Protective coatings for non-oxide ceramics

interface that were in direct contact with the glass dissolved until the glass became saturated with nitrogen. Then the Si(3)N(4) grains moved from their original position towards the free glass surface. The extent of dissolution and consequent grain removal was influenced by the sintering aids used to densify the silicon nitride, and in particular by the refractoriness of the secondary phase thar they formed. In silicon carbide bused systems, the attractive force between the grains is stronger than in silicon nitride. As a consequence, at the processing temperature the liquid glass coating wet the SiC well but did not affect its microstructure because there was no driving force for glass penetration even after long treatments.