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At least 595 records · Page 33

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NASA NTRS1979

A model of Martian surface chemistry

Alkaline earth and alkali metal superoxides and peroxides, gamma-Fe2O3 and carbon suboxide polymer, are proposed to be constituents of the Martian surface material. These reactive substances explain the water modified reactions and thermal behaviors of the Martian samples demonstrated by all of the Viking Biology Experiments. It is also proposed that the syntheses of these substances result mainly from electrical discharges between wind-mobilized particles at Martian pressures; plasmas are initiated and maintained by these discharges. Active species in the plasma either combine to form or react with inorganic surfaces to create the reactive constituents.

Oyama, V. I.↗

NASA NTRS1982

Synthesis of Fire-Extinguishing Dawsonites

Simple nonaqueous process synthesizes sodium or potassium, dawsonites effective against hydrocarbon fuel fires. Fire-extinguishing alkali metal dawsonites are prepared using a finely-pulverized equimolar mixture of hydrogen carbonate, or carbonates and aluminum hydroxide heated for 1 to 6 hours under carbon dioxide pressure.

Altman, R. L.↗

NASA NTRS1981

High power densities from high-temperature materials interactions

Thermionic energy converters and metallic-fluid heat pipes are well suited to serve together synergistically. The two operating cycles appear as simple and isolated as their material problems seem forebodingly deceptive and complicated. Simplified equations verify material properties and interactions as primary influences on the operational effectiveness of both. Each experiences flow limitations in thermal emission and vaporization because of temperature restrictions redounding from thermophysicochemical stability considerations. Topics discussed include: (1) successful limitation of alkali-metal corrosion; (2) protection against external hot corrosive gases; (3) coping with external and internal vaporization; (4) controlling interfacial reactions and diffusion; and (5) meeting other thermophysical challenges; expansion matches and creep.

Morris, J. F.↗

NASA NTRS1981

The geology and geophysics of the Oslo rift

The regional geology and geophysical characteristics of the Oslo graben are reviewed. The graben is part of a Permian age failed continental rift. Alkali olivine, tholefitic, and monzonitic intrusives as well as basaltic lavas outline the extent of the graben. Geophysical evidence indicates that rifting activity covered a much greater area in Skagerrak Sea as well as the Paleozoic time, possibly including the northern Skagerrak Sea as well as the Oslo graben itself. Much of the surficial geologic characteristics in the southern part of the rift have since been eroded or covered by sedimentation. Geophysical data reveal a gravity maximum along the strike of the Oslo graben, local emplacements of magnetic material throughout the Skagerrak and the graben, and a slight mantle upward beneath the rift zone. Petrologic and geophysical maps which depict regional structure are included in the text. An extensive bibliography of pertinent literature published in English between 1960 and 1980 is also provided.

Ruder, M. E.↗

NASA NTRS1981

Negative ions in comets

Negative ion sources in comets are identified and cometary plasma effects caused by negative ions are examined. The primary negative ion sources are shown to be: (1) for the inner coma - photodissociation of HCN, electron attachment of OH, and collision with alkalis; (2) in the vicinity of the nucleus - interplanetary dust collisions with the nucleus; and (3) for both the contaminated solar wind region and sporadic discharges in the nonhomogeneous inner coma plasma - dissociative electron attachment and charge inversion during keV positive ion scattering by cometary dust. Negative ion abundance for Halley's Comet has been estimated to be 10 to the -6th - 10 to the -10th of electron densities.

Wekhof, A.↗

NASA NTRS1981

High power densities from high-temperature material interactions

Thermionic energy conversion (TEC) and metallic-fluid heat pipes (MFHPs), offering unique advantages in terrestrial and space energy processing by virtue of operating on working-fluid vaporization/condensation cycles that accept great thermal power densities at high temperatures, share complex materials problems. Simplified equations are presented that verify and solve such problems, suggesting the possibility of cost-effective applications in the near term for TEC and MFHP devices. Among the problems discussed are: the limitation of alkali-metal corrosion, protection against hot external gases, external and internal vaporization, interfacial reactions and diffusion, expansion coefficient matching, and creep deformation.

Morris, J. F.↗

NASA NTRS1981

Systematics of ground-state potential minima between two main-group atoms or ions

A diagram is presented illustrating the internuclear separations between diatomic molecules or quasi-molecules with the exception of those containing transition metal and rare-earth atoms. As plotted as a function of the atomic numbers of the constituent atoms, the ground-state separations are observed to exhibit dramatic periodicities, as well as a gradual rise with increasing atomic number. The data for van der Waals molecules are not sufficient to predict the results of future experiments, although it is noted that the greatest internuclear separations are those of the alkali earth-rare gas molecules. Finally, it is found that to within the resolution of the diagram, isoelectronic molecules or quasi-molecules along the homonuclear direction have a constant internuclear separation.

