Annealing of hydrogen-impregnated and irradiated vitreous silica

The effects of isochronal thermal annealing are reported for a type I commercial vitreous silica which had been saturated with hydrogen at 45 MPa and irradiated to 56 MGy. It has been shown previously that several hundred wtppm of Si-OH and Si-H are formed in this glass by an identical treatment, accompanied by a decrease in density of 520 +/- 20ppm. Infrared spectra of this glass indicate that it contains free Si-OH, hydrogen-bonded Si-OH, molecular H2O, and Si-H. Annealing of this glass initially results in a large change in the shape of the hydroxyl band, with a shift in intensity from one region to another. The initial change in shape is followed by a gradual decrease in band intensity with a return to the pre-irradiated shape. These changes are interpreted as indicating that the H2O molecules react with the network to form additional Si-OH during the initial stages of annealing. At higher temperatures Si-OH and Si-H begin to react to produce H-2, which diffuses out of the glass. Hydrogen-bonded Si-OH is converted to free Si-OH at even higher temperatures. The infrared band due to Si-H does not change in shape, but decreases in intensity during annealing. Sample density, as measured using a sink-float method, increases by 480 +/- 50ppm during thermal annealing. (C) 2004 Elsevier B.V. All rights reserved.