Interaction of silicate liquid with a sapphire surface

The wetting behaviour 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. When continuous glass films are heat treated at 1600 and 1700°C, the glass dewets the surface to give islands of glass. The heat treatment also causes the alumina surfaces to facet which, in turn, influences the shape of the glass islands. The morphology of the islands with respect to the orientation of the facets is essential in understanding the liquid–solid interfacial energies and the importance of the orientation of the facets. This approach allows sequential study of the interaction between the facets and the silicate liquid. The equilibrium composition of the silicate changes as the temperature changes: solution, precipitation and evaporation processes may all affect the facet and step morphology. This study directly emphasizes the relevance of anisotropy in the α-Al2O3 crystal structure which may ultimately control some of the key issues of processing the materials. © 2000 Taylor and Francis Group, LLC.