasquatucket River, in the former mill raceway several hundred feet to the east and parallel to the river, and in a cross channel between the river and former mill raceway. Volatile organic compounds were detected in 84 of the 104 water-to-vapor diffusion samplers retrieved. Trichloroethylene and tetrachloro-ethylene were the principal volatile organic compounds detected. The highest vapor concentrations measured for these two chemicals were from diffusion samplers located along an approximate 100-foot reach of the Woonasquatucket River about 500 feet downstream of the bridge; here trichloroethylene and tetrachloroethylene vapor concentrations ranged from about 2,000 to 180,000 and 1,600 to 1,400,000 parts per billion by volume, respectively. Upstream and downstream from this reach and along the former mill raceway, trichloroethylene and tetrachloroethylene vapor concentrations from the diffusion samples were generally less than 100 parts per billion by volume. Along the lower reaches of the river and mill raceway, however, and in the cross channel, vapor concentrations of trichloroethylene exceeded 100 parts per billion by volume and tetrachloroethylene exceeded 1,000 parts per billion by volume in several diffusion samples. Although diffusion sample vapor concentrations are higher than water concentrations in surface waters and in ground water, and they should only be interpreted qualitatively as relative values, these values provide important information as to potential discharge areas of contaminants.

Cloud Condensation in Titan's Lower Stratosphere

NASA Technical Reports Server (NTRS)

Romani, Paul N.; Anderson, Carrie M.

2011-01-01

A 1-D condensation model is developed for the purpose of reproducing ice clouds in Titan's lower stratosphere observed by the Composite Infrared Spectrometer (CIRS) onboard Cassini. Hydrogen cyanide (HCN), cyanoacetylene (HC3N), and ethane (C2H6) vapors are treated as chemically inert gas species that flow from an upper boundary at 500 km to a condensation sink near Titan's tropopause (-45 km). Gas vertical profiles are determined from eddy mixing and a downward flux at the upper boundary. The condensation sink is based upon diffusive growth of the cloud particles and is proportional to the degree of supersaturation in the cloud formation regIOn. Observations of the vapor phase abundances above the condensation levels and the locations and properties of the ice clouds provide constraints on the free parameters in the model. Vapor phase abundances are determined from CIRS mid-IR observations, whereas cloud particle sizes, altitudes, and latitudinal distributions are derived from analyses of CIRS far-IR observations of Titan. Specific cloud constraints include: I) mean particle radii of2-3 J.lm inferred from the V6 506 cm- band of HC3N, 2) latitudinal abundance distributions of condensed nitriles, inferred from a composite emission feature that peaks at 160/cm , and 3) a possible hydrocarbon cloud layer at high latitudes, located near an altitude of 60 km, which peaks between 60 and 80 cm l . Nitrile abundances appear to diminish substantially at high northern latitudes over the time period 2005 to 2010 (northern mid winter to early spring). Use of multiple gas species provides a consistency check on the eddy mixing coefficient profile. The flux at the upper boundary is the net column chemical production from the upper atmosphere and provides a constraint on chemical pathways leading to the production of these compounds. Comparison of the differing lifetimes, vapor phase transport, vapor phase loss rate, and particle sedimentation, sheds light on temporal stability of the clouds.

Some mechanisms for the formation of octopus-shaped iron micro-particles

NASA Astrophysics Data System (ADS)

Bica, Ioan

2004-08-01

Fluid spheres (micro-spheres or/and drops) are formed out of the metallic solid (the carbon steel semi-finished product) in the argon plasma of the transferred electric arc. For short intervals of time, the spheres are at rest with relation to vapors. The movement of the vapors around the spheres is in the same plane. It consists of a movement around a circle combined with the movement produced by a definitely located whirl. The molar concentration of the vapors is small in comparison with the molar density of the mixture formed of vapors and gas. At the intersection of the sphere and the plane of movement of the vapors, distinct stagnation point is formed. They constitute points of the beginning/and end of the current lines. Each current line is a carrier of a vapor cylinder. In time, the cylinder-gas interface reaches points of temperature equal to that of the "dew point" for iron. On this occasion a liquid membrane is formed. It delimits the vapor-gas mixture from the rest of the gas. Subsequent to the process of diffusion in non-stationary condition, the membrane becomes thicker and no vapors exist inside the tube. Needle-shaped micro-tubes are formed, in liquid phase, around the fluid sphere. By solidification, micro-particles occur, consisting of a central nucleus around which ligaments branch out.

The Commercial Vapor Diffusion Apparatus (CVDA) STS-95

NASA Technical Reports Server (NTRS)

2004-01-01

The Commercial Vapor Diffusion Apparatus will be used to perform 128 individual crystal growth investigations for commercial and science research. These experiments will grow crystals of several different proteins, including HIV-1 Protease Inhibitor, Glycogen Phosphorylase A, and NAD Synthetase. The Commercial Vapor Diffusion Apparatus supports multiple commercial investigations within a controlled environment. The goal of the Commercial Protein Crystal Growth payload on STS-95 is to grow large, high-quality crystals of several different proteins of interest to industry, and to continue to refine the technology and procedures used in microgravity for this important commercial research.

Ultrahigh-density sub-10 nm nanowire array formation via surface-controlled phase separation.

PubMed

Tian, Yuan; Mukherjee, Pinaki; Jayaraman, Tanjore V; Xu, Zhanping; Yu, Yongsheng; Tan, Li; Sellmyer, David J; Shield, Jeffrey E

2014-08-13

We present simple, self-assembled, and robust fabrication of ultrahigh density cobalt nanowire arrays. The binary Co-Al and Co-Si systems phase-separate during physical vapor deposition, resulting in Co nanowire arrays with average diameter as small as 4.9 nm and nanowire density on the order of 10(16)/m(2). The nanowire diameters were controlled by moderating the surface diffusivity, which affected the lateral diffusion lengths. High resolution transmission electron microscopy reveals that the Co nanowires formed in the face-centered cubic structure. Elemental mapping showed that in both systems the nanowires consisted of Co with undetectable Al or Si and that the matrix consisted of Al with no distinguishable Co in the Co-Al system and a mixture of Si and Co in the Co-Si system. Magnetic measurements clearly indicate anisotropic behavior consistent with shape anisotropy. The dynamics of nanowire growth, simulated using an Ising model, is consistent with the experimental phase and geometry of the nanowires.

Microfabricated valveless devices for thermal bioreactions based on diffusion-limited evaporation.

PubMed

Wang, Fang; Yang, Ming; Burns, Mark A

2008-01-01

Microfluidic devices that reduce evaporative loss during thermal bioreactions such as PCR without microvalves have been developed by relying on the principle of diffusion-limited evaporation. Both theoretical and experimental results demonstrate that the sample evaporative loss can be reduced by more than 20 times using long narrow diffusion channels on both sides of the reaction region. In order to further suppress the evaporation, the driving force for liquid evaporation is reduced by two additional techniques: decreasing the interfacial temperature using thermal isolation and reducing the vapor concentration gradient by replenishing water vapor in the diffusion channels. Both thermal isolation and vapor replenishment techniques can limit the sample evaporative loss to approximately 1% of the reaction content.

Solid- and vapor-phase antimicrobial activities of six essential oils: susceptibility of selected foodborne bacterial and fungal strains.

PubMed

López, P; Sánchez, C; Batlle, R; Nerín, C

2005-08-24

The antimicrobial activity of essential oils (EOs) of cinnamon (Cinnamon zeylanicum), clove (Syzygium aromaticum), basil (Ocimum basillicum), rosemary (Rosmarinus officinalis), dill (Anethum graveolens), and ginger (Zingiber officinalis) was evaluated over a range of concentrations in two types of contact tests (solid and vapor diffusion). The EOs were tested against an array of four Gram-positive bacteria (Staphylococcus aureus, Bacillus cereus, Enterococcus faecalis, and Listeria monocytogenes), four Gram-negative bacteria (Escherichia coli, Yersinia enterocolitica, Salmonella choleraesuis, and Pseudomonas aeruginosa), and three fungi (a yeast, Candida albicans, and two molds, Penicillium islandicum and Aspergillus flavus). The rationale for this work was to test the possibility of creating a protective atmosphere by using natural compounds that could extend the shelf life of packaged foodstuffs while minimizing organoleptic alterations. In the solid diffusion tests, cinnamon and clove gave the strongest (and very similar) inhibition, followed by basil and rosemary, with dill and ginger giving the weakest inhibition. The fungi were the most sensitive microorganisms, followed by the Gram-positive bacterial strains. The Gram-negative strain P. aeruginosa was the least inhibited. The composition of the atmosphere generated by the EOs, and their minimum inhibitory concentrations (MICs), were determined using a disk volatilization method, in which no inhibition from rosemary or basil was observed. Cinnamon and clove, once again, gave similar results for every microorganism. As a general rule, MIC (fungi) < MIC (bacteria) with no clear differences between Gram-positive or -negative strains except for P. aeruginosa, which was not inhibited by any of the EOs in the vapor phase. The atmosphere generated from the EOs was analyzed by means of solid-phase microextraction combined with gas chromatography-ion trap mass spectrometry. Differences among the volatiles in the EOs, which may be responsible for the differences in their antimicrobial performances, were found.

Ge auto-doping and out-diffusion in InGaP grown on Ge substrate and their effects on the ordering of InGaP

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

Wu, Hong-Ming; Ho, Hao-I; Tsai, Shi-Jane

2016-03-21

We report on the Ge auto-doping and out-diffusion in InGaP epilayer with Cu-Pt ordering grown on 4-in. Ge substrate. Ge profiles determined from secondary ion mass spectrometry indicate that the Ge out-diffusion depth is within 100 nm. However, the edge of the wafer suffers from stronger Ge gas-phase auto-doping than the center, leading to ordering deterioration in the InGaP epilayer. In the edge, we observed a residual Cu-Pt ordering layer left beneath the surface, suggesting that the ordering deterioration takes place after the deposition rather than during the deposition and In/Ga inter-diffusion enhanced by Ge vapor-phase auto-doping is responsible for themore » deterioration. We thus propose a di-vacancy diffusion model, in which the amphoteric Ge increases the di-vacancy density, resulting in a Ge density dependent diffusion. In the model, the In/Ga inter-diffusion and Ge out-diffusion are realized by the random hopping of In/Ga host atoms and Ge atoms to di-vacancies, respectively. Simulation based on this model well fits the Ge out-diffusion profiles, suggesting its validity. By comparing the Ge diffusion coefficient obtained from the fitting and the characteristic time constant of ordering deterioration estimated from the residual ordering layer, we found that the hopping rates of Ge and the host atoms are in the same order of magnitude, indicating that di-vacancies are bound in the vicinity of Ge atoms.« less

In Situ Ramp Anneal X-ray Diffraction Study of Atomic Layer Deposited Ultrathin TaN and Ta 1-x Al x N y Films for Cu Diffusion Barrier Applications

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

Consiglio, S.; Dey, S.; Yu, K.

2016-01-01

Ultrathin TaN and Ta 1-xAl xN y films with x = 0.21 to 0.88 were deposited by atomic layer deposition (ALD) and evaluated for Cu diffusion barrier effectiveness compared to physical vapor deposition (PVD) grown TaN. Cu diffusion barrier effectiveness was investigated using in-situ ramp anneal synchrotron X-ray diffraction (XRD) on Cu/1.8 nm barrier/Si stacks. A Kissinger-like analysis was used to assess the kinetics of Cu 3Si formation and determine the effective activation energy (E a) for Cu silicidation. Compared to the stack with a PVD TaN barrier, the stacks with the ALD films exhibited a higher crystallization temperature (Tmore » c) for Cu silicidation. The Ea values of Cu 3Si formation for stacks with the ALD films were close to the reported value for grain boundary diffusion of Cu whereas the Ea of Cu 3Si formation for the stack with PVD TaN is closer to the reported value for lattice diffusion. For 3 nm films, grazing incidence in-plane XRD showed evidence of nanocrystallites in an amorphous matrix with broad peaks corresponding to high density cubic phase for the ALD grown films and lower density hexagonal phase for the PVD grown film further elucidating the difference in initial failure mechanisms due to differences in barrier crystallinity and associated phase.« less

Use of the quartz crystal microbalance to determine the monomeric friction coefficient of polyimides

NASA Technical Reports Server (NTRS)

Bechtold, Mary M.

1995-01-01

When a thin film of polymer is coated on to a quartz crystal microbalance (QCM), the QCM can be used to detect the rate of increase in weight of the polymer film as the volatile penetrant diffuses into the polymer. From this rate information the diffusion coefficient of the penetrant into the polymer can be computed. Calculations requiring this diffusion coefficient lead to values which approximate the monomeric friction coefficient of the polymer. This project has been concerned with the trial of crystal oscillating circuits suitable for driving polymer coated crystals in an atmosphere of penetrant. For these studies done at room temperature, natural rubber was used as an easily applied polymer that is readily penetrated by toluene vapors, qualities anticipated with polyimides when they are tested at T(g) in the presence of toluene. Three quartz crystal oscillator circuits were tested. The simplest circuit used +/- 5 volt dc and had a transistor to transistor logic (TTL) inverter chip that provides a 180 deg phase shift via a feed back loop. This oscillator circuit was stable but would not drive the crystal when the crystal was coated with polymer and subjected to toluene vapors. Removal of a variable resistor from this circuit increased stability but did not otherwise increase performance. Another driver circuit tested contained a two stage differential input, differential output, wide band video amplifier and also contain a feed back loop. The circuit voltage could not be varied and operated at +/- 5 volts dc; this circuit was also stable but failed to oscillate the polymer coated crystal in an atmosphere saturated with toluene vapors. The third oscillator circuit was of similar construction and relied on the same video amplifier but allowed operation with variable voltage. This circuit would drive the crystal when the crystal was submerged in liquid toluene and when the crystal was coated with polymer and immersed in toluene vapors. The frequency readings obtained when using this oscillating circuit are highly variable. This circuit requires further modification to stabilize frequency readings before its use in studies to determine the diffusion coefficient of penetrant molecules into a polymer film coated on a QCM.

Biophysical mechanisms of trichloroethene uptake and loss in baldcypress growing in shallow contaminated groundwater

USGS Publications Warehouse

Nietch, C.T.; Morris, J.T.; Vroblesky, D.A.

1999-01-01

Wetland vegetation may be useful in the remediation of shallow contaminated aquifers. Mesocosm experiments were conducted to describe the regulatory mechanisms affecting trichloroethene (TCE) removal rates from groundwater by flood-adapted wetland trees at a contaminated site. TCE flux through baldcypress [Taxodium distichum (L) Rich] seedlings grown in glass- carboys decreased from day to night and from August to December. The diel fluctuation coincided with changes in leaf-level physiology, as the daytime flux was significantly correlated with net photosynthesis but not with respiration at night. A decrease in seedling water use from summer to winter explained the large seasonal difference in TCE flux. A simple model that simulates gas-phase diffusion through aerenchyma tested the importance of diffusion of TCE vapor from roots to the stem. The modeled diffusive flux was within 64% of the observed value during the winter but could only explain 8% of the summer flux. Seedling water use was a good estimator of flux during the summer. Hence, evapotranspiration (ET) in the summer may serve as a good predictor for the potential of TCE removal by baldcypress trees, while diffusive flux may better approximate potential contaminant loss in the winter.Wetland vegetation may be useful in the remediation of shallow contaminated aquifers. Mesocosm experiments were conducted to describe the regulatory mechanisms affecting trichloroethene (TCE) removal rates from groundwater by flood-adapted wetland trees at a contaminated site. TCE flux through baldcypress [Taxodium distichum (L) Rich] seedlings grown in glass-carboys decreased from day to night and from August to December. The diel fluctuation coincided with changes in leaf-level physiology, as the daytime flux was significantly correlated with net photosynthesis but not with respiration at night. A decrease in seedling water use from summer to winter explained the large seasonal difference in TCE flux. A simple model that simulates gas-phase diffusion through aerenchyma tested the importance of diffusion of TCE vapor from roots to the stem. The modeled diffusive flux was within 64% of the observed value during the winter but could only explain 8% of the summer flux. Seedling water use was a good estimator of flux during the summer. Hence, evapotranspiration (ET) in the summer may serve as a good predictor for the potential of TCE removal by baldcypress trees, while diffusive flux may better approximate potential contaminant loss in the winter.

Swelling kinetics and electrical charge transport in PEDOT:PSS thin films exposed to water vapor.

PubMed

Sarkar, Biporjoy; Jaiswal, Manu; Satapathy, Dillip K

2018-06-06

We report the swelling kinetics and evolution of the electrical charge transport in poly(3,4-ethylene dioxythiophene) polystyrene sulfonate (PEDOT:PSS) thin films subjected to water vapor. Polymer films swell by the diffusion of water vapor and are found to undergo structural relaxations. Upon exposure to water vapor, primarily the hygroscopic PSS shell, which surrounds the conducting PEDOT-rich cores, takes up water vapor and subsequently swells. We found that the degree of swelling largely depends on the PEDOT to PSS ratio. Swelling driven microscopic rearrangement of the conducting PEDOT-rich cores in the PSS matrix strongly influences the electrical charge transport of the polymer film. Swelling induced increase as well as decrease of electrical resistance are observed in polymer films having different PEDOT to PSS ratio. This anomalous charge transport behavior in PEDOT:PSS films is reconciled by taking into account the contrasting swelling behavior of the PSS and the conducting PEDOT-rich cores leading to spatial segregation of PSS in films with PSS as a minority phase and by a net increase in mean separation between conducting PEDOT-rich cores for films having abundance of PSS.

Swelling kinetics and electrical charge transport in PEDOT:PSS thin films exposed to water vapor

NASA Astrophysics Data System (ADS)

Sarkar, Biporjoy; Jaiswal, Manu; Satapathy, Dillip K.

2018-06-01

We report the swelling kinetics and evolution of the electrical charge transport in poly(3,4-ethylene dioxythiophene) polystyrene sulfonate (PEDOT:PSS) thin films subjected to water vapor. Polymer films swell by the diffusion of water vapor and are found to undergo structural relaxations. Upon exposure to water vapor, primarily the hygroscopic PSS shell, which surrounds the conducting PEDOT-rich cores, takes up water vapor and subsequently swells. We found that the degree of swelling largely depends on the PEDOT to PSS ratio. Swelling driven microscopic rearrangement of the conducting PEDOT-rich cores in the PSS matrix strongly influences the electrical charge transport of the polymer film. Swelling induced increase as well as decrease of electrical resistance are observed in polymer films having different PEDOT to PSS ratio. This anomalous charge transport behavior in PEDOT:PSS films is reconciled by taking into account the contrasting swelling behavior of the PSS and the conducting PEDOT-rich cores leading to spatial segregation of PSS in films with PSS as a minority phase and by a net increase in mean separation between conducting PEDOT-rich cores for films having abundance of PSS.

Measurement and Modeling of Water-Vapor Diffusion in Elastomers with Impact in Humidity and Vacuum Measurements

NASA Astrophysics Data System (ADS)

Šetina, Janez; Sefa, Makfir; Erjavec, Bojan; Hudoklin, Domen

2013-03-01

The dynamics of water-vapor dissolution in Viton O-rings is measured with a gravimetric method using a precise mass comparator. A sample gasket was degassed in high vacuum for a sufficiently long period to remove more than 99 % of the dissolved water vapor. After that, it was exposed to the ambient atmosphere with a controlled temperature, and relative humidity and water-vapor uptake curves were measured gravimetrically with a precise balance. The dynamics of a water-vapor release into vacuum from another sample that was previously saturated with water vapor at room temperature was determined. The sample was placed in a vacuum outgassing rate measurement apparatus. The time dependence of the evolved water vapor was calculated by integrating the measured outgassing rate. The physical process of water absorption can be described by the diffusion equation. The geometry of the samples required solving the diffusion equation in cylindrical coordinates. This was done numerically using a finite-difference method. As a result of the modeling, room temperature values of the diffusion constant D, the solubility s, and the permeability K = D× s of water vapor in the sample material (Viton A-401C) were obtained. For sample 1, we obtained D = 8.0 × 10 ^{-8} cm2 {\\cdot } s^{-1} and s = 6.5 × 10^{-7} g {\\cdot } cm^-3 Pa^{-1}, while for sample 2, D = 3.0 × 10^{-7} cm2 s^{-1} and s = 3.5 × 10^{-7} g {\\cdot } cm^{-3} {\\cdot } Pa^{-1}.

Pure wurtzite GaP nanowires grown on zincblende GaP substrates by selective area vapor liquid solid epitaxy

NASA Astrophysics Data System (ADS)

Halder, Nripendra N.; Kelrich, Alexander; Cohen, Shimon; Ritter, Dan

2017-11-01

We report on the growth of single phase wurtzite (WZ) GaP nanowires (NWs) on GaP (111) B substrates by metal organic molecular beam epitaxy following the selective area vapor-liquid-solid (SA-VLS) approach. During the SA-VLS process, precursors are supplied directly to the NW sidewalls, and the short diffusion length of gallium (or its precursors) does not significantly limit axial growth. Transmission electron microscopy (TEM) images reveal that no stacking faults are present along a 600 nm long NW. The lattice constants of the pure WZ GaP obtained from the TEM images agree with values determined previously by x-ray diffraction from non-pure NW ensembles.

Pure wurtzite GaP nanowires grown on zincblende GaP substrates by selective area vapor liquid solid epitaxy.

PubMed

Halder, Nripendra N; Kelrich, Alexander; Cohen, Shimon; Ritter, Dan

2017-11-17

We report on the growth of single phase wurtzite (WZ) GaP nanowires (NWs) on GaP (111) B substrates by metal organic molecular beam epitaxy following the selective area vapor-liquid-solid (SA-VLS) approach. During the SA-VLS process, precursors are supplied directly to the NW sidewalls, and the short diffusion length of gallium (or its precursors) does not significantly limit axial growth. Transmission electron microscopy (TEM) images reveal that no stacking faults are present along a 600 nm long NW. The lattice constants of the pure WZ GaP obtained from the TEM images agree with values determined previously by x-ray diffraction from non-pure NW ensembles.

HYDROCARBON VAPOR DIFFUSION IN INTACT CORE SLEEVES

EPA Science Inventory

The diffusion of 2,2,4-trimethylpentane (TMP) and 2,2,5-trimethylhexane (TMH) vapors put of residually contaminated sandy soil from the U.S. Environmental Protection Agency (EPA) field research site at Traverse City, Michigan, was measured and modeled. The headspace of an intact ...

Self-diffusion Coefficient and Structure of Binary n-Alkane Mixtures at the Liquid-Vapor Interfaces.

PubMed

Chilukoti, Hari Krishna; Kikugawa, Gota; Ohara, Taku

2015-10-15

The self-diffusion coefficient and molecular-scale structure of several binary n-alkane liquid mixtures in the liquid-vapor interface regions have been examined using molecular dynamics simulations. It was observed that in hexane-tetracosane mixture hexane molecules are accumulated in the liquid-vapor interface region and the accumulation intensity decreases with increase in a molar fraction of hexane in the examined range. Molecular alignment and configuration in the interface region of the liquid mixture change with a molar fraction of hexane. The self-diffusion coefficient in the direction parallel to the interface of both tetracosane and hexane in their binary mixture increases in the interface region. It was found that the self-diffusion coefficient of both tetracosane and hexane in their binary mixture is considerably higher in the vapor side of the interface region as the molar fraction of hexane goes lower, which is mostly due to the increase in local free volume caused by the local structure of the liquid in the interface region.

Interdiffusion behavior between NiAlHf coating and Ni-based single crystal superalloy with different crystal orientations

NASA Astrophysics Data System (ADS)

Wang, Ruili; Gong, Xueyuan; Peng, Hui; Ma, Yue; Guo, Hongbo

2015-01-01

NiAlHf coatings were deposited onto Ni-based single crystal (SC) superalloy with different crystal orientations by electron beam physical vapor deposition (EB-PVD). The effects of the crystal orientations of the superalloy substrate on inter-diffusion behavior between the substrate and the NiAlHf coating were investigated. Substrate diffusion zone (SDZ) containing needle-like μ phases and interdiffusion zone (IDZ) mainly consisting of the ellipsoidal and rod-like μ phases were formed in the SC alloy after heat-treatment 10 h at 1100 °C. The thickness of secondary reaction zone (SRZ) formed in the SC alloy with (0 1 1) crystal orientation is about 14 μm after 50 h heat-treatment at 1100 °C, which is relatively thicker than that in the SC alloy with (0 0 1) crystal orientation, whereas the IDZ revealed similar thickness.

Tracing Water Vapor and Ice During Dust Growth

NASA Astrophysics Data System (ADS)

Krijt, Sebastiaan; Ciesla, Fred J.; Bergin, Edwin A.

2016-12-01

The processes that govern the evolution of dust and water (in the form of vapor or ice) in protoplanetary disks are intimately connected. We have developed a model that simulates dust coagulation, dust dynamics (settling, turbulent mixing), vapor diffusion, and condensation/sublimation of volatiles onto grains in a vertical column of a protoplanetary disk. We employ the model to study how dust growth and dynamics influence the vertical distribution of water vapor and water ice in the region just outside the radial snowline. Our main finding is that coagulation (boosted by the enhanced stickiness of icy grains) and the ensuing vertical settling of solids results in water vapor being depleted, but not totally removed, from the region above the snowline on a timescale commensurate with the vertical turbulent mixing timescale. Depending on the strength of the turbulence and the temperature, the depletion can reach factors of up to ˜50 in the disk atmosphere. In our isothermal column, this vapor depletion results in the vertical snowline moving closer to the midplane (by up to 2 gas scale heights) and the gas-phase {{C}}/{{O}} ratio above the vertical snowline increasing. Our findings illustrate the importance of dynamical effects and the need for understanding coevolutionary dynamics of gas and solids in planet-forming environments.

Integrating carbon nanotube forests into polysilicon MEMS: Growth kinetics, mechanisms, and adhesion

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

Ubnoske, Stephen M.; Radauscher, Erich J.; Meshot, Eric R.

The growth of carbon nanotubes (CNTs) on polycrystalline silicon substrates was studied to improve the design of CNT field emission sources for microelectromechanical systems (MEMS) applications and vacuum microelectronic devices (VMDs). Microwave plasma-enhanced chemical vapor deposition (PECVD) was used for CNT growth, resulting in CNTs that incorporate the catalyst particle at their base. The kinetics of CNT growth on polysilicon were compared to growth on Si (100) using the model of Deal and Grove, finding activation energies of 1.61 and 1.54 eV for the nucleation phase of growth and 1.90 and 3.69 eV for the diffusion-limited phase on Si (100)more » and polysilicon, respectively. Diffusivity values for growth on polysilicon were notably lower than the corresponding values on Si (100) and the growth process became diffusion-limited earlier. Evidence favors a surface diffusion growth mechanism involving diffusion of carbon precursor species along the length of the CNT forest to the catalyst at the base. Explanations for the differences in activation energies and diffusivities were elucidated by SEM analysis of the catalyst nanoparticle arrays and through wide-angle X-ray scattering (WAXS) of CNT forests. As a result, methods are presented to improve adhesion of CNT films during operation as field emitters, resulting in a 2.5× improvement.« less

Integrating carbon nanotube forests into polysilicon MEMS: Growth kinetics, mechanisms, and adhesion

DOE PAGES

Ubnoske, Stephen M.; Radauscher, Erich J.; Meshot, Eric R.; ...

2016-11-19

The growth of carbon nanotubes (CNTs) on polycrystalline silicon substrates was studied to improve the design of CNT field emission sources for microelectromechanical systems (MEMS) applications and vacuum microelectronic devices (VMDs). Microwave plasma-enhanced chemical vapor deposition (PECVD) was used for CNT growth, resulting in CNTs that incorporate the catalyst particle at their base. The kinetics of CNT growth on polysilicon were compared to growth on Si (100) using the model of Deal and Grove, finding activation energies of 1.61 and 1.54 eV for the nucleation phase of growth and 1.90 and 3.69 eV for the diffusion-limited phase on Si (100)more » and polysilicon, respectively. Diffusivity values for growth on polysilicon were notably lower than the corresponding values on Si (100) and the growth process became diffusion-limited earlier. Evidence favors a surface diffusion growth mechanism involving diffusion of carbon precursor species along the length of the CNT forest to the catalyst at the base. Explanations for the differences in activation energies and diffusivities were elucidated by SEM analysis of the catalyst nanoparticle arrays and through wide-angle X-ray scattering (WAXS) of CNT forests. As a result, methods are presented to improve adhesion of CNT films during operation as field emitters, resulting in a 2.5× improvement.« less

PAH and OPAH Flux during the Deepwater Horizon Incident

PubMed Central

Tidwell, Lane G.; Allan, Sarah E.; O'Connell, Steven G.; Hobbie, Kevin A.; Smith, Brian W.; Anderson, Kim A.

2016-01-01

Passive sampling devices were used to measure air vapor and water dissolved phase concentrations of 33 polycyclic aromatic hydrocarbons (PAHs) and 22 oxygenated PAHs (OPAHs) at four Gulf of Mexico coastal sites prior to, during and after shoreline oiling from the Deepwater Horizon oil spill (DWH). Measurements were taken at each site over a 13 month period, and flux across the water-air boundary was determined. This is the first report of vapor phase and diffusive flux of both PAHs and OPAHs during the DWH. Vapor phase sum PAH and OPAH concentrations ranged between 6.6 and 210 ng/m3 and 0.02 and 34 ng/m3 respectively. PAH and OPAH concentrations in air exhibited different spatial and temporal trends than in water, and air-water flux of 13 individual PAHs was shown to be at least partially influenced by the DWH incident. The largest PAH volatilizations occurred at the sites in Alabama and Mississippi at nominal rates of 56,000 and 42,000 ng/m2/day in the summer. Naphthalene was the PAH with the highest observed volatilization rate of 52,000 ng/m2/day in June 2010. This work represents additional evidence of the DWH incident contributing to air contamination, and provides one of the first quantitative air-water chemical flux determinations with passive sampling technology. PMID:27391856

Gas-evaporation in low-gravity field (cogelation mechanism of metal vapors) (M-14)

NASA Technical Reports Server (NTRS)

Wada, N.

1993-01-01

When metal and alloy compounds are heated and vaporized in a rare gas such as helium, argon, or xenon, the vaporized substances diffused in the rare gas are supersaturated resulting in a smoke of fine particles of the material congealing as snow or fog. The gas vaporizing method is a fine particle generation method. Though the method has a variety of applications, the material vapor flow is disturbed by gravitational convection on Earth. The inability to elucidate the fine particle generation mechanism results in an obstruction to improving the method to mass production levels. As no convection occurs in microgravity in space, the fine particle generation mechanism influenced only by diffusion can be investigated. Investigators expect that excellent particles with homogeneous diameter distribution can be obtained. Experiment data and facts will assist in improving efficiency, quality, and scale or production processes including element processes such as vaporization, diffusion, and condensation. The objective of this experiment is to obtain important information related to the mechanism of particle formation in the gas atmosphere (smoke particles) and the production of submicron powders of extremely uniform size.

Diffusion mechanisms in chemical vapor-deposited iridium coated on chemical vapor-deposited rhenium

NASA Technical Reports Server (NTRS)

Hamilton, J. C.; Yang, N. Y. C.; Clift, W. M.; Boehme, D. R.; Mccarty, K. F.; Franklin, J. E.

1992-01-01

Radiation-cooled rocket thruster chambers have been developed which use CVD Re coated with CVD Ir on the interior surface that is exposed to hot combustion gases. The Ir serves as an oxidation barrier which protects the structural integrity-maintaining Re at elevated temperatures. The diffusion kinetics of CVD materials at elevated temperatures is presently studied with a view to the prediction and extension of these thrusters' performance limits. Line scans for Ir and Re were fit on the basis of a diffusion model, in order to extract relevant diffusion constants; the fastest diffusion process is grain-boundary diffusion, where Re diffuses down grain boundaries in the Ir overlayer.

Vapor Bubbles

NASA Astrophysics Data System (ADS)

Prosperetti, Andrea

2017-01-01

This article reviews the fundamental physics of vapor bubbles in liquids. Work on bubble growth and condensation for stationary and translating bubbles is summarized and the differences with bubbles containing a permanent gas stressed. In particular, it is shown that the natural frequency of a vapor bubble is proportional not to the inverse radius, as for a gas bubble, but to the inverse radius raised to the power 2/3. Permanent gas dissolved in the liquid diffuses into the bubble with strong effects on its dynamics. The effects of the diffusion of heat and mass on the propagation of pressure waves in a vaporous bubbly liquid are discussed. Other topics briefly touched on include thermocapillary flow, plasmonic nanobubbles, and vapor bubbles in an immiscible liquid.

Water vapor diffusion membranes

NASA Technical Reports Server (NTRS)

Holland, F. F., Jr.; Smith, J. K.

1974-01-01

The program is reported, which was designed to define the membrane technology of the vapor diffusion water recovery process and to test this technology using commercially available or experimental membranes. One membrane was selected, on the basis of the defined technology, and was subjected to a 30-day demonstration trial.

Processing of CuInSe{sub 2}-based solar cells: Characterization of deposition processes in terms of chemical reaction analyses. Phase 2 Annual Report, 6 May 1996--5 May 1997

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

Anderson, T.

This report describes research performed by the University of Florida during Phase 2 of this subcontract. First, to study CIGS, researchers adapted a contactless, nondestructive technique previously developed for measuring photogenerated excess carrier lifetimes in SOI wafers. This dual-beam optical modulation (DBOM) technique was used to investigate the differences between three alternative methods of depositing CdS (conventional chemical-bath deposition [CBD], metal-organic chemical vapor deposition [MOCVD], and sputtering). Second, a critical assessment of the Cu-In-Se thermochemical and phase diagram data using standard CALPHAD procedures is being performed. The outcome of this research will produce useful information on equilibrium vapor compositions (requiredmore » annealing ambients, Sex fluxes from effusion cells), phase diagrams (conditions for melt-assisted growth), chemical potentials (driving forces for diffusion and chemical reactions), and consistent solution models (extents of solid solutions and extending phase diagrams). Third, an integrated facility to fabricate CIS PV devices was established that includes migration-enhanced epitaxy (MEE) for deposition of CIS, a rapid thermal processing furnace for absorber film formation, sputtering of ZnO, CBD or MOCVD of CdS, metallization, and pattern definition.« less

Comparison of electrical and optical characteristics in gas-phase and gas-liquid phase discharges

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

Qazi, H. I. A.; Li, He-Ping, E-mail: liheping@tsinghua.edu.cn; Zhang, Xiao-Fei

This paper presents an AC-excited argon discharge generated using a gas-liquid (two-phase) hybrid plasma reactor, which mainly consists of a powered needle electrode enclosed in a conical quartz tube and grounded deionized water electrode. The discharges in the gas-phase, as well as in the two-phase, exhibit two discharge modes, i.e., the low current glow-like diffuse mode and the high current streamer-like constrict mode, with a mode transition, which exhibits a negative resistance of the discharges. The optical emission spectral analysis shows that the stronger diffusion of the water vapor into the discharge region in the two-phase discharges boosts up themore » generation of OH (A–X) radicals, and consequently, leads to a higher rotational temperature in the water-phase plasma plume than that of the gas-phase discharges. Both the increase of the power input and the decrease of the argon flow rate result in the increase of the rotational temperature in the plasma plume of the water-phase discharge. The stable two-phase discharges with a long plasma plume in the water-phase under a low power input and gas flow rate may show a promising prospect for the degradation of organic pollutants, e.g., printing and dyeing wastewater, in the field of environmental protection.« less

Thickness limitations in carbon nanotube reinforced silicon nitride coatings synthesized by vapor infiltration

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

Eres, Gyula

Chemical vapor infiltration is a convenient method for synthesizing carbon nanotube (CNT)-reinforced ceramic coatings. The thickness over which infiltration is relatively uniform is limited by gas phase diffusion in the pore structure. These effects were investigated in two types of silicon nitride matrix composites. With CNTs that were distributed uniformly on the substrate surface dense coatings were limited to thicknesses of several microns. With dual structured CNT arrays produced by photolithography coatings up to 400 gm thick were obtained with minimal residual porosity. Gas transport into these dual structured materials was facilitated by creating micron sized channels between "CNT pillars"more » (i.e. each pillar consisted of a large number of individual CNTs). The experimental results are consistent with basic comparisons between the rates of gas diffusion and silicon nitride growth in porous structures. This analysis also provides a general insight into optimizing infiltration conditions during the fabrication of thick CNT-reinforced composite coatings. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.« less

Robust three-body water simulation model

NASA Astrophysics Data System (ADS)

Tainter, C. J.; Pieniazek, P. A.; Lin, Y.-S.; Skinner, J. L.

2011-05-01

The most common potentials used in classical simulations of liquid water assume a pairwise additive form. Although these models have been very successful in reproducing many properties of liquid water at ambient conditions, none is able to describe accurately water throughout its complicated phase diagram. The primary reason for this is the neglect of many-body interactions. To this end, a simulation model with explicit three-body interactions was introduced recently [R. Kumar and J. L. Skinner, J. Phys. Chem. B 112, 8311 (2008), 10.1021/jp8009468]. This model was parameterized to fit the experimental O-O radial distribution function and diffusion constant. Herein we reparameterize the model, fitting to a wider range of experimental properties (diffusion constant, rotational correlation time, density for the liquid, liquid/vapor surface tension, melting point, and the ice Ih density). The robustness of the model is then verified by comparing simulation to experiment for a number of other quantities (enthalpy of vaporization, dielectric constant, Debye relaxation time, temperature of maximum density, and the temperature-dependent second and third virial coefficients), with good agreement.

Recombination properties of dislocations in GaN

NASA Astrophysics Data System (ADS)

Yakimov, Eugene B.; Polyakov, Alexander Y.; Lee, In-Hwan; Pearton, Stephen J.

2018-04-01

The recombination activity of threading dislocations in n-GaN with different dislocation densities and different doping levels was studied using electron beam induced current (EBIC). The recombination velocity on a dislocation, also known as the dislocation recombination strength, was calculated. The results suggest that dislocations in n-GaN giving contrast in EBIC are charged and surrounded by a space charge region, as evidenced by the observed dependence of dislocation recombination strength on dopant concentration. For moderate (below ˜108 cm-2) dislocation densities, these defects do not primarily determine the average diffusion length of nonequilibrium charge carriers, although locally, dislocations are efficient recombination sites. In general, it is observed that the effect of the growth method [standard metalorganic chemical vapor deposition (MOCVD), epitaxial lateral overgrowth versions of MOCVD, and hydride vapor phase epitaxy] on the recombination activity of dislocations is not very pronounced, although the average diffusion lengths can widely differ for various samples. The glide of basal plane dislocations at room temperature promoted by low energy electron irradiation does not significantly change the recombination properties of dislocations.

Fluid Dynamics and Thermodynamics of Vapor Phase Crystal Growth

NASA Technical Reports Server (NTRS)

Wiedemeier, H.

1985-01-01

The ground-based research effort under this program is concerned with systematic studies of the effects of variations: (1) of the relative importance of buoyancy-driven convection, and (2) of diffusion and viscosity conditions on crystal properties. These experimental studies are supported by thermodynamic characterizations of the systems, based on which fluid dynamic parameters can be determined. The specific materials under investigation include: the GeSe-GeI4, Ge-GeI4, HgTe-HgI2, and Hg sub (1-x)Cd sub (x) Te-HgI2 systems. Mass transport rate studies of the GeSe-GeI system as a function of orientation of the density gradient relative to the gravity vector demonstrated the validity of flux anomalies observed in earlier space experiments. The investigation of the effects of inert gases on mass flux yielded the first experimental evidence for the existence of a boundary layer in closed ampoules. Combined with a thorough thermodynamic analysis, a transport model for diffusive flow including chemical vapor transport, sublimation, and Stefan flow was developed.

Three-Dimensional Morphology Control Yielding Enhanced Hole Mobility in Air-Processed Organic Photovoltaics: Demonstration with Grazing-Incidence Wide-Angle X-ray Scattering

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

Moore, Levi M. J.; Bhattacharya, Mithun; Wu, Qi

Polymer organic photovoltaic (OPV) device performance is defined by the three-dimensional morphology of the phase-separated domains in the active layer. Here, we determine the evolution of morphology through different stages of tailored solvent vapor and thermal annealing techniques in air-processed poly(3-hexylthiophene-2,5-diyl)/phenyl-C61-butyric acid methyl ester-based OPV blends. A comparative evaluation of the effect of solvent type used for vapor annealing was performed using grazing-incidence wide-angle X-ray scattering, atomic force microscopy, and UV–vis spectroscopy to probe the active-layer morphology. A nonhalogenated orthogonal solvent was found to impart controlled morphological features within the exciton diffusion length scales, enhanced absorbance, greater crystallinity, increased paracrystallinemore » disorder, and improved charge-carrier mobility. Low-boiling, fast-diffusing isopropanol allowed the greatest control over the nanoscale structure of the solvents evaluated and yielded a cocontinuous morphology with narrowed domains and enhanced paths for the charge carrier to reach the anode.« less

Vapor transfer prior to the October 2004 eruption of Mount St. Helens, Washington

USGS Publications Warehouse

Kent, A.J.R.; Blundy, J.; Cashman, K.V.; Copper, K.M.; Donnelly, C.; Pallister, J.S.; Reagan, M.; Rowe, M.C.; Thornber, C.R.

2007-01-01

Dome lavas from the 2004 eruption of Mount St. Helens show elevated Li contents in plagioclase phenocrysts at the onset of dome growth in October 2004. These cannot be explained by variations in plagioclase-melt partitioning, but require elevated Li contents in coexisting melt, a fact confirmed by measurements of Li contents as high as 207 ??g/g in coexisting melt inclusions. Similar Li enrichment has been observed in material erupted prior to and during the climactic May 1980 eruption, and is likewise best explained via pre-eruptive transfer of an exsolved alkali-rich vapor phase derived from deeper within the magma transport system. Unlike 1980, however, high Li samples from 2004 show no evidence of excess (210Pb)/(226 Ra), implying that measurable Li enrichments may occur despite significant differences in the timing and/or extent of magmatic degassing. Diffusion modeling shows that Li enrichment occurred within -1 yr before eruption, and that magma remained Li enriched until immediately before eruption and cooling. This short flux time and the very high Li contents in ash produced by phreatomagmatic activity prior to the onset of dome extrusion suggest that vapor transfer and accumulation were associated with initiation of the current eruption. Overall, observation of a high Li signature in both 1980 and 2004 dacites indicates that Li enrichment may be a relatively common phenomenon, and may prove useful for petrologic monitoring of Mount St. Helens and other silicic volcanoes. Lithium diffusion is also sufficiently rapid to constrain vapor transfer on similar time scales to short-lived radionuclides. ?? 2007 Geological Society of America.

Biomimetic air sampling for detection of low concentrations of molecules and bioagents : LDRD 52744 final report.

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

Hughes, Robert Clark

2003-12-01

Present methods of air sampling for low concentrations of chemicals like explosives and bioagents involve noisy and power hungry collectors with mechanical parts for moving large volumes of air. However there are biological systems that are capable of detecting very low concentrations of molecules with no mechanical moving parts. An example is the silkworm moth antenna which is a highly branched structure where each of 100 branches contains about 200 sensory 'hairs' which have dimensions of 2 microns wide by 100 microns long. The hairs contain about 3000 pores which is where the gas phase molecules enter the aqueous (lymph)more » phase for detection. Simulations of diffusion of molecules indicate that this 'forest' of hairs is 'designed' to maximize the extraction of the vapor phase molecules. Since typical molecules lose about 4 decades in diffusion constant upon entering the liquid phase, it is important to allow air diffusion to bring the molecule as close to the 'sensor' as possible. The moth acts on concentrations as low as 1000 molecules per cubic cm. (one part in 1e16). A 3-D collection system of these dimensions could be fabricated by micromachining techniques available at Sandia. This LDRD addresses the issues involved with extracting molecules from air onto micromachined structures and then delivering those molecules to microsensors for detection.« less

Performance of a Cross-Flow Humidifier with a High Flux Water Vapor Transport Membrane

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

Ahluwalia, R. K.; Wang, X.; Johnson, W. B.

Water vapor transport (WVT) flux across a composite membrane that consists of a very thin perfluorosulfonic acid (PFSA) ionomer layer sandwiched between two expanded polytetrafluoroethylene (PTFE) microporous layers is investigated. Static and dynamic tests are conducted to measure WVT flux for different composite structures; a transport model shows that the underlying individual resistances for water diffusion in the gas phase and microporous and ionomer layers and for interfacial kinetics of water uptake at the ionomer surface are equally important under different conditions. A finite-difference model is formulated to determine water transport in a full-scale (2-m2 active membrane area) planar cross-flowmore » humidifier module assembled using pleats of the optimized composite membrane. In agreement with the experimental data, the modeled WVT flux in the module increases at higher inlet relative humidity (RH) of the wet stream and at lower pressures, but the mass transfer effectiveness is higher at higher pressures. The model indicates that the WVT flux is highest under conditions that maintain the wet stream at close to 100% RH while preventing the dry stream from becoming saturated. The overall water transport is determined by the gradient in RH of the wet and dry streams but is also affected by vapor diffusion in the gas layer and the microporous layer.« less

Characterizations of the Core-Shell Structured MgB2/CARBON Fiber Synthesis by Rf-Sputtering and Thermal Evaporation

NASA Astrophysics Data System (ADS)

Park, Sung Chang; Lim, Yeong Jin; Lee, Tae-Keun; Kim, Cheol Jin

MgB2/carbon fibers have been synthesized by the combination of RF-sputtering of B and thermal evaporation of Mg, followed by co-evaporation. First, boron layer was deposited by RF-sputtering on the carbon fiber with average diameter of 7.1 μm. Later this coated layer of B was reacted with Mg vapor to transform into MgB2. Since the MgB2 reaction proceed with Mg diffusion into the boron layer, Mg vapor pressure and the diffusion time had to be controlled precisely to secure the complete reaction. Also the deposition rate of each element was controlled separately to obtain stoichiometric MgB2, since Mg was evaporated by thermal heating and B by sputtering system. The sintered B target was magnetron sputtered at the RF-power of ~200 W, which corresponded to the deposition rate of ~3.6 Å/s. With the deposition rate of B fixed, the vapor pressure of Mg was controlled by varying the temperature of tungsten boat with heating element control unit between 100 and 900°C. The MgB2 layers with the thickness of 200-950 nm could be obtained and occasionally MgO appeared as a second phase. Superconducting transition temperatures were measured around ~38 K depending on the deposition condition.

Modeling of mechanical properties of II-VI materials

NASA Technical Reports Server (NTRS)

Sher, A.; Berding, M. A.; Van Schilfgaarde, M.; Chen, A.-B.; Patrick, R.

1988-01-01

This paper reviews some new developments in the theory of alloy correlations, order-disorder transitions, and solidus phase-transition curves. It is argued that semiconductor alloys are never truly random, and the various phenomena that drive deviations from random arrangements are introduced. Likely consequences of correlations on the ability to fine-tune the lattice match of epitaxial layers to substrates, on vacancy formation, on diffusion, and on vapor-phase crystal growth are discussed. Examples are chosen for the alloys Hg(1-x)Cd(x)Te, Hg(1-x)Zn(x)Te, Cd(1-y)Zn(y)Te, and CdSe(1-y)Te(y).

Simulation of the early startup period of high-temperature heat pipes from the frozen state by a rarefied vapor self-diffusion model

NASA Technical Reports Server (NTRS)

Cao, Y.; Faghri, A.

1993-01-01

The heat pipe startup process is described physically and is divided into five periods for convenience of analysis. The literature survey revealed that none of the previous attempts to simulate the heat pipe startup process numerically were successful, since the rarefied vapor flow in the heat pipe was not considered. Therefore, a rarefied vapor self-diffusion model is proposed, and the early startup periods, in which the rarefied vapor flow is dominant within the heat pipe, are first simulated numerically. The numerical results show that large vapor density gradients existed along the heat pipe length, and the vapor flow reaches supersonic velocities when the density is extremely low. The numerical results are compared with the experimental data of the early startup period with good agreement.

Water vapor diffusion membrane development

NASA Technical Reports Server (NTRS)

Tan, M. K.

1977-01-01

An application of the water vapor diffusion technique is examined whereby the permeated water vapor is vented to space vacuum to alleviate on-board waste storage and provide supplemental cooling. The work reported herein deals primarily with the vapor diffusion-heat rejection (VD-HR) as it applies to the Space Shuttle. A stack configuration was selected, designed and fabricated. An asymmetric cellulose acetate membrane, used in reverse osmosis application was selected and a special spacer was designed to enhance mixing and promote mass transfer. A skid-mount unit was assembled from components used in the bench unit although no attempt was made to render it flight-suitable. The operating conditions of the VD-HR were examined and defined and a 60-day continuous test was carried out. The membranes performed very well throughout the test; no membrane rupture and no unusual flux decay was observed. In addition, a tentative design for a flight-suitable VD-HR unit was made.

Direct molecular diffusion and micro-mixing for rapid dewatering of LiBr solution

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

Bigham, S; Isfahani, RN; Moghaddam, S

2014-03-01

A slow molecular diffusion rate often limits the desorption process of an absorbate molecule from a liquid absorbent. To enhance the desorption rate, the absorbent is often boiled to increase the liquid vapor interfacial area. However, the growth of bubbles generated during the nucleate boiling process still remains mass-diffusion limited. Here, it is shown that a desorption rate higher than that of boiling can be achieved, if the vapor absorbent interface is continuously replenished with the absorbate-rich solution to limit the concentration boundary layer growth. The study is conducted in a LiBr-water-solution, in which the water molecules' diffusion rate ismore » quite slow. The manipulation of the vapor solution interface concentration distribution is enabled by the mechanical confinement of the solution flow within microchannels, using a hydrophobic vapor-venting membrane and the implementation of microstructures on the flow channel's bottom wall. The microstructures stretch and fold the laminar streamlines within the solution film and produce vortices. The vortices continuously replace the concentrated solution at the vapor solution interface with the water-rich solution brought from the bottom and middle of the flow channel. The physics of the process is described using a combination of experimental and numerical studies. Published by Elsevier Ltd.« less

Atomistic modeling of dropwise condensation

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

Sikarwar, B. S., E-mail: bssikarwar@amity.edu; Singh, P. L.; Muralidhar, K.

The basic aim of the atomistic modeling of condensation of water is to determine the size of the stable cluster and connect phenomena occurring at atomic scale to the macroscale. In this paper, a population balance model is described in terms of the rate equations to obtain the number density distribution of the resulting clusters. The residence time is taken to be large enough so that sufficient time is available for all the adatoms existing in vapor-phase to loose their latent heat and get condensed. The simulation assumes clusters of a given size to be formed from clusters of smallermore » sizes, but not by the disintegration of the larger clusters. The largest stable cluster size in the number density distribution is taken to be representative of the minimum drop radius formed in a dropwise condensation process. A numerical confirmation of this result against predictions based on a thermodynamic model has been obtained. Results show that the number density distribution is sensitive to the surface diffusion coefficient and the rate of vapor flux impinging on the substrate. The minimum drop radius increases with the diffusion coefficient and the impinging vapor flux; however, the dependence is weak. The minimum drop radius predicted from thermodynamic considerations matches the prediction of the cluster model, though the former does not take into account the effect of the surface properties on the nucleation phenomena. For a chemically passive surface, the diffusion coefficient and the residence time are dependent on the surface texture via the coefficient of friction. Thus, physical texturing provides a means of changing, within limits, the minimum drop radius. The study reveals that surface texturing at the scale of the minimum drop radius does not provide controllability of the macro-scale dropwise condensation at large timescales when a dynamic steady-state is reached.« less

Resonant acoustic measurement of vapor phase transport phenomenon in porous media

NASA Astrophysics Data System (ADS)

Schuhmann, Richard; Garrett, Steven

2002-05-01

Diffusion of gases through porous media is commonly described using Fick's law and is characterized by a gas diffusion coefficient modified by a media-specific tortuosity parameter. A phase-locked-loop resonance frequency tracker [J. Acoust. Soc. Am. 108, 2520 (2000)] has been upgraded with an insulated copper resonator and a bellows-sealed piston instrumented with an accelerometer. Average system stability (temperature divided by frequency squared) is about 180 ppm. Glass-bead-filled cores of different lengths are fitted into an o-ring sealed opening at the top of the resonator. The rate at which the tracer gas is replaced by air within the resonator is controlled by the core's diffusion constant. Mean molecular weight of the gas mixture in the resonator is determined in real time from the ratio of the absolute temperature to the square of the fundamental acoustic resonance frequency. Molecular weight of the gas mixture is determined approximately six times per minute. Changes in the gas mixture concentration are exponential in time (within 0.1%) over nearly two decades in concentration. We will report diffusion constants for two different sizes of glass beads, in samples of five different lengths, using two different tracer gases, to establish the validity of this approach. [Work supported by ONR.

The role of thermal vapor diffusion in the subsurface hydrologic evolution of Mars

NASA Technical Reports Server (NTRS)

Clifford, Stephen M.

1991-01-01

The hydrologic response of groundwater to the thermal evolution of the early martian crust is considered. When a temperature gradient is present in a moist porous medium, it gives rise to a vapor-pressure gradient that drives the diffusion of water vapor from regions of high to low temperature. By this process, a geothermal gradient as small as 15 K/km could drive the vertical transport of 1 km of water to the freezing front at the base of the martian crysophere every 10 exp 6-10 exp 7 years, or the equivalent of about 100-1000 km of water over the course of martian geologic history. Models of the thermal history of Mars suggest that this thermally-driven vapor flux may have been as much as 3-5 times greater in the past. The magnitude of this transport suggests that the process of geothermally-induced vapor diffusion may have played a critical role in the initial emplacement of ground ice and the subsequent geomorphic and geochemical evolution of the martian crust.

Field Testing of an Unvented Roof with Fibrous Insulation, Tiles, and Vapor Diffusion Venting

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

Ueno, K.; Lstiburek, J. W.

This research is a test implementation of an unvented tile roof assembly in a hot-humid climate (Orlando, FL; Zone 2A), insulated with air permeable insulation (netted and blown fiberglass). Given the localized moisture accumulation and failures seen in previous unvented roof field work, it was theorized that a 'diffusion vent' (water vapor open, but air barrier 'closed') at the highest points in the roof assembly might allow for the wintertime release of moisture, to safe levels. The 'diffusion vent' is an open slot at the ridge and hips, covered with a water-resistant but vapor open (500+ perm) air barrier membrane.more » As a control comparison, one portion of the roof was constructed as a typical unvented roof (self-adhered membrane at ridge). The data collected to date indicate that the diffusion vent roof shows greater moisture safety than the conventional, unvented roof design.« less

Relation between heat of vaporization, ion transport, molar volume, and cation-anion binding energy for ionic liquids.

PubMed

Borodin, Oleg

2009-09-10

A number of correlations between heat of vaporization (H(vap)), cation-anion binding energy (E(+/-)), molar volume (V(m)), self-diffusion coefficient (D), and ionic conductivity for 29 ionic liquids have been investigated using molecular dynamics (MD) simulations that employed accurate and validated many-body polarizable force fields. A significant correlation between D and H(vap) has been found, while the best correlation was found for -log(DV(m)) vs H(vap) + 0.28E(+/-). A combination of enthalpy of vaporization and a fraction of the cation-anion binding energy was suggested as a measure of the effective cohesive energy for ionic liquids. A deviation of some ILs from the reported master curve is explained based upon ion packing and proposed diffusion pathways. No general correlations were found between the ion diffusion coefficient and molecular volume or the diffusion coefficient and cation/anion binding energy.

Growth and melting of droplets in cold vapors.

PubMed

L'Hermite, Jean-Marc

2009-11-01

A model has been developed to investigate the growth of droplets in a supersaturated cold vapor taking into account their possible solid-liquid phase transition. It is shown that the solid-liquid phase transition is nontrivially coupled, through the energy released in attachment, to the nucleation process. The model is based on the one developed by J. Feder, K. C. Russell, J. Lothe, and G. M. Pound [Adv. Phys. 15, 111 (1966)], where the nucleation process is described as a thermal diffusion motion in a two-dimensional field of force given by the derivatives of a free-energy surface. The additional dimension accounts for droplets internal energy. The solid-liquid phase transition is introduced through a bimodal internal energy distribution in a Gaussian approximation derived from small clusters physics. The coupling between nucleation and melting results in specific nonequilibrium thermodynamical properties, exemplified in the case of water droplets. Analyzing the free-energy landscapes gives an insight into the nucleation dynamics. This landscape can be complex but generally exhibits two paths: the first one can generally be ascribed to the solid state, while the other to the liquid state. Especially at high supersaturation, the growth in the liquid state is often favored, which is not unexpected since in a supersaturated vapor the droplets can stand higher internal energy than at equilibrium. From a given critical temperature that is noticeably lower than the bulk melting temperature, nucleation may end in very large liquid droplets. These features can be qualitatively generalized to systems other than water.

