Characteristic temperatures of enthalpy relaxation in glass

The glass transition temperature, Tg, directly measured by differential scanning calorimetry at 10 K/min is compared with the Tg indirectly determined by fitting viscosity data to a viscosity model for oxide glasses. The results show good match between the two Tg values. A standard, unified approach for measuring Tg is proposed. Characteristic temperatures of enthalpy relaxation in glass are defined, and the relationships between these temperatures are illustrated by performing aging and calorimetric experiments on hyperquenched glasses. The features of the energy release peak, the endothermic pre-peak, and the real glass transition are discussed with respect to their physical origins.