Preparation and characterization of NaNO3 shape-stabilized phase change materials (SS-PCMs) based on anorthite ceramic and cordierite ceramic for solar energy storage

In the current study, molten NaNO3 shape-stabilized phase change materials (SS-PCMs) based on anorthite ceramic and cordierite ceramic were prepared by cold-press sintering method. Chemical compatibility and wettability were considered simultaneously to determine whether the ceramics were qualified as supporting skeleton and the enhancement of the thermal properties of NaNO3 by the ceramics was also investigated. It was found that both anorthite ceramic and cordierite ceramic have good chemical compatibility with NaNO3 and no chemical reaction occurred between them. Physical compatibility was evaluated by measuring the contact angle of molten NaNO3 on a ceramic substrate. Cordierite ceramic exhibited better wettability than anorthite ceramic, although both of the contact angles decreased gradually with increasing temperature. The supercooling of the prepared anorthite ceramic-based SS-PCMs with 45 wt% NaNO3 (45ASS-PCMs) was only 0.7 °C, which was less than 2.5 °C for pure NaNO3 and 2.0 °C for cordierite ceramic-based SS-PCMs with 45 wt% NaNO3 (45CSS-PCMs). The phase transition enthalpy loss of 45ASS-PCMs after 100 thermal cycles was less than 2%, while 45CSS-PCMs reached more than 5%. Anorthite ceramic showed better capabilities than cordierite ceramic in terms of thermal reliability and stability, while cordierite ceramic was better than anorthite ceramic in enhancing thermal conductivity. The evaluation method proposed in this study provided favorable guidance for the matching of PCMs and ceramic supporting skeleton.