Structural study of aged saturated silica gels obtained from tetramethoxysilane sonohydrolysis with different water/tetramethoxysilane molar ratio

Vollet, Dimas R.; Donatti, D. A.; Ruiz, Alberto; Castro, W. C. de

doi:10.1103/physrevb.67.184207

Cited by 7 publications

(4 citation statements)

References 10 publications

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“…The first term in , which gives the volume‐fractal 19 and single‐particle scattering, has also been used to model the scattering from fine silica gels prepared using sol–gel methods 20–23 . The second term in is the surface fractal scattering 24 .…”

Section: Methodsmentioning

confidence: 99%

Structural Changes to the Calcium–Silicate–Hydrate Gel Phase of Hydrated Cement with Age, Drying, and Resaturation

Thomas

Allen

Jennings

2008

Journal of the American Ceramic Society

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The effects of drying to various relative humidity (RH) levels on the internal structure of hydrated cement paste were investigated using small‐angle neutron scattering (SANS). Specimens of young and mature portland cement paste were analyzed in the initial saturated state, in the dried state, and then again after resaturation, allowing reversible and irreversible effects to be separated. While the observed changes on drying are mainly physical in nature, the ability of the microstructure to resist permanent structural rearrangement increased over time as the hydration and aging reactions progressed. Permanent changes to the nanometer‐to‐micrometer scale microstructure induced by drying were quantified by applying a fractal model to the SANS data for resaturated pastes. At RH levels above ≈54%, capillary stresses compact the nanometer‐level pore structure of the calcium–silicate–hydrate (C–S–H) gel phase, increasing the gel density by a mechanism related to that governing the classical “constant rate period” for pure gels. Owing to the restraining effects of the other solid phases in cement paste, this decrease in the volume of the C–S–H gel also increases the intensity of surface fractal scattering that arises from the deposition of hydration product onto the surface of the reacting cement particles. At all RH levels, but particularly below 54%, drying decreases the measured total internal surface area of the specimens. This is attributed to a loss of surface area at particle contacts as the average separation distance between adjacent C–S–H gel nanoparticles decreases on drying.

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Section: Methodsmentioning

confidence: 99%

Structural Changes to the Calcium–Silicate–Hydrate Gel Phase of Hydrated Cement with Age, Drying, and Resaturation

Thomas

Allen

Jennings

2008

Journal of the American Ceramic Society

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“…2,3 The wet gel structure frequently exhibits a mass fractal feature 4 consisting of a continuous solid network imbibed in a liquid phase, which can occupy until about 95 to 98 % of the volume sample. 5,6 Drying is the most critical step of the sol-gel processing for obtaining monoliths or if the textural properties of the wet gels are intended to be preserved. 7 Supercritical drying ͑aerogels͒, freeze drying ͑criogels͒, and evaporation drying ͑xerogels͒ 1 are the usual methods in dried gels production.…”

Section: Introductionmentioning

confidence: 99%

Small-angle x-ray scattering study of the structural evolution of the drying of sonogels with the liquid phase exchanged by acetone

et al. 2004

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The structural evolution on the drying of wet sonogels of silica with the liquid phase exchanged by acetone, obtained from tetraethoxisilane sonohydrolysis, was studied in situ by small-angle x-ray scattering ͑SAXS͒. The periods associated to the structural evolution as determined by SAXS are in agreement with those classical ones established on basis of the features of the evaporation rate of the liquid phase in the obtaining of xerogels. The wet gel can be described as formed by primary particles ͑microclusters͒, with characteristic length a ϳ0.67 nm and surface which is fractal, linking together to form mass fractal structures with mass fractal dimension Dϭ2.24 in a length scale ϳ6.7 nm. As the network collapses while the liquid/vapor meniscus is kept out of the gel volume, the mass fractal structure becomes more compacted by increasing D and decreasing , with smoothing of the fractal surface of the microclusters. The time evolution of the density of the wet gels was evaluated exclusively from the SAXS parameters , D, and a. The final dried acetone-exchanged gel presents Porod's inhomogeneity length of about 2.8 nm and apparently exhibits an interesting singularity D →3, as determined by the mass fractal modeling used to fit the SAXS intensity data for the obtaining of the parameters and D.

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“…Although of the polydisperse character of the system is normally enough to account for this effect, it may be associated to internal structures of the clusters making up the TEOS-derived sonogels, which have been assigned to mass fractal structures [9]. As a matter of fact, PorodÕs law was found not be rigorously followed for samples with small aerosil content.…”

Section: Discussionmentioning

confidence: 98%

Structural study of composites of aerosil fumed silica and tetraethoxysilane-derived sonogels

Donatti¹,

Ruiz²,

Vollet³

2005

Journal of Non-Crystalline Solids

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Structural study of aged saturated silica gels obtained from tetramethoxysilane sonohydrolysis with different water/tetramethoxysilane molar ratio

Cited by 7 publications

References 10 publications

Structural Changes to the Calcium–Silicate–Hydrate Gel Phase of Hydrated Cement with Age, Drying, and Resaturation

Structural Changes to the Calcium–Silicate–Hydrate Gel Phase of Hydrated Cement with Age, Drying, and Resaturation

Small-angle x-ray scattering study of the structural evolution of the drying of sonogels with the liquid phase exchanged by acetone

Structural study of composites of aerosil fumed silica and tetraethoxysilane-derived sonogels

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