Deformation of aerogels during characterization

Scherer, George W.; Smith, Douglas M.; Stein, David J.

doi:10.1016/0022-3093(95)00058-5

Cited by 155 publications

(75 citation statements)

References 13 publications

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“…However, application of this model to strain data obtained on mesoporous glass with dilatometric setups during gas adsorption revealed that Bangham's model alone was only partially able to explain the observed effects [4,5]. The issue of mesopore deformation received renewed attention in the context of drying and characterization of silica aerogels in the 1980's and 90's [6][7][8]. Using in-situ dilatometry measurements Reichenauer and Scherer demonstrated large sorption-induced strains exceeding 40 vol % during the characterization of aerogels with nitrogen sorption at 77 K, which lead to highly erroneous pore size distributions [9][10][11].…”

Section: Introductionmentioning

confidence: 99%

Relationship Between Pore Structure and Sorption-Induced Deformation in Hierarchical Silica-Based Monoliths

Balzer

Morak

Erko³

et al. 2015

Zeitschrift Für Physikalische Chemie

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Abstract:Experimental results on sorption-induced deformation during npentane desorption were obtained by in-situ dilatometry and in-situ small angle X-ray scattering (SAXS). The sample investigated was a silica-based monolith with hierarchical pore structure comprising a macroporous network of struts, each strut containing well-defined cylindrical mesopores ordered on a 2D hexagonal lattice. In-situ dilatometry and in-situ SAXS measurements revealed strain isotherms of similar shape, which are qualitatively in good agreement with recent theoretical predictions. From the relative pressure range of the liquid filled mesopores a pore load modulus of 1.5 GPa is determined. The relative pressure region of mono-and multilayer formation, however, reveals differences between the two independent methods. In particular, the net strain at saturation pressure is considerably larger for in-situ dilatometry. We attribute this observation to the different sensitivity of the two methods to anisotropic deformation in the hierarchical solid framework. While in-situ SAXS measures the mesopore lattice strain and is therefore exclusively sensitive to radial deformation of the struts, dilato-*Corresponding authors: Oskar Paris,

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Section: Introductionmentioning

confidence: 99%

Relationship Between Pore Structure and Sorption-Induced Deformation in Hierarchical Silica-Based Monoliths

Balzer

Morak

Erko³

et al. 2015

Zeitschrift Für Physikalische Chemie

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“…Some of them are known to be deformed during N 2 sorption analysis from intermediate relative pressure [45]. We made here the assumption that the calcination, at relatively high temperature, strengthens our aerogels enough to withstand the capillary forces applied during nitrogen sorption.…”

Section: Calcination and Morphologymentioning

confidence: 99%

Doped TiO 2 aerogels as alternative catalyst supports for proton exchange membrane fuel cells: A comparative study of Nb, V and Ta dopants

Beauger

Testut

Berthon‐Fabry

et al. 2016

Microporous and Mesoporous Materials

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Nb, Ta and V-doped TiO 2 aerogels and xerogels have been synthesized as possible new alternatives to carbon blacks for Proton Exchange Membrane Fuel Cells catalyst supports. A comparative study of different dopants was realized in a single study. Nb, Ta and V showed different behaviors with respect to the final material structure and morphology, composition and electronic conductivity. They are all prone to surface segregation, to different extents. V-doped TiO 2 apart, the rutile structure could only be obtained after calcination in a reducing atmosphere at 800 °C for Nb or Ta-doped TiO 2 . The electronic conductivity exhibited a maximum at 10 at.% for Nb and Ta, 5 at.% for V. Nb revealed to be the most appropriate dopant to increase the electronic conductivity of TiO 2 , followed by Ta and V.4 to 5 orders of magnitude were gained after Nb doping for xerogels conductivity to reach almost 0.1 S cm -1 . The role of point defects was discussed to account for phase transition and evolution of conductivity.

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“…was evaluated from the adsorption data using the total pore volume per mass unit V p through the relation ͑1/ ͒ = ͑1/ a ͒ + V p , assuming the value 2.2 g / cm 3 for the skeletal density a , as frequently quoted for fused silica. It has been pointed out 9 that, in the case of low-density aerogels, the adsorption method applies stress on the sample during measurement leading to an underestimation of pore volume. This seems not to be the case for our samples of aerogels produced from sonogels due to the good agreement, in general, found between the bulk densities measured from direct mass and volume determinations and from the adsorption data.…”

Section: I͑q͒mentioning

confidence: 99%

Mass fractal characteristics of silica sonogels as determined by small-angle x-ray scattering and nitrogen adsorption

Donatti

Vollet²,

Ruiz³

et al. 2005

Phys. Rev. B

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A sample series of silica sonogels was prepared using different water-tetraethoxysilane molar ratio ͑r w ͒ in the gelation step of the process in order to obtain aerogels with different bulk densities after the supercritical drying. The samples were analyzed by means of small-angle x-ray-scattering ͑SAXS͒ and nitrogen-adsorption techniques. Wet sonogels exhibit mass fractal structure with fractal dimension D increasing from ϳ2.1 to ϳ 2.4 and mass-fractal correlation length diminishing from ϳ13 nm to ϳ 2 nm, as r w is changed in the nominal range from 66 to 6. The process of obtaining aerogels from sonogels and heat treatment at 500°C, in general, increases the mass-fractal dimension D, diminishes the characteristic length of the fractal structure, and shortens the fractal range at the micropore side for the formation of a secondary structured particle, apparently evolved from the original wet structure at a high resolution level. The overall mass-fractal dimension D of aerogels was evaluated as ϳ2.4 and ϳ2.5, as determined from SAXS and from pore-size distribution by nitrogen adsorption, respectively. The fine structure of the "secondary particle" developed in the obtaining of aerogels could be described as a surface-mass fractal, with the correlated surface and mass-fractal dimensions decreasing from ϳ2.4 to ϳ 2.0 and from ϳ2.7 to ϳ 2.5, respectively, as the aerogel bulk density increases from 0.25 ͑r w =66͒ up to 0.91 g / cm 3 ͑r w =6͒.

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Deformation of aerogels during characterization

Cited by 155 publications

References 13 publications

Relationship Between Pore Structure and Sorption-Induced Deformation in Hierarchical Silica-Based Monoliths

Relationship Between Pore Structure and Sorption-Induced Deformation in Hierarchical Silica-Based Monoliths

Doped TiO 2 aerogels as alternative catalyst supports for proton exchange membrane fuel cells: A comparative study of Nb, V and Ta dopants

Mass fractal characteristics of silica sonogels as determined by small-angle x-ray scattering and nitrogen adsorption

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