Diffusion coefficients and local structure in basic molten fluorides: in situ NMR measurements and molecular dynamics simulations

Abstract

The local structure and the dynamics of molten LiF-KF mixtures have been studied by nuclear magnetic resonance (NMR) and molecular dynamics simulations. We have measured and calculated the self-diffusion coefficients of fluorine, lithium and potassium across the full composition range around the liquidus temperature and at 1123 K. Close to the liquidus temperature, D(F), D(Li) and D(K) change with composition in a way that mimics the phase diagram shape. At 1123 K D(F), D(Li) and D(K) depend linearly on the LiF molar fraction. These results show that the composition affects the self-diffusion of anions and cations more weakly than the temperature. The activation energy for diffusion was also determined and its value can be correlated with the strength of the anion-cation interaction in molten fluoride salts.