Enhanced Thermophysical Properties of a Quaternary Molten Salt NaNO3–KNO3–NaNO2–Ca(NO3)2 Doped with Al2O3 Nanoparticles

As the key heat storage and transfer medium in concentrated solar power (CSP) systems, molten salts’ thermophysical properties, such as thermal conductivity, specific heat capacity, and thermal stability, critically determine the systems energy conversion efficiency and economic viability. However, conventional molten salts suffer from low thermal conductivity and limited energy storage density, restricting their application in high-temperature thermal energy storage. Recent advances show that doping with nanoparticles, such as Al 2 O 3 , CuO, and SiO 2 , can significantly improve these properties. Nevertheless, systematic studies on quaternary molten salt systems remain scarce. In this work, we focus on the quaternary eutectic salt H15 (15 wt% Ca(NO 3 ) 2 –5.95 wt% NaNO 3 –45.05 wt% KNO 3 –34 wt% NaNO 2 ), which demonstrates a high decomposition temperature of 597.4 °C alongside a relatively low melting point of 84.4 °C and high thermal energy storage density of 1052.41 kJ/kg. To overcome its thermal performance limitations, Al 2 O 3 nanoparticles (0.1 wt% to 3 wt%) were introduced to form a nanocomposite molten salt. The influence of varying nanoparticle loadings was assessed via DSC, HotDisk, SEM, and XRD to examine corresponding changes in phase transition behavior, thermal conductivity, viscosity, and material microstructure. This study provides theoretical and experimental support for developing high-performance, wide temperature-range thermal energy storage materials for advanced CSP systems.