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H. Peterlik, H. Rennhofer, V. Torma, U. Bauer, M. Puchberger, S. Bernstorff, U. Schubert:
"Structural investigation of alumina silica mixed oxide gels prepared from organically modified precursors";
Journal of Non-Crystalline Solids, 353 (2007), 1634 - 1644.

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^sBu)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.

Synchrotron radiation; Microstructure; Silica; Sol-gels (xerogels); Medium-range order