WhiteFusedAlumina

Above 2050°C, pure alumina (Al₂O₃) melts forming a covalent and nonconducting liquid that upon cooling yields a solidified mass of corundum. Corundum is also called in the ceramics and refractory industries white fused alumina. White fused alumina exhibits a fine-grained microstructure with euhedral crystals. most of the large tonnage production uses a tilting electric-arc furnace with three electrodes operating in an AC mode. Once molten and homogeneous, the alumina melt is poured into molds and allowed to cool slowly until demolding. Beta-alumina represents the major impurity observed in white fused alumina due to the concentration of sodium occurring in certain regions. However, the volatilization of the sodium occurs at 2100°C and creates pores that are beneficial. To improve is mechanical strength, usually 2 wt.% of chromia (Cr₂O₃) is added to the melt. Actually, trivalent chromium substitutes isomorphically for the Al³⁺ increasing the toughness of white fused alumina.