Annealing of hydrogen-impregnated and irradiated vitreous silica

Volatilization of boron from E-glass melts

“…Previous work by Shelby and co-workers [5,6] has shown that boron evaporates from E-glass melts under high partial pressures of water vapor, while the hydroxyl concentration in the melt simultaneously increases. Changes in the concentrations of both species can be determined from the infrared spectrum in the region from 4000 to 2000 cm À1 .…”

“…3550 cm À1 is the fundamental stretching band for hydroxyl, while that at ca. 2680 cm À1 is an overtone of the B-O stretching band [5,6,11]. The intensity of each of these bands above background was determined by subtracting the intensity at 4000 cm À1 , where only reflection and scattering losses occur, from the intensity at the band maxima.…”

“…Prior work [6] has shown that the formation of hydroxyl in E-glass reduces the glass transformation temperature for samples treated under conditions where the boron loss is minimal. On the other hand, T g was found to increase when the boron loss was substantial, i.e., the decrease in boron concentration more than offset the gain in hydroxyl concentration.…”

“…This increase in hydroxyl content decreases the connectivity of the vitreous network, which results in a decrease in the glass transformation temperature of the glass and in the melt viscosity [3,4]. While other changes in glass properties also result from the increase in hydroxyl content, those properties involving flow have been found to be most sensitive to changes in the water vapor partial pressure above the melt [3][4][5][6][7][8][9].…”

“…A recent study of the effect of water vapor on the solubility and diffusion of water in E-glass melts indicates that boron volatilization is particularly sensitive to the partial pressure of the water vapor in the atmosphere [5]. Losses of boron counter the effect of gains in hydroxyl concentration on the viscosity and glass transformation temperature of this glass, resulting in variations in these properties which are greater than those which would be desired for a commercial process [6].…”