Effect of in-situ synthesized nano-MgO on thermal properties of NaNO3-KNO3

Nitrate molten salt has been proved promising heat storage materials with good thermophysical properties in concentrating solar power station. Increasing specific heat capacity of molten salt can help enhance its thermal storage capacity. In this paper, the effect of nano-MgO on specific heat capacity of NaNO3-KNO3 is investigated. MgO nanoparticles are synthesized by using in-situ method based on the high temperature decomposition reaction of Mg(OH)2 in solar salt. Materials characteristic analyses using field emission scanning electron microscope (FE-SEM) show that modified salt induces to form needle-like structure. Field emission transmission electron microscope (FE-TEM) was used to obtain the microstructure images of nano-MgO. The diameter of spherical MgO nanoparticlesare about 50-200 nm. The length and width of needle-like nano-MgO are 50-200 nm and 5-30 nm, respectively. In addition, the specific heat capacity of molten salt was measured by differential scanning calorimeter (DSC). Results show that the specific heat capacity of the modified salt is significantly enhanced while the latent heat is slightly decreased. After the samples calcined at 600°C for 1 h, the specific heat capacity is increased by 118.6% in solid state when adding 14.8 wt.% Mg (OH)2, and increased by 168.1% in liquid state when adding 10.4 wt.% Mg (OH)2, respectively. This work discussed the enhancement mechanism of the specific heat capacity is not only related to the MgO nanoparticles, but also the semi-solid layer formed at their surface.