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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 181 records · Page 10
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NASA NTRS1981

The MgO-Al2O3-SiO2 system - Free energy of pyrope and Al2O3-enstatite

The model of fictive ideal components is used to determine Gibbs free energies of formation of pyrope and Al2O3-enstatite from the experimental data on coexisting garnet and orthopyroxene and orthopyroxene and spinel in the temperature range 1200-1600 K. It is noted that Al2O3 forms an ideal solution with MgSiO3. These thermochemical data are found to be consistent with the Al2O3 isopleths that could be drawn using most recent experimental data and with the reversed experimental data on the garnet-spinel field boundary.

Saxena, S. K.↗
NASA NTRS1981

Refractory spherules in the Murchison meteorite - Are they condrules

The textural and mineralogical features of refractory spherules found in the Murchison meteorite are examined in relation to their probable origin. Based on a study of 12 samples it is found that the refractory spherules, with hibonite-bearing or spinel or spinel-perovskite cores surrounded by an iron-rich silicate layer, have compositions similar to those of coexisting irregular inclusions. The shape and internal textures of the spherules, however, suggest formation from a liquid. It is proposed that the spherules may be melted equivalents of the irregular inclusions, and thus may be properly termed chondrules. It is noted that such melting would have involved very high temperatures.

Macdougall, J. D.↗
NASA NTRS1984

Two forsterite-bearing FUN inclusions in the Allende meteorite

Two forsterite-, fassaite-, spinel-rich inclusions in Allende which share common mineralogy and texture with three previously described inclusions are described. These inclusions were at least partially molten at temperatures over 1400 C, and their crystallization sequence was spinel, olivine, fassaite, and Mg-rich melilite. At least some of them experienced partial volatilization of MgO and SiO2 from their outer margins. At least one of the inclusions is highly enriched in MgO relative to CaO and Al2O3 compared to Allende coarse-grained inclusions, although it is just as strongly enriched in refractory trace elements as the latter, relative to C1 chondrites. Two of the objects are FUN inclusions on the basis of their oxygen, magnesium, and silicon isotopic compositions.

Clayton, R. N.↗
NASA NTRS1984

Achondrite ALHA77005 - Alteration of chromite and olivine

The olivine crystals of the 77005 achondrite are brown except for colorless shock lamellae, mottled patches, and grains adjacent to pools of impact melt. Sporadic dark alteration patches in brown olivine and Cr-rich spinel gave the following average electron-microprobe analyses: (olivine) P2O5 0.9, SiO2 57.9, TiO2 0, Al2O3 0.7, Cr2O3 0.4, V2O3 0, Fe2O3 (assumed oxidation state) 17.0, MgO 1.6, CaO 0.2, Na2O 0, K2O 1.8, SO3 (assumed oxidation state) 9.2, Cl 0.1, sum 89.8 wt pct; (spinel) P2O5 3.5, SiO2 2.1, TiO2 2.2, Al2O3 2.1, Cr2O3 13.4, V2O3 0.8, Fe2O3 40.7, MgO 0.9, CaO 0.1, Na2O 0, K2O 2.0, SO3 11.1, Cl 0.1, sum 79.0 wt pct. Ion-microprobe analyses revealed H in both. Rare orange patches in brown olivine from another area gave SiO2 33-35, FeO 30-28, MgO 28-32, sum 93 wt pct. Thermal metamorphism under dry oxidizing conditions is discussed as a possible alternative to shock-induced oxidation for generation of the brown olivine (McSween and Stoeffler, 1980). Because alteration patches transgress shock lamellae, and because sulfatic alteration occurs in fusion crusts of Antarctic meteorites (Gibson et al., 1983), alteration of the 77005 achondrite at the Antarctic surface is preferred to a complex series of processes needed for preterrestrial alteration.

Smith, J. V.↗
NASA NTRS1985

Willy: A prize noble Ur-Fremdling - Its history and implications for the formation of Fremdlinge and CAI

The structure and composition of Willy, a 150-micron-diameter Fremdling in CAI 5241 from the Allende meteorite, are investigated using optical, secondary-electron, and electron-backscatter microscopy and electron-microprobe analysis. The results are presented in diagrams, maps, tables, graphs, and micrographs and compared with those for other Allende Fremdlinge. Willy is found to have a concentric-zone structure comprising a complex porous core of magnetite, metal, sulfide, scheelite, and other minor phases; a compact magnetite-apatite mantle; a thin (20 microns or less) reaction-assemblage zone; and a dense outer rim of fassaite with minor spinel. A multistage formation sequence involving changes in T and fO2 and preceding the introduction of Willy into the CAI (which itself preceded CAI spinel and silicate formation) is postulated, and it is inferred from the apparent lack of post-capture recrystallization that Willy has not been subjected to temperatures in excess of 600 C and may represent the precursor material for many other Fremdlinge.

