Schutz dichter Si3N4-Keramiken gegen Zerstörung durch Hochtemperatur-Oxidation

In temperature range above 1200 degree the stability of silicon nitride materials is more and more influenced by corrosion and creeping processes. The following damages can appear: growing of defects after chemical reactions; initiation and growing of tears; melting and crystallization, developing of bubbles inside of the growing oxide layer; soaking and creeping of the grain boundary phase. This shows that the oxidation stability of the material is determined not only by the structure (amount and composition of the intergranulare phase, amount and kind of crystalline secondary phases) but also by the surface characteristics (porosity, defects, phases). The paper shows possibilities for reaching a high oxidation stability of technical silicon nitrides for both working directions, modification of structure and modification of the materials surfaces