Thermal conductivity of molten alkali halides: The phenomenology and molecular dynamic simulations

Abstract

Semi-phenomenological consideration of the thermal conductivity based on experimental and molecular dynamics (MD) data for molten alkali halides (AHs) near their melting points was carried out on the basis of scaling concepts associated with the vibrational mechanism of heat transfer. As a result, a general formula for the thermal conductivity is proposed for all molten alkali halides which takes into account the difference in vibrational motion of cation and anion. Characteristic frequencies of the cation and anion vibrations were evaluated through vibrational densities of states. These frequencies allow the values of the thermal conductivity among all AHs melts near their melting points to be estimated to a degree of accuracy close to 10%. Additionally, independent of the assumed heat transfer mechanism, direct simulation of the heat flux was performed within the non-equilibrium molecular dynamics approach. The estimated thermal conductivity of alkali halides’ (AHs) melts (M = Li, Na, K; X = F, Cl, Br, I) are in good agreement with most experimental and MD studies via the Kubo-Green linear response formalism.