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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

Compositions of the Surfaces of Pluto and its Satellites

The information we have on the chemical compositions of the surfaces of Pluto and Charon has been obtained from Earth-based near-infrared spectroscopy. These bodies are seen in diffusely scattered sunlight upon which absorption bands diagnostic of specific ices are superimposed. Identified so far on Pluto are molecular nitrogen (N2), methane (CH4), carbon monoxide (CO), and ethane (C2H6), all in the frozen state. Charon has the clear spectral signature of H2O ice in the crystalline phase, plus an absorption band near 2.2 microns identified as a hydrated form of NH3. No diagnostic spectra of Pluto's other satellites are currently available. A fraction of Pluto's CH4 is dissolved in solid N2, which is in the hexagonal beta-phase. When a small concentration of CH4 exists in a N2 crystalline matrix, its absorption bands are shifted in wavelength by a small but detectable amount. Indeed the shifting of the CH4 bands is diagnostic of a host matrix. In the case of Pluto, the N2 band (2.148 microns) itself is detected, but for other trans-Neptunian objects where the N2 band cannot be seen, the shifted CH4 bands demonstrate the presence of N2 or (less likely) some other spectrally neutral and transparent matrix material (e.g., Ar). The absence of detectable CO2 and H2O ices on Pluto, while they are clearly present on the otherwise very similar Triton, is noteworthy. The ices of Pluto distributed non-uniformly across its surface, and the distribution shows long-term (decadal) changes. Both seasonal and secular changes may be occurring through transport across the surface as a result of changing temperature, and by seasonal changes in the vapor pressure equilibrium of the ice with the tenuous and variable atmosphere. Models of the photochemistry of the surface ices and the atmosphere of Pluto predict the presence of several materials not yet detected; the most abundant photoproducts are expected to be C2H2, C4H2, HCN, C2H6; HCN has been detected on Triton. Both Pluto and Charon have surface components in addition to the detected ices. These materials of presently unknown composition serve to reduce the albedos of both bodies below that expected for pure ices, and in the case of Pluto impart a yellow-brown coloration; the color of Charon is more nearly neutral. It is generally thought that the non-ice components are more refractory than the ices and that they may be complex carbonaceous materials derived from the ultraviolet and charged particle processing of the surface ices. Minerals are also plausible candidates for the non-ice fraction. The refractory colored components may constitute bedrock upon which variable amounts of the ices are alternately deposited and evaporated as the seasons change. Water ice is expected to be a component of the bedrock, although it has not yet been reliably identified.

Pluto↗
NASA NTRS1998

Lattice Dynamics of Colloidal Crystals During Photopolymerization of Acrylic Monomer Matrix

The photoinitiated bulk polymerization process, which has been used recently in the manufacture of solid optical diffraction filters, is examined to understand the dynamics of both the crystalline colloidal arrays (CCA) and the host monomer species. Our analysis indicates that volume shrinkage of the monomer, changes in the dielectric properties of the monomer, and inhomogeneities of polymerization reaction rate across the dispersion during the polymerization process, are the major contributors for observed lattice compression and lattice disorder of the CCA of silica spheres in polymerized acrylic/methacrylic ester films. The effect of orientation of photocell with respect to the radiation source on Bragg diffraction of CCA indicated the presence of convective stirring in the thin fluid system during the photopolymerization that deleteriously affects the periodic array structures. To devise reproducible and more efficient optical filters, experimental methods to minimize or eliminate convective instabilities in monomeric dispersions during polymerization are suggested.

Sunkara, H. B,↗
NASA NTRS1994

Infrared spectra of crystalline phase ices condensed on silicate smokes at T less than 20 K

Infrared spectra of H2O, CH3OH, and NH3 condensed at T less than 20 K on amorphous silicate smokes reveal that predominantly crystalline phase ice forms directly on deposit. Spectra of these molecules condensed on aluminum substrates at T less than 20 K indicate that amorphous phase ice forms. On aluminum, crystalline phase H2O and CH3OH are formed by annealing amorphous deposits to 155 K and 130 K, respectively (or by direct deposit at these temperatures); crystalline NH3 is formed by direct deposit at 88 K. Silicate smokes are deposited onto aluminum substrates by evaporation of SiO solid or by combustion of SiH4 with O2 in flowing H2 followed by vapor phase nucleation and growth. Silicate smokes which are oxygen-deficient may contain active surface sites which facilitate the amorphous-to-crystalline phase transition during condensation. Detailed experiments to understand the mechanism are currently in progress. The assumption that amorphous phase ice forms routinely on grains at T less than 80 K is often used in models describing the volatile content of comets or in interpretations of interstellar cloud temperatures. This assumption needs to be reexamined in view of these results.

