Patent ID: 7892510

Claim:
A process for increasing hydroxyl group density of silicon dioxide powder, the process comprising treating a silicon dioxide powder, produced by a flame hydrolysis process and having a hydroxyl group density of less than 2.5 OH/nm 2 , at temperatures of 40 to 700° C., under acid conditions, and for reaction times of 5 minutes to 20 hours, to form a reaction mixture; and subsequently separating the treated silicon dioxide powder from the reaction mixture, wherein the treated silicon dioxide powder has a hydroxyl group density of 2.5 to 4.7 OH/nm 2 and wherein the hydroxyl group density is determined by reaction of the treated silicon dioxide powder with lithium aluminium hydride according to the method of J. Mathias and G. Wannemacher in the Journal of Colloid and Interface Science 125 (1988) 61.