Preparation and characteristics of paraffin/silica aerogel composite phase-change materials and their application to cement

Abstract

In this study, microencapsulated paraffin/silica aerogel composite phase-change materials (MPCMs) were developed and incorporated into cement to impart heat storage/release capabilities. First, the hydrophilically modified MPCMs were subjected to a leakage test. Using a simple stirring method, the composite with an aerogel: paraffin mass ratio of 22:78 was demonstrated to have the best adsorption capacity. Transmission electron microscopy, scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction analyses revealed that the paraffin was stable and physically encapsulated by the aerogel. The differential scanning calorimetry results showed that the encapsulated MPCMs had a fusion latent enthalpy of 94.45 J/g and phase-change temperature range of 20.8–34.4 ℃. The enthalpy was reduced by only 3.87% after 1000 freezing–thawing cycles. In the second part of the experiment, heat-storage cement (HSC) specimens were prepared to investigate the effect of MPCMs modified with silane coupling agents. The proportion of MPCMs and curing temperature were varied, and the effects of these variations on the compressive strengths of HSC stones were investigated. The compressive strength of the HSC samples was improved by adding multiwall carbon nanotubes (MWCNTs) to paraffin to form paraffin/aerogel composite MWCNT micro-encapsulated phase-change materials (CMPCMs). The results show that adding 1.53 wt% MWCNTs increases the thermal conductivity by 50.6% and refines the pore size and strength of the HSC stone. Furthermore, the 7-day strength of the HSC stone increased to 8.6 MPa by adding MWCNTs to 30 wt% modified CMPCM, meeting the requirement standard. Cement hydration calorimetry, performed using a TAM AIR isothermal calorimeter, revealed that MPCMs prolong the induction period of cement hydration, reduce the rate during the acceleration period of cement hydration, and absorb the heat of hydration. Moreover, the thermal regulation behaviour of 10 mm thick HSC plates was tested. The highest temperature difference was determined to be 2.36 ℃ and 1.92 ℃ during the heating and cooling processes, respectively, compared with that of plain cement plate, at the same time. Therefore, HSC panels have potential applications in building thermal management.