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13 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Structural studies of gels and gel-glasses in the SiO2-GeO2 system using vibrational spectroscopy

GeO2 gel and gels in the SiO2-GeO2 system synthesized by the hydrolytic polycondensation of metal alkoxides have been studied by infrared and Raman spectroscopic techniques. The molecular structures, hydroxyl contents, and crystallinity of gels and gel-glasses in relation to the thermal history and GeO2 concentration were investigated. The binary compositions having up to 70 mol percent GeO2 were examined.

Mukherjee, Shyama P.↗
NASA NTRS1987

Glassy GeO2 obtained by the gel process

A comparison is made between GeO2 glass produced by the gel process and by a combined gel and thermal process. The latter appears to be more effective.

Voigt, Bernd↗
NASA NTRS1985

Sol-Gel Glasses

Multicomponent homogeneous, ultrapure noncrystalline gels/gel derived glasses are promising batch materials for the containerless glass melting experiments in microgravity. Hence, ultrapure, homogeneous gel precursors could be used to: (1) investigate the effect of the container induced nucleation on the glass forming ability of marginally glass forming compositions; and (2) investigate the influence of gravity on the phase separation and coarsening behavior of gel derived glasses in the liquid-liquid immiscibility zone of the nonsilicate systems having a high density phase. The structure and crystallization behavior of gels in the SiO2-GeO2 as a function of gel chemistry and thermal treatment were investigated. As are the chemical principles involved in the distribution of a second network former in silica gel matrix being investigated. The procedures for synthesizing noncrystalline gels/gel-monoliths in the SiO2-GeO2, GeO2-PbO systems were developed. Preliminary investigations on the levitation and thermal treatment of germania silicate gel-monoliths in the Pressure Facility Acoustic Levitator were done.

Mukherjee, S. P.↗
NASA NTRS1983

Ultrapure glass optical waveguide: Development in microgravity by the sol gel process

The sol-gel process for the preparation of homogeneous gels in three binary oxide systems was investigated. The glass forming ability of certain compositions in the selected oxide systems (SiO-GeO2, GeO2-PbO, and SiO2-TiO2) were studied based on their potential importance in the design of optical waveguide at longer wavelengths.

Mukherjee, S. P.↗
NASA NTRS1989

'Nose method' of calculating critical cooling rates for glass formation

The use of the so-called 'nose method' for computing critical cooling rates for glass formation is examined and compared with other methods, presenting data for the glass-forming systems SiO2, GeO2, and P2O5. It is shown that, for homogeneous crystallization, the nose-method will give an overestimate of Rc, a conclusion which was drawn after assessing the enfluence of a range of values for the parameters which control crystal growth and nucleation. The paper also proposes an alternative simple procedure (termed the 'cutoff method') for computing critical cooling rates from T-T-T diagrams, which was shown in the SiO2 and GeO2 systems to be superior to the nose method.

Weinberg, Michael C.↗
NASA NTRS1973

Elasticity of some mantle crystal structures. II.

The single-crystal elastic constants are determined as a function of pressure and temperature for rutile structure germanium dioxide (GeO2). The data are qualitatively similar to those of rutile TiO2 measured by Manghnani (1969). The compressibility in the c direction is less than one-half that in the a direction, the pressure derivative of the shear constant is negative, and the pressure derivative of the bulk modulus has a relatively high value of about 6.2. According to an elastic strain energy theory, the negative shear modulus derivative implies that the kinetic barrier to diffusion decreases with increasing pressure.

Wang, H.↗
NASA NTRS1979

Development of high viscosity coatings for advanced Space Shuttle applications

Laboratory studies for increasing the thermal resistance of high viscosity coatings for silica reusable surface insulation are presented. The coatings are intended for the reentry temperature associated with advanced Space Shuttle applications which will involve aerodynamic shear forces during entry from earth orbits. Coating viscosity was increased by (1) reduction in the concentration of the low viscosity additive B2O3; (2) reduction in the particle size of the constituent powders in coatings; and (3) addition of a high viscosity glass former (GeO2). A coating system was produced by combining the three methods which showed apparent higher viscosity than the current coating, while satisfying all the current Shuttle Orbiter coating requirements.

