A strategy for designing microencapsulated composite phase change thermal storage materials with tunable melting temperature

Thermal energy storage technology with high temperature phase change materials (PCMs) plays an increasingly important role in the concentrated solar power plants and industrial waste heat recovery systems. In this study, a novel displacement reaction between tetraethoxysilane as SiO2 source and molten raw Al powder was purposed to successfully prepare Al-Si/Al2O3 high temperature composite PCMs. Interestingly, by proposed synthetic methodology, we not only achieved the in-situ synthesis of Al-Si alloy PCM and Al2O3 shell, but also realized the controllability of Al-Si alloy composition and Al2O3 shell layer thickness. Our results indicated that the melting temperature of the prepared composite PCMs depended on the composition of Al-Si alloy, and could be designed within a certain temperature range (from 574.0 °C to 641.4 °C), instead of a particular temperature point. The melting temperature adjustability of the prepared composite PCMs provided an additional flexibility in different working temperature conditions. Moreover, the prepared composite PCMs exhibited a relatively high thermal storage capacity (248.6 J/g to 331.0 J/g), good thermal stability, excellent repeatable utilization property and certain shell layer self-repairing ability in the working temperature range. Therefore, the prepared composite PCMs can prove to be promising thermal energy storage materials for improving the energy efficiency in various systems under different working temperature conditions. •A novel method was purposed to prepare Al-Si/Al2O3 composite PCMs.•The Al-Si alloy and Al2O3 shell were in-situ prepared by the displacement reaction.•The Al2O3 preparation and Al-Si component adjustment were simultaneously achieved.•The melting temperature of composites can be tuned by altering the Al-Si component.•The melting temperature of composite PCMs can be tuned from 574 °C to 641.4 °C.