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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Petrography and petrology of basaltic achondrite polymict breccias /Howardites/

The reported investigation is based on the results from petrographic observations, electron microprobe analyses of constituent phases, and defocused beam analyses of clasts and glasses. Howardites consist of mostly angular-to-rounded mineral, rock, and breccia clasts compacted in variable grain-sized matrices of finely comminuted materials. Attention is given to ophitic and subophitic rocks, granular basalts and microgabbros, mafic rocks, Al-rich rocks, breccia clasts, impact melt rocks, glasses, meteorite clasts, bulk composition, particle size distribution, howardite component composition, questions of breccia formation, and parent body implications. It is found that the four main rock types found in howardites do have certain analogies to lunar rocks. It is tempting to speculate that both the moon and the basaltic achondrite parent body formed similar rock suites in their evolutionary processes.

Bunch, T. E.↗
NASA NTRS1979

Effects of boron and glass hybrid epoxy-composites on graphite-fiber release in an aircraft fire

Recent studies have shown that the benefits gained by using graphite-epoxy composite structures may not be realized without some risk. The graphite fibers are very good electrical conductors and fibers released into the environment during a fire create a possible hazard to electrical equipment. Several graphite-epoxy hybrids were exposed to a fire and simulated explosion and their graphite fiber retention characteristics were examined. Several low melting-temperature glasses which wet and clump graphite-fibers and a glass/graphite fabric which reduced impact damage were identified as promising hybridizing components to minimize graphite fiber release.

Tompkins, S. S.↗
NASA NTRS1993

Thermal processing of omicron-terphenyl - A Raman study

Raman spectra from omicron-terphenyl sealed in glass capillary tubes were acquired over temperatures ranging from 233 to 343 K. Over this temperature range, omicron-terphenyl can exist in the solid-crystalline, molten, supercooled-liquid, and amorphous-glassy states. Representative structure-sensitive spectra are presented along with a qualitative description. The lattice spectral feature occurring at a Raman shift of 123/cm displays abrupt changes in profile and intensity as melting and glass transition occur. The intensity ratio of the C-C stretching 996/cm line and C-H stretching line at 1008/cm displays a change related to the transformation of the ordered-crystalline phase to the disordered-liquid or glassy state. At a Raman shift of 1162/cm the solid-crystalline state shows a splitting due to the effect of the crystal field. The possibility of using these structure-sensitive Raman characteristics for in situ diagnostics during materials processing is discussed.

Biswas, A.↗
NASA NTRS2012

Glass Solder Approach for Robust, Low-Loss, Fiber-to-Waveguide Coupling

The key advantages of this approach include the fact that the index of interface glass (such as Pb glass n = 1.66) greatly reduces Fresnel losses at the fiber-to-waveguide interface, resulting in lower optical losses. A contiguous structure cannot be misaligned and readily lends itself for use on aircraft or space operation. The epoxy-free, fiber-to-waveguide interface provides an optically pure, sealed interface for low-loss, highpower coupling. Proof of concept of this approach has included successful attachment of the low-melting-temperature glass to the x-y plane of the crystal, successful attachment of the low-meltingtemperature glass to the end face of a standard SMF (single-mode fiber), and successful attachment of a wetted lowmelting- temperature glass SMF to the end face of a KTP crystal. There are many photonic components on the market whose performance and robustness could benefit from this coupling approach once fully developed. It can be used in a variety of fibercoupled waveguide-based components, such as frequency conversion modules, and amplitude and phase modulators. A robust, epoxy-free, contiguous optical interface lends itself to components that require low-loss, high-optical-power handling capability, and good performance in adverse environments such as flight or space operation.

