Effect of MgCl2·6H2O Phase Change Material on Thermal Insulation Performance of Carbon Aerogels

•Highly porous carbon aerogels were synthesized by pyrolizing novalac aerogels.•Physical and thermal properties of CAs were evaluated and the proper CAs for addition of PCM has been selected.•Thermal enhancement effect of the PCM was significantly improved at higher content of PCM.•The gradient impregnation of PCM in carbon aerogel, led to more efficient structure.

The aim of this work is to improve the thermal insulation performance (the time needed for the sample's top surface to reach 140 °C) of carbon aerogels (CAs) using phase change materials (PCMs). CAs were prepared through the carbonization of organic aerogels, synthesized by the sol-gel polymerization of a novolac solution under a solvent-saturated atmosphere. Field emission scanning electron microscopy (FE-SEM), N2 adsorption and time-temperature history behavior (insulation performance) characterization methods were used to investigate the morphology, microstructural and thermal properties of fabricated CAs, respectively. The CA sample prepared from the initial sol containing 20 wt.% of novolac resin was identified as the proper CA sample to be the matrix for MgCl2·6H2O-filled samples. The CAs were impregnated by MgCl2·6H2O using the immersion process. The influence of PCM content on the heat transfer of PCM-filled CAs was also investigated. Results presented here revealed that the amounts of filled PCMs can play an important role in improving the thermal performance of samples, in a specific temperature range (specifically around the melting point of PCM). Moreover, it was found that the low thermal conductivity of CA, combined with the high heat capacity of PCM, increased the time required to reach the top surface temperature of sample (140 °C). Increasing PCM contents enhanced the heat absorption capacity of the samples. In addition, the higher PCM contents resulted in the longer time interval of latent heat absorption. Furthermore, inhomogeneous impregnation of PCM in the structure of carbon aerogels resulted in more efficient structures, as, in this way, PCM can be located in the right place to meet required heat for phase change.