High-temperature ternary Cu-Si-Al alloy as a core-shell microencapsulated phase change material: fabrication via dry synthesis method and its thermal stability mechanism

In the quest for efficient high-temperature thermal energy storage systems (TES) and power-to-heat-to-power systems (PHP), this study focuses on the development of Cu-12.8Si-20Al/Al2O3 core-shell microencapsulated phase change materials (MEPCMs). The Cu-12.8Si-20Al alloy, with melting point range of 738-758 degrees C was selected as the core PCM. Two subsequent physical methods were performed to optimize the MEPCMs: (1) uniformly coating the core with shell nanoparticles via a dry synthesis mechanical impact technique; (2) conducting heat oxidation in an O-2 atmosphere to foster a robust shell structure. To ascertain the optimal structure for the MEPCM, we investigated three shell variants: alpha-Al2O3, AlOOH, and a mixture of both. Significantly, the alpha-Al2O3 nanoparticles manifested a dual-layered shell, defined by an internally sintered alpha-Al2O3 nanoparticles layer and an overlying sub-nanoparticles layer. This construction enhanced the MEPCMs' thermal resilience: allowing them to withstand over 600 cycles of endothermic and exothermic phases, as well as affirming their endurance under extensive 100 h air exposure at 900 degrees C. The synergy between alpha-Al2O3 and AlOOH in the mixed shell revealed a pivotal role of AlOOH, which served as an adept sintering agent to enhance the MEPCM's thermal stability. In conclusion, the Cu-Si-Al/Al2O3 MEPCM was successfully produced as a promising candidate in high-temperature latent heat storage applications.