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Fractal structure of basic silica gels with low Ca content
Author(s) -
Gaboriaud F.,
Chaumont D.,
at A.,
Craievich A.
Publication year - 2000
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889899013448
Subject(s) - small angle x ray scattering , fractal dimension , scattering , fractal , neutron scattering , small angle neutron scattering , chemistry , materials science , crystallography , chemical physics , analytical chemistry (journal) , optics , chromatography , physics , mathematical analysis , mathematics
Several gels were produced by addition of low amounts of calcium ions to strongly basic silico‐alkaline sols. These gels, previously studied by small‐angle x‐ray scattering (SAXS), small‐angle neutron scattering (SANS) and elastic light scattering (ELS), were analysed over a wide range of scattering vectors extending from 8 x 10 −4 Å −1 up to 2 x 10 −4 Å. The joint use of various scattering techniques allowed us the simultaneous characterisation of coarse, medium and fine structural features of the studied gels. Clear discrepancies between SANS and earlier ELS results were attributed to effects of multiple scattering on light scattering experiments. The experimental results demonstrate that the studied gels are composed of aggregates exhibiting a fractal structure within a scale range extending from less than 10 to more than 1000 Å, with the same fractal dimension over the whole scale range. The fractal dimension and so the mechanism of aggregation depend on the initial sol composition and Ca content. The mechanism responsible for gel formation in precursor sols with low calcium concentration ([Ca 2+ ] = 0.3 mol.L −1 ) is reaction limited cluster‐cluster aggregation (RLCA).