Thermodynamics of vitreous transition

Centre National de la Recherche Scientifique, Université Joseph Fourier, Consortium de Recherches pour l’Émergence de Technologies Avancées, B.P. 166, 38042 Grenoble Cedex 09, France
e-mail: Robert.Tournier@grenoble.cnrs.fr

Received: 22 December 2011
Accepted: 1 February 2012

Abstract

The maximum value at equilibrium of the relaxed enthalpy of some glasses is viewed as a linear function of the annealing temperature from the Kauzmann temperature T_K up to a vitreous transition temperature T^*_g which is not time dependent. The frozen enthalpy and entropy at T^*_g are determined from the specific heat difference between glass and undercooled melt which is constant between T_K and T^*_g. The Gibbs free energy change at T^*_g is equal to zero. The vitreous transition is a thermodynamic transition without latent heat. A model is used to describe this phenomenon. A volume energy saving ε_v equivalent to a complementary Laplace pressure has been added to the classical Gibbs free energy change for a crystal formation in a melt. There is a change of the Vogel–Fulcher–Tammann (VFT) temperature at T^*_g corresponding to a decrease of the free volume disappearance temperature. Scaling laws linking the crystal homogeneous nucleation temperatures to T^*_g are used to predict the two VFT temperatures, the thermodynamic vitreous transition induced by vitreous (super)-clusters and the frozen enthalpy and entropy at T^*_g only knowing T^*_g, the melting temperature T_m and the fusion heat ΔH_m of any fragile glass-forming melt.