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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.

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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

Sampling the Uppermost Surface of Airless Bodies

The uppermost surface of an airless body is a critical source of ground-truth information for the various remote sensing techniques that only penetrate nanometers to micrometers into the surface. Such samples will also be vital for understanding conditions at the surface and acquiring information about how the body interacts with its environment, including solar wind interaction, grain charging and levitation [1]. Sampling the uppermost surface while preserving its structure (e.g. porosity, grain-to-grain contacts) however, is a daunting task that has not been achieved on any sample return mission to date.

Noble, S. K.↗
NASA NTRS2013

Curiosity's Mars Hand Lens Imager (MAHLI): Inital Observations and Activities

MAHLI (Mars Hand Lens Imager) is a 2-megapixel focusable macro lens color camera on the turret on Curiosity's robotic arm. The investigation centers on stratigraphy, grain-scale texture, structure, mineralogy, and morphology of geologic materials at Curiosity's Gale robotic field site. MAHLI acquires focused images at working distances of 2.1 cm to infinity; for reference, at 2.1 cm the scale is 14 microns/pixel; at 6.9 cm it is 31 microns/pixel, like the Spirit and Opportunity Microscopic Imager (MI) cameras.

Mars Science Laboratory (MSL)↗
NASA NTRS2018

Sphene Emotional: How Titanite Was Shocked When the Dinosaurs Died

Accessory mineral geochronometers such as zircon, monazite, baddeleyite, and xenotime are increasingly being recognized for their ability to preserve diagnostic microstructural evidence of hypervelocity processes. However, little is known about the response of titanite to shock metamorphism, even though it is a widespread accessory phase and U-Pb geochronometer. Here we report two new mechanical twin modes in titanite within shocked granitoids from the Chicxulub impact structure, Mexico. Titanite grains in the newly acquired International Ocean Discovery Program Site expedition 364 M0077A core preserve multiple sets of polysynthetic twins, most commonly with composition planes (K1), = ~{1̅11}, and shear direction (η1) = <110>, and less commonly with the mode K1 = {130}, η1 = ~<522>. In some grains, {130} deformation bands have formed concurrently with shock twins, indicating dislocation glide with Burgers vector b = [341] can be active at shock conditions. Twinning of titanite in these modes, the presence of planar deformation features in shocked quartz, and lack of diagnostic shock microstructures in zircon in the same samples highlights the utility of titanite as a shock indicator for a shock pressure range between ~12 and ~17 GPa. Given the challenges of identifying ancient impact evidence on Earth and other bodies, microstructural analysis of titanite is here demonstrated to be a new avenue for recognizing impact deformation in materials where other impact evidence may be erased, altered, or did not manifest due to low shock pressure.

Timms, Nicholas E.↗
NASA NTRS1993

Reduced chromium in olivine grains from lunar basalt 15555 - X-ray Absorption Near Edge Structure (XANES)

The oxidation state of Cr in 200-micron regions within individual lunar olivine and pyroxene grains from lunar basalt 15555 was inferred using X-ray Absorption Near Edge Structure (XANES). Reference materials had previously been studied by optical absorption spectroscopy and included Cr-bearing borosilicate glasses synthesized under controlled oxygen fugacity and Cr-doped olivines. The energy dependence of XANES spectral features defined by these reference materials indicated that Cr is predominantly divalent in the lunar olivine and trivalent in the pyroxene. These results, coupled with the apparent f(02)-independence of partitioning coefficients for Cr into olivine, imply that the source magma was dominated by divalent Cr at the time of olivine crystallization.

Sutton, S. R.↗
NASA NTRS1974

Study of radiation damage and structure of Luna 16 sample particles using high-resolution electron microscopes

Using an electron scanning microscope and a high voltage microscope, a study was made of the radiation damage and structure of micron sized grains and grains separated from the 200-mesh fraction of the L-16-19 surface material sample. Then the structural features were compared with those found by studying with the same techniques grains separated from 20 different samples of lunar dust taken from the Apollo 11, Apollo 12, Apollo 14, and Apollo 15 collections. The L-16-19 sample is similar to the most intensely irradiated samples returned to earth by Apollo craft.

