Saxs Study of Silica Sols and Gels

Orcel, G.; Gould, R. W.; Hench, Larry L.

doi:10.1557/proc-73-289

Cited by 6 publications

(4 citation statements)

References 4 publications

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“…Therefore, an effect of formamide additions may be to strengthen the gel by maximizing the extent of condensation without reorganization into a particular structure. This is consistent with observations that formamide increases the microhardness of wet gels and correspondingly the pore size of dried gels, while maintaining a high surface area and large pore volume 1,18 . The values of structural properties such as specific surface area (Sp), specific pore volume (vp) and average pore radius (Rp) for the silica gels heated to 400°C obtained in this work are listed in Table 2.…”

Section: Solsupporting

confidence: 91%

Structural evolution of silica sols modified with formamide

Lenza

Vasconcelos

2001

Mat. Res.

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In this work we investigated the influence of formamide on the acid-catalyzed sol-gel process by Fourier transform infrared spectroscopy (FTIR). Three silica sols were studied: Sol catalyzed with nitric acid without formamide, sol catalyzed with nitric acid containing formamide and sol catalyzed with a mixture of nitric acid and hydrofluoric acid and modified with formamide. Following the time evolution of both the Si-(OH) stretching vibration at around 950 cm-1 and the Si-O-(Si) vibration between 1040 cm-1 and 1200 cm-1 we were able to describe the structural evolution of each sol. The curve of evolution of Si-(OH) stretching vibration corresponding to sol A has a simple asymptotic evolution. In the case of formamide containing sol, we observed a two-step structural evolution indicating that for the system containing formamide the polymerization goes through a temporary stabilization of oligomers, which can explain the non-variation of the Si-O(H) bond wavenumber for a certain time. Gelation times were of several days for gels without formamide and few hours for gels containing additive. The presence of additive resulted in a highly interconnected gel

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Section: Solsupporting

confidence: 91%

Structural evolution of silica sols modified with formamide

Lenza

Vasconcelos

2001

Mat. Res.

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“…The size of the primary particles does not change with density (i.e., the concentration of bis-NAD in the sol), in analogy to silica. 37 Secondary aggregates are larger for medium-density samples (85.2 nm in diameter for bis-NAD-10), but their size decreases as the density increases (60 nm for bis-NAD-20). Guinier Region IV for bis-NAD-5 was located at the edge of the accessible Q-range and the secondary particle size could not be Table 3 for information from the SANS data and for the meaning of Regions IÀIV .…”

Section: Articlementioning

confidence: 94%

Polyimide Aerogels by Ring-Opening Metathesis Polymerization (ROMP)

et al. 2011

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Polyimide aerogel monoliths are prepared by ring-opening metathesis polymerization (ROMP) of a norbornene end-capped diimide, bis-NAD, obtained as the condensation product of nadic anhydride with 4,4 0 -methylenedianiline. The density of the material was varied in the range of 0.13À0.66 g cm À3 by varying the concentration of bis-NAD in the sol. Wet gels experience significant shrinkage, relative to their molds (28%À39% in linear dimensions), but the final aerogels retain high porosities (50%À90% v/v), high surface areas (210À632 m 2 g À1 , of which up to 25% is traced to micropores), and pore size distributions in the mesoporous range (20À33 nm). The skeletal framework consists of primary particles 16À17 nm in diameter, assembling to form secondary aggregates (by SANS and SEM) 60À85 nm in diameter. At lower densities (e.g., 0.26 g cm À3 ), secondary particles are mass fractals (D m = 2.34 ( 0.03) turning to closed-packed surface fractal objects (D S = 3.0) as the bulk density increases (g0.34 g cm À3 ), suggesting a change in the network-forming mechanism from diffusion-limited aggregation of primary particles to a space-filling bond percolation model. The new materials combine facile one-step synthesis with heat resistance up to 200 °C, high mechanical compressive strength and specific energy absorption (168 MPa and 50 J g À1 , respectively, at 0.39 g cm À3 and 88% ultimate strain), low speed of sound (351 m s À1 at 0.39 g cm À3 ) and styrofoam-like thermal conductivity (0.031 W m À1 K À1 at 0.34 g cm À3 and 25 °C); hence, they are reasonable multifunctional candidate materials for further exploration as thermal/acoustic insulation at elevated temperatures.

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“…Their molar ratios were adjusted to have a potash feldspar composition of K20 • A120 3 • 6SiO 2. Si(OCH3) 4 was initially dissolved in methanol as a solvent and formamide 1 was added as a drying control additive to prevent cracks during drying [20]. The TMOS solution was vigorously stirred and K(OCH 3) was added to the solution.…”

Section: Alkoxides Solution Preparationmentioning

confidence: 99%

Sol to gel reaction in the K2OAl2O3SiO2 system

Lee

Tien

Gülari

1994

Journal of Non-Crystalline Solids

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A sol to gel transition reaction of three metal alkoxides with water in the preparation of gel in the K20-AleO 3-SiO 2 system was investigated using in situ viscosity measurements and the Raman scattering technique. The viscosity measurements reveal that the viscosity of the solution and the dependence of the reduced viscosity on polymer concentrations change abruptly near the gelation point. The Raman scattering results suggested that the hydrolysis of the TMOS was the rate-limiting step of the overall reaction. It was also found that a basic solution with excess amounts of water was needed to synthesize a transparent crack-free gel.

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Saxs Study of Silica Sols and Gels

Cited by 6 publications

References 4 publications

Structural evolution of silica sols modified with formamide

Structural evolution of silica sols modified with formamide

Polyimide Aerogels by Ring-Opening Metathesis Polymerization (ROMP)

Sol to gel reaction in the K2OAl2O3SiO2 system

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