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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Alkali metal thermoelectric converter (AMTEC) electrode lifetime studies

Experimental studies are being conducted at JPL to identify long life, high area power density electrodes for AMTEC. Power versus time measurements are being made in a demountable electrode test cell and, for longer term experiments, a self-contained recirculating cell. The experimental apparatus and procedures are described in detail. The results show that thin film molybdenum electrodes can be designed to produce power near 0.5 W/sq cm for over two hundred hours. Also, platinum/tungsten electrodes exhibit power densities that are stable near 0.5 W/sq cm. If the performance of these electrodes is verified for longer periods (thousands of hours), then practical AMTEC systems will be possible.

Bankston, C. Perry↗
NASA NTRS1987

Alkali metal thermoelectric conversion (AMTEC) technology status review

AMTEC operating principles, technical problems, and recent electrode research results are briefly reviewed. The mechanisms responsible for the degradation of thin-film molybdenum electrodes are discussed, and four alternate high-power electrode compositions and morphologies are identified. Separate self-contained recirculating AMTEC cells have demonstrated 19-percent efficiency, 10,000 hr at high temperature, and multicell operation including series connection. Results of systems studies in the 0.5-100 kWe range indicate that AMTEC performance and operating characteristics make it a strong candidate for future space applications.

Bankston, C. P.↗
NASA NTRS1988

Extreme ultraviolet quantum efficiency of opaque alkali halide photocathodes on microchannel plates

Comprehensive measurements are presented for the quantum detection efficiency (QDE) of the microchannel plate materials CsI, KBr, KCl, and MgF2, over the 44-1800 A wavelength range. QDEs in excess of 40 percent are achieved by several materials in specific wavelength regions of the EUV. Structure is noted in the wavelength dependence of the QDE that is directly related to the valence-band/conduction-band gap energy and the onset of atomic-like resonant transitions. A simple photocathode model allows interpretation of these features, together with the QDE efficiency variation, as a function of illumination angle.

Siegmund, O. H. W.↗
NASA NTRS1989

Solar-powered alkali metal vapor lasers

The emission spectrum of the A(1 Sigma u +) - X(1 Sigma g +) band of Na2 has been recorded following excitation by monochromatic radiation in the region of X-A and X-B absorption. The spectral profile has been investigated as a function of excitation wavelength, sodium vapor temperature and buffer gas pressure. Additionally, gain measurements were made for the satellite of the A-X band as a function of the sodium vapor temperature and buffer gas pressure.

Blount, Charles E.↗
NASA NTRS1987

Vapor deposition and condensate flow on combustion turbine blades - Theoretical model to predict/understand some corrosion rate consequences of molten alkali sulfate deposition in the field or laboratory

An analysis is undertaken of aerodynamically- and centrifugally-driven liquid condensate layers on nonisothermal combustion turbines' stator vanes and rotor blades. Attention is given to the quantitative consequences of one possible mechanism for the initiation of 'hot corrosion' in the underlying blade material through a 'fluxing' of the protective oxide coating by the molten salt of the Newtonian condensate film. Illustrative calculations are presented for the condensate streamline pattern and the distributions of the steady-state condensate layer thickness, together with the corresponding oxide dissolution rate, for a test turbine blade.

Rosner, Daniel E.↗
NASA NTRS1990

Positron collisions with alkali-metal atoms

The total cross sections for positron and electron collisions with potassium, sodium, lithium and rubidium are calculated, employing the modified Glauber approximation. The Modified Glauber cross sections for positron collision with potassium and sodium at low intermediate energies are found to agree reasonably well with existing experimental data.

Gien, T. T.↗
NASA NTRS1989

Liquid alkali metals - Equation of state and reduced-pressure, bulk-modulus, sound-velocity, and specific-heat functions

The previous work of Schlosser and Ferrante (1988) on universality in solids is extended to the study of liquid metals. As in the case of solids, to a good approximation, in the absence of phase transitions, plots of the logarithm of the reduced-pressure function H, of the reduced-isothermal-bulk-modulus function b, and of the reduced-sound-velocity function v are all linear in 1-X. Finally, it is demonstrated that ln(Cp/C/v) is also linear in 1-X, where X = (V/V/0/)exp 1/3), and V(0) is the volume at zero pressure.

Schlosser, Herbert↗
NASA NTRS1989

Negative ions from alkali hydrides as a source for H(-) beams

The production of H(-) ions by heating LiH powder in a high-temperature crucible was investigated experimentally and theoretically. It is found that the efficiency of H(-) ion production by this method is high. However, the theory for the negative surface ionization indicates that such high efficiency is not possible at crucible temperatures of about 750 C. The need for a further study of LiH ionization is emphasized.

