Self-diffusion of lithium, sodium, potassium and fluorine in a molten LiF + NaF + KF eutectic mixture

Abstract

The self-diffusion coefficients of lithium, sodium, potassium and fluorine in a molten LiF + NaF + KF (46.5 + 11.5 + 42.0 mol%: FLINAK) eutectic mixture have been measured by the capillary reservoir technique using the tracers ⁶Li, ²⁴Na, ⁴²K and ¹⁸F. The observed self-diffusion coefficients D(in m² s^–1) are expressed according to the Arrhenius equation as follows: D_Li= 3.87 × 10^–7 exp [–(37.2 ± 4.2)× 10³/RT](480–663 °C), D_Na= 4.28 × 10^–7 exp [–(36.2 ± 7.1)× 10³/RT](504–616 °C), D_K= 2.05 × 10^–7 exp [–(32.0 ± 7.5)× 10³/RT](491–613 °C) and D_F= 1.77 × 10^–7 exp [–(30.8 ± 6.7)× 10³/RT](480–663 °C), where R is the gas constant (in J mol^–1K^–1) and T the absolute temperature (in K). The observed self-diffusion coefficients of the ions in molten FLINAK give very similar values to each other and smaller values than given in the literature for other molten salts. These results are explained in terms of the interaction between cations and anions and the volume change on fusion.