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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Pulsed Excimer Laser Processing for Cost-Effective Solar Cells

Residual lattice damage by 5 keV ion implantation and surface flaws induced by wafer cleaning are proven to affect the V sub oc more adversely for laser annealed cells than conventional thermal diffusion. However, an alternative, molecular implantation of molecular species holds potential. The first experimental results are encouraging. The lack of a commercially available mass analyzed implantation with low energy, high fluence ions is constraining.

Wong, D.↗
NASA NTRS1994

Experimental study of lunar and SNC (Mars) magmas

The overall objectives of this research were to evaluate the role of C-O-S-Cl degassing processes in explaining vesiculation, oxidation state and fire-fountaining of lunar magmas by analysis of individual lunar glass spherules, and by experimental determination of equilibrium abundances and diffusion rates of C, S and Cl melt species in lunar glass compositions; and to determine possible primitive SNC magma compositions and the mineralogy of the mantle from which they were derived, and to evaluate P, T, XH2O etc. conditions at which they crystallize to form the SNC meteorites. After funding for one year, a project on the A15 volcanic green glass has been completed to the point of writing a first manuscript. Carbon-oxygen species C-O and CO2 are below detection limits (20 ppm) in these glasses, but there is up to 500 ppm S with concentrations both increasing and decreasing toward the spherule margins. Calculations and modeling indicate that C species could have been present in the volcanic gases, however. In a second project, experiments with low PH2O have resulted in refined estimates of the early intercumulus melt composition in the Chassigny meteorite which is generally accepted as a sample from Mars.

Rutherford, Malcolm J.↗
NASA NTRS1995

Extensional flow convecting a reactant undergoing a first order homogeneous reaction and diffusional mass transfer from a sphere at low to intermediate Peclet and Damkohler numbers

Forced convective diffusion-reaction is considered for viscous axisymmetric extensional convecting velocity in the neighborhood of a sphere. For Peclet numbers in the range 0.1 less than or equal to Pe less than or equal to 500 and for Damkohler numbers increasing with increasing Pe but in the overall range 0.02 less than or equal to Da less than or equal to 10, average and local Sherwood numbers have been computed. By introducing the eigenfunction expansion c(r, Theta) = Sum of c(n)(r)P(n)(cos Theta) into the forced convective diffusion equation for the concentration of a chemical species undergoing a first order homogeneous reaction and by using properties of the Legendre functions Pn(cos Theta), the variable coefficient PDE can be reduced to a system of N + 1 second order ODEs for the radial functions c(sub n)(r), n = 0, 1, 2,..., N. The adaptive grid algorithm of Pereyra and Lentini can be used to solve the corresponding 2(N + 1) first order differential equations as a two-point boundary value problem on 1 less than or equal to r less than or equal to r(sub infinity). Convergence of the expansion for a specific value of N can thus be established and provides 'spectral' behavior as well as the full concentration field c(r, Theta).

Shah, N. Y.↗
NASA NTRS1993

Dissociative recombination in planetary ionospheres

Ionization in planetary atmospheres can be produced by solar photoionization, photoelectron impact ionization, and, in auroral regions, by impact of precipitating particles. This ionization is lost mainly in dissociative recombination (DR) of molecular ions. Although atomic ions cannot undergo DR, they can be transformed locally through ion-molecule reactions into molecular ions, or they may be transported vertically or horizontally to regions of the atmosphere where such transformations are possible. Because DR reactions tend to be very exothermic, they can be an important source of kinetically or internally excited fragments. In interplanetary thermospheres, the neutral densities decrease exponentially with altitude. Below the homopause (or turbopause), the atmosphere is assumed to be throughly mixed by convection and/or turbulence. Above the homopause, diffusion is the major transport mechanism, and each species is distributed according to its mass, with the logarithmic derivative of the density with repect to altitude given approximately by -1/H, where H = kT/mg is the scale height. In this expression, T is the neutral temperature, g is the local acceleratiion of gravity, and m is the mass of the species. Thus lighter species become relatively more abundant, and heavier species less abundant, as the altitude increases. This variation of the neutral composition can lead to changes in the ion composition; furthermore, as the neutral densities decrease, dissociative recombination becomes more important relative to ion-neutral reactions as a loss mechanism for molecular ions.

