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NASA NTRS1988

Glasses in ancient and young Apollo 16 regolith breccias - Populations and ultra Mg-prime glass

Electron microprobe analysis was used to determine the major element compositions of glass spheres and fragments in seven possibly ancient (about 4 Gyr) and three young (less than 4 Gyr) Apollo 16 regolith breccias. It is found that mare glasses are extremely rare in the ancient regolith breccias, and silica-poor gabbroic anorthosite and high-alumina silica-poor glasses are not present in ancient breccias. Ultra Mg-prime glasses are unique to the Apollo 16 regolith breccias and are most common in the ancient breccias. It is suggested that the presence of ultra Mg-prime glasses could indicate the presence of previously unsampled crustal or volcanic rock types on the moon.

Wentworth, Susan J.↗

NASA NTRS1988

Metal with anomalously low Ni and Ge concentrations in the Allan Hills A77081 winonaite

The Ge content of metal in the Allan Hills A77081 winonaite was determined by high-sensitivity electron microprobe analysis. By optimizing analytical conditions for Ge determination, a detection limit of about 75 ppm could be achieved. In A77081 some small kamacite grains contain less Ni and Ge and more Co than coarse-grained metal. These small grains are always associated with sulfide, raising the possibility that anomalous metal is related to eutectic melting. However, when published partition coefficients for Ni and Ge in the Fe-Ni-S system are used to model fractionation of these elements during eutectic melting, one finds that secondary metal should be enriched in Ni and depleted in Ge. Thus, the positive Ni-Ge correlation found in this study is the opposite of the expected trend. No explanation for this discrepancy has yet been found. Nonetheless, the existence of anomalous metal is an indication that A77081, and probably other winonaites as well, have undergone some fractionation. This supports the notion that the high-temperature history of winonaites is related to the formation of IAB iron meteorites, whose silicate inclusions are very similar to winonaites.

Kracher, Alfred↗

NASA NTRS1988

Capture of an olivine micrometeoroid by spacecraft in low-earth orbit

Particulates associated with an impact feature in the solar maximum satellite MEB thermal control blanket are identified as magnesium-rich, Mg/Mg + Fe(2+) = 0.66 - 0.83, olivine and confirm that the impact feature was caused by an olivine micrometeoroid. At a relative impact velocity of about 7 km/s a considerable portion of the micrometeoroid was lost due to back splattering. Analytical electron microscope analysis of recovered particulates shows several degrees of mineralogical and chemical degradation such as mechanical fragmentation, melting, loss of sulfur and iron, and formation of Fe, Ni grains. The results indicate that recovery of information is sufficient to establish the character of the impacted micrometeoroid.

Rietmeijer, Frans J. M.↗

NASA NTRS1988

A chemical and isotopic study of hibonite-rich refractory inclusions in primitive meteorites

Isotopic and chemical analyses of hibonite-rich inclusions from a number of primitive meteorites and, in some cases, of coexisting minerals from carbonaceous and ordinary chondrites, were carried out using ion microprobe (IP). The results of the IP analyses were compared with literature data obtained by INAA and electron microprobe analysis. Results showed that the trace element patterns of the hibonite inclusions analyzed have a number of feautures in common. The results are discussed with reference to the possible chemical processes operating early in the history of the solar system.

Hinton, Richard W.↗

NASA NTRS1989

A characterization study of a hydroxylated polycrystalline tin oxide surface

In this study Auger electron spectroscopy, electron spectroscopy for chemical analysis (ESCA) and electron-stimulated desorption (ESD) have been used to examine a polycrystalline tin oxide surface before and after annealing in vacuum at 500 C. Features due to surface hydroxyl groups are present in both the ESCA and ESD spectra, and ESD shows that several chemical states of hydrogen are present. Annealing at 500 C causes a large reduction in the surface hydrogen concentration but not complete removal.

Hoflund, Gar B.↗

NASA NTRS1990

Raman spectroscopic studies of carbon in extra-terrestrial materials

The measurements obtained here indicate ways in which micro-Raman spectroscopy can be used to elucidate structural characteristics and distribution of carbon in meteorites and interplanetary dust particles (IDPs). Existing information about structurally significant aspects of Raman measurements of graphite is combined with structurally relevant findings from the present micro-Raman studies of carbons prepared by carbonization of polyvinylidine chloride (PVDC) at various temperatures and natural material, as well as several acid residues from the Allende and Murchison meteorites in order to establish new spectra-structure relationships. Structural features of many of the materials in this study have been measured by x ray analysis and electron microscopy: thus, their structural differences can be directly correlated with differences in the Raman spectra. The spectral parameters consequently affirmed as indicators of structure are used as a measure of structure in materials that have unknown carbon structure, especially IDPs. The unique applicability of micro-Raman spectroscopy is realized not only in the ability to conveniently measure spectra of micron-size IDPs, but also micro-sized parts of an inhomogeneous material. Microcrystalline graphite is known to give Raman spectra that differ dependent on crystallite size (see e.g., Lespade, et. al., 1984, or Nemanich and Solin, 1979). The spectral changes that accompany decreasing particle size include increase in the ratio (R) of the intensity of the band near 1350 cm(-1) (D band) to that of the band near 1600 cm(-1) (G band) increase in the half width of the D band (wD) increase in the frequency maximum of the G band and increase in the half-width (wG) of the 2nd order band near 2700 cm(-1) (G) band.