Armstrong, J. T.↗
NASA NTRS1987

Actinide chemistry in Allende Ca-Al-rich inclusions

Fission track radiography is used to investigate the U and Th microscale distribution in a set of Allende-meteorite Ca-Al-rich inclusions. In the Type B inclusions, the major phases melilite and fassaite are important actinide host phases, and on the rims of Type B inclusions and throughout all other inclusions studied, perovskite is the dominant actinide host phase. Results suggest that neither alteration nor loss or gain of an actinide-rich phase appears to have been an important Th/U fractionation mechanism, and that volatility differences may be the dominant factor. Th/U and rare earth element abundance patterns for the spinel and perovskite rim suggest rim formation by volatilization of interior material, and within the constraints of the brief time scale required for this heating, several mechanisms for spinel-perovskite rim formation are possible.

Murrell, M. T.↗
NASA NTRS1987

Phase purity of NiCo2O4, a catalyst candidate for electrolysis of water

NiCo2O4 is shown to be difficult to obtain as a pure phase, and may never have been so obtained. High resolution x-ray diffractometry is required for its precise characterization. Film XRD is not likely to show the asymmetry in the spinel diffraction lines, caused by poorly crystallized NiO, as seen in diffractometer traces. The Co3O4 which is expected to accompany NiO as an impurity in NiCo2O4 syntheses has the same diffraction pattern as the binary oxide. Firings of the co-precipitated hydroxides at 300, 350, and 400 C, including one in pure O2, failed to produce single phase cobaltate. Scanning electron microscopy showed all the sintered products to range over several orders of magnitude in agglomerate/particle size. Surface areas by BET were all in the range 40 to 110 m sq/g, equivalent to particles of 200 to 100 Angstrom diameter. The spinel diffraction line breadths were compatible with those approximate dimensions.

Singer, J.↗
NASA NTRS1987

Phase equilibria in the iron oxide-cobalt oxide-phosphorus oxide system

Two novel ternary compounds are noted in the present study of 1000 C solid-state equilibria in the Fe-Co-P-O system's Fe2O3-FePO4-Co3(Po4)2-CoO region: CoFe(PO4)O, which undergoes incongruent melting at 1130 C, and Co3Fe4(PO4)6, whose incongruent melting occurs at 1080 C. The liquidus behavior-related consequences of rapidly solidified cobalt ferrite formation from cobalt ferrite-phosphate melts are discussed with a view to spinel formation. It is suggested that quenching from within the spinel-plus-liquid region may furnish an alternative to quenching a homogeneous melt.

De Guire, Mark R.↗
NASA NTRS1988

Mineral compositions of plutonic rocks from the Lewis Hills massif, Bay of Islands ophiolite

Mineral compositions of residual and cumulate rocks from the Lewis Hills massif of the Bay of Islands ophiolite complex are reported and interpreted in the context of magnetic processes involved in the geochemical evolution of spatially associated diabase dikes. The mineral compositions reflect greater degrees of partial melting than most abyssal peridotites do and appear to represent the most depleted end of abyssal peridotite compositions. Subsolidus equilibration between Cr-Al spinal and olivine generally has occurred at temperatures of 700 to 900 C. The spinel variations agree with the overall fractionation of basaltic magmas producing spinels with progressively lower Cr numbers. The compositions of clinopyroxenes suggest that the fractionation of two different magma series produced the various cumulate rocks.

Smith, Susan E.↗
NASA NTRS1988

High Tc screen-printed YBa2Cu3O(7-x) films - Effect of the substrate material

Thick films of YBa2Cu3O(7-x) have been deposited on highly polished alumina, magnesia spinel, nickel aluminum titanate (Ni-Al-Ti), and barium tetratitanate (Ba-Ti) substrates by the screen printing technique. Properties of the films were found to be highly sensitive to the choice of the substrate material. The film on Ba-Ti turned green after firing, due to a reaction with the substrate and were insulating. A film on Ni-Al-Ti had a Tc (onset) of about 95 K and lost 90 percent of its resistance by about 75 K. However, even at 4 K it was not fully superconducting, possibly due to a reaction between the film and the substrate and interdiffusion of the reaction products. The film on alumina had Tc (onset) of about 96 K, Tc (zero) of about 66 K, and Delta Tc of about 10 K. The best film was obtained on spinel and had Tc (onset) of about 94 K, zero resistance at 81 K, and a transition width of about 7 K.

