Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “core crystallization”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS2006

Minor Elements in Nakhlite Pyroxenes: Cr in MIL00346

Nakhlites are olivine-bearing clinopyroxene cumulates. Based on petrographic characteristics, they may be divided into groups that cooled at different rates and may have been formed at different depths in a single flow. The order of cooling rate from slowest to fastest is NWA998<Lafayette < Governador Valadares ~ Nakhla < Yamato000593 < NWA817 ~ MIL03346. Nakhlite cumulus pyroxene grains consist of large cores that are nearly homogeneous in major element composition surrounded by thin rims that are zoned to Fe-rich compositions. Detailed study of these pyroxenes is important because they retain a record of the crystallization history of the nakhlite magma. Moreover, because the composition of the nakhlite parent melt cannot be directly determined, inversion of the major and minor element composition of the cumulate pyroxene cores can be used to estimate the composition of that melt. Thus it is important to understand the major and minor element zoning in the cumulus pyroxenes. While major elements are nearly homogeneous, minor elements exhibit distinctive zoning patterns that vary from one nakhlite to another. This paper reports unusual Cr zoning patterns in pyroxenes from MIL03346 (MIL) and contrast these with pyroxenes from Y593.

McKay, G. A.↗
NASA NTRS2006

Additional Complexities in Nakhlite Pyroxenes: A Progress (?) Report

Nakhlites are olivine-bearing clinopyroxene cumulates [e.g., 1]. Based on petrographic characteristics, they may be divided into groups that cooled at different rates and may have been formed at different depths in a single flow [e.g., 2, 3]. The order of cooling rate is Lafayette < Governador Valadares ~ Nakhla < Yamato000593 < NWA817 ~ MIL03346. Nakhlite cumulus pyroxene grains consist of large cores that are nearly homogeneous in major element composition surrounded by thin rims that are zoned to Fe-rich compositions. Detailed study of these pyroxenes is important because they retain a record of the crystallization history of the nakhlite magma. Moreover, because the composition of the nakhlite parent melt cannot be directly determined, inversion of the major and minor element composition of the cumulate pyroxene cores can be used to estimate the composition of that melt. Thus it is important to understand the major and minor element zoning in the cumulus pyroxenes. We recently reported complications in the minor element zoning of nakhlite pyroxenes, especially for Al and Cr [4]. This abstract reports additional complications noted since that report.

McKay, G.↗
NASA NTRS1978

Petrology of a sequence of pyroclastic rocks from the valley of Taurus-Littrow /Apollo 17 landing site/

Thirteen samples of core 74001/2, collected at Shorty Crater by Apollo 17, have been analyzed. The samples, taken from the core section below 5.5 cm and representing most of the major stratigraphic units described by Nagle (1978), consist entirely of whole and fragmented orange and black droplets. The grain shape, degree of crystallinity, breakage, vesicularity, predominant olivine shapes, and phenocryst content of about 18,000 droplets were investigated. The crystalline droplets were found to contain olivine and ilmenite as major phases and pyroxene, Cr-spinel and metallic Fe as minor phases. The grain shape, degree of crystallization, olivine shape and olivine composition suggest that a wide range of cooling rates is represented. The upper part of the core section (above 5.5 cm) has undergone in situ reworking by micrometeorites. The 74001/2 samples are believed to be from an ultramafic pyroclastic deposit brought to the surface by the Shorty Crater impact and originally formed by a lava fountain active in the Taurus-Littrow valley 3.5 b.y. ago. The sequence represented in the sample was most likely deposited over a very short period of time.

Heiken, G.↗
NASA NTRS1972

Petrology of basaltic and monomineralic soil fragments from the Sea of Fertility.

Basaltic and monomineralic fragments from the 150-425 micron size fractions of the Luna 16 core obtained from the Sea of Fertility were studied by optical petrographic, electron microprobe, and single-crystal X-ray diffraction techniques. Three textural varieties were identified in the basalts (intersertal, subophitic, and recrystallized). These textures, the assemblages, and individual mineral compositions (especially pyroxenes) indicate that these basalts crystallized under conditions very similar to those from Apollo 11. The pyroxenes have slightly lower Ti/Al (atomic) ratios than the Apollo 11 pyroxenes. We interpret the presence of octahedral Al as being due to the low TiO2/Al2O3 (weight %) ratio in the bulk rock. All observations made on the fine-grained basalt fragments are consistent with a rapid, near-surface, one-stage crystallization history.

