Advanced manufacturing process of ultrahigh-purity α-Al₂O₃

An advanced method was investigated for production of ultrahigh-purity alumina α-Al₂O₃ (UHPA, 99.999%) with an oxidation of aluminum (purity 99.7%) granules in 0.1 g/mol aqueous solution of potassium hydroxide with a subsequent hydrochloric acid treatment and calcination of the oxidation product at 1450 °C. The evolution of impurities concentration after subsequent acid and thermal treatment was studied. The total concentration of impurities and especially iron impurity was decreased in UHPA while the concentration of alkali metals (K, Na, Li), on the contrary, was increased by the used production method (Al granules → reaction with alkali → acidic treatment + washing → thermal treatment). The proposed method allowed production of UHPA with purity 99.99% and 99.999% from pellets with the initial purity of aluminum 99.70% and 99.99% respectively. The advantage of the studied method of UHPA production is it's low cost and utility.