Effects of Y<sub>2</sub>O<sub>3</sub> Addition on the Sinterability and Microstructure of Mullite (Part 2)

Abstract

The phenomena in the sintering process of Y2O3-added mullite ceramics and the crystallization behavior of liquid phase in sintered bodies were studied using differential thermal analysis, X-ray powder diffractometry, scanning and transmission electron microscopies. The mullite powder compacts containing 2-10wt% Y2O3 were sintered at 1500°C for 2h, and were then cooled in furnace or quenched in order to study the crystallization phenomena. During the firing process, a liquid phase containing Y, Al, Si and O components was formed in the sintered body. When the specimen was cooled in furnace, the liquid phase solidified into glassy state or crystallized depending on the amount of Y2O3. The glass phase in the furnace-cooled specimen could also crystallize on annealing. Some crystallization phenomena of the liquid phase were observed. A small α-Al2O3 grain, which was formed by the solid state reaction between mullite and Y2O3 during the firing process, was observed inside a mullite grain. Larger α-Al2O3 grains, which were formed from the solution-reprecipitation process of liquid phase, were observed in the sintered body.