Nitridation behaviour of silicon with clay and oxide additions: Rate and phase development

Abstract

Samples pressed from fine powders of Si, Si + SiO 2, Si + kaolinite and Si + SiO 2 + Al 2O 3 were nitrided by both the nitrogen demand method and a constant rate of heating using a graphite resistance furnace at temperatures of 1100 to 1450 °C. The nitridation rate for different compositions and input parameters were determined by continuously monitoring the time, temperature and pressure within the furnace. By comparing the different compositions, the effect of impurities, silica and particle size on nitriding rate, phase composition and percent theoretical weight gain were determined. Compositions containing high purity additives were found to nitride at higher temperatures and to be more susceptible to weight loss during nitridation. The prime cause for low weight gains was determined to be volatilization of silicon out of the samples. Si 2N 2O O ′ Sialon was formed in all compositions containing the as-used additives and acted to retain the oxygen within the sample.