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

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.