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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Strontium and oxygen isotope study of M-1, M-3 and M-4 drill core samples from the Manson impact structure, Iowa: Comparison with Haitian K-T impact glasses

Strontium and oxygen isotope analyses were performed on 8 samples from the M-1, M-3, and M-4 cores recently drilled at the Manson impact structure. The samples were three elastic sedimentary rocks (of probable Cretaceous age) which occurred as clasts within the sedimentary clast breccia, two samples of crystalline rock breccia matrix, and three samples of dolomite and limestone. The Sr-87/Sr-86 (corrected to 65 Ma) ratios were much higher than those in impact glasses from the Haitian Cretaceous-Tertiary (K-T) boundary. Isotope mixing calculations demonstrate that neither the silicate or carbonate rocks analyzed from the Manson crater, or mixtures of these rocks are appropriate source materials for the Haitian impact glasses. However, the Sr-87/Sr-86 (65Ma) ratio and delta O-18 value of the Ca-rich Haitian glasses are well reproduced by mixtures of Si-rich Haitian glass with platform carbonate of K-T age.

Blum, Joel D.↗
NASA NTRS1993

The ilmenite liquidus and depths of segregation for high-Ti picrite glasses

Lunar picrite glasses represent primitive and perhaps near primary liquids which have suffered only minor degrees of crystallization or near crustal modification. These glasses are multisaturated with olivine and orthopyroxene at pressures from 20-25 kb. I argue below that high TiO2 mare glasses were indeed equilibrated with orthopyroxene and were segregated from the lunar mantle at mean depths of 400-500 km. The glasses are typically modelled as products of relatively low degrees of melting of an hybridized source resulting from the overturn and mixing of the gravitationally unstable cumulate pile. But the models are neither unique nor, in some cases, correct.

Hess, P. C.↗
NASA NTRS1993

C-O volatiles in Apollo 15 and Apollo 17 picritic glasses

A15 and A17 primitive picritic glasses have been examined by FTIR for the presence of dissolved C-O species to determine the role of C-O gasses on driving lunar fire-fountains. A15 green and yellow glasses were extensively studied and found to be free of dissolved C species down to FTIR detection limits (10-100 ppm; species and sample specific). Preliminary data on A17 orange glasses are similarly devoid of FTIR detectable C-O species. Re-analyses of the C-O driving mechanism theory for mare volcanism demonstrates the need to determine the fO2 of the lunar interior; the factor that most critically determined the role of C gasses in the fire-fountaining events. Oxygen fugacities equivalent to IW-0.5 and above imply dissolved CO3(=) in the primitive glasses at levels above FTIR detection. The f02's below IW-0.5 imply concentrations of CO3(=) below FTIR detection. Recent data suggesting lunar mantle fO2's of IW-2 or less, strongly mitigate against finding FTIR measurable dissolved CO3(=) consistent with the findings of this study.

Rutherford, Malcolm J.↗
NASA NTRS1993

Basaltic magmatism on the Moon. A perspective from volcanic picritic glasses

It is widely accepted that basaltic magmas are products of partial fusion of peridotite within planetary mantles. As such they provide valuable insights into the structure and processes of planetary interiors. Those compositions which approach primary melt compositions provide both a clearer vision of planetary interiors and a starting point at which to understand basaltic evolution. Within the collection of lunar samples returned by the Apollo and Luna missions are homogeneous, picritic glass beads of volcanic origin. These glass beads provide a unique perspective concerning the origin of mare basalts, the characteristics of the lunar interior, and processes culminating in the early differentiation of the moon. In this presentation, we report our ion microprobe derived trace element data from all picritic glasses previously identified. We place this trace element data and literature isotopic and experimental data on the picritic glasses with the framework of mare basaltic magmatism.

Shearer, C. K.↗
NASA NTRS1992

Mechanical failure probability of glasses in Earth orbit

Results of five years of earth-orbital exposure on mechanical properties of glasses indicate that radiation effects on mechanical properties of glasses, for the glasses examined, are less than the probable error of measurement. During the 5 year exposure, seven micrometeorite or space debris impacts occurred on the samples examined. These impacts were located in locations which were not subjected to effective mechanical testing, hence limited information on their influence upon mechanical strength was obtained. Combination of these results with micrometeorite and space debris impact frequency obtained by other experiments permits estimates of the failure probability of glasses exposed to mechanical loading under earth-orbit conditions. This probabilistic failure prediction is described and illustrated with examples.

