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At least 145 records · Page 8

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NASA NTRS1982

Primary igneous carbon in ureilites - Petrological implications

The ureilite meteorites are carbonaceous olivine-pyroxene achondrites. They typically contain up to 4 wt.% carbon (carbonaceous matrix) as graphite, diamond, and lonsdaleite. Shock degradation has effectively obliterated primary textures in the carbonaceous matrix of previously described ureilites, a factor that has hampered efforts to explain the origin of this material. In contrast, the Antarctic ureilite ALHA78019 displays perfectly preserved primary textures in the carbonaceous matrix characterized by euhedral graphite blades intergrown with Fe-Ni metal and sulfide (diamonds are absent). This petrographic feature suggests that most graphite in ureilites originated by crystallization from a C-rich metallic phase. Assuming that fO2 is controlled by C-CO-CO2 reactions, the compositions of silicates and metals in ureilites imply a two-stage redox history. The noble gases and rare earths of ureilites are discussed in light of this model.

Berkely, J. L.↗

NASA NTRS1998

Method for Surface Texturing Titanium Products

The present invention teaches a method of producing a textured surface upon an arbitrarily configured titanium or titanium alloy object for the purpose of improving bonding between the object and other materials such as polymer matrix composites and/or human bone for the direct in-growth of orthopaedic implants. The titanium or titanium alloy object is placed in an electrolytic cell having an ultrasonically agitated solution of sodium chloride therein whereby a pattern of uniform "pock mark" like pores or cavities are produced upon the object's surface. The process is very cost effective compared to other methods of producing rough surfaces on titanium and titanium alloy components. The surface textures produced by the present invention are etched directly into the parent metal at discrete sites separated by areas unaffected by the etching process. Bonding materials to such surface textures on titanium or titanium alloy can thus support a shear load even if adhesion of the bonding material is poor.

Banks, Bruce A.↗

NASA NTRS1996

Development of Y-Ba-Cu-O Superconductors for Magnetic Bearings

The material requirements, material manufacturing and magnetic properties that are relevant to fabrication of High Temperature Superconductor (HTS) magnetic bearings have been discussed. It is found that the seeded-melt-texturing method can be used to fabricate the single domain material that is required to achieve the best magnetic properties. Trapped-field mapping has been used as a non-destructive tool to determine the single-domain nature of the HTS material and quantity of the HTS disks. Both the trapped field and the levitation force of the Y-Ba-Cu-O disks are found to be strongly sensitive to the oxygen content.

Selvamanickam, V.↗

NASA NTRS1974

TDNiCr (ni-20Cr-2ThO2) forging studies

Elevated temperature tensile and stress rupture properties were evaluated for forged TDNiCr (Ni-20Cr-2ThO2) and related to thermomechanical history and microstructure. Forging temperature and final annealed condition had pronounced influences on grain size which, in turn, was related to high temperature strength. Tensile strength improved by a factor of 8 as grain size changed from 1 to 150 microns. Stress-rupture strength was improved by a factor of 3 to 5 by a grain size increase from 10 to 1000 microns. Some contributions to the elevated temperature strength of very large grain material may also occur from the development of a strong texture and a preponderance of small twins. Other conditions promoting the improvement of high temperature strength were: an increase of total reduction, forging which continued the metal deformation inherent in the starting material, a low forging speed, and prior deformation by extrusion. The mechanical properties of optimally forged TDNiCr compared favorably to those of high strength sheet developed for space shuttle application.

Filippi, A. M.↗

NASA NTRS2016

Petrogenesis of Igneous-Textured Clasts in Martian Meteorite Northwest Africa 7034

The martian meteorite Northwest Africa 7034 (and pairings) is a breccia that samples a variety of materials from the martian crust. Several previous studies have identified multiple types of igneous-textured clasts within the breccia [1-3], and these clasts have the potential to provide insight into the igneous evolution of Mars. One challenge presented by studying these small rock fragments is the lack of field context for this breccia (i.e., where on Mars it formed), so we do not know how many sources these small rock fragments are derived from or the exact formation his-tory of these sources (i.e., are the sources mantle de-rived melt or melts contaminated by a meteorite impactor on Mars). Our goal in this study is to examine specific igneous-textured clast groups to determine if they are petrogenetically related (i.e., from the same igneous source) and determine more information about their formation history, then use them to derive new insights about the igneous history of Mars. We will focus on the basalt clasts, FTP clasts (named due to their high concentration of iron, titanium, and phosphorous), and mineral fragments described by [1] (Fig. 1). We will examine these materials for evidence of impactor contamination (as proposed for some materials by [2]) or mantle melt derivation. We will also test the petrogenetic models proposed in [1], which are igneous processes that could have occurred regardless of where the melt parental to the clasts was formed. These models include 1) derivation of the FTP clasts from a basalt clast melt through silicate liquid immiscibility (SLI), 2) derivation of the FTP clasts from a basalt clast melt through fractional crystallization, and 3) a lack of petrogenetic relationship between these clast groups. The relationship between the clast groups and the mineral fragments will also be explored.

