Al–Si @ Al2O3 @ mullite microcapsules for thermal energy storage: Preparation and thermal properties

Abstract

Encapsulation is an effective method to prevent leakage of molten phase change materials (PCMs). However, it is difficult for microcapsules to acquire high latent heat capacity as well as good thermal cycling performance. In the present study, double shell microcapsules, using aluminum silicon alloy as the core, Al2O3 as the inner shell, and mullite as the outer shell, were prepared for heat storage by steam corrosion followed by silica sol immersion and high-temperature calcination. A cross-section of microcapsule showed that the total thickness of the double shell was approximately 1.5 μm. The latent heat storage and latent heat release of the microcapsules were 367.1 J g−1 and 298.4 J g−1 and still remained 90.4% and 80.0% after 3000 thermal cycles, respectively. The latent heat storage and release rate were 72.0 J g−1·min−1 and 20.3 J g−1·min−1, respectively. With an increase of temperature from 40 to 950 °C, the calculated total heat absorption of the microcapsules reached as high as 1850.3 J g−1, 22.7% greater than that without phase change. This double shell microcapsule has a high potential to be used in thermal energy storage systems.