Thermal dehydroxylation of porous glass

Abstract

The thermal removal of hydroxyl groups from porous glass tubing depends on both temperature and time. The general relationship between these two parameters and the residual hydroxyl content in 96 % SiO2 (by weight) reconstructed glass was determined by subjecting porous glass tubes to various temperatures in vacuum and in dry air. The temperature for maximum removal of water decreases as the hold time increases. The optimum temperatures result from a balance in rates of water diffusion and glass sintering which retards diffusion. Increasing the total pressure of the atmosphere surrounding the porous glass during the degassing cycle decreases the net degassing rate. The role of other factors such as composition of the porous glass and pore structure are briefly mentioned.