KINETIC DEMIXING IN ALPHA-ALUMINA DURING COOLING - INFLUENCE ON THE POWDER REACTIVITY

We study the influence of the thermal treatment conditions on the solu te cation redistributions at the near surface of alumina samples. Expe riments have been done both on Mg-doped alpha-alumina powders and on M g- and Ti-doped alpha-alumina single crystals. The results have been a nalyzed taking into account the influence of two competing effects: th e cation redistribution kinetics and the driving force of matter trans port related to the cooling rate and due to the electrochemical potent ial gradient which appears in the material during cooling. The influen ce of the alumina powder characteristics on the sintering kinetics has been followed using dilatometry. As expected, densification is favour ed when the surface area increases. However, a lower shrinkage is obse rved for powders highly contaminated with silicon.