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 350–710 Torr, and with direct current plasma torch powers from 28–35 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 2500-5000 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 2500-3500 K.

中文翻译：

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氦气/丙烷-丁烷气氛对等离子体射流系统中石墨烯合成的影响

对氦/丙烷-丁烷等离子体进行了实验和理论研究，该等离子体能够组装先进的碳纳米结构，例如多层石墨烯薄片。在 350-710 Torr 的压力下产生等离子射流，直流等离子炬功率为 28-35 kW，氦与丙烷-丁烷的质量比为 1:7.5 到 1:5。通过不同的分析技术证实了石墨烯的产生。等离子体射流体积中的非催化合成提供了石墨烯纯度。作为数值模拟的结果，研究了在气相中形成碳相前驱体，即C2二聚体的动力学机制。测定 C2 的浓度，