NITRIDATION BEHAVIOR OF SILICON WITH CLAY AND OXIDE ADDITIONS - RATE AND PHASE DEVELOPMENT

Samples pressed from fine powders of Si, Si + SiO2, Si + kaolinite and Si + SiO2 + Al2O3 were nitrided by both the nitrogen demand method an d a constant rate of heating using a graphite resistance furnace at te mperatures of 1100 to 1450 degrees C. The nitridation rate for differe nt compositions and input parameters were determined by continuously m onitoring the time, temperature and pressure within the furnace. By co mparing the different compositions, the effect of impurities, silica a nd particle size on nitriding rate, phase composition and percent theo retical weight gain were determined. Compositions containing high puri ty additives were found to nitride at higher temperatures and to be mo re susceptible to weight loss during nitridation. The prime cause for low weight gains was determined to be volatilization of silicon out of the samples. Si2N2O/O' Sialon was formed in all compositions containi ng the as-used additives and acted to retain the oxygen within the sam ple. (C) 1997 Elsevier Science Limited.