OXIDATION RESISTANCE OF SILICON-NITRIDE CERAMICS WITH VARIOUS ADDITIVES

Five silicon nitride ceramics with various additives were evaluated for their oxidation resistance at 1300 ° C in flowing dry and wet air. In a dry atmosphere, the oxidation of all types of Si3N4 except one proceeded in two stages with different reaction rates nearly following the parabolic law. In a wet atmosphere, all types showed a linear relationship between weight gain by oxidation and water varpour content. The water vapour in the atmosphere slightly accelerated the oxidation. The influence of oxidation on room-temperature strength was complex, but there was no observed distinguishable difference of the effect on the flexural strength between dry and wet oxidation. © 1990 Chapman and Hall Ltd.