Multicomponent diffusion in molten LiCl-KCl: Dynamical correlations and divergent Maxwell-Stefan diffusivities
Brahmananda Chakraborty, Jin Wang, and Jacob Eapen
Accepted
Multicomponent diffusional mechanisms in ternary LiCl-KCl system are elucidated using the Green-Kubo formalism and equilibrium molecular dynamics (MD) simulations. The Maxwell-Stefan (MS) diffusion matrix is evaluated from the Onsager dynamical matrix which contains the diffusion flux correlation functions. From the temporal behavior of the correlation functions, we observe that the Li-Li and Li-Cl ion pairs have a pronounced cage dynamics that remain noticeably strong for all temperatures. Even though the Onsager coefficients which are the time integrals of the diffusion flux correlation functions portray a relatively smooth variation with various compositions and temperatures, we observe a sign change and a divergent-like behavior for the MS diffusivity of the K-Li ion pair at a temperature of 1095K for the eutectic composition, and at a KCl mole fraction of 0.48 at 1043K. Negative MS diffusivities while unusual are however, shown to satisfy the nonnegative entropic constraints.