Fox, J. L.↗
NASA NTRS2007

Freeze Tape Casting of Functionally Graded Porous Ceramics

Freeze tape casting is a means of making preforms of ceramic sheets that, upon subsequent completion of fabrication processing, can have anisotropic and/or functionally graded properties that notably include aligned and graded porosity. Freeze tape casting was developed to enable optimization of the microstructures of porous ceramic components for use as solid oxide electrodes in fuel cells: Through alignment and grading of pores, one can tailor surface areas and diffusion channels for flows of gas and liquid species involved in fuel-cell reactions. Freeze tape casting offers similar benefits for fabrication of optimally porous ceramics for use as catalysts, gas sensors, and filters.

Sofie, Stephen W.↗
NASA NTRS2011

Step-by-Step Simulation of Radiation of Radiation Chemistry Using Green Functions for Diffusion-Influenced Reactions

The irradiation of biological systems leads to the formation of radiolytic species such as H(raised dot), (raised dot)OH, H2, H2O2, e(sup -)(sub aq), etc.[1]. These species react with neighboring molecules, which result in damage in biological molecules such as DNA. Radiation chemistry is there for every important to understand the radiobiological consequences of radiation[2]. In this work, we discuss an approach based on the exact Green Functions for diffusion-influenced reactions which may be used to simulate radiation chemistry and eventually extended to study more complex systems, including DNA.

Plante, Ianik↗
NASA NTRS1972

A two component model of the diurnal variations in the thermospheric composition

A self-consistent, two-dimensional, two-component diffusion model is presented to describe the diurnal component of thermosphere dynamics. In the regions where oxygen and helium are the minor constituents, diffusion is shown to increase the amplitudes of these constituents and to advance the times of their diurnal maxima by several hours with respect to the gas temperature and the major species. Both effects are in basic agreement with satellite observations. The diffusion process is relatively insignificant for temperature, total mass density, and wind fields. The magnitude of the temperature-density phase delay is discussed with respect to its dependence on the electron density distribution.

Mayr, H. G.↗
NASA NTRS2001

Combustion of Metals in Carbon Dioxide and Reduced-Gravity Environments

Ongoing exploration and future mission2001110444 s to Mars have given impetus to research on the use of natural resources of the planet. Since carbon dioxide (CO2) constitutes approximately 95% of the Mars atmosphere and since it reacts directly and vigorously with several metals, this investigation focuses on metal-CO2 reactions as a possible combination for rocket-propellant production and energy generation. Magnesium (Mg) has been initially selected as the metal fuel owing to its low ignition temperature and high specific impulse and burning rate in CO2. Our studies in this field started with low gravity (g) combustion tests of Mg in O2, CO2, and CO. Reduced gravity provided a clear picture of the burning phenomena by eliminating the intrusive buoyant flows in high-temperature metal reactions and by removing the destructive effect of gravity on the shape of molten metal samples. Suspended cylindrical metal samples of 2, 3, and 4-mm in diameter and length were radiatively ignited in low-g to generate free-floating samples exhibiting a spherically symmetric flame with increasing metal-oxide accumulation in an outer shell. For the Mg-CO2 combination, burning times twice as long as in normal-g and five times longer than in Mg-O2 flames were observed, revealing a diffusion-controlled reaction. The burning time is proportional to the square of the sample diameter. In tests conducted with pure CO, combustion was not possible without constant heating of the sample due to the formation of a thick carbon-containing coating around the Mg sample generated by surface reactions. The following work presents two new studies that attempt to explain some of the low-g experimental observations. First, a simplified one-dimensional, quasi-steady numerical model is developed to obtain temperature, species concentrations, and burning rates of the spherically symmetric diffusion flame around the Mg sample burning in O2 and CO2. Second, a Planar Laser Induced Fluorescence (PLIF) technique is implemented to provide spatially resolved measurements of magnesium oxide (MgO) in the reaction zone of Mg samples burning in O2 and CO2. These experiments reveal fundamental differences between the two combustion systems.

