Xerogel carbon

Studies of capacitance of negatively charged electrodes based on AC and aero/cryo/xerogel carbon in two ILs with the same anion and other cations with an almost similar size, that is, l-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide (EMITFSI) and Af-butyl-A-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) ILs were made (Fig. 27.10). 

Lazzari, M., F. Soavi, and M. Mastragostino. 2008. High voltage, asymmetric EDLCs based on xerogel carbon and hydrophobic IL electrolytes. Journal of Power Sources 178 490-496. 

Lin C, Ritter JA (2000) Carbonization and activation of solgel derived carbon xerogels. Carbon 38 849-861. 

Leonard, A., Job, N., Blacher, S., Pirard, J.-P., Crine, M., Jomaa, W., 2005a. Suitability of convective air drying for the production of resorcinol-formaldehyde and carbon xerogels. Carbon 43 1808-1811. 

Figure 2. SEM images of the Pd/C catalysts obtained on xerogel carbon supports with variable degrees of functionalization.

For other adsorptives the experimental evidence, though less plentiful than with nitrogen, supports the view that at a given temperature the lower closure point is never situated below a critical relative pressure which is characteristic of the adsorptive. Thus, for benzene at 298 K Dubinin noted a value of 017 on active carbons, and on active charcoals Everett and Whitton found 0-19 other values, at 298 K, are 0-20 on alumina xerogel, 0-20-0-22 on titania xerogel and 017-0-20 on ammonium silicomolybdate. Carbon tetrachloride at 298 K gives indication of a minimum closure point at 0-20-0-25 on a number of solids including... 

Presently, the most successful adsorbents arc microporous carbons, but there is considerable interest in other possible adsorbents, mainly porous polymers, silica based xerogels or zeolite type materials. Regardless of the type of material, the above principles still apply to achieving a satisfactory storage capacity. The limiting storage uptake will be directly proportional to the accessible micropore volume per volume of storage capacity. 

Mcntasty el al. [35] and others [13, 36] have measured methane uptakes on zeolites. These materials, such as the 4A, 5A and 13X zeolites, have methane uptakes which are lower than would be predicted using the above relationship. This suggests that either the zeolite cavity is more attractive to 77 K nitrogen than a carbon pore, or methane at 298 K, 3.4 MPa, is attracted more to a carbon pore than a zeolite. The latter proposition is supported by the modeling of Cracknel et al. [37, 38], who show that methane densities in silica cavities will be lower than for the equivalent size parallel slit shaped pore of their model carbon. Results reported by Ventura [39] for silica xerogels lead to a similar conclusion. Thus, porous silica adsorbents with equivalent nitrogen derived micropore volumes to carbons adsorb and deliver less methane. For delivery of 150 V./V a silica based adsorbent would requne a micropore volume in excess of 0.70 ml per ml of packed vessel volume. 

Pekala R.W., Alviso C.T. Carbon aerogels and xerogels. Mater Res Soc Symp Proc 1992 270-3. 

Microporosity is a feature observed in many different materials (e g., activated carbons, aerogels, and xerogels). However, with regard to heterogeneous catalysis, zeolites are practically the only microporous catalysts used at present. The following chapter thus only addresses zeolites and their use in catalysis. 

There is a variety of miscellaneous fillers that are of interest for reinforcing elastomers such as PDMS. Examples are ground-up silica xerogels,119 carbon-coated silica,120 and functionalized silica particles.121-123... 

More recently, models were developed to achieve the elimination of the template under milder conditions. The first relies on the preparation of a dialkyl carbonate system by polycondensation/hydrolysis of the corresponding precursor family 26. Thermal treatment of a non-porous xerogel of 26 at 250-350 °C results in the simultaneous elimination of CO2 and hybrid materials with residual hydroxyalkyl and olefinic functions according to Scheme 18. It is interesting to note that this approach also allows the preparation of materials which cannot be prepared by other routes, such as direct polycondensation of the corresponding allyl and hydroxyalkyl precursors. 

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