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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Solid-gas phase equilibria and thermodynamic properties of cadmium selenide.

Accurate vapor pressures are determined through direct weight loss measurements using the Knudsen effusion technique. The experimental data are evaluated by establishing the mode of vaporization and determining the heat capacity of cadmium selenide at elevated temperatures. Additional information is obtained through a second- and third-law evaluation of data, namely, the heat of formation and the absolute entropy of cadmium selenide. A preferential loss of selenium during the initial heating of CdSe is observed, which leads to a deviation in stoichiometry.

Sigai, A. G.↗
NASA NTRS1972

Development of space stable semitransparent polyquinoxaline films

Three polyphenylquinoxalines underwent preliminary study for potential use as coatings on aircraft and spacecraft. These polymers were prepared from the reaction of 3,3 prime, 4,4 prime-tetraaminodiphenyl ether with p,p prime-oxydibenzil and with m -bis (phenylglyoxalyl) benzene and from the reaction of 3,3 prime, 4,4 prime-tetraaminodiphenylsulfone with p,p prime-oxydibenzil. High purity reactants and solvents were used in polymer preparation to minimize color in the polymer films. High molecular weight polymers were prepared at ambient temperature at 12 to 15 percent concentration by upsetting the stoichiometry by 0.5 to 1.0 percent in favor of the bis (1,2-dicarbonyl) reactant. A portion of each polymer was endcapped with benzil and with o-phenylenediamine. Certain properties of the endcapped and unendcapped versions of each polymer are compared. Uniform films of 2.0 and 0.1 mil thickness were cast from solutions of the unendcapped and endcapped versions of each of the three polymers.

Hergenrother, P. M.↗
NASA NTRS1973

Alkali metal intercalates of molybdenum disulfide.

Study of some of the physicochemical properties of compounds obtained by subjecting natural molybdenite and single crystals of molybdenum disulfide grown by chemical vapor transport to intercalation with the alkali group of metals (Li, Na, K, Rb, and Cs) by means of the liquid ammonia technique. Reported data and results include: (1) the intercalation of the entire alkali metal group, (2) stoichiometries and X-ray data on all of the compounds, and (3) superconductivity data for all the intercalation compounds.

Somoano, R. B.↗
NASA NTRS1973

Moessbauer spectroscopic studies of iron-doped rutile.

Moessbauer spectra were obtained of single crystal and powdered samples of rutile (TiO2) doped to about one percent by weight in isotopically enriched iron. It is shown that the oxidation state may be reversibly altered in situ. After reduction, the oxygen neighbors of the dopant ion are apparently shifted to accomodate the larger ferrous ion. The agreement of calculated quadrupole splittings with experimental results suggests that impurities and oxygen vacancies are uniformly distributed in powdered samples, giving the dopant ions an 'ideal lattice' local environment. The differences between the single crystal and powder sample hyperfine parameters are attributed to variations in stoichiometry, charge compensation mechanisms, or other diffusion related parameters.

Stampfl, P. P.↗
NASA NTRS1974

Holographic recording materials development

Developments in the area of organic cis-trans isomerization systems for holographic memory applications are reported. The chemical research effort consisted of photochemical studies leading to the selection of a stilbene derivative and a polymer matrix system which have greatly improved refractive index differences between the cis and trans isomers as well as demonstrated efficiency of the photoisomerization process. In work on lithium niobate effects of sample stoichiometry and of read and write beam polarizations on recording efficiency were investigated. LiNbO3 was used for a study of angular sensitivity and of capability for simultaneous recording of extended objects without interference. The current status of LiNbO3 as a holographic recording material is summarized.

Source record↗
NASA NTRS1974

Tailor making high performance graphite fiber reinforced PMR polyimides

Studies performed to demonstrate the feasibility of using the polymerization of monomer reactants (PMR) approach to tailor make processable polyimide matrix resins are described. Monomeric reactant solutions containing the dimethyl ester of 3,3',4,4' -benzophenonetetracarboxylic acid, 4, 4' -methylenedianiline and the monomethyl ester of 5-norbornene-2, 3-dicarboxylic acid were used to impregnate Hercules HTS graphite fiber. Six different monomeric reactant stoichiometries were studied. The processing characteristics and elevated temperature mechanical properties of the PMR polyimide/HTS graphite fiber composites are described.