Bence, A. E.↗
NASA NTRS1990

Petrology and mineralogy of Type II, FeO-rich chondrules in Semarkona (LL3.0) - Origin by closed-system fractional crystallization, with evidence for supercooling

The petrology of type II porphyritic olivine chondrules in Semarkona (LL3.0) has been studied in detail. Olivines in these chondrules are euhedral, Fe-rich, and are strongly zoned from cores to rims of grains in FeO (Fa10-30), Cr2O3 (0.2-0.6 wt pct), MnO (0.2-0.7 wt pct), and CaO (0.1-0.4 wt pct). Interstitial mesostasis is rich in Si, Al, and Ca and is glassy with abundant microcrystallites. Minor minerals include troilite, Fe,Ni metal, and chromite. Some olivine grains contain euhedral, fayalite-rich cores that are probably produced during initial supercooling of the chondrule melt. Rare relict grains of forsteritic olivine have compositions very similar to olivines in type IA chondrules in Semarkona and may result from disaggregation of such chondrules. Apart from these relics, all properties of type II chondrules can be described by closed-system fractional crystallization of droplets which were essentially entirely molten. Type IA chondrules may have formed from type II chondrules by loss of Fe and volatiles. Alternatively, the two chondrule types may have formed in regions of considerable diversity in the solar nebula from precursor materials with different Fe/Mg ratios.

Jones, Rhian H.↗
NASA NTRS1972

Some textures in Apollo 12 lunar igneous rocks and in terrestrial analogs.

The interpretation of immature crystallization and some lunar textures characterized by it are the principal objectives of this investigation. A comparative and selective approach is adopted, and particular reference is made to the form and textural relations of olivine in 12009 and of pyroxenes and plagioclase in 12021, and to terrestrial analogs. The optic orientation of the olivines in 12009 is determined, and their skeletal crystallization is illustrated and evaluated. Microprobe and optical data are associated in a textural analysis of an analog from the upper contact of a minor intrusion in Skye. The optic orientation of pyroxene enclosed in plagioclase cores is determined, and the results are plotted stereographically. The need for greater precision in the use of textural terms is stressed, and a new term - intrafasciculate - is introduced for textures in which pyroxene has crystallized within hollow, skeletal plagioclase. Apollo 12 pyroxene-phyric basalts are texturally reviewed, and the crystallization of the phenocrysts is discussed, emphasis being placed on size-independence of skeletal growth.

Drever, H. I.↗
NASA NTRS1993

High-Pressure Equation of State for Partially Ionic Solids

Recently, we showed that the cohesive energy of partially ionic solids may be characterized by a two-term energy relationship consisting of a Coulomb term arising from the valence-charge transfer delta Z between the atoms, and a scaled universal energy function E(sup *)(a(sup *)), which accounts for the partially covalent character of the bond and for the repulsion between the atomic cores for small R; a(sup *) is a scaled length. Normalized cohesive-energy curves of alkali halide crystals and of Ti and Ag halide crystals were obtained, and the cohesive-energy-curve parameters were used to generate theoretical equation-of-state (EOS) curves for the Li, Na, K, Cs, and Ag halides. Good agreement was obtained with the experimental isothermal compression curves over a wide pressure range (0-90 kbar). In this paper we verify that the cohesive-energy relationship is valid for divalent partially ionic solids; physically reasonable charge-transfer values (1.80 less than delta Z less than 2.0) are obtained for MgO, CaO, and CaS. Next, EOS curves for LiF, NaF, Nal, CsCl, Csl, MgO, CaO, and CaS are generated in terms of the cohesive-energy parameters. These EOS's yield excellent fits to experimental isothermal-compression data and to shock-wave data to very high pressures (P(sub max)= 250-1350 kbar).

