Journal ArticleDOI
Effect of aging and pH on the modulus of aerogels
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TLDR
The elastic modulus of an aerogel is related to its density ϱ by E = c(pH)ϱ3.7 for gels made at various pH values; however, the constant of proportionality c depends on pH as mentioned in this paper.Abstract:
The elastic modulus E of an aerogel is related to its density ϱ by E = c(pH)ϱ3.7 for gels made at various pH values; however, the constant of proportionality c depends on pH. It is found that this relation applies regardless of whether the density is varied by lengthy aging or by increasing the concentration of tetramethoxysilane (TMOS) in the initial sol; that is, changes in aging time and [TMOS] evidently have equivalent effects on gel structure. The influence of pH on densification can be understood in terms of competition between polycondensation (P, which produces shrinkage) and dissolution/ reprecipitation (D/R, which increases the rigidity of the network). At low pH, P dominates, but at high pH D/R stiffens the network and inhibits shrinkage.read more
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Silica aerogel; synthesis, properties and characterization
TL;DR: In this article, a review of research work and developments in synthesis, properties and characterization of silica aerogels is presented, with particular attention paid to drying, which is a critical step in aerogel synthesis and makes the production of this material more economical and commercial.
Journal ArticleDOI
An overview on silica aerogels synthesis and different mechanical reinforcing strategies
TL;DR: A review of the literature on the methods for mechanical reinforcing of silica aerogels and discusses the recent achievements in improving the strength and elastic response of native silica gels along with cost effectiveness of each methodology.
Journal ArticleDOI
Aerogels in catalysis
M. Schneider,Alfons Baiker +1 more
TL;DR: In this paper, a solution-sol-gel (SSG) method was used for aerogel preparation and their subsequent liberation from the solvent via critical-point drying or supercritical (or hypercritical) drying (SCD).
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Pore structure evolution in silica gel during aging/drying. III. Effects of surface tension*
TL;DR: In this paper, the physical and chemical structures of gels dried from aprotic solvents were studied by a series of techniques (29 Si MAS-NMR, nitrogen adsorption, SAXS, elemental analysis, TGA).
Journal ArticleDOI
Silica-included heteropoly compounds as solid acid catalysts
TL;DR: In this paper, a silica-included heteropoly compounds were obtained, which were porous materials with mesopores and large surface areas, and were thermally more stable than the acidic ion-exchange resin Amberlyst-15.
References
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Journal ArticleDOI
Sol-gel transition in simple silicates II☆
TL;DR: In this article, a range of conditions in which the rate of hydrolysis was varied from fast to slow with respect to condensation were discussed, and it was shown that higher temperatures were sufficient to densify fine gels by a process which was postulated to consist of polymer relaxation followed by condensation and pore collapse.
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Structure and self-similarity of silica aerogels.
TL;DR: Small-angle neutron scattering from silica aerogels reveals that they form mutually self-similar volume fractals for a wide range of densities and preparations, and indication for a volume-to-surface fractal crossover is obtained.
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Effect of shrinkage on the modulus of silica gel
TL;DR: In this paper, the authors measured the shear modulus of alkoxide-derived silica gels during aging and drying; base-catalyzed gels exhibit phase separation (apparently from segregation of residual partially condensed TEOS).
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Viscoelasticity in silica gel
TL;DR: The elastic modulus, modulus of rupture (MOR), and viscosity of wet silica gels were measured as functions of age of the gels, using a beam-bending method as discussed by the authors.