Bansal, Narottam P.↗
NASA NTRS1988

Phase transformations in xerogels of mullite composition

Monophasic and diphasic xerogels have been prepared as precursors for mullite (3Al2O3-2SiO2). Monophasic xerogel was synthesized from tetraethyl orthosilicate and aluminum nitrate nanohydrate and the diphasic xerogel from colloidal suspension of silica and boehmite. The chemical and structural evolutions, as a function of thermal treatment, in these two types of sol-gel derived mullite precursor powders have been characterized by DTA, TGA, X-ray diffraction, SEM and infrared spectroscopy. Monophasic xerogel transforms to an Al-Si spinel from an amorphous structure at approximately 980 C. The spinel then changes into mullite on further heating. Diphasic xerogel forms mullite at approximately 1360 C. The components of the diphasic powder react independently up to the point of mullite formation. The transformation in the monophasic powder occurs rapidly and yields strongly crystalline mullite with no other phases present. The diphasic powder, however, transforms rather slowly and contains remnants of the starting materials (alpha-Al2O3, cristobalite) even after heating at high temperatures for long times (1600 C, 6 hr). The diphasic powder could be sintered to high density but not the monophasic powder in spite of its molecular level homogeneity.

Hyatt, Mark J.↗
NASA NTRS1989

The evolution of complex type B Allende inclusion - An ion microprobe trace element study

Results are presented of a detailed trace-element and isotopic analyses of the constituent phases in each of the major textural parts (mantle, core, and islands) of a Type B refractory inclusion, the USNM 5241 inclusion from Allende, first described by El Goresy et al. (1985). The REE data on 5241 were found to be largely consistent with a model in which the mantle and the core of 5241 formed sequentially out of a single melt by fractional crystallization. The numerical models of REE evolution in the 5241 melt, especially that of Eu, require that a significant mass of spinel-free island material was assimilated into the evolving melt during the last half of the solidification history of 5241. The trace element results pbtained thus strongly support the interpretation of El Goresy et al. (1985) that the spinel-free islands in the 5241 are trapped xenoliths.

Macpherson, Glenn J.↗
NASA NTRS1989

Corrosion testing of candidates for the alkaline fuel cell cathode

Current/voltage data was obtained for specially made corrosion electrodes of some oxides and of gold materials for the purpose of developing a screening test of catalysts and supports for use at the cathode of the alkaline fuel cell. The data consists of measurements of current at fixed potentials and cyclic voltammograms. These data will have to be correlated with longtime performance data in order to fully evaluate this approach to corrosion screening. Corrosion test screening of candidates for the oxygen reduction electrode of the alkaline fuel cell was applied to two substances, the pyrochlore Pb2Ru2O6.5 and the spinel NiCo2O4. The substrate gold screen and a sample of the IFC Orbiter Pt-Au performance electrode were included as blanks. The pyrochlore data indicate relative stability, although nothing yet can be said about long term stability. The spinel was plainly unstable. For this type of testing to be validated, comparisons will have to be made with long term performance tests.

Singer, Joseph↗
NASA NTRS1990

Phase transformations in xerogels of mullite composition

Monophasic and diphasic xerogels have been prepared as precursors for mullite (3Al203-2Si02). Monophasic xerogel was synthesized from tetraethyl orthosilicate and aluminum nitrate nanohydrate and the diphasic xerogel from colloidal suspension of silica and boehmite. The chemical and structural evolutions, as a function of thermal treatment, in these two types of sol-gel derived mullite precursor powders have been characterized by DTA, TGA, X-ray diffraction, SEM and infrared spectroscopy. Monophasic xerogel transforms to an Al-Si spinel from an amorphous structure at approximately 980 C. The spinel then changes into mullite on further heating. Diphasic xerogel forms mullite at approximately 1360 C. The components of the diphasic powder react independently up to the point of mullite formation. The transformation in the monophasic powder occurs rapidly and yields strongly crystalline mullite with no other phases present. The diphasic powder, however, transforms rather slowly and contains remnants of the starting materials (alpha-Al203, cristobalite) even after heating at high temperatures for long times (1600 C, 6 hr). The diphasic powder could be sintered to high density but not the monophasic powder in spite of its molecular level homogeneity.

Hyatt, Mark J.↗
NASA NTRS1992

Material transport in laser-heated diamond anvil cell melting experiments

A previously undocumented effect in the laser-heated diamond anvil cell, namely, the transport of molten species through the sample chamber, over distances large compared to the laser beam diameter, is presented. This effect is exploited to determine the melting behavior of high-pressure silicate assemblages of olivine composition. At pressures where beta-spinel is the phase melted, relative strengths of partitioning can be estimated for the incompatible elements studied. Iron was found to partition into the melt from beta-spinel less strongly than calcium, and slightly more strongly than manganese. At higher pressures, where a silicate perovskite/magnesiowuestite assemblage is melted, it is determined that silicate perovskite is the liquidus phase, with iron-rich magnesiowuestite accumulating at the end of the laser-melted stripe.