Gelatin-hydroxypropyl methylcellulose water-in-water emulsions as a new bio-based packaging material.

PubMed

Esteghlal, Sara; Niakosari, Mehrdad; Hosseini, Seyed Mohammad Hashem; Mesbahi, Gholam Reza; Yousefi, Gholam Hossein

2016-05-01

Gelatin and hydroxypropyl methylcellulose (HPMC) are two incompatible and immiscible biopolymers which cannot form homogeneous composite films using usual methods. In this study, to prevent phase separation, gelatin-HPMC water-in-water (W/W) emulsion was utilized to from transparent composite films by entrapment the HPMC dispersed droplets in gelatin continuous network. The physicochemical and mechanical properties of emulsion-based films containing different amounts (5-30%) of dispersed phase were determined and compared with those of individual polymer-based films. Incorporating HPMC into W/W emulsion-based films had no significant effect on the tensile strength. The flexibility of composite films decreased at HPMC concentrations below 20%. The depletion layer at the droplets interface reduced the diffusion of water vapor molecules because of its hydrophobic nature, so the water vapor permeability remained constant. Increasing the HPMC content in the emulsion films increased the swelling and decreased the transparency. The entrapment of HPMC in continuous gelatin phase decreased its solubility. Therefore, W/W emulsions are capable of holding two incompatible polymers alongside each other within a homogeneous film network without weakening the physical properties. Copyright © 2016 Elsevier B.V. All rights reserved.

Li diffusion in epitaxial (11 $bar 2$ 0) ZnO thin films

NASA Astrophysics Data System (ADS)

Wu, P.; Zhong, J.; Emanetoglu, N. W.; Chen, Y.; Muthukumar, S.; Lu, Y.

2004-06-01

Zinc oxide (ZnO) possesses many interesting properties, such as a wide energy bandgap, large photoconductivity, and high excitonic binding energy. Chemical-vapor-deposition-grown ZnO films generally show n-type conductivity. A compensation doping process is needed to achieve piezoelectric ZnO, which is needed for surface acoustic wave (SAW), bulk acoustic wave, and micro-electromechanical system devices. In this work, a gas-phase diffusion process is developed to achieve piezoelectric (11bar 20) ZnO films. Comparative x-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements confirmed that high crystal quality and good surface morphology were preserved after diffusion. Photoluminescence (PL) measurements show a broad band emission with a peak wavelength at ˜580 nm, which is associated with Li doping. The SAW, including both Rayleigh-wave and Love-wave modes, is achieved along different directions in piezoelectric (11bar 20) ZnO films grown on an r-plane sapphire substrate.

Effects of thermal vapor diffusion on seasonal dynamics of water in the unsaturated zone

USGS Publications Warehouse

Milly, Paul C.D.

1996-01-01

The response of water in the unsaturated zone to seasonal changes of temperature (T) is determined analytically using the theory of nonisothermal water transport in porous media, and the solutions are tested against field observations of moisture potential and bomb fallout isotopic (36Cl and 3H) concentrations. Seasonally varying land surface temperatures and the resulting subsurface temperature gradients induce thermal vapor diffusion. The annual mean vertical temperature gradient is close to zero; however, the annual mean thermal vapor flux is downward, because the temperature‐dependent vapor diffusion coefficient is larger, on average, during downward diffusion (occurring at high T) than during upward diffusion (low T). The annual mean thermal vapor flux is shown to decay exponentially with depth; the depth (about 1 m) at which it decays to e−1of its surface value is one half of the corresponding decay depth for the amplitude of seasonal temperature changes. This depth‐dependent annual mean flux is effectively a source of water, which must be balanced by a flux divergence associated with other transport processes. In a relatively humid environment the liquid fluxes greatly exceed the thermal vapor fluxes, so such a balance is readily achieved without measurable effect on the dynamics of water in the unsaturated zone. However, if the mean vertical water flux through the unsaturated zone is very small (<1 mm y−1), as it may be at many locations in a desert landscape, the thermal vapor flux must be balanced mostly by a matric‐potential‐induced upward flux of water. This return flux may include both vapor and liquid components. Below any near‐surface zone of weather‐related fluctuations of matric potential, maintenance of this upward flux requires an increase with depth in the annual mean matric potential; this theoretical prediction is supported by long‐term field measurements in the Chihuahuan Desert. The analysis also makes predictions, confirmed by the field observations, regarding the seasonal variations of matric potential at a given depth. The conceptual model of unsaturated zone water transport developed here implies the possibility of near‐surface trapping of any aqueous constituent introduced at the surface.

Low Pressure Vapor-assisted Solution Process for Tunable Band Gap Pinhole-free Methylammonium Lead Halide Perovskite Films

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

Sutter-Fella, Carolin M.; Li, Yanbo; Cefarin, Nicola

Organo-lead halide perovskites have recently attracted great interest for potential applications in thin-film photovoltaics and optoelectronics. Herein, we present a protocol for the fabrication of this material via the low-pressure vapor assisted solution process (LP-VASP) method, which yields ~19% power conversion efficiency in planar heterojunction perovskite solar cells. First, we report the synthesis of methylammonium iodide (CH 3NH 3I) and methylammonium bromide (CH 3NH 3Br) from methylamine and the corresponding halide acid (HI or HBr). Then, we describe the fabrication of pinhole-free, continuous methylammonium-lead halide perovskite (CH 3NH 3PbX 3 with X = I, Br, Cl and their mixture) filmsmore » with the LP-VASP. This process is based on two steps: i) spin-coating of a homogenous layer of lead halide precursor onto a substrate, and ii) conversion of this layer to CH 3NH 3PbI 3-xBr x by exposing the substrate to vapors of a mixture of CH 3NH 3I and CH 3NH 3Br at reduced pressure and 120 °C. Through slow diffusion of the methylammonium halide vapor into the lead halide precursor, we achieve slow and controlled growth of a continuous, pinhole-free perovskite film. The LP-VASP allows synthetic access to the full halide composition space in CH 3NH 3PbI 3-xBr x with 0 ≤ x ≤ 3. Depending on the composition of the vapor phase, the bandgap can be tuned between 1.6 eV ≤ E g ≤ 2.3 eV. In addition, by varying the composition of the halide precursor and of the vapor phase, we can also obtain CH 3NH 3PbI 3-xCl x. Films obtained from the LP-VASP are reproducible, phase pure as confirmed by X-ray diffraction measurements, and show high photoluminescence quantum yield. The process does not require the use of a glovebox.« less

Low Pressure Vapor-assisted Solution Process for Tunable Band Gap Pinhole-free Methylammonium Lead Halide Perovskite Films

DOE PAGES

Sutter-Fella, Carolin M.; Li, Yanbo; Cefarin, Nicola; ...

2017-09-08

Organo-lead halide perovskites have recently attracted great interest for potential applications in thin-film photovoltaics and optoelectronics. Herein, we present a protocol for the fabrication of this material via the low-pressure vapor assisted solution process (LP-VASP) method, which yields ~19% power conversion efficiency in planar heterojunction perovskite solar cells. First, we report the synthesis of methylammonium iodide (CH 3NH 3I) and methylammonium bromide (CH 3NH 3Br) from methylamine and the corresponding halide acid (HI or HBr). Then, we describe the fabrication of pinhole-free, continuous methylammonium-lead halide perovskite (CH 3NH 3PbX 3 with X = I, Br, Cl and their mixture) filmsmore » with the LP-VASP. This process is based on two steps: i) spin-coating of a homogenous layer of lead halide precursor onto a substrate, and ii) conversion of this layer to CH 3NH 3PbI 3-xBr x by exposing the substrate to vapors of a mixture of CH 3NH 3I and CH 3NH 3Br at reduced pressure and 120 °C. Through slow diffusion of the methylammonium halide vapor into the lead halide precursor, we achieve slow and controlled growth of a continuous, pinhole-free perovskite film. The LP-VASP allows synthetic access to the full halide composition space in CH 3NH 3PbI 3-xBr x with 0 ≤ x ≤ 3. Depending on the composition of the vapor phase, the bandgap can be tuned between 1.6 eV ≤ E g ≤ 2.3 eV. In addition, by varying the composition of the halide precursor and of the vapor phase, we can also obtain CH 3NH 3PbI 3-xCl x. Films obtained from the LP-VASP are reproducible, phase pure as confirmed by X-ray diffraction measurements, and show high photoluminescence quantum yield. The process does not require the use of a glovebox.« less

Equatorial ground ice on Mars: Steady-state stability

NASA Technical Reports Server (NTRS)

Mellon, Michael T.; Jakosky, Bruce M.; Postawko, Susan E.

1993-01-01

Current Martian equatorial surface temperatures are too warm for water ice to exist at the surface for any appreciable length of time before subliming into the atmosphere. Subsurface temperatures are generally warmer still and, despite the presence of a diffusive barrier of porous regolith material, it has been shown by Smoluchowski, Clifford and Hillel, and Fanale et al. that buried ground ice will also sublime and be lost to the atmosphere in a relatively short time. We investigate the behavior of this subliming subsurface ice and show that it is possible for ice to maintain at a steady-state depth, where sublimation and diffusive loss to the atmosphere is balanced by resupply from beneath by diffusion and recondensation of either a deeper buried ice deposits or ground water. We examine the behavior of equatorial ground ice with a numercial time-marching molecular diffusion model. In our model we allow for diffusion of water vapor through a porous regolith, variations in diffusivity and porosity with ice content, and recondensation of sublimed water vapor. A regolith containing considerable amounts of ice can still be very porous, allowing water vapor to diffuse up from deeper within the ice layer where temperatures are warmer due to the geothermal gradient. This vapor can then recondense nearer to the surface where ice had previously sublimed and been lost to the atmosphere. As a result we find that ice deposits migrate to find a steady-state depth, which represents a balance between diffusive loss to the atmosphere through the overlying porous regolith and diffusive resupply through a porous icy regolith below. This depth depends primarily on the long-term mean surface temperature and the nature of the geothermal gradient, and is independent of the ice-free porosity and the regolith diffusivity. Only the rate of loss of ground ice depends on diffusive properties.

Diffusive mass transport in agglomerated glassy fallout from a near-surface nuclear test

NASA Astrophysics Data System (ADS)

Weisz, David G.; Jacobsen, Benjamin; Marks, Naomi E.; Knight, Kim B.; Isselhardt, Brett H.; Matzel, Jennifer E.

2018-02-01

Aerodynamically-shaped glassy fallout is formed when vapor phase constituents from the nuclear device are incorporated into molten carriers (i.e. fallout precursor materials derived from soil or other near-field environmental debris). The effects of speciation and diffusive transport of condensing constituents are not well defined in models of fallout formation. Previously we reported observations of diffuse micrometer scale layers enriched in Na, Fe, Ca, and 235U, and depleted in Al and Ti, at the interfaces of agglomerated fallout objects. Here, we derive the timescales of uranium mass transport in such fallout as it cools from 2500 K to 1500 K by applying a 1-dimensional planar diffusion model to the observed 235U/30Si variation at the interfaces. By modeling the thermal transport between the fireball and the carrier materials, the time of mass transport is calculated to be <0.6 s, <1 s, <2 s, and <3.5 s for fireball yields of 0.1 kt, 1 kt, 10 kt, and 100 kt respectively. Based on the calculated times of mass transport, a maximum temperature of deposition of uranium onto the carrier material of ∼2200 K is inferred (1σ uncertainty of ∼200 K). We also determine that the occurrence of micrometer scale layers of material enriched in relatively volatile Na-species as well as more refractory Ca-species provides evidence for an oxygen-rich fireball based on the vapor pressure of the two species under oxidizing conditions. These results represent the first application of diffusion-based modeling to derive material transport, thermal environments, and oxidation-speciation in near-surface nuclear detonation environments.

Diffusive mass transport in agglomerated glassy fallout from a near-surface nuclear test

DOE PAGES

Weisz, David G.; Jacobsen, Benjamin; Marks, Naomi E.; ...

2017-12-15

Aerodynamically-shaped glassy fallout is formed when vapor phase constituents from the nuclear device are incorporated into molten carriers (i.e. fallout precursor materials derived from soil or other near-field environmental debris). The effects of speciation and diffusive transport of condensing constituents are not well defined in models of fallout formation. Previously we reported observations of diffuse micrometer scale layers enriched in Na, Fe, Ca, and 235U, and depleted in Al and Ti, at the interfaces of agglomerated fallout objects. Here in this paper, we derive the timescales of uranium mass transport in such fallout as it cools from 2500 K tomore » 1500 K by applying a 1-dimensional planar diffusion model to the observed 235U/ 30Si variation at the interfaces. By modeling the thermal transport between the fireball and the carrier materials, the time of mass transport is calculated to be <0.6 s, <1 s, <2 s, and <3.5 s for fireball yields of 0.1 kt, 1 kt, 10 kt, and 100 kt respectively. Based on the calculated times of mass transport, a maximum temperature of deposition of uranium onto the carrier material of ~2200 K is inferred (1σ uncertainty of ~200 K). We also determine that the occurrence of micrometer scale layers of material enriched in relatively volatile Na-species as well as more refractory Ca-species provides evidence for an oxygen-rich fireball based on the vapor pressure of the two species under oxidizing conditions. These results represent the first application of diffusion-based modeling to derive material transport, thermal environments, and oxidation-speciation in near-surface nuclear detonation environments.« less

Diffusive mass transport in agglomerated glassy fallout from a near-surface nuclear test

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

Weisz, David G.; Jacobsen, Benjamin; Marks, Naomi E.

Aerodynamically-shaped glassy fallout is formed when vapor phase constituents from the nuclear device are incorporated into molten carriers (i.e. fallout precursor materials derived from soil or other near-field environmental debris). The effects of speciation and diffusive transport of condensing constituents are not well defined in models of fallout formation. Previously we reported observations of diffuse micrometer scale layers enriched in Na, Fe, Ca, and 235U, and depleted in Al and Ti, at the interfaces of agglomerated fallout objects. Here in this paper, we derive the timescales of uranium mass transport in such fallout as it cools from 2500 K tomore » 1500 K by applying a 1-dimensional planar diffusion model to the observed 235U/ 30Si variation at the interfaces. By modeling the thermal transport between the fireball and the carrier materials, the time of mass transport is calculated to be <0.6 s, <1 s, <2 s, and <3.5 s for fireball yields of 0.1 kt, 1 kt, 10 kt, and 100 kt respectively. Based on the calculated times of mass transport, a maximum temperature of deposition of uranium onto the carrier material of ~2200 K is inferred (1σ uncertainty of ~200 K). We also determine that the occurrence of micrometer scale layers of material enriched in relatively volatile Na-species as well as more refractory Ca-species provides evidence for an oxygen-rich fireball based on the vapor pressure of the two species under oxidizing conditions. These results represent the first application of diffusion-based modeling to derive material transport, thermal environments, and oxidation-speciation in near-surface nuclear detonation environments.« less

Effects of allspice, cinnamon, and clove bud essential oils in edible apple films on physical properties and antimicrobial activities.

PubMed

Du, W-X; Olsen, C W; Avena-Bustillos, R J; McHugh, T H; Levin, C E; Friedman, Mendel

2009-09-01

Essential oils (EOs) derived from plants are rich sources of volatile terpenoids and phenolic compounds. Such compounds have the potential to inactivate pathogenic bacteria on contact and in the vapor phase. Edible films made from fruits or vegetables containing EOs can be used commercially to protect food against contamination by pathogenic bacteria. EOs from cinnamon, allspice, and clove bud plants are compatible with the sensory characteristics of apple-based edible films. These films could extend product shelf life and reduce risk of pathogen growth on food surfaces. This study evaluated physical properties (water vapor permeability, color, tensile properties) and antimicrobial activities against Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes of allspice, cinnamon, and clove bud oils in apple puree film-forming solutions formulated into edible films at 0.5% to 3% (w/w) concentrations. Antimicrobial activities were determined by 2 independent methods: overlay of the film on top of the bacteria and vapor phase diffusion of the antimicrobial from the film to the bacteria. The antimicrobial activities against the 3 pathogens were in the following order: cinnamon oil > clove bud oil > allspice oil. The antimicrobial films were more effective against L. monocytogenes than against the S. enterica. The oils reduced the viscosity of the apple solutions and increased elongation and darkened the colors of the films. They did not affect water vapor permeability. The results show that apple-based films with allspice, cinnamon, or clove bud oils were active against 3 foodborne pathogens by both direct contact with the bacteria and indirectly by vapors emanating from the films.

Insights into Mechanistic Models for Evaporation of Organic Liquids in the Environment Obtained by Position-Specific Carbon Isotope Analysis.

PubMed

Julien, Maxime; Nun, Pierrick; Robins, Richard J; Remaud, Gérald S; Parinet, Julien; Höhener, Patrick

2015-11-03

Position-specific isotope effects (PSIEs) have been measured by isotope ratio monitoring (13)C nuclear magnetic resonance spectrometry during the evaporation of 10 liquids of different polarities under 4 evaporation modes (passive evaporation, air-vented evaporation, low pressure evaporation, distillation). The observed effects are used to assess the validity of the Craig-Gordon isotope model for organic liquids. For seven liquids the overall isotope effect (IE) includes a vapor-liquid contribution that is strongly position-specific in polar compounds but less so in apolar compounds and a diffusive IE that is not position-specific, except in the alcohols, ethanol and propan-1-ol. The diffusive IE is diminished under forced evaporation. The position-specific isotope pattern created by liquid-vapor IEs is manifest in five liquids, which have an air-side limitation for volatilization. For the alcohols, undefined processes in the liquid phase create additional PSIEs. Three other liquids with limitations on the liquid side have a lower, highly position-specific, bulk diffusive IE. It is concluded that evaporation of organic pollutants creates unique position-specific isotope patterns that may be used to assess the progress of remediation or natural attenuation of pollution and that the Craig-Gordon isotope model is valid for the volatilization of nonpolar organic liquids with air-side limitation of the volatilization rate.

Laser absorption spectroscopy of water vapor confined in nanoporous alumina: wall collision line broadening and gas diffusion dynamics.

PubMed

Svensson, Tomas; Lewander, Märta; Svanberg, Sune

2010-08-02

We demonstrate high-resolution tunable diode laser absorption spectroscopy (TDLAS) of water vapor confined in nanoporous alumina. Strong multiple light scattering results in long photon pathlengths (1 m through a 6 mm sample). We report on strong line broadening due to frequent wall collisions (gas-surface interactions). For the water vapor line at 935.685 nm, the HWHM of confined molecules are about 4.3 GHz as compared to 2.9 GHz for free molecules (atmospheric pressure). Gas diffusion is also investigated, and in contrast to molecular oxygen (that moves rapidly in and out of the alumina), the exchange of water vapor is found very slow.

Delineation of discharge areas of two contaminant plumes by use of diffusion samplers, Johns Pond, Cape Cod, Massachusetts, 1998

USGS Publications Warehouse

Savoie, Jennifer G.; LeBlanc, D.R.; Blackwood, D.S.; McCobb, T.D.; Rendigs, R. R.; Clifford, Scott

2000-01-01

Diffusion samplers were installed in the bottom of Johns Pond, Cape Cod, Massachusetts, to confirm that volatile organic compounds from the Storm Drain-5 (SD-5) plume emanating from the Massachusetts Military Reservation (MMR) were discharging into the pond. An array of 134 vapor-diffusion samplers was buried by divers about 0.5 feet below the pond bottom in the presumed discharge area of the SD-5 plume and left in place for about 2 weeks to equilibrate. Two areas of high concentrations of volatile organic compounds (VOCs) were identified. Samples from the first area contained trichloroethene (TCE) and tetrachloroethene with concentrations in vapor as high as 890 and 667 parts per billion by volume, respectively. This discharge area is about 1,000 feet wide, extends from 100 to 350 feet offshore, and is interpreted to be the discharge area of the SD-5 plume. Samples from the second area were located closer to shore than the discharge area of the SD-5 plume and contained unexpectedly high vapor concentrations of TCE (more than 40,000 parts per billion by volume). Ground-water samples collected with a drive-point sampler near the second area had aqueous TCE concentrations as high as 1,100 micrograms per liter. Subsequently, a more closely spaced array of 110 vapor-diffusion samplers was installed to map the area of elevated TCE concentrations . The discharge area detected with the samplers is about 75 feet wide and extends from about 25 to 200 feet offshore . TCE vapor concentrations in this area were as high as 42,800 parts per billion by volume. TCE concentrations in micrograms per liter in water-diffusion samples from 15 selected sites in the two discharge areas were about 35 times lower than the TCE concentrations in parts per billion by volume in corresponding vapor-diffusion samples. The difference in values is due to the volatile nature of TCE and the different units of measure. TCE was detected in diffusion samplers set in the pond water column above the plume discharge areas, but the TCE concentrations were 20 to 30 times lower than the corresponding levels in diffusion samplers buried in the pond bottom.

Preparation of amino acid nanoparticles at varying saturation conditions in an aerosol flow reactor

NASA Astrophysics Data System (ADS)

Raula, Janne; Lehtimäki, Matti; Karppinen, Maarit; Antopolsky, Maxim; Jiang, Hua; Rahikkala, Antti; Kauppinen, Esko I.

2012-07-01

Nanoparticle formation of five amino acids, glycine, l-proline, l-valine, l-phenylalanine, and l-leucine was studied. The aim was to explore factors determining nanoparticle formation and crystallinity. The amino acid nanoparticles have been prepared at different saturation conditions in the aerosol reactor. In a condensed state, the particles were formed by droplet drying. The raise in temperature induced the sublimation of amino acids from the aerosol particles. The amino acid vapor was condensed by physical vapor deposition in a rapid cooling process. The diffusion coefficients and nucleation rates of amino acids have been calculated to understand particle formation. Upon the vapor deposition, amino acids formed crystalline nanoparticles except in the case l-phenylalanine according to X-ray diffraction. The crystal polymorph of glycine in the nanoparticles depended on the applied reactor temperature. The preference of crystallographic orientation varied in both the particle formations from condensed and vapor phase. l-Valine, l-phenylalanine, and l-leucine formed leafy-looking particles. These results could be utilized in the fabrication of nano-sized asperities on drug particle surfaces to reduce forces between particles and accordingly increase particle dispersion in dry powder inhalers.

Thermally activated vapor bubble nucleation: The Landau-Lifshitz-Van der Waals approach

NASA Astrophysics Data System (ADS)

Gallo, Mirko; Magaletti, Francesco; Casciola, Carlo Massimo

2018-05-01

Vapor bubbles are formed in liquids by two mechanisms: evaporation (temperature above the boiling threshold) and cavitation (pressure below the vapor pressure). The liquid resists in these metastable (overheating and tensile, respectively) states for a long time since bubble nucleation is an activated process that needs to surmount the free energy barrier separating the liquid and the vapor states. The bubble nucleation rate is difficult to assess and, typically, only for extremely small systems treated at an atomistic level of detail. In this work a powerful approach, based on a continuum diffuse interface modeling of the two-phase fluid embedded with thermal fluctuations (fluctuating hydrodynamics), is exploited to study the nucleation process in homogeneous conditions, evaluating the bubble nucleation rates and following the long-term dynamics of the metastable system, up to the bubble coalescence and expansion stages. In comparison with more classical approaches, this methodology allows us on the one hand to deal with much larger systems observed for a much longer time than possible with even the most advanced atomistic models. On the other, it extends continuum formulations to thermally activated processes, impossible to deal with in a purely determinist setting.

Evaporation-induced cavitation in nanofluidic channels

PubMed Central

Duan, Chuanhua; Karnik, Rohit; Lu, Ming-Chang; Majumdar, Arun

2012-01-01

Cavitation, known as the formation of vapor bubbles when liquids are under tension, is of great interest both in condensed matter science as well as in diverse applications such as botany, hydraulic engineering, and medicine. Although widely studied in bulk and microscale-confined liquids, cavitation in the nanoscale is generally believed to be energetically unfavorable and has never been experimentally demonstrated. Here we report evaporation-induced cavitation in water-filled hydrophilic nanochannels under enormous negative pressures up to -7 MPa. As opposed to receding menisci observed in microchannel evaporation, the menisci in nanochannels are pinned at the entrance while vapor bubbles form and expand inside. Evaporation in the channels is found to be aided by advective liquid transport, which leads to an evaporation rate that is an order of magnitude higher than that governed by Fickian vapor diffusion in macro- and microscale evaporation. The vapor bubbles also exhibit unusual motion as well as translational stability and symmetry, which occur because of a balance between two competing mass fluxes driven by thermocapillarity and evaporation. Our studies expand our understanding of cavitation and provide new insights for phase-change phenomena at the nanoscale. PMID:22343530

Transport of Chemical Vapors from Subsurface Sources to Atmosphere as Affected by Shallow Subsurface and Atmospheric Conditions

NASA Astrophysics Data System (ADS)

Rice, A. K.; Smits, K. M.; Hosken, K.; Schulte, P.; Illangasekare, T. H.

2012-12-01

Understanding the movement and modeling of chemical vapor through unsaturated soil in the shallow subsurface when subjected to natural atmospheric thermal and mass flux boundary conditions at the land surface is of importance to applications such as landmine detection and vapor intrusion into subsurface structures. New, advanced technologies exist to sense chemical signatures at the land/atmosphere interface, but interpretation of these sensor signals to make assessment of source conditions remains a challenge. Chemical signatures are subject to numerous interactions while migrating through the unsaturated soil environment, attenuating signal strength and masking contaminant source conditions. The dominant process governing movement of gases through porous media is often assumed to be Fickian diffusion through the air phase with minimal or no quantification of other processes contributing to vapor migration, such as thermal diffusion, convective gas flow due to the displacement of air, expansion/contraction of air due to temperature changes, temporal and spatial variations of soil moisture and fluctuations in atmospheric pressure. Soil water evaporation and interfacial mass transfer add to the complexity of the system. The goal of this work is to perform controlled experiments under transient conditions of soil moisture, temperature and wind at the land/atmosphere interface and use the resulting dataset to test existing theories on subsurface gas flow and iterate between numerical modeling efforts and experimental data. Ultimately, we aim to update conceptual models of shallow subsurface vapor transport to include conditionally significant transport processes and inform placement of mobile sensors and/or networks. We have developed a two-dimensional tank apparatus equipped with a network of sensors and a flow-through head space for simulation of the atmospheric interface. A detailed matrix of realistic atmospheric boundary conditions was applied in a series of experiments. Water saturation, capillary pressure, air and soil temperature, and relative humidity were continuously monitored. Aqueous TCE was injected into the tank below the water table and allowed to volatilize. TCE concentration exiting the tank head space was measured through interval sampling by direct injection into a gas chromatograph. To quantify the transient concentration of TCE vapor in the soil pore space a novel use of Solid Phase Micro-Extraction (SPME) was developed. Results from our numerical simulations were compared with the experimental data, which demonstrated the importance of considering the interaction of the atmosphere with the subsurface in conceptualization and numerical model development. Results also emphasize that soil saturation and transient sorption have a significant effect on vapor transport through the vadose zone. Follow-up tests and detailed analyses are still underway. Additional applications of this work include carbon sequestration leakage, methane contamination in the shallow subsurface and environmental impact of hydraulic fracturing.

Mechanism of anisotropic surface self-diffusivity at the prismatic ice-vapor interface.

PubMed

Gladich, Ivan; Oswald, Amrei; Bowens, Natalie; Naatz, Sam; Rowe, Penny; Roeselova, Martina; Neshyba, Steven

2015-09-21

Predictive theoretical models for mesoscopic roughening of ice require improved understanding of attachment kinetics occurring at the ice-vapor interface. Here, we use classical molecular dynamics to explore the generality and mechanics of a transition from anisotropic to isotropic self-diffusivity on exposed prismatic surfaces. We find that self-diffusion parallel to the crystallographic a-axis is favored over the c-axis at sub-melt temperatures below about -35 °C, for three different representations of the water-water intermolecular potential. In the low-temperature anisotropic regime, diffusion results from interstitial admolecules encountering entropically distinct barriers to diffusion in the two in-plane directions. At higher temperatures, isotropic self-diffusion occurring deeper within the quasi-liquid layer becomes the dominant mechanism, owing to its larger energy of activation.

Bubble-facilitated VOC transport: Laboratory experiments and numerical modelling

NASA Astrophysics Data System (ADS)

Mumford, K. G.; Soucy, N. C.

2017-12-01

Most conceptual and numerical models of vapor intrusion assume that the transport of volatile organic compounds (VOCs) from the source to near the building foundation is a diffusion-limited processes. However, the transport of VOCs by mobilized gas bubbles through the saturated zone could lead to increased rates of transport and advection through the unsaturated zone, thereby increasing mass flux and risks associated with vapor intrusion. This mobilized gas could be biogenic (methanogenic) but could also result from the partitioning of VOC to trapped atmospheric gases in light non-aqueous phase liquid (LNAPL) smear zones. The potential for bubble-facilitated VOC transport to increase mass flux was investigated in a series of 1D and 2D laboratory experiments. Pentane source zones were emplaced in sand using sequential drainage and imbibition steps to mimic a water table fluctuation and trap air alongside LNAPL residual. This source was placed below an uncontaminated, water saturated sand (occlusion zone) and a gravel-sized (glass beads) unsaturated zone. Water was pumped laterally through the source zone and occlusion zone to deliver the dissolved gases (air) that are required for the expansion of trapped gas bubbles. Images from 2D flow cell experiments were used to demonstrate fluid rearrangement in the source zone and gas expansion to the occlusion zone, and 1D column experiments were used to measure gas-phase pentane mass flux. This flux was found to be 1-2 orders of magnitude greater than that measured in diffusion-dominated control columns, and showed intermittent behavior consistent with bubble transport by repeated expansion, mobilization, coalescence and trapping. Numerical simulation results under a variety of conditions using an approach that couples macroscopic invasion percolation with mass transfer (MIP-MT) between the aqueous and gas phases will also be presented. The results of this study demonstrate the potential for bubble-facilitated transport to increase transport rates linked to vapor intrusion, and will serve as a basis for further development of conceptual and numerical models to investigate the conditions under which this mechanism may play an important role.

Modeling of chemical vapor infiltration for ceramic composites reinforced with layered, woven fabrics

NASA Technical Reports Server (NTRS)

Chung, Gui-Yung; Mccoy, Benjamin J.

1991-01-01

A homogeneous model is developed for the chemical vapor infiltration by one-dimensional diffusion into a system of layered plies consisting of woven tows containing bundles of filaments. The model predictions of the amount of deposition and the porosity of the sample as a function of time are compared with the predictions of a recent nonhomogeneous model with aligned holes formed by the weave. The nonhomogeneous model allows for diffusion through the aligned holes, into the spaces between plies, and into the gaps around filaments; i.e., three diffusion equations apply. Relative to the nonhomogeneous results, the homogeneous model underestimates the amount of deposition, since the absence of holes and spaces allows earlier occlusion of gaps around filaments and restricts the vapor infiltration.

All metalorganic chemical vapor phase epitaxy of p/n-GaN tunnel junction for blue light emitting diode applications

NASA Astrophysics Data System (ADS)

Neugebauer, S.; Hoffmann, M. P.; Witte, H.; Bläsing, J.; Dadgar, A.; Strittmatter, A.; Niermann, T.; Narodovitch, M.; Lehmann, M.

2017-03-01

We report on III-Nitride blue light emitting diodes (LEDs) comprising a GaN-based tunnel junction (TJ) all realized by metalorganic vapor phase epitaxy in a single growth process. The TJ grown atop the LED structures consists of a Mg-doped GaN layer and subsequently grown highly Ge-doped GaN. Long thermal annealing of 60 min at 800 °C is important to reduce the series resistance of the LEDs due to blockage of acceptor-passivating hydrogen diffusion through the n-type doped top layer. Secondary ion mass spectroscopy measurements reveal Mg-incorporation into the topmost GaN:Ge layer, implying a non-abrupt p-n tunnel junction and increased depletion width. Still, significantly improved lateral current spreading as compared to conventional semi-transparent Ni/Au p-contact metallization and consequently a more homogeneous electroluminescence distribution across 1 × 1 mm2 LED structures is achieved. Direct estimation of the depletion width is obtained from electron holography experiments, which allows for a discussion of the possible tunneling mechanism.

Evaluation of the Antibacterial Potential of Liquid and Vapor Phase Phenolic Essential Oil Compounds against Oral Microorganisms

PubMed Central

Wu, Chi-Hao; Ko, Shun-Yao; Chen, Michael Yuanchien; Shih, Yin-Hua; Shieh, Tzong-Ming; Chuang, Li-Chuan; Wu, Ching-Yi

2016-01-01

The aim of the present study was to determine the antibacterial activities of the phenolic essential oil (EO) compounds hinokitiol, carvacrol, thymol, and menthol against oral pathogens. Aggregatibacter actinomycetemcomitans, Streptococcus mutans, Methicillin-resistant Staphylococcus aureus (MRSA), and Escherichia. coli were used in this study. The minimum inhibitory concentrations (MICs), minimum bactericidal concentrations (MBCs), bacterial growth curves, temperature and pH stabilities, and synergistic effects of the liquid and vapor EO compounds were tested. The MIC/MBC of the EO compounds, ranging from the strongest to weakest, were hinokitiol (40–60 μg/mL/40-100 μg/mL), thymol (100–200 μg/mL/200-400 μg/mL), carvacrol (200–400 μg/mL/200-600 μg/mL), and menthol (500-more than 2500 μg/mL/1000-more than 2500 μg/mL). The antibacterial activities of the four EO phenolic compound based on the agar diffusion test and bacterial growth curves showed that the four EO phenolic compounds were stable under different temperatures for 24 h, but the thymol activity decreased when the temperature was higher than 80°C. The combination of liquid carvacrol with thymol did not show any synergistic effects. The activities of the vaporous carvacrol and thymol were inhibited by the presence of water. Continual violent shaking during culture enhanced the activity of menthol. Both liquid and vaporous hinokitiol were stable at different temperatures and pH conditions. The combination of vaporous hinokitiol with zinc oxide did not show synergistic effects. These results showed that the liquid and vapor phases of hinokitiol have strong anti-oral bacteria abilities. Hinokitiol has the potential to be applied in oral health care products, dental materials, and infection controls to exert antimicrobial activity. PMID:27681039

Lemon grass (Cymbopogon citratus) essential oil as a potent anti-inflammatory and antifungal drugs

PubMed Central

Boukhatem, Mohamed Nadjib; Ferhat, Mohamed Amine; Kameli, Abdelkrim; Saidi, Fairouz; Kebir, Hadjer Tchoketch

2014-01-01

Background Volatile oils obtained from lemon grass [Cymbopogon citratus (DC.) Stapf, Poaceae family] are used in traditional medicine as remedies for the treatment of various diseases. Aims In the present study, lemon grass essential oil (LGEO) was evaluated for its in vivo topical and oral anti-inflammatory effects, and for its in vitro antifungal activity using both liquid and vapor phases. Methods The chemical profile of LGEO as determined by gas chromatography–mass spectrometry analysis revealed two major components: geranial (42.2%), and neral (31.5%). The antifungal activity of LGEO was evaluated against several pathogenic yeasts and filamentous fungi using disc diffusion and vapor diffusion methods. Results LGEO exhibited promising antifungal effect against Candida albicans, C. tropicalis, and Aspergillus niger, with different inhibition zone diameters (IZDs) (35–90 mm). IZD increased with increasing oil volume. Significantly, higher anti-Candida activity was observed in the vapor phase. For the evaluation of the anti-inflammatory effect, LGEO (10 mg/kg, administered orally) significantly reduced carrageenan-induced paw edema with a similar effect to that observed for oral diclofenac (50 mg/kg), which was used as the positive control. Oral administration of LGEO showed dose-dependent anti-inflammatory activity. In addition, topical application of LGEO in vivo resulted in a potent anti-inflammatory effect, as demonstrated by using the mouse model of croton oil-induced ear edema. To our knowledge, this is the first such report to be published. The topical application of LGEO at doses of 5 and 10 µL/ear significantly reduced acute ear edema induced by croton oil in 62.5 and 75% of the mice, respectively. In addition, histological analysis clearly confirmed that LGEO inhibits the skin inflammatory response in animal models. Conclusion Results of the present study indicate that LGEO has a noteworthy potential for the development of drugs for the treatment of fungal infections and skin inflammation that should be explored in future studies. PMID:25242268

Lemon grass (Cymbopogon citratus) essential oil as a potent anti-inflammatory and antifungal drugs.

PubMed

Boukhatem, Mohamed Nadjib; Ferhat, Mohamed Amine; Kameli, Abdelkrim; Saidi, Fairouz; Kebir, Hadjer Tchoketch

2014-01-01

Background Volatile oils obtained from lemon grass [Cymbopogon citratus (DC.) Stapf, Poaceae family] are used in traditional medicine as remedies for the treatment of various diseases. Aims In the present study, lemon grass essential oil (LGEO) was evaluated for its in vivo topical and oral anti-inflammatory effects, and for its in vitro antifungal activity using both liquid and vapor phases. Methods The chemical profile of LGEO as determined by gas chromatography-mass spectrometry analysis revealed two major components: geranial (42.2%), and neral (31.5%). The antifungal activity of LGEO was evaluated against several pathogenic yeasts and filamentous fungi using disc diffusion and vapor diffusion methods. Results LGEO exhibited promising antifungal effect against Candida albicans, C.tropicalis, and Aspergillus niger, with different inhibition zone diameters (IZDs) (35-90 mm). IZD increased with increasing oil volume. Significantly, higher anti-Candida activity was observed in the vapor phase. For the evaluation of the anti-inflammatory effect, LGEO (10 mg/kg, administered orally) significantly reduced carrageenan-induced paw edema with a similar effect to that observed for oral diclofenac (50 mg/kg), which was used as the positive control. Oral administration of LGEO showed dose-dependent anti-inflammatory activity. In addition, topical application of LGEO in vivo resulted in a potent anti-inflammatory effect, as demonstrated by using the mouse model of croton oil-induced ear edema. To our knowledge, this is the first such report to be published. The topical application of LGEO at doses of 5 and 10 µL/ear significantly reduced acute ear edema induced by croton oil in 62.5 and 75% of the mice, respectively. In addition, histological analysis clearly confirmed that LGEO inhibits the skin inflammatory response in animal models. Conclusion Results of the present study indicate that LGEO has a noteworthy potential for the development of drugs for the treatment of fungal infections and skin inflammation that should be explored in future studies.

Lemon grass (Cymbopogon citratus) essential oil as a potent anti-inflammatory and antifungal drugs.

PubMed

Boukhatem, Mohamed Nadjib; Ferhat, Mohamed Amine; Kameli, Abdelkrim; Saidi, Fairouz; Kebir, Hadjer Tchoketch

2014-01-01

Volatile oils obtained from lemon grass [Cymbopogon citratus (DC.) Stapf, Poaceae family] are used in traditional medicine as remedies for the treatment of various diseases. In the present study, lemon grass essential oil (LGEO) was evaluated for its in vivo topical and oral anti-inflammatory effects, and for its in vitro antifungal activity using both liquid and vapor phases. The chemical profile of LGEO as determined by gas chromatography-mass spectrometry analysis revealed two major components: geranial (42.2%), and neral (31.5%). The antifungal activity of LGEO was evaluated against several pathogenic yeasts and filamentous fungi using disc diffusion and vapor diffusion methods. LGEO exhibited promising antifungal effect against Candida albicans, C. tropicalis, and Aspergillus niger, with different inhibition zone diameters (IZDs) (35-90 mm). IZD increased with increasing oil volume. Significantly, higher anti-Candida activity was observed in the vapor phase. For the evaluation of the anti-inflammatory effect, LGEO (10 mg/kg, administered orally) significantly reduced carrageenan-induced paw edema with a similar effect to that observed for oral diclofenac (50 mg/kg), which was used as the positive control. Oral administration of LGEO showed dose-dependent anti-inflammatory activity. In addition, topical application of LGEO in vivo resulted in a potent anti-inflammatory effect, as demonstrated by using the mouse model of croton oil-induced ear edema. To our knowledge, this is the first such report to be published. The topical application of LGEO at doses of 5 and 10 µL/ear significantly reduced acute ear edema induced by croton oil in 62.5 and 75% of the mice, respectively. In addition, histological analysis clearly confirmed that LGEO inhibits the skin inflammatory response in animal models. RESULTS of the present study indicate that LGEO has a noteworthy potential for the development of drugs for the treatment of fungal infections and skin inflammation that should be explored in future studies.

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

Barbante, Paolo; Frezzotti, Aldo; Gibelli, Livio

The unsteady evaporation of a thin planar liquid film is studied by molecular dynamics simulations of Lennard-Jones fluid. The obtained results are compared with the predictions of a diffuse interface model in which capillary Korteweg contributions are added to hydrodynamic equations, in order to obtain a unified description of the liquid bulk, liquid-vapor interface and vapor region. Particular care has been taken in constructing a diffuse interface model matching the thermodynamic and transport properties of the Lennard-Jones fluid. The comparison of diffuse interface model and molecular dynamics results shows that, although good agreement is obtained in equilibrium conditions, remarkable deviationsmore » of diffuse interface model predictions from the reference molecular dynamics results are observed in the simulation of liquid film evaporation. It is also observed that molecular dynamics results are in good agreement with preliminary results obtained from a composite model which describes the liquid film by a standard hydrodynamic model and the vapor by the Boltzmann equation. The two mathematical model models are connected by kinetic boundary conditions assuming unit evaporation coefficient.« less

Detection of Explosive Vapors: The Roles of Exciton and Molecular Diffusion in Real-Time Sensing.

PubMed

Ali, Mohammad A; Shoaee, Safa; Fan, Shengqiang; Burn, Paul L; Gentle, Ian R; Meredith, Paul; Shaw, Paul E

2016-11-04

Time-resolved quartz crystal microbalance with in situ fluorescence measurements are used to monitor the sorption of the nitroaromatic (explosive) vapor, 2,4-dinitrotoluene (DNT) into a porous pentiptycene-containing poly(phenyleneethynylene) sensing film. Correlation of the nitroaromatic mass uptake with fluorescence quenching shows that the analyte diffusion follows the Case-II transport model, a film-swelling-limited process, in which a sharp diffusional front propagates at a constant velocity through the film. At a low vapor pressure of DNT of ≈16 ppb, the analyte concentration in the front is sufficiently high to give an average fluorophore-analyte separation of ≈1.5 nm. Hence, a long exciton diffusion length is not required for real-time sensing in the solid state. Rather the diffusion behavior of the analyte and the strength of the binding interaction between the analyte and the polymer play first-order roles in the fluorescence quenching process. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Laser initiated spark development in an air gap.

PubMed

Lindner, F W; Rudolph, W; Brumme, G; Fischer, H

1975-09-01

Spark development is studied by 20-nsec image converter photography. A diffuse and transparent prechannel bridges the gap from the top of the metal vapor jet, which has counterelectrode potential. The prechannel cuts off the development of the cone shaped jet with increasing gap voltage. The final breakdown is initiated by a z-axis, laser induced filament, which expands into the prechannel volume within less, similar10 nsec. This interval represents the final high current thermalization phase of the breakdown. Thermal expansion of the initial spark channel (Braginskii) follows.

Influence of Natural Convection and Thermal Radiation Multi-Component Transport in MOCVD Reactors

NASA Technical Reports Server (NTRS)

Lowry, S.; Krishnan, A.; Clark, I.

1999-01-01

The influence of Grashof and Reynolds number in Metal Organic Chemical Vapor (MOCVD) reactors is being investigated under a combined empirical/numerical study. As part of that research, the deposition of Indium Phosphide in an MOCVD reactor is modeled using the computational code CFD-ACE. The model includes the effects of convection, conduction, and radiation as well as multi-component diffusion and multi-step surface/gas phase chemistry. The results of the prediction are compared with experimental data for a commercial reactor and analyzed with respect to the model accuracy.

Development of high temperature gallium phosphide rectifiers

NASA Technical Reports Server (NTRS)

Craford, M. G.; Keune, D. L.

1972-01-01

Large area high performance, GaP rectifiers were fabricated by means of Zn diffusion into vapor phase epitaxial GaP. Devices with an active area of 0.01 sq cm typically exhibit forward voltages of 3 volts for a bias current of 1 ampere and have reverse breakdown voltages of 300 volts for temperatures from 27 C to 400 C. Typical device reverse saturation current at a reverse bias of 150 volts is less than 10 to the minus 9th power amp at 27 C and less than 0.000050 amp at 400 C.

Metal-boride phase formation on tungsten carbide (WC-Co) during microwave plasma chemical vapor deposition

NASA Astrophysics Data System (ADS)

Johnston, Jamin M.; Catledge, Shane A.

2016-02-01

Strengthening of cemented tungsten carbide by boriding is used to improve the wear resistance and lifetime of carbide tools; however, many conventional boriding techniques render the bulk carbide too brittle for extreme conditions, such as hard rock drilling. This research explored the variation in metal-boride phase formation during the microwave plasma enhanced chemical vapor deposition process at surface temperatures from 700 to 1100 °C. We showed several well-adhered metal-boride surface layers consisting of WCoB, CoB and/or W2CoB2 with average hardness from 23 to 27 GPa and average elastic modulus of 600-730 GPa. The metal-boride interlayer was shown to be an effective diffusion barrier against elemental cobalt; migration of elemental cobalt to the surface of the interlayer was significantly reduced. A combination of glancing angle X-ray diffraction, electron dispersive spectroscopy, nanoindentation and scratch testing was used to evaluate the surface composition and material properties. An evaluation of the material properties shows that plasma enhanced chemical vapor deposited borides formed at substrate temperatures of 800 °C, 850 °C, 900 °C and 1000 °C strengthen the material by increasing the hardness and elastic modulus of cemented tungsten carbide. Additionally, these boride surface layers may offer potential for adhesion of ultra-hard carbon coatings.

Determination of mercury distribution inside spent compact fluorescent lamps by atomic absorption spectrometry

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

Rey-Raap, Natalia; Gallardo, Antonio, E-mail: gallardo@emc.uji.es

Highlights: Black-Right-Pointing-Pointer New treatments for CFL are required considering the aim of Directive 202/96/CE. Black-Right-Pointing-Pointer It is shown that most of the mercury introduced into a CFL is in the phosphor powder. Black-Right-Pointing-Pointer Experimental conditions for microwave-assisted sample digestion followed by AAS measurements are described. Black-Right-Pointing-Pointer By washing the glass it is possible to reduce the concentration below legal limits. - Abstract: In this study, spent compact fluorescent lamps were characterized to determine the distribution of mercury. The procedure used in this research allowed mercury to be extracted in the vapor phase, from the phosphor powder, and the glass matrix.more » Mercury concentration in the three phases was determined by the method known as cold vapor atomic absorption spectrometry. Median values obtained in the study showed that a compact fluorescent lamp contained 24.52 {+-} 0.4 ppb of mercury in the vapor phase, 204.16 {+-} 8.9 ppb of mercury in the phosphor powder, and 18.74 {+-} 0.5 ppb of mercury in the glass matrix. There are differences in mercury concentration between the lamps since the year of manufacture or the hours of operation affect both mercury content and its distribution. The 85.76% of the mercury introduced into a compact fluorescent lamp becomes a component of the phosphor powder, while more than 13.66% is diffused through the glass matrix. By washing and eliminating all phosphor powder attached to the glass surface it is possible to classified the glass as a non-hazardous waste.« less

Mixing of secondary organic aerosols versus relative humidity

PubMed Central

Ye, Qing; Robinson, Ellis Shipley; Ding, Xiang; Ye, Penglin

2016-01-01

Atmospheric aerosols exert a substantial influence on climate, ecosystems, visibility, and human health. Although secondary organic aerosols (SOA) dominate fine-particle mass, they comprise myriad compounds with uncertain sources, chemistry, and interactions. SOA formation involves absorption of vapors into particles, either because gas-phase chemistry produces low-volatility or semivolatile products that partition into particles or because more-volatile organics enter particles and react to form lower-volatility products. Thus, SOA formation involves both production of low-volatility compounds and their diffusion into particles. Most chemical transport models assume a single well-mixed phase of condensing organics and an instantaneous equilibrium between bulk gas and particle phases; however, direct observations constraining diffusion of semivolatile organics into particles containing SOA are scarce. Here we perform unique mixing experiments between SOA populations including semivolatile constituents using quantitative, single-particle mass spectrometry to probe any mass-transfer limitations in particles containing SOA. We show that, for several hours, particles containing SOA from toluene oxidation resist exchange of semivolatile constituents at low relative humidity (RH) but start to lose that resistance above 20% RH. Above 40% RH, the exchange of material remains constant up to 90% RH. We also show that dry particles containing SOA from α-pinene ozonolysis do not appear to resist exchange of semivolatile compounds. Our interpretation is that in-particle diffusion is not rate-limiting to mass transfer in these systems above 40% RH. To the extent that these systems are representative of ambient SOA, we conclude that diffusion limitations are likely not common under typical ambient boundary layer conditions. PMID:27791066

Mixing of secondary organic aerosols versus relative humidity.

PubMed

Ye, Qing; Robinson, Ellis Shipley; Ding, Xiang; Ye, Penglin; Sullivan, Ryan C; Donahue, Neil M

2016-10-24

Atmospheric aerosols exert a substantial influence on climate, ecosystems, visibility, and human health. Although secondary organic aerosols (SOA) dominate fine-particle mass, they comprise myriad compounds with uncertain sources, chemistry, and interactions. SOA formation involves absorption of vapors into particles, either because gas-phase chemistry produces low-volatility or semivolatile products that partition into particles or because more-volatile organics enter particles and react to form lower-volatility products. Thus, SOA formation involves both production of low-volatility compounds and their diffusion into particles. Most chemical transport models assume a single well-mixed phase of condensing organics and an instantaneous equilibrium between bulk gas and particle phases; however, direct observations constraining diffusion of semivolatile organics into particles containing SOA are scarce. Here we perform unique mixing experiments between SOA populations including semivolatile constituents using quantitative, single-particle mass spectrometry to probe any mass-transfer limitations in particles containing SOA. We show that, for several hours, particles containing SOA from toluene oxidation resist exchange of semivolatile constituents at low relative humidity (RH) but start to lose that resistance above 20% RH. Above 40% RH, the exchange of material remains constant up to 90% RH. We also show that dry particles containing SOA from α-pinene ozonolysis do not appear to resist exchange of semivolatile compounds. Our interpretation is that in-particle diffusion is not rate-limiting to mass transfer in these systems above 40% RH. To the extent that these systems are representative of ambient SOA, we conclude that diffusion limitations are likely not common under typical ambient boundary layer conditions.

The effect of silicon on the oxidation behavior of NiAlHf coating system

NASA Astrophysics Data System (ADS)

Dai, Pengchao; Wu, Qiong; Ma, Yue; Li, Shusuo; Gong, Shengkai

2013-04-01

Two types of NiAlHf coatings doped with different content of Si (1 at.% and 2 at.%) were deposited on a Ni3Al based single crystal superalloy IC32 by electron beam physical vapor deposition (EB-PVD) method, respectively. For comparison, NiAlHf coating with 0 at.% Si was also prepared. The oxidation tests were carried out at 1423 K in air. At the initial stage of oxidation, large amount of flake-like θ-Al2O3 was found on NiAlHf coating surface. However, no θ-Al2O3 was observed in 2 at.% Si doped NiAlHf coating except α-Al2O3. It revealed that the Si additions could contribute to the transformation from θ-Al2O3 to α-Al2O3. When oxidation time prolonged to 100 h, it was found that the degradation of NiAlHf coating was very severe with no residual β-phase, which was due to the serious inter-diffusion between the coating and substrate. In contrast, the inter-diffusion in Si-doped coating was reduced with some residual β-phase and R-Ni(Mo, Re) precipitates. The presence of Si could retard the inter-diffusion of elements between coating and substrate, indicating a barrier diffusion effect. As a result, the oxidation resistance of NiAlHf coating was improved significantly.

Volatile organic compounds detected in vapor-diffusion samplers placed in sediments along and near the shoreline at Allen Harbor Landfill and Calf Pasture Point, Davisville, Rhode Island, March-April 1998

USGS Publications Warehouse

Lyford, F.P.; Kliever, J.D.; Scott, Clifford

1999-01-01

Volatile organic compounds are present in ground water at the Allen Harbor Landfill and the Calf Pasture Point sites on the former Naval Construction Battalion Center in Davisville, R.I. Vapor-diffusion samplers were used at the two sites during March-April 1998 to identify possible discharge points for contaminants along the shore of Allen Harbor and in two wetland areas near the shore. Results from vapor-diffusion samplers will be used in conjunction with other site information to evaluate proposed ground-water monitoring programs. Volatile organic compounds were detected in 41 of 115 samplers placed along the shoreline at the Allen Harbor Landfill. Trichloroethylene was the principal volatile organic compound detected of eight target compounds. The highest vapor concentration measured exceeded 300,000 parts per billion by volume in an area where TCE was detected in groundwater from nearby monitoring wells. Other chemicals detected in vapor-diffusion samplers included tetrachloroethylene, toluene, and benzene. Concentrations of individual volatile organic compounds were less than 100 parts per billion by volume in most samplers. Volatile organic compounds, principally trichloroethylene, were detected in 7 of 30 samplers placed along the shoreline at Calf Pasture Point; the highest trichloroethylene concentration was 1,900 parts per billion by volume. A trace concentration of tetrachloroethylene was detected in one of the samplers. One of 24 samplers placed in two wetland areas near the shore (suspected discharge areas for ground-water containing volatile organic compounds) detected trichloroethylene at a vapor concentration of 14 parts per billion by volume.

Role of boundary layer diffusion in vapor deposition growth of chalcogenide nanosheets: the case of GeS.

PubMed

Li, Chun; Huang, Liang; Snigdha, Gayatri Pongur; Yu, Yifei; Cao, Linyou

2012-10-23

We report a synthesis of single-crystalline two-dimensional GeS nanosheets using vapor deposition processes and show that the growth behavior of the nanosheet is substantially different from those of other nanomaterials and thin films grown by vapor depositions. The nanosheet growth is subject to strong influences of the diffusion of source materials through the boundary layer of gas flows. This boundary layer diffusion is found to be the rate-determining step of the growth under typical experimental conditions, evidenced by a substantial dependence of the nanosheet's size on diffusion fluxes. We also find that high-quality GeS nanosheets can grow only in the diffusion-limited regime, as the crystalline quality substantially deteriorates when the rate-determining step is changed away from the boundary layer diffusion. We establish a simple model to analyze the diffusion dynamics in experiments. Our analysis uncovers an intuitive correlation of diffusion flux with the partial pressure of source materials, the flow rate of carrier gas, and the total pressure in the synthetic setup. The observed significant role of boundary layer diffusions in the growth is unique for nanosheets. It may be correlated with the high growth rate of GeS nanosheets, ~3-5 μm/min, which is 1 order of magnitude higher than other nanomaterials (such as nanowires) and thin films. This fundamental understanding of the effect of boundary layer diffusions may generally apply to other chalcogenide nanosheets that can grow rapidly. It can provide useful guidance for the development of general paradigms to control the synthesis of nanosheets.

