Free volume theories of the glass transition and the special case of metallic glasses

Abstract

Theories based on the concepts of free volume and the existence of holes in liquids are briefly reviewed. Available experimental data on the changes in specific heat and thermal expansion at the glass transition temperature and the temperature dependence of viscosity near transition have been utilized to evaluate the hole formation energy and critical hole size in palladium-, platinum- and gold-based metallic glasses. It has been found that in conformity with theoretical predictions, transport in metallic glasses occurs by the movement of highly ionized atoms. A linear relationship exists between the hole formation energy and glass transition temperature of metallic glasses. It is suggested that a high energy of hole formation is a necessary criterion for easy vitrification of metallic melts. The behaviour of vacancies in crystalline metals is compared with the behaviour of holes in metallic glasses.