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At least 451 records · Page 25

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NASA NTRS1984

Phosphoran pyroxene and olivine in silicate inclusions in natural iron-carbon alloy, Disko Island, Greenland

A survey of literature data on the P contents of olivine, pyroxene, and garnet in mantle xenoliths and the bulk P contents of mantle xenoliths shows that available data is ambiguous as to whether mantle P is primarily contained in silicates or in phosphates, even though phosphates are rarely observed in mantle xenoliths. Garnet probably contains more of the mantle's P than olivine or pyroxene. Bulk P contents of mantle xenoliths vary significantly. Estimation of the primitive mantle P content from xenoliths requires interpretation of the partial melting and contamination histories of the xenoliths.

Goodrich, C. A.↗

NASA NTRS1985

Sulfide and sulfate saturation in hydrous silicate melts

A series of hydrothermal experiments was performed over a wide range of pressures, temperatures, oxygen fugacities, and melt FeO content, in order to examine the effects of physical changes on sulfur solubility in fractionated hydrous silicate melts. On the basis of the experimental results, it is concluded that upper crustal oxidation-reduction reactions and crystal fractionation processes may exert considerable influence on the amount of sulfur contained in magmas erupted at the surface. The application of the experimental results to investigations of volatile transport and volcanic degassing processes on the earth, Venus, and Mars is discussed

Carroll, M. R.↗

NASA NTRS1985

Interstellar dust spectra between 2.5 and 3.3 microns - A search for hydrated silicates

Spectra in the 2.5-3.3 micron wavelength region of VI Cyg 12, AFGL 2205, and AFGL 2885 were obtained in a search for bound water, hydroxyl groups, and hydrated minerals in interstellar dust. No new absorption bands were found. Comparison of expected strengths of bands of serpentine and chlorite-like minerals with the data suggests that less than 25 percent and 50 percent, respectively, of the silicate in the grains is composed of these materials.

Knacke, R. F.↗

NASA NTRS1986

Conductimetric determination of decomposition of silicate melts

A description of a procedure is given to detect decomposition of silicate systems in the liquid state by conductivity measurements. Onset of decomposition can be determined from the temperature curves of resistances measured on two pairs of electrodes, one above the other. Degree of decomposition can be estimated from temperature and concentration dependency of conductivity of phase boundaries. This procedure was tested with systems PbO-B2O3 and PbO-B2O3-SiO2.

Kroeger, C.↗

NASA NTRS1986

Lithologic mapping of silicate rocks using TIMS

Common rock-forming minerals have thermal infrared spectral features that are measured in the laboratory to infer composition. An airborne Daedalus scanner (TIMS) that collects six channels of thermal infrared radiance data (8 to 12 microns), may be used to measure these same features for rock identification. Previously, false-color composite pictures made from channels 1, 3, and 5 and emittance spectra for small areas on these images were used to make lithologic maps. Central wavelength, standard deviation, and amplitude of normal curves regressed on the emittance spectra are related to compositional information for crystalline igneous silicate rocks. As expected, the central wavelength varies systematically with silica content and with modal quartz content. Standard deviation is less sensitive to compositional changes, but large values may result from mixed admixture of vegetation. Compression of the six TIMS channels to three image channels made from the regressed parameters may be effective in improving geologic mapping from TIMS data, and these synthetic images may form a basis for the remote assessment of rock composition.

Gillespie, A. R.↗

NASA NTRS1986

The physical basis for spectral variations in thermal infrared emittance of silicates and application to remote sensing

The use of infrared spectroscopy for the remote characterization of planetary surfaces has received attention due to efforts in the investigation of these bodies from space. In the 8 to 14 micron region, a depression in the emittance spectra of rocks (sometimes called reststrahlen) is related to the fundamental stretching vibrations of Si-O bonds and shifts in the locations of this feature are ascribed to variations in rock composition. Thus, it should be possible to investigate, quantify, and model the relationships of reststrahlen spectral band location through silicate mineralogical composition to rock classification. This concept will be tested first through the use of laboratory-acquired data on the infrared spectra and mineralogy of selected mineral and rock samples. As a suitable classification model is developed, it will be tested through overflights of appropriate rock outcrops using the Thermal Infrared Multispectral Scanner (TIMS).

