Equivalence of volume, enthalpy and viscosity relaxation kinetics in glass-forming silicate liquids

Structural relaxation in the glass transition range has been investigated for a series of silicates, aluminosilicates, borosilicates and titanosilicates. In complement to viscometry and drop calorimetry, a newly built instrument has been used for making simultaneous differential thermal analysis and dilatometry measurements. For all materials, the various glass transition temperatures correlate linearly with each other, indicating that the kinetics are the same for viscosity, enthalpy and volume relaxation in the glass transition range. This conclusion has been confirmed by measurements of the actual relaxation kinetics for viscosity and volume made for the so-called E borosilicate glass. That the same volume is observed starting from fictive temperatures higher and lower than the run temperature finally demonstrate that equilibrium volume measurements can be made over significant temperature intervals in the glass transition range, allowing the thermal expansion coefficient of supercooled liquids to be determined accurately.