Preparation of Al@Al<sub>2</sub>O<sub>3</sub> Macrocapsules with High Durability for High-Temperature Thermal Storage
Yunqi Guo, Nan Sheng, Chunyu Zhu
Abstract
Metallic phase change materials (PCMs) are promising candidates for high-temperature thermal energy storage technology in various industrial systems. However, the encapsulation of metallic PCMs to obtain a reliable application is technically difficult. In this paper, novel and durable Al@Al2O3 macrocapsules of millimeter to centimeter size are successfully fabricated using Al powders as raw material. In particular, buffer voids to accommodate the intrinsic thermal volume expansion of a high-temperature PCM are facilely introduced inside macrocapsules. With the help of an organic binding agent, Al powders are rounded up to macrospheres as cores, which are then coated with doughy Al2O3 shell, just like playing plasticine. The macrocapsules are finally prepared after the two-step sintering treatment, first at 300 °C under air to combust binder and second at 1000 °C under Ar or O2 for capsule formation. During the high-temperature sintering under Ar to prepare the best sample, the un-densified Al powder core spheres are fused into Al melts with a smaller size, thereby leaving buffer voids between the core and shell. The core Al PCM of the macrocapsule can present a high latent enthalpy of >357.4 J/g and a melting temperature of around 660 °C. Surprisingly, the macrocapsules showed very good cycling stability and durability up to 500 cycles at our currently still continued test, even under air atmosphere. Therefore, the as-prepared macrocapsules are promising for application in high-temperature thermal storage systems.