Analysis of the Ionic Conduction Behavior in a Few of Room Temperature Molten Fluorides

The average self-diffusion coefficients of cations and anions increased with increasing the HF-concentration and temperature in (CH3)3N·mHF, (CH3)4NF·mHF, (C2H5)3N·mHF, and (C2H5)4NF·mHF melts. The behavior of the self-diffusion coefficients of cations and anions in every melt is in good agreement with an increase in ionic conductivity and a decrease in viscosity. The transference number of (FH)nF− anions estimated from the values of self-diffusion coefficients for each ion in every melt was almost constant and their values were around 0.6 in the (CH3)3N·mHF melt and around 0.7 in the (CH3)4NF·mHF, the (C2H5)3N·mHF, and the (C2H5)4NF·mHF melts. The value of theoretical conductivity (σNMR) obtained from the average self-diffusion coefficients of cations and anions by using Nernst-Einstein equation was higher than the value of experimental ionic conductivity (σ). Therefore, it is concluded that the diffusion of (FH)nF− anions is faster than that of each cation in every melt and that a part of both cation and anion in each melt may associate by interaction between both ions.