DELIVERY OF WATER-SOLUBLE DRUGS USING ACOUSTICALLY-TRIGGERED, PERFLUOROCARBON DOUBLE EMULSIONS

PubMed Central

Fabiilli, Mario L.; Lee, James A.; Kripfgans, Oliver D.; Carson, Paul L.; Fowlkes, J. Brian

2010-01-01

Purpose Ultrasound can be used to release a therapeutic payload encapsulated within a perfluorocarbon (PFC) emulsion via acoustic droplet vaporization (ADV), a process whereby the PFC phase is vaporized and the agent is released. ADV-generated microbubbles have been previously used to selectively occlude blood vessels in vivo. The coupling of ADV-generated drug delivery and occlusion has therapeutically, synergistic potentials. Methods Micron-sized, water-in-PFC-in-water (W1/PFC/W2) emulsions were prepared in a two-step process using perfluoropentane (PFP) or perfluorohexane (PFH) as the PFC phase. Fluorescein or thrombin was contained in the W1 phase. Results Double emulsions containing fluorescein in the W1 phase displayed a 5.7±1.4 fold and 8.2±1.3 fold increase in fluorescein mass flux, as measured using a Franz diffusion cell, after ADV for the PFP and PFH emulsions, respectively. Thrombin was stably retained in four out of five double emulsions. For three out of five formulations tested, the clotting time of whole blood decreased, in a statistically significant manner (p < 0.01), when incubated with thrombin-loaded emulsions exposed to ultrasound compared to emulsions not exposed to ultrasound. Conclusions ADV can be used to spatially and temporally control the delivery of water-soluble compounds formulated in PFC double emulsions. Thrombin release could extend the duration of ADV-generated, microbubble occlusions. PMID:20872050

Near-field cathodoluminescence studies on n-doped gallium nitride films

NASA Astrophysics Data System (ADS)

Nogales, E.; Joachimsthaler, I.; Heiderhoff, R.; Piqueras, J.; Balk, L. J.

2002-07-01

Near-field cathodoluminescence (NFCL) has been used to characterize hydride vapor phase epitaxy grown n-GaN films. This technique can obtain high resolution luminescence images and perform local measurements of the diffusion length for minority carriers in different parts of the sample. NFCL contrast observed in round growth hillocks at the sample surface, with a diameter of less than 10 mum, is compared with that observed by conventional cathodoluminescence in scanning electron microscope (CLSEM) techniques. In particular NFCL images reveal features not detected by CLSEM which is explained by the fact that under near field conditions the signal arises from a depth of only several tens of nanometers and is then directly related to the surface hillocks. Diffusion lengths of about 0.4 and 4 mum have been found for the holes in different regions of the samples at room temperature. The order of magnitude of these minority carriers diffusion lengths is in good agreement with previous measurements performed at different GaN samples with other techniques. The NFCL contrast and the differences in the measured diffusion lengths are discussed and explained by variations in local trap concentrations.

Experimental investigation of the physical properties of medium and heavy oils, their vaporization and use in explosion engines. Part III

NASA Technical Reports Server (NTRS)

Heinlein, Fritz

1926-01-01

The test equipment for studying the vaporization of heavy and medium oils is described as well as some of the experimental properties explored such as vaporization speed and diffusion coefficient. The experiemtal arrangement is also discussed.

Quantitative organic vapor-particle sampler

DOEpatents

Gundel, Lara; Daisey, Joan M.; Stevens, Robert K.

1998-01-01

A quantitative organic vapor-particle sampler for sampling semi-volatile organic gases and particulate components. A semi-volatile organic reversible gas sorbent macroreticular resin agglomerates of randomly packed microspheres with the continuous porous structure of particles ranging in size between 0.05-10 .mu.m for use in an integrated diffusion vapor-particle sampler.

Preparation of pigments for space-stable thermal control coatings

NASA Technical Reports Server (NTRS)

Campbell, W. B.; Smith, R. G.

1972-01-01

The identification and control of vapor phase reaction kinetics to produce pigments by homogeneous nucleation were achieved. A vapor phase apparatus was designed, fabricated, and calibrated through 1800 C. Vapor phase reactions were analyzed, calculations made, and powders of alumina, rutile, zinc orthotitanate (in a mixed phase), calcium tungstate, and lanthana were produced by homogeneous nucleation. Electron microscopy shows uniform particle morphology and size, and supports anticipated advantages of vapor-phase homogeneous nucleation; namely, purity, freedom from defects, and uniform particle sizing without grinding.

Diffusion with chemical reaction: An attempt to explain number density anomalies in experiments involving alkali vapor

NASA Technical Reports Server (NTRS)

Snow, W. L.

1974-01-01

The mutual diffusion of two reacting gases is examined which takes place in a bath of inert gas atoms. Solutions are obtained between concentric spheres, each sphere acting as a source for one of the reactants. The calculational model is used to illustrate severe number density gradients observed in absorption experiments with alkali vapor. Severe gradients result when sq root k/D R is approximately 5 where k, D, and R are respectively the second order rate constant, the multicomponent diffusion constant, and the geometrical dimension of the experiment.

Accounting for the Effect of Noncondensing Gases on Interphasic Heat and Mass Transfer in the Two-Fluid Model Used in the KORSAR Code

NASA Astrophysics Data System (ADS)

Yudov, Yu. V.

2018-03-01

A model is presented of the interphasic heat and mass transfer in the presence of noncondensable gases for the KORSAR/GP design code. This code was developed by FGUP NITI and the special design bureau OKB Gidropress. It was certified by Rostekhnadzor in 2009 for numerical substantiation of the safety of reactor installations with VVER reactors. The model is based on the assumption that there are three types of interphasic heat and mass transfer of the vapor component: vapor condensation or evaporation on the interphase under any thermodynamic conditions of the phases, pool boiling of the liquid superheated above the saturation temperature at the total pressure, and spontaneous condensation in the volume of gas phase supercooled below the saturation temperature at the vapor partial pressure. Condensation and evaporation on the interphase continuously occur in a two-phase flow and control the time response of the interphase heat and mass transfer. Boiling and spontaneous condensation take place only at the metastable condition of the phases and run at a quite high speed. The procedure used for calculating condensation and evaporation on the interphase accounts for the combined diffusion and thermal resistance of mass transfer in all regimes of the two-phase flow. The proposed approach accounts for, in a natural manner, a decrease in the rate of steam condensation (or generation) in the presence of noncondensing components in the gas phase due to a decrease (or increase) in the interphase temperature relative to the saturation temperature at the vapor partial pressure. The model of the interphase heat transfer also accounts for the processes of dissolution or release of noncondensing components in or from the liquid. The gas concentration at the interphase and on the saturation curve is calculated by the Henry law. The mass transfer coefficient in gas dissolution is based on the heat and mass transfer analogy. Results are presented of the verification of the interphase heat and mass transfer used in the KORSAR/GP code based on the data on film condensation of steam-air flows in vertical pipes. The proposed model was also tested by solving a problem of nitrogen release from a supersaturated water solution.

Assessing the potential of quartz crystal microbalance to estimate water vapor transfer in micrometric size cellulose particles.

PubMed

Thoury-Monbrun, Valentin; Gaucel, Sébastien; Rouessac, Vincent; Guillard, Valérie; Angellier-Coussy, Hélène

2018-06-15

This study aims at assessing the use of a quartz crystal microbalance (QCM) coupled with an adsorption system to measure water vapor transfer properties in micrometric size cellulose particles. This apparatus allows measuring successfully water vapor sorption kinetics at successive relative humidity (RH) steps on a dispersion of individual micrometric size cellulose particles (1 μg) with a total acquisition duration of the order of one hour. Apparent diffusivity and water uptake at equilibrium were estimated at each step of RH by considering two different particle geometries in mass transfer modeling, i.e. sphere or finite cylinder, based on the results obtained from image analysis. Water vapor diffusivity values varied from 2.4 × 10 -14  m 2  s -1 to 4.2 × 10 -12  m 2  s -1 over the tested RH range (0-80%) whatever the model used. A finite cylinder or spherical geometry could be used equally for diffusivity identification for a particle size aspect ratio lower than 2. Copyright © 2018 Elsevier Ltd. All rights reserved.

Structure and phase behavior of a confined nanodroplet composed of the flexible chain molecules.

PubMed

Kim, Soon-Chul; Kim, Eun-Young; Seong, Baek-Seok

2011-04-28

A polymer density functional theory has been employed for investigating the structure and phase behaviors of the chain polymer, which is modelled as the tangentially connected sphere chain with an attractive interaction, inside the nanosized pores. The excess free energy of the chain polymer has been approximated as the modified fundamental measure-theory for the hard spheres, the Wertheim's first-order perturbation for the chain connectivity, and the mean-field approximation for the van der Waals contribution. For the value of the chemical potential corresponding to a stable liquid phase in the bulk system and a metastable vapor phase, the flexible chain molecules undergo the liquid-vapor transition as the pore size is reduced; the vapor is the stable phase at small volume, whereas the liquid is the stable phase at large volume. The wide liquid-vapor coexistence curve, which explains the wide range of metastable liquid-vapor states, is observed at low temperature. The increase of temperature and decrease of pore size result in a narrowing of liquid-vapor coexistence curves. The increase of chain length leads to a shift of the liquid-vapor coexistence curve towards lower values of chemical potential. The coexistence curves for the confined phase diagram are contained within the corresponding bulk liquid-vapor coexistence curve. The equilibrium capillary phase transition occurs at a higher chemical potential than in the bulk phase.

Bioheat model evaluations of laser effects on tissues: role of water evaporation and diffusion

NASA Astrophysics Data System (ADS)

Nagulapally, Deepthi; Joshi, Ravi P.; Thomas, Robert J.

2011-03-01

A two-dimensional, time-dependent bioheat model is applied to evaluate changes in temperature and water content in tissues subjected to laser irradiation. Our approach takes account of liquid-to-vapor phase changes and a simple diffusive flow of water within the biotissue. An energy balance equation considers blood perfusion, metabolic heat generation, laser absorption, and water evaporation. The model also accounts for the water dependence of tissue properties (both thermal and optical), and variations in blood perfusion rates based on local tissue injury. Our calculations show that water diffusion would reduce the local temperature increases and hot spots in comparison to simple models that ignore the role of water in the overall thermal and mass transport. Also, the reduced suppression of perfusion rates due to tissue heating and damage with water diffusion affect the necrotic depth. Two-dimensional results for the dynamic temperature, water content, and damage distributions will be presented for skin simulations. It is argued that reduction in temperature gradients due to water diffusion would mitigate local refractive index variations, and hence influence the phenomenon of thermal lensing. Finally, simple quantitative evaluations of pressure increases within the tissue due to laser absorption are presented.

Comparison of cryopreserved human sperm in vapor and liquid phases of liquid nitrogen: effect on motility parameters, morphology, and sperm function.

PubMed

Punyatanasakchai, Piyaphan; Sophonsritsuk, Areephan; Weerakiet, Sawaek; Wansumrit, Surapee; Chompurat, Deonthip

2008-11-01

To compare the effects of cryopreserved sperm in vapor and liquid phases of liquid nitrogen on sperm motility, morphology, and sperm function. Experimental study. Andrology laboratory at Ramathibodi Hospital, Thailand. Thirty-eight semen samples with normal motility and sperm count were collected from 38 men who were either patients of an infertility clinic or had donated sperm for research. Each semen sample was divided into two aliquots. Samples were frozen with static-phase vapor cooling. One aliquot was plunged into liquid nitrogen (-196 degrees C), and the other was stored in vapor-phase nitrogen (-179 degrees C) for 3 days. Thawing was performed at room temperature. Motility was determined by using computer-assisted semen analysis, sperm morphology was determined by using eosin-methylene blue staining, and sperm function was determined by using a hemizona binding test. Most of the motility parameters of sperm stored in the vapor phase were not significantly different from those stored in the liquid phase of liquid nitrogen, except in amplitude of lateral head displacement. The percentages of normal sperm morphology in both vapor and liquid phases also were not significantly different. There was no significant difference in the number of bound sperm in hemizona between sperm cryopreserved in both vapor and liquid phases of liquid nitrogen. Cryopreservation of human sperm in a vapor phase of liquid nitrogen was comparable to cryopreservation in a liquid phase of liquid nitrogen.

Calibration of mass spectrometric measurements of gas phase reactions on steel surfaces

NASA Astrophysics Data System (ADS)

Falk, H.; Falk, M.; Wuttke, T.

2015-03-01

The sampling of the surface-near gas composition using a mass spectrometer (MS-Probe) is a valuable tool within a hot dip process simulator. Since reference samples with well characterized surface coverage are usually not available, steel samples can deliver quantifiable amounts of the process relevant species H2O, CO and H2 using the decarburization reaction with water vapor. Such "artificial calibration samples" (ACS) can be used for the calibration of the MS-Probe measurements. The carbon release rate, which is governed by the diffusion law, was determined by GDOES, since the diffusion coefficients of carbon in steel samples are usually not known. The measured carbon concentration profiles in the ACS after the thermal treatment confirmed the validity of the diffusion model described in this paper. The carbon bulk concentration > 100 ppm is sufficient for the use of a steel material as ACS. The experimental results reported in this paper reveal, that with the MS-Probe the LOQ of less than one monolayer of iron oxide can be achieved.

Separation of gases by diffusion

DOEpatents

Peieris, R. E.; Simon, F. E.; Arms, H. S.

1960-12-13

An apparatus is described for the separation of mixtures of gaseous or vaporous media by diffusion through a permeable membrane. The apparatus consists principally of a housing member having an elongated internal chamber dissected longitudinally by a permeable membrane. Means are provided for producing a pressure difference between opposite sides of the membrane to cause a flow of the media in the chamber therethrough. This pressure difference is alternated between opposite sides of the membrane to produce an oscillating flow through the membrane. Additional means is provided for producing flow parallel to the membrane in opposite directions on the two sides thereof and of the same frequency and in phase wlth the alternating pressure difference. The lighter molecules diffuse through the membrane more readily than the heavier molecules and the parallel flow effects a net transport of the lighter molecules in one direction and the heavier molecules in the opposite direction wlthin the chamber. By these means a concentration gradient along the chamber is established. (auth)

Thin Film Mediated Phase Change Phenomena: Crystallization, Evaporation and Wetting

NASA Technical Reports Server (NTRS)

Wettlaufer, John S.

1998-01-01

We focus on two distinct materials science problems that arise in two distinct microgravity environments: In space and within the space of a polymeric network. In the former environment, we consider a near eutectic alloy film in contact with its vapor which, when evaporating on earth, will experience compositionally induced buoyancy driven convection. The latter will significantly influence the morphology of the crystallized end member. In the absence of gravity, the morphology will be dominated by molecular diffusion and Marangoni driven viscous flow, and we study these phenomena theoretically and experimentally. The second microgravity environment exists in liquids, gels, and other soft materials where the small mass of individual molecules makes the effect of gravity negligible next to the relatively strong forces of intermolecular collisions. In such materials, an essential question concerns how to relate the molecular dynamics to the bulk rheological behavior. Here, we observe experimentally the diffusive motion of a single molecule in a single polymer filament, embedded within a polymer network and find anomalous diffusive behavior.

An approximate analysis of the diffusing flow in a self-controlled heat pipe.

NASA Technical Reports Server (NTRS)

Somogyi, D.; Yen, H. H.

1973-01-01

Constant-density two-dimensional axisymmetric equations are presented for the diffusing flow of a class of self-controlled heat pipes. The analysis is restricted to the vapor space. Condensation of the vapor is related to its mass fraction at the wall by the gas kinetic formula. The Karman-Pohlhausen integral method is applied to obtain approximate solutions. Solutions are presented for a water heat pipe with neon control gas.

Sporicidal Activity of the KMT reagent in its vapor phase against Geobacillus stearothermophilus Spores.

PubMed

Kida, Nori; Mochizuki, Yasushi; Taguchi, Fumiaki

2007-01-01

In an investigation of the sporicidal activity of the KMT reagent, a vapor phase study was performed using five kinds of carriers contaminated with Geobacillus stearothermophilus spores. When 25 ml of the KMT reagent was vaporized in a chamber (capacity; approximately 95 liters), the 2-step heating method (vaporization by a combination of low temperature and high temperature) showed the most effective sporicidal activity in comparison with the 1-step heating method (rapid vaporization). The 2-step heating method appeared to be related to the sporicidal activity of vaporized KMT reagent, i.e., ethanol and iodine, which vaporized mainly when heated at a low temperature such as 55 C, and acidic water, which vaporized mainly when heated at a high temperature such as 300 C. We proposed that the KMT reagent can be used as a new disinfectant not only in the liquid phase but also in the vapor phase in the same way as peracetic acid and hydrogen peroxide.

Effect of water vapor on evolution of a thick Pt-layer modified oxide on the NiCoCrAl alloy at high temperature

NASA Astrophysics Data System (ADS)

Song, Peng; He, Xuan; Xiong, Xiping; Ma, Hongqing; Song, Qunling; Lü, Jianguo; Lu, Jiansheng

2018-03-01

To investigate the effect of water vapor on the novel Pt-containing oxide growth behavior, Pt-addition within the oxide layer on the surface of NiCoCrAl coating and furnace cycle tests were carried out at 1050 °C in air and air plus water vapor. The thick Pt-containing oxide layer on NiCoCrAl exhibits a different oxidation growth behavior compared to the conventional Pt-diffusion metallic coatings. The Pt-containing oxide after oxidation in air plus water vapor showed a much thicker oxide layer compare to the ones without Pt addition, and also presented a much better coating adhesion. During the oxidation process in air, Pt promotes the spinel (NiCr2O4) formation. However, the Cr2O3 formed in air with water vapor and fixed Pt within the complex oxide layer. The water vapor promoted the Ni and Co outer-diffusion, and combined with Pt to form CoPt compounds on the surface of the NiCoCrAl coating system.

Experimental thermal conductivity, thermal diffusivity, and specific heat values for mixtures of nitrogen, oxygen, and argon

NASA Technical Reports Server (NTRS)

Perkins, R. A.; Cieszkiewicz, M. T.

1991-01-01

Experimental measurements of thermal conductivity and thermal diffusivity obtained with a transient hot-wire apparatus are reported for three mixtures of nitrogen, oxygen, and argon. Values of the specific heat, Cp, are calculated from these measured values and the density calculated with an equation of state. The measurements were made at temperatures between 65 and 303 K with pressures between 0.1 and 70 MPa. The data cover the vapor, liquid, and supercritical gas phases for the three mixtures. The total reported points are 1066 for the air mixture (78.11 percent nitrogen, 20.97 percent oxygen, and 0.92 percent argon), 1058 for the 50 percent nitrogen, 50 percent oxygen mixture, and 864 for the 25 percent nitrogen, 75 oxygen mixture. Empirical thermal conductivity correlations are provided for the three mixtures.

Diffuse sunlight based calibration of the water vapor channel in the upc raman lidar

NASA Astrophysics Data System (ADS)

Muñoz-Porcar, Constantino; Comeron, Adolfo; Sicard, Michaël; Barragan, Ruben; Garcia-Vizcaino, David; Rodríguez-Gómez, Alejandro; Rocadenbosch, Francesc

2018-04-01

A method for determining the calibration factor of the water vapor channel of a Raman lidar, based on zenith measurements of diffuse sunlight and on assumptions regarding some system parameters and Raman scattering models, has been applied to the lidar system of Universitat Politècnica de Catalunya (UPC; Technical University of Catalonia, Spain). Results will be analyzed in terms of stability and comparison with typical methods relying on simultaneous radiosonde measurements.

Lanthanide-activated scheelite nanocrystal phosphors prepared by the low-temperature vapor diffusion sol-gel method

DOE PAGES

Culver, Sean P.; Brutchey, Richard L.

2016-10-25

A series of Eu 3+-, Tb 3+-, and Tm 3+-doped CaWO 4 phosphor nanocrystals have been synthesized under benign conditions using the vapor diffusion sol–gel method. Here the high degree of synthetic flexibility inherent to this approach has enabled the synthesis of a CaWO 4:(Eu,Tb) dual-sensitized white light emitting nanocrystal phosphor upon commercial UV excitation at 366 nm with a long lifetime exceeding 1 ms.

New explicit equations for the accurate calculation of the growth and evaporation of hydrometeors by the diffusion of water vapor

NASA Technical Reports Server (NTRS)

Srivastava, R. C.; Coen, J. L.

1992-01-01

The traditional explicit growth equation has been widely used to calculate the growth and evaporation of hydrometeors by the diffusion of water vapor. This paper reexamines the assumptions underlying the traditional equation and shows that large errors (10-30 percent in some cases) result if it is used carelessly. More accurate explicit equations are derived by approximating the saturation vapor-density difference as a quadratic rather than a linear function of the temperature difference between the particle and ambient air. These new equations, which reduce the error to less than a few percent, merit inclusion in a broad range of atmospheric models.

Phase equilibrium measurements on nine binary mixtures

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

Wilding, W.V.; Giles, N.F.; Wilson, L.C.

1996-11-01

Phase equilibrium measurements have been performed on nine binary mixtures. The PTx method was used to obtain vapor-liquid equilibrium data for the following systems at two temperatures each: (aminoethyl)piperazine + diethylenetriamine; 2-butoxyethyl acetate + 2-butoxyethanol; 2-methyl-2-propanol + 2-methylbutane; 2-methyl-2-propanol + 2-methyl-2-butene; methacrylonitrile + methanol; 1-chloro-1,1-difluoroethane + hydrogen chloride; 2-(hexyloxy)ethanol + ethylene glycol; butane + ammonia; propionaldehyde + butane. Equilibrium vapor and liquid phase compositions were derived form the PTx data using the Soave equation of state to represent the vapor phase and the Wilson or the NRTL activity coefficient model to represent the liquid phase. A large immiscibility region existsmore » in the butane + ammonia system at 0 C. Therefore, separate vapor-liquid-liquid equilibrium measurements were performed on this system to more precisely determine the miscibility limits and the composition of the vapor phase in equilibrium with the two liquid phases.« less

Investigation of local evaporation flux and vapor-phase pressure at an evaporative droplet interface.

PubMed

Duan, Fei; Ward, C A

2009-07-07

In the steady-state experiments of water droplet evaporation, when the throat was heating at a stainless steel conical funnel, the interfacial liquid temperature was found to increase parabolically from the center line to the rim of the funnel with the global vapor-phase pressure at around 600 Pa. The energy conservation analysis at the interface indicates that the energy required for evaporation is maintained by thermal conduction to the interface from the liquid and vapor phases, thermocapillary convection at interface, and the viscous dissipation globally and locally. The local evaporation flux increases from the center line to the periphery as a result of multiple effects of energy transport at the interface. The local vapor-phase pressure predicted from statistical rate theory (SRT) is also found to increase monotonically toward the interface edge from the center line. However, the average value of the local vapor-phase pressures is in agreement with the measured global vapor-phase pressure within the measured error bar.

Combustion of liquid-fuel droplets in supercritical conditions

NASA Technical Reports Server (NTRS)

Shuen, J. S.; Yang, Vigor; Hsaio, C. C.

1992-01-01

A comprehensive analysis of liquid-fuel droplet combustion in both subcritical and supercritical environments has been conducted. The formulation is based on the complete conservation equations for both gas and liquid phases, and accommodates variable thermophysical properties, finite-rate chemical kinetics, and a full treatment of liquid-vapor phase equilibrium at the drop surface. The governing equations and associated interfacial boundary conditions are solved numerically using a fully coupled, implicit scheme with the dual time-stepping integration technique. The model is capable of treating the entire droplet history, including the transition from the subcritical to supercritical state. As a specific example, the combustion of n-pentane fuel droplets in air is studied for pressures in the range of 5-140 atm. Results indicate that the ambient gas pressure exerts significant control of droplet gasification and burning processes through its influence on fluid transport, gas-liquid interfacial thermodynamics, and chemical reactions. The droplet gasification rate increases progressively with pressure. However, the data for the overall burnout time exhibit a considerable change in the combustion mechanism at the critical pressure, mainly as a result of reduced mass diffusivity and latent heat of vaporization with increased pressure.

Combustion of liquid fuel droplets in supercritical conditions

NASA Technical Reports Server (NTRS)

Shuen, J. S.; Yang, Vigor

1991-01-01

A comprehensive analysis of liquid-fuel droplet combustion in both sub- and super-critical environments has been conducted. The formulation is based on the complete conservation equations for both gas and liquid phases, and accommodates finite-rate chemical kinetics and a full treatment of liquid-vapor phase equilibrium at the droplet surface. The governing equations and the associated interface boundary conditions are solved numerically using a fully coupled, implicit scheme with the dual time-stepping integration technique. The model is capable of treating the entire droplet history, including the transition from the subcritical to the supercritical state. As a specific example, the combustion of n-pentane fuel droplets in air is studied for pressures of 5-140 atm. Results indicate that the ambient gas pressure exerts significant control of droplet gasification and burning processes through its influences on the fluid transport, gas/liquid interface thermodynamics, and chemical reactions. The droplet gasification rate increases progressively with pressure. However, the data for the overall burnout time exhibits a significant variation near the critical burning pressure, mainly as a result of reduced mass-diffusion rate and latent heat of vaporization with increased pressure. The influence of droplet size on the burning characteristics is also noted.

Metallic diffusion measured by a modified Knudsen technique

NASA Technical Reports Server (NTRS)

Fray, D. J.

1969-01-01

Diffusion coefficient of a metal in high temperature system is determined. From the measurement of the weight loss from a Knudsen cell, the vapor pressure of the escaping species can be calculated. If the only way this species can enter the Knudsen cell is by diffusion through a foil, the weight loss is diffusion flux.

Quantification of vapor intrusion pathways into a slab-on-ground building under varying environmental conditions.

PubMed

Patterson, Bradley M; Davis, Greg B

2009-02-01

Potential hydrocarbon-vapor intrusion pathways into a building through a concrete slab-on-ground were investigated and quantified under a variety of environmental conditions to elucidate the potential mechanisms for indoor air contamination. Vapor discharge from the uncovered open ground soil adjacent to the building and subsequent advection into the building was unlikely due to the low soil-gas concentrations at the edge of the building as a result of aerobic biodegradation of hydrocarbon vapors. When the building's interior was under ambient pressure, a flux of vapors into the building due to molecular diffusion of vapors through the building's concrete slab (cyclohexane 11 and methylcyclohexane 31 mg m(-2) concrete slab day(-1)) and short-term (up to 8 h) cyclical pressure-driven advection of vapors through an artificial crack (cyclohexane 4.2 x 10(3) and methylcyclohexane 1.2 x 10(4) mg m(-2) cracks day(-1)) was observed. The average subslab vapor concentration under the center of the building was 25,000 microg L(-1). Based on the measured building's interiorvapor concentrations and the building's air exchange rate of 0.66 h(-1), diffusion of vapors through the concrete slab was the dominantvapor intrusion pathway and cyclical pressure exchanges resulted in a near zero advective flux. When the building's interior was under a reduced pressure (-12 Pa), advective transport through cracks or gaps in the concrete slab (cyclohexane 340 and methylcyclohexane 1100 mg m(-2) cracks day(-1)) was the dominant vapor intrusion pathway.

Preliminary investigations of protein crystal growth using the Space Shuttle

NASA Technical Reports Server (NTRS)

Delucas, L. J.; Suddath, F. L.; Snyder, R.; Naumann, R.; Broom, M. B.; Pusey, M.; Yost, V.; Herren, B .; Carter, D.

1986-01-01

Four preliminary Shuttle experiments are described which have been used to develop prototype hardware for a more advanced system that will evaluate effects of gravity on protein crystal growth. The first phase of these experiments has centered on the development of micromethods for protein crystal growth by vapor-diffusion techniques (using a space version of the hanging-drop method) and on dialysis using microdialysis cells. Results suggest that the elimination of density-driven sedimentation can effect crystal morphology. In the dialysis experiment, space-grown crystals of concanavalin B were three times longer and 1/3 the thickness of earth-grown crystals.

Improvements to water vapor transmission and capillary absorption measurements in porous materials

Treesearch

Samuel L. Zelinka; Samuel V. Glass; Charles R. Boardman

2016-01-01

The vapor permeability (or equivalently the vapor diffusion resistance factor) and the capillary absorption coefficient are frequently used as inputs to hygrothermal or heat, air, and moisture (HAM) models. However, it has been well documented that the methods used to determine these properties are sensitive to the operator, and wide variations in the properties have...

Using amphibole phenocrysts to track vapor transfer during magma crystallization and transport: An example from Mount St. Helens, Washington

USGS Publications Warehouse

Rowe, M.C.; Kent, A.J.R.; Thornber, C.R.

2008-01-01

In order to evaluate and further constrain models for volatile movement and vapor enrichment of magma stored at shallow levels, amphibole phenocrysts from 2004-2005 Mount St. Helens dacite were analyzed for major and selected trace elements (Li, Cu, Zn, Mn, and REE) and Li isotopes. Several recent studies have examined fluid-mobile trace element abundances in phencryst phases and melt inclusions as a means of tracking volatile movement within subvolcanic magmatic systems, and high Li contents in plagioclase phenocrysts from 1980 and 2004 Mount St. Helens dacites have been interpreted as evidence that shallow magma was fluxed by a Li-bearing vapor phase prior to eruption. In amphibole phenocrysts, Zn and Mn behave compatibly, correlating to FeO* and Al2O3, and show no systematic change with time. In contrast, Li and Cu abundances in amphibole vary by up to 3 orders of magnitude (7.6-1140????g/g and 1.7 to 94????g/g, respectively), and do not generally correlate with either major or trace elements. However, they do correlate moderately well (R2 = 0.54, >> 95% confidence) with each other and show systematic temporal variations that are opposite to those observed for plagioclase, precluding a simple 1-step diffusion model for Li enrichment. We propose a Diffusion-Crystallization Multi-Stage (DCMS) model to explain the temporal variations and co-variations of Li and Cu. In early erupted dacite (October-December 2004) profiles of Li isotopes in conjunction with measured 7Li intensities and core-to-rim increases in Li concentration are characteristic of Li diffusion into the amphiboles, consistent with prior models of plagioclase enrichment. In amphiboles from 2005 dacite, average Li and Cu concentrations are high (??? 260-660????g/g and ??? 29-45????g/g, respectively) and in contrast to amphiboles from earlier-erupted dacite, correlate weakly with Al2O3??wt.%. Amphibole Al2O3 concentrations are an indicator of pressure, with high-Al amphiboles crystallizing at higher pressures, and we suggest that Li and Cu are partitioned into a fluid phase during ascent and crystallization of the magma so that amphiboles crystallizing at lower pressure have correspondingly lower Li and Cu concentrations. However, low Li and Cu in amphiboles from the dacite at the start of the eruption also require crystallization from a low Li-Cu bearing melt or residence times long enough for amphiboles to re-equilibrate with a Li-Cu depleted melt. Estimated residence times suggest that amphiboles in early dacite could have been present since the end of the 1980-1986 eruptive episode at Mount St. Helens. ?? 2008 Elsevier B.V. All rights reserved.

Numerical Modeling of Physical Vapor Transport in Contactless Crystal Growth Geometry

NASA Technical Reports Server (NTRS)

Palosz, W.; Lowry, S.; Krishnam, A.; Przekwas, A.; Grasza, K.

1998-01-01

Growth from the vapor under conditions of limited contact with the walls of the growth ampoule is beneficial for the quality of the growing crystal due to reduced stress and contamination which may be caused by interactions with the growth container. The technique may be of a particular interest for studies on crystal growth under microgravity conditions: elimination of some factors affecting the crystal quality may make interpretation of space-conducted processes more conclusive and meaningful. For that reason, and as a part of our continuing studies on 'contactless' growth technique, we have developed a computational model of crystal growth process in such system. The theoretical model was built, and simulations were performed using the commercial computational fluid dynamics code, (CFD) ACE. The code uses an implicit finite volume formulation with a gray discrete ordinate method radiation model which accounts for the diffuse absorption and reflection of radiation throughout the furnace. The three-dimensional model computes the heat transfer through the crystal, quartz, and gas both inside and outside the ampoule, and mass transport from the source to the crystal and the sink. The heat transport mechanisms by conduction, natural convection, and radiation, and mass transport by diffusion and convection are modeled simultaneously and include the heat of the phase transition at the solid-vapor interfaces. As the thermal boundary condition, temperature profile along the walls of the furnace is used. For different thermal profiles and furnace and ampoule dimensions, the crystal growth rate and development of the crystal-vapor and source-vapor interfaces (change of the interface shape and location with time) are obtained. Super/under-saturation in the ampoule is determined and critical factors determining the 'contactless' growth conditions are identified and discussed. The relative importance of the ampoule dimensions and geometry, the furnace dimensions and its temperature, and the properties of the grown material are analyzed. The results of the simulations are compared with related experimental results on growth of CdTe, CdZnTe, ZnTe, PbTe, and PbSnTe crystals by this technique.

Potentiometric detection of chemical vapors using molecularly imprinted polymers as receptors

PubMed Central

Liang, Rongning; Chen, Lusi; Qin, Wei

2015-01-01

Ion-selective electrode (ISE) based potentiometric gas sensors have shown to be promising analytical tools for detection of chemical vapors. However, such sensors are only capable of detecting those vapors which can be converted into ionic species in solution. This paper describes for the first time a polymer membrane ISE based potentiometric sensing system for sensitive and selective determination of neutral vapors in the gas phase. A molecularly imprinted polymer (MIP) is incorporated into the ISE membrane and used as the receptor for selective adsorption of the analyte vapor from the gas phase into the sensing membrane phase. An indicator ion with a structure similar to that of the vapor molecule is employed to indicate the change in the MIP binding sites in the membrane induced by the molecular recognition of the vapor. The toluene vapor is used as a model and benzoic acid is chosen as its indicator. Coupled to an apparatus manifold for preparation of vapor samples, the proposed ISE can be utilized to determine volatile toluene in the gas phase and allows potentiometric detection down to parts per million levels. This work demonstrates the possibility of developing a general sensing principle for detection of neutral vapors using ISEs. PMID:26215887

Startup analysis for a high temperature gas loaded heat pipe

NASA Technical Reports Server (NTRS)

Sockol, P. M.

1973-01-01

A model for the rapid startup of a high-temperature gas-loaded heat pipe is presented. A two-dimensional diffusion analysis is used to determine the rate of energy transport by the vapor between the hot and cold zones of the pipe. The vapor transport rate is then incorporated in a simple thermal model of the startup of a radiation-cooled heat pipe. Numerical results for an argon-lithium system show that radial diffusion to the cold wall can produce large vapor flow rates during a rapid startup. The results also show that startup is not initiated until the vapor pressure p sub v in the hot zone reaches a precise value proportional to the initial gas pressure p sub i. Through proper choice of p sub i, startup can be delayed until p sub v is large enough to support a heat-transfer rate sufficient to overcome a thermal load on the heat pipe.

Nonlinear dynamics of confined thin liquid-vapor bilayer systems with phase change

NASA Astrophysics Data System (ADS)

Kanatani, Kentaro; Oron, Alexander

2011-03-01

We numerically investigate the nonlinear evolution of the interface of a thin liquid-vapor bilayer system confined by rigid horizontal walls from both below and above. The lateral variation of the vapor pressure arising from phase change is taken into account in the present analysis. When the liquid (vapor) is heated (cooled) and gravity acts toward the liquid, the deflection of the interface monotonically grows, leading to a rupture of the vapor layer, whereas nonruptured stationary states are found when the liquid (vapor) is cooled (heated) and gravity acts toward the vapor. In the latter case, vapor-flow-driven convective cells are found in the liquid phase in the stationary state. The average vapor pressure and interface temperature deviate from their equilibrium values once the interface departs from the flat equilibrium state. Thermocapillarity does not have a significant effect near the thermodynamic equilibrium, but becomes important if the system significantly deviates from it.

Water vapor diffusion membrane development

NASA Technical Reports Server (NTRS)

Tan, M. K.

1976-01-01

A total of 18 different membranes were procured, characterized, and tested in a modified bench-scale vapor diffusion water reclamation unit. Four membranes were selected for further studies involving membrane fouling. Emphasis was placed on the problem of flux decline due to membrane fouling. This is discussed in greater details under "Summary and Discussion on Membrane Fouling Studies" presented in pages 47-51. The system was also investigated for low temperature application on wash-water where the permeated water is not recovered but vented into space vacuum.

Speciation and quantification of vapor phases in soy biodiesel and waste cooking oil biodiesel.

PubMed

Peng, Chiung-Yu; Lan, Cheng-Hang; Dai, Yu-Tung

2006-12-01

This study characterizes the compositions of two biodiesel vapors, soy biodiesel and waste cooking oil biodiesel, to provide a comprehensive understanding of biodiesels. Vapor phases were sampled by purging oil vapors through thermal desorption tubes which were then analyzed by the thermal desorption/GC/MS system. The results show that the compounds of biodiesel vapors can be divided into four groups. They include methyl esters (the main biodiesel components), oxygenated chemicals, alkanes and alkenes, and aromatics. The first two chemical groups are only found in biodiesel vapors, not in the diesel vapor emissions. The percentages of mean concentrations for methyl esters, oxygenated chemicals, alkanes and alkenes, and aromatics are 66.1%, 22.8%, 4.8% and 6.4%, respectively for soy biodiesel, and 35.8%, 35.9%, 27.9% and 0.3%, respectively for waste cooking oil biodiesel at a temperature of 25+/-2 degrees C. These results show that biodiesels have fewer chemicals and lower concentrations in vapor phase than petroleum diesel, and the total emission rates are between one-sixteenth and one-sixth of that of diesel emission, corresponding to fuel evaporative emissions of loading losses of between 106 microg l(-1) and 283 microg l(-1). Although diesels generate more vapor phase emissions, biodiesels still generate considerable amount of vapor emissions, particularly the emissions from methyl esters and oxygenated chemicals. These two chemical groups are more reactive than alkanes and aromatics. Therefore, speciation and quantification of biodiesel vapor phases are important.

Fluid inclusions in minerals from the geothermal fields of Tuscany, Italy

USGS Publications Warehouse

Belkin, H.; de Vivo, B.; Gianelli, G.; Lattanzi, P.

1985-01-01

A reconnaissance study on fluid inclusions from the geothermal fields of Tuscany indicates that the hydrothermal minerals were formed by fluids which were, at least in part, boiling. Four types of aqueous inclusions were recognized: (A) two-phase (liquid + vapor) liquid rich, (B) two-phase (vapor + liquid) vapor rich, (C) polyphase hypersaline liquid rich and (D) three phase-H2O liquid + CO2 liquid + CO2-rich vapor. Freezing and heating microthermometric determinations are reported for 230 inclusions from samples from six wells. It is suggested that boiling of an originally homogeneous, moderately saline, CO2-bearing liquid phase produced a residual hypersaline brine and a CO2-rich vapor phase. There are indications of a temperature decrease in the geothermal field of Larderello, especially in its peripheral zones. ?? 1985.

Crystallization Experiments in the MgO-CO2-H2O system: Role of Amorphous Magnesium Carbonate Precursors in Magnesium Carbonate Hydrated Phases and Morphologies in Low Temperature Hydrothermal Fluids

NASA Astrophysics Data System (ADS)

Giampouras, Manolis; Garcia-Ruiz, Juan Manuel; Garrido, Carlos J.

2017-04-01

Numerous forms of hydrated or basic magnesium carbonates occur in the complex MgO-CO2-H2O system. Mineral saturation states from low temperature hydrothermal fluids in Semail Ophiolite (Oman), Prony Bay (New Caledonia) and Lost City hydrothermal field (mid-Atlantic ridge) strongly indicate the presence of magnesium hydroxy-carbonate hydrates (e.g. hydromagnesite) and magnesium hydroxides (brucite). Study of formation mechanisms and morphological features of minerals forming in the MgO-CO2-H2O system could give insights into serpentinization-driven, hydrothermal, alkaline environments, which are related to early Earth conditions. Temperature, hydration degree, pH and fluid composition are crucial factors regarding the formation, coexistence and transformation of such mineral phases. The rate of supersaturation, on the other hand, is a fundamental parameter to understand nucleation and crystal growth processes. All these parameters can be examined in a solution using different crystallization techniques. In the present study, we applied different crystallization techniques to synthesize and monitor the crystallization of Mg-bearing carbonates and hydroxides under abiotic conditions. Various crystallization techniques (counter-diffusion, vapor diffusion and unseeded solution mixing) were used to screen the formation conditions of each phase, transformation processes and structural development. Mineral and textural characterization of the different synthesized phases were carried out by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy coupled to dispersive energy spectroscopy (FE-SEM-EDS). Experimental investigation of the effect of pH level and silica content under variable reactant concentrations revealed the importance of Amorphous Magnesium Carbonate (AMC) in the formation of hydroxy-carbonate phases (hydromagnesite and dypingite). Micro-structural resemblance between AMC precursors and later stage crystalline phases highlights the critical role of internal molecule re-organization to form crystalline structures. Aggregation of AMC spherulites triggers biomimetic morphologies forming curling laminar structures and rings. The size and number of nesquehonite (MgCO3.3H2O) crystals are controlled by pH and Mg2+ ions at pH < 9. As pH increases, nesquehonite transforms to spherical, rosette-like dypingite and/or hydromagnesite. Crystallization experiments within silica gel impedes the normal growth of prismatic nesquehonite crystals and generates peculiar dendritic crystalline structures. Finally, vapor diffusion techniques resulted in synthesis of NH4+-bearing hydrated compounds after ammonium incorporation when [NH4+]/[Mg2+] ≥ 1 and ≥ 0.5M [NH4+]. Funding: We acknowledge funding from the People programme (Marie Curie Actions - ITN) of the European Union FP7 under REA Grant Agreement n˚ 608001.

Trends in polycyclic aromatic hydrocarbon concentrations in the great lakes atmosphere.

PubMed

Sun, Ping; Blanchard, Pierrette; Brice, Kenneth A; Hites, Ronald A

2006-10-15

Atmospheric polycyclic aromatic hydrocarbon (PAHs) concentrations were measured in both the vapor and particle phases at seven sites near the Great Lakes as a part of the Integrated Atmospheric Deposition Network. Lower molecular weight PAHs, including fluorene, phenanthrene, fluoranthrene, and pyrene, were dominant in the vapor phase, and higher molecular weight PAHs, including chrysene, benzo[a]pyrene, and coronene, were dominant in the particle phase. The highest PAH concentrations in both the vapor and particle phases were observed in Chicago followed by the semiurban site at Sturgeon Point, NY. The spatial difference of PAH concentrations can be explained by the local population density. Long-term decreasing trends of most PAH concentrations were observed in both the vapor and particle phases at Chicago, with half-lives ranging from 3-10 years in the vapor phase and 5-15 years in the particle phase. At Eagle Harbor, Sleeping Bear Dunes, and Sturgeon Point, total PAH concentrations in the vapor phase showed significant, but slow, long-term decreasing trends. At the Sturgeon Point site, which was impacted by a nearby city, particle-phase PAH concentrations also declined. However, most particle-phase PAH concentrations did not show significant long-term decreasing trends at the remote sites. Seasonal trends were also observed for particle-phase PAH concentrations, which were higher in the winter and lower in the summer.

PASSIVE/DIFFUSIVE SAMPLERS FOR PESTICIDES IN RESIDENTIAL INDOOR AIR

EPA Science Inventory

Pesticides applied indoors vaporize from treated surfaces (e.g., carpets and baseboards) resulting in elevated air concentrations that may persist for long periods after applications. Estimating long-term respiratory exposures to pesticide vapors in residential indoor environme...

Re-entrant phase behavior for systems with competition between phase separation and self-assembly

NASA Astrophysics Data System (ADS)

Reinhardt, Aleks; Williamson, Alexander J.; Doye, Jonathan P. K.; Carrete, Jesús; Varela, Luis M.; Louis, Ard A.

2011-03-01

In patchy particle systems where there is a competition between the self-assembly of finite clusters and liquid-vapor phase separation, re-entrant phase behavior can be observed, with the system passing from a monomeric vapor phase to a region of liquid-vapor phase coexistence and then to a vapor phase of clusters as the temperature is decreased at constant density. Here, we present a classical statistical mechanical approach to the determination of the complete phase diagram of such a system. We model the system as a van der Waals fluid, but one where the monomers can assemble into monodisperse clusters that have no attractive interactions with any of the other species. The resulting phase diagrams show a clear region of re-entrance. However, for the most physically reasonable parameter values of the model, this behavior is restricted to a certain range of density, with phase separation still persisting at high densities.

Transmitting and reflecting diffuser. [for ultraviolet light

NASA Technical Reports Server (NTRS)

Keafer, L. S., Jr.; Burcher, E. E.; Kopia, L. P. (Inventor)

1973-01-01

A near-Lambertian diffuser is described which transmits and reflects ultraviolet light. An ultraviolet grade fused silica substrate is coated with vaporized fuse silica. The coating thickness is controlled, one thickness causing ultraviolet light to diffuse and another thickness causing ultraviolet light to reflect a near Lambertian pattern.

Development of Nb{sub 3}Sn Cavity Vapor Diffusion Deposition System

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

Eremeev, Grigory V.; Macha, Kurt M.; Clemens, William A.

2014-02-01

Nb{sub 3}Sn is a BCS superconductors with the superconducting critical temperature higher than that of niobium, so theoretically it surpasses the limitations of niobium in RF fields. The feasibility of technology has been demonstrated at 1.5 GHz with Nb{sub 3}Sn vapor deposition technique at Wuppertal University. The benefit at these frequencies is more pronounced at 4.2 K, where Nb{sub 3}Sn coated cavities show RF resistances an order of magnitude lower than that of niobium. At Jefferson Lab we started the development of Nb{sub 3}Sn vapor diffusion deposition system within an R\\&D development program towards compact light sources. Here we presentmore » the current progress of the system development.« less

A Mass Diffusion Model for Dry Snow Utilizing a Fabric Tensor to Characterize Anisotropy

NASA Astrophysics Data System (ADS)

Shertzer, Richard H.; Adams, Edward E.

2018-03-01

A homogenization algorithm for randomly distributed microstructures is applied to develop a mass diffusion model for dry snow. Homogenization is a multiscale approach linking constituent behavior at the microscopic level—among ice and air—to the macroscopic material—snow. Principles of continuum mechanics at the microscopic scale describe water vapor diffusion across an ice grain's surface to the air-filled pore space. Volume averaging and a localization assumption scale up and down, respectively, between microscopic and macroscopic scales. The model yields a mass diffusivity expression at the macroscopic scale that is, in general, a second-order tensor parameterized by both bulk and microstructural variables. The model predicts a mass diffusivity of water vapor through snow that is less than that through air. Mass diffusivity is expected to decrease linearly with ice volume fraction. Potential anisotropy in snow's mass diffusivity is captured due to the tensor representation. The tensor is built from directional data assigned to specific, idealized microstructural features. Such anisotropy has been observed in the field and laboratories in snow morphologies of interest such as weak layers of depth hoar and near-surface facets.

49 CFR 179.400-19 - Valves and gages.

Code of Federal Regulations, 2014 CFR

2014-10-01

... control of vapor phase pressure, vapor phase venting, liquid transfer and liquid flow rates. All valves... within suitable protective housings. A liquid level gage and a vapor phase pressure gage must be provided... Liquid Tank Car Tanks and Seamless Steel Tanks (Classes DOT-113 and 107A) § 179.400-19 Valves and gages...

49 CFR 179.400-19 - Valves and gages.

Code of Federal Regulations, 2012 CFR

2012-10-01

... control of vapor phase pressure, vapor phase venting, liquid transfer and liquid flow rates. All valves... within suitable protective housings. A liquid level gage and a vapor phase pressure gage must be provided... Liquid Tank Car Tanks and Seamless Steel Tanks (Classes DOT-113 and 107A) § 179.400-19 Valves and gages...

49 CFR 179.400-19 - Valves and gages.

Code of Federal Regulations, 2013 CFR

2013-10-01

... control of vapor phase pressure, vapor phase venting, liquid transfer and liquid flow rates. All valves... within suitable protective housings. A liquid level gage and a vapor phase pressure gage must be provided... Liquid Tank Car Tanks and Seamless Steel Tanks (Classes DOT-113 and 107A) § 179.400-19 Valves and gages...

Effects of Gas-Phase Radiation and Detailed Kinetics on the Burning and Extinction of a Solid Fuel

NASA Technical Reports Server (NTRS)

Rhatigan, Jennifer L.

2001-01-01

This is the first attempt to analyze both radiation and detailed kinetics on the burning and extinction of a solid fuel in a stagnation-point diffusion flame. We present a detailed and comparatively accurate computational model of a solid fuel flame along with a quantitative study of the kinetics mechanism, radiation interactions, and the extinction limits of the flame. A detailed kinetics model for the burning of solid trioxane (a trimer of formaldehyde) is coupled with a narrowband radiation model, with carbon dioxide, carbon monoxide, and water vapor as the gas-phase participating media. The solution of the solid trioxane diffusion flame over the flammable regime is presented in some detail, as this is the first solution of a heterogeneous trioxane flame. We identify high-temperature and low-temperature reaction paths for the heterogeneous trioxane flame. We then compare the adiabatic solution to solutions that include Surface radiation only and gas-phase and surface radiation using a black surface model. The analysis includes discussion of detailed flame chemistry over the flammable regime and, in particular, at the low stretch extinction limit. We emphasize the low stretch regime of the radiatively participating flame, since this is the region representative of microgravity flames. When only surface radiation is included, two extinction limits exist (the blow-off limit, and the low stretch radiative limit), and the burning rate and maximum flame temperatures are lower, as expected. With the inclusion of surface and gas-phase radiation, results show that, while flame temperatures are lower, the burning rate of the trioxane diffusion flame may actually increase at low stretch rate due to radiative feedback from the flame to the surface.

Continuous Determination of High-Vapor Phase Concentrations of Tetrachloroethylene Using On-Line Mass Spectrometry

EPA Science Inventory

A method was developed to determine the vapor concentration of tetrachloroethylene (PCE) at and below its equilibrium vapor phase concentration, 168,000 μg/L (25°C). Vapor samples were drawn by vacuum into a six-port sampling valve and injected through a jet separator into an io...

Stand-off detection of vapor phase explosives by resonance enhanced Raman spectroscopy

NASA Astrophysics Data System (ADS)

Ehlerding, Anneli; Johansson, Ida; Wallin, Sara; Östmark, Henric

2010-10-01

Stand-off measurements on nitromethane (NM), 2,4-DNT and 2,4,6-TNT in vapor phase using resonance Raman spectroscopy have been performed. The Raman cross sections for NM, DNT and TNT in vapor phase have been measured in the wavelength range 210-300 nm under laboratory conditions, in order to estimate how large resonance enhancement factors can be achieved for these explosives. The measurements show that the signal is greatly enhanced, up to 250.000 times for 2,4-DNT and 60.000 times for 2,4,6-TNT compared to the non-resonant signal at 532 nm. For NM the resonance enhancement enabled realistic outdoor measurements in vapor phase at 13 m distance. This all indicate a potential for resonance Raman spectroscopy as a stand-off technique for detection of vapor phase explosives.

Interface Structure of MoO3 on Organic Semiconductors

PubMed Central

White, Robin T.; Thibau, Emmanuel S.; Lu, Zheng-Hong

2016-01-01

We have systematically studied interface structure formed by vapor-phase deposition of typical transition metal oxide MoO3 on organic semiconductors. Eight organic hole transport materials have been used in this study. Ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy are used to measure the evolution of the physical, chemical and electronic structure of the interfaces at various stages of MoO3 deposition on these organic semiconductor surfaces. For the interface physical structure, it is found that MoO3 diffuses into the underlying organic layer, exhibiting a trend of increasing diffusion with decreasing molecular molar mass. For the interface chemical structure, new carbon and molybdenum core-level states are observed, as a result of interfacial electron transfer from organic semiconductor to MoO3. For the interface electronic structure, energy level alignment is observed in agreement with the universal energy level alignment rule of molecules on metal oxides, despite deposition order inversion. PMID:26880185

CVD aluminiding process for producing a modified platinum aluminide bond coat for improved high temperature performance

NASA Technical Reports Server (NTRS)

Nagaraj, Bangalore A. (Inventor); Williams, Jeffrey L. (Inventor)

2003-01-01

A method of depositing by chemical vapor deposition a modified platinum aluminide diffusion coating onto a superalloy substrate comprising the steps of applying a layer of a platinum group metal to the superalloy substrate; passing an externally generated aluminum halide gas through an internal gas generator which is integral with a retort, the internal gas generator generating a modified halide gas; and co-depositing aluminum and modifier onto the superalloy substrate. In one form, the modified halide gas is hafnium chloride and the modifier is hafnium with the modified platinum aluminum bond coat comprising a single phase additive layer of platinum aluminide with at least about 0.5 percent hafnium by weight percent and about 1 to about 15 weight percent of hafnium in the boundary between a diffusion layer and the additive layer. The bond coat produced by this method is also claimed.

Protein-crystal growth experiment (planned)

NASA Technical Reports Server (NTRS)

Fujita, S.; Asano, K.; Hashitani, T.; Kitakohji, T.; Nemoto, H.; Kitamura, S.

1988-01-01

To evaluate the effectiveness of a microgravity environment on protein crystal growth, a system was developed using 5 cubic feet Get Away Special payload canister. In the experiment, protein (myoglobin) will be simultaneously crystallized from an aqueous solution in 16 crystallization units using three types of crystallization methods, i.e., batch, vapor diffusion, and free interface diffusion. Each unit has two compartments: one for the protein solution and the other for the ammonium sulfate solution. Compartments are separated by thick acrylic or thin stainless steel plates. Crystallization will be started by sliding out the plates, then will be periodically recorded up to 120 hours by a still camera. The temperature will be passively controlled by a phase transition thermal storage component and recorded in IC memory throughout the experiment. Microgravity environment can then be evaluated for protein crystal growth by comparing crystallization in space with that on Earth.

NOR-USA Scientific Traverse of East Antarctica: Science and Logistics on a Three-Month Expedition Across Antarctica's Farthest Frontier

NASA Technical Reports Server (NTRS)

Albert, Mary R.

2012-01-01

Dr. Albert's current research is centered on transfer processes in porous media, including air-snow exchange in the Polar Regions and in soils in temperate areas. Her research includes field measurements, laboratory experiments, and theoretical modeling. Mary conducts field and laboratory measurements of the physical properties of natural terrain surfaces, including permeability, microstructure, and thermal conductivity. Mary uses the measurements to examine the processes of diffusion and advection of heat, mass, and chemical transport through snow and other porous media. She has developed numerical models for investigation of a variety of problems, from interstitial transport to freezing of flowing liquids. These models include a two-dimensional finite element code for air flow with heat, water vapor, and chemical transport in porous media, several multidimensional codes for diffusive transfer, as well as a computational fluid dynamics code for analysis of turbulent water flow in moving-boundary phase change problems.

Joining of Silicon Carbide Through the Diffusion Bonding Approach

NASA Technical Reports Server (NTRS)

Halbig, Michael .; Singh, Mrityunjay

2009-01-01

In order for ceramics to be fully utilized as components for high-temperature and structural applications, joining and integration methods are needed. Such methods will allow for the fabrication the complex shapes and also allow for insertion of the ceramic component into a system that may have different adjacent materials. Monolithic silicon carbide (SiC) is a ceramic material of focus due to its high temperature strength and stability. Titanium foils were used as an interlayer to form diffusion bonds between chemical vapor deposited (CVD) SiC ceramics with the aid of hot pressing. The influence of such variables as interlayer thickness and processing time were investigated to see which conditions contributed to bonds that were well adhered and crack free. Optical microscopy, scanning electron microscopy, and electron microprobe analysis were used to characterize the bonds and to identify the reaction formed phases.

Photochemical oxidation of water and reduction of polyoxometalate anions at interfaces of water with ionic liquids or diethylether

PubMed Central

Bernardini, Gianluca; Wedd, Anthony G.; Zhao, Chuan; Bond, Alan M.

2012-01-01

Photoreduction of [P2W18O62]6-, [S2Mo18O62]4-, and [S2W18O62]4- polyoxometalate anions (POMs) and oxidation of water occurs when water–ionic liquid and water–diethylether interfaces are irradiated with white light (275–750 nm) or sunlight. The ionic liquids (ILs) employed were aprotic ([Bmim]X; Bmim = (1-butyl-3-methylimidazolium,X = BF4,PF6) and protic (DEAS = diethanolamine hydrogen sulphate; DEAP = diethanolamine hydrogen phosphate). Photochemical formation of reduced POMs at both thermodynamically stable and unstable water–IL interfaces led to their initial diffusion into the aqueous phase and subsequent extraction into the IL phase. The mass transport was monitored visually by color change and by steady-state voltammetry at microelectrodes placed near the interface and in the bulk solution phases. However, no diffusion into the organic phase was observed when [P2W18O62]6- was photo-reduced at the water–diethylether interface. In all cases, water acted as the electron donor to give the overall process: 4POM + 2H2O + hν → 4POM- + 4H+ + O2. However, more highly reduced POM species are likely to be generated as intermediates. The rate of diffusion of photo-generated POM- was dependent on the initial concentration of oxidized POM and the viscosity of the IL (or mixed phase system produced in cases in which the interface is thermodynamically unstable). In the water-DEAS system, the evolution of dioxygen was monitored in situ in the aqueous phase by using a Clark-type oxygen sensor. Differences in the structures of bulk and interfacial water are implicated in the activation of water. An analogous series of reactions occurred upon irradiation of solid POM salts in the presence of water vapor. PMID:22753501

Modeling and Uncertainty Quantification of Vapor Sorption and Diffusion in Heterogeneous Polymers

DOE PAGES

Sun, Yunwei; Harley, Stephen J.; Glascoe, Elizabeth A.

