Thermal hysteresis in phase-change materials: Encapsulated metal alloy core-shell microparticles

Abstract

Thermal hysteresis (TH) is defined as the temperature difference between the melting points and crystallization temperatures of phase-change materials (PCMs). The magnitude of the TH is proportional to the energy loss in a system. In addition, the latent heats of the PCMs cannot be exploited if the TH is beyond the operation temperature range of a system. In this study, Zn/TiO2, Zn/Al2O3, and Zn/SiO2 core-shell microparticles were synthesized and the TH values of the microparticles were examined. The TH for the microparticles was mainly affected by the ramping rate in differential scanning calorimetry, the shell thermal resistance and the required temperature for heterogeneous nucleation. Given that Al2O3 possesses a superior thermal conductivity than that of TiO2 and SiO2, the Zn/Al2O3 core-shell microparticles provided the smallest TH among the three types of microparticles. The heat capacity of the salt can be enhanced by 6.7% by doping with 10 wt% Zn/Al2O3 microparticles while the viscosity increased from 1.3 to 3 cp. The study provided guidelines to modulate the TH of PCMs, and the concept learned from this study can be applied to enhancing the thermal energy storage in various thermal systems.