Serafini, T. T.↗
NASA NTRS1974

Temperature dependence of electrical conductivity and lunar temperatures

Metallic conduction mechanicsms are probably not important in lunar materials because of the small amounts of free metal and metallic oxides present. This is confirmed by the extremely low conductivities measured to date and the fact that the conductivity increases with temperature. The major conduction mechanicsm appears to be ionic. This conduction mechanism is very strongly controlled by temperature, by deviations from stoichiometry, by electric field strengths, and by oxygen fugacity.

Olhoeft, G. R.↗
NASA NTRS1974

Resin/graphite fiber composites

Processing techniques were developed for the fabrication of both polyphenylquinoxaline and polyimide composites by the in situ polymerization of monomeric reactants directly on the graphite reinforcing fibers, rather than using previously prepared prepolymer varnishes. Void-free polyphenylquinoxaline composites were fabricated and evaluated for room and elevated flexure and shear properties. The technology of the polyimide system was advanced to the point where the material is ready for commercial exploitation. A reproducible processing cycle free of operator judgment factors was developed for fabrication of void-free composites exhibiting excellent mechanical properties and a long time isothermal life in the range of 288 C to 316 C. The effects of monomer reactant stoichiometry and process modification on resin flow were investigated. Demonstration of the utility and quality of this polyimide system was provided through the successful fabrication and evaluation of four complex high tip speed fan blades.

Cavano, P. J.↗
NASA NTRS1975

Compositional effects on mechanical properties of hafnium-carbide-strengthened molybdenum alloys

The mechanical properties of swaged rod thermomechanically processed from arc melted Mo-2Re-Hf-C alloys containing as much as 0.9-mol% HfC were evaluated. The low-temperature ductilities of these alloys were not influenced by the amount of HfC present but by the amount of Hf in excess of stoichiometry. Maximum ductility occurred at 0.2- to 0.3-at.% excess Hf. At 0.3- to 0.5-mol% HfC, alloy strength varied directly with the Mo content of extracted carbide particles, both decreasing as the amount of excess Hf increased. Additions of 2-at.% Re had little effect on strength or ductility. Tensile and creep strengths of Mo-2Re-0.7Hf-0.5C alloy equaled or exceeded those of other high strength Mo alloys.

Witzke, W. R.↗
NASA NTRS1975

Tailor making high performance graphite fiber reinforced PMR polyimides

Studies performed to demonstrate the feasibility of using the polymerization of monomer reactants (PMR) approach in order to 'tailor-make' processable polyimide matrix resins are described. Monomeric reactant solutions containing the dimethyl ester of 3, 3', 4, 4'-benzophenonetetracarboxylic acid, 4, 4'-methylenedianiline and the monomethyl ester of 5-norborene-2, 3-dicarboxylic acid were used to impregnate Hercules HTS graphite fiber. Six different monomeric reactant stoichiometries were studied. The processing characteristics and elevated temperature mechanical properties of the PMR polyimide/HTS graphite fiber composites are described.

Serafini, T. T.↗
NASA NTRS1974

Compositional studies of the lunar regolith at the Apollo 17 site

Major-, minor-, and trace-element abundance data are presented for twenty-two Apollo 17 samples, twelve Apollo 16 samples, and one Apollo 15 basalt. The data were obtained by INAA employing a 14 MeV neutron generator, a Cf-252 isotopic neutron source and nuclear reactor thermal neutrons. Abundance summations for the twenty-four samples analyzed for major and minor abundance elements averaged 98.8 plus or minus 0.3%. Similarities between the Apollo 17 and the Apollo 11 mare basalts are discussed. Abundances in 13 Apollo 17 soils exhibit the greatest compositional range we have observed for soils from a specific landing site. A strong inverse Fe-Al correlation in all lunar materials we have analyzed with the exception of most Apollo 16 samples is defined by the equation: %Fe = -1.36 %Al + 21.5. A strong direct Mn-Fe correlation is defined by the equation: %Fe = 75.9 %Mn + 0.08. Both regression lines appear to have the mare basalts, as one end-member and an unspecified Al-rich component at the other end. Comparisons of the data from direct O determinations and calculated O abundances based on normal stoichiometry are presented.

