Structural investigation of alumina silica mixed oxide gels prepared from organically modified precursors

• Published in: Journal of non-crystalline solids 2007-06, Vol.353 (16), p.1635-1644
• Main Authors: Peterlik, Herwig, Rennhofer, Harald, Torma, Viktoria, Bauer, Ulrike, Puchberger, Michael, Hüsing, Nicola, Bernstorff, Sigrid, Schubert, Ulrich
• Format: Article
• Language: English
• Subjects: Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Medium-range order; Microstructure; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Silica; Sol–gels (xerogels); Synchrotron radiation
• ISSN: 0022-3093; 1873-4812
• DOI: 10.1016/j.jnoncrysol.2007.01.016

The development of the structure of silica/alumina gels was investigated by small angle X-ray scattering (SAXS) through all stages of the preparation process, that is gelation, aging, drying and calcination. Two series of gels were compared; the first was prepared from a single-source precursor, obtained by reaction of 3-oxoethyl-6-trimethoxysilyl-hexan-2-one (OTH-H) with Al(O s Bu) 3. The gels of the second series were prepared from the same precursors, but under conditions where hydrodeacylation of OTH-H occurs. It turned out that both series showed a similar structural development of the gels. Immediately after the start of the reaction small primary particles are formed, the size of which ( r = 0.7 ± 0.1 nm) remains constant through the gelation and aging process. In some samples, Si(OEt) 4 was added as an additional source for Si/O which was incorporated between the primary particles. Condensation proceeds by a slower aggregation of the primary particles, which initially form a rather open network. This network densifies during aging and drying.