Borg, J.↗
NASA NTRS2003

Application of Powder Diffraction Methods to the Analysis of Short- and Long-Range Atomic Order in Nanocrystalline Diamond and SiC: The Concept of the Apparent Lattice Parameter (alp)

Two methods of the analysis of powder diffraction patterns of diamond and SiC nanocrystals are presented: (a) examination of changes of the lattice parameters with diffraction vector Q ('apparent lattice parameter', alp) which refers to Bragg scattering, and (b), examination of changes of inter-atomic distances based on the analysis of the atomic Pair Distribution Function, PDF. Application of these methods was studied based on the theoretical diffraction patterns computed for models of nanocrystals having (i) a perfect crystal lattice, and (ii), a core-shell structure, i.e. constituting a two-phase system. The models are defined by the lattice parameter of the grain core, thickness of the surface shell, and the magnitude and distribution of the strain field in the shell. X-ray and neutron experimental diffraction data of nanocrystalline SiC and diamond powders of the grain diameter from 4 nm up to micrometers were used. The effects of the internal pressure and strain at the grain surface on the structure are discussed based on the experimentally determined dependence of the alp values on the Q-vector, and changes of the interatomic distances with the grain size determined experimentally by the atomic Pair Distribution Function (PDF) analysis. The experimental results lend a strong support to the concept of a two-phase, core and the surface shell structure of nanocrystalline diamond and SiC.

Palosz, B.↗
NASA NTRS1979

Quantitative Analysis of Defects in Silicon

The evaluation and prediction of the conversion efficiency for a variety of silicon samples with differences in structural defects, such as grain boundaries, twin boundaries, precipitate particles, dislocations, etc. are discussed. Quantitative characterization of these structural defects, which were revealed by etching the surface of silicon samples, is performed by using an image analyzer. Due to different crystal growth and fabrication techniques the various types of silicon contain a variety of trace impurity elements and structural defects. The two most important criteria in evaluating the various silicon types for solar cell applications are cost and conversion efficiency.

Natesh, R.↗
NASA NTRS1983

Supercooling and structure of levitation melted Fe-Ni alloys

A study has been made of the effect of supercooling, quenching rate, growth inhibitors, and grain refiners on the structure of levitation-melted Fe- 25 pct Ni alloys. A combination of three morphologies, dendritic, spherical, and mixed dendritic and spherical, is observed in samples superheated or supercooled by less than 175 K. At larger supercooling, however, only the spherical morphology is observed. The grain size and the grain boundary shape are found to be strongly dependent on the subgrain morphology but not on the quenching temperature. Considerable grain growth is evident in samples with spherical and mixed morphologies but not in the dendriitic samples. The average cooling rates during solidification and the heat transfer coefficients at the metal-quenching medium boundary are calculated. For samples solidified in water, molten lead, and ceramic molds, the heat transfer coefficients are 0.41, 0.52, and 0.15 w/sq cm, respectively.

Abbaschian, G. J.↗
NASA NTRS1981

Rate of H2 formation on amorphous grains

The rate of formation of molecular hydrogen from hydrogen atoms adsorbed on amorphous grains taken to represent interstellar dust grains is analyzed. Following a brief review of the structure and thermodynamics of amorphous grains and the evidence that interstellar grains are indeed amorphous, consideration is given to the mechanism of formation of H2 molecules by the impact of H atoms on grains with adsorbed H atoms, and it is concluded that on amorphous grains, molecule formation will only occur if H atoms are adsorbed within a distance on the order of 10 A of each other. Rates of H2 formation on single crystal and polycrystalline grains are then calculated and compared with those for amorphous grains, and it is shown that, except for certain temperatures and high H atom densities, the rates of H2 formation on polycrystalline and amorphous grains are up to a few orders of magnitude lower than on single crystals. The results suggest that amorphous grains will lead to H2 clouds with irregular and sharply delineated features in contrast to the more uniform clouds formed on crystalline grains.

Smoluchowski, R.↗
NASA NTRS1986

Laboratory studies of the infrared small-particle extinction of amorphous silicates

The broad interstellar IR extinction features located at 9.7 and 18 microns wavelength are believed to originate from silicate dust grains. Cosmic abundances suggest that the silicate should have a chemical composition similar to that of olivine, (Mg,Fe)2 SiO4. Olivine is a very common terrestrial silicate mineral of crystalline structure. However, crystalline olivine grains do not fit the interstellar features well. Based on spectroscopic data obtained in laboratory studies and astronomical observations it was concluded that the interstellar silicate grains consist of a material with amorphous rather than crystalline structure. The astronomical arguments and the results obtained in our laboratory experiments which support this view are reviewed.