Santos, A. R.↗

NASA NTRS1984

Dynamic crystallization of silicate melts

Two types of furnaces with differing temperature range capabilities were used to provide variations in melt temperatures and cooling rates in a study of the effects of heterogeneous nucleation on crystallization. Materials of chondrule composition were used to further understanding of how the disequilibrium features displayed by minerals in rocks are formed. Results show that the textures of natural chondrules were duplicated. It is concluded that the melt history is dominant over cooling rate and composition in controlling texture. The importance of nuclei, which are most readily derived from preexisting crystalline material, support an origin for natural chondrules based on remelting of crystalline material. This would be compatible with a simple, uniform chondrule forming process having only slight variations in thermal histories resulting in the wide range of textures.

Russell, W. J.↗

NASA NTRS1977

Polarimetry of satellite surfaces

Available polarization observations of the satellites are reviewed, and the question of what information about satellite surfaces such observations contain is discussed critically. For satellites with negligible atmospheres, polarization measurements should provide useful information on surface texture and on the opacity of the surface materials. However, they are unlikely to yield specific compositional information. For Titan, the only satellite known to have an extensive atmosphere, polarimetry indicates the presence of optically thick clouds; it should be possible to deduce the cloud particle characteristics from such data, especially if more extensive observations, covering the full range of available phase angles and wavelengths, are obtained.

Veverka, J.↗

NASA NTRS1989

An olivine-microchondrule-bearing clast in the Krymka meteorite

A small (150 x 200-micron-size) clast consisting of 20 vol pct olivine microchondrules (with barred and granular textures) and 80 vol pct recrystallized silicate matrix material occurs in Krymka (LL3.1). This is the fourth microchondrule-bearing clast to be described. The chondrules are zoned in FeO with concentrations increasing toward the surface. The clast most closely resembles a previously described radial-pyroxene-microchondrule-bearing clast in Piancaldoli (LL3.4).

Rubin, Alan E.↗

NASA NTRS2011

Organic Carbon Features Identified in the Nakhla Martian Meteorite

We report, for the first time, the identification of specific carbonaceous phases, present within iddingsite alteration zones of the Nakhla meteorite that possess discrete, well defined, structurally coherent morphologies. These structures bear superficial similarity to the carbonaceous nanoglobules [1] found in primitive chondrites interplanetary dust particles, although they are an order-of-magnitude larger in size. Introduction: It has been known for many years that some members of the Martian meteorite clan contain organic matter [e.g., 2-4]. Based on both isotopic measurements [5] and circumstantial observations [4] (e.g., the similarity organic signatures present in both Antarctic finds and non-Antarctic falls) a credible argument has been made for a preterrestrial origin for the majority of these organics. The Nakhla meteorite is of particular interest in that it has been shown to contain both an acid-labile organic fraction as well as an acid-insoluble high molecular weight organic component [4]. Pyrolysis-gas chromatography-mass spectrometry of the latter component indicates it to be composed of aromatic and alkyl-aromatic functionalities bound into a macromolecule phase through ether linkages [4]. However, the spatial, textural and mineralogical associations of this carbonaceous macromolecular material have remained elusive [6].

Mckay, D. S.↗

NASA NTRS1974

Rock 14318 - A polymict lunar breccia with chondritic texture

Rock 14318 is a complex microbreccia consisting of lithic fragments, chondrules, glass spherules, and glass and mineral fragments that are embedded into a fine-grained, partly glassy matrix. Compositions of lithic fragments, glasses and chondrules, in terms of compositional rock and rock suite equivalents, represent members of the ANT (anorthositic-noritic-troctolite) suite; the alkalic high-alumina basalt (KREEP) group; high-alkali quartz basalt; basalt; and dunite. The polymict nature of many lithic fragments suggests that rock 14318 requires at least two, and probably more, impact episodes for its formation. Final agglomeration took place while part of the material was hot, as is indicated by the welded texture, suggesting that the final impact event was a large one, producing a fiery cloud similar to a nuee ardente. The close similarity in texture of lunar rock 14318 to certain polymict-brecciated meteorites such as Siena suggests that meteorites of this type were also formed by complex and successive impact events on the surface of the meteorite parent body, rather than during agglomeration of the parent body.

