Reconstructing oxide surfaces.

Abstract

The work presented here is concentrated on surfaces and interfaces in alumina (Al2O3), anorthite (CaAl2Si2O8), silica (SiO2) and rutile (TiO2). While each of these materials have different crystal structures and measurable properties, they all exhibit similar mechanisms for fundamental behavior. The topics researched and discussed lead into each other. Faceting describes the movement of atoms to a lower energy configuration. While faceting of the surface is only considered, grain boundaries can be faceted. In cross-section, facets resemble grain boundary grooves. Grooves and ridges form where a grain boundary intersects the surface of a material. The grooves facilitate grain boundary migration and diffusion. The surface tension at the groove is governed by Young's equation, which balances the interfacial forces between the solid and vapor. Glass films can wet or dewet the surface a grain boundaries. Whether the film wets or dewets depends on the surface energy of the surface and the liquid. Capillary forces determine the type of dewet patterns formed on the surface. Again, the surface-vapor-liquid interfaces are governed by Young's equation. Liquid films at grain boundaries facilitate densification and grain boundary migration. Liquid phase sintering (LPS) uses capillary forces and the dissolution/reprecipitation process to sinter green compacts to a high density at lower temperatures. Capillary forces and surface tension can also cause the liquid film to penetrate or exude from the grain boundary. Various forms of microscopy have been used to characterize and relate these phenomena.