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, C 2 dimers, was studied. The concentration of C 2 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 C 2 H-involving reactions provide additional C 2 production, leading to the formation of supersaturated vapour from C 2 molecules at temperatures of 2500 to 3500 K.

On the transition of reaction pathway during microwave plasma gas‐phase synthesis of graphene nanosheets: From amorphous to highly crystalline structure

“…From the perspective of the precursor, atmospheric pressure MW plasma decomposition of ethanol (in the aerosol form [ 6 ] or vapourised [ 7,8 ] ) is a well‐established method for the synthesis of good‐quality GNS. In comparison to ethanol and its isomer dimethyl ether (DME), [ 9 ] attempts involving other organic sources (methanol, isopropyl alcohol, [ 9 ] methane, [ 10,11 ] acetylene, [ 12 ] propane–butane, [ 13,14 ] etc.) were not as satisfactory and often resulted in the synthesis of highly disordered structures, suggesting an insufficient understanding of underlying physical and chemical processes.…”

“…These observations were further used in the studies of physical and chemical processes, including chemical kinetics, of decomposition of precursors and consequent nucleation and growth of GNS. Besides the abovementioned model developed by Tsyganov [ 17 ] describing the synthesis in MW surface wave discharge, Shavelkina et al [ 14 ] developed a numerical model of propane–butane/helium plasma jet and showed that C 2 H provided additional C 2 production, leading to the formation of supersaturated vapour from C 2 molecules at temperatures of 2500–3500 K. Nucleation conditions and growth of GNS from Ar/CH 4 gas mixture were described by Meunier et al [ 25 ] in an inductively coupled plasma reactor at reduced pressure (55 kPa), including a study of carbon gas expansion. Their model showed that by varying the plasma expansion angle and methane flow rate, it should be possible to control the thickness and size of GNS.…”

Engineering of graphene flakes in the process of synthesis in DC plasma jets

“…The properties of graphene synthesised in the volume of a plasma flow are determined by its composition and, as shown by modelling the chemical kinetics of the conversion process of a propane–butane mixture in helium plasma, C 2 and C 2 H radicals participate in the nucleation and growth of graphene. 8 Thus, hydrogen has to be present in the graphene structure during the synthesis. The H concentration can be controlled by varying the synthesise parameters and cooling rate.…”

Growth Mechanism and Functional Properties of Gas-Phase Synthesized Few-Layer Graphene

“…However, this synthesis process is realized only at a high-enough temperature environment, above 4500 K, and some of the gas-products stay in the form of simple hydrocarbons (CH4, C2H2, C2H4 etc.) [3,4]. Depending on the plasma source and stability of the environment [5], the precursor can be partially decomposed by a so-called low temperature channel, where higher hydrocarbons and aromatic compounds containing large amounts of hydrogen are produced [6].…”