The morphological transformation of carbon materials from nanospheres to graphene nanoflakes by thermal plasma

Abstract

Carbon materials are synthesized by the thermal decomposition of acetylene using a magnetically rotating arc under atmospheric pressure. The effects of hydrogen addition, gas injection position, acetylene concentration, and reaction temperature on the morphology of pyrolysis products are evaluated. Carbon spherical particles and graphene nanoflakes are also obtained. Results indicate that a large amount of hydrogen, a low carbon flow, and high temperatures can promote the morphological transformation of carbon materials from nanospheres to graphene nanoflakes. Combined with a gas–phase kinetic model and a simulation of computational fluid dynamics, the reaction zone with a critical temperature of 2500 K can be divided basically into nucleation and surface growth, which correspond to the temperature–rise zone and high–temperature maintenance zone, respectively. Essential factors affecting graphene formation may include the formation of sheet–like nuclei and continuous planar growth at the side active sites of the structure. A low collision frequency of precursors and the high temperatures favor the formation of sheets–like nuclei. Planar surface growth requires hydrogen to terminate dangling bonds at edges and a high temperature to induce growth without a curvature.