Comprehensive performance of composite phase change materials based on eutectic chloride with SiO2 nanoparticles and expanded graphite for thermal energy storage system

Abstract

This paper focuses on the formulation, fabrication and characterization of a novel composite for high-temperature heat energy storage. The proposed composite is a shape-stable phase change material consisting of the eutectic chloride (MgCl2–NaCl–KCl) as phase change material, expanded graphite (EG) for heat conduction enhancement and shape stability, and SiO2 nanoparticles for the further improvement of specific heat and thermal conductivity. The composite was prepared following a three-step procedure: mechanical dispersion, tableting and sintering. Concerning the material characterization, a suite of techniques were used, including simultaneous thermal analysis (STA) and laser flash analysis (LFA). The consequences demonstrate that using EG and SiO2 nanoparticles ensure the stability and preventing the leakage of the eutectic chloride. A thorough comparison with the pure ternary chloride shows that the composite specific heat increased up to 1.36 times in solid-state and 1.63 times in liquid-state, and the thermal conductivity increased by 23.2 and 9.2 times in the solid and liquid state, respectively. Upon inspection with scanning electron microscopy, a high-density nanostructure was observed and distributed evenly in the pores of EG, which appear to be the reason for the enhancement of specific heat and thermal conductivity of the material. Finally, the nano-SiO2/MgCl2–NaCl–KCl/EG composite has the advantages of wide working temperature range, shape stability, high specific heat and thermal conductivity, which has a promising application in a high-temperature thermal storage system.