Densification of monolithic silica gels below 1000°C

Klein, Lisa C.; Gallo, Tom; Garvey, G. J.

doi:10.1016/0022-3093(84)90383-1

Cited by 77 publications

(14 citation statements)

References 10 publications

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“…On the other hand, as may be expected, when the silica gel is heated the SSA decrease due to the collapse of pores. Klein et al [3] have shown that, on heating silica gels, the SSA increases around 400~ and comes back to the original value at around 760~ decreasing then with a further rise in temperature. The PSD obtained for these gels showed the same behavior as for the SSA.…”

Section: Resultsmentioning

confidence: 96%

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Further insights into the porous structure of TEOS derived silica gels

Rubio

Oteo

1997

J Sol-Gel Sci Technol

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Abstract. The porous structure of TEOS derived silica gels was studied using nitrogen adsorption at 77 K. Silica gels were prepared using TEOS, H20 and ethanol for different molar ratios. No catalyst was used in this study. Silica gels were also heat treated up to 1000~ The nitrogen sorption isotherms were analyzed by two models: Fractal and Percolation Theories. Using the fractal analysis approach, the surface roughness of the porous structure of silica gels was determined. The surface fractal dimension depends on the hydrolysis conditions and heat treatment. The surface fractal dimension decreases with increasing H20/TEOS molar ratio or heating temperature. For the silica gels studied, the surface fractal dimension changed from 2.6 to 2.5 after heating the gels, and from 2.4 to 2.6 with decreasing H20/TEOS ratio.Using the Percolation theory, we have determined the connectivity of the porous structure of silica gels. The extent of sorption hysteresis of the nitrogen isotherms reflects the connectivity of the pore network. The mean coordination number (connectivity) Z, and the linear dimension of the network, L, have been calculated from the hysteresis of the isotherms. For the as-prepared silica gels, Z was about 8 and L close to 2. On heating the gels, Z decreases to 4 and L increases to 7, results which are in accordance with the collapse of the porous network.

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Section: Resultsmentioning

confidence: 96%

“…These monolithic gels have been converted to glass by heating at temperatures close to 1000~ [3]. During heat treatment, the high specific surface area and porosity decrease abruptly, and the density increases reaching a value close to that of vitreous silica [4].…”

Section: Introductionmentioning

confidence: 99%

Further insights into the porous structure of TEOS derived silica gels

Rubio

Oteo

1997

J Sol-Gel Sci Technol

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“…For a given template sphere size, increases in temperature resulted in a smaller d spacing between diffraction layers due to increased densification of the SiO 2 structure. [20] The densification of silica occurs through further condensation of silanol groups, which results in shrinkage of the silica walls and becomes more pronounced at higher temperatures. For smaller template sizes, the densification at 700°C was less prominant due to the presence of thinner 3DOM walls that undergo a smaller dimensional change compared to the same degree of condensation in samples prepared with larger template sizes.…”

Section: Tuning Color Via Thermal Processingmentioning

confidence: 99%

Inverse Opal SiO₂ Photonic Crystals as Structurally‐Colored Pigments with Additive Primary Colors

Josephson

Miller

Stein

2014

Zeitschrift anorg allge chemie

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Abstract. Porous silica, structured as three-dimensionally ordered macroporous (3DOM) photonic crystal particles, is investigated as a pigment material with structural color. Brightly and uniformly colored 3DOM SiO 2 powders were obtained by templating of a tetraethoxysilane-containing precursor in polymeric colloidal crystals, pyrolysis in an inert atmosphere to maintain a small amount (ca. 5-8 wt %) of residual carbon as a background absorber, and particle size reduction. The color depended on placing optical stop bands in the appropriate range of the visible spectrum. This was achieved through selection of the polymer sphere diameter in the colloidal crystal template and finetuning by the pyrolysis temperature, which controls the extent of condensation and shrinkage of the 3DOM SiO 2 structure. The stop bands

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“…Fully dense oxides can be obtained from gels with appropriate heat treatment [59]. On the other hand, some microporous films can be used up to 500°C without loss of surface area.…”

Section: F Porous Coatingsmentioning

confidence: 99%

Sol-Gel Coatings

Klein¹

1991

Thin Film Processes

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Densification of monolithic silica gels below 1000°C

Cited by 77 publications

References 10 publications

Further insights into the porous structure of TEOS derived silica gels

Further insights into the porous structure of TEOS derived silica gels

Inverse Opal SiO₂ Photonic Crystals as Structurally‐Colored Pigments with Additive Primary Colors

Sol-Gel Coatings

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Densification of monolithic silica gels below 1000°C

Cited by 77 publications

References 10 publications

Further insights into the porous structure of TEOS derived silica gels

Further insights into the porous structure of TEOS derived silica gels

Inverse Opal SiO2 Photonic Crystals as Structurally‐Colored Pigments with Additive Primary Colors

Sol-Gel Coatings

Contact Info

Product

Resources

About

Inverse Opal SiO₂ Photonic Crystals as Structurally‐Colored Pigments with Additive Primary Colors