Microencapsulation of eutectic and hyper-eutectic Al-Si alloy as phase change materials for high-temperature thermal energy storage

Thermal energy storage using phase change materials (PCMs) has been world-widely accepted as an effective technology for energy saving. In this study, Micro-Encapsulated PCMs (MEPCMs) were developed from Al-Si alloys, in which four kinds of Al-Si microspheres with different Al-Si compositions: Al-12%Si, Al-17%Si, Al-20%Si, and Al-30%Si (mass%) were encapsulated by two facile steps for controlling heat storage property. First, boehmite film was formed over the Al-Si microspheres as a precursor shell during boiling in distilled water. Subsequently, the boehmite-coated particles were oxidized by pure oxygen at the high temperatures to ensure the formation of a stable Al2O3 shell. Three different temperatures, 1100 °C, 1150 °C, and 1200 °C, were chosen to study the effect of temperature on the product; the shell morphology, structure, and latent heat storage capacity. Interestingly, the results revealed an increase in MEPCM thermal storage capacity with decreasing Si content and lowering the temperature. The MEPCM melting point was almost identical to its eutectic temperature at ~577 °C, in contrast the larger supercooling was observed for samples with the higher Si content. The cyclic durability of MEPCM was also evaluated through repeated heating and cooling processes in air. The obtained results showed no significant change in both MEPCM structure and thermal storage capacity. It indicated a good repetition durability of MEPCMs oxidized at high temperatures. In conclusion, the Al-Si microencapsulated PCMs appealed great potential as MEPCMs for use in high-temperature thermal energy applications.