The first report in 2001 Nippon Tungsten Review(NTR), Si3N4 ceramics used in this study were introduced to oxygen during preparation by three different methods; 1) pre-oxidation of raw powder, 2) sintering in different atmospheres, and 3) controlling the amount of Al2O3 to be added as a sintering additive. Their oxidation behavior in terms of change in mass, morphological surface composition and cross-section of the specimen was studied between temperature of 1200 and 1400°C. Though mass change could hardly be seen below 1300°C, it was observed remarkably at 1400°C. In isothermal oxidation at 1400°C, as the amount of Al2O3 increased from 2mass% to 4mass%, the mass of the specimen also increased.
So that it was recognized to be necessary to analyze the beginning of the oxidation resistance between temperature of 600 and 1000°C, in order to clear the behavior of the oxidation resistance between temperature of 1200 and 1400°C. In this report, there was a trend that the oxidation of specimens with less introduced oxygen began earlier than that of specimens with more introduced oxygen at 1000°C or lower.