Schlosser, Herbert↗
NASA NTRS1999

Static Magnetic Fields in Semiconductor Floating-Zone Growth

Heat and mass transfer in semiconductor float-zone processing are strongly influenced by convective flows in the zone, originating from sources such as buoyancy convection, thermocapillary (Marangoni) convection, differential rotation, or radio frequency heating. Because semiconductor melts are conducting, flows can be damped by the use of static magnetic fields to influence the interface shape and the segregation of dopants and impurities. An important objective is often the suppression of time-dependent flows and the ensuing dopant striations. In RF-heated Si-FZ - crystals, fields up to O.STesla show some flattening of the interface curvature and a reduction of striation amplitudes. In radiation-heated (small-scale) SI-FZ crystals, fields of 0.2 - 0.5 Tesla already suppress the majority of the dopant striations. The uniformity of the radial segregation is often compromised by using a magnetic field, due to the directional nature of the damping. Transverse fields lead to an asymmetric interface shape and thus require crystal rotation (resulting in rotational dopant striations) to achieve a radially symmetric interface, whereas axial fields introduce a coring effect. A complete suppression of dopant striations and a reduction of the coring to insignificant values, combined with a shift of the axial segregation profile towards a more diffusion-limited case, are possible with axial static fields in excess of 1 Tesla. Strong static magnetic fields, however, can also lead to the appearance of thermoelectromagnetic convection, caused by the interaction of thermoelectric currents with the magnetic field.

Croll, Arne↗
NASA NTRS2017

Grain Size-Dependent Crystal Plasticity Constitutive Model for Polycrystal Materials

A new method to introduce grain size-dependence in classical crystal plasticity constitutive model is developed by considering the resistance to dislocation motion in the grain boundary influence region as equivalent to that of a work hardening. A general framework for the size-dependent constitutive model is derived by implementing this method on a core and mantle model. The work hardening, equivalent to grain boundary effect, is realized by introducing a fictitious, pre-existing, plastic strain grain boundary influence region (mantle) following the principles of classical crystal plasticity. This fictitious plastic strain, in effect, increases the yield strength and decreases the initial hardening coefficient of the grain. With the thickness of grain boundary influence region and the distribution of introduced plastic strain remaining the same, the grain boundary effect increased as the grain size becomes smaller. A simplified model that considers the grain boundary effect on a grain average sense is also developed under this general framework. Implementation of this general framework to the specific cases of crystal plasticity constitutive models is demonstrated by considering the case of power law flow rule and hyperbolic-secant hardening rule. Finally, the grain size-dependent constitutive model is validated by comparing the predicted stress-strain behavior of polycrystal samples with different average grain sizes under uniaxial loading with the experimental results.

Grain Size↗
NASA NTRS1988

Compositional study of a suite of samples from the 28-t Armanty (Xinjiang) iron meteorite

Neutron activation analysis of 15 samples from widely separated locations on the surface of the 28-t Armanty (Xinjiang) group-IIIE iron meteorite showed no compositional variations attributable to magmatic fractionation processes such as fractional crystallization. The homogeneity contrasts with that observed in the Cape York IIIAB iron, in keeping with the idea that the latter is an exceptional case. From the maximum compositional gradients the radius of the IIIE core is estimated at greater than 1 km. One sample taken from a surface formed by fracture associated with its fall to Earth is slightly anomalous in composition. It is suggested that this region is near the border between two parental gamma crystals and has a high content of minor phases.

