Kinetics of vitrification, glass relaxation and devitrification: a unified treatment

Abstract

A generalized survey is made of a series of recent investigations in which a new, generic theory of vitrification is developed. First a derivation is given of the geometry of the thermodynamics of vitrification and of glass stabilization. Out of the momentary values of the thus constructed thermodynamic functions follows, in a consequent way, the phenomenology of the kinetics of glass transition: of vitrification and of glass stabilization (relaxation). Both processes are treated in the framework of an enlarged, non-linear (or quasi-linear) formulation of irreversible thermodynamics as processes of freezing-in and of stabilization of structural disorder, using a generalized internal structural parameter concept. Thus the basic kinetic dependences governing vitrification, glass stabilization and devitrification (including the Kohlrausch stretched-exponent formula, the Stokes–Einstein relation, the Avrami dependence) follow as particular cases of a formalism, directly based on the main principle of thermodynamics of irreversible processes – the phenomenological law – employed here in a non-linear way. The kinetic equations derived from this new approach are compared with existing experimental evidence. In a second step the summarised phenomenological analysis crystallization kinetics in glass-forming systems (and especially the kinetics of overall devitrification) is derived, considering glasses and glass-forming melts as viscoelastic bodies. Significant results, also confirmed by experiment, follow from the interlocking of crystallization and relaxation kinetics.