Walter, Louis S.↗

NASA NTRS1987

An electrochemical series of redox couples in silicate melts - A review and applications to geochemistry

An electrochemical series for redox couples in a glass-forming oxide melt is developed. This series is a quantitative numerical scale of reference reduction potentials of the redox couples in a silicate melt that is a model for basaltic magmas. The redox couples are ordered in terms of their reference reduction potentials; the order appears to be relatively independent of the exact melt composition and temperature. Thus, upon calibration to a desired composition, oxygen fugacity, and temperature, this electrochemical series can provide estimates of redox state proportions in basaltic magmas on different planetary bodies. The geochemical electrochemical series can also be used to understand the interrelationship of the redox state of the magma and the presence of volatile species such as oxygen, water, sulfur gases, and carbon gases.

Schreiber, Henry D.↗

NASA NTRS1988

Tribological properties of alumina-boria-silicate fabric from 25 to 850 C

Demanding tribological properties are required of the materials used for the sliding seal between the sidewalls and the lower wall of the variable area hypersonic engine. Temperatures range from room temperature and below to operating temperatures of 1000 C in an environment of air, hydrogen, and water vapor. Candidate sealing materials for this application are an alumina-boria-silicate, ceramic, fabric rope sliding against the engine walls which may be made from copper- or nickel-based alloys. Using a pin-on-disk tribometer, the friction and wear properties of some of these potential materials and possible lubrication methods are evaluated. The ceramic fabric rope displayed unacceptably high friction coefficients (0.6 to 1.3) and, thus, requires lubrication. Sputtered thin films of gold, silver, and CaF2 reduced the friction by a factor of two. Sprayed coatings of boride nitride did not effectively lubricate the fabric. Static heat treatment tests at 950 C indicate that the fabric is chemically attacked by large quantities of silver, CaF2, and boron nitride. Sputtered films or powder impregnation of the fabric with gold may provide adequate lubrication up to 1000 C without showing any chemical attack.

Dellacorte, Christopher↗

NASA NTRS1987

Roosevelt County 027 - A low-shock ureilite with interstitial silicates and high noble gas concentrations

The RC027 lightly-shocked ureilite contains less than 1 percent of a fine-grained interstitial silicate that has an igneous texture indicating crystallization from an interstitial liquid. RC027 is also noted to exhibit the strongest olivine preferred-orientation thus far observed in a ureilite; its fabric is characteristic of fabrics formed by tabular minerals in a fluid laminar flow regime, and is unlike those formed by synectonic recrystallization and plastic flow. The elemental and isotopic compositions of noble gases in RC027 are typical of previously analyzed ureilites.

Goodrich, Cyrena Anne↗

NASA NTRS1988

The basis for the spectral behaviour of silicates in the thermal infrared and applications to remote sensing

Variations in the thermal infrared (TIR) spectral response of silicate rocks is related to changes in the structures and divalent cation contents of the minerals which form the rocks. These considerations lead to a chemical parameter, SCFM, which reflects mineral structures, rock types, and their spectra. The parameter is the ratio of silica to the abundance of depolymerizing cations, defined as SCFM = SiO2/SiO2 + CaO + MgO + FeO. Parameter SCFM is therefore proposed for use in TIR remote sensing of igneous rocks. It is also demonstrated that two or three broad bands are sufficient for distinguishing among major rock types and the system noise has little effect on the quality of the results. These factors can be traded off against improved spatial resolution in instrument design.

Walter, L. S.↗

NASA NTRS1987

Volatilization-fractionation of silicates related to chondrite composition

The compositions of chondritic meteorites are linked to the solar composition. It is believed that the chemistry of the (generally) drop-shaped chondrules which comprise a large portion of these meteorites may present valuable clues to their formation and, ultimately, to the early conditions and processes of the planets. The purpose of this experiment is to determine the nature of volatilization-fractionation of silicate (and related metallic) compositions related to chondrite composition.

Walter, L. S.↗

NASA NTRS1988

Io - Evidence for silicate volcanism in 1986

Infrared observations of Io during the 1986 apparition of Jupiter indicate that a large eruptive event occurred on the leading side of Io on August 7, 1986, UT. Measurements made at 4.8, 8.7, and 20 micrometers suggest that the source of the event was about 15 kilometers in radius with a model temperature of about 900 K. These measurements indicate that high-temperature volcanic activity on the leading side of Io may be more frequent than previously thought. The inferred temperature is significantly above the boiling point of sulfur in a vacuum (715 K) and thus constitutes strong evidence for active silicate volcanism on the surface of Io.

