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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Effects of microstructure and nonstoichiometry on electrical properties of vanadium dioxide films

Voided growth structures of sputter-deposited films affect strongly their optical and electrical properties. Vanadium dioxide is an interesting material to study effects of film microstructure and nonstoichiometry on electrical properties because its phase transition makes it possible to investigate electrical behavior both in a semiconducting phase and in a metallic phase. Vanadium oxide films were deposited with different vanadium oxygen ratios for substrate temperatures between 250 and 550 C by dc reactive magnetron sputtering. The resistivity ratios between a semiconducting phase and a metallic phase are limited to 1000 order by voided boundaries and oxygen vacancies. The voided boundaries are defined by columnar structure and agglomerated grain growth. The results emphasize the necessity of a combination of deposition to obtain the film with a favorable structure and postdeposition annealing to control the film stoichiometry.

Kusano, Eiji↗
NASA NTRS1986

Method to prepare oxide films

This invention pertains to a method for producing metal oxide films characterized by the fact that the metal elements constituting the main metal alloys contain at least one kind of transition element, and that the metal elements which constitute said metal alloy are thin films of barium and titanium in almost the same mol ratio.

Hirota, T.↗
NASA NTRS1984

Mechanical contact induced transformation from the amorphous to the crystalline state in metallic glass

Friction and wear tests were conducted with 3.2- and 6.4-millimeter-diameter aluminum oxide spheres sliding, in reciprocating motion, on a Fe67Co18B14Si1 metallic foil. Crystallites with a size range of 10 to 150 nanometers were produced on the wear surface of the amorphous alloy. A strong interaction between transition metals and metalloids such as silicon and boron results in strong segregation during repeated sliding, provides preferential transition metal-metalloid clustering in the amorphous alloy, and subsequently produces the diffused honeycomb structure formed by dark grey bands and primary crystals, that is, alpha-Fe in the matrix. Large plastic flow occurs on an amorphous alloy surface with sliding and the flow film of the alloy transfers to the aluminum oxide pin surface. Multiple slip bands due to shear deformation are observed on the side of the wear track. Two distinct types of wear debris were observed as a result of sliding: an alloy wear debris, and/or powdery-whiskery oxide debris.

Miyoshi, K.↗
NASA NTRS1984

Mechanical-contact-induced transformation from the amorphous to the partially crystalline state in metallic glass

Friction and wear tests were conducted with 3.2- and 6.4-millimeter-diameter aluminum oxide spheres sliding, in reciprocating motion, on a Fe67Co18B14Si1 metallic foil. Crystallites with a size range of 10 to 150 nanometers were produced on the wear surface of the amorphous alloy. A strong interaction between transition metals and metalloids such as silicon and boron results in strong segregation during repeated sliding, provides preferential transition metal-metalloid clustering in the amorphous alloy, and subsequently produces the diffused honeycomb structure formed by dark grey bands and primary crystals, that is, alpha-Fe in the matrix. Large plastic flow occurs on an amorphous alloy surface with sliding and the flow film of the alloy transfers to the aluminum oxide pin surface. Multiple slip bands due to shear deformation are observed on the side of the wear track. Two distinct types of wear debris were observed as a result of sliding: an alloy wear debris, and/or powdery-whiskery oxide debris.

Miyoshi, K.↗
NASA NTRS1984

Mechanical-contact-induced transformation from the amorphous to the partially crystalline state in metallic glass

Friction and wear tests were conducted with 3.2- and 6.4-millimeter-diameter aluminum oxide spheres sliding, in reciprocating motion, on a Fe67Co18B14Si1 metallic foil. Crystallites with a size range of 10 to 150 nanometers were produced on the wear surface of the amorphous alloy. A strong interaction between transition metals and metalloids such as silicon and boron results in strong segregation during repeated sliding, provides preferential transition metal-metalloid clustering in the amorphous alloy, and subsequently produces the diffused honeycomb structure formed by dark grey bands and primary crystals, that is, alpha-Fe in the matrix. Large plastic flow occurs on an amorphous alloy surface with sliding and the flow film of the alloy transfers to the aluminum oxide pin surface. Multiple slip bands due to shear deformation are observed on the side of the wear track. Two distinct types of wear debris were observed as a result of sliding: an alloy wear debris, and/or powdery-whiskery oxide debris.

