Planar fibre reinforced carbon aerogels for application in PEM fuel cells

Preparation and Properties of Resorcinol–Formaldehyde Organic and Carbon Gels

“…[10] Nevertheless, using excess F results in a dilution effect, which increases the particle size near the gelation limit. [33] Another major factor that can result in this dilution effect is the reduction of the density of the reactants by increasing the amount of solvent. The solvent can be either distilled (and preferably, deionized) water (W) or an organic solvent (e.g., acetone, methanol, ethanol, n-propanol, or isopropanol).…”

“…Overall, the density of the reactants in the initial solution has a considerable effect on the final density of the RF gel. [33] 102 Ploehn. His major research interests include the design of nanostructured materials for separation and energy transport and storage applications, characterization of nanostructured materials, adsorption processes and vapor-adsorbed phase equilibria, extraction processes and liquid±liq-uid equilibria, absorption processes and vapor±liquid equilibria, equations of state and adsorption isotherm models, and prediction of derived thermodynamic properties for multiphase systems.…”

“…[45] In contrast, high R/C ratios results in large polymer particles (16 to 200 nm in diameter) that are connected by narrow necks in a ªstring-of-pearlsº fashion. [22,23,33,38,47] These two types of gels are commonly described as ªpolymericº and ªcolloidalº RF gels, respectively. [47] Overall, the polymeric RF carbon aerogels have a small particle size, high surface area, high compressive modulus (high mechanical strength), and exhibit substantial shrinkage during supercritical drying, [47] whereas the opposite behavior and characteristics are exhibited by the colloidal RF carbon aerogels.…”

“…This deposition dilutes the solution and results in an effect similar to the one discussed previously. [33] It is also recommended (but not necessary) to prepare the sol mixture in an inert atmosphere (e.g., in a glove box with a N 2 atmosphere) to avoid the possibility of contaminating the gel with components in air such as CO 2 , which may change the pH of the solution. Finally, the containers (molds) containing the reaction products are sealed before being removed from the environmentally controlled chamber, or before being heated, to minimize solvent evaporation.…”

“…The main factors dictating these effects are associated with the hydrophobicity of the solid surface and the comparative ratio of the mean distance between two adjacent surfaces (i.e., volume/ surface ratio) to the characteristic catalytic penetration depth (~1 to 50 lm). [33] In some cases, skin portions of the gel can form around the hydrophilic surfaces (e.g., glass). [33] A general presentation of these effects of the solid surface and surface dimensions is shown in Figure 5.…”