McNeil, Shirley↗
NASA NTRS1978

Core 74001/2 - Grain size and petrology as a key to the rate of in-situ reworking and lateral transport on the lunar surface

A suite of samples from the double drive tube 74001/2 has been studied. Material from this core mainly consists of orange and black droplets interpreted to be volcanic pyroclastic ejecta. Grain size analysis indicates that this material is very homogeneous in its grain size properties. It is also the finest and best sorted suite of soil samples in the lunar collection having a mean grain size of 40 microns and a mean standard deviation of 1.75 phi. The upper 5.5 cm of this core has apparently undergone in situ reworking by meteorites over a period of about 10 million years. This reworked zone contains 'exotic' grains including basalt, mineral fragments, vitric breccias, and agglutinates. One type of agglutinate is unique and has been made primarily from orange and black glass droplets melted and welded together by micrometeorite impacts. Other agglutinates are made mainly from basaltic fragments and minerals. The amount of 'exotic' material added to the core combined with an estimate of the location of the source areas for the 'exotic' material allows us to estimate that a maximum of about 0.36 gm per sq cm of regolith surface is added from a radius of about 1 meter in 10 million years. Furthermore, no more than about 0.01 gm per sq cm of regolith surface is added from a radius of about 100 meters in 10 million years.

Mckay, D. S.↗
NASA NTRS1984

Containerless-Processing Module

High-temperature, containerless-processing module positions and melts molten glass or metal without contact with container wall. Fluid masses manipulated, stirred, and controlled by acoustic forces. Module provides photographic monitoring and transfer of solidified specimens to storage bins.

Wang, T. G.↗
NASA NTRS1984

Structure and recalescence behavior of undercooled nickel-tin alloys

The effects of undercooling on the thermal behavior and structure of Ni-Sn alloys are investigated. Hypoeutectic (Ni-25 wt pct Sn) and eutectic (Ni-32.5 wt pct Sn) compositions of the Ni-Sn alloy were undercooled using a levitation melting with glass encasement technique, and the recalescence of these alloys was measured using a high speed temperature sensing device and a digital oscilloscope. It is observed that in both samples the total solidification and recalescence times decrease with increasing undercooling; the volume fraction of normal lamellar eutectic decreases with increasing undercooling; and in the hypoeutectic sample, the morphology of the primary phase changes from dendritic to spherical with increasing undercooling.

Wu, Yanzhong↗
NASA NTRS1993

Mineralogy of chondritic interplanetary dust particle impact residues from LDEF

A detailed structural and compositional analysis of several impactor residues was performed utilizing transmission electron microscopy, energy dispersive spectroscopy, and electron diffraction. Residues from the interior of several craters in gold surfaces were removed with a tungsten needle, mounted in EMBED-812 epoxy, and ultramicrotomed. The presence in these residues of equilibrated ferromagnesian minerals, recrystallization textures, glass, and melted metal and sulfide bodies decorating grain boundaries is indicative of varying degrees of shock metamorphism in all impact residues we have characterized.

Barrett, R. A.↗
NASA NTRS1993

Multiplicity of chondrule heating events and the coarsening of chondrule textures

Our studies of compound chondrules show that most chondrules experienced at least two thermal events that produced appreciable amounts of melt. I suggest that chondrules were subjected to a hierarchy of brief heating events, the number increasing exponentially with decreasing intensity, and that some of intermediate intensity deposited enough heat to partially melt mesostasis glass and promote the growth of mafic mineral grains. This scenario can account for textures that require improbably low monotonic cooling rates in laboratory simulations, and also for the rarity of glassy chondrule textures despite the ease with which these are produced in the laboratory.

Wasson, John T.↗
NASA NTRS1994

A Chebyshev Collocation Method for Moving Boundaries, Heat Transfer, and Convection During Directional Solidification

Free and moving boundary problems require the simultaneous solution of unknown field variables and the boundaries of the domains on which these variables are defined. There are many technologically important processes that lead to moving boundary problems associated with fluid surfaces and solid-fluid boundaries. These include crystal growth, metal alloy and glass solidification, melting and name propagation. The directional solidification of semi-conductor crystals by the Bridgman-Stockbarger method is a typical example of such a complex process. A numerical model of this growth method must solve the appropriate heat, mass and momentum transfer equations and determine the location of the melt-solid interface. In this work, a Chebyshev pseudospectra collocation method is adapted to the problem of directional solidification. Implementation involves a solution algorithm that combines domain decomposition, finite-difference preconditioned conjugate minimum residual method and a Picard type iterative scheme.