Miyoshi, K.↗
NASA NTRS2003

Modeling of Carbon Nanotube Schottky Barrier Reduction for Holes in Air

A model is proposed for the recently observed lower Schottky barrier for holes in air than in vacuum at a metallic electrode - semiconducting carbon nanotube (CNT) junction. In air, the CNT is oxidized. The oxygen molecules on the CNT surface will attract negative charges and will be negatively charged. The negative charges on the solid surface generally enhance the surface dipole and provide stronger electron confinement within the solid. Thus the CNT work function will increase in air. Then the Schottky barrier for holes will have to increase in air according to the standard band-alignment theory, but this is against the experiment. In order to overcome this difficulty, we propose a new Schottky barrier model, assuming that there is a transition region between the electrode and the CNT, where an appreciable potential can drop. We assume that electrodes are placed at the side of the CNT and the contact is formed via the van der Waals interaction. Since the electrode surface is not atomically flat in practical situations, the contact will not be intimate and there will be a transition region before the usual metallic bulk structure starts. In this view, the Schottky barrier is determined not only by the work function difference of the electrodes and the CNT, but also by the potential drop in the transition region. The oxidation increases the potential drop and leads to a lower Schottky barrier for holes. This relation will be demonstrated in a graphical manner by expressing the potential drop as a function of CNT band bending. The potential drop is comparable to the CNT band gap when, e.g., the transition region is about a few Angstroms thick, the oxygen molecule coverage is about 10 %, and an oxygen molecule is charged by about 0.01-0.1 of the unit charge (1-10 % of molecules are charged). The proposed mechanism prevails for both p - and n-CNTs. The model consistently explains the CNT oxidation experiments reported so far.

Yamada, Toshishige↗
NASA NTRS1995

Fabrication of advanced electrochemical energy materials using sol-gel processing techniques

Advanced materials play an important role in electrochemical energy devices such as batteries, fuel cells, and electrochemical capacitors. They are being used as both electrodes and electrolytes. Sol-gel processing is a versatile solution technique used in fabrication of ceramic materials with tailored stoichiometry, microstructure, and properties. The application of sol-gel processing in the fabrication of advanced electrochemical energy materials will be presented. The potentials of sol-gel derived materials for electrochemical energy applications will be discussed along with some examples of successful applications. Sol-gel derived metal oxide electrode materials such as V2O5 cathodes have been demonstrated in solid-slate thin film batteries; solid electrolytes materials such as beta-alumina for advanced secondary batteries had been prepared by the sol-gel technique long time ago; and high surface area transition metal compounds for capacitive energy storage applications can also be synthesized with this method.

Chu, C. T.↗
NASA NTRS1990

Oxidation characteristics of Ti-25Al-10Nb-3V-1Mo intermetallic alloy

Static oxidation kinetics of the super-alpha 2 titanium-aluminide alloy Ti-25Al-10Nb-3V-1Mo (at. percent) were investigated in air over the temperature range of 650 to 1000 C using thermogravimetric analysis. The oxidation kinetics were complex at all exposure temperatures and displayed up to three distinct oxidation rates. Breakaway oxidation occurred after long exposure times at high temperatures. Oxidation products were determined using x ray diffraction techniques, electron microprobe analysis, and energy dispersive x ray analysis. Oxide scale morphology was examined by scanning electron microscopy of the surfaces and cross sections of oxidized specimens. The oxides during the parabolic stages were compact and multilayered, consisting primarily of TiO2 doped with Nb, a top layer of Al2O3, and a thin bottom layer of TiN. The transition between the second and third parabolic stage was found to be linked to the formation of a TiAl layer at the oxide-metal interface. Porosity was formed during the third stage, causing degradation of the oxide and the beginning of breakaway oxidation.

Wallace, Terryl A.↗
NASA NTRS1992

Oxidation characteristics of Ti-25Al-10Nb-3V-1Mo

Static oxidation kinetics of the super-alpha 2 titanium-aluminide alloy Ti-25Al-10Nb-3V-1Mo (at. percent) were investigated in air over the temperature range of 650 to 1000 C using thermogravimetric analysis. The oxidation kinetics were complex at all exposure temperatures and displayed up to three distinct oxidation rates. Breakaway oxidation occurred after long exposure times at high temperatures. Oxidation products were determined using X-ray diffraction techniques, electron microprobe analysis, and energy dispersive X-ray analysis. Oxide scale morphology was examined by scanning electron microscopy of the surfaces and cross sections of oxidized specimens. The oxides during the parabolic stages were compact and multilayered, consisting primarily of TiO2 doped with Nb, a top layer of Al2O3, and a thin bottom layer of TiN. The transition between the second and third parabolic stage was found to be linked to the formation of a TiAl layer at the oxide-metal interface. Porosity was formed during the third stage, causing degradation of the oxide and the beginning of breakaway oxidation.

