Anwendungsmöglichkeiten und Grenzen thermodynamischer Berechnungen zur Interpretation und Voraussage von Korrosionsprozessen

Examples for the use of thermodynamic calculations of heterogeneous equilibria in connection with the development and the high-temperature application of Si3N4-based materials are presented. The conditions of the transition passive/ active oxydation of Si3N4 ceramics are derived from the calculation of the oxygen partial pressure and the SiO partial pressure. Thermodynamic calculations in the Si-Al-C-O-N system show that the beta-SiAlON phase will react with carbon. AlN is produced and the composition of the beta-SiAlON is shifted in direction of Si3N4. The optimization of the high temperatur properties (mechanical strength, creep behavior, resistance against oxydation) of Si3N4 with Nd2O3/Al2O3 sintering additives is presented as the third example for the application of thermodynamic calculations.