Preparation and characterization of monolithic alumina aerogels

Alumina aerogels were prepared by a sol–gel method combined with the ethanol supercritical drying technique using aluminum tri-sec butoxide and nitric acid as the precursor and catalyzer respectively. This method affords high-surface-area alumina aerogel monoliths without the use of complexing agents. The structure and morphology of the aerogels were investigated by TEM, XRD, FTIR and BET techniques. The results confirmed that the as-prepared alumina aerogel possessed a network microstructure made up of pseudoboehmite fibers and a surface area of 690m2/g. It was transformed to γ-Al2O3 after heat treatment at 800°C without a significant loss in surface area. DMA analysis and hotdisk thermal analysis were performed to characterize the mechanical and thermal properties of the samples. The results indicated that the alumina aerogel was robust and exhibited excellent thermal insulating properties. The elastic modulus was up to 11.4MPa after drying, which is the one of the highest modulus of alumina aerogels ever reported. The thermal conductivities at 30°C and 400°C were 0.028W/mK and 0.065W/mK respectively. ► A new method for the synthesis of monolithic alumina aerogels was presented. ► Nitric acid is introduced to control the hydrolysis and condensation rates of aluminum alkoxide. ► Gelation time increases rapidly with increasing concentration of nitric acid. ► Aerogels obtained via this method were robust and with high surface areas.