KINETICS OF PYROLYTIC CARBON INFILTRATION FORTHE PREPARATION OF CERAMIC/CARBON ANDCARBON/CARBON COMPOSITES

摘要

Carbon/carbon and zeolite/carbon composites have been prepared by pyrolytic carbon infiltration of organic and inorganicsubstrates with different porous structures. The chemical vapour infiltration kinetics of these substrates has been studied in aTGA system and in a fixed bed reactor at atmospheric pressure, using benzene as pyrolytic carbon precursor. The initial rate ofpyrolytic carbon infiltration depends on the surface area of the substrate available to the pyrolytic carbon precursor, irrespectiveof the nature of the substrate studied. At the steady state the decomposition reaction seems to be influenced by the structure of thepyrolytic carbon deposited in the previous step. Activation energy values of about 180 kJ/mol were found for the differentsubstrates used in the temperature range of 973-1073 K, where the cracking reaction of benzene takes place, predominantly, in aheterogeneous form. At higher temperatures homogeneous reactions compete with heterogeneous ones and higher values ofactivation energies (280-380 kJ/mol) were obtained.