Moore, Marla H.↗
NASA NTRS2015

Update on the Chemical Composition Of Crystalline, Smectite, and Amorphous Components for Rocknest Soil and John Klein and Cumberland Mudstone Drill Fines at Gale Crater, Mars

We have previously calculated the chemical compositions of the X-ray-diffraction (XRD) amorphous component of three solid samples (Rocknest (RN) soil, John Klein (JK) drill fines, and Cumberland (CB) drill fines) using major-element chemistry (APXS), volatile-element chemistry (SAM), and crystalline- phase mineralogy (CheMin) obtained by the Curiosity rover as a part of the ongoing Mars Science Laboratory mission in Gale Crater. According to CheMin analysis, the RN and the JK and CB samples are mineralogically distinct in that RN has no detectable clay minerals and both JK and CB have significant concentrations of high-Fe saponite. The chemical composition of the XRD amorphous component is the composition remaining after mathematical removal of the compositions of crystalline components, including phyllosilicates if present. Subsequent to, we have improved the unit cell parameters for Fe-forsterite, augite, and pigeonite, resulting in revised chemical compositions for the XRD-derived crystalline component (excluding clay minerals). We update here the calculated compositions of amorphous components using these revised mineral compositions.

Morris, R. V.↗
NASA NTRS2003

Paramagnetic Attraction of Impurity-Helium Solids

Impurity-helium solids are formed when a mixture of impurity and helium gases enters a volume of superfluid helium. Typical choices of impurity gas are hydrogen deuteride, deuterium, nitrogen, neon and argon, or a mixture of these. These solids consist of individual impurity atoms and molecules as well as clusters of impurity atoms and molecules covered with layers of solidified helium. The clusters have an imperfect crystalline structure and diameters ranging up to 90 angstroms, depending somewhat on the choice of impurity. Immediately following formation the clusters aggregate into loosely connected porous solids that are submerged in and completely permeated by the liquid helium. Im-He solids are extremely effective at stabilizing high concentrations of free radicals, which can be introduced by applying a high power RF dis- charge to the impurity gas mixture just before it strikes the super fluid helium. Average concentrations of 10(exp 19) nitrogen atoms/cc and 5 x 10(exp 18) deuterium atoms/cc can be achieved this way. It shows a typical sample formed from a mixture of atomic and molecular hydrogen and deuterium. It shows typical sample formed from atomic and molecular nitrogen. Much of the stability of Im-He solids is attributed to their very large surface area to volume ratio and their permeation by super fluid helium. Heat resulting from a chance meeting and recombination of free radicals is quickly dissipated by the super fluid helium instead of thermally promoting the diffusion of other nearby free radicals.

Bernard, E. P.↗
NASA NTRS1977

Improved ceramic heat exchange material

Improved corrosion resistant ceramic materials that are suitable for use as regenerative heat exchangers for vehicular gas turbines is reported. Two glass-ceramic materials, C-144 and C-145, have superior durability towards sulfuric acid and sodium sulfate compared to lithium aluminosilicate (LAS) Corning heat exchange material 9455. Material C-144 is a leached LAS material whose major crystalline phase is silica keatite plus mullite, and C-145 is a LAS keatite solid solution (S.S.) material. In comparison to material 9455, material C-144 is two orders of magnitude better in dimensional stability to sulfuric acid at 300 C, and one order of magnitude better in stability to sodium sulfate at 1000 C. Material C-145 is initially two times better in stability to sulfuric acid, and about one order of magnitude better in stability to sodium sulfate. Both C-144 and C-145 have less than 300 ppm delta L/L thermal expansion from ambient to 1000 C, and good dimensional stability of less than approximately 100 ppm delta L/L after exposure to 1000 C for 100 hours. The glass-ceramic fabrication process produced a hexagonal honeycomb matrix having an 85% open frontal area, 50 micrometer wall thickness, and less than 5% porosity.

