Preparation and properties of Al/Al2O3 core-shell microencapsulated phase change material

Highlights: • Al/Al₂O₃ micro-encapsulated phase change materials (MEPCMs) were prepared by adding different amount of Al(OH)₃. • TEM observation was conducted that θ-Al₂O₃ is formed on the surface of the MEPCMs, which is conductive to the durability. • At the condition of 2 g/L Al(OH)₃ addition, the MEPCM can present high latent heat of 180 J/g, with high durability over 100 cycles of melting-solidification. • The shell surface of Al/Al₂O₃ particles is complete and dense after 100 cycles of melting–solidification, the MEPCM particles effectively prevent the leakage of liquid. -- Abstract: With the industrial development, the energy crisis has become a dreadfully serious problem in the world. Therefore, the development of high-durable phase change materials (PCMs) over 600 ℃ is very important for the high-temperature heat energy storage system. An improved three-step process of micro-encapsulated PCMs (MEPCMs) was proposed in this work, including boehmite-precipitation-thermal oxidation treatment, which are beneficial to disperse the thermal stress during high-temperature cycling and restrain crack propagation due to forming a dense and durable Al₂O₃ shell. The cross-section structure, the surface morphology, phase compositions, phase change temperature, thermal durability and cycling stability were simultaneously investigated. In addition, boehmite-precipitation treatment was performed in an aqueous solution with different adding amounts of Al(OH)₃. The thickness of the Al₂O₃ shell layer was adjusted by control of the amount of Al(OH)₃. The latent heat of the MEPCMs with the adding amount of 2 g/L Al(OH)₃ reached 180 J/g, and the released heat was 110 J/g after 100 cycles of melting-solidification. Furthermore, TEM observation further confirmed the formation of θ-Al₂O₃ crystal structure on the surface, which is helpful to the durability. Every MEPCM kept a completely spherical shape and a dense surface after 100 cycles of melting-solidification. Therefore, the MEPCMs with excellent heat storage capacity and high thermal stability were widely used to recycle industry, such as waste heat, building energy conservation and aerospace. In addition, the new processing technology can provide excellent and industrial production of PCMs in the future.