KINETIC DEMIXING OF SOLUTE CATIONS IN ALUMINA SINGLE-CRYSTALS DURING COOLING

In this work me have analyzed the conditions leading to a kinetic demi xing of species in ceramics during cooling. Estimation of cation redis tributions during cooling in a model material shows that a segregation maximum could be observed near surfaces at an intermediate cooling ra te. This result is explained on the basis of two competing effects: th e cation redistribution kinetics and the driving force of matter trans port related to the cooling rate. Experimental results obtained with t itanium and magnesium-doped alpha-alumina single crystals show that th e segregation of titanium increases when the oxygen partial pressure i ncreases and when the cooling rate and annealing temperature decrease. The opposite effect is generally observed for magnesium and other det ected impurities. Complementary characterizations show that these kine tic reactions are also significantly influenced by the impurities pres ent in the material.