Abstract
The SiO2-Al2O3 powders containing 68 to 78wt% Al2O3 were synthesized by spray pyrolysis technique to study their sinterability at 1630°-1650°C. The prepared amorphous powders were transformed directly to crystalline mullite by calcination above 980°C. When heat-treated at temperatures above 1500°C, corundum was detected in the powder composed of 78wt% Al2O3. Densification of the silica-rich powder was accelerated by the formation of glassy phase, and the bulk density of alumina-rich powder also increased with the increase of alumina content. While, in the 3Al2O3⋅2SiO2 region, poor densification was observed. The shape of mullite grain in the sintered body changed from needle-like to roundish in compliance with the increase in alumina content, and corundum particles were observed along the grain-boundary in the sintered specimen of 78wt% Al2O3 content. Glassy phase which consists merely of silicon and oxygen was observed along the grain-boundaries of the 70wt% Al2O3 sintered body.
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