Effect of helium/propane–butane atmosphere on the synthesis of graphene in plasma jet system

Abstract

An experimental and theoretical study was performed on helium/propane–butane plasma, which enabled assembly of advanced carbon nanostructures, such as multilayer graphene flakes. A plasma jet was created at pressures ranging from 350 to 710 Torr, and with direct current plasma torch powers from 28 to 35 kW at varying mass ratios of helium to propane–butane 1:7.5 to 1:5. Graphene production was confirmed by different analytical techniques. The non-catalytic synthesis in the plasma jet volume provided the graphene purity. As a result of numerical simulation, the kinetic mechanism of the formation of carbon phase precursors in the gas phase, namely, C2 dimers, was studied. The concentration of C2 was determined, depending on the temperature and compared with the literature data on the pressure of saturated carbon vapours at temperatures ranging from 2500 to 5000 K. It is shown that the C2H-involving reactions provide additional C2 production, leading to the formation of supersaturated vapour from C2 molecules at temperatures of 2500 to 3500 K.