A sector deposition mechanism of carbon onions operated in a large discharge furnace

Abstract

Due to the lack of comprehensive understanding of the formation mechanism, the preparation of carbon onions by arc discharge is still an uncontrollable process, which restrains their massive and stable production. Taking advantage of the transient nature of the arc discharge, we successfully captured the nanoparticle morphology in each growing stage during the carbon onion formation process in a large discharge furnace with chamber radius of 22.5 cm. Scanning electron microscope images of raw soot show that massive spherical aggregations are enriched in nanoparticles, and high-resolution transmission electron microscope images reveal fairly heterogeneous nanoparticles which are corresponding to varying growing stages of carbon onions. It is proposed that the change from the well-ordered graphite to another ordered polyhedral and nickel-encapsulated carbon onions is via a non-crystalline intermediate state, and carbon onions begin to deposit through a novel sector mechanism, i.e. the inner and outer carbon shells are simultaneously precipitated and grow away from or along the catalyst surface to form a polyhedral or metal encapsulated carbon onion, respectively.