Zhang, Yiqiang↗
NASA NTRS2011

Ionic Liquids to Replace Hydrazine

A method for developing safe, easy-to-handle propellants has been developed based upon ionic liquids (ILs) or their eutectic mixtures. An IL is a binary combination of a typically organic cation and anion, which generally produces an ionic salt with a melting point below 100 deg C. Many ILs have melting points near, or even below, room temperature (room temperature ionic liquids, RTILs). More importantly, a number of ILs have a positive enthalpy of formation. This means the thermal energy released during decomposition reactions makes energetic ILs ideal for use as propellants. In this specific work, to date, a baseline set of energetic ILs has been identified, synthesized, and characterized. Many of the ILs in this set have excellent performance potential in their own right. In all, ten ILs were characterized for their enthalpy of formation, density, melting point, glass transition point (if applicable), and decomposition temperature. Enthalpy of formation was measured using a microcalorimeter designed specifically to test milligram amounts of energetic materials. Of the ten ILs characterized, five offer higher Isp performance than hydrazine, ranging between 10 and 113 seconds higher than the state-of-the-art propellant. To achieve this level of performance, the energetic cations 4- amino-l,2,4-triazolium and 3-amino-1,2,4-triazolium were paired with various anions in the nitrate, dicyanamide, chloride, and 3-nitro-l,2,4-triazole families. Protonation, alkylation, and butylation synthesis routes were used for creation of the different salts.

Koelfgen, Syri↗
NASA NTRS2016

FTIR Analysis of Water in Pyroxene and Plagioclase in ALH 84001 and Nakhlites

Determining the volatile budget of the interior of Mars is crucial for our understanding of that planet's formation, geodynamics, cooling history and the origin of its volcanism and atmosphere as well as its potential for life. Surficial water is evident from spacecraft and rover data in polar caps and the atmosphere, in the presence of river channels, and in the detection of water-bearing minerals. Meteorites, however, are our best candidates for estimating the amount of water present at depth, even if all are crustal samples. The last 10 years have seen a blooming of studies measuring water and halogens in Martian meteorites. The bulk of these studies target phosphate, a typically late-stage phase in the igneous Martian meteorites that potentially would concentrate incompatible element hydrogen (H quantified traditionally as "water", i.e., H2O concentrations in weight) near the end of the crystallization sequence. However, determining the amount of water, F, and Cl in the magma from which a phosphate crystallized from is not straightforward and in most instances not possible. On the other hand, phosphates have turned out to be very useful in identifying hydrothermal processes that could have added water while or after the magma flowed and crystallized. Another caveat of analyzing Martian meteorite phases for water is that shocked phases such as maskelynite and impact melts appear to have incorporated water from the Martian atmosphere, as evidenced by high H isotope ((delta)D) signatures, and therefore their water concentrations cannot be interpreted in terms of deep planetary processes. The best candidates for estimating the water content of the Martian interior have been melt inclusions (glass or amphibole-bearing) which the enclosing mineral (usually olivine) would have prevented from exchanging volatiles with the surroundings after crystallization. Even some of these, however, have high (delta)D, meaning they were affected by H exchange via impact events or with crustal reservoirs or hydrothermal fluids. Here, nominally anhydrous minerals (pyroxene, olivine, plagioclase, or maskelynite) in orthopyroxenite ALH 84001 and selected nakhlites are analyzed for water and major elements, in order to determine 1) whether they contain any water; 2) if they do, what controls its distribution (crystallization, degassing, hydrothermal or impact processes); and 3) if any of these measurements can be used to infer the water contents of the parent magma and their mantle sources. A shock-reverberation experiment was also performed on terrestrial orthopyroxenes (opx) to simulate the heavily shocked conditions of ALH 84001 (> 31 GPa [17]).

