Study on the microstructures and thermal properties of SiO2@NaNO3 microcapsule thermal storage materials

Summary In this paper a novel SiO2@NaNO3 microcapsule thermal storage material is successfully fabricated via water‐limited sol‐gel method. The effects of SiO2 nanoparticles on the microstructures, thermal conductivity, specific heat capacity, latent heat and thermal stability are investigated. SEM and TEM investigation indicates that the spherical SiO2 nanoparticles with an average diameters of 30 nm are coated on the surface of NaNO3 evenly to form a homogeneous and stable core‐shell structure. Microencapsulated composites are characterized by XRD and FTIR to determine the chemical compositions and structures. The thermal conductivity of SiO2@NaNO3 microcapsules is significantly enhanced by 62.9% (0.756 W m−1 K−1) compared with 0.464 W m−1 K−1 of that of NaNO3. In addition, the latent heat, phase change temperature, specific heat capacity and thickness of shell of the microencapsulated NaNO3 with 18.1 wt% SiO2 were 310.1°C, 144.7 J g−1, 1.831 J/(g·K), and 80‐150 nm, respectively. Furthermore, microencapsulated NaNO3 have excellent shape and thermal stability at working temperature range. SiO2 nanoparticles are uniformly attached to the modified NaNO3 by electrostatic interaction to create a physical protective SiO2 barrier, which can effectively inhibit the leakage and cauterization of melting NaNO3. In this work a novel core‐shell structured SiO2@NaNO3 microcapsule thermal storage material with enhanced thermal conductivity and thermal stability was fabricated via water‐limited sol‐gel method.