High-Thermal-Conductive AlN-Shell-Encapsulated Al Phase-Change Macrocapsules for High-Temperature Heat Storage

High-temperature metallic phase-change material is a very promising material alternative to traditional sensible heat-storage materials in thermal energy storage systems. Nevertheless, the challenges such as their susceptibility to corrosive behavior, vulnerability to leakage, and proneness to oxidation in high-temperature liquid phase present significant constraints that hinder their widespread applications. In this article, an approach to fabricate millimeter-scale phase-change capsules for macroscopic encapsulation of Al with high-thermal-conductive AlN shell is introduced. The study encompasses the preparation of Al@AlN macrocapsules with inner cavity, which can accommodate thermal volume expansion, through the direct powder formation combined with a two-step sintering process, under a comparative evaluation of the atmospheric treatments involving N₂, O₂, and Ar. As the result, a calcination temperature of 1000 °C in Ar atmosphere is proper for the capsule formation. The Al metal core of the as-obtained capsule shows a latent heat of fusion of 347.4 J g⁻¹ and a melting temperature of 655.6 °C. The Al@AlN capsules also exhibit good thermal and stability, ensuring their potential application in high-temperature heat storage and utilization.