Mccollister, H. L.↗
NASA NTRS1991

Infrared spectra of solid films formed from vapors containing water and nitric acid

The paper presents infrared spectra recorded at 188 K for crystalline mono- and trihydrates of nitric acid formed by vapor deposition, along with spectra of fully deuterated forms of these compounds. The spectra are interpreted in terms of the known ionic structures of the hydrates and the known spectra of oxonium and nitrate ions. Two additional species were identified: a molecular hydrogen-bonded HNO3-H2O complex, stable only at temperatures below 120 or 150 K, and a substance considered to be a crystalline mixtgure of trihydrate and ice. The relevance of these findings to the stratospheric ozone hole problem is discussed.

Smith, Roland H.↗
NASA NTRS2008

Comparing Wild 2 Particles to Chondrites and IDPS

We compare the observed composition ranges of olivine, pyroxene and Fe-Ni sulfides in Wild 2 grains, comparing these with chondritic IDPs and chondrite classes to explore whether these data suggest affinities to known hydrous materials in particular. Wild 2 olivine has an extremely wide composition range, from Fo4-100 with a pronounced frequency peak at Fo99. The composition range displayed by the low-calcium pyroxene is also very extensive, from En52 to En100, with a significant frequency peak centered at En95. These ranges are as broad or broader than those reported for any other extraterrestrial material. Wild 2 Fe-Ni sulfides mainly have compositions close to that of FeS, with less than 2 atom % Ni - to date, only two pentlandite grains have been found among the Wild-grains suggesting that this mineral is not abundant. The complete lack of compositions between FeS and pentlandite (with intermediate solid solution compositions) suggests (but does not require) that FeS and pentlandite condensed as crystalline species, i.e. did not form as amorphous phases, which later became annealed. While we have not yet observed any direct evidence of water-bearing minerals, the presence of Ni-bearing sulfides, and magnesium-dominated olivine and low-Ca pyroxene does not rule out their presence at low abundance. We do conclude that modern major and minor element compositions of chondrite matrix and IDPs are needed.

Zolensky, Michael↗
NASA NTRS2024

Measuring the Density, Viscosity, and Surface Tension of Molten Titanates Using Electrostatic Levitation in Microgravity

Rare earth and barium titanates are useful as ferroelectric, dielectric, and optical materials. Measurements of their thermophysical properties in the liquid state can help guide melt processing technologies for their manufacture and advance understanding of fragile liquids' behavior and glass formation. Here, we report the density, thermal expansion, viscosity, and surface tension of molten BaTiNsub>2 O 5 , BaTi 4 O 9 , and 83TiO 2 -17RE 2 O 3 (RE = La or Nd). Measurements were made using electrostatic levitation and droplet oscillation techniques in microgravity, which provide access to quiescent liquid droplets and deep supercooling of 510–815 K below the equilibrium melting points. Densities were measured over 900–2400 K. Viscosities were similar for all four compositions, increasing from ∼10 mPa s near 2100 K to ∼30 mPa s near 1750 K. Surface tensions were 450–490 dyn cm −1 for the rare earth titanates and 383–395 dyn cm−1 for the barium titanates; surface tensions of all compositions had small or negligible temperature dependence over 1700–2200 K. For solids recovered after melt quenching, x-ray microtomography revealed the fracture mechanics in crystalline products and minimal internal porosity in glass products, likely arising from entrapped gas bubbles. Internal microstructures were generally similar for products processed either in microgravity or in a terrestrial aerodynamic levitator.

Stephen K Wilke↗
NASA NTRS2019

Preparation, Identification, and Low-Temperature Infrared Spectra of Two Elusive Crystalline Nitrile Ices

Infrared (IR) spectra of the alkyl nitrile ices CH3CN and CH3CH2CN are relevant to the study of the low- temperature chemistry of objects within and beyond the Solar System, but the thermodynamically favored low-temperature crystalline phases of these compounds have not been presented and identified in the planetary- sciences literature. Moreover, there is a large variation in the published IR spectra of these two icy solids, including spectra that are used for the analyses of spacecraft data from the Voyager and Cassini missions. Here the IR spectra of the low-temperature crystalline forms of CH3CN and CH3CH2CN, which are the thermodynamically stable phases at Titan temperatures, are presented for the first time with all samples being made by vapor-phase deposition. Conditions are described for producing these ice phases for both compounds, and new measurements are reported of ice density and refractive index, quantities needed to compute IR absorption coefficients, band strengths, optical constants, and, ultimately, nitrile abundances in extraterrestrial environments. Comparisons are drawn between CH3CN and CH3CH2CN, an earlier prediction on their similar crystallization behaviors is verified, and previous work is examined in light of these new results, including a counterintuitive observation in which the low-temperature phase of an ice is made by heating a high-temperature phase. Applications and extensions are described.