Campbell, Andrew J.↗
NASA NTRS1992

The effects of Venusian mantle convection with multiple phase transitions

Recently there was a flurry of activities in studying the effects of phase transitions in the Earth's mantle. From petrological and geophysical considerations, phase-transitions would also play an important role in venusian dynamics. The basic differences between the two planets are the surface boundary conditions, both thermally and mechanically. In this vein we have studied time-dependent mantle convection with multiple phase transitions and depth-dependent thermal expansivity (alpha is approximately rho(exp -6)), based on high-pressure and temperature measurements. Both the olivine-spinel and spinel-perovskite transitions were simulated by introducing an effective thermal expansivity, as described. Used together with the extended Boussinesq Approximation this method serves as a powerful tool to examine the effects of phase transitions on convection at relatively low computational costs.

Steinbach, V.↗
NASA NTRS1992

Evolution of attached and detached slabs and their associated mantle dynamics

Over the two years of the NASA grant, this project has produced a significant amount of research results related to the plate subduction process and the surface crustal deformation at convergent boundaries (i.e., above subduction zones). While some research objectives are completely accomplished, other research tasks remain active and continue to be investigated at present. A steady state analytic thermal model for subducting slabs was used to examine the torques acting on a descending slab. It is found that gravitational torque vanishes when a slab is dipping either vertically or horizontally, unlike previous studies indicating that the magnitude of gravitational torque decreases as dip angle increases. Subsequently, a new time-dependent, analytic thermal model for a subducting slab was developed. The new model enables us to study transient phenomena associated with plate subduction analytically. On the basis of this model, the nature of slab dip angles was evaluated. Slab dip angles are found to be transient features. As they penetrate into the mantle and increase their lengths, the associated gravitational torque also increases resulting in a downward pulling of the slab to the steeper dip angle. This is especially true once a slab penetrates the olivine-spinel phase boundary at about 400 km depth. However, if the phase transformation does not follow the equilibrium condition, the gravitational torque may have a different behavior. This problem was investigated. Except for fast descending slabs, non-equilibrium phase transformation can only slow down the transient increase of slab dip angles discussed earlier. Its effect is not sufficiently strong to reverse the downward pulling for most of the slabs. However, when slabs subducting at 10 cm/yr or faster, a sufficient amount of metastable olivine can exist beneath 400 km. Because of its low density compared with the surrounding spinel, an upward buoyancy is produced resulting in an upward bending of the slab and possibly an upward rotation of the slab such that smaller dip angles are formed. Seismic studies of the Japanese Slab seem to support this interpretation. The development of oroclinal geometries at convergent boundaries was also examined to study plate obduction which is an important ingredient to the initiation of plate subduction. Although the study suggests that surface features are better modeled by block models, the large scale deformation can be adequately studied by viscous models. Such a model is now under development to complete our original objective to study the initiation of plate subduction. Finally, a three-dimensional, finite element, spherical convective model is developed to study dynamic plate subductions. The model development is now complete and it is being tested to ensure its proper operation. The model is able to generate convection results with a viscosity contrast of about 100. Our research continues to push the viscosity contrast to a level that is appropriate for a subducting slab.

Hsui, Albert T.↗
NASA NTRS1992

Oxygen and iron production by electrolytic smelting of lunar soil

Work during the past year involved two aspects: (1) electrolysis experiments on a larger scale than done before, and (2) collaboration with Carbotek Inc. on design for a lunar magma electrolysis cell. It was demonstrated previously that oxygen can be produced by direct electrolysis of silicate melts. Previous experiments using 50-100 mg of melt have succeeded in measuring melt resistivities, oxygen production efficiencies, and have identified the character of metal products. A series of experiments using 1-8 grams of silicate melt, done in alumina and spinel containers sufficiently large that surface tension effects between the melt and the wall are expected to have minor effect on the behavior of the melt in the region of the electrodes were completed. The purpose of these experiments was to demonstrate the durability of the electrode and container materials, demonstrate the energy efficiency of the electrolysis process, further characterize the nature of the expected metal and spinel products, measure the efficiency of oxygen production and compare to that predicted on the basis of the smaller-scale experiments, and identify any unexpected benefits or problems of the process. Four experimental designs were employed. Detailed results of these experiments are given in the appendix ('Summary of scaling-up experiments'); a general report of the results is given in terms of implications of the experiments on container materials, cathode materials, anode materials, bubble formation and frothing of the melt, cell potential, anode-cathode distance, oxygen efficiency, and energy efficiency.

Colson, R. O.↗