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 temperatur es above 600 degrees C. Transmittance and emissivity in the infrared w ere measured between 1.4 and 18.0 pm using a Bruker IFS 66v spectromet er 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 e mission of traces of solvent and of adsorbed water as well as the rele ase of OH- and organic groups during the pyrolysis. During this transf ormation, electrical conductivity increases which causes the appearanc e 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 netwo rk into a partially carbonised structure with embedded graphitic areas . (C) 1998 Elsevier Science B.V. All rights reserved.