Thermodynamic phase diagram calculations and cryoscopic measurements in the NaCl-CaCl2-MgCl2-CaF2 system

Investigations of the phase diagram of the NaCl-CaCl2-MgCl2-CaF2 reciprocal quaternary system have been performed by thermodynamic phase diagram calcu lations and cryoscopy, A limited concentration region of the system is used as a flux medium for liquid magnesium metal in connection with the casting process. In this connection the knowledge of liquidus temperatures is impo rtant to avoid precipitation from the liquid flux resulting in composition and property changes. Cryoscopic measurements were performed in the composi tion range of 40-60 wt% NaCl, 40-60 wt% CaCl2, 0-15 wt% MgCl2 and 0-10 wt% CaF2. A thermodynamic model has been developed for multicomponent reciproca l molten salt solutions. The parameters of the model were obtained by criti cal evaluation and optimization of available thermodynamic data of the pure components and of 9 binary and 5 ternary subsystems. This thermodynamic mo del makes it possible to calculate crystallization temperatures in this qua ternary reciprocal system. These calculated crystallization temperatures ag ree reasonably well with measured temperatures. An average deviation of 8 d egreesC was observed between calculated and measured data while the uncerta inty in the calculated data was estimated to be +/- 15 degreesC, This shows that it is possible to obtain reliable calculated crystallization temperat ures in multicomponent molten salt systems. This result is very promising i n view of the large amount of experimental work needed to measure such data in the whole composition volume of the multicomponent system.