Kinser, Donald L.↗
NASA NTRS1994

Reduction of lunar mare soil and pyroclastic glass

Mare soil and orange and black pyroclastic glass were reduced in hydrogen gas at temperatures of 900 to 1100 C. The experiments support studies of regolith maturation, lunar volcanism, and the production of oxygen on the moon. The most reactive component in the high-Ti soil was FeO in ilmenite, which was completely reduced to iron metal at all temperatures. Vitreous orange glass crystallized and was partially reduced to iron metal, pyroxene, and minor olivine. Initially devitrified black glass was similarly reduced and converted to iron metal, pyroxene, and minor olivine. The degree of reaction in both glasses increased with temperature.

Allen, C. C.↗
NASA NTRS1994

The nature of agglutinitic glass in the fine-size fraction of lunar soil 10084

Agglutinitic glass contains much of the reduced Fe in lunar soils, and it contributes to the modification of reflectance spectra from lunar soils. Previous work has shown that agglutinitic glass can be compositionally heterogeneous, but the scale of these heterogeneities is not well known. In addition, few data are available on the characteristics of the inclusions in agglutinitic glass. Here we report on our preliminary transmission electron microscope (TEM) examination of agglutinitic glass fragments from the Apollo 11 soil 10084.

Keller, Lindsay P.↗
NASA NTRS1993

Microscopic iron metal on glass and minerals - A tool for studying regolith maturity

A novel method of producing mixtures of glass or minerals with iron metal is presented. A portion of the Fe(2+) in basaltic glass and minerals can be reduced to metal in a few hours at 1100 C and an oxygen fugacity well below the iron-wustite buffer. Part of the iron metals forms rounded submicrometer blebs on the surfaces and in some cases within the grains. A concentration of such blebs equivalent to 20-30 percent of a grain's surface area can totally dominate the reflectance spectra of basaltic glass, pyroxene, and olivine. The production of optically opaque iron metal blebs, combined with the decline in Fe(2+), affects the glass and mineral reflectance spectra in three ways: by lowering the overall reflectivity, reducing the spectral contrast of absorption features, and producing a continuum with a general rise in reflectivity toward longer wavelengths.

Allen, C. C.↗
NASA NTRS1994

Spin glasses and error-correcting codes

In this article, we study a model for error-correcting codes that comes from spin glass theory and leads to both new codes and a new decoding technique. Using the theory of spin glasses, it has been proven that a simple construction yields a family of binary codes whose performance asymptotically approaches the Shannon bound for the Gaussian channel. The limit is approached as the number of information bits per codeword approaches infinity while the rate of the code approaches zero. Thus, the codes rapidly become impractical. We present simulation results that show the performance of a few manageable examples of these codes. In the correspondence that exists between spin glasses and error-correcting codes, the concept of a thermal average leads to a method of decoding that differs from the standard method of finding the most likely information sequence for a given received codeword. Whereas the standard method corresponds to calculating the thermal average at temperature zero, calculating the thermal average at a certain optimum temperature results instead in the sequence of most likely information bits. Since linear block codes and convolutional codes can be viewed as examples of spin glasses, this new decoding method can be used to decode these codes in a way that minimizes the bit error rate instead of the codeword error rate. We present simulation results that show a small improvement in bit error rate by using the thermal average technique.

Belongie, M. L.↗
NASA NTRS1995

Study of Luminescence Characteristics of Trivalent Terbium in Silicate Glass

An important use of silicate glasses doped with terbium oxide (Tb2O3) is their use as fiber optic sensors for high-resolution imaging applications requiring the detection of x-rays (e.g. tomography and radiography). The x-ray radiation is absorbed by the glass, producing electron-hole pairs (excitons). The excitons migrate through the glass matrix and then recombine, emitting characteristic Tb(3+) luminescence in the optical wavelength region. This emission is due to forbidden transitions of 4f electrons and therefore has a long decay time. Long decay time is undesirable when imaging transient events since it results in blurring in time of the images. It has been reported elsewhere that in crystals Tb(3+) ions can act both as luminescence centers and as fluorescence traps. These traps can capture excitons and delay their recombination. This delayed fluorescence is seen as a long lived, secondary component to the luminescence decay curve, or afterglow. Such a secondary decay component to the luminescence decay of Tb(3+) has been observed before in soda glass following pulsed optical excitation. In order to determine the conditions under which afterglow occurs, an understanding of the material's luminescent properties is required.

