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.