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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Diffusion in the system K2O-SrO-SiO2. II - Cation self-diffusion coefficients.

The self-diffusion coefficients were measured by introducing a slab of glass previously irradiated in a reactor between two slabs of unirradiated glass. By heating the specimens, etching them sequentially and determining the radioactivity, self-diffusion coefficients for K and Sr were measured. It is pointed out that the results obtained in the investigations appear to support the proposal that the network of the base glass predominantly controls the activation energy for the diffusion of ions.

Varshneya, A. K.↗
NASA NTRS1980

Extreme ultraviolet optical properties of two SiO2 based low-expansion materials

The reflectances of two low-expansion materials, a recrystallized glass ceramic and a high silica glass, have been measured at five angles of incidence from 15 to 85 deg in the wavelength region from 80 to 310 A and in some cases up to 1050 A. Optical constants are derived and silicon core-level transitions analyzed.

Rife, J.↗
NASA NTRS1981

Effect of CeO2, MgO and Y2O3 additions on the sinterability of a milled Si3N4 with 14.5 wt% SiO2

The sinterability of alpha Si3N4 with 0-5.07 equivalent per cent of CeO2, MgO, or Y2O3 has been studied in the temperature range 1650-1820 C by density measurements and X-ray diffraction analysis. Maximum densities were obtained in the range 1765-1820 C and were 99.6% of theoretical with 2.5% CeO2; 98.5% of theoretical with 1.24 to 1.87% MgO, and 99.2% of theoretical with 2.5% Y2O3. Densities 94% or more of theoretical value were obtained with as little as 0.62 equivalent per cent additive.

Arias, A.↗
NASA NTRS1981

The MgO-Al2O3-SiO2 system - Free energy of pyrope and Al2O3-enstatite

The model of fictive ideal components is used to determine Gibbs free energies of formation of pyrope and Al2O3-enstatite from the experimental data on coexisting garnet and orthopyroxene and orthopyroxene and spinel in the temperature range 1200-1600 K. It is noted that Al2O3 forms an ideal solution with MgSiO3. These thermochemical data are found to be consistent with the Al2O3 isopleths that could be drawn using most recent experimental data and with the reversed experimental data on the garnet-spinel field boundary.

Saxena, S. K.↗
NASA NTRS1982

Radiation-induced defects in SiO2 as determined with XPS

An analytical method based on oxide/substrate intensity ratios is used to deduce the product of the atomic number density and electron mean free path as a function of depth, for the cases of device-quality gate oxides grown on Si substrates and irradiated with zero to 20 eV electrons during in situ X-ray photoelectron spectroscopy. These structures had been thinned stepwise to 25-60 A by means of a wet chemical depth-profiling procedure. Si(3+) species are formed in the Si/SiO2 interface region, and their observation during their relaxation and annihilation is correlated with strained Si-O-Si bonds. The observation of bond of cleavage and bond strain gradients in these samples is used to extend silica devitrification models for the explanation of fixed oxide charge generation and interface states.

Grunthaner, F. J.↗
NASA NTRS1983

Elevation of liquidus temperature in a gel-derived Na2O-SiO2 glass

The liquidus temperatures of a 19 wt% soda-silica glass prepared by gel and conventional techniques were determined. X-ray diffraction measurements of the glasses which were heat-treated at several temperatures were used to experimentally determine the liquidus temperatures. It was found that the gel-derived glass has an elevated liquidus. This result is discussed in relation to the previous discovery that the immiscibility temperature of this gel-derived glass is elevated

Weinberg, M. C.↗
NASA NTRS1983

Techniques for improving the Si-SiO2 interface characterization

The two techniques which have provided most of the information on interface states in MIS-C (metal-insulator-semiconductor-capacitor) structures are the 'quasi-static method' and the 'conductance method'. Sher et al. (1979) and Su et al. (1980) have suggested a number of improvements concerning these methods. The present investigation has the objective to extend the earlier results and to offer a new tentative interpretation of the data. A critical review is conducted of the data collection and reduction techniques for the quasi-static method, taking into account the sample, the quasi-static capacitance, and the surface potential. In connection with a discussion of the conductance method, attention is given to parallel conductance and capacitance measurements, interface-state densities, time constants, and measurements on a (110) surface orientation.

Sher, A.↗
NASA NTRS1984

A thermodynamic model for subsolidus equilibria in the system CaO-MgO-Al2O3-SiO2

It is shown that the high temperature enthalpy of solution data for pure phases and solid solutions in the CMAS system are, for 'gabbroic' and 'peridotitic' compositions, consistent with available phase equilibrium data for the MAS, CAS and CMAS systems. A refined set of values of thermodynamic properties for these phases and solid solutions is tabulated. The small differences between the new data set and that of Helgeson et al. (1978) arise from new data on heat capacity and enthalpy being incorporated. The important constraints applied and the major difficulties in fitting which arose are summarized.

Wood, B. J.↗
NASA NTRS1984

Crystallization of Na2O-SiO2 gel and glass

The crystallization behavior of a 19 wt pct soda silica gel and gel-derived glass was compared to that of the ordinary glass of the same composition. Both bulk and ground glass samples were utilized. X-ray diffraction measurements were made to identify the crystalline phases and gauge the extent of crystallization. It was found that the gel crystallized in a distinctive manner, while the gel glass behavior was not qualitatively different from that of the ordinary glass.

Neilson, G. F.↗
NASA NTRS1984

Electron escape depth variation in thin SiO2 films measured with variable photon energy

A double crystal monochromator at the Stanford Synchrotron Radiation Laboratory is used to study the Si/SiO2 interface, using photon energies of hv = 1950-3700 eV. This photon energy range allows interfaces to be observed through oxide layers 50 A thick or more. Variations in electron escape depth and/or oxide density as a function of distance from the interface are observed over the entire kinetic energy range (100-3600 eV). These differences are attributed to a strained oxide layer near the interface.

Hecht, M. H.↗