Abstract
SiO2 glass was densified by a high pressure MA-8 apparatus composed of eight cubic WC anviles at pressure up to 80kb and temperature up to 920°C, The density of densified SiO2 glass was measured by means of sink-float method, and the stability of densified SiO2 glass accompanied with heat treatment was examined from the density change. It was found that MA-8 apparatus was very appropriate for obtaining the densified glass having no crack and large volume, because the pressure was very closed to the hydrostatic condition. The maximum densification of 2.673 g/cm3 was obtained at 71 kb and 920°C. This was much greater than the density of a-quartz. Reheating the densified SiO2 glass showed that the specimen densified at higher temperature was more stable, and that the density recovered to the original value by heating at 1000°C for a few hours. Activation energy calculated from the decrease of density at the relaxation process of densified SiO2 glass was about 6 kcal/mol. This value is very much smaller than the bonding energy and the activation energy for diffusion. This suggests that the densified state takes place through the displacement of atoms or atom groups in the network structure.