Wallace, T. A.↗
NASA NTRS1993

Reaction of YBa2Cu3O(7-beta) with Gold, Silver, Bismuth and Lead: Substitution Chemistry and Composite Fabrication

The reaction of YBa2Cu3O(7-beta) with Au, Ag, Bi, and Ph ions or metal is described. Three types of materials were produced: a well-defined series of homogeneous superconductors was obtained for Au ion substitution with little effect on T(sub c); attempted Ag and Bi ion substitution resulted in multi-phase samples with slightly enhanced T(sub c); finally, attempts to produce superconducting metal/superconducting ceramic composites with Pb and Bi powders resulted in multi-phase samples with drastically diminished superconducting properties. For Au- substituted superconductors, YBa2(Cu(l-x)Au(x))3O(7-beta), a substitution series (x = 0 - 0.1) has been synthesized. For x = 0.1 there was no change in the a and b lattice parameters (a = 3.826 A and b = 3.889 A) but a 0.06 A c axis expansion to 11.75 A was observed. The valence of Cu and Au in YBa2Au(0.3)Cu(2.7)O(7-beta) was investigated using X-ray Absorption Near-Edge Structure (XANES). X-ray studies indicate that Au goes into the Cu(l) site and Cu K edge XANES shows that this has little effect on the oxidation state of the remaining copper. A small effect on T(sub c) is observed (T(sub c) = 89 K for x = 0.10). Ag and Bi addition results in a rise in T(sub c) and a decrease in (delta)T(sub c) at low levels (x = 0.10 Ag, T(sub c) = 94 K and (delta)T(sub c) = 0.5 K; x = 0.02 Bi, T(sub c) = 94 K and (delta)T(sub c) = 1K) relative to typical values for YBa2Cu3O(7-beta) (T(sub c) = 91 K, (delta)T(sub c) = 2 K). Attempts at fabrication of Pb- and Pb(1-x)Bi(x)-superconductor composites are described. Cold pressing followed by low temperature (200 C) sintering resulted in a composite which excluded flux below 90 K but did not show zero electrical resistance until the metal (alloy) superconducting transition. X-ray diffraction showed the presence of pervoskite and metal. Processing at moderate (450 C) or high (950 C) temperatures resulted in oxygen-depleted pervoskite and/or metal oxides. These materials displayed greatly degraded superconducting properties. Processing at 800 C resulted in high T(sub c) only for composites containing greater than 90% weight fraction ceramic. Reaction of metal with YBa2Cu3O(7-beta) formed superconducting lead/bismuth-based oxides and other binary oxides.

Hepp, Aloysius F.↗
NASA NTRS1995

(abstract) Undercooling Studies of the Bulk Metallic Glass Forming Zr(sub 41.2)Ti(sub 13.8)Cu(sub 12.5)Ni(sub 10.0)Be(sub 22.5) Alloy During Containerless Electrostatic Levitation Processing

Bulk glass forming metallic alloys have long been desired for technological applications and for investigation into liquid undercooling, solidification processes, and thermophysical properties. A glass forming alloy Zr(sub 41.2)Ti(sub 13.8)Cu(sub 12.5)Ni(sub 10.0)Be(sub 22.5) was used to investigate the thermal treatments affecting undercooling and vitrification. The experiments were performed using the high temperature high vacuum electrostatic levitator at JPL. A sample approximately 3 mm in diameter was melted, superheated, undercooled, and solidified while levitated in high vacuum. The results show that when the sample was held above its melting temperature for a sufficient period of time to dissolve oxides and then cooled faster than a critical cooling rate, it undercooled to the glass transition temperature, T(sub g), and formed a glassy alloy. The required critical cooling rate for metallic glass formation was obtained to be between 0.9 K per second and 1.2 K per second for the 42.4 mg sample.

levitation vitrification↗
NASA NTRS1991

In-situ deposition of YBCO high-Tc superconducting thin films by MOCVD and PE-MOCVD

Metal-Organic Chemical Vapor Deposition (MOCVD) offers the advantages of a high degree of compositional control, adaptability for large scale production, and the potential for low temperature fabrication. The capability of operating at high oxygen partial pressure is particularly suitable for in situ formation of high temperature superconducting (HTSC) films. Yttrium barium copper oxide (YBCO) thin films having a sharp zero-resistance transition with T(sub c) greater than 90 K and J(sub c) of approximately 10(exp 4) A on YSZ have been prepared, in situ, at a substrate temperature of about 800 C. Moreover, the ability to form oxide films at low temperature is very desirable for device applications of HTSC materials. Such a process would permit the deposition of high quality HTSC films with a smooth surface on a variety of substrates. Highly c-axis oriented, dense, scratch resistant, superconducting YBCO thin films with mirror-like surfaces have been prepared, in situ, at a reduced substrate temperature as low as 570 C by a remote microwave-plasma enhanced metal-organic chemical vapor deposition (PE-MOCVD) process. Nitrous oxide was used as a reactant gas to generate active oxidizing species. This process, for the first time, allows the formation of YBCO thin films with the orthorhombic superconducting phase in the as-deposited state. The as-deposited films grown by PE-MOCVD show attainment of zero resistance at 72 K with a transition width of about 5 K. MOCVD was carried out in a commercial production scale reactor with the capability of uniform deposition over 100 sq cm per growth run. Preliminary results indicate that PE-MOCVD is a very attractive thin film deposition process for superconducting device technology.

