The infrared absorption spectra of boron oxide glasses of low and high water content have been obtained in the 400-to 4000-~m.-~ region using thin films or fine powders dispersed in a liquid. A structural interpretation of the glass spectra has been made with the aid of the spectra of the closely related materials boric acid, orthorhombic metaboric acid, and partly deuterated boron oxide glass of high water content. It has been shown that the glass spectra are consistent with a random-network structure in which each boron is triangularly coordinated by three oxygens and that the presence of water leads to weak hydrogen bonding between oxygen atoms. No evidence for a substantial amount of tetrahedral coordination of boron by oxygen has been found in glasses of either low or high water content.

absolute number densities of neutral atom and ion a t the ground states by using the absorption or fluorescence technique (1 0, 51, 52). Registry No. Ar, 7440-37-1; Mg, 7439-95-4. LITERATURE CITED (1) Demers, D. R.; Allemand, C. 0. Anal. Chem. 1981, 53, 1915. (2) Fassel. V. A.; Knlseley, R. N. Anal. Chem. 1974, 46, 1llOA. (3) Houk, R. S.; Fassel, V. A.; Flesch, G. D.; Svec, H. J.; Gray, A. L.; Taylor, C. E. (IO) Nojlri, Y.; Tanabe, K.; Uchida, H.; Haraguchl, H.; Fuwa, K.; Wlnefordner, J, D.The use o f aolkhtate %I NMR spectroscopy to analyze q N 4 powders b demonstrated for a series of commercial and research samples. I n particular, two dlfferent commercial powders contaln 20% and 30% amorphous Si3N4 content, as identtfied by the applicatlon of methods described herein.These same materlals had been analyzed by X-ray dmtaction as only crystalline SiaNp NYR spectroscopy is capable of dlstlngulohlng among dlfferent amorphous silicon specks normally found In preparatlons of S13N4 powders. These Include amorphous S13N4, sHlcon oxynltrldes, sllicates, and elemental slllcon. The measurement of concentration of these species Is made for correlatlon wHh properties of powder sinterability.Sinterable silicon nitride (Si3N4) has been intensely investigated since 1974 because of potential applications as a tough, refractory ceramic material (1). The production of reliable and cost-effective structural Si3N, ceramic by sintering of powders must begin with powders that have, among other qualities, an a-phase content in excess of 85% (2). Excessive @-Si3N4 in the powder interfers with microstructure changes that accompany sintering. On the other hand, some a-Si3N4 (amorphous) can aid densification of the final material (3).Oxygen and elemental silicon can also aid sintering, although concentrations in excess of 2% can deteriorate mechanical properties at elevated temperatures. Oxygen normally appears as amorphous silicon oxynitrides and silicates.In view of what is known about the effects of the powder's phase and purity on sinterability and fiial ceramic mechanical properties, it is necessary to have rapid, reliable methods for the determination of the crystallinity and purity of batches of Si3N4 powder before carrying out final product formation and sintering. Traditionally, X-ray powder diffraction has been used to determine the presence of @-Si3N4, silicon oxynitrides, silicates, and silicon in the a-Si,N4 powders. The powder diffraction technique fails, however, in the identification of amorphous species. All amorphous species contribute to the background diffraction signal whose intensity is difficult

The kinetics of K+-Na+ exchange in sodium borosilicate glasses containing 20 mol% Na,O were studied as a function of glass composition and exchange time and temperature. The distribution of K in the glass after exchange in molten KNO, was determined using an electron microprobe. In those specimens which were not chemically attacked by the molten salt, the K profiles were consistent with Fickean behavior. The calculated interdiffusion coefficients varied with local composition m each specimen. This composition dependence and its variation with temperature could be fitted approximately to a mixed-alkali model using the Nernst-Planck relation for diffusive fluxes. However, some deviation from this behavior, presumably as a result of the generation of microscopic stresses around an exchange site, was observed. The dependence of the apparent activation energy, E , on the BISi ratio was analogous to that of the activation energy for ionic conduction in these glasses: E decreased with increasing fraction of nonbridging oxygen. This result disagrees with the presumed behavior in sodium aluminosilicate glasses.

Equations have been developed for the transparency factor applicable to the intensity of x-rays scattered from very weakly absorbing materials in the standard diffractometric technique. The expressions differ from the standard absorption correction because of the variation of effective scattering volume with angle. Both equations and illustrative curves are presented.

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