Fracture-induced change in the internal energy of silicate glasses

Crushing a silicate glass is known to cause fracture-induced permanent strain. In this study, the magnitude of this strain is estimated for SiO2, 15Na2O · 10CaO · 75SiO2, and 10K2O · 38PbO · 52SiO2 glasses from the viewpoint of a change in internal energy. Samples were crushed with a percussion mortar and subsequently annealed. Heat of solution to HFaq was measured and the difference in heat of solution between as-crushed and well-annealed samples was regarded as the fracture-induced change in internal energy. This value is about 10 kJ/mol-SiO2 for SiO2, 7 kJ/mol-SiO2 for soda-lime silicate, and 2 kJ/mol-SiO2 for lead silicate glasses. The annealing behavior indicates that the fracture-induced permanent change is due to densification. The compositional dependence of the permanent change should be due to the difference in free volume of glasses, i.e., glass with large free volume will exhibit large fracture-induced structural change.