West, Mike S.↗
NASA NTRS1993

Numerical Model for Isothermal and Non-Isothermal Crystallization of Liquids and Glasses

A new numerical model of isothermal and non-isothermal first order phase transformations, such as the crystallization of liquids and glasses, is presented. This model computes directly the volume fraction transformed, taking into account time-dependent nucleation rates and cluster-size-dependent growth velocities. The model is applied to the crystallization of lithium disilicate glass, using the appropriate kinetic and thermodynamic parameters. The model is used (1) to determine the validity of common methods for computing the volume fraction transformed as a function of time in isothermal experiments when a time-dependent nucleation rate is expected, (2) to simulate non-isothermal differential scanning calorimetry (DSC) studies of glass devitrification as a function of scan rate, and (3) to compute the effect of preannealing on the DSC peak parameters. A novel behavior of the nucleation rate with scan rate is predicted, arising because the relaxation of the cluster distribution cannot be described by a single relaxation time. Comparisons of the calculations with experimental data on this glass demonstrate the validity of the model.

Kelton, K. F.↗
NASA NTRS1996

Experimental Constraints on the Origin of Lunar High-Ti Ultramafic Glasses

Phase equilibria and dissolution rate experiments are used to develop a petrogenetic model for the high-Ti lunar ultramafic glasses. Near-liquidus phase relations of the Apollo 14 black glass, the most Ti-rich lunar ultramafic glass, are determined to 2.2-GPa. The liquidus is saturated with Cr-spinel at 1-atm, olivine between approximately 0.5- and 1.5-GPa, and low-Ca pyroxene + Cr-spinel above 1.5-GPa. Ilmenite does not crystallize near the liquidus and implies that high-Ti ultramafic glasses are not produced by melting of an ilmenite-saturated source. We infer that high-Ti ultramafic magmas are derived from low-Ti ultramafic parent magmas by assimilation of ilmenite +/- clinopyroxene +/- urKREEP +/- pigeonite in the shallow lunar interior. Heat is provided by adiabatic ascent of the low-Ti ultramafic primary magmas from the deeper lunar interior and crystallization of olivine during assimilation. The assimilation reaction is modeled by mass balance and requires that ilmenite and high-Ca pyroxene are assimilated in a approximately 3:1 ratio, a much higher ratio than the proportion in which these minerals are thought to exist in the lunar interior. In an effort to understand the kinetic controls on this reaction, the dissolution of ilmenite is examined experimentally in both low- and high-Ti lunar magmas. We find that ilmenite dissolves incongruently to Cr-spinel and a high-Ti melt. The dissolution reaction proceeds by a diffusion-controlled mechanism. An assimilation model for the origin of high-Ti melts is developed that leaves the magma ocean cumulates in their initial stratigraphic positions and obviates source hybridization models that require lunar overturn.

Wagner, T. P.↗
NASA NTRS1999

Abundances and Distributions of Volatile Elements (Na, S, Cl, K) Within Lunar Volcanic Glass Spheres

This research developed and applied high-precision analytical methods (electron microprobe) to determine the major- and minor-element abundances (Si, Ti, A], Cr, Fe, Mn, Mg, Ca, Na, K) in three suites of Apollo 14 volcanic green glasses. Since the precision of these data was a factor of 5-10 better than previously published results, the data provided the strongest constraints yet achieved on the geochemical processes that operated at depths less than 400 kilometers inside the Moon. The results of this work were submitted to the 29th Lunar and Planetary Science Conference, formed the basis for a Master's Thesis, and were published in the top-tier geochemical journal. Additional high-precision data on the trace abundances of sodium (Na), sulfur (S), and potassium (K) in the Apollo 17 volcanic orange glasses (74220) were also acquired during this grant-period. These data show diffusion profiles within individual 200-micron diameter, glass spherules that were apparently generated during the fire-fountain eruption of this magma in the presence of a transient vapor phase. Although these results have not yet been published, publication is planned in 2001 after additional numerical modeling has been completed. This work has also catalyzed on-going collaborative work with Professor Timothy Grove (MIT) to analyze and understand the origin of the Apollo 15 volcanic green glasses. That work will be completed for publication in 2001.

