Abnormal Grain Growth Of Alumina: Cao Effect

The critical concentration of Ca required for the onset of abnormal grain growth in alumina was determined by controlled doping of Ca in ultra pure alumina, by sintering under clean contamination-free conditions, and by microstructural characterisation. As in the case of Si, the excess concentration of Ca beyond its solubility limit was inversely related to the average grains size at the moment of first appearance of abnormal grains, which corresponds to the moment of sufficient enrichment of Ca in grain boundaries to form stable intergranular liquid films. However, the critical concentration of Ca was found to be in the range of only a few tens of ppm, which is lower than that of Si by almost 2 orders of magnitude.