High-Temperature Oxidation and Corrosion of Engineering Ceramics

The problems of high-temperature oxidation and corrosion of Si₃N₄ and SiC are discussed. Other ceramics usually do not meet the requirements of structural applications at high temperatures. If the application has to meet very defined limits of size change, it is necessary to specify the exact material composition, as well as the atmosphere composition and physical environment to be able to specify the limits. This is in any case true for extremely reducing conditions or very high temperatures. Under oxidizing conditions, the region between ≈850 and 1100°C should be avoided when salty, sulfurous, and wet fuel conditions are expected. High temperature limits for long-time applications of Si₃N₄ in oxidizing environments are between 1200 and 1400°C, corresponding to eutectic temperatures of the glass phase. The ultimate limit for long-time use of SiC is likely to be between 1700 and 1800°C, where bubble formation and spallation may become inevitable.