Effects of high concentrations of liquid phase and magnesia on the grain growth of alumina

Grain growth phenomenon of alumina in the presence of various quantities of liquid phase and magnesia was investigated at 1600 degrees C, and the data were regressed by a statistical approach. The statistical result indicated that liquid phase, compared with magnesia, was a major factor in determining the grain growth mechanism of alumina. The alumina phase developed into faceted grains when the liquid phase was so abundant as to penetrate all the grain boundaries and junctions of alumina, whether with the doping of magnesia or not. This observation implied that magnesia, when co-existing: with a large quantity of liquid phase, did not effectively reduce the degree of anisotropy in interfacial energy of alumina. Nevertheless, when its concentration was high enough to result in the precipitation of MgAl2O4, it avoided the evolution of elongated alumina grains by pinning the fast moving boundaries. (C) 1998 Elsevier Science Limited and Techna S.r.l.