New strategy to further enhance the thermal insulation performance of silica aerogel: Decline the macropore content between skeletons

Abstract

Silica aerogels are considered as promising porous thermal insulation materials. However, the macropores between skeletons in the microstructure prevent further improvement of the thermal insulation performance. Therefore, it is feasible to decrease the macropores content between skeletons to enhance the thermal insulation performance. In this work, we employed Al2O3 nanoparticles as fillers and utilized high-temperature treatment to shrink the skeletons and reduce the macropores content. The experimental results demonstrate that the Al2O3 nanoparticles are well-dispersion within the skeletons and the diameters of macropores dramatically decrease from 7.55 μm to 0.78 μm. The thermal conductivity declines from 0.0821 to 0.0673 W/ (m K). Furthermore, the silica aerogel is treated at high-temperature environment to further reduce the macropores diameters. As a result, the skeleton structure undergoes significant shrinkage. The micropore volume increases from 0.013 to 0.102 cm3 g−1, and the specific surface area increases from 9.828 to 294.4 m2 g−1. The thermal conductivity decreases from 0.0727 to 0.0368 W/ (m K) with the temperature increasing. Theoretical calculations indicate that the attribution of the thermal conductivity reduction is primarily the weakening of gaseous heat transfer below 400 °C. Above 400 °C, the effect of solid heat transfer becomes stronger than the limitation of gaseous heat transfer, which aligns with the experimental results. This study presents novel strategy for enhancing the thermal insulation performance of silica aerogels.