Eutectic Na2CO3–NaCl salt: A new phase change material for high temperature thermal storage

• The eutectic Na2CO3–NaCl salt has different thermal stability properties under various operation environments. The salt shows more thermal and chemical stability without weight loss in a CO2 atmosphere up to 700 °C as compared with a N2 atmosphere where there was 0.15% weight loss.
• The Na2CO3–NaCl salt shows good thermal properties and stability after 50 and 100 thermal cycles. Thus the salt is promising as a high temperature PCM for CSP application, if used in a CO2 environment or it is encapsulated.

In this work, the eutectic Na2CO3–NaCl molten salt was investigated as a new high temperature phase change material for solar thermal energy storage. The composition of the eutectic binary salt was determined with the aid of FactSage software and its thermophysical properties were investigated using a Simultaneous Thermal Analyzer (STA) and X-Ray Diffraction (XRD). Inductively coupled plasma analysis has shown that the composition of the as-prepared sample is consistent with the nominal one. The STA results exhibit that the melting point of the eutectic salt is 637.0 °C and its heat of fusion is 283.3 J/g whereas its specific heat is a function of temperature, which all are in agreement with the theoretical values determined by the FactSage software. The thermal stability analysis indicates that the eutectic molten salt has good thermal stability without weight loss in a CO2 environment at temperatures below 700 °C, compared with 0.51% weight loss in a N2 atmosphere. The weight loss observed in the latter, is most likely to be due to the salt׳s decomposition at high temperature. The thermophysical properties of the salt such as melting temperature, latent heat of fusion and solidification, varied marginally after 50 and 100 thermal cycle tests. This demonstrates that the eutectic Na2CO3–NaCl salt is a promising high temperature phase change material when used in a CO2 environment or encapsulation.