Digital phase diagram and thermophysical properties of KNO₃-NaNO₃-Ca(NO₃)₂ ternary system for solar energy storage

The molten nitrate salt has become one of the most promising heat storage and transfer medium for solar energy. A series of molten salt systems containing KNO₃-NaNO₃, Ca(NO₃)₂-NaNO₃, KNO₃-Ca(NO₃)₂ and KNO₃-NaNO₃-Ca(NO₃)₂ were designed and prepared to study the liquidus surface, and the thermal stability of the KNO₃-NaNO₃-Ca(NO₃)₂ ternary system was mainly studied. A 3D stable molten temperature diagram was developed to predict melting points and thermal decomposition points in the KNO₃-NaNO₃-Ca(NO₃)₂ ternary system, as well as its eutectic temperature and composition. The predicted eutectic composition is 42% KNO₃-17% NaNO₃-41% Ca(NO₃)₂, which has a low predicted melting point of 129.1 °C and a high predicted decomposition temperature of 597.9 °C. Moreover, a series of melting points and thermal decomposition points obtained from the 3D stable molten temperature diagram were respectively verified experimentally using thermo-gravimetric (TG) and differential scanning calorimetry (DSC) methods. The experimental results were in excellent agreement with that of obtained values from the 3D stable molten temperature diagram.