The thermodynamic properties of sodium and potassium dissolved in their molten chlorides,bromides, and iodides

The saturated vapour pressures are measured as a function of temperature and alkali metal concentration for the liquid solutions Na + NaCl, Na + NaBr, Na + NaI, K + KCl, K + KBr, and K + KI. The sodium and potassium partial pressures are determined. The expressions for their temperature dependence are obtained. Vaporization heats, activity coefficient, partial excess enthalpies and entropies are calculated from the experimental data for sodium and potassium in these solutions. Equations are derived for the redox potential as a function of temperature and the alkali metal concentration in the melts. The cathodic polarization of an iron electrode in molten NaCl, KCl, and NaBr is investigated. The steady-state alkali metal concentration in the cathode layer of the electrolyte is shown to be linear in the current density, varying from ～ 300 to 10⁴ A m^?2. The effective alkali metal diffusion coefficients estimated from the linear relation are much greater than the diffusion coefficients of the cations Na⁺ and K⁺ in the same molten salts. The cathode potentials are found to become nearly independent of the current density when it exceeds ～ 10⁴ A m^?2, the steady-state metal concentration in the cathode layer of the electrolyte being still far from saturated.