Hydrophilic expanded graphite-magnesium nitrate hexahydrate composite phase change materials: Understanding the effect of hydrophilic modification on thermophysical properties

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Abstract

Expanded graphite (EG) has shown excellent performances in compression resilience, thermal conductivity, and adsorption ability. EG can adsorb liquid phase change materials (PCMs) mainly because of capillary action; however, EG is hydrophobic, which makes it less compatible with hydrated salts. Herein, hydrophilic EG (HEG) was prepared with Triton X-100 (TX-100) as surface modifier. The HEG–magnesium nitrate hexahydrate (HEG-MNH) composite as a PCM was investigated for thermal energy storage (TES) to understand the effect of hydrophilic modification on thermophysical properties. The powder-state HEG is added into MNH to prepare HEG-MNH composite PCM, which contains 1.71 wt% of TX-100, 7.29 wt% of EG, and 91.00 wt% of MNH by control variable method. The melting point and latent heat of HEG-MNH composite PCM were 89.05°C and 137.28 J/g, respectively. The endothermic enthalpy change of HEG-MNH composite PCM only decreased by 0.90%, along with the exothermic values of HEG-MNH composite that increased by 3.80% after 100 cycles. The thermal conductivity is higher 5.17 times than that of the pure MNH. Our work suggests that the HEG-MNH composite PCM has a great potential to be used as a PCM for TES.

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