Kraetschmer, W.↗
NASA NTRS1988

Catastrophic volcanism as a cause of shocked features found at the K/T boundary and in cryptoexplosion structures

The presence of quartz grains containing shock lamellae at the Cretaceous/Tertiary (K/T) boundary is viewed by many as the single most compelling evidence of meteoritic or cometary impact because there is no known endogenous mechanism for producing these features. Similarly the presence of shocked quartz, shatter cones, coesite and stishovite at cryptoexplosion structures is comonly taken as conclusive evidence of impact. However, several recent studies have cast doubt on this interpretation. It is argued that basaltic volcanism, although not normally explosive, can under exceptional circumstances produce overpressures sufficiently high to produce shock features. The exceptional circumstances include a high content of volatiles, usually CO2, and no preestablished pathway to the surface. Rapid cooling of the saturated basaltic magma can occur if it underlies a cooler more evolved magma in a chamber. Initial slow cooling and partial exsolution of the volatiles will cause the density of the basaltic magma to become less than that of the overlying magma, leading to overturning and mixing. Gas will escape the magma chamber along planar cracks once the pressure becomes sufficiently high. In the vicinity of the crack tip there is a smallscale deviatoric stress pattern which is thought to be sufficiently high to produce transient cracks along secondary axes in the quartz crystals, causing the planar features. The CO2-rich fluid inclusions which have been found along planar elements of quartz in basement rocks of the Vredefort Dome were likely to have been emplaced by such a process. If the mechanism described is capable of producing shocked features as above, it would require a reassessment of the origin of many cryptoexplosion structures as well as seriously weakening the case for an impact origin of the K/T event.

Loper, D. E.↗
NASA NTRS1999

Accreting Gas and Dust in Pre-Main Sequence Disk Systems

Infrared spectroscopy of pre-main sequence stars with dusty protostellar disks provide information about the evolution of refractory materials in such systems. These systems exhibit varying degrees of strength and structure in the silicate emission band situated at 10 microns wavelength. Band strength is affected by the mean grain size, while band structure is determined by the chemical composition and degree of crystallinity. In some objects, the silicate band is strong and featureless, similar to that seen in the interstellar medium. In others, the band is often weaker, and exhibits structure consistent with the presence of crystalline olivine. In these latter objects, the band is similar to that of some solar system comets. The strength and structure of the silicate band may be related to the processing history of the system.

Sitko, M. L.↗
NASA NTRS2012

On-Going Laboratory Efforts to Quantitatively Address Clay Abundance on Mars

Data obtained at visible and near-infrared wavelengths by OMEGA on MarsExpress and CRISM on MRO provide definitive evidence for the presence of phyllosilicates and other hydrated phases on Mars. A diverse range of both Fe/Mg-OH and Al-OH-bearing phyllosilicates were identified including the smectites, nontronite, saponite, and montmorillonite. In order to constrain the abundances of these phyllosilicates spectral analyses of mixtures are needed. We report on our on-going effort to enable the quantitative evaluation of the abundance of hydrated-hydroxylated silicates when they are contained in mixtures. We include two component mixtures of hydrated/hydroxylated silicates with each other and with two analogs for other martian materials; pyroxene (enstatite) and palagonitic soil (an alteration product of basaltic glass). For the hydrated-hydroxylated silicates we include saponite and montmorillonite (Mg- and Al- rich smectites). We prepared three size separates of each end-member for study: 20-45, 63-90, and 125-150 μm. As the second phase of our effort we used scanning electron microscopy imaging and x-ray diffraction to characterize the grain size distribution, and structural nature, respectively, of the mixtures. Visible and near-infrared reflectance spectra of the 63-90 micrometers grain size of the mixture samples are shown in Figure 1. We discuss the results of our measurements of these mixtures.

