Structural properties of silica gels prepared from oxalic‐acid‐catalyzed tetraethoxysilane sonohydrolysis

About ∼2.1 × 10 −3 mol SiO 2 cm −3 and ∼88%‐volume liquid‐phase silica wet gels were prepared from oxalic‐acid‐catalyzed tetraethoxysilane (TEOS) sonohydrolysis. Aerogels were obtained by supercritical CO 2 extraction. The samples were analyzed by thermogravimetry, small‐angle X‐ray scattering and nitrogen adsorption. Wet gels can be described as mass fractal structures with fractal dimension D ∼ 1.94 and structural characteristic length ξ changing between ∼3.3 to ∼3.0 nm in the studied range of the catalyst concentration. A fraction of the porosity is apparently eliminated in the supercritical process. The values of the BET specific surface S BET , the total pore volume V P and the mean pore size l P of the aerogels were found to change almost randomly around the mean values S BET = 874 m 2 g −1 , V P = 0.961 cm 3 g −1 and l P = 4.4 nm with catalyst concentration variation. These values were not substantially different from those from an equivalent HCl‐catalyzed aerogel. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)