Preparation of Al[sbnd]Si microcapsules with high latent heat and durability via control of shell thickness

Microencapsulation of the Al[sbnd]Si alloy is an effective approach to overcome the challenges of corrosion and oxidation during high temperature operational service when used as phase change heat storage material. Research to date has shown that the prepared microcapsules was not able retain the high latent heat of Al[sbnd]Si alloy and achieve excellent thermal cycling performance at the same time. In this work, Al[sbnd]Si alloy microcapsules with adjustable shell thickness were successfully prepared through hydrothermal reaction, in situ polymerization and heat treatment at different oxygen contents. The phase composition and microstructure of the microcapsules were characterized in detail by XRD and electron microscopy. The thermal performances were tested through thermal cycling and thermal analysis. The results demonstrated that the outer protective shell layer of microcapsules was composed of dense α-Al₂O₃ and the thickness was adjustable from 372 to 1504 nm by controlling the oxygen content during heat treatment. Meanwhile, the regulation mechanism of shell thickness was analyzed. According to thermal analysis, the latent heat of microcapsules could achieve 450 J·g⁻¹, and the latent heat retention was 100 % after 5000 thermal cycles from 500 °C to 650 °C. This work provides new method of adjusting the shell thickness of Al[sbnd]Si microcapsules to achieve an ultra-high thermal performance in terms of latent heat and retention, which promotes the development of applications for metal-based heat storage materials.