Patent ID: 6162413
Filing Date: 2000-12-19
Classification: C01F,C01P

Abstract:
A method for producing .alpha.-alumina having an alumina purity of at least 99.9%, a sodium content of 40 ppm or less, an iron content of 20 ppm or less and a calcium content of 40 ppm or less comprising the steps of:(i) grinding aluminum hydroxide which is produced by the Bayer process or grinding a transition alumina which is obtained by calcining aluminum hydroxide produced by the Bayer process so that the aluminum hydroxide or transition alumina has a 50% diameter (D.sub.50) in a cumulative particle size distribution of 10 .mu.m or less,(ii) calcining the ground aluminum hydroxide or transition alumina in an atmosphere containing at least 10 vol. % of a hydrogen chloride gas, or an atmosphere containing at least 10 vol. % of a chlorine gas and at least 5 vol. % of steam, at a temperature of 600 to 1400.degree. C. to form .alpha.-alumina; wherein the amount of sodium is reduced to 40 ppm or less and the amount of iron is reduced to 20 ppm or less in the .alpha.-alumina formed; and(iii) washing the .alpha.-alumina with water; wherein the amount of calcium is reduced to 40 ppm or less.