Effects of aging and drying conditions on the structural and textural properties of silica gels

Estella, Juncal; Echeverría, Jesús C.; Laguna, Mariano; Garrido, Julián

doi:10.1016/j.micromeso.2007.01.007

Cited by 130 publications

(63 citation statements)

References 20 publications

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“…Many studies reported the strengthening of wet silica gels by means of an exchange into a silane precursor containing solution (TEOS or TMOS), a process more akin to a surface modification step, which prevents the cracking of silica aerogel during supercritical drying [39e42,44e47, 49,50,53,54]. Several studies have also reported on making the gels more rigid by aging them for extended periods of time (multiple days or even weeks) which helps in reducing the shrinkage of the final aerogels produced after supercritical drying [36,37,43,48,56]. In other studies, Davis et al [38] studied the effect of different pore fluids on aging process which helps to prevent the pore collapse upon ambient drying and Reichenauer [51] showed that heat treatment of silica gels in water increased the mechanical stability which enables supercritical drying without significant shrinkage of the gel.…”

Section: Introductionmentioning

confidence: 99%

Effect of aging on silica aerogel properties

Iswar

Malfait

Balog

et al. 2017

Microporous and Mesoporous Materials

141

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Silica aerogels' unique physical and chemical properties make them fascinating materials for a wide variety of applications. In addition to hydrophobization by silylation, aging is very important in the synthesis of silica aerogel by ambient pressure drying. Here we systematically study the effect of aging on the physico-chemical properties of silica aerogel with emphasis on ambient dried materials. Silica gels were aged for different times and at different temperatures in their gelation liquid (without solvent exchange), hydrophobized in hexamethyldisiloxane and subsequently dried either at ambient pressure or from supercritical CO 2 . Dynamic oscillatory rheological measurements demonstrate that aging reinforces the alcogels, particularly at high strain. The specific surface area decreases with increasing aging time and temperature as a consequence of Ostwald ripening processes during aging. With increasing aging time and temperature, the linear shrinkage and bulk density decrease and the pore size and pore volume increase for the ambient dried gels, but remain nearly constant for supercritically dried gels. Small-Angle X-ray scattering does not detect significant structural changes at length scales smaller than about hundred nanometers, but hints at systematic variations at larger length scales. The findings of this study highlight the importance of aging to increase the ability of the gel particle network to withstand irreversible pore collapse during ambient pressure drying.

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Section: Introductionmentioning

confidence: 99%

Effect of aging on silica aerogel properties

Iswar

Malfait

Balog

et al. 2017

Microporous and Mesoporous Materials

141

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“…The sol-gel process offers some advantages over other procedures in obtaining ceramic materials, including (a) lowtemperature synthesis, (b) high-purity materials, and (c) customisable porosity of xerogel products. The structure and porous texture of xerogels synthesised using tetraethoxysilane (TEOS) as a precursor depend on synthesis conditions, namely, pH, temperature, and the precursor:solvent:water molar ratio Estella et al 2007aEstella et al , 2007bMusgo et al 2009). Porous texture is also affected by ageing and drying conditions (Estella et al 2007a).…”

Section: Introductionmentioning

confidence: 99%

Characterisation of hybrid xerogels synthesised in acid media using methyltriethoxysilane (MTEOS) and tetraethoxysilane (TEOS) as precursors

et al. 2011

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The mild synthetic conditions provided by the sol-gel process and the versatility of the colloidal state allow for the mixing of inorganic and organic components at the nanometre scale in virtually any ratio for the preparation of hybrid materials. Our interest in hybrid xerogels focuses on combining their porosity with other properties to prepare optic-fibre sensors. The specific aim of this paper is to synthesise hybrid xerogels in acid media using methyltriethoxysilane (MTEOS) and tetraethoxysilane (TEOS) as silica precursors and to investigate the effect of the MTEOS molar ratio on the structure and porous texture of xerogels. Gelation time exponentially increased as the MTEOS molar ratio increased. Increasing the MTEOS molar ratio yielded xerogels with lower density and lower particle size. The incorporation of MTEOS resulted in new FTIR bands at 1276 and 791 cm −1 , which was attributed to vibrational modes of methyl group. The band around 1092 cm −1 associated with siloxane bonds shifted to lower wavenumbers and split into two bands. The 29 Si spectra only showed the Q n (n = 2, 3, 4) signal in xerogels with 0% MTEOS and the T n (n = 2, 3) signal in xerogels with 100% MTEOS; hybrid xerogels showed both Q and T signals. From XRD peaks at 2θ around 9°, we inferred that xerogels (>70% MTEOS) consisted of nanocrystalline CH 3 -SiO 3/2 species. Increasing the MTEOS molar ratio produced xerogels with lower pore volumes and lower average pore size. The integration of methyl groups on the surface decreased the surface polarity and, in turn, the characteristic energy.

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“…The isotherms presented by the 0-1 wt% GO-SiO 2 aerogels indicate the presence of both mesopores (2-50 nm) and macropores (N 50 nm). The existence of macropores (N50 nm) is evidenced by elevated adsorption at relative pressures above 0.90 and an unsaturated adsorption isotherm [58][59][60]. The isotherm of the 2 wt% GO gel however, persists in a horizontal manner which suggests that the materials is mesoporous and does not contain macropores [57].…”

Section: Resultsmentioning

confidence: 99%

Graphene oxide reinforced high surface area silica aerogels

Dervin

Lang

Perova

et al. 2017

Journal of Non-Crystalline Solids

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Silica aerogel structures were intercalated with graphene oxide (GO) via the addition of GO to the colloidal silica sol and subsequent sol-gel polymerization. The potential of GO to act as a nanofiller, for ambient pressure dried, hydrophobic silica aerogels, was systematically investigated. The influences of 0 to 2 wt% GO loadings, on the physical properties of silica aerogels, were analysed by examining the bulk density, volume shrinkage (%), pore volume and surface area of the composite aerogels. Additionally, the chemical composition of the composite gels was determined using FTIR, Raman, XRD and XPS. The study revealed that a GO addition of as little as 0.5 wt% is capable of supporting the porous framework of silica aerogels and also enhancing the properties of the gels simultaneously. The additions of 0.5 wt% GO increased the surface area and pore volume of the aerogel from 390 to 700 m 2 /g and 0.59 to 0.99 cm 3 , respectively, and decreased aerogel density from 0.19 to 0.14 g/cm 3 . The investigation therefore revealed that intercalation of the silica aerogel matrix with small quantities of GO can inhibit volume shrinkage during drying without hindering the physical properties of silica aerogels.

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Effects of aging and drying conditions on the structural and textural properties of silica gels

Cited by 130 publications

References 20 publications

Effect of aging on silica aerogel properties

Effect of aging on silica aerogel properties

Characterisation of hybrid xerogels synthesised in acid media using methyltriethoxysilane (MTEOS) and tetraethoxysilane (TEOS) as precursors

Graphene oxide reinforced high surface area silica aerogels

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