Synthesis of a novel three-dimensional Na2SO4@SiO2@Al2O3-SiO2 phase change material doped aerogel composite with high thermal resistance and latent heat

摘要

A novel Na2SO4@SiO2@Al2O3-SiO2 phase change material doped aerogel composite (PDAC) using the sol-gel technique is prepared. This new kind of composite material is composed of a core-shell structured Na2SO4@SiO2 phase change material (PCM) with high melting temperature and Al2O3-SiO2 aerogel with high thermal resistance and low thermal conductivity. The effects of PCM amounts and heat treatment temperatures on the physicochemical properties of Na2SO4@SiO2@Al2O3-SiO2 PDCA are investigated. X-ray diffraction (XRD) shows that when the mass percentage of Na2SO4@SiO2 PCM powders increases to 36.7%, the peaks corresponding to Na2SO4 can be well observed. The boehmite phase within Na2SO4@SiO2@Al2O3-SiO2 PDAC can be transformed to gamma-Al2O3 via structural adjustment after heat treatment at 600 *degrees C. The pore size distribution doesn't shift after 600*degrees C heat treatment, and the most probable pore diameter is at around 30 nm. Transmission Electron Microscopy (TEM) shows that the Na2SO4@SiO2 PCM powders with diameters at around 500 nm can be effectively trapped and are homogeneously distributed within the aerogel matrix even after further heat treatment at 1000*degrees C, therefore, liquid leakage can be inhibited during melting process. The peak latent heat of Na2SO4@SiO2@Al2O3-SiO2 PDCA can be as high as 153.84 J/g with the PCM mass percentage at 36.7%. The Brunauer-Emmett-Teller (BET) specific surface area increases from 419.3 m(2)/g to 630.6 m(2)/g due to structural adjustment, and then decreases to 277.7 m(2)/g caused by volume shrinkage. Thermal simulation results show that the total melting time can be 254.8 s, and development of the temperature distribution keeps well with that of the liquid fraction. The velocity distribution of the liquid PCM keeps at 0 due to the constraint of aerogel matrix. This Na2SO4@SiO2@Al2O3-SiO2 PDAC can be a promising high temperature PCM in thermal energy storage applications.