Thermodynamic investigation of the Ca(NO3)2–NaNO3–KNO3 system for solar thermal energy storage

Abstract To eliminate the differences in the mixture with the lowest liquidus temperature of the ternary system Ca(NO3)2–NaNO3–KNO3 reported in the literature, a conformal ionic solution (CIS) model was selected to predict the phase diagram of this system. The predicted results show that there exists one mixture with the lowest liquidus temperature being 116.5 °C, and the compositions are 32.4 mol.% Ca(NO3)2+12.4 mol.% NaNO3+55.2 mol.% KNO3, respectively. Then, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) measurements of the predicted mixture were conducted. The results showed that this salt mixture has a low melting point of 115.6±0.1 °C, which coincides with the melting temperature of the predicted mixture (116.5 °C), and the thermal stability temperature is 500±1 °C. This predicted ternary salt mixture can be seen as a viable thermal energy storage medium for solar plants.