Zirconia Aerogels with High Surface Area Derived from Sols Prepared by Electrolyzing Zirconium Oxychloride Solution: Comparison of Aerogels Prepared by Freeze-Drying and Supercritical CO2(l) Extraction

Abstract

Zirconia aerogels with high surface area of ca. 640 m2/g were prepared from sols made by electrolyzing zirconium oxychloride solutions at room temperature. To obtain the aerogels, supercritical CO2(l) extraction or freeze-drying was applied to remove the solvents from the wet gels. The microstructures and properties of aerogels produced by the two processes were characterized and compared. The aerogel produced by the supercritical CO2(l) drying process (S-aerogel) had a mesoporous structure (pore size, 9.7 nm) and was a transparent monolith, whereas that prepared by the freeze-drying process (F-aerogel) had a microporous structure (pore size, 0.59 nm) and was an opaque white powder, which transformed from amorphous to crystalline solids upon calcination. Moreover, the effects of the yittria on the microstucture and phase structure of the prepared aerogels were investigated.