Comparison between sintered and compressed aerogels

Phalippou, J.; Despetis, Florence; Calas, S.; Faivre, Annelise; Dieudonné, Philippe; Sempéré, R.; Woignier, Thierry

doi:10.1016/j.optmat.2003.11.017

Cited by 21 publications

(18 citation statements)

References 12 publications

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“…The moduli of the model materials displays a power-law dependence on aerogel density with an exponent of approximately 3.0, nearly independent of constituent particle size. This exponent is within the range reported in the literature 8,15,18,20,28 and very similar to that previously found for the bulk modulus in the same models. 38 Measurements of modulus and Poisson's ratio along different axes indicated that these properties are isotropic to within the uncertainty of the data, though there is rather more anisotropy for the low-density materials than for the high density ones.…”

Section: Acs Paragon Plus Environmentsupporting

confidence: 92%

“…These exponents are comparable with those found experimentally,8,15,18,20,28 and agree within uncertainties with those found for the bulk modulus in previous work 38 .Obtaining the Poisson ratio from MD simulations in which all the cell dimensions are controlled directly requires finding the value of ν that yields a constant transverse stress of zero as strain is applied. For this purpose we perform several independent simulations, with ν ranging 0.10 to 0.30.…”

supporting

confidence: 89%

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Computational Study of Uniaxial Deformations in Silica Aerogel Using a Coarse-Grained Model

Ferreiro-Rangel¹,

Gelb

2015

J. Phys. Chem. B

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Simulations of a flexible coarse-grained model are used to study silica aerogels. This model, introduced in a previous study (J. Phys. Chem. C 2007, 111, 15792), consists of spherical particles which interact through weak nonbonded forces and strong interparticle bonds that may form and break during the simulations. Small-deformation simulations are used to determine the elastic moduli of a wide range of material models, and large-deformation simulations are used to probe structural evolution and plastic deformation. Uniaxial deformation at constant transverse pressure is simulated using two methods: a hybrid Monte Carlo approach combining molecular dynamics for the motion of individual particles and stochastic moves for transverse stress equilibration, and isothermal molecular dynamics simulations at fixed Poisson ratio. Reasonable agreement on elastic moduli is obtained except at very low densities. The model aerogels exhibit Poisson ratios between 0.17 and 0.24, with higher-density gels clustered around 0.20, and Young's moduli that vary with aerogel density according to a power-law dependence with an exponent near 3.0. These results are in agreement with reported experimental values. The models are shown to satisfy the expected homogeneous isotropic linear-elastic relationship between bulk and Young's moduli at higher densities, but there are systematic deviations at the lowest densities. Simulations of large compressive and tensile strains indicate that these materials display a ductile-to-brittle transition as the density is increased, and that the tensile strength varies with density according to a power law, with an exponent in reasonable agreement with experiment. Auxetic behavior is observed at large tensile strains in some models. Finally, at maximum tensile stress very few broken bonds are found in the materials, in accord with the theory that only a small fraction of the material structure is actually load-bearing.

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Section: Acs Paragon Plus Environmentsupporting

confidence: 92%

supporting

confidence: 89%

Computational Study of Uniaxial Deformations in Silica Aerogel Using a Coarse-Grained Model

Ferreiro-Rangel¹,

Gelb

2015

J. Phys. Chem. B

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“…The original silica aerogel consists of nano-clusters sticking to each other to form an low-density network. Cold compression of aerogel leads to densification due to the breaking and re-bonding of the ridges between clusters and interpenetration of clusters (e.g., Phalippou et al 2004). The bulk porosity is reduced but not the specific surface area, and thus not the primary size scale of clusters and pores (Perin et al 2003).…”

Section: Stardust Wild 2 Dust Interactions With Aerogelmentioning

confidence: 99%

A TEM study of thermally modified comet 81P/Wild 2 dust particles by interactions with the aerogel matrix during the Stardust capture process

Leroux¹,

Rietmeijer²,

Velbel³

et al. 2008

Meteorit & Planetary Scien

204

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Abstract-We report the results of high-resolution, analytical and scanning transmission electron microscopy (STEM), including intensive element mapping, of severely thermally modified dust from comet 81P/Wild 2 caught in the silica aerogel capture cells of the Stardust mission. Thermal interactions during capture caused widespread melting of cometary silicates, Fe-Ni-S phases, and the aerogel. The characteristic assemblage of thermally modified material consists of a vesicular, silicarich glass matrix with abundant Fe-Ni-S droplets, the latter of which exhibit a distinct core-mantle structure with a metallic Fe,Ni core and a iron-sulfide rim. Within the glassy matrix, the elemental distribution is highly heterogeneous. Localized amorphous "dust-rich" patches contain Mg, Al, and Ca in higher abundances and suggest incomplete mixing of silicate progenitors with molten aerogel. In some cases, the element distribution within these patches seems to depict the outlines of ghost mineral assemblages, allowing the reconstruction of the original mineralogy. A few crystalline silicates survived with alteration limited to the grain rims. The Fe-and CI-normalized bulk composition derived from several sections show CI-chondrite relative abundances for Mg, Al, S, Ca, Cr, Mn, Fe, and Ni. The data indicate a 5 to 15% admixture of fine-grained chondritic comet dust with the silica glass matrix. These strongly thermally modified samples could have originated from a finegrained primitive material, loosely bound Wild 2 dust aggregates, which were heated and melted more efficiently than the relatively coarse-grained material of the crystalline particles found elsewhere in many of the same Stardust aerogel tracks (Zolensky et al. 2006).

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“…During these treatments, the structure of the aerogel is modified and the mechanical properties are improved (Phalippou et al 2004). Figure 9a, b shows the evolution on a log-log plot, of Young's modulus (E), the fracture strength (σ), and the toughness, K IC , as a function of the density, produced by different kinds of catalyst (Fig.…”

Section: Aerogel To Glass Transformation Sinteringmentioning

confidence: 99%

“…However, if this analogy is pertinent when gels are under a tension stress (bending test), they exhibit a more complicated response when the structure is compressed (compression test). The network is linearly elastic under small strains, then exhibits yield, followed by densification and plastic hardening (Pirard et al 1995;Scherer et al 1995;Duffours et al 1995;Perrin et al 2004;Phalippou et al 2004). As a consequence of the plastic shrinkage, it is possible to eliminate the pores and stiffen the gel at room temperature.…”

Section: Introductionmentioning

confidence: 99%