Improved thermal conductivity of form-stable NaNO3: Using the skeleton of porous ceramic modified by SiC

Corrosion and low thermal conductivity are considered as two great challenges for the application of salts-based phase change materials (PCMs). To address these problems, a novel skeleton, namely SiC modified diatomite-based porous ceramic, was prepared to develop form-stable NaNO3 salt. The results showed that a good wettability and chemical compatibility existed between SiC and molten NaNO3. Thermal conductivity of composite PCMs was found to be nearly linearly related with the concentration of SiC. 20% SiC added into the skeleton helped to enhance thermal conductivity of composites by 50%, benefited by the formation of a high thermally conductive heat transfer path. A smaller particle size of SiC contributed to a higher thermal conductivity of composites by increasing the heat transfer area between PCMs and skeleton. Form-stable NaNO3 (56.6%) that had a skeleton modified by 10% SiC (only 4.3% in composites) with particle size of 50 nm possessed a thermal conductivity of 2.06 W/(m·K) at 25 °C, which was 265% higher than that of pure NaNO3. Such composites also performed quite a good stability during the 500 thermal cycles, in terms of chemical compatibility, thermal conductivity, latent heat, phase transition temperature, and mechanical strength. Therefore, the novel composite PCMs exhibited a great application prospect in thermal energy storage.