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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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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Synthesis, characterization and evaluation of CO-oxidation catalysts for high repetition rate CO2 TEA lasers

An extremely active class of noble metal catalysts supported on titania was developed and fabricated at Hughes for the recombination of oxygen (O2) and carbon monoxide (CO) in closed-cycle CO2 TEA lasers. The incipient wetness technique was used to impregnate titania and alumina pellets with precious metals including platinum and palladium. In particular, the addition of cerium (used as an oxygen storage promoter) produced an extremely active Pt/Ce/TiO2 catalyst. By comparison, the complementary Pt/Ce/ gamma-Al2O3 catalyst was considerably less active. In general, chloride-free catalyst precursors proved critical in obtaining an active catalyst while also providing uniform metal distributions throughout the support structure. Detailed characterization of the Pt/Ce/TiO2 catalyst demonstrated uniform dendritic crystal growth of the metals throughout the support. Electron spectroscopy for Chemical Analysis (ESCA) analysis was used to characterize the oxidation states of Pt, Ce and Ti. The performance of the catalysts was evaluated with an integral flow reactor system incorporating real time analysis of O2 and CO. With this system, the transient and steady-state behavior of the catalysts were evaluated. The kinetic evaluation was complemented by tests in a compact, closed-cycle Hughes CO2 TEA laser operating at a pulse repetition rate of 100 Hz with a catalyst temperature of 75 to 95 C. The Pt/Ce/TiO2 catalyst was compatible with a C(13)O(16)2 gas fill.

Moser, Thomas P.↗
NASA NTRS1990

Characterization of the surfaces of platinum/tin oxide based catalysts by Fourier Transform Infrared Spectroscopy (FTIR)

A Pt/SnO2 catalyst has been developed at NASA Langley that is effective for the oxidation of CO at room temperature (1). A mechanism has been proposed to explain the effectiveness of this catalyst (2), but most of the species involved in this mechanism have not been observed under actual catalytic conditions. A number of these species are potentially detectable by Fourier Transform Infrared Spectroscopy (FTIR), e.g., HOSnO sub x, HO sub y PtO sub z, Pt-CO, and SnHCO3. Therefore a preliminary investigation was conducted to determine what might be learned about this particular catalyst by transmission FTIR. The main advantage of FTIR for this work is that the catalyst can be examined under conditions similar to the actual catalytic conditions. This can be of critical importance since some surface species may exist only when the reaction gases are present. Another advantage of the infrared approach is that since vibrations are probed, subtle chemical details may be obtained. The main disadvantage of this approach is that FTIR is not nearly as sensitive as the Ultra High Vacuum (UHV) surface analytical techniques such as Auger, Electron Spectroscopy for Chemical Analysis (ESCA), Electron Energy Loss Spectroscopy (EELS), etc. Another problem is that the assignment of the observed infrared bands may be difficult.

Keiser, Joseph T.↗
NASA NTRS1990

A resistance strain gage with repeatable and cancellable apparent strain for use to 800 C

A temperature compensated static strain gage, which is fabricated from palladium-13w/o chromium (Pd13Cr) alloy and a platinum (Pt) compensator, is being developed and was tested over a temperature range to 800 C at NASA-Lewis. The PdCr compensated strain gage has significantly lower apparent strain to 800 C than other high temperature strain gages. The PdCr compensated gage is protected from oxidation by a flame-sprayed alumina-4w/o zirconia overcoating. Test results to 800 C indicate apparent strain variations of less than 300 micro-epsilon and reproducibility between thermal cycles within 50 micro-epsilon. Apparent strain of the coated PdCr compensated gage can be predicted and cancelled due to its reproducibility and low value.

Lei, Jih-Fen↗
NASA NTRS1990

Carbon-rich particles in Comet Halley

The majority of particles detected in the coma of Comet Halley contain carbon atoms; many of these grains appear to consist preponderately or only of light elements. These light-element particles may be composed of organic compounds. Of the possible combinations of the elements hydrogen, carbon, nitrogen, and oxygen, numerous examples are found of particles containing the combinations (H,C,O,N), (H,C,N), (H,C,O), and (H,C). These results may bear on the recent detection of polyoxymethylene fragments, the observation of cyanojets (CN patterns consistent with release from solid particles), the possible presence of cyanopolyacetylenes or HCN polymer and the make-up of the CHON particles. If cometary matter could reach the surface of the earth without complete disruption, these diverse organic and mixed particles could create unique microenvironments, possibly with significant or even pivotal prebiotic chemical activity. Here a speculative insight into possible relationships between carbon in comets and carbon in life is given, as well as a brief overview of on-going analysis of data from the highly successful Particle Impact Analyzer (PIA) experiment flown on the Giotto spacecraft for the flyby of Comet Halley (development and implementation of PIA was under the direction of J. Kissel of the Max Planck Institute for Kernphysik, Heidelberg). PIA is a time-of-flight analyzer which obtains mass spectra of ions from individual particles impacting on a Pt-Ag foil target within the instrument.

