Thermochemical properties of silicate glasses and liquids: A review

Abstract

A prerequisite for thermodynamic modeling of silicate melts is a knowledge of basic thermodynamic data for glasses and liquids. The recent advances in the measurement and rationalization of these data are thus reviewed in this paper, with particular emphasis on the influence of the thermal history of glasses on their various thermochemical properties. Above room temperature the heat capacities of glasses (Cpg) do not depend sensitively on thermal history. They are almost additive functions of the chemical composition, which can now be empirically calculated to within about 1%. In contrast, the heat capacities of liquids (Cpl) do not generally vary linearly with composition, especially for aluminosilicates. But more experimental data would be useful to improve the accuracy of the models proposed for calculating the heat capacity of molten rocks. The available enthalpies of fusion (ΔHf), which depend measurably on the thermal history of the glasses used in solution calorimetry measurements, are summarized for silicates of geochemical or theoretical interest, and new values have been derived for some additional compositions. The usefulness of these data for calculating the entropies of liquids is pointed out, in particular for calculating the entropies and configurational entropies of the liquids. Finally, available enthalpies of mixing of glasses and liquids are also summarized. A few examples are used to illustrate the major influence of the thermal history of glasses on their mixing properties, and it is suggested that the ternary excess enthalpies of mixing observed in simple systems could be a spurious consequence of neglecting this influence.