Kinetics of pressure relaxation in a compressed alkali borosilicate glass

Isothermal relaxation experiments were conducted on a mildly densified alkali borosilicate glass with an initial fictive pressure of 500 MPa. Annealing under ambient pressure at various temperatures below the glass transition leads to a gradually decreasing fictive pressure, monitored by ex situ density measurements. Relaxation times are extracted from the temporal evolution of the corresponding reaction coordinate, and an activation energy of 761 ± 40 kJ/mol is found. The timescale of pressure relaxation is similar to that of shear relaxation, but the pressure-dependence of viscosity must be considered for this assessment.