Selective preparation of polyhedral graphite particles and multi-wall carbon nanotubes by a transferred arc under atmospheric pressure

High-purity polyhedral graphite particles (PGPs) and multi-wall carbon nanotubes (MWNTs) were selectively synthesized by a transferred arc discharge method under atmospheric pressure. PGPs and MWNTs were characterized by the field emission scanning electron microscope (FE-SEM), transition electron microscopy (TEM), and Raman spectroscopy. The products were successfully controlled by varying the arc current and the anode diameter. PGPs were the main products in the case of a relatively high arc current of 100 A or a large anode diameter of 30 mm, while MWNTs were the main products when the arc current was reduced to 80 A or the anode diameter was decreased to 15 and 10 mm. The ratio of carbon ions to carbon radicals near the cathode tip was employed to explain the mechanisms of PGP and MWNT formation. Relatively high ratio of carbon ions to carbon radicals contributed to the formation of PGPs. In contrast, relatively low ratio of carbon ions to carbon radicals led to the formation of MWNTs.