Kurat, G.↗

NASA NTRS1978

Ion beam technology applications study

Specific perceptions and possible ion beam technology applications were obtained as a result of a literature search and contact interviews with various institutions and individuals which took place over a 5-month period. The use of broad beam electron bombardment ion sources is assessed for materials deposition, removal, and alteration. Special techniques examined include: (1) cleaning, cutting, and texturing for surface treatment; (2) crosslinking of polymers, stress relief in deposited layers, and the creation of defect states in crystalline material by ion impact; and (3) ion implantation during epitaxial growth and the deposition of neutral materials sputtered by the ion beam. The aspects, advantages, and disadvantages of ion beam technology and the competitive role of alternative technologies are discussed.

Sellen, J. M., Jr.↗

NASA NTRSDate not supplied

Computational Characterization and Model Verification for 3D Microstructure Reconstruction of Additively-Manufactured Materials

The goal of this study is to characterize and validate the texture and grain topology of additively-manufactured anisotropic three-dimensional (3D) polycrystalline microstructures. The special focus is on developing methodologies to compare the grain shapes and orientations of two-dimensional (2D) and 3D microstructure representations using the same metric. To generate statistical data, synthetic microstructures are reconstructed from experimental data using Markov random field (MRF). The statistical similarity between the experimental and synthetic microstructures is verified by comparing their grain topologies. A universal measure to compare 2D and 3D grains is portrayed through the concept of image moments that are invariant to shape transformations. The graphical plots developed based on moment invariants to compare the 2D and 3D grains are used to verify the synthetic model

Materials Characterization↗

NASA NTRS1992

Unusual materials effects observed on the thermal control surfaces experiment (S0069)

A number of unusual effects were observed on the Thermal Control Surfaces Experiment (TCSE) test samples, front cover, and structural components. These effects include atomic oxygen (AO) texturing of the exposed surface of the silver Teflon (Ag/FEP) thermal control material, 'brownish' discoloration of the Ag/FEP material, changes in fluorescence of thermal control paint samples, and meteoroid/debris impact effects on silver Teflon.

Zwiener, James M.↗

NASA NTRS1975

Characteristics of metal particles in Apollo 16 rocks

It is pointed out that FeNi metal particles, composed predominantly of kamacite and ranging in size from less than 1 micron to more than 2 mm across, are ubiquitous in the lunar samples returned by the Apollo and Luna missions. The metal particles seldom exceed 1% of the volume of a lunar sample. However, their study has proven to be of considerable potential value in a number of aspects of lunar petrogenesis related to thermal history, equilibration temperatures, reduction processes and oxygen fugacities during magmatic crystallization and subsolidus reduction and oxidation, and the meteoritic component of lunar rocks based on Ni-Co contents of individual metal particles. Detailed studies have been conducted of the textures and compositions of the metal particles in 19 Apollo 16 rock samples representing material from the North Ray and the South Ray ejecta and/or fall-back blankets. It was found that the textures and compositions of the metal particles in the Apollo 16 rocks can be correlated with their host petrology.

Misra, K. C.↗

NASA NTRS1982

Surface texturing of fluoropolymers

A method is disclosed for improving surface texture for adhesive bonding, metal bonding, substrate plating, decal substrate preparation, and biomedical implant applications. The surface to be bonded is dusted in a controlled fashion to produce a disbursed layer of fine mesh particles which serve as masks. The surface texture is produced by impinging gas ions on the masked surface. The textured surface takes the form of pillars or cones. The bonding material, such as a liquid epoxy, flows between the pillars which results in a bond having increased strength. For bonding metals a thin film of metal is vapor or sputter deposited onto the textured surface. Electroplating or electroless plating is then used to increase the metal thickness in the desired amount.