Clark, Benton C.↗
NASA NTRS1990

Electrochemical incineration of wastes

The novel technology of waste removal in space vehicles by electrochemical methods is presented to convert wastes into chemicals that can be eventually recycled. The important consideration for waste oxidation is to select a right kind of electrode (anode) material that should be stable under anodic conditions and also a poor electrocatalyst for oxygen and chlorine evolution. On the basis of long term electrolysis experiments on seven different electrodes and on the basis of total organic carbon reduced, two best electrodes were identified. The effect of redox ions on the electrolyte was studied. Though most of the experiments were done in mixtures of urine and waste, the experiments with redox couples involved 2.5 M sulfuric acid in order to avoid the precipitation of redox ions by urea. Two methods for long term electrolysis of waste were investigated: (1) the oxidation on Pt and lead dioxide electrodes using the galvanostatic methods; and (2) potentiostatic method on other electrodes. The advantage of the first method is the faster rate of oxidation. The chlorine evolution in the second method is ten times less then in the first. The accomplished research has shown that urine/feces mixtures can be oxidized to carbon dioxide and water, but current densities are low and must be improved. The perovskite and Ti4O7 coated with RuO2 are the best electrode materials found. Recent experiment with the redox agent improves the current density, however, sulphuric acid is required to keep the redox agent in solution to enhance oxidation effectively. It is desirable to reduce the use of acid and/or find substitutes.

Bhardwaj, R. C.↗
NASA NTRS1989

Pressure dependence of the melting temperature of metals

A new method for the analysis of the experimental data for the pressure dependence of the melting temperature of metals is presented. The method combines Lindemann's law, the Debye model, and a first-order equation of state with the experimental observation that the Grueneisen parameter divided by the volume is constant. It is observed that, based on these assumptions, in the absence of phase transitions, plots of the logarithm of the normalized melting temperature versus the logarithm of the normalized pressure are straight lines. It is found that the normalized-melting--temperature versus normalized-pressure curves accurately satisfy the linear relationship for Al, Ag, Au, Cs, Cu, K, Na, Pt, and Rb. In addition, this technique provides a sensitive tool for detecting phase transitions.

Schlosser, Herbert↗
NASA NTRS1990

Laboratory studies of the electrical conductivity of silicate perovskites at high pressures and temperatures

The electrical conductivities of two silicate perovskites and a perovskite-magnesiowuestite assemblage, all having an atomic ratio of Mg to Fe equal to 0.88/0.12, have been measured with alternating current and direct current (dc) techniques at simultaneously high pressures and temperatures. Measurements up to pressures of 80 GPa and temperatures of 3500 K, using a laser-heated diamond anvil cell, demonstrate that the electrical conductivity of these materials remains below 10-3 S/m at lower mantle conditions. The activation energies for electrical conduction are between 0.1 and 0.4 eV from the data, and the conduction in these perovskites is ascribed to an extrinsic electronic process. The new measurements are in agreement with a bound that was previously obtained from dc measurements for the high-PT conductivity of perovskite-dominated assemblages. The results show that the electrical conductivity of (Mg/0.88/Fe/0.12)SiO3 perovskite differs significantly from that of the earth's deep mantle, as inferred from geophysical observations.

Li, Xiaoyuan↗
NASA NTRS1990

Wavelengths and intensities of a platinum/neon hollow cathode lamp in the region 1100-4000 A

The spectrum of a platinum hollow cathode lamp containing neon carrier gas was recorded photographically and photoelectrically with a 10.7 m normal-incidence vacuum spectrograph. Wavelengths and intensities were determined for about 3000 lines in the region 1100-4000 A. The uncertainty of the measured wavelengths is estimated to be + or - 0.0020 A. Ritz-type wavelengths are given for about 550 classified lines of Pt II with uncertainites varying from + or - 0.0004 A to + or - 0.0025 A. The uncertainty of the relative intensities is estimated to be about 20 percent.