Macklin, John↗

NASA NTRS1989

Geochemistry of polymict ureilite EET83309, and a partially-disruptive impact model for ureilite origin

Bulk-compositional data for the EET83309 polymict ureilite were obtained using INAA and radiochemistry procedures and electron probe analysis. It was found that the EET83309 has a bulk composition indistinguishable from ordinary ('monomict') ureilites for all elements except light-middle REEs (which are present in much higher concentrations), suggesting that polymict ureilites are mixtures of ordinary ureilites which were mixed on a very small number of parent bodies. Despite the light-REE enrichments, polymict ureilites are nearly devoid of basaltic (Al-rich) material. It is suggested that the missing basalt may have been blown off the parent body by a partially disruptive collision with a large C-rich projectile. This impact model of ureilite origin reconciles many paradoxical aspects of ureilite composition.

Warren, Paul H.↗

NASA NTRS1990

Upward ion flow in ionospheric holes on Venus

The nature of ion flow within two ionospheric holes on the nightside of Venus was investigated using ion composition measurements made by the ion mass spectrometer on the Pioneer Venus Orbiter. A comparison of the altitude profiles of the observed ion densities with those expected under diffusive equilibrium conditions indicates that the major ions O(+), NO(+), and O2(+), as well as the minor ions H(+) and He(+) flow upward and away from Venus along the axes of the holes. This result agrees with a quantitative evaluation of the ion flow speeds appearing in expressions derived from the equations for conservation of mass and momentum of the ions and electrons. The analysis shows that all ion species flow upward in the holes because the upward force produced by the plasma pressure gradient exceeds all downward forces. However, the nature of the ion source required to maintain such flow is not known.

Hartle, R. E.↗

NASA NTRS1990

Mineralogical comparison of the Y86032-type lunar meteorites to feldspathic fragmental breccia 67016

Mineralogical characteristics of lunar meteorites Y82193 and Y86032 were compared to those of Apollo-16 fieldspathic fragmental breccia 67016, using results from electron microprobe analysis and TEM. It was found that the pyroxene mineralogy and chemistry of granulitic clasts in 67016 breccia and the Y86032-type lunar meteorites were much alike, suggesting that the formation processes of the fieldspathic fragmental breccias are also important in the genesis of lunar meteorites. There were differences in matrix microtextures, however, implying that 67016 and Y86032-type breccia formation temperatures were different.

Takeda, H.↗

NASA NTRS1990

Classification of four ordinary chondrites from Spain

Based on optical microsocpy and electron microprobe analysis of mafic minerals, four previously poorly described ordinary chondrites from Spain are classified. The classifications of Guarena (H6), Olmedilla de Alarcon (H5) and Reliegos (L5) are confirmed. Molina is reclassified as H5, based on new data.

Mccoy, T. J.↗

NASA NTRS1990

A study of hydrogen environment effects on microstructure property behavior of NASA-23 alloy and related alloy systems

This work is part of the overall advanced main combustion chamber (AMCC) casting characterization program of the Materials and Processes Laboratory of the Marshall Space Flight Center. The influence of hydrogen on the tensile properties and ductility behavior of NASA-23 alloy were analyzed. NASA-23 and other referenced alloys in cast and hipped conditions were solution treated and aged under selected conditions and characterized using optical metallography, scanning electron microscopy, and electron microprobe analysis techniques. The yield strength of NASA-23 is not affected much by hydrogen under tensile tests carried at 5000 psig conditions; however, the ultimate strength and ductility properties are degraded. This implies that the physical mechanisms operating would be related to the plastic deformation process. The fracture surfaces characteristics of NASA-23 specimens tensile tested in hydrogen, helium, and air were also analyzed. These revealed surface cracks around specimen periphery with the fracture surface showing a combination of intergranular and transgranular modes of fracture. It is seen that the specimens charged in hydrogen seem to favor a more brittle fracture mode in comparison to air and helium charged specimens. The AMCC casting characterization program is to be analyzed for their hydrogen behavior. As a result of this program, the basic microstructural factors and fracture characteristics in some cases were analyzed.

Diwan, Ravinder M.↗

NASA NTRS1991

Near field interaction of microwave signals with a bounded plasma plume

The objective was to study the effect of the arcjet thruster plume on the performance of an onboard satellite reflector antenna. A project summary is presented along with sections on plasma and electromagnetic modeling. The plasma modeling section includes the following topics: wave propagation; plasma analysis; plume electron density model; and the proposed experimental program. The section on electromagnetic modeling includes new developments in ray modeling and the validation of three dimensional ray results.