2015-08-13

A high-fidelity model of kinetic and equilibrium sorption and diffusion is developed and exercised. The gas-diffusion model is coupled with a triple-sorption mechanism: Henry’s law absorption, Langmuir adsorption, and pooling or clustering of molecules at higher partial pressures. Sorption experiments are conducted and span a range of relative humidities (0-95%) and temperatures (30-60°C). Kinetic and equilibrium sorption properties and effective diffusivity are determined by minimizing the absolute difference between measured and modeled uptakes. Uncertainty quantification and sensitivity analysis methods are described and exercised herein to demonstrate the capability of this modeling approach. Water uptake in silica-filled and unfilled poly(dimethylsiloxane) networksmore » is investigated; however, the model is versatile enough to be used with a wide range of materials and vapors.« less

Production of higher quality bio-oils by in-line esterification of pyrolysis vapor

DOEpatents

Hilten, Roger Norris; Das, Keshav; Kastner, James R; Bibens, Brian P

2014-12-02

The disclosure encompasses in-line reactive condensation processes via vapor phase esterification of bio-oil to decease reactive species concentration and water content in the oily phase of a two-phase oil, thereby increasing storage stability and heating value. Esterification of the bio-oil vapor occurs via the vapor phase contact and subsequent reaction of organic acids with ethanol during condensation results in the production of water and esters. The pyrolysis oil product can have an increased ester content and an increased stability when compared to a condensed pyrolysis oil product not treated with an atomized alcohol.

Vapor phase elemental sulfur amendment for sequestering mercury in contaminated soil

DOEpatents

Looney, Brian B.; Denham, Miles E.; Jackson, Dennis G.

2014-07-08

The process of treating elemental mercury within the soil is provided by introducing into the soil a heated vapor phase of elemental sulfur. As the vapor phase of elemental sulfur cools, sulfur is precipitated within the soil and then reacts with any elemental mercury thereby producing a reaction product that is less hazardous than elemental mercury.

Diffusive transfer to membranes as an effective interface between gel electrophoresis and mass spectrometry

NASA Astrophysics Data System (ADS)

Ogorzalek Loo, Rachel R.; Mitchell, Charles; Stevenson, Tracy I.; Loo, Joseph A.; Andrews, Philip C.

1997-12-01

Diffusive transfer was examined as a blotting method to transfer proteins from polyacrylamide gels to membranes for ultraviolet matrix-assisted laser desorption ionization (MALDI) mass spectrometry. The method is well-suited for transfers from isoelectric focusing (IEF) gels. Spectra have been obtained for 11 pmol of 66 kDa albumin loaded onto an IEF gel and subsequently blotted to polyethylene. Similarly, masses of intact carbonic anhydrase and hemoglobin were obtained from 14 and 20 pmol loadings. This methodology is also compatible with blotting high molecular weight proteins, as seen for 6 pmol of the 150 kDa monoclonal antibody anti-[beta]-galactosidase transferred to Goretex. Polypropylene, Teflon, Nafion and polyvinylidene difluoride (PVDF) also produced good spectra following diffusive transfer. Only analysis from PVDF required that the membrane be kept wet prior to application of matrix. Considerations in mass accuracy for analysis from large-area membranes with continuous extraction and delayed extraction were explored, as were remedies for surface charging. Vapor phase CNBr cleavage was applied to membrane-bound samples for peptide mapping.

Microgravity

NASA Image and Video Library

2004-04-15

The Commercial Vapor Diffusion Apparatus will be used to perform 128 individual crystal growth investigations for commercial and science research. These experiments will grow crystals of several different proteins, including HIV-1 Protease Inhibitor, Glycogen Phosphorylase A, and NAD Synthetase. The Commercial Vapor Diffusion Apparatus supports multiple commercial investigations within a controlled environment. The goal of the Commercial Protein Crystal Growth payload on STS-95 is to grow large, high-quality crystals of several different proteins of interest to industry, and to continue to refine the technology and procedures used in microgravity for this important commercial research.

Combined heat and mass transfer device for improving separation process

DOEpatents

Tran, Thanh Nhon

1999-01-01

A two-phase small channel heat exchange matrix simultaneously provides for heat transfer and mass transfer between the liquid and vapor phases of a multi-component mixture at a single, predetermined location within a separation column, significantly improving the thermodynamic efficiency of the separation process. The small channel heat exchange matrix is composed of a series of channels having a hydraulic diameter no greater than 5.0 millimeters for conducting a two-phase coolant. In operation, the matrix provides the liquid-vapor contacting surfaces within the separation column, such that heat and mass are transferred simultaneously between the liquid and vapor phases. The two-phase coolant allows for a uniform heat transfer coefficient to be maintained along the length of the channels and across the surface of the matrix. Preferably, a perforated, concave sheet connects each channel to an adjacent channel to facilitate the flow of the liquid and vapor phases within the column and to increase the liquid-vapor contacting surface area.

Combined heat and mass transfer device for improving separation process

DOEpatents

Tran, T.N.

1999-08-24

A two-phase small channel heat exchange matrix simultaneously provides for heat transfer and mass transfer between the liquid and vapor phases of a multi-component mixture at a single, predetermined location within a separation column, significantly improving the thermodynamic efficiency of the separation process. The small channel heat exchange matrix is composed of a series of channels having a hydraulic diameter no greater than 5.0 millimeters for conducting a two-phase coolant. In operation, the matrix provides the liquid-vapor contacting surfaces within the separation column, such that heat and mass are transferred simultaneously between the liquid and vapor phases. The two-phase coolant allows for a uniform heat transfer coefficient to be maintained along the length of the channels and across the surface of the matrix. Preferably, a perforated, concave sheet connects each channel to an adjacent channel to facilitate the flow of the liquid and vapor phases within the column and to increase the liquid-vapor contacting surface area. 12 figs.

Inhomogeneities in particle composition of single, levitated aerosol particles observed by Mie resonance spectroscopy

NASA Astrophysics Data System (ADS)

Krieger, Ulrich; Lienhard, Daniel; Bastelberger, Sandra; Steimer, Sarah

2014-05-01

Recent observations have indicated that organic aerosol particles in the atmosphere may exist in an amorphous semi-solid or even solid (i.e. glassy) state, e.g. [1]. The influence of highly viscous and glassy states on the timescale of aerosol particle equilibration with respect to water vapor have been investigated for some model systems of atmospheric aerosol, e.g. [2,3]. In particular, it has been shown that the kinetics of the water absorption/desorption process is controlled entirely by liquid-phase diffusion of water molecules for a highly viscous aerosol particle. A liquid phase diffusion model based on numerically solving the non-linear diffusion equation predicts strong internal gradients in water concentration when condensed phase diffusion impedes the water uptake from the gas phase [2]. Here we observe and quantify the internal concentration gradients in single, levitated, micron size aerosol particles of aqueous shikimic acid using elastic Mie resonance spectroscopy. A single, aqueous particle is levitated in an electro-dynamic balance (for details see [2]), dried for several days at room temperature, cooled to the target temperature and exposed to a rapid change in relative humidity. In addition to measuring the elastically backscattered light of a "white light" LED source and recording the full spectrum with a spectrograph as in [2], we use a tunable diode laser (TDL) to scan high resolution TE- and TM spectra. This combination allows observing various Mie resonance mode orders simultaneously. Since we perform the experiment at low temperatures and low humidities the changes in the Mie-spectra due to water uptake are sufficiently slow to resolve the kinetics. Experimental Mie resonance spectra are inverted to concentration profiles of water within the particle by applying the numerical diffusion model [2] in conjunction with Mie calculations of multilayered spheres [4]. [1] A. Virtanen et al. (2010): An amorphous solid state of biogenic secondary organic aerosol particles, Nature 467, 824-827. [2] B. Zobrist et al. (2011): Ultra-slow water diffusion in aqueous sucrose glasses, Phys. Chem. Chem. Phys. 13, 3514-3526. [3] D. L. Bones, J. P. Reid, D. M. Lienhard, and U. K. Krieger (2012): Comparing the mechanism of water condensation and evaporation in glassy aerosol, PNAS 109, 11613-11618. [4] O. Peña and U. Pal (2009): Scattering of electromagnetic radiation by a multilayered sphere, Comput. Phys. Commun. 180, 2348-2354.

Applying CLIPS to control of molecular beam epitaxy processing

NASA Technical Reports Server (NTRS)

Rabeau, Arthur A.; Bensaoula, Abdelhak; Jamison, Keith D.; Horton, Charles; Ignatiev, Alex; Glover, John R.

1990-01-01

A key element of U.S. industrial competitiveness in the 1990's will be the exploitation of advanced technologies which involve low-volume, high-profit manufacturing. The demands of such manufacture limit participation to a few major entities in the U.S. and elsewhere, and offset the lower manufacturing costs of other countries which have, for example, captured much of the consumer electronics market. One such technology is thin-film epitaxy, a technology which encompasses several techniques such as Molecular Beam Epitaxy (MBE), Chemical Beam Epitaxy (CBE), and Vapor-Phase Epitaxy (VPE). Molecular Beam Epitaxy (MBE) is a technology for creating a variety of electronic and electro-optical materials. Compared to standard microelectronic production techniques (including gaseous diffusion, ion implantation, and chemical vapor deposition), MBE is much more exact, though much slower. Although newer than the standard technologies, MBE is the technology of choice for fabrication of ultraprecise materials for cutting-edge microelectronic devices and for research into the properties of new materials.

Flame Radiation, Structure, and Scalar Properties in Microgravity Laminar Fires

NASA Technical Reports Server (NTRS)

Feikema, Douglas; Lim, Jongmook; Sivathanu, Yudaya

2007-01-01

Results from microgravity combustion experiments conducted in the Zero Gravity Research Facility (ZGF) 5.18 second drop facility are reported. The results quantify flame radiation, structure, and scalar properties during the early phase of a microgravity fire. Emission mid-infrared spectroscopy measurements have been completed to quantitatively determine the flame temperature, water and carbon dioxide vapor concentrations, radiative emissive power, and soot concentrations in microgravity laminar methane/air, ethylene/nitrogen/air and ethylene/air jet flames. The measured peak mole fractions for water vapor and carbon dioxide are found to be in agreement with state relationship predictions for hydrocarbon/air combustion. The ethylene/air laminar flame conditions are similar to previously reported results including those from the flight project, Laminar Soot Processes (LSP). Soot concentrations and gas temperatures are in reasonable agreement with similar results available in the literature. However, soot concentrations and flame structure dramatically change in long-duration microgravity laminar diffusion flames as demonstrated in this report.

Apparatus for diffusion-gap thermal desalination

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

Lowenstein, Andrew

A thermal distillation apparatus including evaporation surfaces that are wetted with a solution, and from which at least some of the volatile solvent contained in the solution evaporates, condensers having an external surface in close proximity to, but not touching, a corresponding one of the one or more evaporation surfaces, and on which vapors of the solvent condense, releasing thermal energy that heats a flow of the solution moving upward within the condensers, spacers that prevent contact between the evaporating surfaces and the condensers, wherein spaces between the evaporating surfaces and the condensers are filled with a gaseous mixture composedmore » of solvent vapor and one or more non-condensable gases, and except for diffusion of the solvent vapor relative to the non-condensable gases, the gaseous mixture is stationary.« less

Kinetic Monte Carlo Simulations of Oxygen Diffusion in Environmental Barrier Coating Materials

NASA Technical Reports Server (NTRS)

Good, Brian S.

2017-01-01

Ceramic Matrix Composite (CMC) materials are of interest for use in next-generation turbine engine components, offering a number of significant advantages, including reduced weight and high operating temperatures. However, in the hot environment in which such components operate, the presence of water vapor can lead to corrosion and recession, limiting the useful life of the components. Such degradation can be reduced through the use of Environmental Barrier Coatings (EBCs) that limit the amount of oxygen and water vapor reaching the component. Candidate EBC materials include Yttrium and Ytterbium silicates. In this work we present results of kinetic Monte Carlo (kMC) simulations of oxygen diffusion, via the vacancy mechanism, in Yttrium and Ytterbium disilicates, along with a brief discussion of interstitial diffusion.

Direct methanol fuel cell and system

DOEpatents

Wilson, Mahlon S.

2004-10-26

A fuel cell having an anode and a cathode and a polymer electrolyte membrane located between anode and cathode gas diffusion backings uses a methanol vapor fuel supply. A permeable polymer electrolyte membrane having a permeability effective to sustain a carbon dioxide flux equivalent to at least 10 mA/cm.sup.2 provides for removal of carbon dioxide produced at the anode by reaction of methanol with water. Another aspect of the present invention includes a superabsorpent polymer material placed in proximity to the anode gas diffusion backing to hold liquid methanol or liquid methanol solution without wetting the anode gas diffusion backing so that methanol vapor from the liquid methanol or liquid methanol-water solution is supplied to the membrane.

Gas/Particle Partitioning of Organic Acids and Organic Aerosols in a Ponderosa Pine Forest in Colorado during BEACHON-RoMBAS 2011

NASA Astrophysics Data System (ADS)

Jimenez, J. L.; Yatavelli, L.; Stark, H.; Hayes, P. L.; Campuzano-Jost, P.; Thompson, S.; Kimmel, J. R.; Day, D. A.; Cubison, M. J.; Thornton, J. A.; Jayne, J.; Worsnop, D. R.

2012-12-01

The Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics & Nitrogen - Rocky Mountain Biogenic Aerosol Study (BEACHON-RoMBAS) took place at Manitou Forest, CO, during July-Aug. 2011. Gas and particle-phase organic acids were analyzed in real time using a micro-orifice volatilization impactor chemical ionization high-resolution time-of-flight mass spectrometer (MOVI-HRToF-CIMS; Yatavelli et al., AS&T 2012; Yatavelli & Thornton, AS&T 2010) with acetate as the reagent ion. During the gas sampling phase (when the MOVI was at room temperature) aerosol was collected on the MOVI impactor, and was subsequently thermally desorbed over 10 min. under nitrogen, allowing the collection of temperature-programmed thermal desorption (TPTD) mass spectra of particle-phase species. The high resolution of the instrument allows the determination of the elemental composition of most detected ions. Positive Matrix Factorization (PMF) is shown to be very useful to quantify the CIMS backgrounds during the different phases of operation. Two methods were used to estimate the volatility of the detected species. First, the fraction of each species in the particle phase (Fp) vs carbon number was found to approximately follow partitioning theory, both for the alkanoic acids and also for the total acid signal, after accounting for the effect of the oxidation state on vapor pressure. Fp was found to respond on timescales of ~1 h to changes in ambient temperature, indicating that diffusion limitations to evaporation are not major for the aerosol at this site. Preliminary results suggest that Fp depends more strongly on vapor pressure and temperature than on RH, suggesting preferential partitioning for the organic phase rather than the water phase. Secondly, the volatility of individual or groups of acids can be quantified based on the TPTD signal based on calibration with multiple acids of known vapor pressure at concentrations similar to ambient, analogous to the methods of Chattopadhyay and Ziemann (Anal. Chem. 2001) and Faulhaber et al. (AMT, 2009) for other TPTD techniques. The log of the vapor pressure of each compound is shown to be strongly related to the inverse of the desorption temperature for standards spanning 6 orders of magnitude in vapor pressure. A shift in the calibration curve when compared to other techniques is attributed to differences in time available for evaporation and physical arrangement of the particles on the aerosol collection surface. A method to remove the broadening of the transfer function is used to produce more accurate volatility distributions ("basis sets", VBS). Results of both methods are compared, also focusing on key species such as pinic, pinonic, tricarballylic, and oxalic acids. The effects of gas-phase adsorption on the thermogram signal are estimated based on tests sampling through a teflon filter. In addition, an Aerodyne Aerosol Mass Spectrometer (AMS) sampled ambient air and also air that had been thermally denuded at different temperatures. The method of Faulhaber et al is used to derive an estimated volatility distribution for the total organic aerosol and the organic acid fraction (based on m/z 44, CO2+), which are compared to the CIMS results.

A simplified counter diffusion method combined with a 1D simulation program for optimizing crystallization conditions.

PubMed

Tanaka, Hiroaki; Inaka, Koji; Sugiyama, Shigeru; Takahashi, Sachiko; Sano, Satoshi; Sato, Masaru; Yoshitomi, Susumu

2004-01-01

We developed a new protein crystallization method has been developed using a simplified counter-diffusion method for optimizing crystallization condition. It is composed of only a single capillary, the gel in the silicon tube and the screw-top test tube, which are readily available in the laboratory. The one capillary can continuously scan a wide range of crystallization conditions (combination of the concentrations of the precipitant and the protein) unless crystallization occurs, which means that it corresponds to many drops in the vapor-diffusion method. The amount of the precipitant and the protein solutions can be much less than in conventional methods. In this study, lysozyme and alpha-amylase were used as model proteins for demonstrating the efficiency of this method. In addition, one-dimensional (1-D) simulations of the crystal growth were performed based on the 1-D diffusion model. The optimized conditions can be applied to the initial crystallization conditions for both other counter-diffusion methods with the Granada Crystallization Box (GCB) and for the vapor-diffusion method after some modification.

Sorption and modeling of mass transfer of toxic chemical vapors in activated-carbon fiber-cloth adsorbers

USGS Publications Warehouse

Lordgooei, M.; Sagen, J.; Rood, M.J.; Rostam-Abadi, M.

1998-01-01

A new activated-carbon fiber-cloth (ACFC) adsorber coupled with an electrothermal regenerator and a cryogenic condenser was designed and developed to efficiently capture and recover toxic chemical vapors (TCVs) from simulated industrial gas streams. The system was characterized for adsorption by ACFC, electrothermal desorption, and cryogenic condensation to separate acetone and methyl ethyl ketone from gas streams. Adsorption dynamics are numerically modeled to predict system characteristics during scale-up and optimization of the process in the future. The model requires diffusivities of TCVs into an activated-carbon fiber (ACF) as an input. Effective diffusivities of TCVs into ACFs were modeled as a function of temperature, concentration, and pore size distribution. Effective diffusivities for acetone at 65 ??C and 30-60 ppmv were measured using a chromatography method. The energy factor for surface diffusion was determined from comparison between the experimental and modeled effective diffusivities. The modeled effective diffusivities were used in a dispersive computational model to predict mass transfer zones of TCVs in fixed beds of ACFC under realistic conditions for industrial applications.

Ultra-fast vapor generation by a graphene nano-ratchet: a theoretical and simulation study.

PubMed

Ding, Hongru; Peng, Guilong; Mo, Shenqiu; Ma, Dengke; Sharshir, Swellam Wafa; Yang, Nuo

2017-12-14

Vapor generation is of prime importance for a broad range of applications: domestic water heating, desalination and wastewater treatment, etc. However, slow and inefficient evaporation limits its development. In this study, a nano-ratchet, a multilayer graphene with cone-shaped nanopores (MGCN), to accelerate vapor generation has been proposed. By performing molecular dynamics simulation, we found that air molecules were spontaneously transported across MGCN and resulted in a remarkable pressure difference, 21 kPa, between the two sides of MGCN. We studied the dependence of the pressure difference on the ambient temperature and geometry of MGCN in detail. Through further analysis of the diffusive transport, we found that pressure difference depended on the competition between ratchet transport and Knudsen diffusion and it was further found that ratchet transport is dominant. The significant pressure difference could lead to a 15-fold or greater enhancement of vapor generation, which shows the wide applications of this nano-ratchet.

Effect of polyethyleneimine modified graphene on the mechanical and water vapor barrier properties of methyl cellulose composite films.

PubMed

Liu, Hongyu; Liu, Cuiyun; Peng, Shuge; Pan, Bingli; Lu, Chang

2018-02-15

A series of novel methyl cellulose (MC) composite films were prepared using polyethyleneimine reduced graphene oxide (PEI-RGO) as an effective filler for water vapor barrier application. The as-prepared PEI-RGO/MC composites were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, tensile test and scanning electron microscopy. The experimental and theoretical results exhibited that PEI-RGO was uniformly dispersed in the MC matrix without aggregation and formed an aligned dispersion. The addition of PEI-RGO resulted in an enhanced surface hydrophobicity and a tortuous diffusion pathway for water molecules. Water vapor permeability of PEI-RGO/MC with loading of 3.0% of surface modified graphene was as low as 5.98×10 -11 gmm -2 s -1 Pa -1 . The synergistic effects of enhanced surface hydrophobicity and tortuous diffusion pathway were accounted for the improved water vapor barrier performance of the PEI-RGO/MC composite films. Copyright © 2017 Elsevier Ltd. All rights reserved.

Differential water sorption studies on Kevlar 49 and As-polymerized poly(p-phenylene terephthalamide): determination of water transport properties.

PubMed

Mooney, Damian A; MacElroy, J M Don

2007-11-06

Water vapor sorption experiments have been conducted on Kevlar 49 at 30 degrees C over a range of water vapor pressures in 0-90% of saturation and on the as-polymerized form of the material at 30, 45, and 60 degrees C over a series of water vapor pressures of 0-60%, 0-25%, and 0-15%, respectively. For each of the differential steps in water vapor pressure, dynamic uptake curves were generated and analyzed according to a number of different mathematical models, including Fickian, Coaxial cylindrical, and intercalation models. The intercalation model was demonstrated to be the most successful model and considered two time-scales involved in the diffusion process, i.e., a penetrant-diffusive time-scale and a polymer-local-matrix-relaxation time-scale. The success of this model reinforces previously reported adsorption and desorption isotherms which suggested that water may penetrate into the surface layers of the polymer crystallite through a process known as intercalation.

Stability limit of liquid water in metastable equilibrium with subsaturated vapors.

PubMed

Wheeler, Tobias D; Stroock, Abraham D

2009-07-07

A pure liquid can reach metastable equilibrium with its subsaturated vapor across an appropriate membrane. This situation is analogous to osmotic equilibrium: the reduced chemical potential of the dilute phase (the subsaturated vapor) is compensated by a difference in pressure between the phases. To equilibrate with subsaturated vapor, the liquid phase assumes a pressure that is lower than its standard vapor pressure, such that the liquid phase is metastable with respect to the vapor phase. For sufficiently subsaturated vapors, the liquid phase can even assume negative pressures. The appropriate membrane for this metastable equilibrium must provide the necessary mechanical support to sustain the difference in pressure between the two phases, limit nonhomogeneous mechanisms of cavitation, and resist the entry of the dilutant (gases) into the pure phase (liquid). In this article, we present a study of the limit of stability of liquid water--the degree of subsaturation at which the liquid cavitates--in this metastable state within microscale voids embedded in hydrogel membranes. We refer to these structures as vapor-coupled voids (VCVs). In these VCVs, we observed that liquid water cavitated when placed in equilibrium with vapors of activity aw,vapair

Development of an Advanced Computational Model for OMCVD of Indium Nitride

NASA Technical Reports Server (NTRS)

Cardelino, Carlos A.; Moore, Craig E.; Cardelino, Beatriz H.; Zhou, Ning; Lowry, Sam; Krishnan, Anantha; Frazier, Donald O.; Bachmann, Klaus J.

1999-01-01

An advanced computational model is being developed to predict the formation of indium nitride (InN) film from the reaction of trimethylindium (In(CH3)3) with ammonia (NH3). The components are introduced into the reactor in the gas phase within a background of molecular nitrogen (N2). Organometallic chemical vapor deposition occurs on a heated sapphire surface. The model simulates heat and mass transport with gas and surface chemistry under steady state and pulsed conditions. The development and validation of an accurate model for the interactions between the diffusion of gas phase species and surface kinetics is essential to enable the regulation of the process in order to produce a low defect material. The validation of the model will be performed in concert with a NASA-North Carolina State University project.

Liquid-liquid diffusion crystallization improves the X-ray diffraction of EndoS, an endo-β-N-acetylglucosaminidase from Streptococcus pyogenes with activity on human IgG.

PubMed

Trastoy, Beatriz; Lomino, Joseph V; Wang, Lai Xi; Sundberg, Eric J

2013-12-01

Endoglycosidase S (EndoS) is an enzyme secreted by Streptococcus pyogenes that specifically hydrolyzes the β-1,4-di-N-acetylchitobiose core glycan on immunoglobulin G (IgG) antibodies. One of the most common human pathogens and the cause of group A streptococcal infections, S. pyogenes secretes EndoS in order to evade the host immune system by rendering IgG effector mechanisms dysfunctional. On account of its specificity for IgG, EndoS has also been used extensively for chemoenzymatic synthesis of homogeneous IgG glycoprotein preparations and is being developed as a novel therapeutic for a wide range of autoimmune diseases. The structural basis of its enzymatic activity and substrate specificity, however, remains unknown. Here, the purification and crystallization of EndoS are reported. Using traditional hanging-drop and sitting-drop vapor-diffusion crystallization, crystals of EndoS were grown that diffracted to a maximum of 3.5 Å resolution but suffered from severe anisotropy, the data from which could only be reasonably processed to 7.5 Å resolution. When EndoS was crystallized by liquid-liquid diffusion, it was possible to grow crystals with a different space group to those obtained by vapor diffusion. Crystals of wild-type endoglycosidase and glycosynthase constructs of EndoS grown by liquid-liquid diffusion diffracted to 2.6 and 1.9 Å resolution, respectively, with a greatly diminished anisotropy. Despite extensive efforts, the failure to reproduce these liquid-liquid diffusion-grown crystals by vapor diffusion suggests that these crystallization methods each sample a distinct crystallization space.

Moving beyond the limits of mass transport in liquid absorbent microfilms through the implementation of surface-induced vortices

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

Bigham, S; Yu, DZ; Chugh, D

2014-02-01

The slow diffusion of an absorbate molecule into an absorbent often makes the absorption process a rate-limiting step in many applications. In cases involving an absorbate with a high heat of phase change, such as water absorption into a LiBr (lithium bromide) solution, the absorption rate is further slowed due to significant heating of the absorbent. Recently, it has been demonstrated that constraining a LiBr solution film by a hydrophobic porous structure enables manipulation of the solution flow thermohydraulic characteristics. Here, it is shown that mass transport mode in a constrained laminar solution flow can be changed from diffusive tomore » advective. This change in mode is accomplished through stretching and folding the laminar streamlines within the solution film via the implementation of micro-scale features on the flow channel surface. The process induces vortices within the solution film, which continuously bring concentrated solution from the bottom and middle of the solution channel to its interface with the vapor phase, thus leading to a significant enhancement in the absorption rate. The detailed physics of the involved transport processes is elucidated using the LBM (Lattice Boltzmann Method). Published by Elsevier Ltd.« less

Trends in polycyclic aromatic hydrocarbon concentrations in the Great Lakes atmosphere

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

Ping Sun; Pierrette Blanchard; Kenneth A. Brice

2006-10-15

Atmospheric polycyclic aromatic hydrocarbon (PAHs) concentrations were measured in both the vapor and particle phases at seven sites near the Great Lakes as a part of the Integrated Atmospheric Deposition Network. Lower molecular weight PAHs, including fluorene, phenanthrene, fluoranthrene, and pyrene, were dominant in the vapor phase, and higher molecular weight PAHs, including chrysene, benzo(a)pyrene, and coronene, were dominant in the particle phase. The highest PAH concentrations in both the vapor and particle phases were observed in Chicago followed by the semiurban site at Sturgeon Point, NY. The major sources of PAHs in and around Chicago are vehicle emissions, coalmore » and natural gas combustion, and coke production. The spatial difference of PAH concentrations can be explained by the local population density. Long-term decreasing trends of most PAH concentrations were observed in both the vapor and particle phases at Chicago, with half-lives ranging from 3-10 years in the vapor phase and 5-15 years in the particle phase. At Eagle Harbor, Sleeping Bear Dunes, and Sturgeon Point, total PAH concentrations in the vapor phase showed significant, but slow, long-term decreasing trends. At the Sturgeon Point site, which was impacted by a nearby city, particle-phase PAH concentrations also declined. However, most particle-phase PAH concentrations did not show significant long-term decreasing trends at the remote sites. Seasonal trends were also observed for particle-phase PAH concentrations, which were higher in the winter and lower in the summer. 36 refs., 4 figs., 1 tab.« less

Method and turbine for extracting kinetic energy from a stream of two-phase fluid

NASA Technical Reports Server (NTRS)

Elliott, D. G. (Inventor)

1979-01-01

An axial flow separator turbine is described which includes a number of nozzles for delivering streams of a two-phase fluid along linear paths. A phase separator which responsively separates the vapor and liquid is characterized by concentrically related annuli supported for rotation within the paths. The separator has endless channels for confining the liquid under the influence of centrifugal forces. A vapor turbine fan extracts kinetic energy from the liquid. Angular momentum of both the liquid phase and the vapor phase of the fluid is converted to torque.

Studies on Aspirin Crystals Generated by a Modified Vapor Diffusion Method.

PubMed

Mittal, Amit; Malhotra, Deepak; Jain, Preeti; Kalia, Anupama; Shunmugaperumal, Tamilvanan

2016-08-01

The objectives of the current investigation were (1) to study the influence of selected two different non-solvents (diethylether and dichloromethane) on the drug crystal formation of a model drug, aspirin (ASP-I) by the modified vapor diffusion method and (2) to characterize and compare the generated crystals (ASP-II and ASP-III) using different analytical techniques with that of unprocessed ASP-I. When compared to the classical vapor diffusion method which consumes about 15 days to generate drug crystals, the modified method needs only 12 h to get the same. Fourier transform-infrared spectroscopy (FT-IR) reveals that the internal structures of ASP-II and ASP-III crystals were identical when compared with ASP-I. Although the drug crystals showed a close similarity in X-ray diffraction patterns, the difference in the relative intensities of some of the diffraction peaks (especially at 2θ values of around 7.7 and 15.5) could be attributed to the crystal habit or crystal size modification. Similarly, the differential scanning calorimetry (DSC) study speculates that only the crystal habit modifications might occur but without involving any change in internal structure of the generated drug polymorphic form I. This is further substantiated from the scanning electron microscopy (SEM) pictures that indicated the formation of platy shape for the ASP-II crystals and needle shape for the ASP-III crystals. In addition, the observed slow dissolution of ASP crystals should indicate polymorph form I formation. Thus, the modified vapor diffusion method could routinely be used to screen and legally secure all possible forms of other drug entities too.

Two-phase thermodynamic model for efficient and accurate absolute entropy of water from molecular dynamics simulations.

PubMed

Lin, Shiang-Tai; Maiti, Prabal K; Goddard, William A

2010-06-24

Presented here is the two-phase thermodynamic (2PT) model for the calculation of energy and entropy of molecular fluids from the trajectory of molecular dynamics (MD) simulations. In this method, the density of state (DoS) functions (including the normal modes of translation, rotation, and intramolecular vibration motions) are determined from the Fourier transform of the corresponding velocity autocorrelation functions. A fluidicity parameter (f), extracted from the thermodynamic state of the system derived from the same MD, is used to partition the translation and rotation modes into a diffusive, gas-like component (with 3Nf degrees of freedom) and a nondiffusive, solid-like component. The thermodynamic properties, including the absolute value of entropy, are then obtained by applying quantum statistics to the solid component and applying hard sphere/rigid rotor thermodynamics to the gas component. The 2PT method produces exact thermodynamic properties of the system in two limiting states: the nondiffusive solid state (where the fluidicity is zero) and the ideal gas state (where the fluidicity becomes unity). We examine the 2PT entropy for various water models (F3C, SPC, SPC/E, TIP3P, and TIP4P-Ew) at ambient conditions and find good agreement with literature results obtained based on other simulation techniques. We also validate the entropy of water in the liquid and vapor phases along the vapor-liquid equilibrium curve from the triple point to the critical point. We show that this method produces converged liquid phase entropy in tens of picoseconds, making it an efficient means for extracting thermodynamic properties from MD simulations.

Environmentally Resistant Mo-Si-B-Based Coatings

NASA Astrophysics Data System (ADS)

Perepezko, J. H.; Sossaman, T. A.; Taylor, M.

2017-06-01

High-temperature applications have demonstrated aluminide-coated nickel-base superalloys to be remarkably effective, but are reaching their service limit. Alternate materials such as refractory (e.g., W, Mo) silicide alloys and SiC composites are being considered to extend high temperature capability, but the silica surfaces on these materials require coatings for enhanced environmental resistance. This can be accomplished with a Mo-Si-B-based coating that is deposited by a spray deposition of Mo followed by a chemical vapor deposition of Si and B by pack cementation to develop an aluminoborosilica surface. Oxidation of the as-deposited (Si + B)-pack coatings proceeds with partial consumption of the initial MoSi2 forming amorphous silica. This Si depletion leads to formation of a B-saturated Mo5Si3 (T1) phase. Reactions between the Mo and the B rich phases develop an underlying Mo5SiB2 (T2) layer. The T1 phase saturated with B has robust oxidation resistance, and the Si depletion is prevented by the underlying diffusion barrier (T2). Further, due to the natural phase transformation characteristics of the Mo-Si-B system, cracks or scratches to the outer silica and T1 layers can be repaired from the Si and B reservoirs of T2 + MoB layer to yield a self-healing characteristic. Mo-Si-B-based coatings demonstrate robust performance up to at least 1700 °C not only to the rigors of elevated temperature oxidation, but also to CMAS attack, hot corrosion attack, water vapor and thermal cycling.

PREDICTION OF THE VAPOR PRESSURE, BOILING POINT, HEAT OF VAPORIZATION AND DIFFUSION COEFFICIENT OF ORGANIC COMPOUNDS

EPA Science Inventory

The prototype computer program SPARC has been under development for several years to estimate physical properties and chemical reactivity parameters of organic compounds strictly from molecular structure. SPARC solute-solute physical process models have been developed and tested...

Microgravity nucleation and particle coagulation experiments support

NASA Technical Reports Server (NTRS)

Lilleleht, L. U.; Lass, T. J.

1987-01-01

A hollow sphere model is developed to predict the range of supersaturation ratio values for refractory metal vapors in a proposed experimental nucleation apparatus. Since the experiments are to be carried out in a microgravity environment, the model neglects the effects of convection and assumes that the only transfer of vapors through an inert gas atmosphere is by conduction and molecular diffusion. A consistent set of physical properties data is assembled for the various candidate metals and inert ambient gases expected to be used in the nucleation experiments. Transient partial pressure profiles are computed for the diffusing refractory species for two possible temperature distributions. The supersaturation ratio values from both candidate temperature profiles are compared with previously obtained experimetnal data on a silver-hydrogen system. The model is used to simulate the diffusion of magnesium vapor through argon and other inert gas atmospheres over ranges of initial and boundary conditions. These results identify different combinations of design and operating parameters which are liekly to produce supersaturation ratio values high enough to induce homogeneous nucleation in the apparatus being designed for the microgravity nucleation experiments.

Byproduct-free mass production of compound semiconductor nanowires: zinc phosphide

NASA Astrophysics Data System (ADS)

Chen, Yixi; Polinnaya, Rakesh; Vaddiraju, Sreeram

2018-05-01

A method for the mass production of compound semiconductor nanowires that involves the direct reaction of component elements in a chemical vapor deposition chamber (CVD) is presented. This method results in nanowires, without the associated production of any other byproducts such as nanoparticles or three-dimensional (3D) bulk crystals. Furthermore, no unreacted reactants remain mixed with the nanowire product in this method. This byproduct-free nanowire production thus circumvents the need to tediously purify and collect nanowires from a mixture of products/reactants after their synthesis. Demonstration made using zinc phosphide (Zn3P2) material system as an example indicated that the direct reaction of zinc microparticles with phosphorus supplied via the vapor phase results in the production of gram quantities of nanowires. To enhance thermal transport and achieve the complete reaction of zinc microparticles, while simultaneously ensuring that the microparticles do not agglomerate into macroscale zinc particles and partly remain unreacted (owing to diffusion limitations), pellets composed of mixtures of zinc and a sacrificial salt, NH4Cl, were employed as the starting material. The sublimation by decomposition of NH4Cl in the early stages of the reaction leaves a highly porous pellet of zinc composed of only zinc microparticles, which allows for inward diffusion of phosphorus/outward diffusion of zinc and the complete conversion of zinc into Zn3P2 nanowires. NH4Cl also aids in removal of any native oxide layer present on the zinc microparticles that may prevent their reaction with phosphorus. This method may be used to mass produce many other nanowires in a byproduct-free manner, besides Zn3P2.

Vapor phase pyrolysis

NASA Technical Reports Server (NTRS)

Steurer, Wolfgang

1992-01-01

The vapor phase pyrolysis process is designed exclusively for the lunar production of oxygen. In this concept, granulated raw material (soil) that consists almost entirely of metal oxides is vaporized and the vapor is raised to a temperature where it dissociates into suboxides and free oxygen. Rapid cooling of the dissociated vapor to a discrete temperature causes condensation of the suboxides, while the oxygen remains essentially intact and can be collected downstream. The gas flow path and flow rate are maintained at an optimum level by control of the pressure differential between the vaporization region and the oxygen collection system with the aid of the environmental vacuum.

A numerical analysis of high-temperature heat pipe startup from the frozen state

NASA Technical Reports Server (NTRS)

Cao, Y.; Faghri, A.

1993-01-01

Continuum and rarefied vapor flows co-exist along the heat pipe length for most of the startup period. A two-region model is proposed in which the vapor flow in the continuum region is modeled by the compressible Navier-Stokes equations, and the vapor flow in the rarefied region is simulated by a self-diffusion model. The two vapor regions are linked with appropriate boundary conditions, and heat pipe wail, wick, and vapor flow are solved as a conjugate problem. The numerical solutions for the entire heat pipe startup process from the frozen state are compared with the corresponding experimental data with good agreement.

Tritium Plume Dynamics in the Shallow Unsaturated Zone Adjacent to an Arid Waste Disposal Facility

NASA Astrophysics Data System (ADS)

Maples, S.; Andraski, B. J.; Stonestrom, D. A.; Cooper, C. A.; Michel, R. L.; Pohll, G. M.

2012-12-01

Previous studies at the U.S. Geological Survey's Amargosa Desert Research Site (ADRS) in southern Nevada have documented two plumes of tritiated water-vapor (3HHOg) adjacent to a closed, commercial low-level radioactive waste disposal facility. Wastes were disposed on-site from 1962-92. Tritium has moved long distances (> 400 m) through a shallow (1-2-m depth) dry gravelly layer—orders of magnitude further than anticipated by standard transport models. Geostatistical methods, spatial moment analyses and tritium flux calculations were applied to assess shallow plume dynamics. A grid-based plant-water sampling method was utilized to infer detailed, field-scale 3HHOg concentrations at 5-yr intervals during 2001-11. Results indicate that gravel-layer 3HHOg mass diminished faster than would be expected from radioactive decay (~70% in 10 yr). Both plumes exhibited center-of-mass stability, suggesting that bulk-plume movement is minimal during the period of study. Nonetheless, evidence of localized lateral advancement along some margins, combined with increases in the spatial covariance of concentration distribution, indicates intra-plume mass redistribution is ongoing. Previous studies have recognized that vertical movement of tritiated water from sub-root-zone gravel into the root-zone contributes to atmospheric release via evapotranspiration. Estimates of lateral and vertical tritium fluxes during the study period indicate (1) vertical tritiated water fluxes were dominated by diffusive-vapor fluxes (> 90%), and (2) vertical diffusive-vapor fluxes were roughly an order of magnitude greater than lateral diffusive-vapor fluxes. This behavior highlights the importance of the atmosphere as a tritium sink. Estimates of cumulative vertical diffusive-vapor flux and radioactive decay with time were comparable to observed declines in total shallow plume mass with time. This suggests observed changes in plume mass may (1) be attributed, in considerable part, to these removal mechanisms, and (2) appreciable input from the adjacent disposal facility is not occurring at this time.

In situ growth of ceramic quantum dots in polyaniline host via water vapor flow diffusion as potential electrode materials for energy applications

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

Mombrú, Dominique; Romero, Mariano, E-mail: mromero@fq.edu.uy; Faccio, Ricardo, E-mail: rfaccio@fq.edu.uy

In situ preparation of polyaniline-ceramic nanocomposites has recently demonstrated that the electrical properties are highly improved with respect to the typical ex situ preparations. In this report, we present for the first time, to the best of our knowledge, the in situ growth of titanium oxide quantum dots in polyaniline host via water vapor flow diffusion as an easily adaptable route to prepare other ceramic-polymer nanocomposites. The main relevance of this method is the possibility to prepare ceramic quantum dots from alkoxide precursors using water vapor flow into any hydrophobic polymer host and to achieve good homogeneity and size-control. Inmore » addition, we perform full characterization by means of high-resolution transmission electron microscopy, X-ray powder diffraction, small angle X-ray scattering, thermogravimetric and calorimetric analyses, confocal Raman microscopy and impedance spectroscopy analyses. The presence of the polymer host and interparticle Coulomb repulsive interactions was evaluated as an influence for the formation of ~3–8 nm equally-sized quantum dots independently of the concentration. The polyaniline polaron population showed an increase for the quantum dots diluted regime and the suppression at the concentrated regime, ascribed to the formation of chemical bonds at the interface, which was confirmed by theoretical simulations. In agreement with the previous observation, the in situ growth of ceramic quantum dots in polyaniline host via water vapor flow diffusion could be very useful as a novel approach to prepare electrode materials for energy conversion and storage applications. - Highlights: • In situ growth of titanium oxide quantum dots in polyaniline host via water vapor flow diffusion. • Polyaniline charge carriers at the interface and charge interactions between quantum dots. • Easy extrapolation to sol-gel derived quantum dots into polymer host as potential electrode materials.« less

Wafer-Fused Orientation-Patterned GaAs

DTIC Science & Technology

2008-02-13

frequencies utilizing existing industrial foundries. 15. SUBJECT TERMS Orientation-patterned Gallium Arsenide, hydride vapor phase epitaxy, quasi-phase... Gallium Arsenide, hydride vapor phase epitaxy, quasi-phase-matching, nonlinear frequency conversion 1. INTRODUCTION Quasi-phase-matching (QPM)1...and E. Lallier, “Second harmonic generation of CO2 laser using thick quasi-phase-matched GaAs layer grown by hydride vapour phase epitaxy

Diffusion of biomass pyrolysis products in H-ZSM-5 by molecular dynamics simulations

DOE PAGES

Bu, Lintao; Nimlos, Mark R.; Robichaud, David J.; ...

2016-12-13

Diffusion of biomass pyrolysis vapors and their upgraded products is an essential catalytic property of zeolites during catalytic fast pyrolysis and likely plays a critical role in the selectivity of these catalysts. Characterizing the diffusivities of representative biofuel molecules is critical to understand shape selectivity and interpret product distribution. Yet, experimental measurements on the diffusivities of oxygenated biofuel molecules at pyrolysis temperatures are very limited in the literature. As an alternative approach, we conducted MD simulations to measure the diffusion coefficients of several selected molecules that are representative of biomass pyrolysis vapors, namely water, methanol, glycolaldehyde, and toluene in H-ZSM-5more » zeolite. The results show the diffusion coefficients calculated via MD simulations are consistent with available NMR measurements at room temperature. The effect of molecular weight and molecular critical diameter on the diffusivity among the chosen model compounds is also examined. Furthermore, we have characterized the diffusivities of representative biofuel molecules, namely xylene isomers, in H-ZSM-5. Our calculations determined that the ratio of the diffusion coefficients for xylene isomers is p-xylene: o-xylene: m-xylene ≈ 83:3:1 at 700 K. Furthermore, our results also demonstrate the different diffusivity between p-xylene and toluene is due to the molecular orientations when the molecules diffuse along the channels in H-ZSM-5 and provide deep insight into the effect of molecular orientation on its diffusivity.« less

Recent results and new hardware developments for protein crystal growth in microactivity

NASA Technical Reports Server (NTRS)

Delucas, L. J.; Long, M. M.; Moore, K. M.; Smith, C.; Carson, M.; Narayana, S. V. L.; Carter, D.; Clark, A. D., Jr.; Nanni, R. G.; Ding, J.

1993-01-01

Protein crystal growth experiments have been performed on 16 space shuttle missions since April, 1985. The initial experiments utilized vapor diffusion crystallization techniques similar to those used in laboratories for earth-based experiments. More recent experiments have utilized temperature induced crystallization as an alternative method for growing high quality protein crystals in microgravity. Results from both vapor diffusion and temperature induced crystallization experiments indicate that proteins grown in microgravity may be larger, display more uniform morphologies, and yield diffraction data to significantly higher resolutions than the best crystals of these proteins grown on earth.

Deriving properties of low-volatile substances from isothermal evaporation curves

NASA Astrophysics Data System (ADS)

Ralys, Ricardas V.; Uspenskiy, Alexander A.; Slobodov, Alexander A.

2016-01-01

Mass flux occurring when a substance evaporates from an open surface is proportional to its saturated vapor pressure at a given temperature. The proportionality coefficient that relates this flux to the vapor pressure shows how far a system is from equilibrium and is called the accommodation coefficient. Under vacuum, when a system deviates from equilibrium to the greatest extent possible, the accommodation coefficient equals unity. Under finite pressure, however, the accommodation coefficient is no longer equal to unity, and in fact, it is much less than unity. In this article, we consider the isothermal evaporation or sublimation of low-volatile individual substances under conditions of thermogravimetric analysis, when the external pressure of the purging gas is equal to the atmospheric pressure and the purging gas rate varies. When properly treated, the dependence of sample mass over time provides us with various information on the properties of the examined compound, such as saturated vapor pressure, diffusion coefficient, and density of the condensed (liquid or solid) phase at the temperature of experiment. We propose here the model describing the accommodation coefficient as a function of both substance properties and experimental conditions. This model gives the final expression for evaporation rate, and thus for mass dependence over time, with approximation parameters resulting in the properties being sought.

Focus Article: Theoretical aspects of vapor/gas nucleation at structured surfaces

NASA Astrophysics Data System (ADS)

Meloni, Simone; Giacomello, Alberto; Casciola, Carlo Massimo

2016-12-01

Heterogeneous nucleation is the preferential means of formation of a new phase. Gas and vapor nucleation in fluids under confinement or at textured surfaces is central for many phenomena of technological relevance, such as bubble release, cavitation, and biological growth. Understanding and developing quantitative models for nucleation is the key to control how bubbles are formed and to exploit them in technological applications. An example is the in silico design of textured surfaces or particles with tailored nucleation properties. However, despite the fact that gas/vapor nucleation has been investigated for more than one century, many aspects still remain unclear and a quantitative theory is still lacking; this is especially true for heterogeneous systems with nanoscale corrugations, for which experiments are difficult. The objective of this focus article is analyzing the main results of the last 10-20 years in the field, selecting few representative works out of this impressive body of the literature, and highlighting the open theoretical questions. We start by introducing classical theories of nucleation in homogeneous and in simple heterogeneous systems and then discuss their extension to complex heterogeneous cases. Then we describe results from recent theories and computer simulations aimed at overcoming the limitations of the simpler theories by considering explicitly the diffuse nature of the interfaces, atomistic, kinetic, and inertial effects.

Contactless Growth of ZnSe Single Crystals by Physical Vapor Transport

NASA Technical Reports Server (NTRS)

Su, Ching-Hua; George, M. A.; Feth, S.; Lehoczky, S. L.

1998-01-01

ZnSe crystals were grown by self-seeded physical vapor transport (PVT) technique in the horizontal configuration. The source materials were heat treated by H2 reduction to remove the oxide followed by baking under dynamic vacuum to adjust the source composition toward that of congruent sublimation. Contactless growth of ZnSe single crystals have been performed consistently using three different source materials. The crystals grew away from the wall during the later stage of the growth with large (110) facets tend to align parallel to the gravity direction. The Scanning Electron Micrography (SEM) micrographs and the Atomic Force Microscope (AFM) images showed that large (110) terraces and steps dominate the as-grown facets. The measured residual gas pressures in the processed ampoules agree well among various source materials and the major components were CO and H2. No preferred growth direction was found. The one-dimensional diffusion model on the mass flux of a multi-species PVT system was employed to analyze the conditions for contactless growth. The calculated thermal profile for supersaturation is very close to the thermal profile measured inside the empty furnace bore in the region of contactless growth. The effects of convective flows in the vapor phase inside the ampoule on the growth processes are discussed.

Vapors and Droplets Mixture Deposition of Metallic Coatings by Very Low Pressure Plasma Spraying

NASA Astrophysics Data System (ADS)

Vautherin, B.; Planche, M.-P.; Bolot, R.; Quet, A.; Bianchi, L.; Montavon, G.

2014-04-01

In recent years, the very low pressure plasma-spraying (VLPPS) process has been intensely developed and implemented to manufacture thin, dense and finely structured ceramic coatings for various applications, such as Y2O3 for diffusion barriers, among other examples. This paper aims at presenting developments carried out on metallic coatings. Aluminum was chosen as a demonstrative material due to its "moderate" vaporization enthalpy (i.e., 38.23 KJ cm-3) compared to the one of copper (i.e., 55.33 KJ cm-3), cobalt (i.e., 75.03 KJ cm-3), or even tantalum (i.e., 87.18 KJ cm-3). The objective of this work is primarily to better understand the behavior of a solid precursor injected into the plasma jet leading to the formation of vapors and to better control the factors affecting the coating structure. Nearly dense aluminum coatings were successfully deposited by VLPPS at 100 Pa with an intermediate power plasma torch (i.e., Sulzer Metco F4 type gun with maximum power of 45 kW). Optical emission spectroscopy (OES) was implemented to study and analyze the vapor behavior into the plasma jet. Simplified CFD modeling allowed better understanding of some of the thermo-physical mechanisms. The effect of powder-size distribution, substrate temperature and spray distance were studied. The phase composition and microstructural features of the coatings were characterized by XRD and SEM. Moreover, Vickers microhardness measurements were implemented.

Measuring Spatial Variability of Vapor Flux to Characterize Vadose-zone VOC Sources: Flow-cell Experiments

DOE PAGES

Mainhagu, Jon; Morrison, C.; Truex, Michael J.; ...

2014-08-05

A method termed vapor-phase tomography has recently been proposed to characterize the distribution of volatile organic contaminant mass in vadose-zone source areas, and to measure associated three-dimensional distributions of local contaminant mass discharge. The method is based on measuring the spatial variability of vapor flux, and thus inherent to its effectiveness is the premise that the magnitudes and temporal variability of vapor concentrations measured at different monitoring points within the interrogated area will be a function of the geospatial positions of the points relative to the source location. A series of flow-cell experiments was conducted to evaluate this premise. Amore » well-defined source zone was created by injection and extraction of a non-reactive gas (SF6). Spatial and temporal concentration distributions obtained from the tests were compared to simulations produced with a mathematical model describing advective and diffusive transport. Tests were conducted to characterize both areal and vertical components of the application. Decreases in concentration over time were observed for monitoring points located on the opposite side of the source zone from the local–extraction point, whereas increases were observed for monitoring points located between the local–extraction point and the source zone. We found that the results illustrate that comparison of temporal concentration profiles obtained at various monitoring points gives a general indication of the source location with respect to the extraction and monitoring points.« less

Three dimensional modeling of cirrus during the 1991 FIRE IFO 2: Detailed process study

NASA Technical Reports Server (NTRS)

Jensen, Eric J.; Toon, Owen B.; Westphal, Douglas L.

1993-01-01

A three-dimensional model of cirrus cloud formation and evolution, including microphysical, dynamical, and radiative processes, was used to simulate cirrus observed in the FIRE Phase 2 Cirrus field program (13 Nov. - 7 Dec. 1991). Sulfate aerosols, solution drops, ice crystals, and water vapor are all treated as interactive elements in the model. Ice crystal size distributions are fully resolved based on calculations of homogeneous freezing of solution drops, growth by water vapor deposition, evaporation, aggregation, and vertical transport. Visible and infrared radiative fluxes, and radiative heating rates are calculated using the two-stream algorithm described by Toon et al. Wind velocities, diffusion coefficients, and temperatures were taken from the MAPS analyses and the MM4 mesoscale model simulations. Within the model, moisture is transported and converted to liquid or vapor by the microphysical processes. The simulated cloud bulk and microphysical properties are shown in detail for the Nov. 26 and Dec. 5 case studies. Comparisons with lidar, radar, and in situ data are used to determine how well the simulations reproduced the observed cirrus. The roles played by various processes in the model are described in detail. The potential modes of nucleation are evaluated, and the importance of small-scale variations in temperature and humidity are discussed. The importance of competing ice crystal growth mechanisms (water vapor deposition and aggregation) are evaluated based on model simulations. Finally, the importance of ice crystal shape for crystal growth and vertical transport of ice are discussed.

Melt-Vapor Phase Diagram of the Te-S System

NASA Astrophysics Data System (ADS)

Volodin, V. N.; Trebukhov, S. A.; Kenzhaliyev, B. K.; Nitsenko, A. V.; Burabaeva, N. M.

2018-03-01

The values of partial pressure of saturated vapor of the constituents of the Te-S system are determined from boiling points. The boundaries of the melt-vapor phase transition at atmospheric pressure and in vacuum of 2000 and 100 Pa are calculated on the basis of partial pressures. A phase diagram that includes vapor-liquid equilibrium fields whose boundaries allow us to assess the behavior of elements upon distillation fractioning is plotted. It is established that the separation of elements is possible at the first evaporation-condensation cycle. Complications can be caused by crystallization of a sulfur solid solution in tellurium.

Ionic Vapor Composition in Critical and Supercritical States of Strongly Interacting Ionic Compounds.

PubMed

Chaban, Vitaly V; Prezhdo, Oleg V

2016-05-12

The critical point, CP (T, P), of the phase diagram quantifies the minimum amount of kinetic energy needed to prevent a substance from existing in a condensed phase. Therefore, the CP is closely related to the properties of the fluid far below the critical temperature. Approaches designed to predict thermophysical properties of a system necessarily aim to provide reliable estimates of the CP. Vice versa, CP estimation is impossible without knowledge of the vapor phase behavior. We report ab initio Born-Oppenheimer molecular dynamics (BOMD) simulations of sodium and potassium chlorides, NaCl and KCl, at and above their expected CPs. We advance the present knowledge regarding the existence of ionic species in the vapor phase by establishing significant percentages of atomic clusters: 29-30% in NaCl and 34-38% in KCl. A neutral pair of counterions is the most abundant cluster in the ionic vapors (ca. 35% of all vaporized ions exist in this form). Unexpectedly, an appreciable fraction of clusters is charged. The ionic vapor composition is determined by the vapor density, rather than the nature of the alkali ion. The previously suggested CPs of NaCl and KCl appear overestimated, based on the present simulations. The reported results offer essential insights into the ionic fluid properties and assist in development of thermodynamic theories. The ab initio BOMD method has been applied to investigate the vapor phase composition of an ionic fluid for the first time.

