Solidification of two fused cast Al2O3-ZrO2-SiO2 materials in an aero acoustic levitator

Due to their excellent high-temperature properties and corrosion resistance, AZS materials are widely used in glas making. Two industrially available fused cast AZS materials were chosen for this study. One composition was close to the ternary eutectic of zirconia, mullite, and corundum. The other material was close to mullite composition with approx ten wt% ZrO2. The microstructure and phase composition of the received material was analyzed. Additionally, the materials were remelted in an aero acoustic levitator. The fused cast grains and the remelted samples showed significant differences in the microstructure and phase composition. Due to the high cooling rates and homogeneous nucleation under containerless conditions, both materials tended to form a glassy phase. Cooling samples with a pre-existent nucleus or controlled conditions yielded a fine-grained crystalline microstructure. For conventional cooling, the silica and alumina-rich material exhibited large corundum precipitates. In contrast, the containerless processed sample showed primary precipitation of mullite.