Zhao, J.↗
NASA NTRS1990

Dissociation of O(2-)2 defects into paramagnetic O(-) in wide band-gap insulators - A magnetic susceptibility study of magnesium oxide

The magnetic susceptibility of single-crystal MgO has been measured in the temperature range 300-1000 K, using a Faraday balance. The high-purity crystal (less than 100 ppm transition metals), grown from the melt in a H2O-containing atmosphere, was found to be paramagnetic due to the presence of defects on the O(2-) sublattice. The defects derive from OH(-) introduced into the MgO matrix by the dissolution of traces of H2O during crystal growth. The OH(-) converts into O(2-)2 and H2. Each O(2-)2 represents two coupled, spin-paired O(-) states. The observed strongly temperature-dependent paramagnetism can be described by three contributions that overlay the intrinsic diamagnetism of MgO and arise from the low level of transition-metal impurities, O(-) generated by 0(2-)2 dissociation, and O(-) states trapped by quenching from high temperatures from previous experiments.

Batllo, F.↗
NASA NTRS2010

Surface and bulk modified high capacity layered oxide cathodes with low irreversible capacity loss

The present invention includes compositions, surface and bulk modifications, and methods of making of (1-x)Li[Li.sub.1/3Mn.sub.2/3]O.sub.2.xLi[Mn.sub.0.5-yNi.sub.0.5-yCo.sub.2- y]O.sub.2 cathode materials having an O3 crystal structure with a x value between 0 and 1 and y value between 0 and 0.5, reducing the irreversible capacity loss in the first cycle by surface modification with oxides and bulk modification with cationic and anionic substitutions, and increasing the reversible capacity to close to the theoretical value of insertion/extraction of one lithium per transition metal ion (250-300 mAh/g).

Manthiram, Arumugam↗
NASA NTRS1973

Radiative lifetimes and band oscillator strengths for metal oxides. II - SiO E 1 Sigma /+/-X 1 Sigma /+/

Use of an electron-beam phase-shift apparatus to obtain the radiative lifetimes for vibrational levels of the SiO E 1 Sigma (+) state. It is found that the radiative lifetimes for the vibrational transitions of the E-X band are independent of the vibrational upper state. The measured phase shifts yield cascade free lifetimes of 10.5 plus or minus 1.1 nsec for v' from 1 to 7. Spectroscopic data from Elander and Lagerqvist (1971) were used to calculate potential curves by the Klein-Dunham procedure, and Franck-Condon factors and r-centroids for the transition were computed.

Elander, N.↗
NASA NTRS1987

Magnetic particles

Metal oxide containing polymers and particularly styrene, acrylic or protein polymers containing fine, magnetic iron oxide particles are formed by combining a NO.sub.2 -substituted polymer with an acid such as hydrochloric acid in the presence of metal, particularly iron particles. The iron is oxidized to fine, black Fe.sub.3 O.sub.4 particles which deposit selectively on the polymer particles. Nitrated polymers are formed by reacting functionally substituted, nitrated organic compounds such as trinitrobenzene sulfonate or dinitrofluoro benzene with a functionally coreactive polymer such as an amine modified acrylic polymer or a protein. Other transition metals such as cobalt can also be incorporated into polymers using this method.

Chang, Manchium↗
NASA NTRS1982

Synthesis of Perfluorinated Polymers

Long-chain perfluoropolyethers containing functional pendent groups were investigated as possible candidates for new sealants and elastomers that function in extreme environments. Of specific interest was development of materials exhibiting high thermal and oxidative stability at temperatures around 400 degrees C, low-temperature flexibility with glass transition at about 50 degrees C, and hydrolytic stability as well as compatibility with metals and resistance to fuels.

Rosser, R. W.↗
NASA NTRS2010

Molybdenum Valence in Basaltic Silicate Melts

The moderately siderophile element molybdenum has been used as an indicator in planetary differentiation processes, and is particularly relevant to core formation [for example, 1-6]. However, models that apply experimental data to an equilibrium differentiation scenario infer the oxidation state of molybdenum from solubility data or from multivariable coefficients from metal-silicate partitioning data [1,3,7]. Partitioning behavior of molybdenum, a multivalent element with a transition near the J02 of interest for core formation (~IW-2) will be sensitive to changes in JO2 of the system and silicate melt structure. In a silicate melt, Mo can occur in either 4+ or 6+ valence state, and Mo6+ can be either octahedrally or tetrahedrally coordinated. Here we present first XANES measurements of Mo valence in basaltic run products at a range of P, T, and JO2 and further quantify the valence transition of Mo.

Danielson, L. R.↗