Synthesis of Al@Al2O3 microcapsules by a triple-coating method for high-temperature thermal energy storage

Metallic aluminum (Al) has a high melting point and high thermal storage density, making it a proper candidate for high-temperature thermal storage applications including waste heat recovery and solar thermal utilization. To solve the problems of easy leakage after melting, high reactivity and high corrosiveness during application, microcapsules with a stable alumina shell were developed based on a triple coating method. The preparation process was divided into three steps: (1) generation of a boehmite layer on the surface of the Al powders via boiling water treatment, which was designed to slow down the corrosion of the precursor in the subsequent treatment; (2) production of Al(OH)3 gel layer on the surface of the particles through Sol-gel treatment and (3) formation of the final dense Al2O3 shell after thermal oxidation treatment. The synthesized Al@Al2O3 microcapsules had a melting point of 655.5 °C and a latent heat of 227 J/g. Notably, the latent heat of microcapsules remained almost constant after 100 melting-solidification cycle experiments, indicating a good cycling properties. In summary, the newly developed Al@Al2O3 microcapsules have a broad application prospect in the field of high-temperature thermal storage. © 2023 Elsevier Ltd