Thermodynamic analysis of LiF–BeF2 and KF–BeF2 melts by a structural model

An earlier structural model for binary silicate melts and glasses is extended to MF–BeF2 (M = Li, K) systems. The evaluation of the thermodynamic properties as well as the phase diagrams for the binary LiF–BeF2 system and the integral enthalpy of mixing of the KF–BeF2 system are carried out with this model. This thermodynamic model is based on the assumption that each alkali fluoride produces the depolymerization of BeF2 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 analysed and represented with a small number of parameters. The model predicts the chain-length distribution of polymeric ions, even though these are not explicitly treated as structural units of the model. The calculated fluoride polyanion chain-length distribution for the LiF–BeF2 system is in quantitative agreement with the predictions reported in the literature.