Patent ID: 7736613
Filing Date: 2010-06-15
Classification: C03B,C03C,C30B,Y10T

Abstract:
1. A process for modifying a synthetic silica powder, the process comprising: placing in a vacuum vessel a synthetic silica powder produced by a sol-gel process from a metal alkoxide precursor, wherein the synthetic silica powder comprises gases adsorbed on the powder and has residual carbon and residual hydroxyl groups therein; heating the synthetic silica powder in the vacuum vessel in a range of from a degas temperature of the synthetic silica powder to a temperature below the sintering temperature of the synthetic silica powder while evacuating the vacuum vessel to a pressure of 5 Pa or less, wherein the adsorbed gases are removed from the synthetic silica powder, without sintering the synthetic silica powder, so as to reduce residual carbon in the synthetic silica powder to less than 2 ppm and residual hydroxyl groups in the synthetic silica powder to less than 50 ppm; introducing into the vacuum vessel an atmosphere consisting of helium after removing the adsorbed gases from the synthetic silica powder, wherein the helium is introduced into the vacuum vessel while the synthetic silica powder is still at a temperature of 700° C. or more, such that helium is fully adsorbed on the synthetic silica powder; and, cooling the synthetic silica powder in the atmosphere consisting of helium to a temperature of 400° C. or less to form a modified synthetic silica powder, wherein the degas temperature is about 700° C. or more, and the sintering temperature is 1400° C. or more.