Chemical structure, medium range order, and crystalline reference state of multicomponent oxide liquids and glasses

A thermodynamic description frame for oxide glasses and melts in unfolded, starting from one-component systems and reaching to systems with many components. The description frame is based on the identification and exploitation of the constitutional relations of mineral phases in the crystalline standard state of a given system at 298 K. Glasses and their melts are described as mixtures of the constitutional phases in their vitreous or liquid state, respectively. This description allows to predict integral thermodynamic properties of glasses and glass melts at an accuracy of <5%, and activity coefficients of individual oxides at < +/-0.3 on a logarithmic scale. The relative concentrations of components for a given composition reflect the coexistence of short-range order structural entities termed chemical structure. The temperature dependence of the configurational entropy S, is calculated for a multicomponent basalt and float glass melt. Viscosities derived from S-c by the medium-range order Adam-Gibbs theory are in excellent agreement with experimental data. (C) 2004 Elsevier B.V. All rights reserved.