Reader, Joseph↗
NASA NTRS1989

Strategic materials availability and supply

An evaluation is made of the supply sources and current availability of elements involved in superalloy compositions, as well as of development trends in the substitution of strategic materials for superalloys, giving attention to the results thus far achieved by NASA's Conservation of Strategic Aerospace Materials program, which formally operated only from 1980 to 1984 but whose various research initiatives have been continued under other NASA programs. Peacetime and wartime economies' need and probable availability analyses are presented for bauxite/aluminum, the Pt-group metals, and the alloying elements Mn, Nb, Ta, Co, Cr, Ni, W, Fe, Cu, Ti, Mo, and Mg.

Stephens, Joseph R.↗
NASA NTRS1991

Optimum Platinum Loading In Pt/SnO2 CO-Oxidizing Catalysts

Platinum on tin oxide (Pt/SnO2) good catalyst for oxidation of carbon monoxide at or near room temperature. Catalytic activity peaks at about 17 weight percent Pt. Catalysts with platinum loadings as high as 46 percent fabricated by technique developed at Langley Research Center. Work conducted to determine optimum platinum loading for this type of catalyst. Major application is removal of unwanted CO and O2 in CO2 lasers.

Schryer, David R.↗
NASA NTRS1990

Winds and turbulence above San Nicolas Island during FIRE

Winds and turbulence above San Nicolas Island (SNI) were continuously monitored during the First ISCCP Regional Experiment (FIRE) with a Doppler sodar (1600 Hz) and an ultrahigh frequencies (UHF) (400 MHz) wind profiler. Individual profiles were logged from 1 through 19 July 1987 at 30 sec to 2 min intervals; preliminary processing of hourly averaged winds from 100 to 2300 m is complete. These wind profiles have been combined with intermittent radiosonde profiles to construct time-height sections of parameters such as the Richardson Number. Analysis now in progress includes interpretation of the sodar (C 2/T) and profiler (C 2/N, C 2/q) reflectivity profiles. These profiles are being combined with radiometric and ceilometer data for investigations of vertical transport and cloud base/top entrainment processes. Finally, by using the SNI data in conjunction with soundings made from the research vessel Pt. Sur, the relationship between changes in the SNI winds and mesoscale and synoptic-scale weather features is being investigated.

White, Allen B.↗
NASA NTRS1990

All-electron molecular Dirac-Hartree-Fock calculations: The group 4 tetrahydrides CH4, SiH4, GeH4, SnH4 and PbH4

A basis-set-expansion Dirac-Hartree-Fock program for molecules is described. Bond lengths and harmonic frequencies are presented for the ground states of the group 4 tetrahydrides, CH4, SiH4, GeH4, SnH4, and PbH4. The results are compared with relativistic effective core potential (RECP) calculations, first-order perturbation theory (PT) calculations and with experimental data. The bond lengths are well predicted by first-order perturbation theory for all molecules, but non of the RECP's considered provides a consistent prediction. Perturbation theory overestimates the relativistic correction to the harmonic frequencies; the RECP calculations underestimate the correction.

Dyall, Kenneth G.↗
NASA NTRS1991

Interactions of atomic oxygen with material surfaces in low Earth orbit: Preliminary results from experiment A0114

The University of Alabama at Huntsville atomic oxygen experiment consisted of two trays of 64 one inch diameter solid samples. One tray was placed on the leading edge and one on the trailing edge of the spacecraft. Half of each sample was covered to provide a control. Thus it was intended that the effects of atomic oxygen and solar ultraviolet radiation on the surface properties of each material could be distinguised from each other and from the effects of aging. Sixteen of the samples were placed on a thermally isolated plate of highly polished aluminum, while the main plate was coated with the thermal control coating S13-GLO. Though the experiment was entirely passive, it was hoped that the effects of thermal activation might be observed, if present. The plates were expected to stabilize at temperatures differing by 20 to 30 C. The experiment also carried a device to measure the spacecraft altitude and several oxygen atom reflectometers which have not been analyzed to date. The samples included thin films of metals Os, Ir, Pt, Ni, W, Mo, and Al coated onto fused silica optical flats; metal carbides (WC, SiC), solid carbons of various types, eight polymers and some other coatings of various types.

Gregory, John C.↗
NASA NTRS1990

Recovery of precious metals in space

This program is proceeding along the lines compatible with the objective of developing feasible separation and recovery processes for precious metals in a space environment. Efficient, compact, solvent extraction systems (both single and multistage) capable of high selectivity and rapid equilibration that are based on chelate and ion pair complexes are being explored. Two research projects were undertaken: (1) study of the time-dependent aspects of the formation of Pd(2) extractable chelate complexes; and (2) development of a multistage countercurrent distribution process for the separation and recovery of Pd(2) and Pt(2) ions.

