Thermodynamic Mechanism for Cation Diffusion Through an Intergranular Phase: Application to Environmental Reactions with Nitrogen Ceramics

摘要: A mechanistic model for the migration of cations from a continuous intergranular phase in response to environmental reaction at surface polyphase silicon nitrides is described. It predicts that composition may be modified and controlled, with consequential beneficial or detrimental effects, by deliberate formation scales rich poor impurity cations. Two examples are illustrated, “purification” using an SiO2 layer leading high temperature strength enhancement degradation corrosion when CaO employed.