SYNTHESIS AND CHARACTERIZATION OF PHENOLIC-FURFURAL BASED CARBON AEROGELS

Alcogels were formed by solutionsolgel polymerization of phenolic novolac and furfural in 1propanol. The alcogels, after drying in supercritical petroleum ether at 250?℃ and 7?MPa for one hour, were pyrolyzed to yield carbon aerogels at 850?℃ for three hours under a nitrogen atmosphere. The effect of ratios of phenolic to furfural on volume shrinkage of the gels during the drying and pyrolyzing process, and on micro, meso and macropore volume and morphologies of carbon aerogels was investigated. It is found that, with increasing ratios of phenolic to furfural under otherwise identical condition, volume shrinkage of gels in the drying process increases whereas volume shrinkage of organic aerogels in the pyrolysis process decreases. Although the overall volume shrinkage is the sum of the two, the overall volume shrinkage increases with increasing ratio, indicating that the total volume shrinkage is governed by the drying process. The macropore volume decreases with the ratio much more than the meso-pore and micropore volumes, while the latter two volumes simultaneously decrease and then increase with increasing ratio. The porosity of carbon aerogels, when the concentration of reactants is defined, is determined by the volume shrinkage of gels in the drying and pyrolysis steps, and this is dependent on the cross-linking density of the polymers that form the alcogels. The domain sizes of a carbon aerogel formed at low ratio are smaller than that at high ratio where sintering is apparently occurring.