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
