Polymerisation et croissance des particules de carbone produites par une decharge electrique

Abstract

The polymerisation and the growth of carbon particles have been reinvestigated. Hydrocarbon molecules have first been dissociated by heating the gas by a condensed electrical discharge. The absorption spectrum of the decaying plasma has then been measured using time resolving technique. These spectra show the same main features as those found using flash photolysis technique. However, the apparent lifetime of the C 2 molecules in its lower state is found to be much shorter. The broad absorption feature having its maximum at about 3900 Å has also a much shorter lifetime. It is suggested that it might be due not to a molecular electron transition but to the scattering of light by non-absorbing spheres. The data available for the Mie extinction coefficients allow to check this tentative interpretation. These experiments seem to agree with the recent results obtained using the classical pyrolysis technique for heating hydrocarbon molecules, which reveals also the existence of two successive processes in the formation and the growth of carbon particles. In our case, we would first have formation of C 2, C 3, etc....molecules growing rapidly to become small carbon “nuclei”. This rapid process is followed by a very different one in which the growth into larger carbon particles proceeds through the direct catalytic dissociation of the hydrocarbon molecules on the carbon particle surface.