In situ infrared observation of the pyrolysis process of carbon aerogels

Carbon aerogels are generated by a pyrolytic transformation of organic recorcinol formaldehyde aerogels in an inert atmosphere at temperatures above 600 degrees C. Transmittance and emissivity in the infrared were measured between 1.4 and 18.0 pm using a Bruker IFS 66v spectrometer with an attached heatable transmittance/emissivity module which can be evacuated. This allows detailed analysis of chemical and physical changes during pyrolysis. In combination with TGA and DSC measurements, various steps of the transformation process can be identified: the emission of traces of solvent and of adsorbed water as well as the release of OH- and organic groups during the pyrolysis. During this transformation, electrical conductivity increases which causes the appearance of a broadband semi-metal-like absorbance in the infrared. Also the angular dependence of the infrared emissivity changes drastically upon pyrolysis. The results indicate a transformation of the organic network into a partially carbonised structure with embedded graphitic areas. (C) 1998 Elsevier Science B.V. All rights reserved.