Banks, B. A.↗

NASA NTRS2003

Experimental Simulation of Shock Reequilibration of Fluid Inclusions During Meteorite Impact

Fluid inclusions are microscopic volumes of fluid trapped within minerals as they precipitate. Fluid inclusions are common in terrestrial minerals formed under a wide array of geological settings from surface evaporite deposits to kimberlite pipes. While fluid inclusions in terrestrial rocks are the rule rather than the exception, only few fluid inclusion-bearing meteorites have been documented. The rarity of fluid inclusions in meteoritic material may be explained in two ways. First, it may reflect the absence of fluids (water?) on meteorite parent bodies. Alternatively, fluids may have been present when the rock formed, but any fluid inclusions originally trapped on the parent body were destroyed by the extreme P-T conditions meteorites often experience during impact events. Distinguishing between these two possibilities can provide significant constraints on the likelihood of life on the parent body. Just as textures, structures, and compositions of mineral phases can be significantly altered by shock metamorphism upon hypervelocity impact, fluid inclusions contained within component minerals may be altered or destroyed due to the high pressures, temperatures, and strain rates associated with impact events. Reequilibration may occur when external pressure-temperature conditions differ significantly from internal fluid isochoric conditions, and result in changes in fluid inclusion properties and/or textures. Shock metamorphism and fluid inclusion reequilibration can affect both the impacted target material and the meteoritic projectile. By examining the effects of shock deformation on fluid inclusion properties and textures we may be able to better constrain the pressure-temperature path experienced by shocked materials and also gain a clearer understanding of why fluid inclusions are rarely found in meteoritic samples.

Madden, M. E. Elwood↗

NASA NTRS1978

Phobos - Photometry and origin of dark markings on crater floors

Viking Orbiter 1 close encounter pictures of Phobos reveal unusual dark patches on the floors of many craters. Photometry of these features indicates that they have a similar normal reflectance but a phase coefficient 30% larger than the average surface. These facts suggest that the 'dark' material has a similar composition but a much rougher texture than the average surface of Phobos. By analogy with terrestrial impact, explosion and laboratory craters, the dark patches are interpreted as impact generated melt pools which remain visible on Phobos due to the low value of g and consequent small amount of fallback ejecta and slumping. Since blanketing by ejecta from subsequent impacts and micrometeoroid erosion should eventually obliterate such features, they should be more conspicuous in the fresher craters. Similar features should be visible on small asteroids and other low g bodies. However, they are not prominent on the surface of Deimos - possibly because most of the craters imaged at high resolution on the outer satellite appear to have been blanketed by several meters of fine-grained material.

Goguen, J.↗

NASA NTRS2015

Interstellar and Solar System Organic Matter Preserved in Interplanetary Dust

Interplanetary dust particles (IDPs) collected in the Earth's stratosphere derive from collisions among asteroids and by the disruption and outgassing of short‐period comets. Chondritic porous (CP) IDPs are among the most primitive Solar System materials. CP‐IDPs have been linked to cometary parent bodies by their mineralogy, textures, C‐content, and dynamical histories. CP‐IDPs are fragile, fine‐grained (less than um) assemblages of anhydrous amorphous and crystalline silicates, oxides and sulfides bound together by abundant carbonaceous material. Ancient silicate, oxide, and SiC stardust grains exhibiting highly anomalous isotopic compositions are abundant in CP‐IDPs, constituting 0.01 - 1 % of the mass of the particles. The organic matter in CP‐IDPs is isotopically anomalous, with enrichments in D/H reaching 50x the terrestrial SMOW value and 15N/14N ratios up to 3x terrestrial standard compositions. These anomalies are indicative of low T (10‐100 K) mass fractionation in cold molecular cloud or the outermost reaches of the protosolar disk. The organic matter shows distinct morphologies, including sub‐um globules, bubbly textures, featureless, and with mineral inclusions. Infrared spectroscopy and mass spectrometry studies of organic matter in IDPs reveals diverse species including aliphatic and aromatic compounds. The organic matter with the highest isotopic anomalies appears to be richer in aliphatic compounds. These materials also bear similarities and differences with primitive, isotopically anomalous organic matter in carbonaceous chondrite meteorites. The diversity of the organic chemistry, morphology, and isotopic properties in IDPs and meteorites reflects variable preservation of interstellar/primordial components and Solar System processing. One unifying feature is the presence of sub‐um isotopically anomalous organic globules among all primitive materials, including IDPs, meteorites, and comet Wild‐2 samples returned by the Stardust mission.

Messenger, Scott↗