Experimental Study Of Graphene Preparation From Ethylene By Arc Plasma Pyrolysis

Graphene has tremendous potential applications in many fields,such as electronic devices,mechanical apparatuses,biomedicine and materials science due to its high strength mechanical properties,high thermal and electrical conductivity,and optical and electromagnetic properties.It is considered to be a material that will revolutionize the future.The plasma gas-phase synthesis of graphene has the advantages of requiring no catalyst,no solvent and nosubstrate,occurring via one-step synthesis,and occurring as a continuous preparation;given these advantages,this method is expected to be the primary method used for the large-scale preparation of graphene.However,the intrinsic connection between the process conditions of graphene preparation and its formation mechanism is currently under-researched,leading to its limited controllability on a large scale.To address this issue,this paper firstly investigated the effects of arc current and ethylene flow on the product morphology and structure by using a magnetic rotating thermal plasma experimental device.The characteristics of the product were characterized by transmission electron microscopy,Raman spectroscopy,X-ray diffraction,etc.The results revealed that a higher temperature and a lower carbon concentration,are favorable for the production of graphene with fewer layers,fewer defects,and higher purity.A suitable H/C ratio and higher carbon concentration were the key factors for the formation of macromolecular carbonaceous clusters,which formed semi-graphite particles after gas-liquid-solid transformation.The overgrowth of graphene and the aggregation of small molecules of PAHs in the low temperature region are favorable for the formation of carbon nanospheres.Subsequently,the influence of oxidizing buffer gas CO2 and reducing buffer gas H2 on the morphology and structure of the product was studied.The results showed that a suitable flow of CO2 and H2 is beneficial to improve the purity of graphene and reduce the defects and the number of layers of graphene.The small flow rates of CO2 and H2 improved the product morphological structure less,and the large flow rates led to more carbon nanosphere particles in the products.The addition of CO2 and H2 inhibited the formation of semi-graphite particles.The addition of H2 to the buffer gas will improve the graphitization of the products,but CO2 has a negative effect on the formation of the product morphological structure.Finally,the effects of residence time on the morphological structure of the products and the growth evolution of graphene under different operating conditions were investigated.The results show that the long residence time of graphene in high temperature leads to curling and bending of graphene to form jellyfish-like graphene and carbon nanosphere particles,while the shorter residence time is favorable to the formation of graphene with low defects,few layers and high purity.The high temperature and low carbon concentration are favorable to make the reactor precursors tend to be a deviation from supersaturation status,which makes the nucleation decrease and keeps the planar growth.The formation of semi-graphite particles is later than that of graphene,and the macromolecular carbonaceous clusters need sufficient residence time to form,followed by the formation of semi-graphite particles.In this paper,the influence of operating conditions on the morphological structure of carbon nanomaterials is systematically investigated,and the formation mechanism of carbon nanomaterials prepared by gas-phase plasma method is analyzed and discussed,which provides a reference for the controllable preparation of carbon nanomaterials.