Peslier, A. H.↗
NASA NTRS2017

Combustion Joining of Regolith Tiles for In-Situ Fabrication of Launch/Landing Pads on the Moon and Mars

To mitigate dust problems during launch-landing operations in lunar and Mars missions, it is desired to build solid pads on the surface. Recently, strong tiles have been fabricated from lunar regolith simulants using high-temperature sintering. The present work investigates combustion joining of these tiles through the use of exothermic intermetallic reactions. Specifically, nickel aluminum (1:1 mole ratio) mixture was placed in a gap between the tiles sintered from JSC-1A lunar regolith simulant. Upon ignition by a laser, a self-sustained propagation of the combustion front over the mixture occurred. Joining was improved with increasing the tile thickness from 6.3 mm to 12.7 mm. The temperatures sufficient for melting the glass phase of JSC-1A were recorded for 12.7-mm tiles, which explains the observed better joining.

Ferguson, Robert E.↗
NASA NTRS2017

Combustion Joining of Regolith Tiles for In-Situ Fabrication of Launch/Landing Pads on the Moon and Mars

To mitigate dust problems during launch/landing operations in lunar and Mars missions, it is desired to build solid pads on the surface. Recently, strong tiles have been fabricated from lunar regolith simulants using high-temperature sintering. The present work investigates combustion joining of these tiles through the use of exothermic intermetallic reactions. Specifically, nickel/aluminum (1:1 mole ratio) mixture was placed in a gap between the tiles sintered from JSC-1A lunar regolith simulant. Upon ignition by a laser, a self-sustained propagation of the combustion front over the mixture occurred. Joining was improved with increasing the tile thickness from 6.3 mm to 12.7 mm. The temperatures sufficient for melting the glass phase of JSC-1A were recorded for 12.7-mm tiles, which explains the observed better joining.

Ferguson, Robert E.↗
NASA NTRS1990

Molten (Mg0.88Fe0.12)2SiO4 at lower mantle conditions - Melting products and structure of quenched glasses

Infrared spectra of quenched magnesium silicate glasses synthesized by fusing olivine at pressures in excess of 50 GPa and temperatures greater than 2500 K demonstrate that silicon is dominantly present in four-fold coordination with respect to oxygen within these quenched glasses. This low coordination is attributed, by analogy with the structural behavior of glasses compressed at 300 K, to the instability of higher coordinations in glasses of these compositions on decompression. Spectra of glasses formed in a hydrous environment document that water is extensively soluble in melts at these high pressures and temperatures. Also, these results are consistent with the melting of (Mg0.88Fe0.12)2SiO4 compositions to liquids near pyroxene in stoichiometry under these conditions, with iron-rich magnesiowuestite being the liquidus phase.

Williams, Quentin↗
NASA NTRS1974

Apollo 17 orange glass - Textural and morphological characteristics of devitrification

Results of a study are presented concerning (1) the significance of nonexcentroradial growth textures in Apollo 17 orange glass and a comparison of these textures with those that develop in lunar and meteoritic chondrules, (2) the development and the nature of the crystalline-glass interface, and (3) the morphology and growth characteristics of olivine and of the opaque mineral oxides that result by devitrification of the orange glass. Observations of the orange glass soil are contrasted with subsequent partial melting of orange glass spherules that were incorporated into mildly metamorphosed breccias, and the quench textures that result in these larger cooling units are compared with the textures produced by supercooling of small particulate spherules. Results show that the expected changes in viscosity due to partial melting and recrystallization do not affect the shape of individual particles, and that neither the thermal gradients that need to be invoked across 20-100 micron spheres nor collision of glass particles during lava fountaining can account for the devitrification textures observed.

Haggerty, S. E.↗
NASA NTRS1978

The Luna 24 highland component

Highland lithologies represent a very small but significant component of the Luna 24 drill core. They consist predominantly of melt rocks and glasses of probable impact origin, which are distinguished from their mare counterparts by their CaO/Al2O3 (weight) ratios no more than 0.8 and Fe/(Fe + Mg) (atomic) ratios of no more than 0.4. Compositions equivalent to highland basalt dominate the melt rock and glass fraction. Minor lithologies include possible plutonic lithic and monomineralic fragments. The high proportion of highland basalt relative to the other highland lithologic types, the absence of KREEP basalts, and the low KREEP content of the highland melt rocks and glasses in the Luna 24 soil are also characteristic of the Luna 20 site located in the highland terrain south of Mare Crisium.

Bence, A. E.↗