Latent heat storage using alloys as phase change materials (PCMs) is an attractive option for high-temperature thermal energy storage. Encapsulation of these PCMs is essential for their successful use. However, so far, technology for producing microencapsulated PCMs (MEPCMs) that can be used above 500°C has not been established. Therefore, in this study, we developed Al-Si alloy microsphere MEPCMs covered by α-Al₂O₃ shells. The MEPCM was prepared in two steps: (1) the formation of an AlOOH shell on the PCM particles using a boehmite treatment and (2) heat-oxidation treatment in an O₂ atmosphere to form a stable α-Al₂O₃ shell. The MEPCM presented a melting point of 573°C and latent heat of 247 J g⁻¹. The cycling performance showed good durability. These results indicated the possibility of using MEPCM at high temperatures. The MEPCM developed in this study has great promise in future energy and chemical processes, such as exergy recuperation and process intensification.

The wide application of organic phase change materials for thermal energy storage and management is limited by their low thermal conductivity and poor shape stability. In this work, anisotropic thermally conductive and shape-stabilized phase change composites (PCCs) were successfully prepared with vertically aligned carbon fibers as supporting scaffolds. The aligned and hollow carbon fiber scaffolds with different densities were facilely fabricated by the direct carbonization of rolled cotton sheets with aligned and hollow cellulose fibers. PCCs were obtained by vacuum impregnation of paraffin wax. Because of the interconnected hollow carbon fiber frameworks with vertically aligned fibers and high porosity, PCCs present enhanced anisotropic thermal conductivity and good shape stability against leakage. The thermal conductivity in the axial direction along the fibers is higher than that in the lateral direction, since the aligned fiber scaffolds act as the thermal conduction pathway. The thermal conductivity of a PCC with a carbon ratio of 8.8 wt% is 0.77 W K⁻¹ m⁻¹ (>3 times that of pure paraffin) in the axial direction, while the value in the lateral direction is 0.58 W K⁻¹ m⁻¹. This work provides a novel strategy for designing anisotropic thermally conductive and shape-stabilized PCCs with potential applications in advanced thermal management and storage.

A microencapsulated Al–Si phase change material with a multi-layered Al ₂ O ₃ shell.