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

Abstract

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.