Carbon aerogels from dilute catalysis of resorcinol with formaldehyde

Aqueous polycondensation of resorcinol with formaldehyde leads to organic gels the structure of which can be controlled by the reaction parameters. The amount of catalyst controls the size of the particles constituting the gel network. We could show that for very low catalyst concentrations in a high dilution of reactants, the particle growth can be further enhanced if the reaction temperature is kept low, and the gel time is prolonged. The resultant structure is largely affected by this treatment, producing particles with sizes of about 2 mu m and average pore sizes of up to 7 mu m Due to these coarse structures it is possible to dry these RF gels subcritically with very little shrinkage. The structure has been studied by nitrogen sorption, small angle X-ray scattering and acoustic sound propagation. The change of the elastic modulus caused by pyrolysis at around 1000 degrees C has been investigated. Mechanical properties of carbon aerogels are correlated with their electrical properties. The derived carbon aerogels have large specific surface areas, very little mesopore volume however, micron-sized macropores. (C) 1997 Elsevier Science B.V.