In situ crystallization of silicate glass films deposited on α-Al2O3

Polycrystalline alumina compacts often contain amorphous films at grain boundaries and triple junctions as a result of the liquid-phase sintering process. An anorthite-based composition (CaAl2Si2O8) is typical of the glassy phases observed in these materials. With appropriate heat treatments the glass phase can be crystallized, which can influence the properties of the bulk material. Deposition of a thin film of glass on single-crystal α-Al2O3 is being used to study the influence of specific crystallographic orientations on the alumina-glass interface properties. Vapor-phase growth of glass on different orientations of α-Al2O3 has been accomplished previously and, through subsequent thermal treatments, the alumina was shown to facet preferentially when in contact with a glassy phase. In the present study, calcium-aluminosilicate glass films were grown on single-crystal α-Al2O3 at relatively low substrate temperatures (<950°C) by pulsed-laser deposition. These films were then heated in the electron microscope to determine the effect of α-Al2O3 crystallography on crystallization of calcium-aluminosilicate glasses.