Abstract: Aluminum oxide powder in the form of aggregates of primary-particles, which has a BET surface area of from 10 to 90 m2/g and comprises as crystalline phases, in addition to gamma-aluminum oxide and/or theta-aluminum oxide, at least 30% of delta-aluminum oxide. It is prepared by vaporizing aluminum chloride and burning the vapor together with hydrogen and air, the ratio of primary air/secondary air being 0.01 to 2, the exit speed vB of the reaction mixture from the burner being at least 10 m/s, the lambda value being 1 to 4, the gamma value being 1 to 3 and the value of gamma*vB/lambda being greater than or equal to 55. Dispersion comprising the aluminum oxide powder. Coating composition comprising the dispersion.

Abstract: Aluminium oxide powder in the form of aggregates of primary- particles, which has a BET surface area of from 10 to 90 m2/g and comprises as crystalline phases, in addition to gamma- aluminium oxide and/or theta-aluminium oxide, at least 30% of delta-aluminium oxide. It is prepared by vaporizing aluminium chloride and burning the vapour together with hydrogen and air, the ratio of primary air/secondary air being 0.01 to 2, the exit speed vB of the reaction mixture from the burner being at least 10 m/s, the lambda value being 1 to 4, the gamma value being 1 to 3 and the value of gamma * vB/lambda being greater than or equal to 55. Dispersion comprising the aluminium oxide powder. Coating composition comprising the dispersion.