Investigation of aluminosilicate refractory for solid oxide fuel cell applications

NASA Astrophysics Data System (ADS)

Gentile, Paul Steven

Stationary solid oxide fuel cells (SOFCs) have been demonstrated to provide clean and reliable electricity through electro-chemical conversion of various fuel sources (CH4 and other light hydrocarbons). To become a competitive conversion technology the costs of SOFCs must be reduced to less than $400/kW. Aluminosilicate represents a potential low cost alternative to high purity alumina for SOFC refractory applications. The objectives of this investigation are to: (1) study changes of aluminosilicate chemistry and morphology under SOFC conditions, (2) identify volatile silicon species released by aluminosilicates, (3) identify the mechanisms of aluminosilicate vapor deposition on SOFC materials, and (4) determine the effects of aluminosilicate vapors on SOFC electrochemical performance. It is shown thermodynamically and empirically that low cost aluminosilicate refractory remains chemically and thermally unstable under SOFC operating conditions between 800°C and 1000°C. Energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) of the aluminosilicate bulk and surface identified increased concentrations of silicon at the surface after exposure to SOFC gases at 1000°C for 100 hours. The presence of water vapor accelerated surface diffusion of silicon, creating a more uniform distribution. Thermodynamic equilibrium modeling showed aluminosilicate remains stable in dry air, but the introduction of water vapor indicative of actual SOFC gas streams creates low temperature (<1000°C) silicon instability due to the release of Si(OH)4 and SiO(OH) 2. Thermal gravimetric analysis and transpiration studies identified a discrete drop in the rate of silicon volatility before reaching steady state conditions after 100-200 hours. Electron microscopy observed the preferential deposition of vapors released from aluminosilicate on yttria stabilized zirconia (YSZ) over nickel. The adsorbent consisted of alumina rich clusters enclosed in an amorphous siliceous layer. Silicon penetrated the YSZ along grain boundaries, isolating grains in an insulating glassy phase. XPS did not detect spectra shifts or peak broadening associated with formation of new Si-Zr-Y-O phases. SOFC electrochemical performance testing at 800-1000°C attributed rapid degradation (0.1% per hour) of cells exposed to aluminosilicate vapors in the fuel stream predominately to ohmic polarization. EDS identified silicon concentrations above impurity levels at the electrolyte/active anode interface.

Vapor-crystal phase transition in synthesis of paracetamol films by vacuum evaporation and condensation

NASA Astrophysics Data System (ADS)

Belyaev, A. P.; Rubets, V. P.; Antipov, V. V.; Bordei, N. S.; Zarembo, V. I.

2014-03-01

We report on the structural and technological investigations of the vapor-crystal phase transition during synthesis of paracetamol films of the monoclinic system by vacuum evaporation and condensation in the temperature range 220-320 K. The complex nature of the transformation accompanied by the formation of a gel-like phase is revealed. The results are interpreted using a model according to which the vapor-crystal phase transition is not a simple first-order phase transition, but is a nonlinear superposition of two phase transitions: a first-order transition with a change in density and a second-order phase transition with a change in ordering. Micrographs of the surface of the films are obtained at different phases of formation.

Predictions and Verification of an Isotope Marine Boundary Layer Model

NASA Astrophysics Data System (ADS)

Feng, X.; Posmentier, E. S.; Sonder, L. J.; Fan, N.

2017-12-01

A one-dimensional (1D), steady state isotope marine boundary layer (IMBL) model is constructed. The model includes meteorologically important features absent in Craig and Gordon type models, namely height-dependent diffusion/mixing and convergence of subsiding external air. Kinetic isotopic fractionation results from this height-dependent diffusion which starts as pure molecular diffusion at the air-water interface and increases linearly with height due to turbulent mixing. The convergence permits dry, isotopically depleted air subsiding adjacent to the model column to mix into ambient air. In δD-δ18O space, the model results fill a quadrilateral, of which three sides represent 1) vapor in equilibrium with various sea surface temperatures (SSTs) (high d18O boundary of quadrilateral); 2) mixture of vapor in equilibrium with seawater and vapor in the subsiding air (lower boundary depleted in both D and 18O); and 3) vapor that has experienced the maximum possible kinetic fractionation (high δD upper boundary). The results can be plotted in d-excess vs. δ18O space, indicating that these processes all cause variations in d-excess of MBL vapor. In particular, due to relatively high d-excess in the descending air, mixing of this air into the MBL causes an increase in d-excess, even without kinetic isotope fractionation. The model is tested by comparison with seven datasets of marine vapor isotopic ratios, with excellent correspondence; >95% of observational data fall within the quadrilateral area predicted by the model. The distribution of observations also highlights the significant influence of vapor from the nearby converging descending air on isotopic variations in the MBL. At least three factors may explain the <5% of observations that fall slightly outside of the predicted region in both δD-δ18O and d-excess - δ18O space: 1) variations in seawater isotopic ratios, 2) variations in isotopic composition of subsiding air, and 3) influence of sea spray. The model can be used for understanding the effects of boundary layer processes and meteorological conditions on isotopic composition of vapor within, and vapor fluxes through the MBL, and how changes in moisture source regions affect the isotopic composition of precipitation. The model can be applied to modern as well as paleo- climate conditions.

New Density Functional Approach for Solid-Liquid-Vapor Transitions in Pure Materials

NASA Astrophysics Data System (ADS)

Kocher, Gabriel; Provatas, Nikolas

2015-04-01

A new phase field crystal (PFC) type theory is presented, which accounts for the full spectrum of solid-liquid-vapor phase transitions within the framework of a single density order parameter. Its equilibrium properties show the most quantitative features to date in PFC modeling of pure substances, and full consistency with thermodynamics in pressure-volume-temperature space is demonstrated. A method to control either the volume or the pressure of the system is also introduced. Nonequilibrium simulations show that 2- and 3-phase growth of solid, vapor, and liquid can be achieved, while our formalism also allows for a full range of pressure-induced transformations. This model opens up a new window for the study of pressure driven interactions of condensed phases with vapor, an experimentally relevant paradigm previously missing from phase field crystal theories.

Thermocouple psychrometry

USGS Publications Warehouse

Andraski, Brian J.; Scanlon, Bridget R.; Dane, Jacob H.; Topp, G. Clarke

2002-01-01

Thermocouple psychrometry is a technique that infers the water potential of the liquid phase of a sample from measurements within the vapor phase that is in equilibrium with the sample. The theoretical relation between water potential of the liquid phase and relative humidity of the vapor phase is given by the Kelvin equation Ψ = energy/volume = (RT/Vw) ln(p/po) [3.2.3–1]where ψ is water potential (sum of matric and osmotic potential, MPa), R is the universal gas constant (8.314 × 10-6 MJ mol-1 K-1), T is temperature (K), Vw is molar volume of water (1.8 × 10-5 m3 mol-1), and p/po is relative humidity expressed as a fraction where p is actual vapor pressure of air in equilibrium with the liquid phase (MPa) and po is saturation vapor pressure (MPa) at T.

The interaction of evaporative and convective instabilities

NASA Astrophysics Data System (ADS)

Ozen, O.

Evaporative convection arises in a variety of natural and industrial processes, such as drying of lakebeds, heat pipe technology and dry-eye syndrome. The phenomenon of evaporative convection leads to an interfacial instability where an erstwhile flat surface becomes undulated as a control variable, such as temperature drop, exceeds a critical value. This instability has been investigated by others assuming that the vapor phase is infinitely deep and passive, i.e. vapor fluid dynamics has been ignored. However, when we look at some engineering processes, such as distillation columns, heat pipes and drying technologies where phase change takes place we might imagine that the assumption of an infinitely deep vapor layer or at least that of a passive vapor is inappropriate. Previous work on convection in bilayer systems with no phase-change suggests that active vapor layers play a major role in determining the stability of an interface. Hence, for the case of convection with phase-change, we will address this issue and try to answer the question whether the infinitely deep and passive vapor layer is a valid assumption. We have also investigated, theoretically, the gravity and surface tension gradient-driven instabilities occurring during the evaporation of a liquid into its own vapor taking into account the fluid dynamics of both phases and the finiteness of the domains of each phase, i.e. the liquid and its vapor are assumed to be confined between two horizontal plates, and different heating arrangements are applied. The effects of fluid layer depths, the evaporation rate and the temperature gradient applied across the fluids on the stability of the interface are studied. The modes of the flow pattern are determined for each scenario. The physics of the instability are explained and a comparison is made with the results of similar, yet physically different problems.

Vapour phase growth and characterization of II-VI mixed crystals

NASA Astrophysics Data System (ADS)

Reddy, D. R.; Reddy, B. K.

1992-02-01

All II-VI semiconductors with melting temperatures well above 1000 degree(s)C and with appreciable congruent vaporization well below their melting temperatures leave little scope for any growth technique except for the slow but efficient vaporphase growth method. Theoretical flaw in diffusion models of vapor phase growth was corrected by Factor and Garrett by incorporating the flow velocity term which otherwise would lead to segregation of constituents. An additional degree of freedom arising from the presence of two components was well utilized to finely control the stoichiometry in binaries. In mixed II-VI systems the components are either three or four, depending on whether the system is a ternary or a quaternary. The added degrees of freedom make it very difficult to control stoichiometry. However, Igaki et al. demonstrated the feasibility of control of stoichiometry in CdSxSe1-x. In this paper, a self-sealing vaporphase growth technique used for both ternary and quaternary system is described. The systems studied are CdSxSe1-x, (ZnSe)x(CdTe)1-x and (ZnTe)x(CdSe)1-x. Results on growth mechanism, miscibility, structure, band gap variation, conductivity type variation with 'x' and transport properties are presented in a comparative way and discussed. CdSxSe1-x system in the entire 'X' has the same crystal structure and type of conductivity. The second system has the same zincblend structure but the type of conductivity is very sensitive to thermal treatment. In the last system both structure and types of conductivity are different. The discontinuities in properties associated with this divergent end compound are presented and discussed. Among the physical properties/parameters studied crystal structure, bandgap and nature of conductivity are tailorable, and magnitudes of conductivity and dielectric properties are very difficult to control in the crystals grown by this vapor phase method.

Observation of vapor bubble of non-azeotropic binary mixture in microgravity with a two-wavelength interferometer

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

Abe, Yoshiyuki; Iwasaki, Akira

1999-07-01

Although non-azeotropic mixtures are considered to be promising working fluids in advanced energy conversion systems, the primary technical problems in the heat transfer degradation in phase change processes cause economical handicap to wide-spread applications. The boiling behavior of mixtures still remains a number of basic questions being not answered yet, and the present authors believe that the most essential information for the boiling process in non-azeotropic mixtures is how temperature and concentration profiles are developed around the bubbles. The present study attempts at understanding fundamental heat and mass transfer mechanisms in nucleate pool boiling of non-azeotropic binary mixtures, and withmore » the knowledge to develop a passive boiling heat transfer enhancement eventually. To this end, the authors have employed microgravity environment for rather detailed observation around vapor bubbles in the course of boiling inception and bubble growth. A two-wavelength Mach-Zehnder interferometer has been developed, which withstands mechanical shock caused by gravity change from very low gravity of the order of 10{sup {minus}5} g to relatively high gravity of approximately 8 g exposed during deceleration period. A series of experiments on single vapor bubbles for CFC113 single component and CFC12/CFC112 non-azeotropic binary mixture have been conducted under a high quality microgravity conditions available in 10-second free-fall facility of Japan Microgravity Center (JAMIC). The results for single component liquid showed a strong influence due to Marangoni effect caused by the temperature profile around the bubble. The results for non-azeotropic binary mixture showed, however, considerably different behavior from single component liquid. Both temperature and concentration profiles around a single vapor bubble were evaluated from the interferograms. The temperature and concentration layers established around the bubbles were nearly one order of magnitude larger than those predicted by thermal diffusion and mass diffusion. The temperature and concentration profiles evaluated from the present experiments suggest the role of Marangoni effects due to both concentration profile and temperature profile around the bubble interface.« less

Alumina-Forming MAX Phases in Turbine Material Systems

NASA Technical Reports Server (NTRS)

Smialek, James L.; Harder, Bryan J.; Garg, Arnita; Nesbitt, James A.

2015-01-01

Coatings for high temperature turbine components are based on low conductivity YSZ thermal barriers and protective NiAl, NiCoCrAlY bond coats. Good oxidation hot corrosion resistance, intermediate CTE, and strain tolerance of Ti2AlC and Cr2AlC MAX phases are thus of special interest. Their alumina scale growth follows a cubic law in accord with FeCrAlY alloys, with oxygen grain boundary diffusivity: Dgb 1.8 x 10-10 exp(-375 kJmole) m3s. Protective cubic kinetics are also found in high pressure burner rig (6 atm., 25 ms) and TGA tests of MAXthal 211Ti2AlC. The initial portion (0.1 hr) is dominated by fast TiO2 growth (with little evidence of scale volatility in high pressure water vapor, as found for SiO2 scales). Bulk Ti2AlC and Cr2AlC substrates show promise as potential bond coats for YSZ TBCs in 1000-1200 C furnace life (500 h) tests. Cr2AlC is proving to be very resistant to 700-900 C Na2SO4 hot corrosion and is of interest for disk alloys. Preliminary diffusion bonded Cr2AlC-superalloy hybrid couples have survived 1000 hr interrupted furnace tests at 800C with no indication of cracking or debonding. Diffusion zones of -NiAl+Cr7C3 were produced in these above 1000 C, but did not grow to any great extent after 1000 hr at 800 C. Processing as coatings presents challenges, however the basic properties of MAX phases provide novel opportunities for high temperature turbine components.

Characterization of the Dynamic Pressure Response of Fuels in Microchannels

NASA Astrophysics Data System (ADS)

Haendler, Brenda; Pisano, Albert; Liepmann, Dorian

2004-11-01

In order to create a self-pumping fuel vaporization and delivery systems for a MEMS rotary engine power system, the dynamic pressure response due to phase eruption of fuels in micro channels must be characterized. Testing is done using micro channels with diameters the same order of magnitude as the critical bubble radius, a constant mass flow rate syringe pump, and a steady heat source. Pressure changes in the micro channel due to the periodic movement of the phase change meniscus are measured for a variety of flow conditions. A discrete Fourier transform is performed on the data to determine the dominant frequencies in the signal. Critical trends are discussed comparing both the frequency and the amplitude of the pressure spikes for a variety of temperatures and flow rates. The results presented on the trends in the pressure signature due to phase eruption for fuels are then related back to the fuel delivery system, which is using a nozzle-diffuser design to accomplish positive flow rectification given the periodic pressure condition at the phase eruption interface.

An Indirect Method for Vapor Pressure and Phase Change Enthalpy Determination by Thermogravimetry

NASA Astrophysics Data System (ADS)

Giani, Samuele; Riesen, Rudolf; Schawe, Jürgen E. K.

2018-07-01

Vapor pressure is a fundamental property of a pure substance. This property is the pressure of a compound's vapor in thermodynamic equilibrium with its condensed phase (solid or liquid). When phase equilibrium condition is met, phase coexistence of a pure substance involves a continuum interplay of vaporization or sublimation to gas and condensation back to their liquid or solid form, respectively. Thermogravimetric analysis (TGA) techniques are based on mass loss determination and are well suited for the study of such phenomena. In this work, it is shown that TGA method using a reference substance is a suitable technique for vapor pressure determination. This method is easy and fast because it involves a series of isothermal segments. In contrast to original Knudsen's approach, where the use of high vacuum is mandatory, adopting the proposed method a given experimental setup is calibrated under ambient pressure conditions. The theoretical framework of this method is based on a generalization of Langmuir equation of free evaporation: The real strength of the proposed method is the ability to determine the vapor pressure independently of the molecular mass of the vapor. A demonstration of this method has been performed using the Clausius-Clapeyron equation of state to derive the working equation. This algorithm, however, is adaptive and admits the use of other equations of state. The results of a series of experiments with organic molecules indicate that the average difference of the measured and the literature vapor pressure amounts to about 5 %. Vapor pressure determined in this study spans from few mPa up to several kPa. Once the p versus T diagram is obtained, phase transition enthalpy can additionally be calculated from the data.

Vapor Growth of Binary and Ternary Chalcogenides in Preparation for Microgravity Experiments

NASA Technical Reports Server (NTRS)

Su, C.; Whitaker, Ann F. (Technical Monitor)

2001-01-01

In the bulk crystal growth of some technologically important semiconducting chalcopyrites, such as ZnTe, CdS, ZnSe and ZnS, vapor growth techniques have significant advantages over melt growth techniques due to the high melting points of these materials. The realization of routine production of high-quality single crystals of these semiconductors requires a fundamental, systematic and in-depth study on the PVT growth process and crystal growth by vapor transport in low gravity offers a set of unique conditions for this study. Previously, two reasons have been put forward to account for this. The first is weight-related reductions in crystal strain and defects. These are thought to be caused by the weight of the crystals during processing at elevated temperatures and retained on cooling, particularly for materials with a low yield strength. The second, and more general, reason is related to the reduction in density-gradient driven convection. The PVT crystal growth process consists of essentially three processes: sublimation of the source material, transport of the vapor species and condensation of the vapor species to form the crystal. The latter two processes can be affected by the convection caused by gravitational accelerations on Earth. Reductions in such convection in low gravity is expected to yield a nearly diffusion-limited growth condition which results in more uniform growth rates (on the microscopic scale) and hence greater crystalline perfection and compositional homogeneity. The reduction of convective contamination by performing flight experiments in a reduced gravity environment will help to understand the relation between fluid phase processes (growth parameters) and defect and impurity incorporation in grown crystals.

Evaporation Kinetics of Polyol Droplets: Determination of Evaporation Coefficients and Diffusion Constants

NASA Astrophysics Data System (ADS)

Su, Yong-Yang; Marsh, Aleksandra; Haddrell, Allen E.; Li, Zhi-Ming; Reid, Jonathan P.

2017-11-01

In order to quantify the kinetics of mass transfer between the gas and condensed phases in aerosol, physicochemical properties of the gas and condensed phases and kinetic parameters (mass/thermal accommodation coefficients) are crucial for estimating mass fluxes over a wide size range from the free molecule to continuum regimes. In this study, we report measurements of the evaporation kinetics of droplets of 1-butanol, ethylene glycol (EG), diethylene glycol (DEG), and glycerol under well-controlled conditions (gas flow rates and temperature) using the previously developed cylindrical electrode electrodynamic balance technique. Measurements are compared with a model that captures the heat and mass transfer occurring at the evaporating droplet surface. The aim of these measurements is to clarify the discrepancy in the reported values of mass accommodation coefficient (αM, equals to evaporation coefficient based on microscopic reversibility) for 1-butanol, EG, and DEG and improve the accuracy of the value of the diffusion coefficient for glycerol in gaseous nitrogen. The uncertainties in the thermophysical and experimental parameters are carefully assessed, the literature values of the vapor pressures of these components are evaluated, and the plausible ranges of the evaporation coefficients for 1-butanol, EG, and DEG as well as uncertainty in diffusion coefficient for glycerol are reported. Results show that αM should be greater than 0.4, 0.2, and 0.4 for EG, DEG, and 1-butanol, respectively. The refined values are helpful for accurate prediction of the evaporation/condensation rates.

Water-vapor pressure control in a volume

NASA Technical Reports Server (NTRS)

Scialdone, J. J.

1978-01-01

The variation with time of the partial pressure of water in a volume that has openings to the outside environment and includes vapor sources was evaluated as a function of the purging flow and its vapor content. Experimental tests to estimate the diffusion of ambient humidity through openings and to validate calculated results were included. The purging flows required to produce and maintain a certain humidity in shipping containers, storage rooms, and clean rooms can be estimated with the relationship developed here. These purging flows are necessary to prevent the contamination, degradation, and other effects of water vapor on the systems inside these volumes.

The numerical methods for the development of the mixture region in the vapor explosion simulations

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

Yang, Y.; Ohashi, H.; Akiyama, M.

An attempt to numerically simulate the process of the vapor explosion with a general multi-component and multi-dimension code is being challenged. Because of the rapid change of the flow field and extremely nonuniform distribution of the components in the system of the vapor explosion, the numerical divergence and diffusion are subject to occur easily. A dispersed component model and a multiregion scheme, by which these difficulties can be effectively overcome, were proposed. The simulations have been performed for the processes of the premixing and the fragmentation propagation in the vapor explosion.

Melting of superheated molecular crystals

NASA Astrophysics Data System (ADS)

Cubeta, Ulyana; Bhattacharya, Deepanjan; Sadtchenko, Vlad

2017-07-01

Melting dynamics of micrometer scale, polycrystalline samples of isobutane, dimethyl ether, methyl benzene, and 2-propanol were investigated by fast scanning calorimetry. When films are superheated with rates in excess of 105 K s-1, the melting process follows zero-order, Arrhenius-like kinetics until approximately half of the sample has transformed. Such kinetics strongly imply that melting progresses into the bulk via a rapidly moving solid-liquid interface that is likely to originate at the sample's surface. Remarkably, the apparent activation energies for the phase transformation are large; all exceed the enthalpy of vaporization of each compound and some exceed it by an order of magnitude. In fact, we find that the crystalline melting kinetics are comparable to the kinetics of dielectric α-relaxation in deeply supercooled liquids. Based on these observations, we conclude that the rate of non-isothermal melting for superheated, low-molecular-weight crystals is limited by constituent diffusion into an abnormally dense, glass-like, non-crystalline phase.

Physicochemical processes in embryonic plant tissue during the transition to the state of cold anabiosis and storage at liquid nitrogen temperature

NASA Astrophysics Data System (ADS)

Khodko, A. T.; Lysak, Yu. S.

2017-10-01

Critical opalescence phenomenon was observed in the cytoplasm of garlic embryonic tissue—meristem—upon cooling in liquid nitrogen vapor, indicating liquid-liquid phase transition in the system. It was established that cells of the meristem tissue survive the cooling-thawing cycle. We suggest that the transition of meristem tissue to the state of anabiosis is mainly due to a drastic slowing of the diffusion in the cytoplasm caused by the passage of the solution through the critical point, followed by the formation of a dispersed system—a highly concentrated emulsion—as a result of a liquid-liquid phase transition. This macrophase separation is characteristic of polymer-solvent systems. We established the regime of cooling down to liquid nitrogen temperature and subsequent thawing in the cryopreservation cycle for the biological object under study, which ensures the preservation of tissue viability.

Systematic Improvement of Protein Crystals by Determining the Supersolubility Curves of Phase Diagrams

PubMed Central

Saridakis, Emmanuel; Chayen, Naomi E.

2003-01-01

A systematic approach for improving protein crystals by growing them in the metastable zone using the vapor diffusion technique is described. This is a simple technique for optimization of crystallization conditions. Screening around known conditions is performed to establish a working phase diagram for the crystallization of the protein. Dilutions of the crystallization drops across the supersolubility curve into the metastable zone are then carried out as follows: the coverslips holding the hanging drops are transferred, after being incubated for some time at conditions normally giving many small crystals, over reservoirs at concentrations which normally yield clear drops. Fewer, much larger crystals are obtained when the incubation times are optimized, compared with conventional crystallization at similar conditions. This systematic approach has led to the structure determination of the light-harvesting protein C-phycocyanin to the highest-ever resolution of 1.45 Å. PMID:12547801

Chemical vapor deposition of W-Si-N and W-B-N

DOEpatents

Fleming, James G.; Roherty-Osmun, Elizabeth Lynn; Smith, Paul M.; Custer, Jonathan S.; Jones, Ronald V.; Nicolet, Marc-A.; Madar, Roland; Bernard, Claude

1999-01-01

A method of depositing a ternary, refractory based thin film on a substrate by chemical vapor deposition employing precursor sources of tungsten comprising WF.sub.6, either silicon or boron, and nitrogen. The result is a W--Si--N or W--B--N thin film useful for diffusion barrier and micromachining applications.

Comparison of Sampling Methods to Determine the Impact of Aerobic Biodegradation on Benzene Concentrations at UST Sites

EPA Science Inventory

This material will be interesting to regulators and contractors who collect samples of soil gas to estimate the potential for vapor intrusion of buildings. In the absence of biodegradation, transport of vapors through the unsaturated zone is expected to be by diffusion, and t...

Evaluation of a New Passive Diffusion Sampler for Monitoring for Soil Gas and Ground Water at Two UST Sites

EPA Science Inventory

Historically, conventional practice to estimate intrusion of fuel vapors from soil and ground water to buildings measures the concentration of BTEX beneath the building using vapor probes or monitoring wells screened across the water table. Standard practice assumes that the co...

Terahertz injection lasers based on PbSnSe alloy with an emission wavelength up to 46.5 μm

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

Maremyanin, K. V., E-mail: kirillm@ipmras.ru; Rumyantsev, V. V.; Ikonnikov, A. V.

2016-12-15

Diffusion injection lasers based on Pb{sub 1} {sub –} {sub x}Sn{sub x}Se alloy, emitting in a wide spectral range of 10–46.5 μm depending on the composition and temperatures are fabricated. A technology for growing high-quality single crystals from the vapor phase under conditions of free growth is developed. The dependences of the total emission intensity on the pump current and the emission spectra of injection lasers based on Pb{sub 1–x}Sn{sub x}Se are studied. In these samples, lasing of long-wavelength radiation to a record wavelength of 46.5 μm is achieved.

Preparation for microgravity - The role of the Microgravity Material Science Laboratory

NASA Technical Reports Server (NTRS)

Johnston, J. Christopher; Rosenthal, Bruce N.; Meyer, Maryjo B.; Glasgow, Thomas K.

1988-01-01

Experiments at the NASA Lewis Research Center's Microgravity Material Science Laboratory using physical and mathematical models to delineate the effects of gravity on processes of scientific and commercial interest are discussed. Where possible, transparent model systems are used to visually track convection, settling, crystal growth, phase separation, agglomeration, vapor transport, diffusive flow, and polymer reactions. Materials studied include metals, alloys, salts, glasses, ceramics, and polymers. Specific technologies discussed include the General Purpose furnace used in the study of metals and crystal growth, the isothermal dendrite growth apparatus, the electromagnetic levitator/instrumented drop tube, the high temperature directional solidification furnace, the ceramics and polymer laboratories and the center's computing facilities.

Composition and method for brazing graphite to graphite

DOEpatents

Taylor, A.J.; Dykes, N.L.

1982-08-10

A brazing material is described for joining graphite structures that can be used up to 2800/sup 0/C. The brazing material is formed of a paste-like composition of hafnium carbide and uranium oxide with a thermosetting resin. The uranium oxide is converted to uranium dicarbide during the brazing operation and then the hafnium carbide and uranium dicarbide form a liquid phase at a temperature about 2600/sup 0/C with the uranium diffusing and vaporizing from the joint area as the temperature is increased to about 2800/sup 0/C so as to provide a brazed joint consisting essentially of hafnium carbide. The resulting brazed joint is chemically and thermally compatible with the graphite structures.

Laboratory Studies of DIB Carriers

NASA Technical Reports Server (NTRS)

Allamandola, L. J.

1995-01-01

Spectroscopic studies of the following potential diffuse interstellar band (DIB) carriers are reviewed: unspecified organics, carbon chains, polycyclic aromatic hydrocarbons (PAHs), fullerenes and derivatives, as well as porphyrins and related material. An assessment of each is given, along with suggestions for further experimental studies needed to fully test each candidate. Of the experimental techniques in common use matrix isolation spectroscopy with neon matrices is the most appropriate for the DIBs. The low vapor pressure and high reactivity of these materials preclude gas phase studies on many of these species. At this point, given the type and quality of published data available, carbon chains and PARs are the most promising candidates for a number of the DIBs.

Vapor Phase Deposition Using Plasma Spray-PVD™

NASA Astrophysics Data System (ADS)

von Niessen, K.; Gindrat, M.; Refke, A.

2010-01-01

Plasma spray—physical vapor deposition (PS-PVD) is a low pressure plasma spray technology to deposit coatings out of the vapor phase. PS-PVD is a part of the family of new hybrid processes recently developed by Sulzer Metco AG (Switzerland) on the basis of the well-established low pressure plasma spraying (LPPS) technology. Included in this new process family are plasma spray—chemical vapor deposition (PS-CVD) and plasma spray—thin film (PS-TF) processes. In comparison to conventional vacuum plasma spraying and LPPS, these new processes use a high energy plasma gun operated at a work pressure below 2 mbar. This leads to unconventional plasma jet characteristics which can be used to obtain specific and unique coatings. An important new feature of PS-PVD is the possibility to deposit a coating not only by melting the feed stock material which builds up a layer from liquid splats, but also by vaporizing the injected material. Therefore, the PS-PVD process fills the gap between the conventional PVD technologies and standard thermal spray processes. The possibility to vaporize feedstock material and to produce layers out of the vapor phase results in new and unique coating microstructures. The properties of such coatings are superior to those of thermal spray and EB-PVD coatings. This paper reports on the progress made at Sulzer Metco to develop functional coatings build up from vapor phase of oxide ceramics and metals.

Comparison of precursor infiltration into polymer thin films via atomic layer deposition and sequential vapor infiltration using in-situ quartz crystal microgravimetry

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

Padbury, Richard P.; Jur, Jesse S., E-mail: jsjur@ncsu.edu

Previous research exploring inorganic materials nucleation behavior on polymers via atomic layer deposition indicates the formation of hybrid organic–inorganic materials that form within the subsurface of the polymer. This has inspired adaptations to the process, such as sequential vapor infiltration, which enhances the diffusion of organometallic precursors into the subsurface of the polymer to promote the formation of a hybrid organic–inorganic coating. This work highlights the fundamental difference in mass uptake behavior between atomic layer deposition and sequential vapor infiltration using in-situ methods. In particular, in-situ quartz crystal microgravimetry is used to compare the mass uptake behavior of trimethyl aluminummore » in poly(butylene terephthalate) and polyamide-6 polymer thin films. The importance of trimethyl aluminum diffusion into the polymer subsurface and the subsequent chemical reactions with polymer functional groups are discussed.« less

Insights into gold-catalyzed plasma-assisted CVD growth of silicon nanowires

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

Chen, Wanghua, E-mail: wanghua.chen@polytechnique.edu; Roca i Cabarrocas, Pere

2016-07-25

Understanding and controlling effectively the behavior of metal catalyst droplets during the Vapor-Liquid-Solid growth of nanowires are crucial for their applications. In this work, silicon nanowires are produced by plasma-assisted Chemical Vapor Deposition using gold as a catalyst. The influence of hydrogen plasma on nanowire growth is investigated experimentally and theoretically. Interestingly, in contrast to conventional chemical vapor deposition, the growth rate of silicon nanowires shows a decrease as a function of their diameters, which is consistent with the incorporation of silicon via sidewall diffusion. We show that Ostwald ripening of catalyst droplets during nanowire growth is inhibited in themore » presence of a hydrogen plasma. However, when the plasma is off, the diffusion of Au atoms on the nanowire sidewall can take place. Based on this observation, we have developed a convenient method to grow silicon nanotrees.« less

Kinetic vaporization of heavy metals during fluidized bed thermal treatment of municipal solid waste.

PubMed

Yu, Jie; Sun, Lushi; Xiang, Jun; Hu, Song; Su, Sheng

2013-02-01

Heavy metals volatilization during thermal treatment of model solid waste was theoretically and experimentally investigated in a fluidized bed reactor. Lead, cadmium, zinc and copper, the most four conventional heavy metals were investigated. Particle temperature model and metal diffusion model were established to simulate the volatilization of CdCl(2) evaporation and investigate the possible influencing factors. The diffusion coefficient, porosity and particle size had significant effects on metal volatilization. The higher diffusion coefficient and porosity resulted in the higher metal evaporation. The influence of redox conditions, HCl, water and mineral matrice were also investigated experimentally. The metal volatilization can be promoted by the injection of HCl, while oxygen played a negative role. The diffusion process of heavy metals within particles also had a significant influence on kinetics of their vaporization. The interaction between heavy metals and mineral matter can decrease metal evaporation amount by forming stable metallic species. Copyright © 2012 Elsevier Ltd. All rights reserved.

Enhanced kinetics of Al{sub 0.97}Ga{sub 0.03}As wet oxidation through the use of hydrogenation

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

Le Du, M.; Sagnes, I.; Beaudoin, G.

2006-09-11

This letter reports on a different kinetic behavior of the wet thermal oxidation process resulting in Al{sub x}O{sub y} material depending on the AlAs material growth method, molecular beam epitaxy (MBE) or metal organic vapor phase epitaxy (MOVPE). A higher oxidation rate for MOVPE-grown materia is systemically found. Considering the major role of hydrogen in the wet oxidation reaction, it is believed this observation could be linked with the higher hydrogen residual concentration in MOVPE layers. Using a hydrogen plasma, MBE-grown Al{sub 0.97}Ga{sub 0.03}As layers were hydrogened prior to oxidation. This hydrogenated sample showed a ten times enhanced oxidation ratemore » as compared to the nonhydrogenated Al{sub 0.97}Ga{sub 0.03}As sample. This behavior is mainly attributed to a hydrogen induced modification of the diffusion limited regime, enhancing the diffusion length of oxidizing species and reaction products in the oxidized layers.« less

SEPARATION OF GASES BY DIFFUSIION

DOEpatents

Peierls, R.E.; Simon, F.E.; Arms, H.S.

1960-12-13

A method and apparatus are given for the separation of mixtures of gaseous or vaporous media by diffusion through a permeable membrane. The apparatus consists principally of a housing member having an elongated internal chamber dissected longitudinally by a permeable membrane. Means are provided for producing a pressure difference between opposite sides of the membrane to cause a flow of the media in the chamber therethrough. This pressure difference is alternated between opposite sides of the membrane to produce an oscillating flow through the membrane. Additional means is provided for producing flow parallel to the membrane in opposite directions on the two sides thereof and of the same frequency and in phase with the alternating pressure difference. The lighter molecules diffuse through the membrane more readily than the heavier molecules and the parallel flow effects a net transport of the lighter molecules in one direction and the heavier molecules in the opposite direction within the chamber. By these means a concentration gradient along the chamber is established.

Towards a bulk approach to local interactions of hydrometeors

NASA Astrophysics Data System (ADS)

Baumgartner, Manuel; Spichtinger, Peter

2018-02-01

The growth of small cloud droplets and ice crystals is dominated by the diffusion of water vapor. Usually, Maxwell's approach to growth for isolated particles is used in describing this process. However, recent investigations show that local interactions between particles can change diffusion properties of cloud particles. In this study we develop an approach for including these local interactions into a bulk model approach. For this purpose, a simplified framework of local interaction is proposed and governing equations are derived from this setup. The new model is tested against direct simulations and incorporated into a parcel model framework. Using the parcel model, possible implications of the new model approach for clouds are investigated. The results indicate that for specific scenarios the lifetime of cloud droplets in subsaturated air may be longer (e.g., for an initially water supersaturated air parcel within a downdraft). These effects might have an impact on mixed-phase clouds, for example in terms of riming efficiencies.

An Atmospheric Tape Recorder: The Imprint of Tropical Tropopause Temperatures on Stratospheric Water Vapor

NASA Technical Reports Server (NTRS)

Mote, Philip W.; Rosenlof, Karen H.; McIntyre, Michael E.; Carr, Ewan S.; Gille, John C.; Holton, James R.; Kinnersley, Jonathan S.; Pumphrey, Hugh C.; Russell, James M., III; Waters, Joe W.

1996-01-01

We describe observations of tropical stratospheric water vapor q that show clear evidence of large-scale upward advection of the signal from annual fluctuations in the effective 'entry mixing ratio' q(sub E) of air entering the tropical stratosphere. In other words, air is 'marked,' on emergence above the highest cloud tops, like a signal recorded on an upward moving magnetic tape. We define q(sub E) as the mean water vapor mixing ratio, at the tropical tropopause, of air that will subsequently rise and enter the stratospheric 'overworld' at about 400 K. The observations show a systematic phase lag, increasing with altitude, between the annual cycle in q(sub E) and the annual cycle in q at higher altitudes. The observed phase lag agrees with the phase lag calculated assuming advection by the transformed Eulerian-mean vertical velocity of a q(sub E) crudely estimated from 100-hPa temperatures, which we use as a convenient proxy for tropopause temperatures. The phase agreement confirms the overall robustness of the calculation and strongly supports the tape recorder hypothesis. Establishing a quantitative link between q(sub E) and observed tropopause temperatures, however, proves difficult because the process of marking the tape depends subtly on both small- and large-scale processes. The tape speed, or large-scale upward advection speed, has a substantial annual variation and a smaller variation due to the quasi-biennial oscillation, which delays or accelerates the arrival of the signal by a month or two in the middle stratosphere. As the tape moves upward, the signal is attenuated with an e-folding time of about 7 to 9 months between 100 and 50 hPa and about 15 to 18 months between 50 and 20 hPa, constraining possible orders of magnitude both of vertical diffusion K(sub z) and of rates of mixing in from the extratropics. For instance, if there were no mixing in, then K(sub z) would be in the range 0.03-0.09 m(exp 2)/s; this is an upper bound on K(sub z).

The effect of heated vapor-phase acidification on organic carbon concentrations and isotopic values in geologic rock samples

NASA Astrophysics Data System (ADS)

Wang, R. Z.; West, A. J.; Yager, J. A.; Rollins, N.; Li, G.; Berelson, W.

2016-12-01

Carbon signatures recorded in the modern and geologic rock record can give insight on the Earth's carbon cycle through time. This is especially true for organic carbon (OC), which can help us understand how the biosphere has evolved over Earth's history. However, carbon recorded in rocks is a combination of OC and inorganic carbon (IC) mostly in the form of carbonate minerals. To measure OC, IC must therefore first be removed through a process called "decarbonation." This is often done through a leaching process with hydrochloric acid (HCl). However, three well known problems exist for the decarbonation process: 1) Incomplete removal of IC, 2) Unintentional removal of OC, and 3) Addition of false carbon blank. Currently, vapor (gas) phase removal of OC is preferred to liquid phase treatment because it has been shown that OC is lost to solubilization during liquid phase acidification. Vapor phase treatment is largely thought to avoid the problem of OC loss, but this has not yet been rigorously investigated. This study investigates that assumption and shows that vapor phase treatment can cause unintentional OC loss. We show that vapor phase treatment must be sensitive to rock type and treatment length to produce robust OC isotopic measurements and concentrations.

Preliminary evaluation of the role of K2S in MHD hot stream seed recovery

NASA Technical Reports Server (NTRS)

Bennett, J. E.; Kohl, F. J.

1979-01-01

Results are presented for recent analytical and experimental studies of the role of K2S in MHD hot stream seed recovery. The existing thermodynamic data base was found to contain large uncertainties and to be nonexistent for vapor phase K2S. Knudsen cell mass spectrometric experiments were undertaken to determine the vapor species in equilibrium with K2S(c). K atoms and S2 molecules ere found to be the major vapor phase species in vacuum, accounting for greater than 99 percent of the vapor phase. Combustion gas deposition studies using No. 2 Diesel fuel were also undertaken and revealed that condensed phase K2SO3 may potentially be an important compound in the MHD stream at near-stoichiometric combustion.

Non-Ballistic Vapor-Driven Ejecta

NASA Technical Reports Server (NTRS)

Wrobel, K. E.; Schultz, P. H.; Heineck, J. T.

2004-01-01

Impact-induced vaporization is a key component of early-time cratering mechanics. Previous experimental [1,2] and computational [e.g., 3] studies focused on the generation and expansion of vapor clouds in an attempt to better understand vaporization in hypervelocity impacts. Presented here is a new experimental approach to the study of impact-induced vaporization. The three-dimensional particle image velocimetry (3D PIV) system captures interactions between expanding vapor phases and fine particulates. Particles ejected early in the cratering process may be entrained in expanding gas phases generated at impact, altering their otherwise ballistic path of flight. 3D PIV allows identifying the presence of such non-ballistic ejecta from very early times in the cratering process.

Evaporation enhancement in soils: a critical review

NASA Astrophysics Data System (ADS)

Rutten, Martine; van de Giesen, Nick

2015-04-01

Temperature gradients in the top layer of the soil are, especially during the daytime, steeper than would be expected if thermal conduction was the primary heat transfer mechanism. Evaporation seems to have significant influence on the soil heat budget. Only part of the surface soil heat flux is conducted downwards, increasing the soil temperatures, and part is used for evaporation, acting as a sink to the soil heat budget. For moist soils, the evaporation is limited by the transport of water molecules to the surface. The classical view is that water vapor is transported from the evaporation front to the surface by diffusion. Diffusion is mixing due to the random movement of molecules resulting in flattening concentration gradients. In soil, the diffusive vapor flux and the resulting latent heat flux are generally small. We found that transport enhancement is necessary in order to sustain vapor fluxes that are large enough to sustain latent heat fluxes, as well as being large enough to explain the observed temperature gradients. Enhancement of vapor diffusion is a known phenomenon, subject to debate on the explanations of underlying mechanism. In an extensive literature review on vapor enhancement in soils, the plausibility of various mechanisms was assessed. We reviewed mechanisms based on (combinations of) diffusive, viscous, buoyant, capillary and external pressure forces including: thermodiffusion, dispersion, Stefan's flow, Knudsen diffusion, liquid island effect, hydraulic lift, free convection, double diffusive convection and forced convection. The analysis of the order of magnitude of the mechanisms based on first principles clearly distinguished between plausible and implausible mechanisms. Thermodiffusion, Stefan's flow, Knudsen effects, liquid islands do not significantly contribute to enhanced evaporation. Double diffusive convection seemed unlikely due to lack of experimental evidence, but could not be completely excluded from the list of potential mechanisms. Hydraulic lift, the mechanism that small capillaries lift liquid water to the surface where it evaporates, does significantly contribute to enhanced evaporation from soils, also from dryer soils. The experimental evidence for and the theoretical underpinnings of this mechanism are convincing. However, we sought mechanisms that both explain enhanced evaporation and steep temperature gradients in the soil during the daytime. These often observed gradients consist of a sharp decrease of temperature with a depth up to the depth of the evaporation front. Hydraulic lift cannot explain this because the evaporation front is located at the surface. One remaining mechanism is forced convection due to atmospheric pressure fluctuations, also referred to as wind pumping. Wind pumping causes displacement and flow velocities too small for significant convective and too small for significant dispersive transport, when steady state dispersion formulations are used. However, experiments do indicate significant dispersive transport that can be explained by dispersion under unsteady flow conditions. Forced convection due to pressure fluctuations seems to be the only mechanism that can explain both enhanced evaporation and the steep temperature gradients.

Diffusive counter dispersion of mass in bubbly media.

PubMed

Goldobin, Denis S; Brilliantov, Nikolai V

2011-11-01

We consider a liquid bearing gas bubbles in a porous medium. When gas bubbles are immovably trapped in a porous matrix by surface-tension forces, the dominant mechanism of transfer of gas mass becomes the diffusion of gas molecules through the liquid. Essentially, the gas solution is in local thermodynamic equilibrium with vapor phase all over the system, i.e., the solute concentration equals the solubility. When temperature and/or pressure gradients are applied, diffusion fluxes appear and these fluxes are faithfully determined by the temperature and pressure fields, not by the local solute concentration, which is enslaved by the former. We derive the equations governing such systems, accounting for thermodiffusion and gravitational segregation effects, which are shown not to be neglected for geological systems-marine sediments, terrestrial aquifers, etc. The results are applied for the treatment of non-high-pressure systems and real geological systems bearing methane or carbon dioxide, where we find a potential possibility of the formation of gaseous horizons deep below a porous medium surface. The reported effects are of particular importance for natural methane hydrate deposits and the problem of burial of industrial production of carbon dioxide in deep aquifers.

Long-Term Cyclic Oxidation Behavior of Uncoated and Coated Re-108 and In-939 at 980 and 870 C

NASA Technical Reports Server (NTRS)

Lee, K. N.; Barrett, C. A.; Smith, J.

1999-01-01

Very long-term cyclic oxidation behavior of Re-108 and ln-939 with and without a protective coating was evaluated at 980 and 870 C, respectively. Re-108 and ln-939 without a protective coating began to show rapid weight loss at 3000 h due to scale spallation, indicating the need for an oxidation protective coating for longer than thousands of hours of oxidative life. NiAl-base coatings of a vapor phase aluminide (VPA), a pack aluminide (CODEP), and a slurry paint aluminide (SERMALOY J) were applied on Re-108 and ln-939. VPA and CODEP on Re-108 and all three coatings on ln-939 showed excellent cyclic oxidation resistance out to 10000 hr. Coated alloys were annealed in an inert atmosphere to determine the loss of Al from the coating into the alloy substrate through diffusion. The Al loss from the coating through diffusion was twice as great as the Al loss through oxidation after 10000 h of cyclic exposure. Oxidation life of VPA-coated Re-108 was estimated by calculating the amount of Al initially available for protective oxidation and the amount of Al lost through oxidation and diffusion.

Modeling and control of diffusion and low-pressure chemical vapor deposition furnaces

NASA Astrophysics Data System (ADS)

De Waard, H.; De Koning, W. L.

1990-03-01

In this paper a study is made of the heat transfer inside cylindrical resistance diffusion and low-pressure chemical vapor deposition furnaces, aimed at developing an improved temperature controller. A model of the thermal behavior is derived which also covers the important class of furnaces equipped with semitransparent quartz process tubes. The model takes into account the thermal behavior of the thermocouples. It is shown that currently used temperature controllers are highly inefficient for very large scale integration applications. Based on the model an alternative temperature controller of the linear-quadratic-Gaussian type is proposed which features direct wafer temperature control. Some simulation results are given.

Laser scattering in a hanging drop vapor diffusion apparatus for protein crystal growth in a microgravity environment

NASA Technical Reports Server (NTRS)

Casay, G. A.; Wilson, W. W.

1992-01-01

One type of hardware used to grow protein crystals in the microgravity environment aboard the U.S. Space Shuttle is a hanging drop vapor diffusion apparatus (HDVDA). In order to optimize crystal growth conditions, dynamic control of the HDVDA is desirable. A critical component in the dynamically controlled system is a detector for protein nucleation. We have constructed a laser scattering detector for the HDVDA capable of detecting the nucleation stage. The detector was successfully tested for several scatterers differing in size using dynamic light scattering techniques. In addition, the ability to detect protein nucleation using the HDVDA was demonstrated for lysozyme.

Growth mechanism and elemental distribution of beta-Ga2O3 crystalline nanowires synthesized by cobalt-assisted chemical vapor deposition.

PubMed

Wang, Hui; Lan, Yucheng; Zhang, Jiaming; Crimp, Martin A; Ren, Zhifeng

2012-04-01

Long beta-Ga2O3 crystalline nanowires are synthesized on patterned silicon substrates using chemical vapor deposition technique. Advanced electron microscopy indicates that the as-grown beta-Ga2O3 nanowires are consisted of poly-crystalline (Co, Ga)O tips and straight crystalline beta-Ga2O3 stems. The catalytic cobalt not only locates at the nanowire tips but diffuses into beta-Ga2O3 nanowire stems several ten nanometers. A solid diffusion growth mechanism is proposed based on the spatial elemental distribution along the beta-Ga2O3 nanowires at nanoscale.

Evaluation of surface tension and Tolman length as a function of droplet radius from experimental nucleation rate and supersaturation ratio: metal vapor homogeneous nucleation.

PubMed

Onischuk, A A; Purtov, P A; Baklanov, A M; Karasev, V V; Vosel, S V

2006-01-07

Zinc and silver vapor homogeneous nucleations are studied experimentally at the temperature from 600 to 725 and 870 K, respectively, in a laminar flow diffusion chamber with Ar as a carrier gas at atmospheric pressure. The size, shape, and concentration of aerosol particles outcoming the diffusion chamber are analyzed by a transmission electron microscope and an automatic diffusion battery. The wall deposit is studied by a scanning electron microscope (SEM). Using SEM data the nucleation rate for both Zn and Ag is estimated as 10(10) cm(-3) s(-1). The dependence of critical supersaturation on temperature for Zn and Ag measured in this paper as well as Li, Na, Cs, Ag, Mg, and Hg measured elsewhere is analyzed. To this aim the classical nucleation theory is extended by the dependence of surface tension on the nucleus radius. The preexponent in the formula for the vapor nucleation rate is derived using the formula for the work of formation of noncritical embryo [obtained by Nishioka and Kusaka [J. Chem. Phys. 96, 5370 (1992)] and later by Debenedetti and Reiss [J. Chem. Phys. 108, 5498 (1998)

A kinetic model for heterogeneous condensation of vapor on an insoluble spherical particle.

PubMed

Luo, Xisheng; Fan, Yu; Qin, Fenghua; Gui, Huaqiao; Liu, Jianguo

2014-01-14

A kinetic model is developed to describe the heterogeneous condensation of vapor on an insoluble spherical particle. This new model considers two mechanisms of cluster growth: direct addition of water molecules from the vapor and surface diffusion of adsorbed water molecules on the particle. The effect of line tension is also included in the model. For the first time, the exact expression of evaporation coefficient is derived for heterogeneous condensation of vapor on an insoluble spherical particle by using the detailed balance. The obtained expression of evaporation coefficient is proved to be also correct in the homogeneous condensation and the heterogeneous condensation on a planar solid surface. The contributions of the two mechanisms to heterogeneous condensation including the effect of line tension are evaluated and analysed. It is found that the cluster growth via surface diffusion of adsorbed water molecules on the particle is more important than the direct addition from the vapor. As an example of our model applications, the growth rate of the cap shaped droplet on the insoluble spherical particle is derived. Our evaluation shows that the growth rate of droplet in heterogeneous condensation is larger than that in homogeneous condensation. These results indicate that an explicit kinetic model is benefit to the study of heterogeneous condensation on an insoluble spherical particle.

Physics of lithium bromide (LiBr) solution dewatering through vapor venting membranes

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

Isfahani, RN; Fazeli, A; Bigham, S

2014-01-01

The physics of water desorption from a lithium bromide (LiBr) solution flow through an array of microchannels capped by a porous membrane is studied. The membrane allows the vapor to exit the flow and retains the liquid. Effects of different parameters such as wall temperature, solution and vapor pressures, and solution mass flux on the desorption rate were studied. Two different mechanisms of desorption are analyzed. These mechanisms consisted of: (1) direct diffusion of water molecules out of the solution and their subsequent flow through the membrane and (2) formation of water vapor bubbles within the solution and their ventingmore » through the membrane. Direct diffusion was the dominant desorption mode at low surface temperatures and its magnitude was directly related to the vapor pressure, the solution concentration, and the heated wall temperature. Desorption at the boiling regime was predominantly controlled by the solution flow pressure and mass flux. Microscale visualization studies suggested that at a critical mass flux, some bubbles are carried out of the desorber through the solution microchannels rather than being vented through the membrane. Overall, an order of magnitude higher desorption rate compare to a previous study on a membrane-based desorber was achieved. Published by Elsevier Ltd.« less

Field Testing of an Unvented Roof with Fibrous Insulation, Tiles and Vapor Diffusion Venting

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

Ueno, K.; Lstiburek, J. W.

This research is a test implementation of an unvented tile roof assembly in a hot-humid climate (Orlando, FL; Zone 2A), insulated with air permeable insulation (netted and blown fiberglass). Given the localized moisture accumulation and failures seen in previous unvented roof field work, it was theorized that a 'diffusion vent' (water vapor open, but air barrier 'closed') at the highest points in the roof assembly might allow for the wintertime release of moisture, to safe levels. The 'diffusion vent' is an open slot at the ridge and hips, covered with a water-resistant but vapor open (500+ perm) air barrier membrane.more » As a control comparison, one portion of the roof was constructed as a typical unvented roof (self-adhered membrane at ridge). The data collected to date indicate that the diffusion vent roof shows greater moisture safety than the conventional, unvented roof design. The unvented roof had extended winter periods of 95-100% RH, and wafer (wood surrogate RH sensor) measurements indicating possible condensation; high moisture levels were concentrated at the roof ridge. In contrast, the diffusion vent roofs had drier conditions, with most peak MCs (sheathing) below 20%. In the spring, as outdoor temperatures warmed, all roofs dried well into the safe range (10% MC or less). Some roof-wall interfaces showed moderately high MCs; this might be due to moisture accumulation at the highest point in the lower attic, and/or shading of the roof by the adjacent second story. Monitoring will be continued at least through spring 2016 (another winter and spring).« less

Radial inhomogeneities in particle composition of single, levitated aerosol particles observed by Mie resonance spectroscopy (Invited)

NASA Astrophysics Data System (ADS)

Krieger, U. K.; Steimer, S.; Lienhard, D.; Bastelberger, S.

2013-12-01

Recent observations have indicated that organic aerosol particles in the atmosphere may exist in an amorphous semi-solid or even solid (i.e. glassy) state, e.g. [1]. The influence of highly viscous and glassy states on the timescale of aerosol particle equilibration with respect to water vapor have been investigated for some model systems of atmospheric aerosol, e.g. [2,3]. In particular, it has been shown that the kinetics of the water absorption/desorption process is controlled entirely by liquid-phase diffusion of water molecules for a highly viscous aerosol particle. A liquid phase diffusion model based on numerically solving the non-linear diffusion equation predicts strong internal gradients in water concentration when condensed phase diffusion impedes the water uptake from the gas phase [2]. Here we observe and quantify the internal concentration gradients in single, levitated, micron size aerosol particles of aqueous MBTCA (3-methyl-1,2,3-Butanetricarboxylic acid) and shikimic acid using elastic Mie resonance spectroscopy. A single, aqueous particle is levitated in an electro-dynamic balance (for details see [2]), dried for several days at room temperature, cooled to the target temperature and exposed to a rapid change in relative humidity. In addition to measuring the elastically backscattered light of a 'white light ' LED source and recording the full spectrum with a spectrograph as in [2], we use a tunable diode laser (TDL) to scan high resolution TE- and TM spectra. This combination allows observing various Mie resonance mode orders simultaneously. Since we perform the experiment at low temperatures and low humidities the changes in the Mie-spectra due to water uptake are sufficiently slow to resolve the kinetics. Experimental Mie resonance spectra are inverted to concentration profiles of water within the particle by applying the numerical diffusion model [2] in conjunction with Mie calculations of multilayered spheres [4]. Potential implications for gas to particle partitioning and heterogeneous chemistry are discussed. [1] A. Virtanen et al. (2010): An amorphous solid state of biogenic secondary organic aerosol particles, Nature 467, 824-827. [2] B. Zobrist et al. (2011): Ultra-slow water diffusion in aqueous sucrose glasses, Phys. Chem. Chem. Phys. 13, 3514-3526. [3] D. L. Bones, J. P. Reid, D. M. Lienhard, and U. K. Krieger (2012): Comparing the mechanism of water condensation and evaporation in glassy aerosol, PNAS 109, 11613-11618. [4] O. Peña and U. Pal (2009): Scattering of electromagnetic radiation by a multilayered sphere, Comput. Phys. Commun. 180, 2348-2354.

Vapor-liquid coexistence of the Stockmayer fluid in nonuniform external fields.

PubMed

Samin, Sela; Tsori, Yoav; Holm, Christian

2013-05-01

We investigate the structure and phase behavior of the Stockmayer fluid in the presence of nonuniform electric fields using molecular simulation. We find that an initially homogeneous vapor phase undergoes a local phase separation in a nonuniform field due to the combined effect of the field gradient and the fluid vapor-liquid equilibrium. This results in a high-density fluid condensing in the strong field region. The system polarization exhibits a strong field dependence due to the fluid condensation.

Contribution for Iron Vapor and Radiation Distribution Affected by Current Frequency of Pulsed Arc

NASA Astrophysics Data System (ADS)

Shimokura, Takuya; Mori, Yusuke; Iwao, Toru; Yumoto, Motoshige

Pulsed GTA welding has been used for improvement of stability, weld speed, and heat input control. However, the temperature and radiation power of the pulsed arc have not been elucidated. Furthermore, arc contamination by metal vapor changes the arc characteristics, e.g. by increasing radiation power. In this case, the metal vapor in pulsed GTA welding changes the distribution of temperature and radiation power as a function of time. This paper presents the relation between metal vapor and radiation power at different pulse frequencies. We calculate the Fe vapor distribution of the pulsed current. Results show that the Fe vapor is transported at fast arc velocity during the peak current period. During the base current period, the Fe vapor concentration is low and distribution is diffuse. The transition of Fe vapor distribution does not follow the pulsed current; the radiation power density distribution differs for high frequencies and low frequencies. In addition, the Fe vapor and radiation distribution are affected by the pulsed arc current frequency.

Water vapor radiometry research and development phase

NASA Technical Reports Server (NTRS)

Resch, G. M.; Chavez, M. C.; Yamane, N. L.; Barbier, K. M.; Chandlee, R. C.

1985-01-01

This report describes the research and development phase for eight dual-channel water vapor radiometers constructed for the Crustal Dynamics Project at the Goddard Space Flight Center, Greenbelt, Maryland, and for the NASA Deep Space Network. These instruments were developed to demonstrate that the variable path delay imposed on microwave radio transmissions by atmospheric water vapor can be calibrated, particularly as this phenomenon affects very long baseline interferometry measurement systems. Water vapor radiometry technology can also be used in systems that involve moist air meteorology and propagation studies.

Blast from pressurized carbon dioxide released into a vented atmospheric chamber

NASA Astrophysics Data System (ADS)

Hansen, P. M.; Gaathaug, A. V.; Bjerketvedt, D.; Vaagsaether, K.

