Thermodynamic modeling of alkali metal oxide-silica binary melts

The evaluation of the thermodynamic properties as well as the phase diagrams for the binary Na2O-SiO2, K2O-SiO2, and Li2O-SiO2 systems are carried out with a structural model for silicate melts and glasses. This thermodynamic model is based on the assumption that each metallic oxide produces the depolymerization reaction of silica network with a characteristic free-energy change. A least squares optimization program permits all available thermodynamic and phase diagram data to be optimized simultaneously. In this manner, data for these binary systems have been analyzed and represented with a small number of parameters. The resulting equations represent the thermodynamic and phase diagram data for these alkali metal oxide-silica systems within experimental error limits. In particular, the measured limiting liquidus slope at X-SiO2 = 1 is well reproduced.