Acetic-acid-catalyzed and subcritically dried carbon aerogels with a nanometer-sized structure and a wide density range

Brandt, R.; Fricke, J.

doi:10.1016/j.jnoncrysol.2004.06.039

Cited by 44 publications

(26 citation statements)

References 20 publications

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“…The RF gels studied here exhibit a high degree of crosslinking within their structures, which has been shown to reduce the degree of diffusion in polyethylene materials [36]; hence, similar behaviour would be expected here and compounds the expected low diffusivity for a polar organic material and a non-polar gas, such as nitrogen. The use of alternative techniques to estimate surface area have shown widely different correlations when compared with BET surface area [33,35,37,38], suggesting that there are limitations in any selected technique, whereas other authors have also highlighted the potential of microporous materials including carbonaceous samples, to undergo deformation during the adsorption of probe gases including nitrogen [39]. It may therefore be argued that as the adsorption methods adopted here use a final pressure close to the saturated vapour pressure of nitrogen at 77 K, all porous voids are filled within the process, and that the absorption character of the materials studied here can be quantified by the microporous character observed within the material.…”

Section: Resultsmentioning

confidence: 99%

The impact of deuterium oxide on the properties of resorcinol-formaldehyde gels

Prostredny

Ballantine

Šefčı́k

et al. 2018

J Sol-Gel Sci Technol

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Resorcinol-formaldehyde gels offer a range of properties that can be exploited in a variety of applications, but better understanding of gel formation mechanisms is needed to enable rational control and optimisation of the physico-chemical characteristics of these materials. Our previous studies have focussed on investigating the formation pathways of these gels, using nuclear magnetic resonance and dynamic light-scattering techniques, as well as evaluating their final physical and chemical properties, via sorption and spectroscopic methods. Nuclear magnetic resonance has been used over the years to probe the chemical species formed during resorcinol-formaldehyde gel polymerisation, but the technique typically involves the prior addition of deuterium oxide to provide a deuterium lock for NMR measurements. However, the effect of deuterium oxide to resorcinol-formaldehyde systems is currently unknown, although the substitution of water by deuterium oxide has been previously reported to alter the chemical and physical properties of reacting systems. In this work we examine the effect of adding deuterium oxide to resorcinol-formaldehyde sol-gel synthesis at different dilution levels and the impact that this addition has on the final characteristics of the synthesised gels, in order to assess the validity of using NMR with a deuterium lock for the investigation of polymerisation mechanism in resorcinol-formaldehyde sol-gel processes. • High catalyst concentration systems less affected due to shorter gelation times• Low catalyst concentration systems more greatly affected due to weaker structure•

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Section: Resultsmentioning

confidence: 99%

The impact of deuterium oxide on the properties of resorcinol-formaldehyde gels

Prostredny

Ballantine

Šefčı́k

et al. 2018

J Sol-Gel Sci Technol

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“…In principle, highly porous carbon xerogels like the system investigated offer themselves for many applications, however, the sodium impurity detected confines the underlying system to applications, where a higher ash content is uncritical. If highly pure carbons are required, other base systems using catalysts without metal cations are to be preferred [14,19,38,39].…”

Section: Discussionmentioning

confidence: 99%

Porous organic and carbon xerogels derived from alkaline aqueous phenol–formaldehyde solutions

2011

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Porous carbons were synthesized from the low cost precursors phenol and formaldehyde in aqueous solution, catalysed with NaOH. The xerogels were ambient pressure dried without prior solvent exchange. For an excess of formaldehyde, the resulting carbon xerogels show porosities up to 90%, with a predominant fraction of macroporosity, specific surface areas up to 768 m 2 /g and mesopore volumes up to 0.59 cm 3 /g. Small-angle X-ray scattering reveals fractal behaviour for many samples. Relevant sodium impurities up to 3-4 wt% in the organic and carbon samples cannot be avoided, even by washing of the samples. As possible reason for the high sodium content, the formation of crown ether like calix [6] arene is assumed. Overall, the sodium impurities detected confine the use of this system to applications, where higher ash contents are uncritical.

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“…The densities of these carbon materials are significantly different from 'heavy carbons' such as pristine graphite (2.26 g·cm −3 ), DVD grown carbon films (2.14 g·cm −3 [58]), or carbon nanotube forests (1.6 to 0.38 g·cm −3 [59]). Some techniques allow the production of carbons in a wide density range (0.20 to 1.4 g·cm −3 [60]). 1a shows a He-ion microscopy image of a foam sample with a 2 mm field of view.…”

Section: Densitymentioning

confidence: 99%