Comparative Thermal Study of Pristine SiO₂ and SiO₂-Modified Expanded Graphite-Based Paraffin Composite for Thermal Energy Storage

The present research proposes a synthesis of shape-stable phase change materials composed of paraffin encapsulated in SiO₂ NPs, and SiO₂-modified expanded graphite (SiO₂@EG) has been prepared and investigated for thermal energy storage. In this regard, the effect of different wt.% (10, 15, and 20 wt.%) impregnation of SiO₂ NPs and SiO₂@expanded graphite on paraffin wax has been studied. The leakage proof ability of all the prepared composite materials named S1, S2, S3, SG1, SG2, and SG3 has been analyzed via the leakage test. The SiO₂@EG with 10 wt.% outstandingly adsorbed paraffin as compared to the pristine SiO₂ NPs. As a result, paraffin was well stabilized in SiO₂@EG porous networks without leakage, owing to capillary forces, surface tension, and hydrogen bonding interactions. The DSC thermograms indicated that the melting latent heat of S3 and SG1 is around ~ 177.5 and 180.6 J/g with a melting temperature of ~ 56.98 and ~ 60 °C. In addition, SG1 and S3 exhibited good cycling durability along with chemical stability after 500 repeated melting/freezing cycles. The thermal properties and chemical structures of S3 and SG1 composites have been investigated after 500 thermal cycles. The laser flash analyzer (LFA) results revealed that the thermal conductivity of S3 and SG1 composite increases significantly from 0.19 to 0.55 and 0.79 W/m °C. The high thermal efficiency and inexpensiveness would make the SG1 form-stable PCMs suitable for scale-up applications in TES.