PROPERTIES OF ALUMINA AEROGELS PREPARED UNDER DIFFERENT CONDITIONS

Alumina aerogels were prepared by the sol-gel method and two different supercritical drying methods. In one method, alumina wet gel was supercritically dried under the supercritical condition of carbon dioxide and ethanol mixture in a CO2 extractor (80-degrees-C, 15.7 MPa). In the other method, alumina wet gel was supercritically dried under the supercritical condition of ethanol itself in an autoclave (270-degrees-C, 26.5 MPa). The physical properties of the alumina aerogels were measured for the different drying methods. Fibrillar crystals of boehmite were observed in the alumina aerogel supercritically dried in the autoclave. The properties of the alumina aerogels were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, infrared spectra, and Al-27 magic angle spinning nuclear magnetic resonance. The alumina aerogels had differing properties and differing behaviors in the firing process according to the supercritical drying conditions.