Interaction of silicate liquid with a sapphire surface

The wetting behaviour of a calcium aluminosilicate liquid in contact with s apphire of four crystallographically different orientations has been invest igated using scanning electron microscopy and atomic force microscopy. When continuous glass films are heat treated at 1600 and 1700 degreesC, the gla ss dewets the surface to give islands of glass. The heat treatment also cau ses the alumina surfaces to facet which, in turn, influences the shape of t he glass islands. The morphology of the islands with respect to the orienta tion of the facets is essential in understanding the liquid-solid interfaci al energies and the importance of the orientation of the facets. This appro ach allows sequential study of the interaction between the facets and the s ilicate 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 th e relevance of anisotropy in the alpha -Al2O3 crystal structure which may u ltimately control some of the key issues of processing the materials.