Preparation and thermal properties of n-eicosane/nano-SiO2/expanded graphite composite phase-change material for thermal energy storage

Composite phase-change materials (CPCM) were prepared using n-eicosane as phase-change material, nano-SiO2 as supporting matrix, and expanded graphite (EG) as thermal conductivity promoter. Nano-SiO2 with strong adsorption performance can prevent leakage of n-eicosane in CPCM. Adding expanded graphite significantly enhanced thermal conductivity of CPCM. Leakage tests showed that the maximum mass proportion of n-eicosane in CPCM was 70 wt%. Fourier transformation infrared spectroscopy (FT-IR), an X-ray diffractometer (XRD), and a scanning electronic microscope (SEM) were used to determine chemical structures, crystal phases, and morphologies of CPCM. The DSC results indicated that the melting latent heat of CPCM was 135.80 J/g with a melting temperature of 35.35 °C, and that the solidifying latent heat of CPCM was 125.93 J/g with a solidifying temperature of 36.23 °C. Thermal conductivity meter (TCM) test results showed that CPCM had high thermal conductivity, representing a 15%–137% increase compared to CPCM without EG. Thermal properties and chemical structures of CPCM were investigated after 100 thermal cycles. The results indicated that CPCM3 (with 7 wt% EG) had good structure and thermal stability. Thermal conductivity of CPCM3 is 2.37 times that of CPCM without EG. Therefore, CPCM3 has potential application prospects for thermal energy storage.