Alumina aerogels prepared via rapid supercritical extraction

Abstract

Alumina aerogels with surface areas from 460 to 840 m2/g and bulk densities from 0.025 to 0.079 g/cm3 were successfully fabricated using variations of an aluminum isopropoxide-based recipe developed by Armor and Carlson and the rapid supercritical extraction (RSCE) process developed at Union College. By utilizing the Union College RSCE method, it is possible to convert an alumina aerogel precursor mixture into aerogel monoliths in as little as 7.5 h. This process is safer than methanol extraction in an autoclave and faster and simpler than liquid CO2 solvent exchange and extraction. By increasing the concentration of aqueous HNO3 used in the precursor mixture, we were able to fabricate aerogels with significantly increased surface area, decreased bulk density, and altered microstructure. We attribute the observed variation in these aerogel properties at a given HNO3 concentration to environmental factors such as humidity. The ability to more easily fabricate alumina aerogels with desirable properties will assist in making them a viable option for catalytic and other applications.