Thermodynamic modelling of M2O-SiO2 (М – Li, Na, K) melts as applying to mixed alkali systems

A Gibbs energy minimisation approach is used to study silicate melts of Li2O–SiO2, Na2O–SiO2, K2O–SiO2 and Li2O–K2O–SiO2 systems. The list of possible components includes 0.5M2Si2O5, M2SiO3, 0.5M6Si2O7 and M4SiO4, where М = Li, Na, K. The thermodynamic functions are assumed to be equal to those of silicon-oxygen tetrahedra Q3–Q0. The structural unit Q4 corresponds to the thermodynamic functions of pure SiO2. Li2O–K2O–SiO2 melts containing 33 and 40 mol.% of alkali oxide are studied according to a mixed alkali system model. The correspondence of the developed models with actual systems was determined by comparing the results of thermodynamic modelling with experimental Raman spectroscopy melt data along with the limits of their applicability.