2018-03-01

This study describes the blast from pressurized carbon dioxide (CO2) released from a high-pressure reservoir into an openly vented atmospheric chamber. Small-scale experiments with pure vapor and liquid/vapor mixtures were conducted and compared with simulations. A motivation was to investigate the effects of vent size and liquid content on the peak overpressure and impulse response in the atmospheric chamber. The comparison of vapor-phase CO2 test results with simulations showed good agreement. This numerical code described single-phase gas dynamics inside a closed chamber, but did not model any phase transitions. Hence, the simulations described a vapor-only test into an unvented chamber. Nevertheless, the simulations reproduced the incident shock wave, the shock reflections, and the jet release inside the atmospheric chamber. The rapid phase transition did not contribute to the initial shock strength in the current test geometry. The evaporation rate was too low to contribute to the measured peak overpressure that was in the range of 15-20 kPa. The simulation results produced a calculated peak overpressure of 12 kPa. The liquid tests showed a significantly higher impulse compared to tests with pure vapor. Reducing the vent opening from 0.1 to 0.01 m2 resulted in a slightly higher impulse calculated at 100 ms. The influence of the vent area on the calculated impulse was significant in the vapor-phase tests, but not so clear in the liquid/vapor mixture tests.

Thermal analysis of 3-mol%-yttria-stabilized tetragonal zirconia powder doped with copper oxide

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

Seidensticker, J.R.; Mayo, M.J.

Thermal analysis was performed upon 3-mol%-yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) which had been doped with CuO using an aqueous adsorption technique. Cyclic differential thermal analysis (DTA) scans indicated that the CuO present on the powder surfaces first transforms to Cu{sub 2}O and then melts. The molten Cu{sub 2}O then reacts with yttria at the powder surfaces to form a new phase containing Y, Cu, and O. Because Y takes time to diffuse to the particle surfaces, the apparent melting point of this new phase appears at higher temperatures in initial DTA scans than in subsequent scans. Vaporization of the moltenmore » copper-oxide-rich phase at the temperatures studied causes a gradual shift in composition from Y{sub 2}Cu{sub 4}O{sub 5} to the less copper-rich Y{sub 2}Cu{sub 2}O{sub 5} phase. The presence of the Y{sub 2}Cu{sub 2}O{sub 5} phase in CuO-doped 3Y-TZP allows for previous sintering and superplasticity results to be explained.« less

Level set immersed boundary method for gas-liquid-solid interactions with phase-change

NASA Astrophysics Data System (ADS)

Dhruv, Akash; Balaras, Elias; Riaz, Amir; Kim, Jungho

2017-11-01

We will discuss an approach to simulate the interaction between two-phase flows with phase changes and stationary/moving structures. In our formulation, the Navier-Stokes and heat advection-diffusion equations are solved on a block-structured grid using adaptive mesh refinement (AMR) along with sharp jump in pressure, velocity and temperature across the interface separating the different phases. The jumps are implemented using a modified Ghost Fluid Method (Lee et al., J. Comput. Physics, 344:381-418, 2017), and the interface is tracked with a level set approach. Phase transition is achieved by calculating mass flux near the interface and extrapolating it to the rest of the domain using a Hamilton-Jacobi equation. Stationary/moving structures are simulated with an immersed boundary formulation based on moving least squares (Vanella & Balaras, J. Comput. Physics, 228:6617-6628, 2009). A variety of canonical problems involving vaporization, film boiling and nucleate boiling is presented to validate the method and demonstrate the its formal accuracy. The robustness of the solver in complex problems, which are crucial in efficient design of heat transfer mechanisms for various applications, will also be demonstrated. Work supported by NASA, Grant NNX16AQ77G.

Incorporating Phase-Dependent Polarizability in Non-Additive Electrostatic Models for Molecular Dynamics Simulations of the Aqueous Liquid-Vapor Interface.

PubMed

Bauer, Brad A; Warren, G Lee; Patel, Sandeep

2009-02-10

We discuss a new classical water force field that explicitly accounts for differences in polarizability between liquid and vapor phases. The TIP4P-QDP (4-point transferable intermolecular potential with charge dependent-polarizability) force field is a modification of the original TIP4P-FQ fluctuating charge water force field of Rick et al.(1) that self-consistently adjusts its atomic hardness parameters via a scaling function dependent on the M-site charge. The electronegativity (χ) parameters are also scaled in order to reproduce condensed-phase dipole moments of comparable magnitude to TIP4P-FQ. TIP4P-QDP is parameterized to reproduce experimental gas-phase and select condensed-phase properties. The TIP4P-QDP water model possesses a gas phase polarizability of 1.40 Å(3) and gas-phase dipole moment of 1.85 Debye, in excellent agreement with experiment and high-level ab initio predictions. The liquid density of TIP4P-QDP is 0.9954(±0.0002) g/cm(3) at 298 K and 1 atmosphere, and the enthalpy of vaporization is 10.55(±0.12) kcal/mol. Other condensed-phase properties such as the isobaric heat capacity, isothermal compressibility, and diffusion constant are also calculated within reasonable accuracy of experiment and consistent with predictions of other current state-of-the-art water force fields. The average molecular dipole moment of TIP4P-QDP in the condensed phase is 2.641(±0.001) Debye, approximately 0.02 Debye higher than TIP4P-FQ and within the range of values currently surmised for the bulk liquid. The dielectric constant, ε = 85.8 ± 1.0, is 10% higher than experiment. This is reasoned to be due to the increase in the condensed phase dipole moment over TIP4P-FQ, which estimates ε remarkably well. Radial distribution functions for TIP4P-QDP and TIP4P-FQ show similar features, with TIP4P-QDP showing slightly reduced peak heights and subtle shifts towards larger distance interactions. Since the greatest effects of the phase-dependent polarizability are anticipated in regions with both liquid and vapor character, interfacial simulations of TIP4P-QDP were performed and compared to TIP4P-FQ, a static polarizability analog. Despite similar features in density profiles such as the position of the GDS and interfacial width, enhanced dipole moments are observed for the TIP4P-QDP interface and onset of the vapor phase. Water orientational profiles show an increased preference (over TIP4P-FQ) in the orientation of the permanent dipole vector of the molecule within the interface; an enhanced z-induced dipole moment directly results from this preference. Hydrogen bond formation is lower, on average, in the bulk for TIP4P-QDP than TIP4P-FQ. However, the average number of hydrogen bonds formed by TIP4P-QDP in the interface exceeds that of TIP4P-FQ, and observed hydrogen bond networks extend further into the gaseous region. The TIP4P-QDP interfacial potential, calculated to be -11.98(±0.08) kcal/mol, is less favorable than that for TIP4P-FQ by approximately 2% as a result of a diminished quadrupole contribution. Surface tension is calculated within a 1.3% reduction from the experimental value. Results reported demonstrate TIP4P-QDP as a model comparable to the popular TIP4P-FQ while accounting for a physical effect previously neglected by other water models. Further refinements to this model, as well as future applications are discussed.

Incorporating Phase-Dependent Polarizability in Non-Additive Electrostatic Models for Molecular Dynamics Simulations of the Aqueous Liquid-Vapor Interface

PubMed Central

Bauer, Brad A.; Warren, G. Lee; Patel, Sandeep

2012-01-01

We discuss a new classical water force field that explicitly accounts for differences in polarizability between liquid and vapor phases. The TIP4P-QDP (4-point transferable intermolecular potential with charge dependent-polarizability) force field is a modification of the original TIP4P-FQ fluctuating charge water force field of Rick et al.1 that self-consistently adjusts its atomic hardness parameters via a scaling function dependent on the M-site charge. The electronegativity (χ) parameters are also scaled in order to reproduce condensed-phase dipole moments of comparable magnitude to TIP4P-FQ. TIP4P-QDP is parameterized to reproduce experimental gas-phase and select condensed-phase properties. The TIP4P-QDP water model possesses a gas phase polarizability of 1.40 Å3 and gas-phase dipole moment of 1.85 Debye, in excellent agreement with experiment and high-level ab initio predictions. The liquid density of TIP4P-QDP is 0.9954(±0.0002) g/cm3 at 298 K and 1 atmosphere, and the enthalpy of vaporization is 10.55(±0.12) kcal/mol. Other condensed-phase properties such as the isobaric heat capacity, isothermal compressibility, and diffusion constant are also calculated within reasonable accuracy of experiment and consistent with predictions of other current state-of-the-art water force fields. The average molecular dipole moment of TIP4P-QDP in the condensed phase is 2.641(±0.001) Debye, approximately 0.02 Debye higher than TIP4P-FQ and within the range of values currently surmised for the bulk liquid. The dielectric constant, ε = 85.8 ± 1.0, is 10% higher than experiment. This is reasoned to be due to the increase in the condensed phase dipole moment over TIP4P-FQ, which estimates ε remarkably well. Radial distribution functions for TIP4P-QDP and TIP4P-FQ show similar features, with TIP4P-QDP showing slightly reduced peak heights and subtle shifts towards larger distance interactions. Since the greatest effects of the phase-dependent polarizability are anticipated in regions with both liquid and vapor character, interfacial simulations of TIP4P-QDP were performed and compared to TIP4P-FQ, a static polarizability analog. Despite similar features in density profiles such as the position of the GDS and interfacial width, enhanced dipole moments are observed for the TIP4P-QDP interface and onset of the vapor phase. Water orientational profiles show an increased preference (over TIP4P-FQ) in the orientation of the permanent dipole vector of the molecule within the interface; an enhanced z-induced dipole moment directly results from this preference. Hydrogen bond formation is lower, on average, in the bulk for TIP4P-QDP than TIP4P-FQ. However, the average number of hydrogen bonds formed by TIP4P-QDP in the interface exceeds that of TIP4P-FQ, and observed hydrogen bond networks extend further into the gaseous region. The TIP4P-QDP interfacial potential, calculated to be -11.98(±0.08) kcal/mol, is less favorable than that for TIP4P-FQ by approximately 2% as a result of a diminished quadrupole contribution. Surface tension is calculated within a 1.3% reduction from the experimental value. Results reported demonstrate TIP4P-QDP as a model comparable to the popular TIP4P-FQ while accounting for a physical effect previously neglected by other water models. Further refinements to this model, as well as future applications are discussed. PMID:23133341

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.

Properties of model atomic free-standing thin films.

PubMed

Shi, Zane; Debenedetti, Pablo G; Stillinger, Frank H

2011-03-21

We present a computational study of the thermodynamic, dynamic, and structural properties of free-standing thin films, investigated via molecular dynamics simulation of a glass-forming binary Lennard-Jones mixture. An energy landscape analysis is also performed to study glassy states. At equilibrium, species segregation occurs, with the smaller minority component preferentially excluded from the surface. The film's interior density and interface width depend solely on temperature and not the initialization density. The atoms at the surface of the film have a higher lateral diffusivity when compared to the interior. The average difference between the equilibrium and inherent structure energies assigned to individual particles, as a function of the distance from the center of the film, increases near the surface. A minimum of this difference occurs in the region just under the liquid-vapor interface. This suggests that the surface atoms are able to sample the underlying energy landscape more effectively than those in the interior, and we suggest a possible relationship of this observation to the recently reported formation of stable glasses by vapor phase deposition.

Reactive codoping of GaAlInP compound semiconductors

DOEpatents

Hanna, Mark Cooper [Boulder, CO; Reedy, Robert [Golden, CO

2008-02-12

A GaAlInP compound semiconductor and a method of producing a GaAlInP compound semiconductor are provided. The apparatus and method comprises a GaAs crystal substrate in a metal organic vapor deposition reactor. Al, Ga, In vapors are prepared by thermally decomposing organometallic compounds. P vapors are prepared by thermally decomposing phospine gas, group II vapors are prepared by thermally decomposing an organometallic group IIA or IIB compound. Group VIB vapors are prepared by thermally decomposing a gaseous compound of group VIB. The Al, Ga, In, P, group II, and group VIB vapors grow a GaAlInP crystal doped with group IIA or IIB and group VIB elements on the substrate wherein the group IIA or IIB and a group VIB vapors produced a codoped GaAlInP compound semiconductor with a group IIA or IIB element serving as a p-type dopant having low group II atomic diffusion.

Wetting phenomenon in the liquid-vapor phase coexistence of a partially miscible Lennard-Jones binary mixture

NASA Astrophysics Data System (ADS)

Ramírez-Santiago, Guillermo; Díaz-Herrera, Enrique; Moreno Razo, José A.

2004-03-01

We have carried out extensive equilibrium MD simulations to study wetting phenomena in the liquid-vapor phase coexistence of a partially miscible binary LJ mixture. We find that in the temperature range 0.60 ≤ T^* < 0.80, the system separates forming a liquid A-liquid B interface in coexistence with the vapor phase. At higher temperatures, 0.80 ≤ T^* < 1.25 the liquid phases are wet by the vapor phase. By studying the behavior of the surface tension as a function of temperature we estimate the wetting transition temperature (WTT) to be T^*_w≃ 0.80. The adsorption of molecules at the liquid-liquid interface shows a discontinuity at about T^*≃ 0.79 suggesting that the wetting transition is a first order phase transition. These results are in agreement with some experiments carried out in fluid binary mixtures. In addition, we estimated the consolute temperature to be T^* _cons≃ 1.25. The calculated phase diagram of the mixture suggest the existence of a tricritical point.

Deformability of adsorbents during adsorption and principles of the thermodynamics of solid-phase systems

NASA Astrophysics Data System (ADS)

Tovbin, Yu. K.

2017-09-01

A microscopic theory of adsorption, based on a discrete continuum lattice gas model for noninert (including deformable) adsorbents that change their lattice parameters during adsorption, is presented. Cases of the complete and partial equilibrium states of the adsorbent are considered. In the former, the adsorbent consists of coexisting solid and vapor phases of adsorbent components, and the adsorbate is a mobile component of the vapor phase with an arbitrary density (up to that of the liquid adsorbate phase). The adsorptive transitioning to the bound state changes the state of the near-surface region of the adsorbent. In the latter, there are no equilibrium components of the adsorbent between the solid and vapor phases. The adsorbent state is shown to be determined by its prehistory, rather than set by chemical potentials of vapor of its components. Relations between the microscopic theory and thermodynamic interpretations are discussed: (1) adsorption on an open surface, (2) two-dimensional stratification of the adsorbate mobile phase on an open homogeneous surface, (3) small microcrystals in vacuum and the gas phase, and (4) adsorption in porous systems.

Chemical vapor deposition of W-Si-N and W-B-N

DOEpatents

Fleming, J.G.; Roherty-Osmun, E.L.; Smith, P.M.; Custer, J.S.; Jones, R.V.; Nicolet, M.; Madar, R.; Bernard, C.

1999-06-29

A method of depositing a ternary, refractory based thin film on a substrate by chemical vapor deposition employing precursor sources of tungsten comprising WF[sub 6], either silicon or boron, and nitrogen. The result is a W-Si-N or W-B-N thin film useful for diffusion barrier and micromachining applications. 10 figs.

New Force Field Model for Propylene Glycol: Insight to Local Structure and Dynamics.

PubMed

Ferreira, Elisabete S C; Voroshylova, Iuliia V; Koverga, Volodymyr A; Pereira, Carlos M; Cordeiro, M Natália D S

2017-12-07

In this work we developed a new force field model (FFM) for propylene glycol (PG) based on the OPLS all-atom potential. The OPLS potential was refined using quantum chemical calculations, taking into account the densities and self-diffusion coefficients. The validation of this new FFM was carried out based on a wide range of physicochemical properties, such as density, enthalpy of vaporization, self-diffusion coefficients, isothermal compressibility, surface tension, and shear viscosity. The molecular dynamics (MD) simulations were performed over a large range of temperatures (293.15-373.15 K). The comparison with other force field models, such as OPLS, CHARMM27, and GAFF, revealed a large improvement of the results, allowing a better agreement with experimental data. Specific structural properties (radial distribution functions, hydrogen bonding and spatial distribution functions) were then analyzed in order to support the adequacy of the proposed FFM. Pure propylene glycol forms a continuous phase, displaying no microstructures. It is shown that the developed FFM gives rise to suitable results not only for pure propylene glycol but also for mixtures by testing its behavior for a 50 mol % aqueous propylene glycol solution. Furthermore, it is demonstrated that the addition of water to the PG phase produces a homogeneous solution and that the hydration interactions prevail over the propylene glycol self-association interactions.

Hydrogen transport and hydrogen embrittlement in stainless steels

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

Perng, T.P.

1985-01-01

In order to understand the kinetics of gaseous hydrogen-induced slow crack growth (SCG) in metastable austenitic stainless steels, hydrogen permeation and/or cracking velocity were measured and compared for three types of stainless steels. These included austenitic, ferritic, and duplex (..gamma../..cap alpha..) alloys. Deformation in AISI 301 resulted in various amounts of ..cap alpha..' martensite, which enhanced the effective hydrogen diffusivity and permeability. No phase transformation was observed in deformed AISI 310. The effective hydrogen diffusivity in this alloy was slightly reduced after plastic deformation, presumably by dislocation trapping. In either the dynamic or static tensile test, AISI 301 exhibited themore » greatest hydrogen embrittlement and therefore the highest SCG velocity among all the alloys tested in this work. The SCG velocity was believed to be controlled by the rate of accumulation of hydrogen in the embrittlement region ahead of the crack tip and therefore could be explained with the hydrogen transport parameters measured from the permeation experiments. The relatively high SCG velocity in AISI 301 was probably due to the fast transport of hydrogen through the primarily stress-induced ..cap alpha..' phase around the crack. No SCG was observed in AISI 310. The presence of H/sub 2/O vapor was found to reduce both the hydrogen permeation and SCG velocity.« less

Relaxation of contact-line singularities solely by the Kelvin effect and apparent contact angles for isothermal volatile liquids in contact with air

NASA Astrophysics Data System (ADS)

Rednikov, Alexey; Colinet, Pierre

2013-11-01

The contact (triple) line of a volatile liquid on a flat solid is studied theoretically. Like with a pure-vapor atmosphere [Phys. Rev. E 87, 010401, 2013], but here for isothermal diffusion-limited evaporation/condensation in the presence of an inert gas, we rigorously show that the notorious contact-line singularities (related to motion or phase change itself) can be regularized solely on account of the Kelvin effect (curvature dependence of the saturation conditions). No disjoining pressure, precursor films or Navier slip are in fact needed to this purpose, and nor are they taken into consideration here (``minimalist'' approach). The model applies to both perfect (zero Young's angle) and partial wetting, and is in particular used to study the related issue of evaporation-induced contact angles. Their modification by the contact-line motion (either advancing or receding) is assessed. The formulation is posed for a distinguished immediate vicinity of the contact line (the ``microregion''), the corresponding problem decoupling to leading order, here up to one unknown coefficient, from what actually happens at the macroscale. The lubrication approximation (implying sufficiently small contact angles) is used in the liquid, coupled with the diffusion equation in the gaz phase. Supported by ESA and BELSPO PRODEX and F.R.S.-FNRS.

Investigation of nucleation kinetics in H2SO4 vapor through modeling of gas phase kinetics coupled with particle dynamics

NASA Astrophysics Data System (ADS)

Carlsson, Philip T. M.; Zeuch, Thomas

2018-03-01

We have developed a new model utilizing our existing kinetic gas phase models to simulate experimental particle size distributions emerging in dry supersaturated H2SO4 vapor homogeneously produced by rapid oxidation of SO2 through stabilized Criegee-Intermediates from 2-butene ozonolysis. We use a sectional method for simulating the particle dynamics. The particle treatment in the model is based on first principles and takes into account the transition from the kinetic to the diffusion-limited regime. It captures the temporal evolution of size distributions at the end of the ozonolysis experiment well, noting a slight underrepresentation of coagulation effects for larger particle sizes. The model correctly predicts the shape and the modes of the experimentally observed particle size distributions. The predicted modes show an extremely high sensitivity to the H2SO4 evaporation rates of the initially formed H2SO4 clusters (dimer to pentamer), which were arbitrarily restricted to decrease exponentially with increasing cluster size. In future, the analysis presented in this work can be extended to allow a direct validation of quantum chemically predicted stabilities of small H2SO4 clusters, which are believed to initiate a significant fraction of atmospheric new particle formation events. We discuss the prospects and possible limitations of the here presented approach.

Development of Vapor-Phase Catalytic Ammonia Removal System

NASA Technical Reports Server (NTRS)

Flynn, Michael; Fisher, John; Kiss, Mark; Borchers, Bruce; Tleimat, Badawi; Tleimat, Maher; Quinn, Gregory; Fort, James; Nalette, Tim; Baker, Gale;

Experimental study of flash boiling spray vaporization through quantitative vapor concentration and liquid temperature measurements

NASA Astrophysics Data System (ADS)

Zhang, Gaoming; Hung, David L. S.; Xu, Min

2014-08-01

Flash boiling sprays of liquid injection under superheated conditions provide the novel solutions of fast vaporization and better air-fuel mixture formation for internal combustion engines. However, the physical mechanisms of flash boiling spray vaporization are more complicated than the droplet surface vaporization due to the unique bubble generation and boiling process inside a superheated bulk liquid, which are not well understood. In this study, the vaporization of flash boiling sprays was investigated experimentally through the quantitative measurements of vapor concentration and liquid temperature. Specifically, the laser-induced exciplex fluorescence technique was applied to distinguish the liquid and vapor distributions. Quantitative vapor concentration was obtained by correlating the intensity of vapor-phase fluorescence with vapor concentration through systematic corrections and calibrations. The intensities of two wavelengths were captured simultaneously from the liquid-phase fluorescence spectra, and their intensity ratios were correlated with liquid temperature. The results show that both liquid and vapor phase of multi-hole sprays collapse toward the centerline of the spray with different mass distributions under the flash boiling conditions. Large amount of vapor aggregates along the centerline of the spray to form a "gas jet" structure, whereas the liquid distributes more uniformly with large vortexes formed in the vicinity of the spray tip. The vaporization process under the flash boiling condition is greatly enhanced due to the intense bubble generation and burst. The liquid temperature measurements show strong temperature variations inside the flash boiling sprays with hot zones present in the "gas jet" structure and vortex region. In addition, high vapor concentration and closed vortex motion seem to have inhibited the heat and mass transfer in these regions. In summary, the vapor concentration and liquid temperature provide detailed information concerning the heat and mass transfer inside flash boiling sprays, which is important for the understanding of its unique vaporization process.

Modeling long-term uptake and re-volatilization of semi-volatile organic compounds (SVOCs) across the soil-atmosphere interface.

PubMed

Bao, Zhongwen; Haberer, Christina; Maier, Uli; Beckingham, Barbara; Amos, Richard T; Grathwohl, Peter

2015-12-15

Soil-atmosphere exchange is important for the environmental fate and atmospheric transport of many semi-volatile organic compounds (SVOCs). This study focuses on modeling the vapor phase exchange of semi-volatile hydrophobic organic pollutants between soil and the atmosphere using the multicomponent reactive transport code MIN3P. MIN3P is typically applied to simulate aqueous and vapor phase transport and reaction processes in the subsurface. We extended the code to also include an atmospheric boundary layer where eddy diffusion takes place. The relevant processes and parameters affecting soil-atmosphere exchange were investigated in several 1-D model scenarios and at various time scales (from years to centuries). Phenanthrene was chosen as a model compound, but results apply for other hydrophobic organic compounds as well. Gaseous phenanthrene was assumed to be constantly supplied to the system during a pollution period and a subsequent regulation period (with a 50% decline in the emission rate). Our results indicate that long-term soil-atmosphere exchange of phenanthrene is controlled by the soil compartment - re-volatilization thus depends on soil properties. A sensitivity analysis showed that accumulation and transport in soils in the short term is dominated by diffusion, whereas in the long term groundwater recharge and biodegradation become relevant. As expected, sorption causes retardation and slows down transport and biodegradation. If atmospheric concentration is reduced (e.g. after environmental regulations), re-volatilization from soil to the atmosphere occurs only for a relatively short time period. Therefore, the model results demonstrate that soils generally are sinks for atmospheric pollutants. The atmospheric boundary layer is only relevant for time scales of less than one month. The extended MIN3P code can also be applied to simulate fluctuating concentrations in the atmosphere, for instance due to temperature changes in the topsoil. Copyright © 2015. Published by Elsevier B.V.

Physical and photoelectrochemical properties of Sb-doped SnO2 thin films deposited by chemical vapor deposition: application to chromate reduction under solar light

NASA Astrophysics Data System (ADS)

Outemzabet, R.; Doulache, M.; Trari, M.

2015-05-01

Sb-doped SnO2 thin films (Sb-SnO2) are prepared by chemical vapor deposition. The X-ray diffraction indicates a rutile phase, and the SEM analysis shows pyramidal grains whose size extends up to 200 nm. The variation of the film thickness shows that the elaboration technique needs to be optimized to give reproducible layers. The films are transparent over the visible region. The dispersion of the optical indices is evaluated by fitting the diffuse reflectance data with the Drude-Lorentz model. The refractive index ( n) and absorption coefficient ( k) depend on both the conditions of preparation and of the doping concentration and vary between 1.4 and 2.0 and 0.2 and 0.01, respectively. Tin oxide is nominally non-stoichiometric, and the conduction is dominated by thermally electrons jump with an electron mobility of 12 cm2 V-1 s-1 for Sb-SnO2 (1 %). The ( C 2- V) characteristic in aqueous electrolyte exhibits a linear behavior from which an electrons density of 4.15 × 1018 cm-3 and a flat-band potential of -0.83 V SCE are determined. The electrochemical impedance spectroscopy shows a semicircle attributed to a capacitive behavior with a low density of surface states. The center lies below the real axis with a depletion angle (12°), due to a constant phase element, i.e., a deviation from a pure capacitive behavior, presumably attributed to the roughness and porosity of the film. The straight line at low frequencies is attributed to the Warburg diffusion. The energy diagram reveals the photocatalytic feasibility of Sb-SnO2. As application, 90 % of the chromate concentration (20 mg L-1, pH ~3) disappears after 6 h of exposure to solar light.

Dispersion of Vapor from LNG Spills -- Simulation in a Meteorological Wind Tunnel of Spills at China Lake Naval Weapons Center, California.

DTIC Science & Technology

1979-03-01

and Diffusion Laboratory Department of Civil Engineering, , / """..,--. Colorado State University DOT-CG-75279-A) )V Fnrt Cnl lin. Colorado 80523 ype...Film Aspirating Probe ......... .. 20 3.5.2 Errors in Concentration Measurement . . 21 4.0 TEST PROGRAM RESULTS ..... ............... .. 23 4.1...Coriolis Force Viscous Diffusivity Prandtl number Pr = v/(k/P C ViThrma Diffusivity0 0 p Thermal Diffusivity Eckert number Ec = /Cpo (AT)o 5 For exact

Plant-based plume-scale mapping of tritium contamination in desert soils

USGS Publications Warehouse

Andraski, Brian J.; Stonestrom, David A.; Michel, R.L.; Halford, K.J.; Radyk, J.C.

2005-01-01

Plant-based techniques were tested for field-scale evaluation of tritium contamination adjacent to a low-level radioactive waste (LLRW) facility in the Amargosa Desert, Nevada. Objectives were to (i) characterize and map the spatial variability of tritium in plant water, (ii) develop empirical relations to predict and map subsurface contamination from plant-water concentrations, and (iii) gain insight into tritium migration pathways and processes. Plant sampling [creosote bush, Larrea tridentata (Sessé & Moc. ex DC.) Coville] required one-fifth the time of soil water vapor sampling. Plant concentrations were spatially correlated to a separation distance of 380 m; measurement uncertainty accounted for <0.1% of the total variability in the data. Regression equations based on plant tritium explained 96 and 90% of the variation in root-zone and sub-root-zone soil water vapor concentrations, respectively. The equations were combined with kriged plant-water concentrations to map subsurface contamination. Mapping showed preferential lateral movement of tritium through a dry, coarse-textured layer beneath the root zone, with concurrent upward movement through the root zone. Analysis of subsurface fluxes along a transect perpendicular to the LLRW facility showed that upward diffusive-vapor transport dominates other transport modes beneath native vegetation. Downward advective-liquid transport dominates at one endpoint of the transect, beneath a devegetated road immediately adjacent to the facility. To our knowledge, this study is the first to document large-scale subsurface vapor-phase tritium migration from a LLRW facility. Plant-based methods provide a noninvasive, cost-effective approach to mapping subsurface tritium migration in desert areas.

A 1-D Cryothermal Model of Ceres’ Megaregolith: Predictions for Surface Vapor Flux, Subsurface Temperatures and Pore Ice Distribution

NASA Astrophysics Data System (ADS)

Reynolds, Dylan; Wood, Stephen E.; Bapst, Jonathan; Mehlhaff, Joshua; Griffiths, Stephen G.

2014-11-01

We have applied a self-consistent 1-D model for heat diffusion, vapor diffusion, and ice condensation/sublimation, and surface energy balance to investigate our hypothesis for the source of the recently observed water vapor around Ceres [1]. As described in a companion presentation [2], we find that the estimated global flux of 6 kg/s can be produced by steady-state sublimation of subsurface ice driven by the “geothermal” temperature gradient for a heat flux of 1 mW/m2 - the value estimated for a chondritic abundance of heat-producing elements [3,4]. We will present a detailed description of our Ceres cryothermal diffusion model and comparisons with previous models. One key difference is the use of a new physics-based analytic model (‘MaxRTCM’) for calculating the thermal conductivity (Kth) of planetary regolith [5] that has been validated by comparisons to a wide range of laboratory data [6]. MaxRTCM predicts much lower Kth values in the upper regolith than those in previous work [3]. It also accounts for a process first modeled in a study of unstable equatorial ground ice on Mars [7,8], where vapor diffusing up from a receding ice table toward the surface can recondense at shallower depths - eventually forming a steady-state profile of pore ice volume fraction that increases with depth and maintains a constant flux of vapor at all depths [7]. Using MaxRTCM we calculate the corresponding Kth(z) profiles and will present predictions and implications of the resulting temperature profile in the upper few kilometers of Ceres’ megaregolith.References: [1] Küppers et al. (2014), Nature, 505(7484), 525-527. [2] Wood et al., 2014, this meeting. [3] Fanale & Salvail (1989) Icarus 82, 97-110. [4] McCord and Sotin (2005) JGR 110, E05009. [5] Wood (2013) LPSC Abs. 44, 3077. [6] Wood (2014), Icarus, in revision. [7] Mellon et al. (1997), JGR, 102, 19357-69. [8] Clifford (1993), JGR, 98, 10973-11016.

A fundamental study of chromium deposition on solid oxide fuel cell cathode materials

NASA Astrophysics Data System (ADS)

Tucker, Michael C.; Kurokawa, Hideto; Jacobson, Craig P.; De Jonghe, Lutgard C.; Visco, Steven J.

Chromium contamination of metal oxides and SOFC cathode catalysts is studied in the range 700-1000 °C. Samples are exposed to a moist air atmosphere saturated with volatile Cr species in the presence and absence of direct contact between the sample and ferritic stainless steel powder. Chromium contamination of the samples is observed to occur via two separate pathways: surface diffusion from the stainless steel surface and vapor deposition from the atmosphere. Surface diffusion dominates in all cases. Surface diffusion is found to be a significant source of Cr contamination for LSM and LSCF at 700, 800, and 1000 °C. Vapor deposition of Cr onto LSCF was observed at each of these temperatures, but was not observed for LSM at 700 or 800 °C. Comparison of the behavior for LSM, LSCF, and single metal oxides suggests that Mn and Co, respectively, are responsible for the Cr contamination of these catalysts.

Kinetic Monte Carlo Simulations of Oxygen Diffusion in Environmental Barrier Coating Materials

NASA Technical Reports Server (NTRS)

Good, Brian S.

2017-01-01

Ceramic Matrix Composite (CMC) materials are of interest for use in next-generation turbine engine components, offering a number of significant advantages, including reduced weight and high operating temperatures. However, in the hot environment in which such components operate, the presence of water vapor can lead to corrosion and recession, limiting the useful life of the components. Such degradation can be reduced through the use of Environmental Barrier Coatings (EBCs) that limit the amount of oxygen and water vapor reaching the component. Candidate EBC materials include Yttrium and Ytterbium silicates. In this work we present results of kinetic Monte Carlo (kMC) simulations of oxygen diffusion, via the vacancy mechanism, in Yttrium and Ytterbium disilicates, along with a brief discussion of interstitial diffusion. An EBC system typically includes a bond coat located between the EBC and the component surface. Bond coat materials are generally chosen for properties other than low oxygen diffusivity, but low oxygen diffusivity is nevertheless a desirable characteristic, as the bond coat could provide some additional component protection, particularly in the case where cracks in the coating system provide a direct path from the environment to the bond coat interface. We have therefore performed similar kMC simulations of oxygen diffusion in this material.

Interfacial nonequilibrium and Bénard-Marangoni instability of a liquid-vapor system

NASA Astrophysics Data System (ADS)

Margerit, J.; Colinet, P.; Lebon, G.; Iorio, C. S.; Legros, J. C.

2003-10-01

We study Bénard-Marangoni instability in a system formed by a horizontal liquid layer and its overlying vapor. The liquid is lying on a hot rigid plate and the vapor is bounded by a cold parallel plate. A pump maintains a reduced pressure in the vapor layer and evacuates the vapor. This investigation is undertaken within the classical quasisteady approximation for both the vapor and the liquid phases. The two layers are separated by a deformable interface. Temporarily frozen temperature and velocity distributions are employed at each instant for the stability analysis, limited to infinitesimal disturbances (linear regime). We use irreversible thermodynamics to model the phase change under interfacial nonequilibrium. Within this description, the interface appears as a barrier for transport of both heat and mass. Hence, in contrast with previous studies, we consider the possibility of a temperature jump across the interface, as recently measured experimentally. The stability analysis shows that the interfacial resistances to heat and mass transfer have a destabilizing influence compared to an interface that is in thermodynamic equilibrium. The role of the fluctuations in the vapor phase on the onset of instability is discussed. The conditions to reduce the system to a one phase model are also established. Finally, the influence of the evaporation parameters and of the presence of an inert gas on the marginal stability curves is discussed.

Vaporization and recondensation dynamics of indocyanine green-loaded perfluoropentane droplets irradiated by a short pulse laser

NASA Astrophysics Data System (ADS)

Yu, Jaesok; Chen, Xucai; Villanueva, Flordeliza S.; Kim, Kang

2016-12-01

Phase-transition droplets have been proposed as promising contrast agents for ultrasound and photoacoustic imaging. Short pulse laser activated perfluorocarbon-based droplets, especially when in a medium with a temperature below their boiling point, undergo phase changes of vaporization and recondensation in response to pulsed laser irradiation. Here, we report and discuss the vaporization and recondensation dynamics of perfluoropentane droplets containing indocyanine green in response to a short pulsed laser with optical and acoustic measurements. To investigate the effect of temperature on the vaporization process, an imaging chamber was mounted on a temperature-controlled water reservoir and then the vaporization event was recorded at 5 million frames per second via a high-speed camera. The high-speed movies show that most of the droplets within the laser beam area expanded rapidly as soon as they were exposed to the laser pulse and immediately recondensed within 1-2 μs. The vaporization/recondensation process was consistently reproduced in six consecutive laser pulses to the same area. As the temperature of the media was increased above the boiling point of the perfluoropentane, the droplets were less likely to recondense and remained in a gas phase after the first vaporization. These observations will help to clarify the underlying processes and eventually guide the design of repeatable phase-transition droplets as a photoacoustic imaging contrast agent.

Application of Thioether for Vapor Phase Lubrication

NASA Technical Reports Server (NTRS)

Graham, E. Earl

1997-01-01

The objective of these studies was to identify the optimal conditions for vapor phase lubrication using Thioether for both sliding and rolling wear. The important variable include; (1) The component materials including M50 steel, monel and silicon nitride. (2) The vapor concentration and flow rate. (3) The temperature in the range of 600 F to 1500 F. (4) The loads and rolling and/or sliding speeds.

String flash-boiling in gasoline direct injection simulations with transient needle motion

DOE PAGES

Baldwin, Eli T.; Grover, Jr., Ronald O.; Parrish, Scott E.; ...

2016-09-06

A computational study was performed to investigate the influence of transient needle motion on gasoline direct injection (GDI) internal nozzle flow and near-field sprays. Simulations were conducted with a compressible Eulerian flow solver modeling liquid, vapor, and non-condensable gas phases with a diffuse interface. Variable rate generation and condensation of fuel vapor were captured using the homogeneous relaxation model (HRM). The non-flashing (spray G) and flashing (spray G2) conditions specified by the Engine Combustion Network were modeled using the nominal spray G nozzle geometry and transient needle lift and wobble were based upon ensemble averaged x-ray imaging preformed at Argonnemore » National Lab. The minimum needle lift simulated was 5 μm and dynamic mesh motion was achieved with Laplacian smoothing. The results were qualitatively validated against experimental imaging and the experimental rate of injection profile was captured accurately using pressure boundary conditions and needle motion to actu- ate the injection. Needle wobble was found to have no measurable effect on the flow. Low needle lift is shown to result in vapor generation as fuel rushes past the needle. In conclusion, the internal injector flow is shown to contain many transient and interacting vortices which cause perturbations in the spray angle, fluctuations in the mass flux, and frequently result in string flash-boiling.« less

String flash-boiling in gasoline direct injection simulations with transient needle motion

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

Baldwin, Eli T.; Grover, Jr., Ronald O.; Parrish, Scott E.

A computational study was performed to investigate the influence of transient needle motion on gasoline direct injection (GDI) internal nozzle flow and near-field sprays. Simulations were conducted with a compressible Eulerian flow solver modeling liquid, vapor, and non-condensable gas phases with a diffuse interface. Variable rate generation and condensation of fuel vapor were captured using the homogeneous relaxation model (HRM). The non-flashing (spray G) and flashing (spray G2) conditions specified by the Engine Combustion Network were modeled using the nominal spray G nozzle geometry and transient needle lift and wobble were based upon ensemble averaged x-ray imaging preformed at Argonnemore » National Lab. The minimum needle lift simulated was 5 μm and dynamic mesh motion was achieved with Laplacian smoothing. The results were qualitatively validated against experimental imaging and the experimental rate of injection profile was captured accurately using pressure boundary conditions and needle motion to actu- ate the injection. Needle wobble was found to have no measurable effect on the flow. Low needle lift is shown to result in vapor generation as fuel rushes past the needle. In conclusion, the internal injector flow is shown to contain many transient and interacting vortices which cause perturbations in the spray angle, fluctuations in the mass flux, and frequently result in string flash-boiling.« less

The Vapor-phase Multi-stage CMD Test for Characterizing Contaminant Mass Discharge Associated with VOC Sources in the Vadose Zone: Application to Three Sites in Different Lifecycle Stages of SVE Operations

PubMed Central

Brusseau, M.L.; Mainhagu, J.; Morrison, C.; Carroll, K.C.

2015-01-01

Vapor-phase multi-stage contaminant mass discharge (CMD) tests were conducted at three field sites to measure mass discharge associated with contaminant sources located in the vadose zone. The three sites represent the three primary stages along the soil vapor extraction (SVE) operations lifecycle- pre/initial-SVE, mid-lifecycle, and near-closure. A CMD of 32 g/d was obtained for a site at which soil vapor SVE has been in operation for approximately 6 years, and for which mass removal is currently in the asymptotic stage. The contaminant removal behavior exhibited for the vapor extractions conducted at this site suggests that there is unlikely to be a significant mass of non-vapor-phase contaminant (e.g., DNAPL, sorbed phase) remaining in the advective domains, and that most remaining mass is likely located in poorly accessible domains. Given the conditions for this site, this remaining mass is hypothesized to be associated with the low-permeability (and higher water saturation) region in the vicinity of the saturated zone and capillary fringe. A CMD of 25 g/d was obtained for a site wherein SVE has been in operation for several years but concentrations and mass-removal rates are still relatively high. A CMD of 270 g/d was obtained for a site for which there were no prior SVE operations. The behavior exhibited for the vapor extractions conducted at this site suggest that non-vapor-phase contaminant mass (e.g., DNAPL) may be present in the advective domains. Hence, the asymptotic conditions observed for this site most likely derive from a combination of rate-limited mass transfer from DNAPL (and sorbed) phases present in the advective domain as well as mass residing in lower-permeability (“non-advective”) regions. The CMD values obtained from the tests were used in conjunction with a recently developed vapor-discharge tool to evaluate the impact of the measured CMDs on groundwater quality. PMID:26047819

The vapor-phase multi-stage CMD test for characterizing contaminant mass discharge associated with VOC sources in the vadose zone: Application to three sites in different lifecycle stages of SVE operations.

PubMed

Brusseau, M L; Mainhagu, J; Morrison, C; Carroll, K C

2015-08-01

Vapor-phase multi-stage contaminant mass discharge (CMD) tests were conducted at three field sites to measure mass discharge associated with contaminant sources located in the vadose zone. The three sites represent the three primary stages of the soil vapor extraction (SVE) operations lifecycle-pre/initial-SVE, mid-lifecycle, and near-closure. A CMD of 32g/d was obtained for a site at which soil vapor SVE has been in operation for approximately 6years, and for which mass removal is currently in the asymptotic stage. The contaminant removal behavior exhibited for the vapor extractions conducted at this site suggests that there is unlikely to be a significant mass of non-vapor-phase contaminant (e.g., DNAPL, sorbed phase) remaining in the advective domains, and that most remaining mass is likely located in poorly accessible domains. Given the conditions for this site, this remaining mass is hypothesized to be associated with the low-permeability (and higher water saturation) region in the vicinity of the saturated zone and capillary fringe. A CMD of 25g/d was obtained for a site wherein SVE has been in operation for several years but concentrations and mass-removal rates are still relatively high. A CMD of 270g/d was obtained for a site for which there were no prior SVE operations. The behavior exhibited for the vapor extractions conducted at this site suggest that non-vapor-phase contaminant mass (e.g., DNAPL) may be present in the advective domains. Hence, the asymptotic conditions observed for this site most likely derive from a combination of rate-limited mass transfer from DNAPL (and sorbed) phases present in the advective domain as well as mass residing in lower-permeability ("non-advective") regions. The CMD values obtained from the tests were used in conjunction with a recently developed vapor-discharge tool to evaluate the impact of the measured CMDs on groundwater quality. Copyright © 2015 Elsevier B.V. All rights reserved.

Measurements of Parameters Controlling the Emissions of Organophosphate Flame Retardants in Indoor Environments.

PubMed

Liang, Yirui; Liu, Xiaoyu; Allen, Matthew R

2018-05-15

Emission of semivolatile organic compounds (SVOCs) from source materials usually occurs very slowly in indoor environments due to their low volatility. When the SVOC emission process is controlled by external mass transfer, the gas-phase concentration in equilibrium with the material ( y 0 ) is used as a key parameter to simplify the source models that are based on solid-phase diffusion. A material-air-material (M-A-M) configured microchamber method was developed to rapidly measure y 0 for a polyisocyanurate rigid foam material containing organophosphate flame retardants (OPRFs). The emission test was conducted in 44 mL microchambers for target OPFRs, including tris(2-chloroethyl) phosphate (CASRN: 115-96-8), tris(1-chloro-2-propyl) phosphate (CASRN: 13674-84-5), and tris(1,3-dichloro-2-propyl) phosphate (CASRN: 13674-87-8). In addition to the microchamber emission test, two other types of tests were conducted to determine y 0 for the same foam material: OPFR diffusive tube sampling tests from the OPFR source foam using stainless-steel thermal desorption tubes and sorption tests of OPFR on an OPFR-free foam in a 53 L small chamber. Comparison of parameters obtained from the three methods suggests that the discrepancy could be caused by a combination of theoretical, experimental, and computational differences. Based on the y 0 measurements, a linear relationship between the ratio of y 0 to saturated vapor pressure concentration and material-phase mass fractions has been found for phthalates and OPFRs.

Heat storage system utilizing phase change materials government rights

DOEpatents

Salyer, Ival O.

2000-09-12

A thermal energy transport and storage system is provided which includes an evaporator containing a mixture of a first phase change material and a silica powder, and a condenser containing a second phase change material. The silica powder/PCM mixture absorbs heat energy from a source such as a solar collector such that the phase change material forms a vapor which is transported from the evaporator to the condenser, where the second phase change material melts and stores the heat energy, then releases the energy to an environmental space via a heat exchanger. The vapor is condensed to a liquid which is transported back to the evaporator. The system allows the repeated transfer of thermal energy using the heat of vaporization and condensation of the phase change material.

Core-based intrinsic fiber-optic absorption sensor for the detection of volatile organic compounds

NASA Astrophysics Data System (ADS)

Klunder, Gregory L.; Russo, Richard E.

1995-03-01

A core-based intrinsic fiber-optic absorption sensor has been developed and tested for the detection of volatile organic compounds. The distal ends of transmitting and receiving fibers are connected by a small cylindrical section of an optically clear silicone rubber. The silicone rubber acts both as a light pipe and as a selective membrane into which the analyte molecules can diffuse. The sensor has been used to detect volatile organics (trichloroethylene, 1,1-dichloroethylene, and benzene) in both aqueous solutions and in the vapor phase or headspace. Absorption spectra obtained in the near-infrared (near-IR) provide qualitative and quantitative information about the analyte. Water, which has strong broad-band absorption in the near-IR, is excluded from the spectra because of the hydrophobic properties of the silicone rubber. The rate-limiting step is shown to be the diffusion through the Nernstian boundary layer surrounding the sensor and not the diffusion through the silicone polymer. The rate of analyte diffusion into the sensor, as measured by the t(sub 90) values (the time required for the sensor to reach 90% of the equilibrium value), is 30 min for measurements in aqueous solutions and approximately 3 min for measurements made in the headspace. The limit of detection obtained with this sensor is approximately 1.1 ppm for trichloroethylene in an aqueous solution.

Isolation, purification, crystallization, and preliminary X-ray diffraction study of the crystals of HU protein from M. gallisepticum

NASA Astrophysics Data System (ADS)

Nikolaeva, A. Yu.; Timofeev, V. I.; Boiko, K. M.; Korzhenevskii, D. A.; Rakitina, T. V.; Dorovatovskii, P. V.; Lipkin, A. V.

2015-11-01

HU proteins are involved in bacterial DNA and RNA repair. Since these proteins are absent in cells of higher organisms, inhibitors of HU proteins can be used as effective and safe antibiotics. The crystallization conditions for the M. gallisepticum HU protein were found and optimized by the vapor-diffusion method. The X-ray diffraction data set was collected to 2.91 Å resolution from the crystals grown by the vapor-diffusion method on a synchrotron source. The crystals of the HU protein belong to sp. gr. P41212 and have the following unit-cell parameters: a = b = 97.94 Å, c = 77.92 Å, α = β = γ = 90°.

Liquid-phase and vapor-phase dehydration of organic/water solutions

DOEpatents

Huang, Yu [Palo Alto, CA; Ly, Jennifer [San Jose, CA; Aldajani, Tiem [San Jose, CA; Baker, Richard W [Palo Alto, CA

2011-08-23

Processes for dehydrating an organic/water solution by pervaporation or vapor separation using fluorinated membranes. The processes are particularly useful for treating mixtures containing light organic components, such as ethanol, isopropanol or acetic acid.

Vaporization of a solid surface in an ambient gas

NASA Astrophysics Data System (ADS)

Benilov, M. S.; Jacobsson, S.; Kaddani, A.; Zahrai, S.

2001-07-01

The net flux of vapour from a solid surface in an ambient gas is analysed with the aim to estimate the effect of vaporization cooling on the energy balance of an arc cathode under conditions typical for a high-power current breaker. If the ratio of the equilibrium vapour pressure pv to the ambient pressure p∞ is smaller than unity, the removal of vapour from the surface is due to diffusion into the bulk of the gas. As a consequence, the net flux of the vapour from the surface is much smaller than the emitted flux. An estimate of the diffusion rate under conditions typical for a high-power current breaker indicates that vaporization cooling plays a minor role in the energy balance of the cathode in this case. If ratio pv/p∞ is above unity, the flow of the vapour from the surface appears and the net flux is comparable to the emitted flux. A simple analytical solution has been obtained for this case, which is in a good agreement with results of the Monte Carlo modelling of preceding authors. If pv/p∞ exceeds approximately 4.5, vaporization occurs as into vacuum and the net flux is about 0.82 of the emitted flux.

Expanding Taylor bubble under constant heat flux

NASA Astrophysics Data System (ADS)

Voirand, Antoine; Benselama, Adel M.; Ayel, Vincent; Bertin, Yves

2016-09-01

Modelization of non-isothermal bubbles expanding in a capillary, as a contribution to the understanding of the physical phenomena taking place in Pulsating Heat Pipes (PHPs), is the scope of this paper. The liquid film problem is simplified and solved, while the thermal problem takes into account a constant heat flux density applied at the capillary tube wall, exchanging with the liquid film surrounding the bubble and also with the capillary tube outside medium. The liquid slug dynamics is solved using the Lucas-Washburn equation. Mass and energy balance on the vapor phase allow governing equations of bubble expansion to be written. The liquid and vapor phases are coupled only through the saturation temperature associated with the vapor pressure, assumed to be uniform throughout the bubble. Results show an over-heating of the vapor phase, although the particular thermal boundary condition used here always ensures an evaporative mass flux at the liquid-vapor interface. Global heat exchange is also investigated, showing a strong decreasing of the PHP performance to convey heat by phase change means for large meniscus velocities.

Simultaneous imaging of fuel vapor mass fraction and gas-phase temperature inside gasoline sprays using two-line excitation tracer planar laser-induced fluorescence.

PubMed

Zigan, Lars; Trost, Johannes; Leipertz, Alfred

2016-02-20

This paper reports for the first time, to the best of our knowledge, on the simultaneous imaging of the gas-phase temperature and fuel vapor mass fraction distribution in a direct-injection spark-ignition (DISI) spray under engine-relevant conditions using tracer planar laser-induced fluorescence (TPLIF). For measurements in the spray, the fluorescence tracer 3-pentanone is added to the nonfluorescent surrogate fuel iso-octane, which is excited quasi-simultaneously by two different excimer lasers for two-line excitation LIF. The gas-phase temperature of the mixture of fuel vapor and surrounding gas and the fuel vapor mass fraction can be calculated from the two LIF signals. The measurements are conducted in a high-temperature, high-pressure injection chamber. The fluorescence calibration of the tracer was executed in a flow cell and extended significantly compared to the existing database. A detailed error analysis for both calibration and measurement is provided. Simultaneous single-shot gas-phase temperature and fuel vapor mass fraction fields are processed for the assessment of cyclic spray fluctuations.

Inter-diffusion analysis of joint interface of tungsten-rhenium couple

NASA Astrophysics Data System (ADS)

Hua, Y. F.; Li, Z. X.; Zhang, X.; Du, J. H.; Huang, C. L.; Du, M. H.

2011-09-01

The tungsten-rhenium couple was prepared by using glow plasma physical vapor deposition (PVD) on the isotropic fine grained graphite (IG) substrates. Diffusion anneals of the tungsten-rhenium couple were conducted at the temperature from 1100 °C to 1400 °C to investigate the inter-diffusion behaviors. The results showed that the thickness of the inter-diffusion zone increased with increasing annealing temperature. The relationship between the inter-diffusion coefficient and the annealing temperature accorded with the Arrhenius manner. The value of inter-diffusion activation energies was 189 kJ/mole (1.96 eV). The service time of tungsten-rhenium multilayer diffusion barrier was limited by the inter-diffusion for rhenium and tungsten rather than the diffusion of carbon in rhenium.

Segregating gas from melt: an experimental study of the Ostwald ripening of vapor bubbles in magmas

USGS Publications Warehouse

Lautze, Nicole C.; Sisson, Thomas W.; Mangan, Margaret T.; Grove, Timothy L.

2011-01-01

Diffusive coarsening (Ostwald ripening) of H2O and H2O-CO2 bubbles in rhyolite and basaltic andesite melts was studied with elevated temperature–pressure experiments to investigate the rates and time spans over which vapor bubbles may enlarge and attain sufficient buoyancy to segregate in magmatic systems. Bubble growth and segregation are also considered in terms of classical steady-state and transient (non-steady-state) ripening theory. Experimental results are consistent with diffusive coarsening as the dominant mechanism of bubble growth. Ripening is faster in experiments saturated with pure H2O than in those with a CO2-rich mixed vapor probably due to faster diffusion of H2O than CO2 through the melt. None of the experimental series followed the time1/3 increase in mean bubble radius and time-1 decrease in bubble number density predicted by classical steady-state ripening theory. Instead, products are interpreted as resulting from transient regime ripening. Application of transient regime theory suggests that bubbly magmas may require from days to 100 years to reach steady-state ripening conditions. Experimental results, as well as theory for steady-state ripening of bubbles that are immobile or undergoing buoyant ascent, indicate that diffusive coarsening efficiently eliminates micron-sized bubbles and would produce mm-sized bubbles in 102–104 years in crustal magma bodies. Once bubbles attain mm-sizes, their calculated ascent rates are sufficient that they could transit multiple kilometers over hundreds to thousands of years through mafic and silicic melt, respectively. These results show that diffusive coarsening can facilitate transfer of volatiles through, and from, magmatic systems by creating bubbles sufficiently large for rapid ascent.

Molecular Self-Assembly of Group 11 Pyrazolate Complexes as Phosphorescent Chemosensors for Detection of Benzene

NASA Astrophysics Data System (ADS)

Ghazalli, N. F.; Yuliati, L.; Lintang, H. O.

2018-01-01

We highlight the systematic study on vapochromic sensing of aromatic vapors such as benzene using phosphorescent trinuclear pyrazolate complexes (2) with supramolecular assembly of a weak intermolecular metal-metal interaction consisting of 4-(3,5-dimethoxybenzyl)-3,5-dimethyl pyrazole ligand (1) and group 11 metal ions (Cu(I), Ag(I), Au(I)). The resulting chemosensor 2(Cu) revealed positive response to benzene vapors in 5 mins by blue-shifting its emission band in 44 nm (from 616 to 572 nm) and emitted bright orange to green, where this change cannot be recovered even with external stimuli. Comparing to 2(Ag) with longer metal-metal distance (473 nm) with same sensing time and quenching in 37%, 2(Au) gave quenching in 81% from its original intensity at 612 nm with reusability in 82% without external stimuli and emitted less emissive of red-orange from its original color. The shifting phenomenon in 2(Cu) suggests diffusion of benzene vapors to inside molecules for formation of intermolecular interaction with Cu(I)-Cu(I) interaction while quenching phenomenon in 2(Au) suggests diffusion of benzene vapors to between the Au(I)-Au(I) interaction. These results indicate that suitable molecular structure of ligand and metal ion in pyrazolate complex is important for designing chemosensor in the detection of benzene vapors.

Effect of Sodium Sulfite, Sodium Dodecyl Sulfate, and Urea on the Molecular Interactions and Properties of Whey Protein Isolate-Based Films

PubMed Central

Schmid, Markus; Prinz, Tobias K.; Stäbler, Andreas; Sängerlaub, Sven

2017-01-01

Whey protein coatings and cast films are promising for use as food packaging materials. Ongoing research is endeavoring to reduce their permeability. The intention of this study was to evaluate the effect of the reactive additives sodium sulfite, sodium dodecyl sulfate (SDS), and urea on the oxygen barrier, water vapor barrier, and protein solubility of whey protein cast films. The concentration of the reactive additives was 1 to 20 wt.-%. Dried whey protein cast films were used as substrate materials. The water vapor transmission rate, the oxygen permeability, and the protein solubility were measured. Effective diffusion coefficients and effective sorption coefficients were calculated from the results of the water vapor sorption experiments. The presence of sodium sulfite resulted in an increased number of hydrophobic interactions and hydrogen bonds and a slightly decreased number of disulfide bonds. The oxygen permeability decreased from 68 to 46 cm3 (STP/standard temperature and pressure) 100 μm (m2 d bar)−1 for 1 wt.-% SDS in the whey protein cast film. The water vapor transmission rate decreased from 165 to 44 g 100 μm (m2 d)−1 measured at 50 to 0% r. h. for 20 wt.-% SDS in the whey protein cast film. The reduction in the water vapor transmission rate correlated with the lower effective diffusion coefficient. PMID:28149835

Effect of sodium sulfite, sodium dodecyl sulfate, and urea on the molecular interactions and properties of whey protein isolate-based films

NASA Astrophysics Data System (ADS)

Schmid, Markus; Prinz, Tobias K.; Stäbler, Andreas; Sängerlaub, Sven

2016-12-01

Whey protein coatings and cast films are promising for use as food packaging materials. Ongoing research is endeavoring to reduce their permeability. The intention of this study was to evaluate the effect of the reactive additives sodium sulfite, sodium dodecyl sulfate (SDS), and urea on the oxygen barrier, water vapor barrier, and protein solubility of whey protein cast films. The concentration of the reactive additives was 1 to 20 wt.-%. Dried whey protein cast films were used as substrate materials. The water vapor transmission rate, the oxygen permeability, and the protein solubility were measured. Effective diffusion coefficients and effective sorption coefficients were calculated from the results of the water vapor sorption experiments. The presence of sodium sulfite resulted in an increased number of hydrophobic interactions and hydrogen bonds and a slightly decreased number of disulfide bonds. The oxygen permeability decreased from 68 to 46 cm³ (STP / standard temperature and pressure) 100 µm (m² d bar)-1 for 1 wt.-% SDS in the whey protein cast film. The water vapor transmission rate decreased from 165 to 44 g 100 µm (m² d)-1 measured at 50 to 0 % r. h. for 20 wt.-% SDS in the whey protein cast film. The reduction in the water vapor transmission rate correlated with the lower effective diffusion coefficient.

