Evolution of size distribution and morphology of carbon nanoparticles during ethylene pyrolysis

The effects of furnace temperature and residence time on particle size distributions (PSDs) of carbon black, which is a type of carbon nanoparticle, were studied with a scanning mobility particle sizer. Particles were classified according to their mobility diameters by a differential mobility analyzer, followed by thermophoretic sampling by scanning electron microscopy to investigate their carbon black morphologies. PSDs were power-law distributions at short residence times and log-normal distributions at long residence times; these distributions indicate that agglomeration increases with increasing residence time. In addition, few 2.5-nm-sized particles existed above 1540 ± 40 K, while the critical size was 3 nm at 1350 ± 40 K. This finding indicates that the critical size of nuclei changes with temperature. At high temperatures of 1776 and 1676 K, the 100 and 180-nm-sized particles, whose primary particles kept their shape, had very complex morphologies. In contrast, at low temperature at 1570 K, the morphologies of 100 and 180-nm-sized aggregates are relativity simple, and primary particles nearly fused together in those aggregates. These observations indicate that the nucleation rate and fusing behavior change with temperature.