Multicomponent diffusion in molten LiCl-KCl: Dynamical correlations and divergent Maxwell-Stefan diffusivities

摘要

Multicomponent diffusional mechanisms in the ternary LiCl-KCl system are elucidated using the Green-Kubonformalism and equilibrium molecular dynamics simulations. The Maxwell-Stefan (MS) diffusion matrix is evaluatednfrom the Onsager dynamical matrix that contains the diffusion flux correlation functions. From the temporalnbehavior of the correlation functions,we observe that the Li-Li and Li-Cl ion pairs have a pronounced cage dynamicsnthat remains noticeably strong even at high temperatures. Even though the Onsager coefficients, which are thentime integrals of the diffusion flux correlation functions, portray a relatively smooth variation across various compositionsnand temperatures, we observe a sign change and a divergent-like behavior for theMS diffusivity of theKLinion pair at a temperature of∼1100Kfor the eutectic composition, and at a KCl mole fraction of∼0.49 at 1043 K.nNegative MS diffusivities, while unusual, are however shown to satisfy the nonnegative entropic constraints.