The microstructure of sol-gel-derived α-alumina, which was doped with 0.6wt%TiO2 and sintered (1450C, 1h), consisted of thin platelets, with (00•1) faces, in a matrix of equiaxed grains. Short facets at the edges of the platelets developed mainly parallel to the {10•2} planes, while some were parallel to the {11•3} planes. Other edges exhibited irregular curved boundaries. The basal surfaces of the platelets were coated with thin layers (0.5 to 6nm) of an amorphous Ti-containing aluminosilicate phase. This was also present at triple-points. No amorphous phase was found on the short faceted boundaries, on curved boundaries at platelet edges, or at the grain boundaries of equiaxed matrix grains. However, Ti enrichment was observed at all of the boundaries; thus suggesting that Ti segregation alone did not account for the development of the anisotropic microstructure.

A.Kebbede, G.L.Messing, A.H.Carim: Journal of the American Ceramic Society, 1997, 80[11], 2814-20