Delano, John W.↗
NASA NTRS1993

High Tech Art: Chameleon Glass

Dichroic Glass is a technology wherein extremely thin films of metal are vacuum deposited on a glass surface. The coated glass shields spacecraft instruments from cosmic radiation and protects human vision from unfiltered sunlight in space. Because the coating process allows some wavelengths of light and color to reflect and others to pass through, a chameleon effect is produced. Murray Schwartz, a former aerospace engineer, has based his business KROMA on this NASA optical technology. He produces dichroic stained glass windows, mobiles and jewelry. The technique involves deposition of super thin layers of metal oxides applied one layer at a time in a specific order and thickness for the desired effect. His product line is unique and has been very successful.

Source record↗
NASA NTRS2004

Determining the Oxygen Fugacity of Lunar Pyroclastic Glasses Using Vanadium Valence - An Update

We have been developing an oxygen barometer based on the valence state of V (V(2+), V(3+), V(4+), and V(5+)) in solar system basaltic glasses. The V valence is determined by synchrotron micro x-ray absorption near edge structure (XANES), which uses x-ray absorption associated with core-electronic transitions (absorption edges) to reveal a pre-edge peak whose intensity is directly proportional to the valence state of an element. XANES has advantages over other techniques that determine elemental valence because measurements can be made non-destructively in air and in situ on conventional thin sections at a micrometer spatial resolution with elemental sensitivities of approx. 100 ppm. Recent results show that fO2 values derived from the V valence technique are consistent with fO2 estimates determined by other techniques for materials that crystallized above the IW buffer. The fO2's determined by V valence (IW-3.8 to IW-2) for the lunar pyroclastic glasses, however, are on the order of 1 to 2.8 log units below previous estimates. Furthermore, the calculated fO2's decrease with increasing TiO2 contents from the A17 VLT to the A17 Orange glasses. In order to investigate these results further, we have synthesized lunar green and orange glasses and examined them by XANES.

Karner, J. M.↗
NASA NTRS2005

Crystallization Kinetics of a Solid Oxide Fuel Cell Seal Glass by Differential Thermal Analysis

Crystallization kinetics of a barium calcium aluminosilicate glass (BCAS), a sealant material for planar solid oxide fuel cells, have been investigated by differential thermal analysis (DTA). From variation of DTA peak maximum temperature with heating rate, the activation energy for glass crystallization was calculated to be 259 kJ/mol. Development of crystalline phases on thermal treatments of the glass at various temperatures has been followed by powder x-ray diffraction. Microstructure and chemical composition of the crystalline phases were investigated by scanning electron microscopy and energy dispersive spectroscopic (EDS) analysis. BaSiO3 and hexacelsian (BaAl2Si2O8) were the primary crystalline phases whereas monoclinic celsian (BaAl2Si2O8) and (Ba(x), Ca(y))SiO4 were also detected as minor phases. Needle-shaped BaSiO3 crystals are formed first, followed by the formation of other phases at longer times of heat treatments. The glass does not fully crystallize even after long term heat treatments at 750 to 900 C.

Bansal, Narottam P.↗
NASA NTRS2005

Boron Nitride Nanotubes-Reinforced Glass Composites

Boron nitride nanotubes of significant lengths were synthesized by reaction of boron with nitrogen. Barium calcium aluminosilicate glass composites reinforced with ~4 weight percent of BN nanotubes were fabricated by hot pressing. Ambient-temperature flexure strength and fracture toughness of the glass-BN nanotube composites were determined. The strength and fracture toughness of the composite were higher by as much as 90 and 35 percent, respectively, than those of the unreinforced glass. Microscopic examination of the composite fracture surfaces showed pullout of the BN nanotubes. The preliminary results on the processing and improvement in mechanical properties of BN nanotube reinforced glass matrix composites are being reported here for the first time.

Bansal, Narottam↗
NASA NTRS2000

Float processing of high-temperature complex silicate glasses and float baths used for same

A float glass process for production of high melting temperature glasses utilizes a binary metal alloy bath having the combined properties of a low melting point, low reactivity with oxygen, low vapor pressure, and minimal reactivity with the silicate glasses being formed. The metal alloy of the float medium is exothermic with a solvent metal that does not readily form an oxide. The vapor pressure of both components in the alloy is low enough to prevent deleterious vapor deposition, and there is minimal chemical and interdiffusive interaction of either component with silicate glasses under the float processing conditions. Alloys having the desired combination of properties include compositions in which gold, silver or copper is the solvent metal and silicon, germanium or tin is the solute, preferably in eutectic or near-eutectic compositions.

Cooper, Reid Franklin↗