Ceramics-Silikáty 49 (2) 91-96 (2005)

MODELING OF THE REVERSIBLE PART OF STEPSCAN DSC MEASUREMENT OF THE GLASS TRANSITION

M. Chromčíková, J. Holubová, M. Liška, Z. Černošek, E. Černošková

The reversible part of StepScan DSC record of a glass in the region of the glass transition was interpreted as a measure of the conversion degree a of the A « B type equilibrium reaction identified with a reversible part of glass « undercooled melt transition. The temperature course of the conversion degree, a(T), was expressed in terms of the temperature dependence of the equilibrium constant alternatively with the temperature dependent and temperature independent reaction enthalpy. Experimental data of eight various inorganic and organic glasses were fitted by the proposed model. The formalism of temperature independent formal reaction enthalpy was sufficient to reach an acceptable quality of the fit, i.e. the fit accuracy level of an average experimental error. The model of temperature dependent formal reaction enthalpy was found inappropriate due to strong inter-correlations between the regression parameters. In contrary to the previously reported model the proposed model yields the maximum conversion rate at the conversion degree lower than 0.5.

Keywords: Glass, Glass transition, Dynamic DSC, StepScan DSC, Relaxation phenomena, Thermodynamic modeling