Investigation on the micromorphology and thermophysical properties of NaNO3 heat storage materials modified by solution combustion.

Nitrate has a wide temperature range, wide operating temperature, low vapor pressure, low cost, strong heat transfer and stable chemical properties. It is widely used in solar thermal power generation heat storage material. In this paper, the alkali salt NaNO3 was modified by solution combustion method with citric acid as fuel. The structure and thermal properties of the prepared salts were studied by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). The results show that the solution combustion process improves the structure and thermal properties of NaNO3, and the resulting product has a new phase. The particle size and microscopic morphology of the prepared salt were changed. As the proportion of fuel increases, the hollow cuboid structure gradually grows on the surface and inside of the modified salt. The microstructure obtained is different at different ignition temperatures, and a finer and even rod-like structure is obtained at an ignition temperature of 600 °C. The specific heat capacity of all modified samples has been improved, among which solid specific heat and liquid specific heat have increased the most, respectively 3.10 J/g·K and 3.19 J/g·K, which are 140.31% and 131.16% higher than the base salt, respectively. This work not only studies the specific heat capacity of NaNO3 modified by solution combustion, but also explores the effect of micromorphology and new phase formation on its performance, which provides innovative ideas for improving the specific heat capacity of molten salt heat storage materials.