Structural characteristics of silica sonogels prepared with different proportions of TEOS and TMOS |
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Authors: | DR Vollet LM Nunes A Ibañez Ruiz |
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Institution: | a Unesp - Universidade Estadual Paulista, IGCE, Departamento de Física, Cx.P. 178, 13500-970 Rio Claro (SP), Brazil b Centro Universitário Hermínio Ometto - Uniararas, 13607-339 Araras (SP), Brazil |
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Abstract: | Sonohydrolysis of mixtures of tetraethoxysilane (TEOS) and tetramethoxysilane (TMOS) with different TMOS/(TMOS + TEOS) molar ratio R was carried out to obtain ∼2.0 × 10−3 mol SiO2/cm3 and ∼86%-volume liquid phase wet gels. Aerogels were obtained by supercritical CO2 extraction in autoclave. The samples were analyzed by small-angle X-ray scattering (SAXS) and nitrogen adsorption. The structure of the wet gels can be described as a mass fractal structure with fractal dimension D ∼ 2.2 and characteristic length ξ increasing from ∼4.6 nm for pure TEOS to ∼6.4 nm for pure TMOS. A fraction of the porosity is eliminated with the supercritical process. The fundamental role of the TMOS/(TMOS + TEOS) molar ratio on the structure of the aerogels is to increase the porosity and the pore mean size as R changes from pure TEOS to pure TMOS. The supercritical process increases the mass fractal dimension and shortens the fractality domain in the mesopore region. A secondary structure appearing in the micropore region of the aerogels can be described as a mass/surface fractal structure with correlated mass fractal dimension Dm ∼ 2.6 and surface fractal dimension Ds ∼ 2.3. |
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Keywords: | 61 10 Eq 61 43 Hv 81 20 Fw 82 70 Gg |
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