CORRELATION BETWEEN THE WIDTH OF THE GLASS-TRANSITION REGION AND THE TEMPERATURE-DEPENDENCE OF THE VISCOSITY OF HIGH-TG GLASSES

A correlation exists between the width of the glass transition region measured using DTA or DSC during heating and the activation enthalpy DELTAH(eta)* for the shear viscosity of high-Tg inorganic glasses. This is demonstrated by the constancy of a dimensionless parameter C = (DELTAH(eta)*/R)(1/Tg - 1/Tg'), where Tg and Tg' are temperatures marking the extrapolated onset and finish of the transition region on the DTA or DSC trace. The logarithm of the shear viscosity at Tg, log eta (Tg), is also approximately constant for high-Tg glasses. Using the universal values of C and log eta (Tg), fairly reliable estimates of shear viscosities from the transition range through the working range can be made from the Tg and Tg' values obtained using DTA or DSC.