Hefferlin, R.↗

NASA NTRS1980

Nonbonded interactions in membrane active cyclic biopolymers. IV - Cation dependence

Interactions of valinomycin and form of its analogs in several conformations with the central ions Li(+), Na(+), K(+), Rb(+) and Cs(+) are investigated as part of a study of the specific preference of valinomycin for potassium and the mechanisms of carrier-mediated ion transport across membranes. Ion binding energies and conformational potential energies are calculated taking into account polarization energy formulas and repulsive energy between the central ion and the ligand atoms for conformations representing various stages in ion capture and release for each of the two ring chiralities of valinomycin and its analogs. Results allow the prediction of the chirality and conformation most likely to be observed for a given analog, and may be used to synthesize analogs with a desired rigidity or flexibility. The binding energies with the alkali metal cations are found to decrease with increasing ion size, and to be smaller than the corresponding ion hydration energies. It is pointed out that the observed potassium preference may be explainable in terms of differences between binding and hydration energies. Binding energies are also noted to depend on ligand conformation.

Radhakrishnan, R.↗

NASA NTRS1982

Improved Heat-of-Fusion Energy Storage

Alkali metal/alkali-halide mixtures proposed for preventing solid buildup during energy recovery. When mixture melts (by absorption of heat of fusion), it forms two immiscible liquids. Salt-rich phase is heavier and has higher melting/recrysallization temperature; so during energy recovery salt crystallizes in this phase first. Since heat exchanger for energy recovery is in lighter metal-rich phase, solids do not form and there is no reduction of heat-recovery efficiency.

Chen, K. H.↗

NASA NTRS1980

Study of radiatively sustained cesium plasmas for solar energy conversion

The results of a study aimed at developing a high temperature solar electric converter are reported. The converter concept is based on the use of an alkali plasma to serve as both an efficient high temperature collector of solar radiation as well as the working fluid for a high temperature working cycle. The working cycle is a simple magnetohydrodynamic (MHD) Rankine cycle employing a solid electrode Faraday MHD channel. Research milestones include the construction of a theoretical model for coupling sunlight in a cesium plasma and the experimental demonstration of cesium plasma heating with a solar simulator in excellent agreement with the theory. Analysis of a solar MHD working cycle in which excimer laser power rather than electric power is extracted is also presented. The analysis predicts a positive gain coefficient on the cesium-xenon excimer laser transition.

Palmer, A. J.↗

NASA NTRS1970

Separator for alkaline electric cells and method of making

Modified cellulose ether films having an increased electrolytic conductivity and a useable flexibility and in certain instances an increased flexibility are presented. Battery separator membranes comprising a cellulose ether and a minor proportion of a compatible water soluble base selected from the group consisting of alkali metal and ammonium hydroxides, aliphatic amines, and aliphatic hydroxyamines are used.

Pfluger, H. L.↗

NASA NTRS1970

Alkaline electrochemical cells and method of making

Equilibrated cellulose ether membranes of increased electrolytic conductivity for use as separators in concentrated alkaline electrochemical cells are investigated. The method of making such membranes by equilibration to the degree desired in an aqueous alkali solution mantained at a temperature below about 10 C is described.

Hoyt, H. E.↗

NASA NTRS1982

Advanced ceramic coating development for industrial/utility gas turbines

A program was conducted with the objective of developing advanced thermal barrier coating (TBC) systems. Coating application was by plasma spray. Duplex, triplex and graded coatings were tested. Coating systems incorporated both NiCrAly and CoCrAly bond coats. Four ceramic overlays were tested: ZrO2.82O3; CaO.TiO2; 2CaO.SiO2; and MgO.Al2O3. The best overall results were obtained with a CaO.TiO2 coating applied to a NiCrAly bond coat. This coating was less sensitive than the ZrO2.8Y2O3 coating to process variables and part geometry. Testing with fuels contaminated with compounds containing sulfur, phosphorus and alkali metals showed the zirconia coatings were destabilized. The calcium titanate coatings were not affected by these contaminants. However, when fuels were used containing 50 ppm of vanadium and 150 ppm of magnesium, heavy deposits were formed on the test specimens and combustor components that required frequent cleaning of the test rig. During the program Mars engine first-stage turbine blades were coated and installed for an engine cyclic endurance run with the zirconia, calcium titanate, and calcium silicate coatings. Heavy spalling developed with the calcium silicate system. The zirconia and calcium titanate systems survived the full test duration. It was concluded that these two TBC's showed potential for application in gas turbines.

