ABSTRACT
Because the sintering temperature is above the recrystallization temperature, recrystallization also takes place. In the case of ceramics, recrystallization results in large grain formation.
Pure alumina is extracted from bauxite ore. Bauxite is a mixture of two hydrates: gibbsite (Al2O3·3H2O), and diaspore (Al2O3·H2O). The purication of bauxite ore is done by the Bayer process, which involves solution and precipitation. The precipitate obtained is aluminum hydroxide. Dehydration of aluminum hydroxide gives α-Al2O3 (corundum). This process gives rise to a purity of 99.9%. The major impurities are Na2O, SiO2, Fe2O3, TiO2, CaO, Ga2O3, and B2O3.
