Preparation And Thermal Properties Of Expanded Graphite Reinforced Erythritol Phase Change Composites

The heat exchange efficiency of organic phase change materials(PCMs) can be enhanced by increasing their thermal conductivity. As a medium-temperature PCM with extremely high latent heat of fusion, erythritol is a promising candidate in areas of thermal protection and latent heat thermal energy storage(LHTES). In the present work, several methods were used to fabricate expanded graphite(EG) reinforced erythritol PCMs, so as to increase the thermal conductivity of erythritol without any side effects.EG was obtained by heat treatment. The effect of heat treatment on the properties of EG, including microstructure, expansion degree, and graphitization degree was studied. Higher heat treatment temperature could accelerate the release of oxygen-functional groups and rapidly improved the expansion degree of EG. The X-ray diffraction(XRD) method was used to measure the graphitization degree of EG. Heat treatment with moderate temperature and enough holding time helps the rearrangement of carbon atoms, which indicates a higher degree of graphitization.Respectively, direct mixing method, mix & ultrasonic method, preform method and pre-ultrasonic method were used to prepare EG/erythritol phase change composites(PCCs) with a mass fraction of EG between 0.5wt.%~6.0wt.%. No chemical reaction was detected between EG and erythritol with the help of XRD and Infrared spectrum. PCCs prepared by the methods with ultrasonic exhibit higher relative density. Ultrasonic treatment crushes the structure of EG and turns it into graphite nano-platelets(GNPs) and thus lowers the porosity of PCCs. Higher power of ultrasonic and longer treatment could accelerate this process and benefit the relative density of PCCs.GNPs stimulated the nucleation of erythritol and reduced the fusing temperature of PCCs. The internal energy of the system was raised by EG and pores, which could lower the latent heat and specific heat of PCCs. Besides, the introduction of EG enhanced the specific heat of PCCs due to the significant interfacial thermal resistant between EG and erythritol. Models based on the effective medium theory were used to predict and analyze the thermal conductivity of PCCs. It turned out that EG remained in morphological integrity enhanced the thermal conductivity of PCCs significantly by forming long-range heat-transfer network. The thermal conductivity of PCCs with 6.0wt.% of EG was as large as 680% of pure erythritol. The results of thermal cycling tests showed that more latent heat can be reserved with the addition of EG. No phase or chemical construction change was detected during the thermal cycling process.