Miller, M. D.↗
NASA NTRS1975

Pyroxenes and olivines: Structural implications of shock-wave data for high pressure phases

The nature of the shock-induced, high-pressure phases of olivine and pyroxene rocks is examined in the light of data for the densities of a new class of perovskite-related silicate structures. Also examined are some new Hugoniot and release adiabat data for bronzite. Reexamining available shock data for magnesian pyroxenes and olivines leads to the conclusion that they define a mixed phase (or disequilibrium) region to about the 100 GPa range, related to the kinetics of phase transformation in these silicates. By recognizing this point, certain discrepancies in previous interpretations of shock data can be explained. A set of theoretical Hugonoits for pyroxene and olivine stoichiometry, perovskite-bearing assemblages was constructed based on their properties deduced from high-pressure work, showing that the shock data is compatible with transformations to perovskites in the 45-7GPa region. Finally, the shock data indicate very similar properties for olivine and pyroxene at high pressures making them both equally likely candidates for the lower mantle.

Jeanloz, R.↗
NASA NTRS1975

Plasma polymerization of an ethylene-nitrogen gas mixture

A procedure has been developed whereby nitrogen can be incorporated into an organic film from an ethylene-nitrogen gas mixture using an internal electrode capacitively coupled radio frequency reactor. The presence of nitrogen has been shown directly by infrared transmittance spectra and electron spectroscopic chemical analysis data, and further indirect evidence was provided by dielectric measurements and by the reverse osmosis properties of the film. Preparation of a nitrogen containing film did not require vapor from an organic nitrogen containing liquid monomer. Some control over the bonding and stoichiometry of the polymer film was provided by the added degree of freedom of the nitrogen partial pressure in the gas mixture. This new parameter strongly affected the dielectric properties of the plasma polymerized film and could affect the reverse osmosis behavior.

Hudis, M.↗
NASA NTRS1976

Composition effects on mechanical properties of HfC-strengthened molybdenum alloys

The mechanical properties of swaged rod thermomechanically processed from arc-melted Mo-2Re-Hf-C alloys containing as much as 0.9 mol pct HfC have been evaluated. The low temperature ductilities of these alloys were not influenced by the amount of HfC present but by the amount of Hf in excess of stoichiometry. Maximum ductility occurred at 0.2 to 0.3 at. pct excess Hf. At 0.3 to 0.5 mol pct HfC, alloy strength varied directly with the Mo content of extracted carbide particles, both decreasing as the amount of excess Hf increased. Additions of 2 at. pct Re had little effect on strength or ductility. Tensile and creep strengths of Mo-2Re-0.7Hf-0.5C alloy equaled or exceeded those of other high strength Mo alloys.

Witzke, W. R.↗
NASA NTRS1976

Low-gravity processing of superconducting compounds

Low gravity conditions can be sustained on earth for several seconds in an evacuated drop tube. Because radiation cooling is most effective at high temperatures, the refractive metals and alloys are prime candidates for free fall solidification. The results of initial experiments on droplet formation, droplet release, critical size and evaporation losses are given. The time required for free fall solidification of different size droplets is calculated. The materials studied were copper, niobium and vanadium, and a niobium-tin alloys. Improvements in purity, composition, homogeneity and stoichiometry are expected during free fall solidification of niobium based alloys which should become evident in an increase in the superconducting transition temperature.

Otto, G. H.↗
NASA NTRS1976

Sputtering

The potential of using the sputtering process as a deposition technique is reviewed; however, the manufacturing and sputter etching aspects are also discussed. The basic mechanism for dc and rf sputtering is described. Sputter deposition is presented in terms of the unique advantageous features it offers such as versatility, momentum transfer, stoichiometry, sputter etching, target geometry (coating and complex surfaces), precise controls, flexibility, ecology, and sputtering rates. Sputtered film characteristics, such as strong adherence and coherence and film morphology, are briefly evaluated in terms of varying the sputtering parameters. Also discussed are some of the specific industrial areas which are turning to sputter deposition techniques.

Spalvins, T.↗
NASA NTRS1977

Estimate of conjugate gamma and gamma prime compositions in Ni-base superalloys

Approaches for estimating the composition of the matrix phase of alloys from the melt composition are reviewed. The first method is based on assigning essentially fixed stoichiometry to precipitating phases and is typified by PHACOMP. The second method uses analytical geometry to interpret phase diagrams and is applicable to a two-phase region of a six-component Ni-base system. The geometric method is also applicable to commercial Ni-base superalloys.

Dreshfield, R. L.↗