Phase relations and thermodynamic properties in the ternary reciprocal system LiFNaFNa3AlF6Li3AlF6

The ternary reciprocal sytem LiFNaFNa₃AlF₆Li₃AlF₆ has been investigated by thermal analysis, differential thermal analysis, quenching, X-ray diffraction, microscopy, and calorimetry. The phase diagrams of the following systems are given: LiFNaF (revised), LiFAlF₃, Na₃AlF₆LiF, and LiFNaFNa₃AlF₆Li₃AlF₆. Some values of heat of mixing and heat content in the system have been measured.It is shown that molten mixtures in this system can be treated as consisting of the following species: Li⁺, Na⁺, AlF^3-₆, AlF₃ and F^-. At high contents of alkali fluoride the dissociation of the AlF^3-₆ ion to AlF₃ and F^- will, however, be negligible.On the basis of the calorimetric data, heats of mixing and dissociation, together with the degree of dissociation of AlF^3-₆, in the systems LiFAlF₃ and LiFNa₃AlF₆ have been calculated. The partial Gibbs free energy, enthalpy and entropy of Na₃AlF₆ in the system LiFNa₃AlF₆ have also been calculated. Finally the activity of Na₃AlF₆ in the latter system has been calculated by treating it as a part of the ternary reciprocal system 3LiF+Na₃AlF₆→Li₃AlF₆+3NaFA satisfactory agreement between the Flood, Førland and Grjotheim theory and the experimental values is obtained at small Na₃AlF₆ concentrations.