Thermodynamic Properties of CaCl2-CaF2-CaO System: Phase Diagram Investigation

The CaCl2-CaF2-CaO phase diagram was investigated in the CaO low region (<40 mol.%). CaCl2-CaF2 and CaCl2-CaO binary diagrams, constituting the ternary system, were first studied by Differential Scanning Calorimetry (DSC) measurements and X-Ray Diffraction (XRD) characterization; a good agreement was obtained between the phase diagram models calculated with FactSage® software (FTsalt database) and present experimental data. As the CaF2-CaO liquidus could not be measured by DSC due to the high melting temperature, this diagram was calculated using FTsalt database combined with FToxid database of FactSage® software. The ternary phase diagram was obtained by calculations and exhibits an eutectic at the composition CaCl2-CaF2-CaO (78.2-15.7-6.1 mol.%) melting at 637°C, and five peritectic points. Measurements of relevant vertical cross-sections for three CaCl2-CaF2 compositions (50-50, 40-60 and 30-70 mol.%) up to 18 mol.% CaO are in agreement with the ternary phase diagram model. For each section, the liquidus temperature is constant up to around 11 mol.% CaO and then sharply increases. Moreover, an increase of CaF2 content in CaCl2-CaF2 melt leads to a decrease of the CaO solubility in isothermal condition.

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