Thermal Performances and Stability of Capric Acid-Stearic Acid-Paraffin Wax Adsorbed into Expanded Graphite in Vacuum Conditions

A new form-stable composite phase change material (CPCM) of capric acid-stearic acid-paraffin wax/expanded graphite (CSPW/EG) was prepared by vacuum adsorption. CSPW has a minimum crystallization temperature of 21.9 degrees C at the eutectic mass proportion of 74.7:8.3:17 by the step cooling curve method and has a phase change temperature of 25.27 degrees C and an enthalpy of 126.82 J/g by differential scanning calorimetry (DSC). The mixing proportion of CSPW to EG was determined to be 10:1 based on the enthalpy change and leakage of CPCMs; the enthalpy and phase transition temperature of CSPW/EG were 119.26 J/g and 27.14 degrees C, respectively. The microstructure, crystal structure, and chemical structure of CSPW/EG were characterized by using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). The initial weight loss temperature of CSPW/EG was 159.8 degrees C, which is far beyond the working temperature. The heat storage-release experiments and 1000 melting-solidification cycles also confirmed that CSPW/EG has excellent heat energy storage and temperature control ability, thermal reliability, and great potential in practical engineering heat storage applications.