Modified diatomite-based porous ceramic to develop shape-stabilized NaNO₃ salt with enhanced thermal conductivity for thermal energy storage

Low thermal conductivity and corrosion problem of NaNO₃ salt-based phase change materials (PCMs) are regarded as two critical barriers for their applications in thermal energy storage. To address the above problem, a diatomite-based porous ceramic modified by CaCO₃ was firstly used to develop shape-stabilized NaNO₃ in this work. Particularly, contribution of modified diatomite-based ceramic on improving thermal conductivity of the composite was investigated. Compared with traditional diatomite-based skeleton, diatomite-based ceramic was found to contribute to a 129% higher thermal conductivity of composites, benefited by the generation of a dense and continuous skeleton that consisted of newly formed cristobalite phase with a higher thermal conductivity. While crack occurred on the composite with diatomite-based ceramic after 100 thermal cycles, resulting in the leakage of salt and the decrease of thermal conductivity. By contrast, diatomite-based ceramic modified by no more than 40 wt% CaCO₃ effectively avoided the crack of composites, exhibiting quite a stability in shape and thermal conductivity during 500 thermal cycles. The modified ceramic was shown to improve the thermal conductivity of loaded NaNO₃ by 118%, up to 1.22 W/(m·K) at 25 °C. The results also indicated that the modified ceramic hardly changed the phase transition temperature of NaNO₃, but decreased the latent heat of composites, while possessed a much higher capacity to load salt (57 wt% NaNO₃) than that of other porous ceramics. The composite with modified ceramic was demonstrated to have a good cycling stability in thermal properties as well, which performed a considerable potential in thermal energy storage.