THE INFILTRATION OF CARBON-FIBER FELTS AND COMPOSITES BY PYROLYTIC CARBON DEPOSITION FROM PROPYLENE

A flow system has been developed to simultaneously obtain data to determine kinetic parameters for the conversion of propylene and the resulting deposition of carbon on carbon fiber substrates. A kinetic scheme is proposed which involves homogeneous initiation of a carbon precursor by a first order reaction of propylene, growth of the precursor by a radical propagation reaction, and ultimately deposition of the precursor on the substrate. The model developed permits the prediction of initial carbon deposition rates based solely on operating conditions. The kinetic parameters determined include an activation energy of approximately 87 kcal/mole for carbon deposition in open structured, carbonized rayon and polyacrylonitrile felts, and a lower activation energy of 68 kcal/mole for a less porous composite substrate which may indicate significant diffusional limitations. The rate of carbon deposition in all cases investigated was found to increase with temperature, residence time, and propylene feed concentration. Also, propylene was found to be converted with an overall order of 1.45, an activation energy of 52.6 kcal/mole, and a preexponential factor of 1012.8 ml.45/mole.45/s for propylene feeds of 5 to 15%. © 1990.