Structure of carbon aerogels near the gelation limit of the resorcinol-formaldehyde precursor

Resorcinol-formaldehyde (RF) gels with a very high molar ratio of resorcinol/catalyst (R/C), e.g., 1500 and a low relative molar mass content of resorcinol + formaldehyde (RF-ratio) of about 30% can be ambient pressure dried with minimal shrinkage. The resulting RF-aerogels exhibit average cluster and pore sizes > 50 nm. Upon pyrolysis the RF-aerogels are transformed into carbon aerogels exhibiting the same morphology of the gel network but in addition showing a high amount of microporosity (< 2 nm). Below an RF-ratio of thirty mass percent the average particle and pore size increase to several hundred nanometers. The macro- and microscopic properties of these aerogels were investigated by scanning electron microscopy, permeability measurements, small angle X-ray scattering and CO, sorption. (C) 1998 Elsevier Science B.V. All rights reserved.