Direct determination of minority carrier diffusion lengths at axial GaAs nanowire p-n junctions.

PubMed

Gutsche, Christoph; Niepelt, Raphael; Gnauck, Martin; Lysov, Andrey; Prost, Werner; Ronning, Carsten; Tegude, Franz-Josef

2012-03-14

Axial GaAs nanowire p-n diodes, possibly one of the core elements of future nanowire solar cells and light emitters, were grown via the Au-assisted vapor-liquid-solid mode, contacted by electron beam lithography, and investigated using electron beam induced current measurements. The minority carrier diffusion lengths and dynamics of both, electrons and holes, were determined directly at the vicinity of the p-n junction. The generated photocurrent shows an exponential decay on both sides of the junction and the extracted diffusion lengths are about 1 order of magnitude lower compared to bulk material due to surface recombination. Moreover, the observed strong diameter-dependence is well in line with the surface-to-volume ratio of semiconductor nanowires. Estimating the surface recombination velocities clearly indicates a nonabrupt p-n junction, which is in essential agreement with the model of delayed dopant incorporation in the Au-assisted vapor-liquid-solid mechanism. Surface passivation using ammonium sulfide effectively reduces the surface recombination and thus leads to higher minority carrier diffusion lengths. © 2012 American Chemical Society

Pumped two-phase heat transfer loop

NASA Technical Reports Server (NTRS)

Edelstein, Fred

1988-01-01

A pumped loop two-phase heat transfer system, operating at a nearly constant temperature throughout, includes several independently operating grooved capillary heat exchanger plates supplied with working fluid through independent flow modulation valves connected to a liquid supply line, a vapor line for collecting vapor from the heat exchangers, a condenser between the vapor and the liquid lines, and a fluid circulating pump between the condenser and the heat exchangers.

Pumped two-phase heat transfer loop

NASA Technical Reports Server (NTRS)

Edelstein, Fred (Inventor)

1987-01-01

A pumped loop two-phase heat transfer system, operating at a nearly constant temperature throughout, includes a plurality of independently operating grooved capillary heat exchanger plates supplied with working fluid through independent flow modulation valves connected to a liquid supply line, a vapor line for collecting vapor from the heat exchangers, a condenser between the vapor and the liquid lines, and a fluid circulating pump between the condenser and the heat exchangers.

Synthesis of TiO2 Nanoparticles from Ilmenite Through the Mechanism of Vapor-Phase Reaction Process by Thermal Plasma Technology

NASA Astrophysics Data System (ADS)

Samal, Sneha

2017-11-01

Synthesis of nanoparticles of TiO2 was carried out by non-transferred arc thermal plasma reactor using ilmenite as the precursor material. The powder ilmenite was vaporized at high temperature in plasma flame and converted to a gaseous state of ions in the metastable phase. On cooling, chamber condensation process takes place on recombination of ions for the formation of nanoparticles. The top-to-bottom approach induces the disintegration of complex ilmenite phases into simpler compounds of iron oxide and titanium dioxide phases. The vapor-phase reaction mechanism was carried out in thermal plasma zone for the synthesis of nanoparticles from ilmenite compound in a plasma reactor. The easy separation of iron particles from TiO2 was taken place in the plasma chamber with deposition of light TiO2 particles at the top of the cooling chamber and iron particles at the bottom. The dissociation and combination process of mechanism and synthesis are studied briefly in this article. The product TiO2 nanoparticle shows the purity with a major phase of rutile content. TiO2 nanoparticles produced in vapor-phase reaction process shows more photo-induced capacity.

FIELD TRAPPING OF SUBSURFACE VAPOR PHASE PETROLEUM HYDROCARBONS

EPA Science Inventory

Soil gas samples from intact soil cores were collected on adsorbents at a field site, then thermally desorbed and analyzed by laboratory gas chromatography (GC). ertical concentration profiles of predominant vapor phase petroleum hydrocarbons under ambient conditions were obtaine...

Vapor-based interferometric measurement of local evaporation rate and interfacial temperature of evaporating droplets.

PubMed

Dehaeck, Sam; Rednikov, Alexey; Colinet, Pierre

2014-03-04

The local evaporation rate and interfacial temperature are two quintessential characteristics for the study of evaporating droplets. Here, it is shown how one can extract these quantities by measuring the vapor concentration field around the droplet with digital holographic interferometry. As a concrete example, an evaporating freely receding pending droplet of 3M Novec HFE-7000 is analyzed at ambient conditions. The measured vapor cloud is shown to deviate significantly from a pure-diffusion regime calculation, but it compares favorably to a new boundary-layer theory accounting for a buoyancy-induced convection in the gas and the influence upon it of a thermal Marangoni flow. By integration of the measured local evaporation rate over the interface, the global evaporation rate is obtained and validated by a side-view measurement of the droplet shape. Advective effects are found to boost the global evaporation rate by a factor of 4 as compared to the diffusion-limited theory.

Radiative transfer model for aerosols in infrared wavelengths for passive remote sensing applications.

PubMed

Ben-David, Avishai; Embury, Janon F; Davidson, Charles E

2006-09-10

A comprehensive analytical radiative transfer model for isothermal aerosols and vapors for passive infrared remote sensing applications (ground-based and airborne sensors) has been developed. The theoretical model illustrates the qualitative difference between an aerosol cloud and a chemical vapor cloud. The model is based on two and two/four stream approximations and includes thermal emission-absorption by the aerosols; scattering of diffused sky radiances incident from all sides on the aerosols (downwelling, upwelling, left, and right); and scattering of aerosol thermal emission. The model uses moderate resolution transmittance ambient atmospheric radiances as boundary conditions and provides analytical expressions for the information on the aerosol cloud that is contained in remote sensing measurements by using thermal contrasts between the aerosols and diffused sky radiances. Simulated measurements of a ground-based sensor viewing Bacillus subtilis var. niger bioaerosols and kaolin aerosols are given and discussed to illustrate the differences between a vapor-only model (i.e., only emission-absorption effects) and a complete model that adds aerosol scattering effects.

Elemental Mercury Diffusion Processes and Concentration at the Lunar Poles

NASA Technical Reports Server (NTRS)

Moxley, Frederick; Killen, Rosemary M.; Hurley, Dana M.

2011-01-01

In 2009, the Lyman Alpha Mapping Project (LAMP) spectrograph onboard the Lunar Reconnaissance Orbiter (LRO) spacecraft made the first detection of element mercury (Hg) vapor in the lunar exosphere after the Lunar Crater Observing and Sensing Satellite (LCROSS) Centaur rocket impacted into the Cabeus crater in the southern polar region of the Moon. The lunar regolith core samples from the Apollo missions determined that Hg had a devolatilized pattern with a concentration gradient increasing with depth, in addition to a layered pattern suggesting multiple episodes of burial and volatile loss. Hg migration on the lunar surface resulted in cold trapping at the poles. We have modeled the rate at which indigenous Hg is lost from the regolith through diffusion out of lunar grains. We secondly modeled the migration of Hg vapor in the exosphere and estimated the rate of cold-trapping at the poles using a Monte Carlo technique. The Hg vapor may be lost from the exosphere via ionization, Jeans escape, or re-impact into the surface causing reabsorption.

Surface Stability and Growth Kinetics of Compound Semiconductors: An Ab Initio-Based Approach

PubMed Central

Kangawa, Yoshihiro; Akiyama, Toru; Ito, Tomonori; Shiraishi, Kenji; Nakayama, Takashi

2013-01-01

We review the surface stability and growth kinetics of III-V and III-nitride semiconductors. The theoretical approach used in these studies is based on ab initio calculations and includes gas-phase free energy. With this method, we can investigate the influence of growth conditions, such as partial pressure and temperature, on the surface stability and growth kinetics. First, we examine the feasibility of this approach by comparing calculated surface phase diagrams of GaAs(001) with experimental results. In addition, the Ga diffusion length on GaAs(001) during molecular beam epitaxy is discussed. Next, this approach is systematically applied to the reconstruction, adsorption and incorporation on various nitride semiconductor surfaces. The calculated results for nitride semiconductor surface reconstructions with polar, nonpolar, and semipolar orientations suggest that adlayer reconstructions generally appear on the polar and the semipolar surfaces. However, the stable ideal surface without adsorption is found on the nonpolar surfaces because the ideal surface satisfies the electron counting rule. Finally, the stability of hydrogen and the incorporation mechanisms of Mg and C during metalorganic vapor phase epitaxy are discussed. PMID:28811438

The effect of environment on thermal barrier coating lifetime

DOE PAGES

Pint, Bruce A.; Unocic, Kinga A.; Haynes, James Allen

2016-03-15

While the water vapor content of the combustion gas in natural gas-fired land-based turbines is ~10%, it can be 20–85% with coal-derived (syngas or H 2) fuels or innovative turbine concepts for more efficient carbon capture. Additional concepts envisage working fluids with high CO 2 contents to facilitate carbon capture and sequestration. To investigate the effects of changes in the gas composition on thermal barrier coating (TBC) lifetime, furnace cycling tests (1-h and 100-h cycles) were performed in air with 10, 50, and 90 vol. % water vapor and CO 2-10% H 2O and compared to prior results in drymore » air or O 2. Two types of TBCs were investigated: (1) diffusion bond coatings (Pt-diffusion or Pt-modified aluminide) with commercial electron-beam physical vapor-deposited yttria-stabilized zirconia (YSZ) top coatings on second-generation superalloy N5 and N515 substrates and (2) high-velocity oxygen fuel (HVOF) sprayed MCrAlYHfSi bond coatings with air plasma-sprayed YSZ top coatings on superalloys X4, 1483, or 247 substrates. For both types of coatings exposed in 1-h cycles, the addition of water vapor resulted in a decrease in coating lifetime, except for Pt-diffusion coatings which were unaffected by the environment. In 100-h cycles, environment was less critical, perhaps because coating failure was chemical (i.e., due to interdiffusion) rather than mechanical. As a result, in both 1-h and 100-h cycles, CO 2 did not appear to have any negative effect on coating lifetime.« less

In situ growth of ceramic quantum dots in polyaniline host via water vapor flow diffusion as potential electrode materials for energy applications

NASA Astrophysics Data System (ADS)

Mombrú, Dominique; Romero, Mariano; Faccio, Ricardo; Castiglioni, Jorge; Mombrú, Alvaro W.

2017-06-01

In situ preparation of polyaniline-ceramic nanocomposites has recently demonstrated that the electrical properties are highly improved with respect to the typical ex situ preparations. In this report, we present for the first time, to the best of our knowledge, the in situ growth of titanium oxide quantum dots in polyaniline host via water vapor flow diffusion as an easily adaptable route to prepare other ceramic-polymer nanocomposites. The main relevance of this method is the possibility to prepare ceramic quantum dots from alkoxide precursors using water vapor flow into any hydrophobic polymer host and to achieve good homogeneity and size-control. In addition, we perform full characterization by means of high-resolution transmission electron microscopy, X-ray powder diffraction, small angle X-ray scattering, thermogravimetric and calorimetric analyses, confocal Raman microscopy and impedance spectroscopy analyses. The presence of the polymer host and interparticle Coulomb repulsive interactions was evaluated as an influence for the formation of 3-8 nm equally-sized quantum dots independently of the concentration. The polyaniline polaron population showed an increase for the quantum dots diluted regime and the suppression at the concentrated regime, ascribed to the formation of chemical bonds at the interface, which was confirmed by theoretical simulations. In agreement with the previous observation, the in situ growth of ceramic quantum dots in polyaniline host via water vapor flow diffusion could be very useful as a novel approach to prepare electrode materials for energy conversion and storage applications.

Theoretical Basis for Estimated Test Times and Conditions for Drop Tower and Space-Based Droplet Burning Experiments With Methanol and N-Heptane

NASA Technical Reports Server (NTRS)

Marchese, Anthony J.; Dryer, Fredrick L.; Choi, Mun Y.

1994-01-01

In order to develop an extensive envelope of test conditions for NASA's space-based Droplet Combustion Experiment (DCE) as well those droplet experiments which can be performed using a drop tower, the transient vaporization and combustion of methanol and n-heptane droplets were simulated using a recently developed fully time-dependent, spherically symmetric droplet combustion model. The transient vaporization of methanol and n-heptane was modeled to characterize the instantaneous gas phase composition surrounding the droplet prior to the introduction of an ignition source. The results for methanol/air showed that the entire gas phase surrounding a 2 mm methanol droplet deployed in zero-g .quickly falls outside the lean flammability limit. The gas phase surrounding an identically-sized n-heptane droplet, on the other hand, remains flammable. The combustion of methanol was then modeled considering a detailed gas phase chemical kinetic mechanism (168 steps, 26 species) and the effect of the dissolution of flame-generated water into the liquid droplet. These results were used to determine the critical ignition diameter required to achieve quasi-steady droplet combustion in a given oxidizing environment. For droplet diameters greater than the critical ignition diameter, the model predicted a finite diameter at which the flame would extinguish. These extinction diameters were found to vary significantly with initial droplet diameter. This phenomenon appears to be unique to the transient heat transfer, mass transfer and chemical kinetics of the system and thus has not been reported elsewhere to date. The extinction diameter was also shown to vary significantly with the liquid phase Lewis number since the amount of water present in the droplet at extinction is largely governed by the rate at which water is transported into the droplet via mass diffusion. Finally, the numerical results for n-heptane combustion were obtained using both 2 step and 96 step semi-emperical chemical kinetic mechanisms. Neither mechanism exhibited the variation of extinction diameter with initial diameter.

Gas-liquid chromatography with a volatile "stationary" liquid phase.

PubMed

Wells, P S; Zhou, S; Parcher, J F

2002-05-01

A unique type of gas-liquid chromatography is described in which both mobile and "stationary" phases are composed of synthetic mixtures of helium and carbon dioxide. At temperatures below the critical point of the binary mixture and pressures above the vapor pressure of pure liquid carbon dioxide, helium and carbon dioxide can form two immiscible phases over extended composition ranges. A binary vapor phase enriched in helium can act as the mobile phase for chromatographic separations, whereas a CO2-rich liquid in equilibrium with the vapor phase, but condensed on the column wall, can act as a pseudostationary phase. Several examples of chromatographic separations obtained in "empty" capillary columns with no ordinary stationary liquid phase illustrate the range of conditions that produce such separations. In addition, several experiments are reported that confirm the proposed two-phase hypothesis. The possible consequences of the observed chromatographic phenomenon in the field of supercritical fluid chromatography with helium headspace carbon dioxide are discussed.

Reduction of degradation in vapor phase transported InP/InGaAsP mushroom stripe lasers

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

Jung, H.; Burkhardt, E.G.; Pfister, W.

1988-10-03

The rapid degradation rate generally observed in InP/InGaAsP mushroom stripe lasers can be considerably decreased by regrowing the open sidewalls of the active stripe with low-doped InP in a second epitaxial step using the hydride vapor phase transport technique. This technique does not change the fundamental laser parameters like light-current and current-voltage characteristics. Because of this drastic reduction in degradation, the vapor phase epitaxy regrown InP/InGaAsP mushroom laser seems to be an interesting candidate for application in optical communication.

Liquid-vapor phase equilibria and the thermodynamic properties of 2-methylpropanol- n-alkyl propanoate solutions

NASA Astrophysics Data System (ADS)

Suntsov, Yu. K.; Goryunov, V. A.; Chuikov, A. M.; Meshcheryakov, A. V.

2016-08-01

The boiling points of solutions of five binary systems are measured via ebulliometry in the pressure range of 2.05-103.3 kPa. Equilibrium vapor phase compositions, the values of the excess Gibbs energies, enthalpies, and entropies of solution of these systems are calculated. Patterns in the changes of phase equilibria and thermodynamic properties of solutions are established, depending on the compositions and temperatures of the systems. Liquid-vapor equilibria in the systems are described using the equations of Wilson and the NRTL (Non-Random Two-Liquid Model).

Frequency response of a vaporization process to distorted acoustic disturbances

NASA Technical Reports Server (NTRS)

Heidmann, M. F.

1972-01-01

The open-loop response properties expressed as the mass vaporized in phase and out of phase with the pressure oscillations were numerically evaluated for a vaporizing n-heptane droplet. The evaluation includes the frequency dependence introduced by periodic oscillation in droplet mass and temperature. A given response was achieved over a much broader range of frequency with harmonically distorted disturbances than with sinusoidal disturbances. The results infer that distortion increases the probability of incurring spontaneous and triggered instability in any rocket engine combustor by broadening the frequency range over which the vaporization process can support an instability.

Comparison of forcefields for molecular dynamics simulations of hydrocarbon phase diagrams

NASA Astrophysics Data System (ADS)

Pisarev, V. V.; Zakharov, S. A.

2018-01-01

Molecular dynamics calculations of vapor-liquid equilibrium of methane-n-butane mixture are performed. Three force-field models are tested: the TraPPE-UA united-atom forcefield, LOPLS-AA all-atom forcefield and a fully flexible version of the TraPPE-EH all-atom forcefield. All those forcefields reproduce well the composition of liquid phase in the mixture as a function of pressure at the 300 K isotherm, while significant discrepancies from experimental data are observed in the saturated vapor compositions with OPLS-AA and TraPPE-UA forcefields. The best agreement with the experimental phase diagram is found with TraPPE-EH forcefield which accurately reproduces compositions of both liquid and vapor phase. This forcefield can be recommended for simulation of two-phase hydrocarbon systems.

Role of Co-Vapors in Vapor Deposition Polymerization

PubMed Central

Lee, Ji Eun; Lee, Younghee; Ahn, Ki-Jin; Huh, Jinyoung; Shim, Hyeon Woo; Sampath, Gayathri; Im, Won Bin; Huh, Yang–Il; Yoon, Hyeonseok

2015-01-01

Polypyrrole (PPy)/cellulose (PPCL) composite papers were fabricated by vapor phase polymerization. Importantly, the vapor-phase deposition of PPy onto cellulose was assisted by employing different co-vapors namely methanol, ethanol, benzene, water, toluene and hexane, in addition to pyrrole. The resulting PPCL papers possessed high mechanical flexibility, large surface-to-volume ratio, and good redox properties. Their main properties were highly influenced by the nature of the co-vaporized solvent. The morphology and oxidation level of deposited PPy were tuned by employing co-vapors during the polymerization, which in turn led to change in the electrochemical properties of the PPCL papers. When methanol and ethanol were used as co-vapors, the conductivities of PPCL papers were found to have improved five times, which was likely due to the enhanced orientation of PPy chain by the polar co-vapors with high dipole moment. The specific capacitance of PPCL papers obtained using benzene, toluene, water and hexane co-vapors was higher than those of the others, which is attributed to the enlarged effective surface area of the electrode material. The results indicate that the judicious choice and combination of co-vapors in vapor-deposition polymerization (VDP) offers the possibility of tuning the morphological, electrical, and electrochemical properties of deposited conducting polymers. PMID:25673422

Three-dimensional kinetic and fluid dynamic modeling and three iterative algorithms for side-pumped alkali vapor lasers

NASA Astrophysics Data System (ADS)

Shen, Binglin; Xu, Xingqi; Xia, Chunsheng; Pan, Bailiang

2017-11-01

Combining the kinetic and fluid dynamic processes in static and flowing-gas diode-pumped alkali vapor lasers, a comprehensive physical model with three cyclically iterative algorithms for simulating the three-dimensional pump and laser intensities as well as temperature distribution in the vapor cell of side-pumped alkali vapor lasers is established. Comparison with measurement of a static side-pumped cesium vapor laser with a diffuse type hollow cylinder cavity, and with classical and modified models is made. Influences of flowed velocity and pump power on laser power are calculated and analyzed. The results have demonstrated that for high-power side-pumped alkali vapor lasers, it is necessary to take into account the three-dimensional distributions of pump energy, laser energy and temperature in the cell to simultaneously obtain the thermal features and output characteristics. Therefore, the model can deepen the understanding of the complete kinetic and fluid dynamic mechanisms of a side-pumped alkali vapor laser, and help with its further experimental design.

MODELING COMPARATIVE THERMAL PERFORMANCE OF LIGHTWEIGHT FABRICS USING A COMPUTATIONAL DESIGN TOOL

DTIC Science & Technology

2017-04-14

lost through clothing = ( T / Rc ) + ( pv / Ret ) (5) T = temperature difference between skin and environment (°C) Rc...thermal resistance (m²-°C/Watt)  pv = vapor pressure difference between skin and environment (Pa) Ret = water vapor diffusion resistance (m²-Pa/Watt...clothing, and the external environment (wind, temperature, humidity, solar radiation). Activity: Stationary Anatomic Build: Newton, Fine

The role of moisture on combustion of pyrolysis gases in wildland fires

Treesearch

Selina C. Ferguson; Ambarish Dahale; Babak Shotorban; S. Mahalingam; David R. Weise

2013-01-01

The role of water vapor, originated from the moisture content in vegetation, on the combustion process was investigated via simulating an opposed diffusion flame and a laminar premixed flame with pyrolysis gases as the fuel and air as the oxidizer. The fuel was mixed with water vapor, and the simulation was repeated for various water mole fractions. In both of the...

Heterogeneously entrapped, vapor-rich melt inclusions record pre-eruptive magmatic volatile contents

NASA Astrophysics Data System (ADS)

Steele-MacInnis, Matthew; Esposito, Rosario; Moore, Lowell R.; Hartley, Margaret E.

2017-04-01

Silicate melt inclusions (MI) commonly provide the best record of pre-eruptive H2O and CO2 contents of subvolcanic melts, but the concentrations of CO2 and H2O in the melt (glass) phase within MI can be modified by partitioning into a vapor bubble after trapping. Melt inclusions may also enclose vapor bubbles together with the melt (i.e., heterogeneous entrapment), affecting the bulk volatile composition of the MI, and its post-entrapment evolution. In this study, we use numerical modeling to examine the systematics of post-entrapment volatile evolution within MI containing various proportions of trapped vapor from zero to 95 volume percent. Modeling indicates that inclusions that trap only a vapor-saturated melt exhibit significant decrease in CO2 and moderate increase in H2O concentrations in the melt upon nucleation and growth of a vapor bubble. In contrast, inclusions that trap melt plus vapor exhibit subdued CO2 depletion at equivalent conditions. In the extreme case of inclusions that trap mostly the vapor phase (i.e., CO2-H2O fluid inclusions containing trapped melt), degassing of CO2 from the melt is negligible. In the latter scenario, the large fraction of vapor enclosed in the MI during trapping essentially serves as a buffer, preventing post-entrapment modification of volatile concentrations in the melt. Hence, the glass phase within such heterogeneously entrapped, vapor-rich MI records the volatile concentrations of the melt at the time of trapping. These numerical modeling results suggest that heterogeneously entrapped MI containing large vapor bubbles represent amenable samples for constraining pre-eruptive volatile concentrations of subvolcanic melts.

Layer Protecting the Surface of Zirconium Used in Nuclear Reactors.

PubMed

Ashcheulov, Petr; Skoda, Radek; Skarohlíd, Jan; Taylor, Andrew; Fendrych, Frantisek; Kratochvílová, Irena

2016-01-01

Zirconium alloys have very useful properties for nuclear facilities applications having low absorption cross-section of thermal electrons, high ductility, hardness and corrosion resistance. However, there is also a significant disadvantage: it reacts with water steam and during this (oxidative) reaction it releases hydrogen gas, which partly diffuses into the alloy forming zirconium hydrides. A new strategy for surface protection of zirconium alloys against undesirable oxidation in nuclear reactors by polycrystalline diamond film has been patented- Czech patent 305059: Layer protecting the surface of zirconium alloys used in nuclear reactors and PCT patent: Layer for protecting surface of zirconium alloys (Patent Number: WO2015039636-A1). The zirconium alloy surface was covered by polycrystalline diamond layer grown in plasma enhanced chemical vapor deposition apparatus with linear antenna delivery system. Substantial progress in the description and understanding of the polycrystalline diamond/ zirconium alloys interface and material properties under standard and nuclear reactors conditions (irradiation, hot steam oxidation experiments and heating-quenching cycles) was made. In addition, process technology for the deposition of protective polycrystalline diamond films onto the surface of zirconium alloys was optimized. Zircaloy2 nuclear fuel pins were covered by 300 nm thick protective polycrystalline diamond layer (PCD) using plasma enhanced chemical vapor deposition apparatus with linear antenna delivery system. The polycrystalline diamond layer protects the zirconium alloy surface against undesirable oxidation and consolidates its chemical stability while preserving its functionality. PCD covered Zircaloy2 and standard Zircaloy2 pins were for 30 min. oxidized in 1100°C hot steam. Under these conditions α phase of zirconium changes to β phase (more opened for oxygen/hydrogen diffusion). PCD anticorrosion protection of Zircaloy nuclear fuel assemblies can significantly prolong lifetime of Zirconium alloy in nuclear reactors even above Zirconium phase transition temperatures. Even after ion beam irradiation (10 dpa, 3 MeV Fe(2+)) the diamond film still shows satisfactory structural integrity with both sp(3) and sp(2) carbon phases. Zircaloy2 under the carbon-based protective layer after hot steam oxidation test differed from the original Zircaloy2 material composition only very slightly, proving that the diamond coating increases the material resistance to high temperature oxidation. Zirconium alloys nuclear fuel pins' surfaces were covered by compact and homogeneous polycrystalline diamond layers consisting of sp(3) and sp(2) carbon phases with a high crystalline diamond content and low roughness. Diamond withstands very high temperatures, has excellent thermal conductivity and low chemical reactivity, it does not degrade over time and (important for the nuclear fuel cladding) being pure carbon, it has perfect neutron cross-section properties. Moreover, polycrystalline diamond layers consisting of crystalline (sp(3)) and amorphous (sp(2)) carbon phases could have suitable thermal expansion. Zirconium alloys coated with polycrystalline diamond film are protected against undesirable changes and processes. Further, the polycrystalline diamond layer prevents the reaction between the alloy surface and water vapor. During such reaction, water molecules dissociate and initiate formation of zirconium dioxide and hydrogen, accompanied by the release of large amount of heat. Thus the protective layer prevents the formation of hydrogen and the release of reaction heat. Few relevant patents to the topic have been reviewed and cited.

Cu-Zn binary phase diagram and diffusion couples

NASA Technical Reports Server (NTRS)

Mccoy, Robert A.

1992-01-01

The objectives of this paper are to learn: (1) what information a binary phase diagram can yield; (2) how to construct and heat treat a simple diffusion couple; (3) how to prepare a metallographic sample; (4) how to operate a metallograph; (5) how to correlate phases found in the diffusion couple with phases predicted by the phase diagram; (6) how diffusion couples held at various temperatures could be used to construct a phase diagram; (7) the relation between the thickness of an intermetallic phase layer and the diffusion time; and (8) the effect of one species of atoms diffusing faster than another species in a diffusion couple.

Comparison of methods for the measurement of mist and vapor from light mineral oil-based metalworking fluids.

PubMed

Simpson, Andrew T

2003-11-01

The measurement of oil mist derived from metalworking fluids formulated with light mineral oils can be highly inaccurate when using traditional filter sampling. This is due to evaporation of oil from the filter. In this work the practicability of an alternative approach measuring total oil mist and vapor was investigated. Combinations of inhalable particle samplers with backup sorbent vapor traps and standard vapor sampling on pumped and diffusive sorbent tubes were evaluated with gravimetric, infrared spectroscopic, and gas chromatographic analytical methods against the performance requirements of European Standard EN 482. An artificial aerosol was used to compare the methods against a reference method of filter sampler in series with three impingers. Multi-orifice samplers were used with standard 8-mm diameter charcoal tubes at 2 L/min without any signs of channelling or significant breakthrough, as were conical inhalable samplers with XAD-2 tubes at 1 L/min. Most combinations of samplers had a bias of less than 3 percent, but solitary pumped charcoal tubes underestimated total oil by 13 percent. Diffusive sampling was affected by impaction of mist particles and condensation of oil vapor. Gravimetric analysis of filters revealed significant potential sample loss during storage, with 4 percent being lost after one day when stored at room temperature and 2 percent when refrigerated. Samples left overnight in the balance room to equilibrate lost 24 percent. Infrared spectroscopy gave more precise results for vapor than gas chromatography (p = 0.002). Gas chromatography was less susceptible to bias from contaminating solvent vapors than infrared spectroscopy, but was still vulnerable to petroleum distillates. Under the specific test conditions (one oil type and mist particle size), all combinations of methods examined complied with the requirements of European Standard EN 484. Total airborne oil can be measured accurately; however, care must be taken to avoid contamination by hydrocarbon solvent vapors during sampling.

Long-Term Cyclic Oxidation Behavior of Uncoated and Coated Re-108 and In-939 at 980 and 870 C

NASA Technical Reports Server (NTRS)

Lee, K. N.; Barrett, C. A.; Smith, J.

2000-01-01

Very long-term cyclic oxidation behavior of Re108 and In939 with and without a protective coating was evaluated at 980 and 870 C, respectively. Re-108 and In-939 without a protective coating began to show a rapid weight loss at 3000 h due to scale spallation, indicating the need for an oxidation protective coating for longer than thousands of hours of oxidative life. NiAl-base coatings of a vapor phase aluminide (VPA), a pack aluminide (CODEP), and a slurry paint aluminide (SERMALOY J) were applied on Re-108 and In-939. The VPA and CODEP on Re-108 and all three coatings on In-939 showed excellent cyclic oxidation resistance out to 10,000 h. Coated alloys were annealed in an inert atmosphere to determine the loss of Al from the coating into the alloy substrate through diffusion. The Al loss from the coating through diffusion was twice as great as the Al loss through oxidation after 10,000 h of cyclic exposure. The oxidation life of VPA-coated Re-108 was estimated by calculating the amount of Al initially available for protective oxidation and the amount of Al lost through oxidation and diffusion.

Growth kinetics and island evolution during double-pulsed molecular beam epitaxy of InN

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

Kraus, A.; Hein, C.; Bremers, H.

The kinetic processes of InN growth using alternating source fluxes with sub-monolayer In pulses in plasma-assisted molecular beam epitaxy have been investigated. Growth at various temperatures reveals the existence of two growth regimes. While growth at low temperatures is solely governed by surface diffusion, a combination of decomposition, desorption, and diffusion becomes decisive at growth temperatures of 470 °C and above. At this critical temperature, the surface morphology changes from a grainy structure to a structure made of huge islands. The formation of those islands is attributed to the development of an indium adlayer, which can be observed via reflection highmore » energy electron diffraction monitoring. Based on the growth experiments conducted at temperatures below T{sub Growth} = 470 °C, an activation energy for diffusion of 0.54 ± 0.02 eV has been determined from the decreasing InN island density. A comparison between growth on metalorganic vapor phase epitaxy GaN templates and pseudo bulk GaN indicates that step edges and dislocations are favorable nucleation sites. Based on the results, we developed a growth model, which describes the main mechanisms of the growth.« less

Observational Constraints on Modeling Growth and Evaporation Kinetics of Isoprene SOA

NASA Astrophysics Data System (ADS)

Zaveri, R. A.; Shilling, J. E.; Zelenyuk, A.; Liu, J.; Wilson, J. M.; Laskin, A.; Wang, B.; Fast, J. D.; Easter, R. C.; Wang, J.; Kuang, C.; Thornton, J. A.; Setyan, A.; Zhang, Q.; Onasch, T. B.; Worsnop, D. R.

2014-12-01

Isoprene is thought to be a major contributor to the global secondary organic aerosol (SOA) budget, and therefore has the potential to exert a significant influence on earth's climate via aerosol direct and indirect radiative effects. Both aerosol optical and cloud condensation nuclei properties are quite sensitive to aerosol number size distribution, as opposed to the total aerosol mass concentration. Recent studies suggest that SOA particles can be highly viscous, which can affect the kinetics of SOA partitioning and size distribution evolution when the condensing organic vapors are semi-volatile. In this study, we examine the growth kinetics of SOA formed from isoprene photooxidation in the presence of pre-existing Aitken and accumulation mode aerosols in: (a) the ambient atmosphere during the CARES field campaign, and (b) the environmental chamber at PNNL. Each growth episode is analyzed and interpreted with the updated MOSAIC aerosol box model, which performs kinetic gas-particle partitioning of SOA and takes into account diffusion and chemical reaction within the particle phase. The model is initialized with the observed aerosol size distribution and composition at the beginning of the experiment, and the total amount of SOA formed in the model at any given time is constrained by the observed total amount of SOA formed. The variable model parameters include the number of condensing organic species, their gas-phase formation rates, their effective volatilities, and their bulk diffusivities in the Aitken and accumulation modes. The objective of the constrained modeling exercise is then to determine which model configuration is able to best reproduce the observed size distribution evolution, thus providing valuable insights into the possible mechanism of SOA formation. We also examine the evaporation kinetics of size-selected particles formed in the environmental chamber to provide additional constraints on the effective volatility and bulk diffusivity of the organic species. Our results suggest that SOA formed from isoprene photooxidation is semi-volatile, and the resulting size distribution evolution is highly sensitive to the phase state (bulk diffusivity) of the pre-existing aerosol. Implications of these findings on further SOA model development and evaluation strategy will be discussed.

Resonant Acoustic Measurement of Vapor Phase Transport Phenomenon

NASA Astrophysics Data System (ADS)

Schuhmann, R. J.; Garrett, S. L.; Matson, J. V.

2002-12-01

A major impediment to accurate non steady-state diffusion measurements is the ability to accurately measure and track a rapidly changing gas concentration without disturbing the system. Non-destructive methods that do not interfere with system dynamics have been developed in the past. These methods, however, have tended to be cumbersome or inaccurate at low concentrations. A new experimental approach has been developed to measure gaseous diffusion in free air and through porous materials. The method combines the traditional non steady-state laboratory methodology with resonant acoustic gas analysis. A phase-locked-loop (PLL) resonance frequency tracker is combined with a thermally insulated copper resonator. A piston sealed with a metal bellows excites the fundamental standing wave resonance of the resonator. The PLL maintains a constant phase difference (typically 90§) between the accelerometer mounted on the piston and a microphone near the piston to track the resonance frequency in real time. A capillary or glass bead filled core is fitted into an o-ring sealed opening at the end of the resonator opposite the bellows. The rate at which the tracer gas is replaced by air within the resonator is controlled by the diffusion coefficient of the gas in free air through the capillary (DA) or by the effective diffusion coefficient of the gas through the core (De). The mean molecular weight of the gas mixture in the resonator is directly determined six times each minute from the ratio of the absolute temperature to the square of the fundamental acoustic resonance frequency. Average system stability (temperature divided by frequency squared) is better than 350 ppm. DA values for a 0.3-inch diameter capillary were in excellent agreement with published values. De values for porous media samples (0.5 mm glass beads) of four different lengths (1 through 4 inches) using three different tracer gases (He, CH4, Kr) will be reported. Comments will be offered regarding tracer gas selection and device orientation and their effect on experimental results. [Work supported by the Office of Naval Research.

Influence of Hydrogen Bonding on the Surface Diffusion of Molecular Glasses: Comparison of Three Triazines

DOE PAGES

Chen, Yinshan; Zhu, Men; Laventure, Audrey; ...

2017-06-26

Surface grating decay measurements have been performed on three closely related molecular glasses to study the effect of intermolecular hydrogen bonds on surface diffusion. The three molecules are derivatives of bis(3,5-dimethyl-phenylamino)-1,3,5-triazine and differ only in the functional group R at the 2-position, with R being C 2H 5, OCH 3, and NHCH 3, and referred to as “Et”, “OMe”, and “NHMe”, respectively. Of the three molecules, NHMe forms more extensive intermolecular hydrogen bonds than Et and OMe and was found to have slower surface diffusion. For Et and OMe, surface diffusion is so fast that it replaces viscous flow asmore » the mechanism of surface grating decay as temperature is lowered. In contrast, no such transition was observed for NHMe under the same conditions, indicating significantly slower surface diffusion. This result is consistent with the previous finding that extensive intermolecular hydrogen bonds slow down surface diffusion in molecular glasses and is attributed to the persistence of hydrogen bonds even in the surface environment. Here, this result is also consistent with the lower stability of the vapor-deposited glass of NHMe relative to those of Et and OMe and supports the view that surface mobility controls the stability of vapor-deposited glasses.« less

Consistent simulation of droplet evaporation based on the phase-field multiphase lattice Boltzmann method

NASA Astrophysics Data System (ADS)

Safari, Hesameddin; Rahimian, Mohammad Hassan; Krafczyk, Manfred

2014-09-01

In the present article, we extend and generalize our previous article [H. Safari, M. H. Rahimian, and M. Krafczyk, Phys. Rev. E 88, 013304 (2013), 10.1103/PhysRevE.88.013304] to include the gradient of the vapor concentration at the liquid-vapor interface as the driving force for vaporization allowing the evaporation from the phase interface to work for arbitrary temperatures. The lattice Boltzmann phase-field multiphase modeling approach with a suitable source term, accounting for the effect of the phase change on the velocity field, is used to solve the two-phase flow field. The modified convective Cahn-Hilliard equation is employed to reconstruct the dynamics of the interface topology. The coupling between the vapor concentration and temperature field at the interface is modeled by the well-known Clausius-Clapeyron correlation. Numerous validation tests including one-dimensional and two-dimensional cases are carried out to demonstrate the consistency of the presented model. Results show that the model is able to predict the flow features around and inside an evaporating droplet quantitatively in quiescent as well as convective environments.

Consistent simulation of droplet evaporation based on the phase-field multiphase lattice Boltzmann method.

PubMed

Safari, Hesameddin; Rahimian, Mohammad Hassan; Krafczyk, Manfred

2014-09-01

In the present article, we extend and generalize our previous article [H. Safari, M. H. Rahimian, and M. Krafczyk, Phys. Rev. E 88, 013304 (2013)] to include the gradient of the vapor concentration at the liquid-vapor interface as the driving force for vaporization allowing the evaporation from the phase interface to work for arbitrary temperatures. The lattice Boltzmann phase-field multiphase modeling approach with a suitable source term, accounting for the effect of the phase change on the velocity field, is used to solve the two-phase flow field. The modified convective Cahn-Hilliard equation is employed to reconstruct the dynamics of the interface topology. The coupling between the vapor concentration and temperature field at the interface is modeled by the well-known Clausius-Clapeyron correlation. Numerous validation tests including one-dimensional and two-dimensional cases are carried out to demonstrate the consistency of the presented model. Results show that the model is able to predict the flow features around and inside an evaporating droplet quantitatively in quiescent as well as convective environments.

An Examination of the Phase Transition Thermodynamics of (S)- and (RS)-Naproxen as a Basis for the Design of Enantioselective Crystallization Processes.

PubMed

Buchholz, Hannes; Emel'yanenko, Vladimir N; Lorenz, Heike; Verevkin, Sergey P

2016-05-01

A detailed experimental analysis of the phase transition thermodynamics of (S)-naproxen and (RS)-naproxen is reported. Vapor pressures were determined experimentally via the transpiration method. Sublimation enthalpies were obtained from the vapor pressures and from independent TGA measurements. Thermodynamics of fusion which have been well-studied in the literature were systematically remeasured by DSC. Both sublimation and fusion enthalpies were adjusted to one reference temperature, T = 298 K, using measured heat capacities of the solid and the melt phase by DSC. Average values from the measurements and from literature data were suggested for the sublimation and fusion enthalpies. In order to prove consistency of the proposed values the vaporization enthalpies obtained by combination of both were compared to vaporization enthalpies obtained by the group-additivity method and the correlation-gas chromatography method. The importance of reliable and precise phase transition data for thermochemical calculations such as the prediction of solid/liquid phase behaviour of chiral compounds is highlighted. Copyright © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

Beer Law Constants and Vapor Pressures of HgI2 over HgI2(s,l)

NASA Technical Reports Server (NTRS)

Su, Ching-Hua; Zhu, Shen; Ramachandran, N.; Burger, A.

2002-01-01

Optical absorption spectra of the vapor phase over HgI2(s,l) were measured at sample temperatures between 349 and 610 K for wavelengths between 200 and 600 nm. The spectra show the samples sublimed congruently into HGI2 without any observed Hg or I2 absorption spectra. The Beer's Law constants for 15 wavelengths between 200 and 440 nm were derived. From these constants the vapor pressure of HgI2, P, was found to be a function of temperature for the liquid and the solid beta-phases: ln P(atm) = -7700/T(K) + 12.462 (liquid phase) and ln P(atm) = -10150/T(K) + 17.026 (beta-phase). The expressions match the enthalpies of vaporization and sublimation of 15.30 and 20.17 kcal/mole respectively, for the liquid and the beta-phase HgI2. The difference in the enthalpies gives an enthalpy of fusion of 4.87 kcal/mole, and the intersection of the two expressions gives a melting point of 537 K.

Transient-pressure analysis in geothermal steam reservoirs with an immobile vaporizing liquid phase

USGS Publications Warehouse

Moench, A.F.; Atkinson, P.G.

1978-01-01

A finite-difference model for the radial horizontal flow of steam through a porous medium is used to evaluate transient-pressure behavior in the presence of an immobile vaporizing or condensing liquid phase. Graphs of pressure drawdown and buildup in terms of dimensionless pressure and time are obtained for a well discharging steam at a constant mass flow rate for a specified time. The assumptions are made that the steam is in local thermal equilibrium with the reservoir rocks, that temperature changes are due only to phase change, and that effects of vapor-pressure lowering are negligible. Computations show that when a vaporizing liquid phase is present the pressure drawdown exhibits behavior similar to that observed in noncondensable gas reservoirs, but delayed in time. A theoretical analysis allows for the computation of this delay and demonstrates that it is independent of flow geometry. The response that occurs upon pressure buildup is markedly different from that in a noncondensable gas system. This result may provide a diagnostic tool for establishing the existence of phase-change phenomena within a reservoir. ?? 1979.

Order parameter free enhanced sampling of the vapor-liquid transition using the generalized replica exchange method.

PubMed

Lu, Qing; Kim, Jaegil; Straub, John E

2013-03-14

The generalized Replica Exchange Method (gREM) is extended into the isobaric-isothermal ensemble, and applied to simulate a vapor-liquid phase transition in Lennard-Jones fluids. Merging an optimally designed generalized ensemble sampling with replica exchange, gREM is particularly well suited for the effective simulation of first-order phase transitions characterized by "backbending" in the statistical temperature. While the metastable and unstable states in the vicinity of the first-order phase transition are masked by the enthalpy gap in temperature replica exchange method simulations, they are transformed into stable states through the parameterized effective sampling weights in gREM simulations, and join vapor and liquid phases with a succession of unimodal enthalpy distributions. The enhanced sampling across metastable and unstable states is achieved without the need to identify a "good" order parameter for biased sampling. We performed gREM simulations at various pressures below and near the critical pressure to examine the change in behavior of the vapor-liquid phase transition at different pressures. We observed a crossover from the first-order phase transition at low pressure, characterized by the backbending in the statistical temperature and the "kink" in the Gibbs free energy, to a continuous second-order phase transition near the critical pressure. The controlling mechanisms of nucleation and continuous phase transition are evident and the coexistence properties and phase diagram are found in agreement with literature results.

Crystallization of Membrane Proteins by Vapor Diffusion

PubMed Central

Delmar, Jared A.; Bolla, Jani Reddy; Su, Chih-Chia; Yu, Edward W.

2016-01-01

X-ray crystallography remains the most robust method to determine protein structure at the atomic level. However, the bottlenecks of protein expression and purification often discourage further study. In this chapter, we address the most common problems encountered at these stages. Based on our experiences in expressing and purifying antimicrobial efflux proteins, we explain how a pure and homogenous protein sample can be successfully crystallized by the vapor diffusion method. We present our current protocols and methodologies for this technique. Case studies show step-by-step how we have overcome problems related to expression and diffraction, eventually producing high quality membrane protein crystals for structural determinations. It is our hope that a rational approach can be made of the often anecdotal process of membrane protein crystallization. PMID:25950974

Microgravity

NASA Image and Video Library

1994-02-16

These Vapor Diffusion Apparatus (VDA) trays were first flown in the Thermal Enclosure System (TES) during the USMP-2 (STS-62) mission. Each tray can hold 20 protein crystal growth chambers. Each chamber contains a double-barrel syringe; one barrel holds protein crystal solution and the other holds precipitant agent solution. During the microgravity mission, a torque device is used to simultaneously retract the plugs in all 20 syringes. The two solutions in each chamber are then mixed. After mixing, droplets of the combined solutions are moved onto the syringe tips so vapor diffusion can begin. During the length of the mission, protein crystals are grown in the droplets. Shortly before the Shuttle's return to Earth, the experiment is deactivated by retracting the droplets containing protein crystals, back into the syringes.

Simultaneous infrared and UV-visible absorption spectra of matrix-isolated carbon vapor

NASA Technical Reports Server (NTRS)

Kurtz, Joe; Huffman, Donald R.

1989-01-01

Carbon molecules were suggested as possible carriers of the diffuse interstellar bands. In particular, it was proposed that the 443 nm diffuse interstellar band is due to the same molecule which gives rise to the 447 nm absorption feature in argon matrix-isolated carbon vapor. If so, then an associated C-C stretching mode should be seen in the IR. By doing spectroscopy in both the IR and UV-visible regions on the same sample, the present work provides evidence for correlating UV-visible absorption features with those found in the IR. Early data indicates no correlation between the strongest IR feature (1997/cm) and the 447 nm band. Correlation with weaker IR features is being investigated.

Vapor-liquid phase separator studies

NASA Technical Reports Server (NTRS)

Yuan, S. W. K.; Lee, J. M.; Kim, Y. I.; Hepler, W. A.; Frederking, T. H. K.

1983-01-01

Porous plugs serve as both entropy rejection devices and phase separation components separating the vapor phase on the downstream side from liquid Helium 2 upstream. The liquid upstream is the cryo-reservoir fluid needed for equipment cooling by means of Helium 2, i.e Helium-4 below its lambda temperature in near-saturated states. The topics outlined are characteristic lengths, transport equations and plug results.

Phase-transitional Fe3O4/perfluorohexane Microspheres for Magnetic Droplet Vaporization.

PubMed

Wang, Ronghui; Zhou, Yang; Zhang, Ping; Chen, Yu; Gao, Wei; Xu, Jinshun; Chen, Hangrong; Cai, Xiaojun; Zhang, Kun; Li, Pan; Wang, Zhigang; Hu, Bing; Ying, Tao; Zheng, Yuanyi

2017-01-01

Activating droplets vaporization has become an attractive strategy for ultrasound imaging and physical therapy due to the significant increase in ultrasound backscatter signals and its ability to physically damage the tumor cells. However, the current two types of transitional droplets named after their activation methods have their respective limitations. To circumvent the limitations of these activation methods, here we report the concept of magnetic droplet vaporization (MDV) for stimuli-responsive cancer theranostics by a magnetic-responsive phase-transitional agent. This magnetic-sensitive phase-transitional agent-perfluorohexane (PFH)-loaded porous magnetic microspheres (PFH-PMMs), with high magnetic-thermal energy-transfer capability, could quickly respond to external alternating current (AC) magnetic fields to produce thermal energy and trigger the vaporization of the liquid PFH. We systematically demonstrated MDV both in vitro and in vivo. This novel trigger method with deep penetration can penetrate the air-filled viscera and trigger the vaporization of the phase-transitional agent without the need of pre-focusing lesion. This unique MDV strategy is expected to substantially broaden the biomedical applications of nanotechnology and promote the clinical treatment of tumors that are not responsive to chemical therapies.

First-order wetting transition at a liquid-vapor interface

NASA Technical Reports Server (NTRS)

Schmidt, J. W.; Moldover, M. R.

1983-01-01

Evidence from reflectance and contact angle measurements is presented that three-phase mixtures of i-C3H7OH-C7F14 exhibit a first-order wetting phase transition at the liquid-vapor interface at 38 C. Equilibration phenomena support this interpretation. Ellipsometry was used to measure the apparent thickness of the intruding layer in the three-phase mixture. At temperatures slightly above the wetting temperature T(w), the intruding layer's thickness is several hundred angstroms and its variation with temperature is extremely weak. Below T(w), three-phase contact can occur between the vapor and both the upper and lower liquid phases; one of the angles which characterizes this contact has a very simple temperature dependence. The thickness of the intruding layer, monitored as the solutions approached equilibrium, is found to depend quite weakly on the height spanned by the upper liquid phase in the vicinity of a first-order wetting transition.

Hybrid vapor phase-solution phase growth techniques for improved CZT(S,Se) photovoltaic device performance

DOEpatents

Chang, Liang-Yi; Gershon, Talia S.; Haight, Richard A.; Lee, Yun Seog

2016-12-27

A hybrid vapor phase-solution phase CZT(S,Se) growth technique is provided. In one aspect, a method of forming a kesterite absorber material on a substrate includes the steps of: depositing a layer of a first kesterite material on the substrate using a vapor phase deposition process, wherein the first kesterite material includes Cu, Zn, Sn, and at least one of S and Se; annealing the first kesterite material to crystallize the first kesterite material; and depositing a layer of a second kesterite material on a side of the first kesterite material opposite the substrate using a solution phase deposition process, wherein the second kesterite material includes Cu, Zn, Sn, and at least one of S and Se, wherein the first kesterite material and the second kesterite material form a multi-layer stack of the absorber material on the substrate. A photovoltaic device and method of formation thereof are also provided.

Assessment of Mitigation Systems on Vapor Intrusion ...

EPA Pesticide Factsheets

Vapor intrusion is the migration of subsurface vapors, including radon and volatile organic compounds (VOCs), in soil gas from the subsurface to indoor air. Vapor intrusion happens because there are pressure and concentration differentials between indoor air and soil gas. Indoor environments are often negatively pressurized with respect to outdoor air and soil gas (for example, from exhaust fans or the stack effect), and this pressure difference allows soil gas containing subsurface vapors to flow into indoor air through advection. In addition, concentration differentials cause VOCs and radon to migrate from areas of higher to lower concentrations through diffusion, which is another cause of vapor intrusion. Current practice for evaluating the vapor intrusion pathway involves a multiple line of evidence approach based on direct measurements in groundwater, external soil gas, subslab soil gas, and/or indoor air. No single line of evidence is considered definitive, and direct measurements of vapor intrusion can be costly, especially where significant spatial and temporal variability require repeated measurements at multiple locations to accurately assess the chronic risks of long-term exposure to volatile organic compounds (VOCs) like chloroform, perchloroethylene (PCE), and trichloroethylene (TCE).

Vapor deposition routes to conformal polymer thin films

PubMed Central

Moni, Priya; Al-Obeidi, Ahmed

2017-01-01

Vapor phase syntheses, including parylene chemical vapor deposition (CVD) and initiated CVD, enable the deposition of conformal polymer thin films to benefit a diverse array of applications. This short review for nanotechnologists, including those new to vapor deposition methods, covers the basic theory in designing a conformal polymer film vapor deposition, sample preparation and imaging techniques to assess film conformality, and several applications that have benefited from vapor deposited, conformal polymer thin films. PMID:28487816

Potential for advection of volatile organic compounds in ground water to the Cochato River, Baird & McGuire Superfund Site, Holbrook, Massachusetts, March and April 1998

USGS Publications Warehouse

Savoie, Jennifer G.; Lyford, Forest P.; Clifford, Scott

1999-01-01

In March and April 1998, a network of water-to-vapor diffusion samplers was installed along the Cochato River at the Baird & McGuire Superfund Site in Holbrook, Massachusetts, where a plume of volatile organic compounds (VOCs) is present in ground water. The purpose of installing the sampler network was to determine if VOCs were present in river-bottom sediments while a ground-water extraction system was operating and after the system had been shut down for two weeks. Water-to-water diffusion samplers placed at selected locations provided supplemental information about concentrations of VOCs in pore water in the river-bottom sediments. Water levels in piezometers and river stage were measured concurrently to determine if ground water was discharging to the river. Benzene, toluene, ethylbenzene and xylenes (BTEX compounds) were detected in water-tovapor and water-to-water diffusion samplers located in the area where the plume is known to pass beneath the river for both pumping and nonpumping conditions. Concentrations of total BTEX compounds in water-to-vapor diffusion samplers ranged from non-detect upriver and downriver from the plume area to greater than 200 parts per million by volume in the plume area. Concentrations of total BTEX compounds were not significantly different for pumping than for non-pumping conditions. Concentrations of total BTEX compounds in water-to-water diffusion samplers ranged from non-detect to 680 micrograms per liter. The limited number of water-to-water diffusion samplers did not indicate that concentrations were higher for pumping or non-pumping conditions. Trichloroethylene and tetrachloroethylene also were detected in water-to-vapor diffusion samplers downriver from the area where the BTEX compounds were detected. Water levels in four piezometers were consistently higher than the river stage, indicating an upward hydraulic gradient and ground-water discharge to the river. The concentrations of VOCs in riverbottom sediments and the upward hydraulic gradients observed indicate that contaminants from the Baird & McGuire ground-water plume were discharging to the Cochato River during the study period for both pumping and non-pumping conditions. 

Condensed phase conversion and growth of nanorods and other materials instead of from vapor

DOEpatents

Geohegan, David B.; Seals, Roland D.; Puretzky, Alex A.; Fan, Xudong

2010-10-19

Compositions, systems and methods are described for condensed phase conversion and growth of nanorods and other materials. A method includes providing a condensed phase matrix material; and activating the condensed phase matrix material to produce a plurality of nanorods by condensed phase conversion and growth from the condensed phase matrix material instead of from vapor. The compositions are very strong. The compositions and methods provide advantages because they allow (1) formation rates of nanostructures necessary for reasonable production rates, and (2) the near net shaped production of component structures.

Structural and dynamic properties of liquid tin from a new modified embedded-atom method force field

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

Vella, Joseph R.; Chen, Mohan; Stillinger, Frank H.

We developed a new modified embedded-atom method (MEAM) force field for liquid tin. Starting from the Ravelo and Baskes force field [Phys. Rev. Lett. 79, 2482 (1997)], the parameters are adjusted using a simulated annealing optimization procedure in order to obtain better agreement with liquid-phase data. The predictive capabilities of the new model and the Ravelo and Baskes force field are evaluated using molecular dynamics by comparing to a wide range of first-principles and experimental data. The quantities studied include crystal properties (cohesive energy, bulk modulus, equilibrium density, and lattice constant of various crystal structures), melting temperature, liquid structure, liquidmore » density, self-diffusivity, viscosity, and vapor-liquid surface tension. We show that although the Ravelo and Baskes force field generally gives better agreement with the properties related to the solid phases of tin, the new MEAM force field gives better agreement with liquid tin properties.« less

Investigation of sorption interactions between oil shale principal mineral phases and organic compounds

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

Bowen, J.M.

