Kinetic demixing in α-alumina during cooling: Influence on the powder reactivity

We study the influence of the thermal treatment conditions on the solute cation redistributions at the near surface of alumina samples. Experiments have been done both on Mg-doped α-alumina powders and on Mg- and Ti-doped α-alumina single crystals. The results have been analyzed taking into account the influence of two competing effects: the cation redistribution kinetics and the driving force of matter transport related to the cooling rate and due to the electrochemical potential gradient which appears in the material during cooling. The influence of the alumina powder characteristics on the sintering kinetics has been followed using dilatometry. As expected, densification is favoured when the surface area increases. However, a lower shrinkage is observed for powders highly contaminated with silicon.