Thermal stability of the eutectic composition in LiNO3–NaNO3–KNO3 ternary system used for thermal energy storage

Abstract

The new eutectic composition in the LiNO3–NaNO3–KNO3 ternary salt system has a very low melting point (118°C) and is a potential candidate for use in parabolic trough solar power generation. The short and long-term thermal stabilities and reliability of the eutectic composition in this ternary system were determined using the Thermogravimetric Analyzer (TGA) and Differential Scanning Calorimetry (DSC), respectively. The system demonstrates excellent short-term thermal stability and reliability during thermal cycling. However, the system showed 8% weight loss during long-term thermal stability test. Long-term isothermal stepwise study reveals that below 435°C the weight change is minimal and this temperature is taken as the upper limit of thermal stability of the system. The eutectic composition in the ternary system was characterized by XRD and SEM techniques before and after the thermal stability experiments to identify the morphology and compositions of the phases. From the present study it can be concluded that the major contributor to the weight loss is the dissociation of lithium nitrate to lithium oxides.