Microstructure development and solid state reactions during liquid phase sintering

Microstructure development during heating of alumina powders coated with precursors of various metal oxides has been examined. EM studies revealed that the alumina particle surfaces act as sites for heterogeneous nucleation. The solid solution between alumina and titania after the nucleation of rutile on the surface of alumina resulted in sintering rate enhancement, while the slow self-diffusion characteristics of zirconia resulted in {open_quotes}droplets{close_quotes} on the surface of alumina which impeded the grain boundary migration. The final structure of the alumina simultaneously doped with cupric oxide and titania or bismuth oxide and titania was reached in the presence of a liquid phase but large shrinkage occurred before the liquid formed. It was concluded that when a solid state reaction takes place between a matrix phase and a second phase or between second phases during heating, matter transfer is faster and thereby, the sintering is accelerated.