Highly thermally stable alumina-based aerogels modified by partially hydrolyzed aluminum tri-sec-butoxide

Highly thermally stable alumina-based aerogels are synthesized by the acetone-aniline in situ water formation method and modified by partially hydrolyzed aluminum tri-sec-butoxide at different temperatures (25, 45, and 60 degrees C). The effects of modification, especially modification temperature, on microstructure and thermal stability of alumina-based aerogels are investigated. After the modification, the morphologies of alumina-based aerogels change from the network structures with interconnected needle-like particles to those with stacked sheet-like particles, resulting in a better heat resistance. The thermal stability of alumina-based aerogels enhances with the increasing modification temperature, whereas the high temperature (more than 60 degrees C) would lead to the dissolution of wet gels during the modification process due to the high solubility. After annealing at 1200 degrees C for 2 h, the 45 degrees C-modified alumina-based aerogel exhibits the best thermal stability with the lowest linear shrinkage of similar to 7% and the highest specific surface area of 154 m(2)/g. In addition, the modified aerogels remain in the theta-Al2O3 phase while the unmodified one transforms into alpha-Al2O3 phase after 1300 degrees C annealing. The alumina-based aerogels are further reinforced by incorporating with mullite fiber felt and TiO2. The obtained composites show ultralow thermal conductivities of 0.065, 0.086, and 0.118 W/mK at 800, 1000, and 1200 degrees C, respectively.