Temperature-dependent densification of sodium borosilicate glass

Abstract

Densified glasses recovered from a high-pressure state are of potential technological interest due to their modified physical and chemical properties. Here we investigate the temperature-dependent densification behavior of a sodium borosilicate glass in a gas pressure chamber at 1 GPa. The temperature is varied for a 30 min treatment between 0.6T_g and 1.15T_g, where T_g is the glass transition temperature, and the treatment duration is varied between 10 and 10 000 min for compression at 0.9T_g. Permanent densification occurs for temperatures above 0.7T_g and the degree of densification increases with increasing compression temperature and time, until attaining an approximately constant value for temperatures above T_g. The same temperature and time dependence is also found for the glass mechanical properties (hardness and brittleness) and the network structure, i.e., fraction of three-fold versus four-fold coordinated boron atoms and ring versus non-ring trigonal boron atoms, and the extent of mixing of Si and B. The results provide insights into the temperature-dependence of the network densification and the relative roles of viscous flow and more localized rearrangements.