Johnson, Torrence V.↗

NASA NTRS1989

Tribological properties of alumina-boria-silicate fabric from 25 C to 850 C

Dellacorte, Christopher↗

NASA NTRS1989

C-O-H ratios of silicate melt inclusions in basalts from the Galapagos Spreading Center near 95 deg W - A laser decrepitation mass spectrometry study

Ratios of C, O, and H dissolved in silicate glass inclusions and pillow rind glasses in samples from the Galapagos Spreading Center near 95 deg W were analyzed (using laser volatilization and mass spectrometry), and the data were assessed in terms of mantle source compositions, oxygen fugacity, kinetic fractionation, and magmatic degassing. It was found that glass inclusions in the Galapagos failing rift lavas are higher and more variable in CO2/H2O (about 0.641) relative to inclusions in propagating rift lavas (about 0.245). This difference is considered to reflect different degrees of degassing during contrasting magmatic histories of the two regions.

Yonover, Robert N.↗

NASA NTRS1990

The infrared spectrum of Comet Bradfield (1987s) and the silicate emission feature

Infrared (1-20 microns) observations of Comet Bradfield (1987s) from three observatories are reported. Silicate emission is prominent in all the data, from heliocentric distance r = 0.87 to 1.45 AU. A CVF spectrum at r = 1.45 AU shows a peak at 11.3 microns identified as crystalline olivine; the spectral shape is similar to that in Halley. Dust optical properties are similar to those of the grains in Halley's jets. Dust production rate near perihelion was about 10 to the 6th g/s and varied as N exp-2. It is suggested that some differences in grain properties among comets could result from difference in the thermal history of the nuclear surface and the relative fraction of the dust particles originating in the subsurface icy layer versus the devolatilized mantle.

Hanner, M. S.↗

NASA NTRS1990

Laboratory studies of the electrical conductivity of silicate perovskites at high pressures and temperatures

The electrical conductivities of two silicate perovskites and a perovskite-magnesiowuestite assemblage, all having an atomic ratio of Mg to Fe equal to 0.88/0.12, have been measured with alternating current and direct current (dc) techniques at simultaneously high pressures and temperatures. Measurements up to pressures of 80 GPa and temperatures of 3500 K, using a laser-heated diamond anvil cell, demonstrate that the electrical conductivity of these materials remains below 10-3 S/m at lower mantle conditions. The activation energies for electrical conduction are between 0.1 and 0.4 eV from the data, and the conduction in these perovskites is ascribed to an extrinsic electronic process. The new measurements are in agreement with a bound that was previously obtained from dc measurements for the high-PT conductivity of perovskite-dominated assemblages. The results show that the electrical conductivity of (Mg/0.88/Fe/0.12)SiO3 perovskite differs significantly from that of the earth's deep mantle, as inferred from geophysical observations.

Li, Xiaoyuan↗

NASA NTRS1990

Silicate liquid immiscibility in isothermal crystallization experiments

The role of silicate liquid immiscibility (SLI) in the petrogenesis of lunar granites was investigated in experiments in which four glasses were synthesized from reagent-grade oxides and carbonates with the compositions of two of the sets of coexisting liquids reported by Hess et al. (1975): a KREEP basalt derivative and a mare basalt derivative. Isothermal crystallization experiments showed that SLI is a stable phenomenon in residual lunar liquids saturated with plagioclase, and is likely to produce large compositional separations. The results indicate that controlled-cooling-rate experiments of Rutherford et al. (1974), and Hess et al. (1975, 1978) were substantially correct analogs of the natural process of liquid immiscibility.

Longhi, J.↗

NASA NTRS1991

Experimental study of the electrolysis of silicate melts

To produce oxygen from lunar resources, it may be feasible to melt and electrolyze local silicate ores. This possibility was explored experimentally with synthesized melts of appropriate compositions. Platinum electrodes were employed at a melt temperature of 1425 C. When silicon components of the melt were reduced, the platinum cathode degraded rapidly, which prompted the substitution of a graphite cathode substrate. Discrete particles containing iron or titanium were found in the solidified electrolyte after three hours of electrolysis. Electrolyte conductivities did not decrease substantially, but the escape of gas bubbles, in some cases, appeared to be hindered by high viscosity of the melt.

Keller, R.↗