Functional surface modification of Al-Si@Al2O3 microencapsulated phase change material

Abstract

Core-shell structured Al-Si@Al2O3 microencapsulated phase change material (MEPCM) has shown promise for high-temperature latent heat thermal energy storage applications, and has recently been proposed as a thermo-regulating catalyst support. However, the reported performances of MEPCMs are lower than those of conventional catalyst supports, owing to low specific surface areas of the former. MEPCMs were originally prepared in two steps: boehmite treatment and thermal oxidation treatment. This study was aimed at modifying the MEPCM shell surface morphology to increase its specific surface area by introducing additives and adjusting the pH of solutions during boehmite treatment. Al-25 wt% Si alloy powder as raw material was hot-stirred in distilled water at 100 °C, for 3 h to form AlOOH layers, the Al2O3 shell-precursors, on the surface of AlSi particles. Different metal-nitrate solutions (metal: La, Ni, Zn, Fe, Ca, Mg) were added during boehmite treatment to control the particle surface precipitate. The boehmite-treated samples were filtered, dried, and heat-oxidized in air at 1000 °C for 3 h to form the Al2O3-shell-MEPCMs. Interestingly, upon addition of metal-nitrate solutions during boehmite treatment, a significant amount of AlOOH or Al(OH)3 crystal-grains were formed. The MEPCM sample prepared using La nitrate solution exhibited remarkably high specific surface area of 40.9 m2 g−1, in contrast to the sample formed without any additive (2.4 m2 g−1), indicating higher suitability as a catalyst support. Thus, the MEPCM shell surface morphology could be easily controlled to increase surface area and facilitate catalyst-support activity.