Srivastava, S. K.↗
NASA NTRS1989

Low temperature multi-alkali photocathode processing technique for sealed intensified CCD tubes

A low temperature photocathode process has been used to fabricate an intensified CCD visual photocathode image tube, by incorporating a thinned, backside-illumined CCD as the target anode of a digicon tube of Hubble Space Telescope (HST) design. The CCD digicon tube employs the HST's sodium bialkali photocathode and MgF2 substrate, thereby allowing a direct photocathode quantum efficiency comparison between photocathodes produced by the presently employed low temperature process and those of the conventional high temperature process. Attention is given to the processing chamber used, as well as the details of gas desorption and photocathode processing.

Doliber, D. L.↗
NASA NTRS1990

Lifetime studies of high power rhodium/tungsten and molybdenum electrodes for application to AMTEC (alkali metal thermal-to-electric converter)

A detailed and fundamental model for the electrochemical behavior of AMTEC electrodes is developed which can aid in interpreting the processes which occur during prolonged operation of these electrodes. Because the sintering and grain growth of metal particles is also a well-understood phenomenon, the changes in electrode performance which accompany its morphological evolution may be anticipated and modeled. The grain growth rate observed for porous Mo AMTEC electrodes is significantly higher than that predicted from surface diffusion data obtained at higher temperatures and incorporated into the grain growth model. The grain growth observed under AMTEC conditions is also somewhat higher than that measured for Mo films on BASE (beta-alumina solid electrolyte) substrates in vacuum or at similar temperatures. Results of modeling indicate that thin Mo electrodes may show significant performance degradation for extended operation (greater than 10,000 h) at higher operating temperatures (greater than 1150 K), whereas W/Rh and W/Pt electrodes are expected to show adequate performance at 1200 K for lifetimes greater than 10,000 h. It is pointed out that current collection grids and leads must consist of refractory metals such as Mo and W which do not accelerate sintering or metal migration.

Williams, R. M.↗
NASA NTRS1991

Source processes for the alkali metals in the atmosphere of Mercury

A large (fivefold) increase in Mercury's potassium (K) column abundance on October 14, 1987, has been reported by Sprague et al. (1990), who attributed the enhancement to diffusion through the surface in the Caloris Basin, from depths of order 10 km. The postulated source rate is much larger than any previously estimated diffusion rate, and, if true, certainly affects consideration of the origin of other atmospheric species. However, Killen et al. (1991) have pointed out that the claim is not supported by the published observations of K or sodium as a whole. Sprague et al. (1991) have responded by further hypothesizing the existence of several other sources of gas diffusing out of the regolith, all of which are time variable. In any case, the Sprague et al. data indicate large variations in abundance, and it is important to understand the cause. With this issue in mind, the available abundance estimates for correlation with possible controlling physical parameters has ben examined. A significant correlation between the average zenith K column abundance and indices of solar activity has been found.

Shemansky, D. E.↗
NASA NTRS1992

Pressure-induced coordination changes in alkali-germanate melts - An in situ spectroscopic investigation

The structure of liquid Na2Ge2O5-H2O, a silicate melt analog, has been studied with Raman spectroscopy to pressures of 2.2 gigapascals. Upon compression, a peak near more than 240 wavenumbers associated with octahedral GeO6 groups grows relative to a peak near 500 wavenumbers associated with tetrahedral GeO4 groups. This change corresponds to an increase in octahedral germanium in the liquid from near 0 percent at ambient pressures to more than 50 percent at a pressure of 2.2 gigapascals. Silicate liquids pausibly undergo similar coordination changes at depth in the earth. Such structural changes may generate decreases in the fusion slopes of silicates at high pressures as well as neutrally buoyant magmas within the transition zone of the earth's mantle.

Farber, Danial L.↗
NASA NTRS1991

Theoretical study of the spectroscopy of the alkali oxides LiO, NaO, and KO

A state-averaged complete-active-space self-consistent-field multireference configuration-interaction method is presented to characterize the bound-bound emission from the CPi-2 state into the two lowest ionic states of LiO, NaO, and KO. Ab initio calculations use the experimental results obtained by Woodward et al. (1989) of the emitting state as CPi-2, but indicate that the tentative experimental band assignments are incorrect.

Langhoff, Stephen R.↗
NASA NTRS1993

Relativistic Corrections to the Properties of the Alkali Fluorides

Relativistic corrections to the bond lengths, dissociation energies and harmonic frequencies of KF, RbF and CsF have been obtained at the self-consistent field level by dissociating to ions. The relativistic corrections to the bond lengths, harmonic frequencies and dissociation energies to the ions are very small, due to the ionic nature of these molecules and the similarity of the relativistic and nonrelativistic ionic radii.

Dyall, Kenneth G.↗
NASA NTRS1995

Directly Deposited Current Collecting Grids for Alkali Metal Thermal-to-Electric Converter Electrodes

Current collection in porous thin film electrodes on solid electrolytes has been improved by using thick film grids to decrease sheet and contact resistance in RhW and PtW electrodes. The grids are directly deposited on the solid electrolyte either by sputter- or photodeposition, and the electrode deposited over the grid. Comparison of the performance of electrodes having such underlying grids with that of electrodes without such grids has shown performance, as measured by current or power produced, to be improved by 10-30% in electrodes with grids.

Ryan, M. A.↗