The effect of yttrium on densification and grain growth in α-alumina

The grain growth and densification have been investigated in very high-purity α-alumina doped with varying amounts of yttrium (0 to 3000 wt ppm of yttria) and sintered in air at 1450, 1550 and 1650 °C. Yttrium doping inhibited densification and coarsening at 1450 °C, but had very little effect at 1550 °C and no effect at 1650 °C. The change in densification behaviour is suggested to be related to the transition with increasing temperature from grain boundary diffusion to lattice diffusion controlled densification. The coarsening rate increases faster with temperature than the densification rate. This was correlated with a higher measured activation energy for grain growth than for the diffusion processes, which control the densification.