Al/Al2O3 core/shell microencapsulated phase change material for high-temperature applications

The purpose of this study was to prepare an Al/Al2O3 core–shell microencapsulated phase-change material (MEPCM) for a high-temperature thermal energy storage (TES) system. Al (melting temperature: 660 °C) was selected as a raw material for use as a phase change material (PCM). The MEPCM was prepared in two steps: (1) the formation of an AlOOH precursor shell on the PCM microspheres via boehmite treatment in boiled distilled water and (2) heat oxidation treatment in an O2 atmosphere to form a stable Al2O3 shell. The effects of the heat oxidation temperature on the shell morphology, shell structure, heat capacity, and cyclic durability of the prepared MEPCMs were examined. The resultant MEPCM was a core–shell-type structure composed of a stable α-Al2O3 shell and an Al core. The melting temperature of the MEPCMs was close to that of pure Al, and small supercooling of approximately 10 K was observed. Although the increase of the heat oxidation temperature reduced the heat-storage capacity of the MEPCMs (273–301 J g−1) as larger amounts of Al were consumed to form α-Al2O3, the repetition durability of the developed specimens was improved by increasing the heat-treatment temperature. In conclusion, the Al-based MEPCM is a potential candidate for high-temperature TES applications owing to its high melting temperature, high thermal storage capacity, and small degree of supercooling.