Macro-encapsulated metallic phase change material over 1000 °C for high-temperature thermal storage

This study reports the successful fabrication of Cu@Al2O3 macro-encapsulated metallic PCMs for high-temperature thermal storage over 1000 °C. Cu powders are employed as raw material which are spherulitized to core balls in millimeter-size, and subsequently the core balls are cladded with Al2O3 ceramic shells. After the low-temperature pre-sintering and subsequent high-temperature sintering treatment, the Cu@Al2O3 macrocapsules which contain gaps between the shells and cores are successfully prepared. The core balls are consisted of Cu powders which are not densified but are porous, offering buffer spaces to accommodate the thermal volume expansion during high-temperature sintering and melting of Cu. As a comparison, Cu@Al2O3 macrocapsules prepared by directly coating the commercial solid Cu balls are leaky. Thermal analysis indicates that the metallic core PCM has a melting temperature of 1063 °C and a latent heat of around 210 J/g. The macrocapsules are also highly durable as confirmed by the melting-solidification cycling test. These results demonstrate that the Cu@Al2O3 macrocapsules are applicable as high-temperature heat storage media, which can find useable applications in advanced high-temperature thermal energy storage systems.