Interaction of Silicate Liquid with Sapphire Surfaces

Abstract

The wetting behavior of a calcium aluminosilicate liquid in contact with sapphire of four crystallographically different orientations has been investigated using scanning electron microscopy and atomic force microscopy. Continuous layers of glass films heat-treated at 1600°C and 1700°C result in dewet pockets of glass on the surface. The heat treatment also causes the alumina surfaces to facet which presents interesting shapes to the glass pockets. The morphology of the pockets with respect to the orientation of the facets is useful in understanding qualitatively the liquid-solid interfacial energies relative to the orientation of the facets. This approach enables a sequential study of the interaction between the facets and the silicate liquid. Based on temperature, the equilibrium composition of the silicate changes by solution-precipitation and evaporation processes which affects the facet and step morphology. This experiment directly emphasizes the relevance of anisotropy in the α-Al₂O₃ crystal structure which may ultimately control some of the key issues of materials’ processing.