Mars↗
NASA NTRS1990

The formation and structure of fluffy cometary nuclei from random accumulation of grains

It is now generally accepted that solid bodies in the solar system are formed by accumulation of solid grains. The mechanism of formation of smaller bodies, less than some tens of kilometers in radius, is investigated. These include planetesimals and comets. Results indicate that essentially complete agglomeration occurs for relative velocities of less than about 1000 cm/sec and fairly efficient mass build-up occurs up to 5000/cm. These velocities are consistent with current models of the primordial solar nebula. The temperature produced in a collision will be under 20 K. For ice/dust grains, the resultant aggregates will be of low density with their volatiles preserved. Cometary nuclei with radii of a few km will be irregularly shaped and fragile with low mean density and significant interanl density variations. The characteristics of such a structure could account for the observed properties of comets.

Donn, B. D.↗
NASA NTRS1992

Galactic worms. I - Catalog of worm candidates

A catalog of candidates for the Galactic worms that are possibly the walls surrounding the superbubbles is compiled; 118 isolated structures that appear both in H I and in IR (60 and 100 microns). Fifty-two are possibly associated with H II regions. It is found that the 100-micron emissivity increases systematically toward the Galactic interior, which is consistent with the increase of the general interstellar radiation field. The 100-micron emissivity of the structures associated with the H II regions is larger than that of the structures without associated H II regions. The 60-100-micron ratio is large, 0.28 +/- 0.03, which may indicate that the grains associated with the atomic gas have a relatively large population of small grains. Thirty-five structures appear in the 408-MHz continuum. The IR and the radio continuum properties suggest that the 408-MHz continuum emission in those structures is very likely thermal. The implications of these results on the ionization of gas far from the Galactic plane are discussed.

Koo, Bon-Chul↗
NASA NTRS2005

Constraints on Grain Formation Around Carbon Stars from Laboratory Studies of Presolar Graphite

We report the results of an investigation into the physical conditions in the mass outflows of asymptotic giant branch (AGB) carbon stars that are required for the formation of micron-sized presolar graphite grains, either with or without internal crystals of titanium carbide (TiC). In addition to providing detailed information about stellar nucleosynthesis, the structure and composition of presolar grains give unique information about the conditions of grain formation. In the present work we use laboratory observations of presolar graphite to gain insight into the physical conditions in circumstellar outflows from carbon AGB stars. The periodic pulsation of AGB stars enhances the gas density through shocks in the stellar atmosphere above the photosphere, promoting the condensation of dust grains. Copious mass outflow occurs largely because grains are coupled to the radiation field of the star, which accelerates them by radiation pressure; momentum is in turn transferred to gas molecules by collisions with grains. The dust/gas mixture is effectively a two-component fluid whose motion depends on atmospheric structure and which, in turn, influences that structure. In particular, the radiation pressure on the grains determines the velocity field of the outflow and thus the density distribution, while the density distribution itself determines the conditions of radiative transfer within the outflow and thus the effective radiation pressure.

Bernatowicz, T. J.↗
NASA NTRS2015

Complete Tem-Tomography: 3D Structure of Gems Cluster

GEMS (glass with embedded metal and sulfide) grains in interplanetary dust particles (IDPs) are considered to be one of the ubiquitous and fundamental building blocks of solids in the Solar System. They have been considered to be interstellar silicate dust that survived various metamorphism or alteration processes in the protoplanetary disk but the elemental and isotopic composition measurements suggest that most of them have been formed in the protoplanetary disk as condensates from high temperature gas. This formation model is also supported by the formation of GEMS-like grains with respect to the size, mineral assemblage, texture and infrared spectrum by condensation experiments from mean GEMS composition materials. Previous GEMS studies were performed only with 2D observation by transmission electron microscopy (TEM) or scanning TEM (STEM). However, the 3D shape and structure of GEMS grains and the spatial distribution of Fe/FeS's has critical information about their formation and origin. Recently, the 3D structure of GEMS grains in ultrathin sections of cluster IDPs was revealed by electron tomography using a TEM/STEM (JEM-2100F, JEOL). However, CT images of thin sections mounted on Cu grids acquired by conventional TEM-tomography are limited to low tilt angles (e. g., less than absolute value of 75 deg. In fact, previous 3D TEM observations of GEMS were affected by some artifacts related to the limited tilt range in the TEM used. Complete tomographic images should be acquired by rotating the sample tilt angle over a range of more than absolute value of 80 deg otherwise the CT images lose their correct structures. In order to constrain the origin and formation process of GEMS grains more clearly, we performed complete electron tomography for GEMS grains. Here we report the sample preparation method we have developed for this study, and the preliminary results.

Matsuno, J.↗