Superhydrophobic, heat-resistant alumina-methylsilsesquioxane hybrid aerogels with enhanced thermal insulating performance in high humidity

Heat-resistant alumina aerogels serve as prospective thermal insulating materials in the high-temperature fields, whereas the inherent hydrophilicity and thermal coarsening restrict their thermal insulating application. In this study, superhydrophobic, heat-resistant alumina-methylsilsesquioxane hybrid aerogels (AlMSAs) were prepared via in-situ sol-gel method combined with supercritical drying to overcome the aforesaid obstacles. The transformation from hydrophilicity to hydrophobicity is achieved by regulating the molar ratio of methyltriethoxysilane. The aerogel exhibits homogenous superhydrophobicity with contact angle reaching up to 152.6 degrees when the molar ratio of Al to Si is 2 (AlMSA2). AlMSAs show superior heat resistance up to 1300 degrees C, suffering no alpha-Al2O3 transition and minor grain growth. Quartz fiber reinforced alumina-based aerogel composite (QFAlMSA2) is prepared to study the thermal insulating performance in practical application. The thermal conductivity of QFAlMSA2 reversibly increases by 5.0% subject to 90% relative humidity (36 degrees C) for one month due to the superhydrophobicity. QFAlMSA2 exhibits a low thermal conductivity of 0.0542 W/(m center dot K) after being calcined at 1200 degrees C and a moderate temperature of 113 degrees C when exposed to a butane flame for 30 min. This study offers meaningful insights into developing alumina-based aerogel materials for high-moisture and high-temperature thermal insulations.