The thermophysical properties of binary mixtures of molten alkali fluoride salts. Part I: Prediction of thermodynamic properties through use of the Soft-Sphere Equation of State

•The thermodynamic properties of molten LiF, NaF, and KF were modeled.•The Soft-Sphere Equation of State (SSEOS) was used for this.•Parameters of SSEOS were determined by regression to data.•SSEOS was then modified to work on binary mixtures of salts.

A Soft-Sphere Equation of State for the calculation of the thermodynamic properties of molten fluoride salts and fluoride salt mixtures is presented. The molten salt mixtures considered contained lithium fluoride (LiF), sodium fluoride (NaF), and potassium fluoride (KF). The parameters of the equation of state were determined by multi-property non-linear regression between experimental data and values calculated from the equation. A mixing rule was developed to represent the thermodynamic properties of binary mixtures of these three compounds. The correlations are valid in the liquid phase for temperatures ranging from 765 K to about 1,550 K, depending on the salt. Comparison of the experimental data to values calculated from the correlations indicates that densities can be calculated to within ±1%, enthalpies within ±5%, and sound speeds within ±4%.