Branch, M. C.↗
DOE OSTI2024

Anion Selectivities in Zwitterion Grafted Nanopores: Effect of Zwitterion Architecture

The separation of ions of similar charge is a crucial challenge in many applications, from water treatment to precious metal recovery. Membranes with cross-linked zwitterionic amphiphilic copolymer (ZAC-X) selective layers, which feature self-assembled, zwitterion-lined nanodomains for permeation, offer unique permselectivity between monovalent anions (e.g. $\mathrm{Cl^-}$/$\mathrm{F^-}$). This has motivated studies on the mechanisms of transport and selectivity in this family of materials. In this study, we conducted molecular dynamics simulations of aqueous salt solutions within zwitterion-functionalized nanopores to elucidate the influence of dipole orientation of the ZI ligands on anion diffusivities, partitioning, and permeabilities. Here, our model compares systems with contrasting ZI organization: surface-cation-anion ($\mathrm{S\text{-}ZI^{+}\text{-}ZI^{-}}$, Motif A) and surface-anion-cation ($\mathrm{S\text{-}ZI^{-}\text{-}ZI^{+}}$, Motif B). Our results reveal that Motif A exhibits less pronounced ion pairing due to a spatial separation in the radial profiles of cations and anions. Motif B demonstrates prominent ion pairing for smaller anions owing to their overlap with cation distributions. Further, our potential of mean force profiles reveal that anion partitioning increases with anion size in both ligand motifs, whereas Motif B exhibits significantly higher partitioning selectivity towards larger anions compared to Motif A. Our results for ion diffusivities show that the self-diffusivities of both anions and cations are lower for Motif B compared to Motif A. Such trends in anion partitioning and diffusivities can be explained by differences in the interactions and steric hindrance experienced by the anionic species in Motifs A and B. Finally, our results for anion permselectivity, obtained by combining partitioning and diffusivity, indicate that partitioning trends dominate over diffusivity trends. Consequently, anion permeability increases with anion size, and ligand Motif B yields much higher permselectivity towards larger anions compared to ligand Motif A.

anions↗
NASA NTRS1973

A two-component model of the diurnal variations in the thermospheric composition.

A self consistent two-component diffusion model is presented to describe the diurnal component of the thermosphere dynamics. In the regions where oxygen and helium are the minor constituents the diffusion process is shown to increase significantly the amplitudes of these constituents and to advance the times of their diurnal maxima by several hours with respect to the gas temperature and to the major species. Both effects are in basic agreement with satellite observations. The diffusion process is however relatively insignificant for temperature, total mass density and wind fields.

Mayr, H. G.↗
NASA NTRS1982

Surface diffusion activation energy determination using ion beam microtexturing

The activation energy for impurity atom (adatom) surface diffusion can be determined from the temperature dependence of the spacing of sputter cones. These cones are formed on the surface during sputtering while simultaneously adding impurities. The impurities form clusters by means of surface diffusion, and these clusters in turn initiate cone formation. Values are given for the surface diffusion activation energies for various materials on polycrystalline Cu, Al, Pb, Au, and Ni. The values for different impurity species on each of these substrates are approximately independent of impurity species within the experimental uncertainty, suggesting the absence of strong chemical bonding effects on the diffusion.