Garofalini, S. H.↗
NASA NTRS1984

Coordination of Fe, Ga and Ge in high pressure glasses by Moessbauer, Raman and X-ray absorption spectroscopy, and geological implications

For some time, it has been recognized that the structure of silicate liquids has a great bearing on such magma properties as viscosity, diffusivity, and thermal expansion and on the extrapolation of thermodynamic quantities outside of the experimentally measurable range. In this connection it is vital to know if pressure imposes changes in melt structure similar to the pressure-induced reconstructive transformations in crystals. In the present study on 1 bar and high pressure glasses, an investigation is conducted regarding the coordination of Fe(3+) in Fe silicate glasses by Moessbauer spectroscopy. Raman spectroscopy is employed to explore the coordinations of Ge(4+) in GeO2 glasses and of Ga(3+) in NaGa silicate glasses, while the coordination of Ga(3+) in NaGaSiO4 glasses is studied with the aid of methods of X-ray absorption spectroscopy.

Fleet, M. E.↗
NASA NTRS1985

Glass formation and properties in the system calcia-gallia-germania

The critical cooling rate for glass formation, R sub c was measured for four compositions in the system calcia-gallia-germania. The activation energy, E, and frequency factor, nu, for the crystallization process were determined by reheating the glasses at varied constant heating rates and measuring the temperature of crystallization. Both E and nu increased, with increasing germania content of the glass, whereas R sub c decreased. The density, refractive index, and Abbe number were also measured; all decreased with increasing GeO2 content. These results are compared with those for calcia-gallia-silica glasses of comparable compositions.

Angel, P. W.↗
NASA NTRS2001

Impact and Collisional Processes in the Solar System

A series of impact experiments on anhydrite CaSO4, in which vaporized sample accelerates an element in a velocity interferometer, generate velocity data that we have recently reanalyzed using an explicit entropy generating finite difference code. The shock pressure required from the onset, and complete vaporization of 30% porous and 70% crystal density anhydrite is 52 +/- 3 and 122 +/- 13 GPa. Using observed acid leaching in non-marine K/T ejecta in North America, and the sharp global increase in Sr-87/Sr-86 ratios recorded at 65 Ma in marine rocks, we demonstrated that global acidification is primarily due to the SO2 released by anhydrite volatilization, and not HNO3 formed from bolide-induced air pyrolysis. Shock temperatures for crystal CaCO3 are measured from 3000 to 7000 K in the 90 to 160 GPa pressure range. These temperatures are much lower than calculated theoretically indicating that possibly bond breakdown at the shock front is occurring. This is the first mineral in which this effect has ever been seen. New data defining the ion species which are produced upon impact of volatilization of metals and minerals using a pulse ultraviolet laser to simulate intense shock heating from a projectile impact indicate that in shock experiments we can for the first time study the speciation of neutrals using a moderate resolution time-of-flight mass spectrometer. Measurements of the gas species from a series of proposed impact experiments appear to be quite feasible. We will attempt these experiments in the next year. Measurements of the impact induced shock wave decay in SiO2 and GeO2 glass are underway to measure these pure oxide properties. Predictive calculations indicate that the pressure will decay as r(exp -2.7) in the phase transition regime, versus a much lower rate of r(exp -1.18), if a phase transition does not occur.

Ahrens, Thomas J.↗
NASA NTRS2006

Single-Phase Rare-Earth Oxide/Aluminum Oxide Glasses

Glasses that comprise rare-earth oxides and aluminum oxide plus, optionally, lesser amounts of other oxides, have been invented. The other oxide(s) can include SiO2, B2O3, GeO2, and/or any of a variety of glass-forming oxides that have been used heretofore in making a variety of common and specialty glasses. The glasses of the invention can be manufactured in bulk single-phase forms to ensure near uniformity in optical and mechanical characteristics, as needed for such devices as optical amplifiers, lasers, and optical waveguides (including optical fibers). These glasses can also be formulated to have high indices of refraction, as needed in some of such devices.

Weber, J. K. Richard↗