Phase diagram of the system Na3AlF6–NaF–Na2SO4

In the phase diagram of the system NaF–Na2SO4, a binary compound Na3FSO4 exists. The compound allows to divide the ternary system Na3AlF6–NaF–Na2SO4 into the two subsystems Na3AlF6–NaF–Na3FSO4 and Na3AlF6–Na2SO4–Na3FSO4. Experimental coordinates of the eutectic point in the subsystem Na3AlF6–NaF–Na3FSO4 are: 7.6 mole%Na3AlF6+54.6 mole% NaF+37.8 mole% Na2SO4, 761°C. Experimental coordinates of the eutectic point in the subsystem Na3AlF6–Na2SO4–Na3FSO4 are: 4.6 mole% Na3AlF6+26.3 mole% NaF+69.1 mole% Na2SO4, 733°C. Thermodynamic model for calculation of the system Na3AlF6–NaF–Na2SO4 is presented. The thermodynamic model describes well all available thermodynamic data of the system, viz. enthalpies of mixing and solid–liquid phase equilibria.