Modified preparation of Al2O3@Al-Si microencapsulated phase change material for high-temperature thermal storage with high durability over 3000 cycles

This study presents the modified preparation of microencapsulated PCM (MEPCM) of Al-Si (Al-25 wt%Si as core; melting point of 577 °C) microspheres, which are highly durable over 3000 cycles and have higher latent heat than our previous study. A modified three-step encapsulation process, including boehmite-precipitation-heat oxidation treatments, is proposed for the formation of compact and durable α-Al2O3 shells. Specifically, the boehmite and precipitation treatments are conducted in different amount of Al(OH)3-added aqueous solutions, which are naturally pH neutral. The thickness of shells in this work is controlled by the addition of Al(OH)3. The surface morphology, shell crystal structure, heat capacity, and cyclic durability of the prepared MEPCMs are carefully investigated. At the optimized conditions, the MEPCM can present higher latent heat of larger than 200 J g-1. Moreover, the modified process introduces the formation of a single-phase shell consisting of small grains of α-Al2O3, which is beneficial to the high durability. The high durability over 3000 cycles can reinforce the practical application in the future, for example, which can be applied to a concentrated solar power plant for more than 6 years.