Rossnagel, S. M.↗
DOE OSTI2023

Significant Roles of Surface Hydrides in Enhancing the Performance of Cu/BaTiO 2.8 H 0.2 Catalyst for CO 2 Hydrogenation to Methanol

Abstract Tuning the anionic site of catalyst supports can impact reaction pathways by creating active sites on the support or influencing metal‐support interactions when using supported metal nanoparticles. This study focuses on CO 2 hydrogenation over supported Cu nanoparticles, revealing a 3‐fold increase in methanol yield when replacing oxygen anions with hydrides in the perovskite support (Cu/BaTiO 2.8 H 0.2 yields ~146 mg/h/gCu vs. Cu/BaTiO 3 yields ~50 mg/h/gCu). The contrast suggests that significant roles are played by the support hydrides in the reaction. Temperature programmed reaction and isotopic labelling studies indicate that BaTiO 2.8 H 0.2 surface hydride species follow a Mars van Krevelen mechanism in CO 2 hydrogenation, promoting methanol production. High‐pressure steady‐state isotopic transient kinetic analysis (SSITKA) studies suggest that Cu/BaTiO 2.8 H 0.2 possesses both a higher density and more active and selective sites for methanol production compared to Cu/BaTiO 3 . An operando high‐pressure diffuse reflectance infrared spectroscopy (DRIFTS)‐SSITKA study shows that formate species are the major surface intermediates over both catalysts, and the subsequent hydrogenation steps of formate are likely rate‐limiting. However, the catalytic reactivity of Cu/BaTiO 2.8 H 0.2 towards the formate species is much higher than Cu/BaTiO 3 , likely due to the altered electronic structure of interface Cu sites by the hydrides in the support as validated by density functional theory (DFT) calculations.

He, Yang↗
NASA NTRS1990

Analysis of Pt/SnO(sub x) during catalysis of CO oxidation

Temperature-programmed reduction using 6kPaH2 suggests that a sample consisting of 3 percent Pt supported directly on SnO2 is, under conditions of catalysis of CO oxidation used here, best represented as 3 percent Pt/SnO sub x, since the support is likely to partially reduced, probably in the vicinity of the metal/oxide interface. Catalytic measurements at 421 to 424 K show that this 3 percent Pt/SnO sub x is significantly more active per unit area of Pt than 6 percent Pt/SiO2 in catalyzing the oxidation of CO. In situ micro-FTIR reveals that while the latter has predominantly linearly bound CO on the surface under reaction conditions, the Pt/SnO sub x also has a species absorbing at 2168 cm(exp -1) which may be CO upon Pt in a positive oxidation state or weakly chemisorbed CO on zero-valent Pt. This may be directly involved in the low temperature oxidation of CO on the Pt/SnO sub x, since being weakly held the activation energy for its surface diffusion to the metal/oxide interface will be low; such mobile species could allow the high rates of surface transport and an increase in the fraction of the surface over which the CO oxidation occurs. FTIR also reveals carbonate-type species on the P/SnO sub c surface.

Sermon, Paul A.↗
NASA NTRS2000

Vapor Transport Within the Thermal Diffusion Cloud Chamber

A review of the equations used to determine the 1-D vapor transport in the thermal diffusion cloud chamber (TDCC) is presented. These equations closely follow those of the classical Stefan tube problem in which there is transport of a volatile species through a noncondensible, carrier gas. In both cases, the very plausible assumption is made that the background gas is stagnant. Unfortunately, this assumption results in a convective flux which is inconsistent with the momentum and continuity equations for both systems. The approximation permits derivation of an analytical solution for the concentration profile in the Stefan tube, but there is no computational advantage in the case of the TDCC. Furthermore, the degree of supersaturation is a sensitive function of the concentration profile in the TD CC and the stagnant background gas approximation can make a dramatic difference in the calculated supersaturation. In this work, the equations typically used with a TDCC are compared with very general transport equations describing the 1-D diffusion of the volatile species. Whereas no pressure dependence is predicted with the typical equations, a strong pressure dependence is present with the more general equations given in this work. The predicted behavior is consistent with observations in diffusion cloud experiments. It appears that the new equations may account for much of the pressure dependence noted in TDCC experiments, but a comparison between the new equations and previously obtained experimental data are needed for verification.

