Study on preparation and thermal properties of sodium nitrate/silica composite as shape-stabilized phase change material

A sodium nitrate (NaNO₃)/silica (SiO₂) composite was prepared as a shape-stabilized phase change material by a sol-gel procedure. In this composite, NaNO₃ acted as the phase change material and SiO₂ was used as the supporting material. The maximal weight percentage of NaNO₃ in the composite was determined to be 60 wt.%. The chemical composition, morphology, structure and thermal properties were investigated by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), thermal gravimetric analysis (TGA), differential scanning calorimeter (DSC) and Laser thermal conductivity meter. The DSC results indicated that the enthalpies of melting and freezing of the NaNO₃/SiO₂ (60 wt.% NaNO₃) composite were 108 kJ/kg and 110 kJ/kg, and the corresponding temperatures of the phase transition were 302°C and 300°C, respectively. In the temperature range of lower than 500°C the phase change enthalpy of the composite was increased with the increase of the roasting temperature.