Wasson, John T.↗
NASA NTRS1989

Meteoritic basalts

The objectives were to: explain the abundances of siderophile elements in the SNC meteorite suite, of putative Martian origin; discover the magmatic origins and possibly magma compositions behind the Nakhla meteorite, one of the SNC meteorites; and a re-evaluation of the petrology of Angra dos Reis, a unique meteorite linked to the earliest planetary bodies of the solar nebula. A re-evaluation of its petrography showed that the accepted scenario for its origin, as a cumulate igneous rock, was not consistent with the meteorite's textures (Treiman). More likely is that the meteorite represents a prophyritic igneous rock, originally with magma dominant. Studies of the Nakhla meteorite, of possible Martian origin, although difficult, were successful. It became necessary to reject the basic categorization of Nakhla: that is was a cumulate igneous rock. Detailed studies of the chemical zoning of Nakhlas' minerals, coupled with the failure of experimental studies to yield expected results, forced the conclusion that Nakhla is not a cumulate rock in the usual sense: a rock composed of igneous crystals and intercrystal magma. Study of the siderophile element abundances in the SNC meteorite groups involved trying to find reasonable core formation processes and parameters that would reproduce the observed abundances. Modelling was successful, and delimited a range of models which overlap with those reasonable from geophysical constraints.

Treiman, Allan H.↗
NASA NTRS1993

An alternative representation of the ice canopy for calculating microwave brightness temperatures over a thunderstorm

Passive microwave brightness temperatures (TBs) at 92 and 183 GHz from an aircraft thunderstorm overflight are compared with values calculated from radar-derived hydrometeor profiles and a modified proximity sounding. Two methods for modeling particles in the ice canopy are contrasted. The first is a 'traditional' approach employing Marshall-Palmer ice spheres. The second, or 'alternative', method partitions 20 percent of the ice water content into a Marshall-Palmer component for graupel and hail, and 80 percent into a modified gamma spherical particle size distribution function representing ice crystals. Results from the alternative approach are superior to those from the traditional method in the anvil and mature convective core. In the decaying convective region, the traditional approach yields better agreement with observed magnitudes. Neither method, however, matches the geometry of the observed TB depression associated with the decaying convective core. This is likely due to the presence of graupel, which is not detected as a special signature in radar reflectivity, but does diminish TBs through scattering. Brightness temperatures at the relatively high microwave frequencies considered are shown to be very sensitive to the ice-particle size distribution.

Muller, Bradley M.↗
NASA NTRS2007

Liquidus Phases of the Richardson H5 Chondrite at High Pressures and Temperatures

Part of early mantle evolution may include a magma ocean, where core formation began before the proto-Earth reached half of its present radius. Temperatures were high and bombardment and accretion were still occurring, suggesting that the proto-Earth consisted of a core and an at least partially liquid mantle, the magma ocean. As the Earth accreted, pressure near the core increased and the magma ocean decreased in volume and became shallower as it began to cool and solidify. As crystals settled, or floated, the composition of the magma ocean could change significantly and begin to crystallize different minerals from the residual liquid. Therefore, the mantle may be stratified following the P-T phase diagram for the bulk silicate Earth. To understand mantle evolution, it is necessary to know liquidus phase relations at high pressures and temperatures. In order to model the evolution of the magma ocean, high pressure and temperature experiments have been conducted to simulate the crystallization process using a range of materials that most likely resemble the bulk composition of the early Earth.

Channon, M.↗
NASA NTRS2017

Examining the Possibility of Carbon as a Light Element in the Core of Mercury

Results from the MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) spacecraft have shown elevated abundances of C on the surface of Mercury. Peplowski et al. used GRS data from MESSENGER to show an average northern hemisphere abundance of C on the planet of 0 to 4.1 wt% C at the three-sigma detection limit. Confirmation of C on the planet prompts many questions regarding the role of C during the differentiation and evolution of Mercury. The elevated abundances of both S and C on Mercury's surface, coupled with the low abundances of iron, suggest that the oxygen fugacity of the planet is several log10 units below the Iron-Wustite buffer. These observations spark questions about the bulk composition of Mercury's core. This experimental study seeks to understand the impact of C as a light element on potential mercurian core compositions. In order to address this question, experiments were conducted at 1 GPa and a variety of temperatures (700 - 1500 C) on metal compositions ranging from Si5Fe95 to Si22Fe78, possibly representative of the mercurian core. All starting metals were completely enclosed in a graphite capsule to ensure C saturation at a given set of run conditions. All elements, including C, were analyzed using electron probe microanalysis. Precautions were taken to ensure accurate measurements of C with this technique including using the LDE2 crystal, the cold finger on the microprobe to minimize contamination and increase the vacuum, and an instrument with no oil based pumps. Based on the superliquidus experimental results in the present study, as Fe-rich cores become more Si-rich, the C content of that core composition will decrease. Furthermore, although C concentration at graphite saturation (CCGS) varies from a liquid to a solid, temperature does not seem to play a substantial role in CCGS, at least at 1 GPa.

