Preparation of dense mullite polycrystals by reaction sintering of kaolin materials and alumina and their microstructure

摘要

Dense and single-phase mullite polycrystals were prepared by reaction sintering of relatively pure kaolins with several kinds of alumina. Removal of coarse kaolin particles >1 μm by sedimentation substantially improved thermal reactivity and sinterability of kaolin and its mixtures with alumina. As for mixtures of refined kaolin and submicron corundum powder having a mullite composition, relative densities of above 98% were accomplished by heat-treatment at 1650°C for 1 h. Effect of alumina particle size on thermal reactivity between alumina and kaolin was investigated, and the difference in thermal reaction sequence between alumina and kaolin was clarified. A combination of sub-micron corundum and elutriated kaolin yielded a monodispersed and fine-grained mullite polycrystals.