| Metal material,as one kind of the most commonly used material,plays a pivotal role in infrastructure,transportation,and aerospace industry in daily life.But the corrosion behaviors of active metals are widespread,and seriously affect the service lives of metals,which will bring huge losses to the development of national economic and industrial,and may even endanger human life.Therefore,the problem of corrosion behaviors of active metals has become a major issue to be solved urgently.Traditional anti-corrosion coatings can't meet the demands because of their poor temperature resistance and other shortcomings.Sometimes traditional anti-corrosion coatings may even change the physical and chemical properties of materials.So it has become an inexorable trend to develop an ultra-thin anti-corrosion coating which does not affect the properties of substrates.Graphene,which is a two-dimensional material consisting of monolayer or multilayer of carbon atoms,is the thinnest of any known material.The unique hexagonal honeycomb structure makes graphene have many excellent properties,such as high thermal and chemical stability,low permeability and good mechanical strength.So graphene have the potential to be a new ultra-thin anti-corrosion material and replace traditional anti-corrosion coatings.CVD graphene films can protect metal substrates from corrosion to a certain extent.However,the structural defects such as holes and grain boundaries are inevitable in CVD graphene,which will damage the protective effect of graphene.So passivation of the defects of graphene can enhance the corrosion resistance of metals so as to make graphene protect metals completely.In this paper,graphene was prepared by the method of atmospheric pressure chemical vapor deposition(APCVD)on Cu foil.Optical microscopy(OM),scanning electron microscopy(SEM),high resolution transmission electron microscopy(HRTEM),Raman spectroscopy(Raman)and UV-visible absorption spectroscopy(UV-vis)were used to characterize the morphologies and structures of graphene.The effect of growth time and flow rates of CH4 on the growth of graphene was studied in order to find the optimum conditions of graphene.The results indicate that graphene becomes continuous gradually and the number of layers of graphene increases with the growth time,and when the growth time is extended to 15 min,the number of layers of graphene is of three.With the extension of the growth time,the number of layers will not increase,performing self-limiting growth behavior.It's difficult to generate graphene when the flow rate of CH4 is low.When the flow rate of CH4 is 2 sccm,graphene begins to grow.Gradually increasing the flow rate of CH4,graphene becomes continuous and the number of layers of graphene increase.When the flow rate is 10 sccm,continuous graphene is prepared,and the number of layers is of three.Further increasing the flow rate of CH4,graphene nucleation density increases,and the continuity of graphene gets worse.The corrosion resistance of graphene and its mechanism were studied by electrochemical tests in 0.1 M NaCl.The results demonstrate that although monolayer graphene can not protect the Cu substrate from corrosion due to its defects and discontinuity,multilayer graphene can protect Cu foil substrate from corrosion.Among them,graphene with growth time of 15 min performs the best corrosion resistance because of its low defect density and continuity,and the corrosion resistance increase by about 10 times comparing with pure Cu foil.We further studied the effect of Al2O3 grown by atomic layer deposition(ALD)on the corrosion resistance of graphene films.After passivation of defects,the corrosion resistance of graphene has been obviously improved.After passivation,the corrosion current densities of monolayer,bilayer and three layers graphene lower by 80%,88%,56% respectively,and the values of Rf + Rc increase by 67.6,34.3,6.1 times respectively.So the passivation of defects can make graphene protect metals completely. |
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