Vogan, J. W.↗

NASA NTRS1981

Advances in space power research and technology at the National Aeronautics and Space Administration

Progress and plans in various areas of the NASA Space Power Program are discussed. Solar cell research is narrowed to GaAs, multibandgap, and thin Si cells for arrays in planar and concentrator configurations, with further work to increase cell efficiency, radiation hardness, develop flexible encapsulants, and reduce cost. Electrochemical research is concentrating on increasing energy and power density, cycle and wet stand life, reliability and cost reduction of batteries. Further development of the Ni-H2 battery and O2-H2 fuel cell to multihundred kW with a 5 year life and 30,000 cycles is noted. Basic research is ongoing for alkali metal anodes for high energy density secondary cells. Nuclear thermoelectric propulsion is being developed for outer planets exploration propulsion systems, using Si-Ge generators, and studies with rare earth chalcogenides and sulfides are mentioned. Power Systems Management seeks to harmonize increasing power supply levels with inner and outer spacecraft environments, circuits, demands, and automatic monitoring. Concomitant development of bipolar transistors, an infrared rectenna, spacecraft charging measurement, and larger heat pipe transport capacity are noted.

Mullin, J. P.↗

NASA NTRS1981

Towards a high-temperature solar electric converter

The concept of an ultrahigh-temperature solar electric heat-engine converter is examined in which an alkali plasma would serve as both the high-temperature collector of solar radiation and as the working fluid for a high-temperature working cycle. The working cycle would be a simple magnetohydrodynamic Rankine cycle. Theoretical and experimental results obtained to date are summarized. These include: (1) an experimental confirmation of the theoretical prediction that a plasma temperature of about 2800 K can be reached through heating cesium vapor by sunlight concentrated to approximately 300 W per sq cm; and (2) the establishment of a theoretical model of the complete solar heated plasma magnetohydrodynamic cycle.

Dunning, G. J.↗

NASA NTRS1981

Foraging westward for pristine nonmare rocks - Complications for petrogenetic models

New advances are reported concerning an investigation which is being conducted to find and characterize more 'pristine' (compositionally endogenous) lunar rocks. Eleven nonmare samples are characterized petrographically and (except for two clasts that were prohibitively small) by chemical composition. The samples are assessed whether they are pristine on the basis of diagnostic features discussed by Warren and Wasson (1977). Five samples are found to be almost certainly pristine. They include the alkali-rich anorthosite 12073c, the troctolite 14179c, the anorthositic troctolite 14321c1, the troctolitic anorthosite 14321c2, and the anorthositic norite 15565c. Correlations between petrochemistry and longitude are also investigated, taking into account Eu fractionations, Sc-Ti-Sm fractionations, and Ca/Na-Mg/Fe fractionations.

Warren, P. H.↗

NASA NTRS1982

Petrogenesis of light and dark portions of the Leighton gas-rich chondritic breccia

Individual dark fractions of the Leighton chondritic breccia are all enriched in volatile/mobile trace elements. Concentrations of the most highly volatile/mobile elements correlate with degree of equilibration, as expressed by compositional variability for silicates. Individual light clasts in the same meteorite are equilibrated and generally volatile-poor, except for enrichments in Rb and Cs. These alkali elements may have been redistributed by feldspar formation during metamorphism. Enrichments of other trace elements in dark portions may have been caused by mobilization during metamorphism in the parent body interior and deposition in the cooler surface layers. An alternative model involves accretional mixing of a diverse compositional population of primitive H group materials to form dark materials. Subsequent integration of light and dark materials was accomplished by impacts into a regolith.

Mcsween, H. Y., Jr.↗

NASA NTRS1982

Containerless melting and solidification of materials with an aerodynamic levitation system

A simple aerodynamic system which can heat, melt, cool, and solidify (in a containerless fashion) small, roughly spherical (diameter 1.5-4 mm) samples of materials is described. The principal components of the system are an aerodynamic levitation tube and an elliptical radiant heater. The materials processed, i.e., melted and resolidified, in the system include lead and an alkali borosilicate glass. The processing of a glass bead is described. In addition, the physical phenomena which may generate the levitation force in the tube are briefly discussed.

Oran, W. A.↗