Discussion of Thermally Activated Approaches to Glass Fracture

A review of the Charles and Hillig approach to thermally activated crack growth mechanisms indicates that this theory may be applicable to cracking in vacuum at high temperatures but not to stress‐corrosion cracking in aqueous solutions. For stress‐corrosion mechanisms, the ramifications are 2‐fold: (1) Thermal activation analysis shows that the true activation energy in soda‐lime glasses is closer to 0.55 × 10⁵ J/mol (13.2 kcal/mol) than to the 1.2×10⁵ J/mol (29 kcal/mol) obtained using the Charles and Hillig approach; and (2) other models for slow crack growth controlled by bulk diffusion of H₂, OH^‐, or Na⁺‐H⁺ are suggested and shown to be consistent with much of the observed phenomena.