Hudson, Reggie L.↗
NASA NTRS2019

Preparation, Identification, and Low-Temperature Infrared Spectra of Two Elusive Crystalline Nitrile Ices

Infrared (IR) spectra of the alkyl nitrile ices CH3CN and CH3CH2CN are relevant to the study of the low- temperature chemistry of objects within and beyond the Solar System, but the thermodynamically favored low-temperature crystalline phases of these compounds have not been presented and identified in the planetary- sciences literature. Moreover, there is a large variation in the published IR spectra of these two icy solids, including spectra that are used for the analyses of spacecraft data from the Voyager and Cassini missions. Here the IR spectra of the low-temperature crystalline forms of CH3CN and CH3CH2CN, which are the thermody-namically stable phases at Titan temperatures, are presented for the first time with all samples being made by vapor-phase deposition. Conditions are described for producing these ice phases for both compounds, and new measurements are reported of ice density and refractive index, quantities needed to compute IR absorption coefficients, band strengths, optical constants, and, ultimately, nitrile abundances in extraterrestrial environments. Comparisons are drawn between CH3CN and CH3CH2CN, an earlier prediction on their similar crystallization behaviors is verified, and previous work is examined in light of these new results, including a counter- intuitive observation in which the low-temperature phase of an ice is made by heating a high-temperature phase. Applications and extensions are described.

Hudson, Reggie L.↗
NASA NTRS2019

Preparation, Identification, and Low-Temperature Infrared Spectra of Two Elusive Crystalline Nitrile Ices

Infrared (IR) spectra of the alkyl nitrile ices CH3CN and CH3CH2CN are relevant to the study of the low-temperature chemistry of objects within and beyond the Solar System, but the thermodynamically favored low-temperature crystalline phases of these compounds have not been presented and identified in the planetary-sciences literature. Moreover, there is a large variation in the published IR spectra of these two icy solids, including spectra that are used for the analyses of spacecraft data from the Voyager and Cassini missions. Here the IR spectra of the low-temperature crystalline forms of CH3CN and CH3CH2CN, which are the thermodynamically stable phases at Titan temperatures, are presented for the first time with all samples being made by vapor-phase deposition. Conditions are described for producing these ice phases for both compounds, and new measurements are reported of ice density and refractive index, quantities needed to compute IR absorption coefficients, band strengths, optical constants, and, ultimately, nitrile abundances in extraterrestrial environments. Comparisons are drawn between CH3CN and CH3CH2CN, an earlier prediction on their similar crystallization behaviors is verified, and previous work is examined in light of these new results, including a counter-intuitive observation in which the low-temperature phase of an ice is made by heating a high-temperature phase. Applications and extensions are described.

Reggie L Hudson↗
NASA NTRS2019

Preparation, Identification, and Low-Temperature Infrared Spectra of Two Elusive Crystalline Nitrile Ices

Infrared (IR) spectra of the alkyl nitrile ices CH3CN and CH3CH2CN are relevant to the study of the low-temperature chemistry of objects within and beyond the Solar System, but the thermodynamically favored low-temperature crystalline phases of these compounds have not been presented and identified in the planetary-sciences literature. Moreover, there is a large variation in the published IR spectra of these two icy solids, including spectra that are used for the analyses of spacecraft data from the Voyager and Cassini missions. Here the IR spectra of the low-temperature crystalline forms of CH3CN and CH3CH2CN, which are the thermodynamically stable phases at Titan temperatures, are presented for the first time with all samples being made by vapor-phase deposition. Conditions are described for producing these ice phases for both compounds, and new measurements are reported of ice density and refractive index, quantities needed to compute IR absorption coefficients, band strengths, optical constants, and, ultimately, nitrile abundances in extraterrestrial environments. Comparisons are drawn between CH3CN and CH3CH2CN, an earlier prediction on their similar crystallization behaviors is verified, and previous work is examined in light of these new results, including a counter-intuitive observation in which the low-temperature phase of an ice is made by heating a high-temperature phase. Applications and extensions are described.

