Thermal-physical properties of nanoparticle-seeded nitrate molten salts

Molten salts have been used extensively as energy storing materials, however, their thermophysical properties, such as specific heat capacity and thermal conductivity have limited their applications. In this study, potassium nitrate and sodium-potassium nitrate (NaNO3:KNO3 with 60:40 molar ratio) are used as the base salts and different types of nanoparticles, which are iron oxide (Fe2O3), titanium dioxide (TiO2) and copper oxide (CuO), are dispered to form various nanosalts. Laser flash analysis is used to measure thermal diffusivity and dynamic scanning calorimeter for specific heat, latent heat and melting temperature of the molten salts and nanosalts over a wide range of temperature up to 773 K. The addition of Fe2O3 into sodium-potassium nitrate salt increases the effective thermal diffusivity up to 50%. The highest increase in the latent heat reaches 14.45% for 1 wt % CuO-binary nitrate salt. The total thermal energy storage of nanosalt increases up to 6% including both sensible and latent heat, which is due to the formation of the interface layer between nanoparticles and salts. The morphology of nanosalt measured by scanning electron microscopy shows a heterogeneous dispersion of nanoparticles, including agglomerated areas that could be responsible for the degradation of the performance.