Freiser, H.↗
NASA NTRS1991

Effect of Polymer Electrode Morphology on Performance of a Lithium/Polypyrrole Battery

A variety of conducting polymer batteries were described in the recent literature. In this work, a Li/Polypyrrole secondary battery is described. The effect of controlling the morphology of the polymer on enhancement of counterion diffusion in the polymer phase is explored. A method of preparing conducting polymers was developed which yields high surface area per unit volume of electrode material. A porous membrane is used as a template in which to electrochemically polymerize pyrrole, then the membrane is dissolved, leaving the polymer in a fibrillar form. Conventionally, the polymer is electrochemically polymerized as a dense polymer film on a smooth Pt disk electrode. Previous work has shown that when the polymer is electrochemically polymerized in fribrillar form, charge transport rates are faster and charge capacities are greater than for dense, conventionally grown films containing the same amount of polymer. The purpose is to expand previous work by further investigating the possibilities of the optimization of transport rates in polypyrrole films by controlling the morphology of the films. The utility of fibrillar polypyrrole as a cathode material in a lithium/polymer secondary battery is then assessed. The performance of the fibrillar battery is compared to the performance of an analogous battery which employed a conventionally grown polypyrrole film. The study includes a comparison of cyclic voltammetry, shape of charge/discharge curves, discharge time and voltage, cycle life, coulombic efficiencies, charge capacities, energy densities, and energy efficiencies.

Nicholson, Marjorie Anne↗
NASA NTRS1991

The potential for crustal resources on Mars

Martian resources pose not only an interesting scientific challenge but also have immense astronautical significance because of their ability to enhance mission efficiency, lower launch and program costs, and stimulate the development of large Mars surface facilities. Although much terrestrial mineralization is associated with plate tectonics and Mars apparently possesses a thick, stationary lithosphere, the presence of crustal swells, rifting, volcanism, and abundant volatiles indicates that a number of sedimentary, hydrothermal, dry-magma mineral concentration processes may have operated on Mars. For example, in Colorado Plateau-style (roll-front) deposits, uranium precipitation is localized by redox variations in groundwater. Also, evaporites (either in salt pans or even interstitially in pore spaces) might concentrate Cl, Li, and K. Many Martian impact craters have been modified by volcanism and probably have been affected by rising magma bodies interacting with ground ice or water. Such conditions might produce hydrothermal circulations and element concentrations. If the high sulfur content found by the Viking landers typifies Martian abundances, sulfide ore bodies may have been formed locally. Mineral-rich Africa seems to share many volcanic and tectonic characteristics with portions of Mars and may suggest Mars' potential mineral wealth. For example, the rifts of Valles Marineris are similar to the rifts in east Africa, and may both result from a large mantle plume rising from the interior and disrupting the surface. The gigantic Bushveld complex of South Africa, an ancient layered igneous intrusion that contains ores of chromium and Pt-group metals, illustrates the sort of dry-magma processes that also could have formed local element concentrations on Mars, especially early in the planet's history when heat flow was higher.

Cordell, Bruce M.↗
NASA NTRS1991

Equivalent crystal theory of alloys

Equivalent Crystal Theory (ECT) is a new, semi-empirical approach to calculating the energetics of a solid with defects. The theory has successfully reproduced surface energies in metals and semiconductors. The theory of binary alloys to date, both with first-principles and semi-empirical models, has not been very successful in predicting the energetics of alloys. This procedure is used to predict the heats of formation, cohesive energy, and lattice parameter of binary alloys of Cu, Ni, Al, Ag, Au, Pd, and Pt as functions of composition. The procedure accurately reproduces the heats of formation versus composition curves for a variety of binary alloys. The results are then compared with other approaches such as the embedded atom and lattice parameters of alloys from pure metal properties more accurately than Vegard's law is presented.

Bozzolo, Guillermo↗
NASA NTRS1991

Crystallization kinetics of a lithia-silica glass - Effect of sample characteristics and thermal analysis measurement techniques

DTA and both isothermal and nonisothermal DSC techniques are presently used to investigate the crystallization kinetics of a 40 (mol) percent Li2O-60 percent SiO2 glass as a function of glass powder particle size, the use of either alumina or Pt as the crucible material, the use of N, O, or Ar atmospheres, and surface pretreatments of the glass powder with deionized water, HCl, or HF. Neither the furnace atmosphere nor the crucible material had a significant effect on activation energy, frequency factor, or Avrami exponent. Washings of the glass with the three different fluids decreased the crystallization temperature by 25 to 30 C.

Ray, Chandra S.↗