Vander Kaaden, Kathleen↗
NASA NTRS1982

UHV studies of the interaction of CO with small supported metal particles, Pd/mica

The interaction of carbon monoxide with small palladium particles supported on UHV-cleaved and heat-treated single-crystal mica was studied. The Pd particles were characterized and tested using the techniques of flash thermal desorption, Auger electron spectroscopy, core electron energy loss spectroscopy, and transmission electron microscopy. Evidence is presented for CO decomposition on Pd particles during CO adsorption-desorption experiments. The rate of CO decomposition increased rapidly with diminishing particle size. Residual carbon from CO decomposition blocked CO adsorption and had a strong poisoning effect on the CO oxidation reaction.

Doering, D. L.↗
NASA NTRS2007

Oxidation State of Nakhlites as inferred from Fe-Ti oxide Equilibria and Augite/Melt Europium Partitioning

Recent studies have shown that Martian magmas had wide range of oxygen fugacities (fO2) and that this variation is correlated with the variation of La/Yb ratio and isotopic characteristics of the Martian basalts, shergottite meteorites. The origin of this correlation must have important information about mantle sources and Martian evolution. In order to understand this correlation, it is necessary to know accurate value of oxidation state of other Martian meteorite groups. Nakhlites, cumulate clinopyroxenites, are another major group of Martian meteorites and have distinctly different trace element and isotopic characteristics from shergottites. Thus, estimates of oxidation state of nakhlites will give us important insight into the mantle source in general. Several workers have estimated oxidation state of nakhlites by using Fe-Ti oxide equilibrium. However, Fe-Ti oxides may not record the oxidation state of the parent melt of the nakhlite because it is a late-stage mineral. Furthermore, there is no comprehensive study which analyzed all nakhlite samples at the same time. Therefore, in this study (1) we reduced the uncertainty of the estimate using the same electron microprobe and the same standards under the same condition for Fe-Ti oxide in 6 nakhlites and (2) we also performed crystallization experiments to measure partition coefficients of Eu into pyroxene in the nakhlite system in order to estimate fO2 when the pyroxene core formed (i.e. Eu oxybarometer [e.g. 2,6]).

Makishima, J.↗
NASA NTRS1976

Lafayette meteorite - Petrology and opaque mineralogy

The Lafayette meteorite is a calcium-rich achondrite composed predominantly of cumulus clinopyroxene with minor iron-rich olivine and rare interstitial feldspar. The opaque oxide minerals are magnetite-ilmenite intergrowths, an apparently homogenous Cr-rich titaniferous magnetite, and discrete ilmenite. Pyrite, the major sulfide mineral, occasionally displays lamellar intergrowths of marcasite that appear to be of primary origin. Troilite occurs as inclusions in ilmenite or interstitial to the silicate minerals. Bulk chemical composition of the glass in the fusion crust is comparable with that of the Nakhla meteorite. The glass contains abundant skeletal crystals of magnetite as well as very rare, zoned magnetite grains with rims enriched in Mg and depleted in Ti relative to the cores. Although no brecciation is visible in the Lafayette meteorite, the presence of deformed twin lamellae in the clinopyroxene indicates some deformation has occurred.

Boctor, N. Z.↗
NASA NTRS2006

Ingestible Thermometer Pill Aids Athletes in Beating the Heat

Developed by Goddard Space Flight Center and the Johns Hopkins University Applied Physics Laboratory to monitor the core body temperature of astronauts during space flight, the ingestible "thermometer pill" has a silicone-coated exterior, with a microbattery, a quartz crystal temperature sensor, a space-aged telemetry system, and microminiaturized circuitry on the interior.

Source record↗