THERMODYNAMICS OF THE SYSTEM NAF-AIF3 .6. REVISION

Literature data are reviewed to derive enthalpies and entropies of Na3AlF6 and NaF, and they are combined with electrochemical and equilibrium data to yield free energies of formation of Na3AlF6 from the constituent fluorides. Liquidus data and measurements of the Na content of Al in equilibrium with the melts then enable the calculation of the free energy of formation, enthalpy, and entropy of all mixtures liquid at 1293 K. In stoichiometric Na3AlF6 at 1293 K, aNaF =0.37 and aAlF 3 = 4.9 × 10-4. The activity coefficient of Na in dilute solution in Al is given by RT ln γNa = (40 967 + 9.480 T) J. At 1293 K the partial pressure of NaAlF4 is given by pNaA1F4/bar = 27aNaF . aAif 3- A heavier species- suggested to be NaAl3F10-is present in the vapor above AlF3-rich melts. © 1990 The Minerals, Metals & Material Society.