Control of mesoporosity of carbon gels prepared by sol–gel polycondensation and freeze drying

Yamamoto, Takuji; Nishimura, Takehiro; Suzuki, Tetsuo; Tamon, Hajime

doi:10.1016/s0022-3093(01)00619-6

Cited by 154 publications

(88 citation statements)

References 12 publications

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“…[4] Moreover, the peak radius of the PSD increases when increasing the R/C ratio or decreasing the C/W ratio. [34] A monodispersed pore structure is obtained with either very low R/C or very high R/W ratios, whereas an increase in the R/C ratio or a decrease in the R/W ratio produces polydispersed pore structures. [4] Moreover, the size of the gel particles can be promoted to the micrometer scale when using high R/C ratios, low concentrations of reactants (low R/W ratio), or, equivalently, low C/W ratio as shown in Figure 2, [34] and low gelation temperatures, which necessarily increases the time for gelation.…”

Section: Materials and Initial Solution Recipesmentioning

confidence: 99%

“…After the completion of this step, the colloidal particles begin to aggregate and assemble into a stiff, interconnected structure locally resembling a string of pearls that fills the original volume of the aqueous solution. [46] To prepare for gelation (polymerization), typically R and F are mixed with the polymerization C and the solvent (see the previous section for guidelines on the appropriate proportions), and stirred for a short period (between 5 [34] and 30 min [37] ) to form a homogeneous mixture that is commonly called the sol. The addition of any additives to the gels, such as carbon cloths for reinforcing the final gels, [30] is usually done during this initial stage.…”

Section: Gelation and Curingmentioning

confidence: 99%

“…[31] Rinsing the aquagel twice with tert-butanol, for example, is sufficient for exchanging the aqueous solution. [32] Moreover, the density change of the cryogels freeze-dried with tert-butanol is much smaller than that with water, [34] and it causes the formation of more mesopores. [32] The reactant concentrations and time of curing also have significant effects on the micro-and mesoporosities of the cryogels.…”

Section: Freeze-dryingmentioning

confidence: 99%

“…These carbonized RF structures are often called carbon gels. Pyrolysis of RF gels is most commonly carried out in a tube furnace under a constant, moderate (~200 cm 3 min ±1 ) flow of inert gas, such as N 2 , argon or He at room temperature for~one hour (to replace all the air in the furnace), [34] and eventually at a fixed temperature ranging from 600 to 2100 C. [11] The desired pyrolysis temperature is generally approached gradually using temperature programming. Interestingly, the electrical conductivity of the sample increases significantly during this transformation, as indicated by the common appearance of a broadband, semi-metal-like infrared absorbance.…”

Section: Pyrolysis (Carbonization)mentioning

confidence: 99%

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Preparation and Properties of Resorcinol–Formaldehyde Organic and Carbon Gels

Al‐Muhtaseb¹,

Ritter²

2003

Advanced Materials

983

795

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A brief overview on the preparation and properties of resorcinol–formaldehyde organic and carbon gels reveals very interesting features about their structural and performance characteristics. The resulting nanostructure was very sensitive to the various synthesis and processing conditions. This leads to a remarkable potential for designing and tailoring these materials to fit specific applications. Based on step‐by‐step comparisons of the published studies, approximate generalizations on the specific roles the synthesis and processing conditions play on the final properties are provided. Overall, resorcinol–formaldehyde organic gels undergo two main stages during synthesis. The first stage is associated with the preparation of the sol mixture, and the subsequent gelation and curing of the gel. The second stage is associated with the drying of the wet gel. The most important factors that affect the properties of the organic gel during the first stage are the catalyst concentration, the initial gel pH, and the concentration of the solids in the sol. The most important factors that affect the properties of the organic gel during the second stage are the drying procedure (e.g., super‐ or subcritical drying), and the difference between the surface tensions of the solvent before and after drying. The corresponding resorcinol–formaldehyde carbon gels are produced from the organic gels during a third stage, which is associated with carbonization or activation. Depending on the conditions, carbonization and activation both impact the structural and performance characteristics significantly.

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Section: Materials and Initial Solution Recipesmentioning

confidence: 99%

Section: Gelation and Curingmentioning

confidence: 99%

Section: Freeze-dryingmentioning

confidence: 99%

Section: Pyrolysis (Carbonization)mentioning

confidence: 99%

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Preparation and Properties of Resorcinol–Formaldehyde Organic and Carbon Gels

Al‐Muhtaseb¹,

Ritter²

2003

Advanced Materials

983

795

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“…Many researchers, however, discuss the structuring of RF gels in terms of the same colloid aggregation mechanism as in inorganic sol-gel (e.g. Yamamoto et al, 2001). It has recently been shown that in situ small-angle X-ray scattering (SAXS) does not enable discrimination between the two mechanisms (Gommes & Roberts, 2008).…”

Section: Introductionmentioning

confidence: 99%

Critical opalescence points to thermodynamic instability: relevance to small-angle X-ray scattering of resorcinol–formaldehyde gel formation at low pH

et al. 2008

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Author(s) of this paper may load this reprint on their own web site or institutional repository provided that this cover page is retained. Republication of this article or its storage in electronic databases other than as specified above is not permitted without prior permission in writing from the IUCr.For further information see http://journals.iucr.org/services/authorrights.html Many research topics in condensed matter research, materials science and the life sciences make use of crystallographic methods to study crystalline and non-crystalline matter with neutrons, X-rays and electrons. Articles published in the Journal of Applied Crystallography focus on these methods and their use in identifying structural and diffusioncontrolled phase transformations, structure-property relationships, structural changes of defects, interfaces and surfaces, etc. Developments of instrumentation and crystallographic apparatus, theory and interpretation, numerical analysis and other related subjects are also covered. The journal is the primary place where crystallographic computer program information is published.Crystallography Journals Online is available from journals.iucr.org J. Appl. Cryst. (2008 During the formation at low pH of resorcinol-formaldehyde gels with a structure in the micrometre range, small-angle X-ray scattering exhibits a nonmonotonic intensity variation as a function of reaction time. The data are analyzed in terms of scattering by statistical fluctuations of polymer concentration, the amplitude of which is maximal close to the critical point for phase separation between polymer and solvent. The data do not carry any morphological information, but they unambiguously show that the driving force of the gel formation is a thermodynamic instability of the polymerizing solution.

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