Enthalpy relaxation in Na₂O-CaO-SiO₂ glass - Mazurin's versus Moynihan's approximation of relaxation times

Abstract

DSC heating curves of the 15Na₂O-10CaO-75SiO₂ glass were analyzed by nonlinear least squares regression treatment in the frame of Narayanaswamy - Tool relaxation model with the time-temperature dependence of relaxation time alternatively approximated by Mazurin's (TNMa) or Moynihan's (TNMo) expression. Four different heating rates (5 °C/min., 10 °C/min., 20 °C/min., and 50 °C/min.) were used for recording the DSC curve of each glass. The glasses for the DSC experiment were prepared by controlled cooling with the cooling rate of 50°C/min. It was statistically proved, that both used models give comparable results. On the other hand, significant differences between the parameter estimates of relaxation model were identified for various heating rates. It was concluded that the multirespond regression treatment is needed to overcome this ambiguity.