1988-09-01

The interactions between minerals representative of the bulk composition of oil shales and organic compounds that have been found in oil shale leachates were investigated. The method used to directly determine the type of interactions that could take place between organic compounds and oil shale mineral phases was Fourier transform infrared spectroscopy (FTIR) using several advanced detection methods, including diffuse reflectance (DRIFT) and photoacoustics (PAS). The minerals that were investigated include quartz, calcite, and dolomite, which are known to figure significantly in the composition of processed oil shales. The organic chemical compounds used were chosen from a list of compoundsmore » identified in spent oil shale leachates, and they include pyridine, phenol, p-cresol, and acetone. The sorption interactions for the study were prepared by exposing each of the minerals to the organic compounds by three different methods. These were vapor deposition, direct application, and immersion in an aqueous solution at pH 12. 41 refs., 3 figs., 4 tabs.« less

Graphical Interface for the Study of Gas-Phase Reaction Kinetics: Cyclopentene Vapor Pyrolysis

NASA Astrophysics Data System (ADS)

Marcotte, Ronald E.; Wilson, Lenore D.

2001-06-01

The undergraduate laboratory experiment on the pyrolysis of gaseous cyclopentene has been modernized to improve safety, speed, and precision and to better reflect the current practice of physical chemistry. It now utilizes virtual instrument techniques to create a graphical computer interface for the collection and display of experimental data. An electronic pressure gauge has replaced the mercury manometer formerly needed in proximity to the 500 °C pyrolysis oven. Students have much better real-time information available to them and no longer require multiple lab periods to get rate constants and acceptable Arrhenius parameters. The time saved on manual data collection is used to give the students a tour of the computer interfacing hardware and software and a hands-on introduction to gas-phase reagent preparation using a research-grade high-vacuum system. This includes loading the sample, degassing it by the freeze-pump-thaw technique, handling liquid nitrogen and working through the logic necessary for each reconfiguration of the diffusion pump section and the submanifolds.

Structural and dynamic properties of liquid tin from a new modified embedded-atom method force field

NASA Astrophysics Data System (ADS)

Vella, Joseph R.; Chen, Mohan; Stillinger, Frank H.; Carter, Emily A.; Debenedetti, Pablo G.; Panagiotopoulos, Athanassios Z.

2017-02-01

A new modified embedded-atom method (MEAM) force field is developed for liquid tin. Starting from the Ravelo and Baskes force field [Phys. Rev. Lett. 79, 2482 (1997), 10.1103/PhysRevLett.79.2482], the parameters are adjusted using a simulated annealing optimization procedure in order to obtain better agreement with liquid-phase data. The predictive capabilities of the new model and the Ravelo and Baskes force field are evaluated using molecular dynamics by comparing to a wide range of first-principles and experimental data. The quantities studied include crystal properties (cohesive energy, bulk modulus, equilibrium density, and lattice constant of various crystal structures), melting temperature, liquid structure, liquid density, self-diffusivity, viscosity, and vapor-liquid surface tension. It is shown that although the Ravelo and Baskes force field generally gives better agreement with the properties related to the solid phases of tin, the new MEAM force field gives better agreement with liquid tin properties.

Structural and dynamic properties of liquid tin from a new modified embedded-atom method force field

DOE PAGES

Vella, Joseph R.; Chen, Mohan; Stillinger, Frank H.; ...

2017-02-01

We developed a new modified embedded-atom method (MEAM) force field for liquid tin. Starting from the Ravelo and Baskes force field [Phys. Rev. Lett. 79, 2482 (1997)], the parameters are adjusted using a simulated annealing optimization procedure in order to obtain better agreement with liquid-phase data. The predictive capabilities of the new model and the Ravelo and Baskes force field are evaluated using molecular dynamics by comparing to a wide range of first-principles and experimental data. The quantities studied include crystal properties (cohesive energy, bulk modulus, equilibrium density, and lattice constant of various crystal structures), melting temperature, liquid structure, liquidmore » density, self-diffusivity, viscosity, and vapor-liquid surface tension. We show that although the Ravelo and Baskes force field generally gives better agreement with the properties related to the solid phases of tin, the new MEAM force field gives better agreement with liquid tin properties.« less

Heteroepitaxial growth of 3-5 semiconductor compounds by metal-organic chemical vapor deposition for device applications

NASA Technical Reports Server (NTRS)

Collis, Ward J.; Abul-Fadl, Ali

1988-01-01

The purpose of this research is to design, install and operate a metal-organic chemical vapor deposition system which is to be used for the epitaxial growth of 3-5 semiconductor binary compounds, and ternary and quaternary alloys. The long-term goal is to utilize this vapor phase deposition in conjunction with existing current controlled liquid phase epitaxy facilities to perform hybrid growth sequences for fabricating integrated optoelectronic devices.

Evidence for extreme partitioning of copper into a magmatic vapor phase.

PubMed

Lowenstern, J B; Mahood, G A; Rivers, M L; Sutton, S R

1991-06-07

The discovery of copper sulfides in carbon dioxide- and chlorine-bearing bubbles in phenocryst-hosted melt inclusions shows that copper resides in a vapor phase in some shallow magma chambers. Copper is several hundred times more concentrated in magmatic vapor than in coexisting pantellerite melt. The volatile behavior of copper should be considered when modeling the volcanogenic contribution of metals to the atmosphere and may be important in the formation of copper porphyry ore deposits.

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

Chen, Yinshan; Zhu, Men; Laventure, Audrey

Surface grating decay measurements have been performed on three closely related molecular glasses to study the effect of intermolecular hydrogen bonds on surface diffusion. The three molecules are derivatives of bis(3,5-dimethyl-phenylamino)-1,3,5-triazine and differ only in the functional group R at the 2-position, with R being C 2H 5, OCH 3, and NHCH 3, and referred to as “Et”, “OMe”, and “NHMe”, respectively. Of the three molecules, NHMe forms more extensive intermolecular hydrogen bonds than Et and OMe and was found to have slower surface diffusion. For Et and OMe, surface diffusion is so fast that it replaces viscous flow asmore » the mechanism of surface grating decay as temperature is lowered. In contrast, no such transition was observed for NHMe under the same conditions, indicating significantly slower surface diffusion. This result is consistent with the previous finding that extensive intermolecular hydrogen bonds slow down surface diffusion in molecular glasses and is attributed to the persistence of hydrogen bonds even in the surface environment. Here, this result is also consistent with the lower stability of the vapor-deposited glass of NHMe relative to those of Et and OMe and supports the view that surface mobility controls the stability of vapor-deposited glasses.« less

Procedure 5 Quality Assurance Requirements For Vapor Phase Mercury Continuous Emissions Monitoring Systems And Sorbent Trap Monitoring Systems Used For Compliance Determination At Stationary Sources

EPA Pesticide Factsheets

Promulgated quality assurance Procedure 5 Quality Assurance Requirements For Vapor Phase Mercury Continuous Emissions Monitoring Systems And Sorbent Trap Monitoring Systems Used For Compliance Determination At Stationary Sources

The Observed Properties of Liquid Helium at the Saturated Vapor Pressure

NASA Astrophysics Data System (ADS)

Donnelly, Russell J.; Barenghi, Carlo F.

1998-11-01

The equilibrium and transport properties of liquid 4He are deduced from experimental observations at the saturated vapor pressure. In each case, the bibliography lists all known measurements. Quantities reported here include density, thermal expansion coefficient, dielectric constant, superfluid and normal fluid densities, first, second, third, and fourth sound velocities, specific heat, enthalpy, entropy, surface tension, ion mobilities, mutual friction, viscosity and kinematic viscosity, dispersion curve, structure factor, thermal conductivity, latent heat, saturated vapor pressure, thermal diffusivity and Prandtl number of helium I, and displacement length and vortex core parameter in helium II.

Mutual influence of molecular diffusion in gas and surface phases

NASA Astrophysics Data System (ADS)

Hori, Takuma; Kamino, Takafumi; Yoshimoto, Yuta; Takagi, Shu; Kinefuchi, Ikuya

2018-01-01

We develop molecular transport simulation methods that simultaneously deal with gas- and surface-phase diffusions to determine the effect of surface diffusion on the overall diffusion coefficients. The phenomenon of surface diffusion is incorporated into the test particle method and the mean square displacement method, which are typically employed only for gas-phase transport. It is found that for a simple cylindrical pore, the diffusion coefficients in the presence of surface diffusion calculated by these two methods show good agreement. We also confirm that both methods reproduce the analytical solution. Then, the diffusion coefficients for ink-bottle-shaped pores are calculated using the developed method. Our results show that surface diffusion assists molecular transport in the gas phase. Moreover, the surface tortuosity factor, which is known to be uniquely determined by physical structure, is influenced by the presence of gas-phase diffusion. This mutual influence of gas-phase diffusion and surface diffusion indicates that their simultaneous calculation is necessary for an accurate evaluation of the diffusion coefficients.

Numerical Simulation of Nanostructure Growth

NASA Technical Reports Server (NTRS)

Hwang, Helen H.; Bose, Deepak; Govindan, T. R.; Meyyappan, M.

2004-01-01

Nanoscale structures, such as nanowires and carbon nanotubes (CNTs), are often grown in gaseous or plasma environments. Successful growth of these structures is defined by achieving a specified crystallinity or chirality, size or diameter, alignment, etc., which in turn depend on gas mixture ratios. pressure, flow rate, substrate temperature, and other operating conditions. To date, there has not been a rigorous growth model that addresses the specific concerns of crystalline nanowire growth, while demonstrating the correct trends of the processing conditions on growth rates. Most crystal growth models are based on the Burton, Cabrera, and Frank (BCF) method, where adatoms are incorporated into a growing crystal at surface steps or spirals. When the supersaturation of the vapor is high, islands nucleate to form steps, and these steps subsequently spread (grow). The overall bulk growth rate is determined by solving for the evolving motion of the steps. Our approach is to use a phase field model to simulate the growth of finite sized nanowire crystals, linking the free energy equation with the diffusion equation of the adatoms. The phase field method solves for an order parameter that defines the evolving steps in a concentration field. This eliminates the need for explicit front tracking/location, or complicated shadowing routines, both of which can be computationally expensive, particularly in higher dimensions. We will present results demonstrating the effect of process conditions, such as substrate temperature, vapor supersaturation, etc. on the evolving morphologies and overall growth rates of the nanostructures.

Surface CHEMKIN (Version 4. 0): A Fortran package for analyzing heterogeneous chemical kinetics at a solid-surface---gas-phase interface

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

Coltrin, M.E.; Kee, R.J.; Rupley, F.M.

1991-07-01

Heterogeneous reaction at the interface between a solid surface and adjacent gas is central to many chemical processes. Our purpose for developing the software package SURFACE CHEMKIN was motivated by our need to understand the complex surface chemistry in chemical vapor deposition systems involving silicon, silicon nitride, and gallium arsenide. However, we have developed the approach and implemented the software in a general setting. Thus, we expect it will find use in such diverse applications as chemical vapor deposition, chemical etching, combustion of solids, and catalytic processes, and for a wide range of chemical systems. We believe that it providesmore » a powerful capability to help model, understand, and optimize important industrial and research chemical processes. The SURFACE CHEMKIN software is designed to work in conjunction with the CHEMKIN-2 software, which handles the chemical kinetics in the gas phase. It may also be used in conjunction with the Transport Property Package, which provides information about molecular diffusion. Thus, these three packages provide a foundation on which a user can build applications software to analyze gas-phase and heterogeneous chemistry in flowing systems. These packages should not be considered programs'' in the ordinary sense. That is, they are not designed to accept input, solve a particular problem, and report the answer. Instead, they are software tools intended to help a user work efficiently with large systems of chemical reactions and develop Fortran representations of systems of equations that define a particular problem. It is up the user to solve the problem and interpret the answer. 11 refs., 15 figs., 5 tabs.« less

Development of an Evaporation Sub-model and Simulation of Multiple Droplet Impingement in Volume of Fluid Method

NASA Astrophysics Data System (ADS)

Potham, Sathya Prasad

Droplet collision and impingement on a substrate are widely observed phenomenon in many applications like spray injection of Internal Combustion Engines, spray cooling, spray painting and atomizers used in propulsion applications. Existing Lagrangian models do not provide a comprehensive picture of the outcome of these events and may involve model constants requiring experimental data for validation. Physics based models like Volume of Fluid (VOF) method involve no parametric tuning and are more accurate. The aim of this thesis is to extend the basic VOF method with an evaporation sub-model and implement in an open source Computational Fluid Dynamics (CFD) software, OpenFOAM. The new model is applied to numerically study the evaporation of spherical n-heptane droplets impinging on a hot wall at atmospheric pressure and a temperature above the Leidenfrost temperature. An additional vapor phase is introduced apart from the liquid and gas phases to understand the mixing and diffusion of vapor and gas phases. The evaporation model is validated quantitatively and qualitatively with fundamental problems having analytical solutions and published results. The effect of droplet number and arrangement on evaporation is studied by three cases with one (Case 1), two (Case 2) and four (Case 3) droplets impinging on hot wall in film boiling regime at a fixed temperature of wall and a constant non-dimensional distance between droplets. Droplet lift and spread, surface temperature, heat transfer, and evaporation rate are examined. It was observed that more liquid mass evaporated in Case 1 compared to the other cases. Droplet levitation begins early in Case 1 and very high levitation observed was partially due to contraction of its shape from elongated to a more circular form. Average surface temperature was also considerably reduced in Case 1 due to high droplet levitation.

Effect of gamma-ray irradiation on structural properties of GaAsN films grown by metal organic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Klangtakai, Pawinee; Sanorpim, Sakuntam; Wattanawareekul, Atiwat; Suwanyangyaun, Pattana; Srepusharawoot, Pornjuk; Onabe, Kentaro

2015-05-01

The effects of gamma-ray irradiation on the structural properties of GaAs1-xNx films (N concentration=1.9 and 5.1 at%) grown by metal organic vapor phase epitaxy on GaAs (001) substrates were investigated. The GaAs1-xNx films were irradiated by gamma rays with irradiation strength of 0-2.0 MGy. Scanning electron microscopy and atomic force microscopy results showed that a gamma ray with a strength of 0, 0.5, 1.0, 1.5, and 2.0 MGy formed holes with a density of 0.0, 8.8, 9.4, 11.5, and 11.9 μm-2, respectively, on the surface of a GaAs0.981N0.019 film with low N content. On the other hand, the irradiated high-N-content GaAs0.949N0.051 film exhibited a cross-hatch pattern, which was induced by partial strain relaxation at high N levels, with a line density of 0.0, 0.21, 0.37, 0.67, and 0.26 μm-1 corresponding to an irradiation strength of 0, 0.5, 1.0, 1.5, and 2.0 MGy, respectively. The high-resolution X-ray diffraction and Raman scattering results revealed an increase in N incorporation and strain relaxation after irradiation. In addition, the GaAs0.949N0.051 films exhibited phase separation, which took place via N out-diffusion across the interface when the irradiation strength exceeded 1.0 MGy. Based on these results, the main cause of structural change was determined to be the irradiation effects including displacement damage and gamma-ray heating.

Mid-infrared laser-absorption diagnostic for vapor-phase fuel mole fraction and liquid fuel film thickness

NASA Astrophysics Data System (ADS)

Porter, J. M.; Jeffries, J. B.; Hanson, R. K.

2011-02-01

A novel two-wavelength mid-infrared laser-absorption diagnostic has been developed for simultaneous measurements of vapor-phase fuel mole fraction and liquid fuel film thickness. The diagnostic was demonstrated for time-resolved measurements of n-dodecane liquid films in the absence and presence of n-decane vapor at 25°C and 1 atm. Laser wavelengths were selected from FTIR measurements of the C-H stretching band of vapor n-decane and liquid n-dodecane near 3.4 μm (3000 cm-1). n-Dodecane film thicknesses <20 μm were accurately measured in the absence of vapor, and simultaneous measurements of n-dodecane liquid film thickness and n-decane vapor mole fraction (300 ppm) were measured with <10% uncertainty for film thicknesses <10 μm. A potential application of the measurement technique is to provide accurate values of vapor mole fraction in combustion environments where strong absorption by liquid fuel or oil films on windows make conventional direct absorption measurements of the gas problematic.

The gas phase emitter effect of lanthanum within ceramic metal halide lamps and its dependence on the La vapor pressure and operating frequency

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

Ruhrmann, C.; Hoebing, T.; Bergner, A.

2015-08-07

The gas phase emitter effect increases the lamp lifetime by lowering the work function and, with it, the temperature of the tungsten electrodes of metal halide lamps especially for lamps in ceramic vessels due to their high rare earth pressures. It is generated by a monolayer on the electrode surface of electropositive atoms of certain emitter elements, which are inserted into the lamp bulb by metal iodide salts. They are vaporized, dissociated, ionized, and deposited by an emitter ion current onto the electrode surface within the cathodic phase of lamp operation with a switched-dc or ac-current. The gas phase emittermore » effect of La and the influence of Na on the emitter effect of La are studied by spatially and phase-resolved pyrometric measurements of the electrode tip temperature, La atom, and ion densities by optical emission spectroscopy as well as optical broadband absorption spectroscopy and arc attachment images by short time photography. An addition of Na to the lamp filling increases the La vapor pressure within the lamp considerably, resulting in an improved gas phase emitter effect of La. Furthermore, the La vapor pressure is raised by a heating of the cold spot. In this way, conditions depending on the La vapor pressure and operating frequency are identified, at which the temperature of the electrodes becomes a minimum.« less

Numerical simulation of superheated vapor bubble rising in stagnant liquid

NASA Astrophysics Data System (ADS)

Samkhaniani, N.; Ansari, M. R.

2017-09-01

In present study, the rising of superheated vapor bubble in saturated liquid is simulated using volume of fluid method in OpenFOAM cfd package. The surface tension between vapor-liquid phases is considered using continuous surface force method. In order to reduce spurious current near interface, Lafaurie smoothing filter is applied to improve curvature calculation. Phase change is considered using Tanasawa mass transfer model. The variation of saturation temperature in vapor bubble with local pressure is considered with simplified Clausius-Clapeyron relation. The couple velocity-pressure equation is solved using PISO algorithm. The numerical model is validated with: (1) isothermal bubble rising and (2) one-dimensional horizontal film condensation. Then, the shape and life time history of single superheated vapor bubble are investigated. The present numerical study shows vapor bubble in saturated liquid undergoes boiling and condensation. It indicates bubble life time is nearly linear proportional with bubble size and superheat temperature.

Sol–gel synthesis of MCM-41 silicas and selective vapor-phase modification of their surface

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

Roik, N.V., E-mail: roik_nadya@ukr.net; Belyakova, L.A.

2013-11-15

Silica particles with uniform hexagonal mesopore architecture were synthesized by template directed sol–gel condensation of tetraethoxysilane or mixture of tetraethoxysilane and (3-chloropropyl)triethoxysilane in a water–ethanol–ammonia solution. Selective functionalization of exterior surface of parent materials was carried out by postsynthetic treatment of template-filled MCM-41 and Cl-MCM-41 with vapors of (3-chloropropyl)triethoxysilane and 1,2-ethylenediamine in vacuum. The chemical composition of obtained mesoporous silicas was estimated by IR spectroscopy and chemical analysis of surface products of reactions. Characteristics of porous structure of resulting materials were determined from the data of X-ray, low-temperature nitrogen ad-desorption and transmission electron microscopy measurements. Obtained results confirm invariability ofmore » highly ordered mesoporous structure of MCM-41 and Cl-MCM-41 after their selective postsynthetic modification in vapor phase. It was proved that proposed method of vapor-phase functionalization of template-filled starting materials is not accompanied by dissolution of the template and chemical modification of pores surface. This provides preferential localization of grafted functional groups onto the exterior surface of mesoporous silicas. - Graphical abstract: Sol–gel synthesis and postsynthetic chemical modification of template-filled MCM-41 and Cl-MCM-41 with (3-chloropropyl)triethoxysilane and 1,2-ethylenediamine in vapor phase. Display Omitted - Highlights: • Synthesis of MCM-41 silica by template directed sol–gel condensation. • Selective vapor-phase functionalization of template-filled silica particles. • Preferential localization of grafted groups onto the exterior surface of mesoporous silicas.« less

Intergranular diffusion and embrittlement of a Ni-16Mo-7Cr alloy in Te vapor environment

NASA Astrophysics Data System (ADS)

Cheng, Hongwei; Li, Zhijun; Leng, Bin; Zhang, Wenzhu; Han, Fenfen; Jia, Yanyan; Zhou, Xingtai

2015-12-01

Nickel and some nickel-base alloys are extremely sensitive to intergranular embrittlement and tellurium (Te) enhanced cracking, which should be concerned during their serving in molten salt reactors. Here, a systematic study about the effects of its temperature on the reaction products at its surface, the intergranular diffusion of Te in its body and its embrittlement for a Ni-16Mo-7Cr alloy contacting Te is reported. For exposed to Te vapor at high temperature (823-1073 K), the reaction products formed on the surface of the alloy were Ni3Te2, CrTe, and MoTe2, and the most serious embrittlement was observed at 1073 K. The kinetic measurement in terms of Te penetration depth in the alloy samples gives an activation energy of 204 kJ/mol. Electron probe microanalysis confirmed the local enrichment of Te at grain boundaries. And clearly, the embrittlement was results from the intergranular diffusion and segregation of element Te.

Dependence of growth of the phases of multiphase binary systems on the diffusion parameters

NASA Astrophysics Data System (ADS)

Molokhina, L. A.; Rogalin, V. E.; Filin, S. A.; Kaplunov, I. A.

2017-12-01

A mathematical model of the diffusion interaction of a binary system with several phases on the equilibrium phase diagram is presented. The theoretical and calculated dependences of the layer thickness of each phase in the multiphase diffusion zone on the isothermal annealing time and the ratio of the diffusion parameters in the neighboring phases with an unlimited supply of both components were constructed. The phase formation and growth in the diffusion zone during "reactive" diffusion corresponds to the equilibrium state diagram for two components, and the order of their appearance in the diffusion zone depends only on the ratio of the diffusion parameters in the phases themselves and on the duration of the incubation periods. The dependence of phase appearance on the incubation periods, annealing time, and difference in the movement rates of the components across the interface boundaries was obtained. An example of the application of the model for processing the experimental data on phase growth in a two-component three-phase system was given.

Nano powders, components and coatings by plasma technique

DOEpatents

McKechnie, Timothy N [Brownsboro, AL; Antony, Leo V. M. [Huntsville, AL; O'Dell, Scott [Arab, AL; Power, Chris [Guntersville, AL; Tabor, Terry [Huntsville, AL

2009-11-10

Ultra fine and nanometer powders and a method of producing same are provided, preferably refractory metal and ceramic nanopowders. When certain precursors are injected into the plasma flame in a reactor chamber, the materials are heated, melted and vaporized and the chemical reaction is induced in the vapor phase. The vapor phase is quenched rapidly to solid phase to yield the ultra pure, ultra fine and nano product. With this technique, powders have been made 20 nanometers in size in a system capable of a bulk production rate of more than 10 lbs/hr. The process is particularly applicable to tungsten, molybdenum, rhenium, tungsten carbide, molybdenum carbide and other related materials.

Nano powders, components and coatings by plasma technique

NASA Technical Reports Server (NTRS)

McKechnie, Timothy N. (Inventor); Antony, Leo V. M. (Inventor); O'Dell, Scott (Inventor); Power, Chris (Inventor); Tabor, Terry (Inventor)

2009-01-01

Ultra fine and nanometer powders and a method of producing same are provided, preferably refractory metal and ceramic nanopowders. When certain precursors are injected into the plasma flame in a reactor chamber, the materials are heated, melted and vaporized and the chemical reaction is induced in the vapor phase. The vapor phase is quenched rapidly to solid phase to yield the ultra pure, ultra fine and nano product. With this technique, powders have been made 20 nanometers in size in a system capable of a bulk production rate of more than 10 lbs/hr. The process is particularly applicable to tungsten, molybdenum, rhenium, tungsten carbide, molybdenum carbide and other related materials.

Irradiation of fish fillets: Relation of vapor phase reactions to storage quality

USGS Publications Warehouse

Spinelli, J.; Dollar, A.M.; Wedemeyer, G.A.; Gallagher, E.C.

1969-01-01

Fish fillets irradiated under air, nitrogen, oxygen, or carbon dioxide atmospheres developed rancidlike flavors when they were stored at refrigerated temperatures. Packing and irradiating under vacuum or helium prevented development of off-flavors during storage.Significant quantities of nitrate and oxidizing substances were formed when oxygen, nitrogen, or air were present in the vapor or liquid phases contained in a Pyrex glass model system exposed to ionizing radiation supplied by a 60Co source. It was demonstrated that the delayed flavor changes that occur in stored fish fillets result from the reaction of vapor phase radiolysis products and the fish tissue substrates.

VAPOR PRESSURES, LIQUID MOLAR VOLUMES, VAPOR NON- IDEALITIES, AND CRITICAL PROPERTIES OF SOME FLUORINATED ETHERS: CF3OCF2OCF3, CF3OCF2 CF2H, c-CF2CF2CF2O, CF3OCF2H, AND CF3OCH3; AND OF CCl3F AND CF2ClH

EPA Science Inventory

Vapor pressures, compressibilities, expansivities, and molar volumes of the liquid phase have been measured between room temperature and the critical temperature for a series of fluorinated ethers: CF3OCF2OCF3, CF3OCF2CF2H, c-CF2CF2CF2O, CF3OCF2H, and CF3OCH3. Vapor-phase non-ide...

Vapor-Liquid Equilibrium in the Mixture 1,1-Difluoroethane C2H4F2 + C4H8 2-Methylpropene (EVLM1131, LB5730_E)

NASA Astrophysics Data System (ADS)

Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

This document is part of Subvolume A 'Binary Liquid Systems of Nonelectrolytes I' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Vapor-Liquid Equilibrium in the Mixture 1,1-Difluoroethane C2H4F2 + C4H8 2-Methylpropene (EVLM1131, LB5730_E)' providing data from direct measurement of pressure and mole fraction in vapor phase at variable mole fraction in liquid phase and constant temperature.

EFFECT OF VAPOR-PHASE BIOREACTOR OPERATION ON BIOMASS ACCUMULATION, DISTRIBUTION, AND ACTIVITY. (R826168)

EPA Science Inventory

Excess biomass accumulation and activity loss in vapor-phase bioreactors (VPBs) can lead to unreliable long-term operation. In this study, temporal and spatial variations in biomass accumulation, distribution and activity in VPBs treating toluene-contaminated air were monitored o...

Extreme water loss and abiotic O2 buildup on planets throughout the habitable zones of M dwarfs.

PubMed

Luger, R; Barnes, R

2015-02-01

We show that terrestrial planets in the habitable zones of M dwarfs older than ∼1 Gyr could have been in runaway greenhouses for several hundred million years following their formation due to the star's extended pre-main sequence phase, provided they form with abundant surface water. Such prolonged runaway greenhouses can lead to planetary evolution divergent from that of Earth. During this early runaway phase, photolysis of water vapor and hydrogen/oxygen escape to space can lead to the loss of several Earth oceans of water from planets throughout the habitable zone, regardless of whether the escape is energy-limited or diffusion-limited. We find that the amount of water lost scales with the planet mass, since the diffusion-limited hydrogen escape flux is proportional to the planet surface gravity. In addition to undergoing potential desiccation, planets with inefficient oxygen sinks at the surface may build up hundreds to thousands of bar of abiotically produced O2, resulting in potential false positives for life. The amount of O2 that builds up also scales with the planet mass; we find that O2 builds up at a constant rate that is controlled by diffusion: ∼5 bar/Myr on Earth-mass planets and up to ∼25 bar/Myr on super-Earths. As a result, some recently discovered super-Earths in the habitable zone such as GJ 667Cc could have built up as many as 2000 bar of O2 due to the loss of up to 10 Earth oceans of water. The fate of a given planet strongly depends on the extreme ultraviolet flux, the duration of the runaway regime, the initial water content, and the rate at which oxygen is absorbed by the surface. In general, we find that the initial phase of high luminosity may compromise the habitability of many terrestrial planets orbiting low-mass stars.

Adsorption and solvation of ethanol at the water liquid-vapor interface: a molecular dynamics study

NASA Technical Reports Server (NTRS)

Wilson, M. A.; Pohorille, A.

1997-01-01

The free energy profiles of methanol and ethanol at the water liquid-vapor interface at 310K were calculated using molecular dynamics computer simulations. Both alcohols exhibit a pronounced free energy minimum at the interface and, therefore, have positive adsorption at this interface. The surface excess was computed from the Gibbs adsorption isotherm and was found to be in good agreement with experimental results. Neither compound exhibits a free energy barrier between the bulk and the surface adsorbed state. Scattering calculations of ethanol molecules from a gas phase thermal distribution indicate that the mass accommodation coefficient is 0.98, and the molecules become thermalized within 10 ps of striking the interface. It was determined that the formation of the solvation structure around the ethanol molecule at the interface is not the rate-determining step in its uptake into water droplets. The motion of an ethanol molecule in a water lamella was followed for 30 ns. The time evolution of the probability distribution of finding an ethanol molecule that was initially located at the interface is very well described by the diffusion equation on the free energy surface.

Titanium-Catalyzed Silicon Nanostructures Grown by APCVD

NASA Astrophysics Data System (ADS)

Usman, Mohammad A. U.; Smith, Brady J.; Jackson, Justin B.; De Long, Matthew C.; Miller, Mark S.

2015-01-01

We report on growth of Ti-catalyzed silicon nanostructures (SNCs) through atmospheric-pressure chemical vapor deposition. An extensive growth study relating the growth condition parameters, including the partial pressure of SiCl4 gas, reaction temperature, and reaction time, was carried out to obtain insight into the growth regimes for the observed SNCs. Based on phase diagram analysis of Ti-Si alloy and growth rate analysis of the silicon nanowires (SNWs) and silicon nanoplatelets, we believe the growth mechanism to be strongly dependent on the thermodynamics of the system, exhibiting a delicate balance that can easily tip between the growth and etching regimes of the system. Three types of SNCs were observed frequently throughout the study: nanowires, nanoplatelets, and balls. Regimes for highly etched growth were also noted through growth conditions plots. Ti-catalyzed SNWs grown using SiCl4 gas strongly suggest growth occurring through a type of vapor-solid-solid (VSS) mechanism that is limited by diffusion through the solid-catalyst interface. On the other hand, the two-dimensional SNP morphologies suggest growth occurring through the twin-plane mechanism at the edges, at 10 nm to 100 nm scales, also through a similar, VSS mechanism.

Modeling of InP metalorganic chemical vapor deposition

NASA Technical Reports Server (NTRS)

Black, Linda R.; Clark, Ivan O.; Kui, J.; Jesser, William A.

1991-01-01

The growth of InP by metalorganic chemical vapor deposition (MOCVD) in a horizontal reactor is being modeled with a commercially available computational fluid dynamics modeling code. The mathematical treatment of the MOCVD process has four primary areas of concern: 1) transport phenomena, 2) chemistry, 3) boundary conditions, and 4) numerical solution methods. The transport processes involved in CVD are described by conservation of total mass, momentum, energy, and atomic species. Momentum conservation is described by a generalized form of the Navier-Stokes equation for a Newtonian fluid and laminar flow. The effect of Soret diffusion on the transport of particular chemical species and on the predicted deposition rate is examined. Both gas-phase and surface chemical reactions are employed in the model. Boundary conditions are specified at the inlet and walls of the reactor for temperature, fluid flow and chemical species. The coupled set of equations described above is solved by a finite difference method over a nonuniform rectilinear grid in both two and three dimensions. The results of the 2-D computational model is presented for gravity levels of zero- and one-g. The predicted growth rates at one-g are compared to measured growth rates on fused silica substrates.

Investigation of Tropical Transport with UARS Data

NASA Technical Reports Server (NTRS)

Dunkerton, Timothy J.

1999-01-01

Measurements of trace constituents obtained by instruments aboard the Upper Atmosphere Research Satellite (UARS) have been used to study transport processes associated with the quasi-biennial oscillation, laterally propagating Rossby waves, and upward propagating Kelvin waves in the tropical and subtropical upper troposphere and stratosphere. Mean vertical motions, vertical diffusivities and in-mixing rates were inferred from observations of the 'tape recorder' signal in near-equatorial stratospheric water vapor. The effect of the quasi-biennial oscillation (QBO) on tracer distributions in the upper half of the stratosphere was seen in a spectacular 'staircase' pattern, predominantly in the winter hemisphere, revealing the latitudinally asymmetric nature of QBO transport due to induced mean meridional circulations and modulation of lateral mixing associated with planetary Rossby waves. The propagation of Rossby waves across the equator in the westerly phase of the QBO was seen in tracer fields and corroborating United Kingdom Meteorological Office (UKMO) analyses; a modeling study of the effect of these waves on typical QBO wind profiles was performed. Water vapor in the upper troposphere and lower stratosphere was found to exhibit signatures of the tropical intraseasonal oscillation (TIO) and faster Kelvin waves in the two regions, respectively.

Acoustically-Enhanced Direct Contact Vapor Bubble Condensation

NASA Astrophysics Data System (ADS)

Boziuk, Thomas; Smith, Marc; Glezer, Ari

2017-11-01

Rate-limited, direct contact vapor condensation of vapor bubbles that are formed by direct steam injection through a nozzle in a quiescent subcooled liquid bath is accelerated using ultrasonic (MHz-range) actuation. A submerged, low power actuator produces an acoustic beam whose radiation pressure deforms the liquid-vapor interface, leading to the formation of a liquid spear that penetrates the vapor bubble to form a vapor torus with a significantly larger surface area and condensation rate. Ultrasonic focusing along the spear leads to the ejection of small, subcooled droplets through the vapor volume that impact the vapor-liquid interface and further enhance the condensation. High-speed Schlieren imaging of the formation and collapse of the vapor bubbles in the absence and presence of actuation shows that the impulse associated with the collapse of the toroidal volume leads to the formation of a turbulent vortex ring in the liquid phase. Liquid motions near the condensing vapor volume are investigated in the absence and presence of acoustic actuation using high-magnification PIV and show the evolution of a liquid jet through the center of the condensing toroidal volume and the formation and advection of vortex ring structures whose impulse appear to increase with temperature difference between the liquid and vapor phases. High-speed image processing is used to assess the effect of the actuation on the temporal and spatial variations in the characteristic scales and condensation rates of the vapor bubbles.

Space cryogenics components based on the thermomechanical effect - Vapor-liquid phase separation

NASA Technical Reports Server (NTRS)

Yuan, S. W. K.; Frederking, T. H. K.

1989-01-01

Applications of the thermomechanical effect has been qualified including incorporation in large-scale space systems in the area of vapor-liquid phase separation (VLPS). The theory of the porous-plug phase separator is developed for the limit of a high thermal impedance of the solid-state grains. Extensions of the theory of nonlinear turbulent flow are presented based on experimental results.

Vapor Wall Deposition in Chambers: Theoretical Considerations

NASA Astrophysics Data System (ADS)

McVay, R.; Cappa, C. D.; Seinfeld, J.

2014-12-01

In order to constrain the effects of vapor wall deposition on measured secondary organic aerosol (SOA) yields in laboratory chambers, Zhang et al. (2014) varied the seed aerosol surface area in toluene oxidation and observed a clear increase in the SOA yield with increasing seed surface area. Using a coupled vapor-particle dynamics model, we examine the extent to which this increase is the result of vapor wall deposition versus kinetic limitations arising from imperfect accommodation of organic species into the particle phase. We show that a seed surface area dependence of the SOA yield is present only when condensation of vapors onto particles is kinetically limited. The existence of kinetic limitation can be predicted by comparing the characteristic timescales of gas-phase reaction, vapor wall deposition, and gas-particle equilibration. The gas-particle equilibration timescale depends on the gas-particle accommodation coefficient αp. Regardless of the extent of kinetic limitation, vapor wall deposition depresses the SOA yield from that in its absence since vapor molecules that might otherwise condense on particles deposit on the walls. To accurately extrapolate chamber-derived yields to atmospheric conditions, both vapor wall deposition and kinetic limitations must be taken into account.

Study of the effect of wind speed on evaporation from soil through integrated modeling of the atmospheric boundary layer and shallow subsurface.

PubMed

Davarzani, Hossein; Smits, Kathleen; Tolene, Ryan M; Illangasekare, Tissa

2014-01-01

In an effort to develop methods based on integrating the subsurface to the atmospheric boundary layer to estimate evaporation, we developed a model based on the coupling of Navier-Stokes free flow and Darcy flow in porous medium. The model was tested using experimental data to study the effect of wind speed on evaporation. The model consists of the coupled equations of mass conservation for two-phase flow in porous medium with single-phase flow in the free-flow domain under nonisothermal, nonequilibrium phase change conditions. In this model, the evaporation rate and soil surface temperature and relative humidity at the interface come directly from the integrated model output. To experimentally validate numerical results, we developed a unique test system consisting of a wind tunnel interfaced with a soil tank instrumented with a network of sensors to measure soil-water variables. Results demonstrated that, by using this coupling approach, it is possible to predict the different stages of the drying process with good accuracy. Increasing the wind speed increases the first stage evaporation rate and decreases the transition time between two evaporative stages (soil water flow to vapor diffusion controlled) at low velocity values; then, at high wind speeds the evaporation rate becomes less dependent on the wind speed. On the contrary, the impact of wind speed on second stage evaporation (diffusion-dominant stage) is not significant. We found that the thermal and solute dispersion in free-flow systems has a significant influence on drying processes from porous media and should be taken into account.

Study of the effect of wind speed on evaporation from soil through integrated modeling of the atmospheric boundary layer and shallow subsurface

PubMed Central

Davarzani, Hossein; Smits, Kathleen; Tolene, Ryan M; Illangasekare, Tissa

2014-01-01

In an effort to develop methods based on integrating the subsurface to the atmospheric boundary layer to estimate evaporation, we developed a model based on the coupling of Navier-Stokes free flow and Darcy flow in porous medium. The model was tested using experimental data to study the effect of wind speed on evaporation. The model consists of the coupled equations of mass conservation for two-phase flow in porous medium with single-phase flow in the free-flow domain under nonisothermal, nonequilibrium phase change conditions. In this model, the evaporation rate and soil surface temperature and relative humidity at the interface come directly from the integrated model output. To experimentally validate numerical results, we developed a unique test system consisting of a wind tunnel interfaced with a soil tank instrumented with a network of sensors to measure soil-water variables. Results demonstrated that, by using this coupling approach, it is possible to predict the different stages of the drying process with good accuracy. Increasing the wind speed increases the first stage evaporation rate and decreases the transition time between two evaporative stages (soil water flow to vapor diffusion controlled) at low velocity values; then, at high wind speeds the evaporation rate becomes less dependent on the wind speed. On the contrary, the impact of wind speed on second stage evaporation (diffusion-dominant stage) is not significant. We found that the thermal and solute dispersion in free-flow systems has a significant influence on drying processes from porous media and should be taken into account. PMID:25309005

Phase equilibria of H2SO4, HNO3, and HCl hydrates and the composition of polar stratospheric clouds

NASA Technical Reports Server (NTRS)

Wooldridge, Paul J.; Zhang, Renyi; Molina, Mario J.

1995-01-01

Thermodynamic properties and phase equilibria behavior for the hydrates and coexisting pairs of hydrates of common acids which exist in the stratosphere are assembled from new laboratory measurements and standard literature data. The analysis focuses upon solid-vapor and solid-solid-vapor equilibria at temperatures around 200 K and includes new calorimetric and vapor pressure data. Calculated partial pressures versus 1/T slopes for the hydrates and coexisting hydrates agree well with experimental data where available.

Phase Equilibria of H2SO4, HNO3, and HCl Hydrates and the Composition of Polar Stratospheric Clouds

NASA Technical Reports Server (NTRS)

Wooldridge, Paul J.; Zhang, Renyi; Molina, Mario J.

1995-01-01

Thermodynamic properties and phase equilibria behavior for the hydrates and coexisting pairs of hydrates of common acids which exist in the stratosphere are assembled from new laboratory measurements and standard literature data. The analysis focuses upon solid-vapor and solid-solid-vapor equilibria at temperatures around 200 K and includes new calorimetric and vapor pressure data. Calculated partial pressures versus 1/T slopes for the hydrates and coexisting hydrates agree well with experimental data where available.

Seeded Physical Vapor Transport of Cadmium-Zinc Telluride Crystals: Growth and Characterization

NASA Technical Reports Server (NTRS)

Palosz, W.; George, M. A.; Collins, E. E.; Chen, K.-T.; Zhang, Y.; Burger, A.

1997-01-01

Crystals of Cd(1-x)Zn(x)Te with x = 0.2 and 40 g in weight were grown on monocrystalline cadmium-zinc telluride seeds by closed-ampoule physical vapor transport with or without excess (Cd + Zn) in the vapor phase. Two post-growth cool-down rates were used. The crystals were characterized using low temperature photoluminescence, atomic force microscopy, chemical etching, X-ray diffraction and electrical measurements. No formation of a second, ZnTe-rich phase was observed.

Investigating Vaporization of Silica through Laser Driven Shock Wave Experiments

NASA Astrophysics Data System (ADS)

Kraus, R. G.; Swift, D. C.; Stewart, S. T.; Smith, R.; Bolme, C. A.; Spaulding, D. K.; Hicks, D.; Eggert, J.; Collins, G.

2010-12-01

Giant impacts melt and vaporize a significant amount of the bolide and target body. However, our ability to determine how much melt or vapor a given impact creates depends strongly on our understanding of the liquid-vapor phase boundary of geologic materials. Our current knowledge of the liquid-vapor equilibrium for one of the most important minerals, SiO2, is rather limited due to the difficulty of performing experiments in this area of phase space. In this study, we investigate the liquid-vapor coexistence region by shocking quartz into a supercritical fluid state and allowing it to adiabatically expand to a state on the liquid-vapor phase boundary. Although shock compression and release has been used to study the liquid-vapor equilibrium of metals [1], few attempts have been made at studying geologic materials by this method [2]. Shock waves were produced by direct ablation of the quartz sample using the Jupiter Laser Facility of Lawrence Livermore National Laboratory. Steady shock pressures of 120-360 GPa were produced in the quartz samples: high enough to force the quartz into a supercritical fluid state. As the shock wave propagates through the sample, we measure the shock velocity using a line imaging velocity interferometer system for any reflector (VISAR) and shock temperature using a streaked optical pyrometer (SOP). When the shock wave reaches the free surface of the sample, the material adiabatically expands. Upon breakout of the shock at the free surface, the SOP records a distinct drop in radiance due to the lower temperature of the expanded material. For a subset of experiments, a LiF window is positioned downrange of the expanding silica. When the expanding silica impacts the LiF window, the velocity at the interface between the expanding silica and LiF window is measured using the VISAR. From the shock velocity measurements, we accurately determine the shocked state in the quartz. The post-shock radiance measurements are used to constrain the temperature on the liquid-vapor phase boundary (e.g., [3]) at much higher pressures than previously possible using a 2 stage gas gun [4, 5]. The density on the liquid-vapor phase boundary is constrained by comparing the velocity at the silica-LiF interface to numerical simulations that use equations of state with systematically varied liquid-vapor phase boundaries. We present the results within the context of understanding vaporization during giant impact events. [1] Brannon, R.M. and L.C. Chhabildas (1995) Int. J. Impact Engng. 17, 109-120. [2] Kurosawa, K. and S. Sugita (2010) J. Geophys. Res. in press. [3] Stewart, S.T., A. Seifter, and A.W. Obst (2008) Geophys. Res. Lett., 35, (23). [4] Lyzenga, G.A., T.J. Ahrens, and A.C. Mitchell (1983) J. Geophys. Res. , 88, (NB3), 2431-2444. [5] Boslough, M.B. (1988) J. Geophys. Res., 93, (B6), 6477-6484.

Solid-state diffusion-controlled growth of the phases in the Au-Sn system

NASA Astrophysics Data System (ADS)

Baheti, Varun A.; Kashyap, Sanjay; Kumar, Praveen; Chattopadhyay, Kamanio; Paul, Aloke

2018-01-01

The solid state diffusion-controlled growth of the phases is studied for the Au-Sn system in the range of room temperature to 200 °C using bulk and electroplated diffusion couples. The number of product phases in the interdiffusion zone decreases with the decrease in annealing temperature. These phases grow with significantly high rates even at the room temperature. The growth rate of the AuSn4 phase is observed to be higher in the case of electroplated diffusion couple because of the relatively small grains and hence high contribution of the grain boundary diffusion when compared to the bulk diffusion couple. The diffraction pattern analysis indicates the same equilibrium crystal structure of the phases in these two types of diffusion couples. The analysis in the AuSn4 phase relating the estimated tracer diffusion coefficients with grain size, crystal structure, the homologous temperature of experiments and the concept of the sublattice diffusion mechanism in the intermetallic compounds indicate that Au diffuses mainly via the grain boundaries, whereas Sn diffuses via both the grain boundaries and the lattice.

Heterogeneous reactions of chlorine nitrate and hydrogen chloride on type I polar stratospheric clouds

NASA Technical Reports Server (NTRS)

Leu, Ming-Taun; Moore, Steven B.; Keyser, Leon F.

1991-01-01

A fast-flow reactor coupled with a quadrupole mass spectrometer was used to study the heterogeneous reactions ClONO2 + HCl yields Cl2 + HNO3 (1) and ClONO2 + H2O yields HOCl + HNO3 (2) on vapor-deposited HNO3-H2O ice substrates. It was found that the sticking coefficient of HCl on these substrates was a strong function of the substrate composition, ranging from about 2 x 10 exp -5 at nitric acid trihydrate composition to 6 x 10 exp -3 at 45 wt pct HNO3. The HNO3-H2O ice substrates were found to have large internal surface areas, and corrections for gas-phase diffusion within the porous ices were applied to observed loss rates.

Formation Dynamics of Potassium-Based Graphite Intercalation Compounds: An Ab Initio Study

NASA Astrophysics Data System (ADS)

Jiang, Xiankai; Song, Bo; Tománek, David

2018-04-01

This paper is a contribution to the Physical Review Applied collection in memory of Mildred S. Dresselhaus. We use ab initio molecular dynamics simulations to study the microscopic dynamics of potassium intercalation in graphite. Upon adsorbing on graphite from the vapor phase, K atoms transfer their valence charge to the substrate. K atoms adsorbed on the surface diffuse rapidly along the graphene basal plane and eventually enter the interlayer region following a "U -turn" across the edge, gaining additional energy. This process is promoted at higher coverages associated with higher K pressure, leading to the formation of a stable intercalation compound. We find that the functionalization of graphene edges is an essential prerequisite for intercalation since bare edges reconstruct and reconnect, closing off the entry channels for the atoms.

On the transition between two-phase and single-phase interface dynamics in multicomponent fluids at supercritical pressures

NASA Astrophysics Data System (ADS)

Dahms, Rainer N.; Oefelein, Joseph C.

2013-09-01

A theory that explains the operating pressures where liquid injection processes transition from exhibiting classical two-phase spray atomization phenomena to single-phase diffusion-dominated mixing is presented. Imaging from a variety of experiments have long shown that under certain conditions, typically when the pressure of the working fluid exceeds the thermodynamic critical pressure of the liquid phase, the presence of discrete two-phase flow processes become diminished. Instead, the classical gas-liquid interface is replaced by diffusion-dominated mixing. When and how this transition occurs, however, is not well understood. Modern theory still lacks a physically based model to quantify this transition and the precise mechanisms that lead to it. In this paper, we derive a new model that explains how the transition occurs in multicomponent fluids and present a detailed analysis to quantify it. The model applies a detailed property evaluation scheme based on a modified 32-term Benedict-Webb-Rubin equation of state that accounts for the relevant real-fluid thermodynamic and transport properties of the multicomponent system. This framework is combined with Linear Gradient Theory, which describes the detailed molecular structure of the vapor-liquid interface region. Our analysis reveals that the two-phase interface breaks down not necessarily due to vanishing surface tension forces, but due to thickened interfaces at high subcritical temperatures coupled with an inherent reduction of the mean free molecular path. At a certain point, the combination of reduced surface tension, the thicker interface, and reduced mean free molecular path enter the continuum length scale regime. When this occurs, inter-molecular forces approach that of the multicomponent continuum where transport processes dominate across the interfacial region. This leads to a continuous phase transition from compressed liquid to supercritical mixture states. Based on this theory, a regime diagram for liquid injection is developed that quantifies the conditions under which classical sprays transition to dense-fluid jets. It is shown that the chamber pressure required to support diffusion-dominated mixing dynamics depends on the composition and temperature of the injected liquid and ambient gas. To illustrate the method and analysis, we use conditions typical of diesel engine injection. We also present a companion set of high-speed images to provide experimental validation of the presented theory. The basic theory is quite general and applies to a wide range of modern propulsion and power systems such as liquid rockets, gas turbines, and reciprocating engines. Interestingly, the regime diagram associated with diesel engine injection suggests that classical spray phenomena at typical injection conditions do not occur.

Beer Law Constants and Vapor Pressures of HgI2 over HgI2(s,l)

NASA Technical Reports Server (NTRS)

Su, Ching-Hua; Zhu, Shen; Ramachandran, N.; Burger, A.; Whitaker, Ann F. (Technical Monitor)

2001-01-01

The optical absorption spectra of the vapor phase over HgI2(s,l) were measured for wavelengths between 200 and 600 nm. The spectra show that the sample sublimed congruently into HgI2 with no Hg or I2 absorption spectrum observed. The Beer's Law constants for 15 wavelengths between 200 and 440 nm were determined. From these constants the vapor pressure of H912, P, was established as a function of temperatures for the liquid and the solid Beta-phases. The expressions correspond to the enthalpies of vaporization and sublimation of 15.30 and 20.17 Kcal/mole, respectively, for the liquid and the Beta-phase HgI2. The difference in the enthalpies gives an enthalpy of fusion of 4.87 Kcal/mole and the intersection of the two expressions gives a melting point of 537 K.

Plasma Spray-PVD: A New Thermal Spray Process to Deposit Out of the Vapor Phase

NASA Astrophysics Data System (ADS)

von Niessen, Konstantin; Gindrat, Malko

2011-06-01

Plasma spray-physical vapor deposition (PS-PVD) is a low pressure plasma spray technology recently developed by Sulzer Metco AG (Switzerland). Even though it is a thermal spray process, it can deposit coatings out of the vapor phase. The basis of PS-PVD is the low pressure plasma spraying (LPPS) technology that has been well established in industry for several years. In comparison to conventional vacuum plasma spraying (VPS) or low pressure plasma spraying (LPPS), the new proposed process uses a high energy plasma gun operated at a reduced work pressure of 0.1 kPa (1 mbar). Owing to the high energy plasma and further reduced work pressure, PS-PVD is able to deposit a coating not only by melting the feed stock material which builds up a layer from liquid splats but also by vaporizing the injected material. Therefore, the PS-PVD process fills the gap between the conventional physical vapor deposition (PVD) technologies and standard thermal spray processes. The possibility to vaporize feedstock material and to produce layers out of the vapor phase results in new and unique coating microstructures. The properties of such coatings are superior to those of thermal spray and electron beam-physical vapor deposition (EB-PVD) coatings. In contrast to EB-PVD, PS-PVD incorporates the vaporized coating material into a supersonic plasma plume. Owing to the forced gas stream of the plasma jet, complex shaped parts such as multi-airfoil turbine vanes can be coated with columnar thermal barrier coatings using PS-PVD. Even shadowed areas and areas which are not in the line of sight of the coating source can be coated homogeneously. This article reports on the progress made by Sulzer Metco in developing a thermal spray process to produce coatings out of the vapor phase. Columnar thermal barrier coatings made of Yttria-stabilized Zircona (YSZ) are optimized to serve in a turbine engine. This process includes not only preferable coating properties such as strain tolerance and erosion resistance but also the simultaneous coverage of multiple air foils.

Referred Air Method 25E: Determination of a Vapor Phase Organic Concentration in Waste Samples

EPA Pesticide Factsheets

This method is applicable for determining the vapor pressure of waste. The headspace vapor of the sample is analyzed for carbon content by a headspace analyzer, which uses a flame ionization detector (FID).

Acute and chronic neuropsychological consequences of mercury vapor poisoning in two early adolescents.

PubMed

Yeates, K O; Mortensen, M E

1994-04-01

Mercury is an extremely toxic heavy metal that can devastate the central nervous system. The neuropsychological consequences of mercury vapor intoxication have been studied primarily in adults. We present two adolescent half-siblings, ages 13 and 15, who were unintentionally exposed to concentrated mercury vapor for 3 months. Both children participated in neuropsychological evaluations shortly after being diagnosed with mercury toxicity, and again 1 year later. Results from the initial assessments documented functional deficits consistent with diffuse encephalopathy. Upon follow-up, neuropsychological functioning had improved, but deficits remained in visuoperceptual and constructional skills, nonverbal memory, and conceptual abstraction. The deficits persisted despite removal from exposure, return of urinary and blood mercury to acceptable levels, and resolution of neuropsychiatric symptoms. The deficits were similar to, but more severe than, those found in adults suffering from mercury vapor intoxication. The results suggest that the developing brain may be especially vulnerable to mercury vapor toxicity.

Oxidation of Al2O3 Scale-Forming MAX Phases in Turbine Environments

NASA Astrophysics Data System (ADS)

Smialek, James L.

2018-03-01

High temperature oxidation of alumina-forming MAX phases, Ti2AlC and Cr2AlC, were examined under turbine engine environments and coating configurations. Thermogravimetric furnace tests of Ti2AlC showed a rapid initial transient due to non-protective TiO2 growth. Subsequent well-behaved cubic kinetics for alumina scale growth were shown from 1273 K to 1673 K (1000 °C to 1400 °C). These possessed an activation energy of 335 kJ/mol, consistent with estimates of grain boundary diffusivity of oxygen ( 375 kJ/mol). The durability of Ti2AlC under combustion conditions was demonstrated by high pressure burner rig testing at 1373 K to 1573 K (1100 °C to 1300 °C). Here good stability and cubic kinetics also applied, but produced lower weight gains due to volatile TiO(OH)2 formation in water vapor combustion gas. Excellent thermal stability was also shown for yttria-stabilized zirconia thermal barrier coatings deposited on Ti2AlC substrates in 2500-hour furnace tests at 1373 K to 1573 K (1100 °C to 1300 °C). These sustained a record 35 µm of scale as compared to 7 μm observed at failure for typical superalloy systems. In contrast, scale and TBC spallation became prevalent on Cr2AlC substrates above 1423 K (1150 °C). Cr2AlC diffusion couples with superalloys exhibited good long-term mechanical/oxidative stability at 1073 K (800 °C), as would be needed for corrosion-resistant coatings. However, diffusion zones containing a NiAl-Cr7C3 matrix with MC and M3B2 particulates were commonly formed and became extensive at 1423 K (1150 °C).

Visualization of Two-Phase Fluid Distribution Using Laser Induced Exciplex Fluorescence

NASA Astrophysics Data System (ADS)

Kim, J. U.; Darrow, J.; Schock, H.; Golding, B.; Nocera, D.; Keller, P.

1998-03-01

Laser-induced exciplex (excited state complex) fluorescence has been used to generate two-dimensional images of dispersed liquid and vapor phases with spectrally resolved two-color emissions. In this method, the vapor phase is tagged by the monomer fluorescence while the liquid phase is tracked by the exciplex fluorescence. A new exciplex visualization system consisting of DMA and 1,4,6-TMN in an isooctane solvent was developed.(J.U. Kim et al., Chem. Phys. Lett. 267, 323-328 (1997)) The direct ca

Investigation of the abnormal Zn diffusion phenomenon in III-V compound semiconductors induced by the surface self-diffusion of matrix atoms

NASA Astrophysics Data System (ADS)

Tang, Liangliang; Xu, Chang; Liu, Zhuming

2017-01-01

Zn diffusion in III-V compound semiconductorsare commonly processed under group V-atoms rich conditions because the vapor pressure of group V-atoms is relatively high. In this paper, we found that group V-atoms in the diffusion sources would not change the shaped of Zn profiles, while the Zn diffusion would change dramatically undergroup III-atoms rich conditions. The Zn diffusions were investigated in typical III-V semiconductors: GaAs, GaSb and InAs. We found that under group V-atoms rich or pure Zn conditions, the double-hump Zn profiles would be formed in all materials except InAs. While under group III-atoms rich conditions, single-hump Zn profiles would be formed in all materials. Detailed diffusion models were established to explain the Zn diffusion process; the surface self-diffusion of matrix atoms is the origin of the abnormal Zn diffusion phenomenon.