Phase Equilibrium in the LiF–NaBr–Na3FSO4 System

The stable sectional section of LiF–NaBr–Na3FSO4 of the four-component mutual system Li+, Na+||F–, Br–, SO₄^{2 - } has been studied using the methods of physical and chemical analysis: differential thermal analysis (DTA), differential scanning calorimetry (DSC), and thermogravimetry (TG). The characteristics of the eutectic composition containing 22% LiF, 26% NaBr, and 52% Na3FSO4 in equivalent percentages have been determined. The equivalence factor of the compound is taken as 1/3. The melting point is 559. 0 ± 1. 5°C, and the specific enthalpy of melting is 317. 40 ± 9. 52 J/g. The experimental data obtained in the work, as well as information on two-component systems studied earlier, served as the basis for constructing a three-dimensional model of the LiF–NaBr–Na3FSO4 system. It is used for theoretical construction: isothermal sections in the temperature range of 570, 600, 650, and 700°C; the liquidus surface of the system with isotherms; and the material balance diagram of the equilibrium coexisting phases of any arbitrarily selected composition of the system. In the present article, the equilibrium coexisting phases were calculated for a mixture of 33% LiF + 33% NaBr + 34% Na3FSO4 in the temperature range of 400–700°С.