Ferguson, Frank T.↗
NASA NTRSDate not supplied

From the Interstellar Medium to Ocean Worlds: new challenges for Laboratory Astrophysics

From the Interstellar Medium to Ocean Worlds: new challenges for Laboratory Astrophysics For the past 35+ years, laboratory experiments in Astrophysics have been focusing on identifying and understanding the molecular species and chemistry occurring in interstellar environments, such as the diffuse interstellar medium (ISM) and dense molecular clouds. A significant portion of these laboratory efforts concerns investigations of carbon-based molecules ranging in size from a single carbon atom (e.g., CO, CO2, H2CO) to large polycyclic aromatic hydrocarbon (PAH) molecules potentially consisting of more than one hundred carbon atoms as well as their reactions with H2O and other interstellar species. The laboratory facilities built to conduct these investigations are capable of monitoring the chemistry and measuring the spectra under a wide range of interstellar conditions (e.g., low temperatures and pressures). The past 15 years of space exploration revealed the presence of at least nine other Ocean Worlds, besides Earth, in our Solar System. These worlds include moons and dwarf planets, ice-covered surfaces, subsurface oceans, as well as geysers venting H2O and other compounds, including organics in at least one environment, into space. Although these worlds represent environments that are significantly different from those traditionally considered the realm of Laboratory Astrophysics, their facilities are well situated to provide insight into the chemistry occurring in and around these worlds as well as experimental data for the interpretation of observations from missions visiting these Ocean World. This presentation will discuss the areas where Laboratory Astrophysics can provide experimental data to help understand the chemistry, and mission data of Ocean Worlds, and the challenges research into Ocean Worlds presents to our current facilities and how they can be overcome. Lastly, this presentation will introduce the new ICEE (In-situ Carbon Evolution Experiments) facility at NASA Ames Research Center as an example of how a lab dedicated to Laboratory Astrophysics can adapt itself to also meet the needs for Ocean Worlds research.

Andrew Lige Mattioda↗
NASA NTRS2001

Reaction Kernel Structure of a Slot Jet Diffusion Flame in Microgravity

Diffusion flame stabilization in normal earth gravity (1 g) has long been a fundamental research subject in combustion. Local flame-flow phenomena, including heat and species transport and chemical reactions, around the flame base in the vicinity of condensed surfaces control flame stabilization and fire spreading processes. Therefore, gravity plays an important role in the subject topic because buoyancy induces flow in the flame zone, thus increasing the convective (and diffusive) oxygen transport into the flame zone and, in turn, reaction rates. Recent computations show that a peak reactivity (heat-release or oxygen-consumption rate) spot, or reaction kernel, is formed in the flame base by back-diffusion and reactions of radical species in the incoming oxygen-abundant flow at relatively low temperatures (about 1550 K). Quasi-linear correlations were found between the peak heat-release or oxygen-consumption rate and the velocity at the reaction kernel for cases including both jet and flat-plate diffusion flames in airflow. The reaction kernel provides a stationary ignition source to incoming reactants, sustains combustion, and thus stabilizes the trailing diffusion flame. In a quiescent microgravity environment, no buoyancy-induced flow exits and thus purely diffusive transport controls the reaction rates. Flame stabilization mechanisms in such purely diffusion-controlled regime remain largely unstudied. Therefore, it will be a rigorous test for the reaction kernel correlation if it can be extended toward zero velocity conditions in the purely diffusion-controlled regime. The objectives of this study are to reveal the structure of the flame-stabilizing region of a two-dimensional (2D) laminar jet diffusion flame in microgravity and develop a unified diffusion flame stabilization mechanism. This paper reports the recent progress in the computation and experiment performed in microgravity.

Takahashi, F.↗