Thermodynamic optimization of the (Na2O + SiO2 + NaF + SiF4) reciprocal system using the Modified Quasichemical Model in the Quadruplet Approximation

Highlights: → We model the Na2O-SiO2-NaF-SiF4 reciprocal system based on a comprehensive review of all available experimental data. → The assessment includes Na2O-SiO2 and NaF-SiF4 binary systems. → Improvements to the Modified Quasichemical Model in the Quadruplet Approximation are presented. → The very strong short-range ordering among first-nearest and second-nearest neighbors in this system is reproduced. → This work constitutes the first assessment for all compositions and temperatures of a reciprocal oxyfluoride system. - Abstract: All available thermodynamic and phase diagram data for the condensed phases of the ternary reciprocal system (NaF + SiF4 + Na2O + SiO2) have been critically assessed. Model parameters for the unary (SiF4), the binary systems and the ternary reciprocal system have been found, which permit to reproduce the most reliable experimental data. The Modified Quasichemical Model in the Quadruplet Approximation was used for the oxyfluoride liquid solution, which exhibits strong first-nearest-neighbor and second-nearest-neighbor short-range ordering. This thermodynamic model takes into account both types of short-range ordering as well as the coupling between them. Model parameters have been estimated for the hypothetical high-temperature liquid SiF4.