(456b) Chemical Erosion of Silica Nitride Ceramics

The high temperature mechanical and fracture properties of bulk ceramics such as Si3N4 and SiC are dominated by the strength and chemical stability of the thin intergranular glassy film (IGF) that forms during the liquid phase sintering process. This IGF interface is susceptible to chemical erosion, particularly at elevated temperature and pressure. We are interested in understanding the mechanism of chemical erosion of the silica-nitride material exposed to gases such as carbon monoxide or water at elevated temperature. It has been previously demonstrated that the weak IGF interface can be strengthened by using sintering additives such as rare-earth oxides which segregate to the IGF and induce local ordering. In this study, we performed solid-state, density functional (DFT) simulations of chemisorption, surface and in-bulk diffusion for various models of the IGF interface. The impact of rare-earth oxides on chemisorption and diffusive processes will also be discussed.