Strengthening of silica gels and aerogels by washing and aging processes

Einarsrud, Mari Ann; Nilsen, Elin; Rigacci, Arnaud; Pajonk, G.M.; Buathier, Serge; Valette, Dominique; Durant, Marcel; Chevalier, Bruno; Nitz, Peter; Ehrburger‐Dolle, Françoise

doi:10.1016/s0022-3093(01)00423-9

Cited by 93 publications

(64 citation statements)

References 15 publications

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“…Several studies reported on the influence of the aging conditions used during silica aerogel synthesis [36e59]. 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].…”

Section: Introductionmentioning

confidence: 99%

Effect of aging on silica aerogel properties

Iswar

Malfait

Balog

et al. 2017

Microporous and Mesoporous Materials

129

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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

129

View full text Add to dashboard Cite

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“…Also, stiffness of the gels prepared by other precursors, for example polyethoxydisiloxane, can be increased by soaking in the polyethoxydisiloxane solution [Einarsrud 2001]. It was observed that such aging increases both cluster and particle dimensions.…”

Section: Aging Processmentioning

confidence: 99%

“…It was observed that such aging increases both cluster and particle dimensions. Low-density aerogels with a surface area of ~ 700 m 2 /g have been reported [Einarsrud 2001]. …”

Section: Aging Processmentioning

confidence: 99%

Synthesis of silica aerogels and their application as drug delivery system.

Смирнова

Arlt

2004

Supercritical Fluids as Solvents and Reaction Media

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“…Since the thermal conductivity of aerogels is related to their nanoporous structure, it may be possible to improve the thermal conductivity of these silicone aerogels by appropriate engineering of the material during sol-gel processing. For TEOS based aerogels extensive research [8][9][10][11][12][13][14] has been reported on the influence of sol-gel process parameters, such as the use of different precursors, catalysts for hydrolysis and condensation, the ratio of precursor to solvent, the ratio of precursor to water, catalyst concentration, aging time, solvents for gel surface modification and drying methods. However, for MTMS based silicone aerogels far less is known about how porous structures respond to solgel processing parameters.…”

Section: Introductionmentioning

confidence: 99%

Control of porous structure in flexible silicone aerogels produced from methyltrimethoxysilane (MTMS): the effect of precursor concentration in sol–gel solutions

Mao

Russell

2015

J Mater Sci

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This is a repository copy of Control of porous structure in flexible silicone aerogels produced from methyltrimethoxysilane (MTMS) ReuseUnless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. Control of porous structure in flexible silicone aerogels produced from methyltrimethoxysilane (MTMS): The effect of precursor concentration in solgel solutions Control of porous structure in flexible silicone aerogels produced from methyltrimethoxysilane (MTMS): The effect of precursor concentration in sol- AbstractControllable nanoporous structure in MTMS based silicone aerogels is required to improve their thermal conductivity. Silicone aerogels were formed in a two-step acid-base catalysed sol-gel process combined with supercritical drying. The influence of MTMS concentration, specifically the molar ratio of methanol:MTMS and water: MTMS in the sol-gel process was studied in relation to the porous structure of resultant silicone aerogels. Samples were characterised to determine the dimensions of micro, meso and macro-pore structure by means of both nitrogen gas adsorption-desorption for detection of pores less than 300 nm and by analysis of FEG-SEM images for pores greater than 300 nm. Porosity, pore volume distribution and BET surface area in the silicone aerogels were all found to be influenced by adjustment of the molar ratio of methanol:MTMS and the molar ratio of water:MTMS during sol-gel processing.

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Strengthening of silica gels and aerogels by washing and aging processes

Cited by 93 publications

References 15 publications

Effect of aging on silica aerogel properties

Effect of aging on silica aerogel properties

Synthesis of silica aerogels and their application as drug delivery system.

Control of porous structure in flexible silicone aerogels produced from methyltrimethoxysilane (MTMS): the effect of precursor concentration in sol–gel solutions

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