Thermal analysis of the stable KCl–KBr–K3FSO4 triangle in the KCl–KBr–KF–K2SO4 system
摘要
Phase equilibria in the stable KCl–KBr–K3FSO4 cutting triangle of the quaternary KF–KCl–KBr–K2SO4 system were studied by differential thermal analysis (DTA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). For the K3FSO4 compound, the enthalpy of fusion was determined to be 68.59 ± 2.06 kJ mol−1 at a melting temperature of 871 ± 1.5 °C, and the enthalpy of the polymorphic transition was found to be 2.65 ± 0.08 kJ mol−1 at 560 ± 1.5 °C. The polymorphic transition temperature was 560 °C, which is somewhat lower than the values reported in previous studies. The T−x phase diagram of the polythermal section [40 mol % K3FSO4 + 60 mol % KCl]–[40 mol % K3FSO4 + 60 mol % KBr] was experimentally examined by DTA. It was established that a continuous series of solid solutions based on potassium chlorides and bromides forms in the system. Thermal effects associated with the α ⇄ β polymorphic transition of the K3FSO4 compound were also observed. On the univariant equilibrium line, the composition with the minimum crystallization temperature was identified: point