Synthesis of Al-25 wt% Si@Al2O3@Cu microcapsules as phase change materials for high temperature thermal energy storage

High temperature phase change materials (PCMs) are drawing increasing attentions globally due to their high latent heat storage ability for solar thermal energy. Encapsulation of PCMs is an effective method for preventing the leakage of liquid PCM during heat storage, which makes PCMs easier to handle. In this paper, the synthesis of microencapsulated PCM (MEPCM) with Al-25 wt% Si core (spheres, average diameter 36 mu m) and Al2O3@Cu multilayered shell is reported, which works at temperature up to 500 degrees C. The homogeneous and effective composite shell is synthesized in multi-steps: First, a boehmite (AlOOH) shell is formed by boiling treatment in water, which is then transferred to Al2O3 shell by heating at 500 degrees C. Second, the Al2O3 covered particles are etched with HCl solution. Third, electroless plating of Cu layer is carried out to form the multilayered MEPCM. The surface morphology, cross-sectional structure, and thermal durability and stability of the MEPCM are investigated. The core/shell Al-25 wt%Si@Al2O3@Cu particles can maintain their integrity even after 100 melting solidification cycles with a low breakage ratio of about 1.7%. The results indicate that as-prepared MEPCM can be used for high temperature thermal energy storage such as solar thermal power generation. The success of Cu plating on spherical particles can also be applied to fabricate other Cu coated PCMs due to expected high thermal conductivity of Cu, especially for the low temperature ones such as organic PCMs.