Ices, IR spectroscopy, Titan, organic chemistry, i↗
NASA NTRS1983

A note on the composition and structure of interstellar grains

The plausibility of relatively pure diatomic oxide crystals forming in the expanding atmospheres of cool stars is commented on, and the likelihood of SiO grains condensing is discussed on the basis of laboratory nucleation experiments. Results of annealing experiments are used to consider the further evolution of silicon oxide and silicate grains. The evidence shows that SiO solids form only when SiO condenses directly onto surfaces, and that the probability of pure crystalline SiO grains forming is rather small.

Nuth, J. A.↗
NASA NTRS2012

885-nm Pumped Ceramic Nd:YAG Master Oscillator Power Amplifier Laser System

The performance of a traditional diode pumped solid-state laser that is typically pumped with 808-nm laser diode array (LDA) and crystalline Nd:YAG was improved by using 885-nm LDAs and ceramic Nd:YAG. The advantage is lower quantum defect, which will improve the thermal loading on laser gain medium, resulting in a higher-performance laser. The use of ceramic Nd:YAG allows a higher Nd dopant level that will make up the lower absorption at the 885-nm wavelength on Nd:YAG. When compared to traditional 808-nm pump, 885-nm diodes will have 30% less thermal load (or wasted heat) and will thus see a similar percentage improvement in the overall laser efficiency. In order to provide a more efficient laser system for future flight missions that require the use of low-repetition- rate ( 1% Nd. To make certain that the absorption at 885 nm is on the same par as the 808-nm diode, the Nd:YAG material needs to be doped with higher concentration of Nd. Ceramic Nd:YAG is the only material that can be tailored to specific needs.

Yu, Anthony↗
NASA NTRS1980

Simulation studies of a model of high-density metallic hydrogen

Upper bounds for the ground-state energies of liquid and solid phases of metallic hydrogen and metallic deuterium have been calculated with variational methods and Monte Carlo techniques. At four densities (0.8, 1.2, 1.36, and 1.488) crystalline phases are clearly preferred in the sense that the energy difference, when compared to the liquid, is in excess of the errors inherent in the numerical procedures. At a fifth density (1.6), the energy differences between solid and liquid phases are smaller than these errors.

Mon, K. K.↗
NASA NTRS1987

On the absence of convective stability in materials preparation on earth

The yield in the production and the performance of electronic and optical solid state devices is frequently limited by nonuniformities in the composition and structure of the underlying crystalline material. The formation of such inhomogeneities can be favored by convective heat and mass transfer during the preparation. Hence, it is often desirable to establish purely diffusive conditions in materials preparation. It has been thought that buoyancy-driven convection can be readily excluded by appropriate orientation of the density gradient with respect to the gravity vector. Such expectations overlook, however, that materials preparation processes are inherently associated with multidimensional density gradients. Hence, it is concluded, there will always be convective contributions to transport in materials processing on earth.

Rosenberger, Franz↗
NASA NTRS2010

U.S. Materials Science on the International Space Station: Status and Plans

This viewgraph presentation reviews the current status and NASA plans for materials science on the International Space Station. The contents include: 1) Investigations Launched in 2009; 2) DECLIC in an EXPRESS rack; 3) Dynamical Selection of Three-Dimensional Interface Patterns in Directional Solidification (DSIP); 4) Materials Science Research Rack (MSRR); 5) Materials Science Laboratory; 6) Comparison of Structure and Segregation in Alloys Directionally Solidified in Terrestrial and Microgravity Environments (MICAST/CETSOL); 7) Coarsening in Solid Liquid Mixtures 2 Reflight (CSLM 2R); 8) Crystal Growth Investigations; 9) Levitator Investigations; 10) Quasi Crystalline Undercooled Alloys for Space Investigation (QUASI); 11) The Role of Convection and Growth Competition in Phase Selection in Microgravity (LODESTARS); 12) Planned Additional Investigations; 13) SETA; 14) METCOMP; and 15) Materials Science NRA.

Chiaramonte, Francis P.↗