Ling, Hao↗

NASA NTRS1990

Classification of five new chondrite finds from Roosevelt County, New Mexico

Five small, weathered meteorites recovered from Roosevelt County, New Mexico, USA, are called Roosevelt County 066-070. Based on optical microscopy and electron microprobe analysis of mafic minerals, RC 066-070 are classified as L5a chondrites. RC 068 and 069 are tentatively paired. RC 066 and RC 067 are not paired with RC 068 and RC 069. RC 066, 067 and 070 do not appear to be paired with each other or with RC 001-031.

Pun, Aurora↗

NASA NTRS1991

Diffusion mechanisms in Ir-coated Re for high-temperature, radiation-cooled rocket thrusters

Materials used for radiation-cooled rocket thrusters must be capable of surviving under extreme conditions of high temperatures and oxidizing environments. Thruster chambers were developed using chemical-vapor-deposited (CVD) Re coated with CVD Ir on the inside surface which is exposed to hot combustion gases. Ir serves as an oxidation barrier protecting the Re which maintains structural integrity at high temperatures. In order to predict and extend the performance limits of these Ir-coated Re thrusters, the diffusion kinetics of CVD materials at temperature are studied. Thruster end ring sections were examined using electron microprobe analysis both before and after exposure to high temperature vacuum environments. The resulting elemental maps for Re, Ir, and Mo in the near-surface region allow identification of diffusion mechanisms operating at these temperatures. Line scans for Ir and Re were fit using a diffusion model to extract relevant diffusion constants. The fastest diffusion process is seen to be grain boundary diffusion with Re diffusing down grain boundaries in the Ir overlayer. The measured dependence of the diffusion rate on temperature will allow prediction of operating lifetimes for these thrusters.

Hamilton, J. C.↗

NASA NTRS1992

Thermal degradation study of silicon carbide threads developed for advanced flexible thermal protection systems

Silicon carbide (SiC) fiber is a material that may be used in advanced thermal protection systems (TPS) for future aerospace vehicles. SiC fiber's mechanical properties depend greatly on the presence or absence of sizing and its microstructure. In this research, silicon dioxide is found to be present on the surface of the fiber. Electron Spectroscopy for Chemical Analysis (ESCA) and Scanning Electron Microscopy (SEM) show that a thin oxide layer (SiO2) exists on the as-received fibers, and the oxide thickness increases when the fibers are exposed to high temperature. ESCA also reveals no evidence of Si-C bonding on the fiber surface on both as-received and heat treated fibers. The silicon oxide layer is thought to signal the decomposition of SiC bonds and may be partially responsible for the degradation in the breaking strength observed at temperatures above 400 C. The variation in electrical resistivity of the fibers with increasing temperature indicates a transition to a higher band gap material at 350 to 600 C. This is consistent with a decomposition of SiC involving silicon oxide formation.

Tran, Huy Kim↗

NASA NTRS1993

Orbiter lessons learned: A guide to future vehicle development

Topics addressed are: (1) wind persistence loads methodology; (2) emphasize supportability in design of reusable vehicles; (3) design for robustness; (4) improved aerodynamic environment prediction methods for complex vehicles; (5) automated integration of aerothermal, manufacturing, and structures analysis; (6) continued electronic documentation of structural design and analysis; and (7) landing gear rollout load simulations.

Greenberg, Harry Stan↗

NASA NTRS1992

Heat pipe fatigue test specimen: Metallurgical evaluation

An innovative creep/fatigue test was run to simulate the temperature, mechanical load, and sodium corrosion conditions expected in a heat pipe designed to supply thermal energy to a Stirling cycle power converter. A sodium-charged Inconel 718 heat pipe with a Nickel 200 screen wick was operated for 1090 hr at temperatures between 950 K (1250 F) and 1050 K (1430 F) while being subjected to creep and fatigue loads in a servo-hydraulic testing machine. After testing, the heat pipe was sectioned and examined using optical microscopy, scanning electron microscopy, and electron microprobe analysis with wavelength dispersive x-ray spectroscopy. The analysis concentrated on evaluating topographic, microstructural, and chemical changes in the sodium exposed surfaces of the heat pipe wall and wick. Surface changes in the evaporator, condenser, and adiabatic sections of the heat pipe were examined in an effort to correlate the changes with the expected sodium environment in the heat pipe. This report describes the setup, operating conditions, and analytical results of the sodium heat pipe fatigue test.

Walak, Steven E.↗

NASA NTRS1993

Matrix and fine-grained rims in the unequilibrated CO3 chondrite, ALHA77307 - Origins and evidence for diverse, primitive nebular dust components

SEM, TEM, and electron microprobe analysis were used to investigate in detail the mineralogical and chemical characteristics of dark matrix and fine-grained rims in the unequilibrated CO3 chondrite ALHA77307. Data obtained revealed that there was a remarkable diversity of distinct mineralogical components, which can be identified using their chemical and textural characteristics. The matrix and rim components in ALHA77307 formed by disequilibrium condensation process as fine-grained amorphous dust that is represented by the abundant amorphous component in the matrix. Subsequent thermal processing of this condensate material, in a variety of environments in the nebula, caused partial or complete recrystallization of the fine-grained dust.

Brearley, Adrian J.↗