High‐Pressure Effects on Oxide Glasses: II, Subsequent Heat Treatment

The annealing or volume variation with time of both silica and boron oxide glasses densified in the rigid state was studied. Appreciable annealing of silica glass was observed at temperatures as low as 200°C and of boron oxide glass at even room temperature. This anomalous volume flow depended on temperature, time, and specific volume and was characterized by small apparent relaxation times and activation energies. The differences between this type of volume relaxation and other properties such as delayed elasticity, cold flow, and stabilization are discussed. Devitrification to α ‐cristobalite observed at temperatures as low as 500°C is attributed to the presence of shear stresses.