TEM studies of carbon nanofibres formed on Ni catalyst by polyethylene pyrolysis

Carbon nanofibres (CNF) have been formed by polyethylene pyrolysis, using a Ni catalyst and a hydrogen - argon gaseous mixture. The temperature interval of 500 - 700 degrees C was chosen, because small sized Ni catalyst particles are formed in this case. TEM and high resolution TEM studies revealed catalyst particles of spherical, oval, conical and faceted shapes, some of which have been twinned. The variety of shapes and sizes can be explained by the different values of the surface tension forces in the catalyst and in graphite in the various cases. Unusual 'burst' CNFs, distinguished by the alternation of dense and sparse regions, have been found in the deposit. A model of a periodic process, based on the decay of Ni carbide, is assumed for the explanation of the 'burst' CNF formation.