Use of the Soft-Sphere Equation of State to predict the thermodynamic properties of the molten salt mixtures LiF–BeF2, NaF–BeF2, and KF–BeF2

• The thermodynamic properties of molten BeF2 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 LiF–BeF2, NaF–BeF2, and KF–BeF2.

A Soft-Sphere Equation of State for the calculation of the thermodynamic properties of molten fluoride salt mixtures is presented. The mixtures considered were binary mixtures of beryllium difluoride (BeF2) and alkali fluorides, which include 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 the binary mixtures. The correlations are valid in the liquid phase for temperatures ranging from 550 K to about 1200 K, depending on the salt. Comparison of the experimental data to values calculated from the correlations indicates that densities can be calculated to within ±4%, enthalpies within ±5%, and heat capacities within ±6%.