Preparation And Performance Of Ni-rGO Superhydrophobic Composite Coating By Electrodeposition

At the late stage of oilfield development,with the application of CO2 flooding and water flooding,the corrosion problem of downhole tubing is serious,especially the loss caused by CO2 corrosion.Superhydrophobic surfaces have broad application prospects in the fields of corrosion protection,antifouling and frosting,and oil-water separation.One of the most critical problems of all superhydrophobic surfaces is their long-term stability to wear,corrosion and erosion during service.Graphene has excellent mechanical properties and chemical stability.By composite electrodeposition with the addition of graphene oxide in the bath,graphene is used as reinforcing phase to improve the hardness and long-term durability of coatings,in the meantime,the hydrophobicity of coatings can be maintained,which is of great significance in the widespread industry application of superhydrophobic surfacesThe composition of bath and the process parameters were adjusted to prepare the nickel superhydrophobic coatings.The optimized plating bath consisted of 250 g·L^-1 Ni Cl2·6H2O,30g·L^-1 boric acid,150 g·L^-1 ammonium chloride and 0.15 g·L^-1 sodium dodecyl sulfate.The electrodeposition process was carried out in two steps with stirring,firstly the current density of 7 A·dm^-2 was applied for 20 min and then the current density of 15 A·dm^-2 was applied for5 min.Finally,the coating was modified in molten myristic acid for 2 hours.The prepared nickel superhydrophobic coating has a flower-like rough morphology with a water contact angle of 158.87°.The graphene oxide was prepared by the improved Hummers method.The plating bath added with the graphene oxide was dispersed by ultrasonic for one hour before electrodeposition.The nickel-reduced graphene oxide superhydrophobic coating was prepared under the same process parameters.Compared with graphene oxide,the intensity of D and G peaks in Raman spectrum of the composite coating are reversed,and the corresponding characteristic peaks of the oxygen-containing functional groups in the FT-IR spectrum are obviously weakened.The presence of reduced graphene oxide in the coating was determined by scanning electron microscopy and energy dispersive spectroscopy,indicating that the graphene oxide was reduced into the coating at the cathode during the electrodeposition process.With the increase of the concentration of graphene oxide in bath,the hydrophobicity,microhardness and corrosion resistance of coatings layer are improved to some extent.When the concentration of graphene oxide is 0.6 g·L^-1,the prepared Ni-r GO superhydrophobic composite coating has a pinecone-like multi-scale hierarchical structure with the water contact angle of up to 162.87°and microhardness of 537.86 HV0.2.The corrosion current density and charge transfer resistance of the coating are 5.47?10^-9 A·cm^-2 and 1.35?10⁶Ω·cm² respectively.However,with further increase of the graphene oxide concentration in plating bath,the performance of coating is decreased.The Ni-rGO superhydrophobic composite coatings possess low adhesiveness and good self-cleaning performance,and have good durability not only at room temperature but also in the high-temperature and high-pressure environment.After immersion for seven days at 80℃with pressure of carbon dioxide of 3 MPa,the contact angle of coatings was maintained at148.11°.The high corrosion resistance and durability of coatings are mainly attributed to the construction of the multi-scale roughness of the coating and the favorable effects due to the thermal stability and chemical stability of the reduced graphene oxide itself.