Aerogel porosity

Isobutene and tran -2-butene were the main reaction products. Neither C3-C5 nor C2-C6 by-products were observed among the reaction products, as in the case of smaU-pore zeolites, suggesting that the reaction followed a monomolecular mechanism and that there was no dimerization, probably due to an effect of the carbon aerogel porosity. 

Figure 10.11 Equilibrium DCE sorption at room temperature by 6 aerogel (porosity [P] equal to 90%, filled circles), 5 powder (empty circles), and y aerogels (porosity [P] equal to 90%, triangles) as determined by FTIR measurements. For the sake of comparison DCE sorption from activated carbon is also reported (thin line data from M. H Stanzel [182]). (Reproduced with permission from Daniel, C, Sannino, D., Guerra, G. Syndiotactic polystyrene aerogels Adsorption in amorphous pores and adsorption in crystalline nanocavities. Chem. Mater., 20,577-582 (2008) [170]).

Thus, the porosity of an aerogel is ia excess of 90% and can be as high as 99.9%. As a consequence of such a high porosity, aerogels have large internal surface area and pore volume. 

Two more recent appHcations for amorphous siHcas are expected to grow to large volumes. Precipitated siHcas are used ia the manufacture of separator sheets placed between cells ia automotive batteries. Their function is to provide a controlled path for the migration of conductive ions as a result of the porosity of the siHca particles. Additionally, both precipitated siHcas and aerogels are being developed for use ia low temperature iasulation, where the low thermal conductivity of the dry siHca powders makes them useful ia consumer products such as refrigerators (83). 

M. Mirzaeian and P.J. Hall, Preparation of controlled porosity carbon aerogels for energy storage in rechargeable lithium oxygen batteries, Electrochim. Acta, 54(28) 7444-7451, December 2009. 

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