Molecular dynamics study of the transport properties and local structures of molten binary systems (Li, Na)Cl, (Li, K)Cl and (Na, K)Cl

The structures and dynamic properties of molten alkali binary chlorides LiCl-NaCl, LiCl-KCl and KCl-NaCl at 1100 K have been calculated across the full composition range in this paper in detail by molecular dynamics simulations. The effects of LiCl on the local structures and transport properties as the self-diffusion coefficients, viscosities and ionic conductivities of molten NaCl and KCl as well as the mixing effects between NaCl and KCl have been calculated and analyzed. The results reveal that the Tosi-Fumi potential predicts negative composition dependence for density and positive composition dependences for ionic diffusivity and ionic conductivity as the contents of LiCl are increased for molten LiCl-NaCl and LiCl-KCl. As the KCl contents are increased, the ionic diffusivity of molten KCl-NaCl shows weak composition dependence. However, the density and ionic conductivity exhibit negative composition dependences. The transport performances of these mixed melts are dominated by the local structures and interatomic forces. The shear viscosities of the mixtures decrease firstly and then increase under the influences of these two factors. For molten KCl or NaCl, with the addition of a smaller cation (Li+), the interactions between counter ions and closed packs between anions are weakened, while closed packs between cations are promoted. What's more, the smaller the added ion is, the more pronounced the effects are. However, the addition of a larger cation presents the opposite effects.