Heat capacity of molten alkali halides

Experimental data on the heat capacities of molten alkali halides near their melting points are analyzed depending on cation-anion composition. The isochoric heat capacities of all 20 liquid alkali halides were calculated using thermodynamic perturbation theory (TPT) based on a reference system of charged hard spheres + charge-induced dipole contribution to pairwise ionic interaction. Changes in the heat capacity depending on the ratio of ionic radii and polarizabilities are identified and described. On this basis, recommended heat capacity values are selected from the various experimental data. It is shown that the reduced isochoric heat capacity (C-V/k(B)) should increase with a mismatch in the cation and anion radii as an even function with a minimum. Charge-induced dipole interactions lead to a breaking of the specific Coulomb symmetry, resulting in a more significant increase in the heat capacity for salts containing the smallest cations, as well as the anions with largest size and polarizability. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study analyzes the heat capacities of molten alkali halides based on thermodynamic perturbation theory (TPT) and describes their changes depending on ionic radii and polarizabilities. The research shows that the heat capacity increases as an even function with a minimum when there is a mismatch in the cation and anion radii, and the heat capacity is significantly increased by charge-induced dipole interactions.