Model of oxide scale growth on Si3N4 ceramics: nitrogen diffusion through oxide scale and pore formation

Model of oxide scale growth on Si3N4 ceramics has been developed. It accounts for the formation of a porous SiO2 layer between the dense SiO2 scale and ceramics. Pores are filled with nitrogen, which is formed as a result of a chemical reaction of oxygen with silicon nitride at the interface between the oxide scale and ceramics. Oxygen diffuses through the oxide scale to the chemical reaction site. Differential equations of the model describe the growth of the total thickness of the oxide scale and movement of the boundary between the porous SiO2 layer and dense SiO2. This model can be used to describe oxidation kinetics of silicon nitride ceramics, sialons, other nitrides (TiN, ZrN, etc.) and, in general, materials that form a protective oxide scale having a low permeability for gaseous oxidation products.