SURFACE-INDUCED DEVITRIFICATION OF GLASSES - THE INFLUENCE OF ELASTICSTRAINS

The influence of elastic strains on devitrification processes in glass es is investigated. It is shown that in the vicinity and below the vit rification temperature, T(g), thermodynamic inhibition of crystallizat ion has to be taken into account in addition to kinetic inhibition of crystallization connected with the extremely low values of the mobilit y (large values of the viscosity). This thermodynamic inhibition resul ts from the evolution of elastic fields due to a difference in the spe cific volumes of the vitreous and crystalline states of the substance. The inhibiting term is of the same order of magnitude as the thermody namic driving force of crystallization (and may even exceed it). It is considerably diminished for devitrification at the surface of a glass . In this way, elastic strains can be considered as the origin both fo r the absence of bulk devitrification ard for preferential surface cry stallization of glasses in systems with different specific volumes of the vitreous and crystalline states.