Electrodeposition And CO₂ Corrosion Resistance Of Y₂O₃/ZrO₂ Nanocomposite Coatings

CO₂ corrosion is one of the serious corrosions that often encounter in the petrochemical industry,which seriously threatens the safe production of oil and gas.The traditional anti-corrosion process is mainly by adding chemical inhibitors.Isolating the metal from the corrosive medium by preparing a coating resistant to CO₂ corrosion is a new method to solve the CO₂ corrosion of the oil field transmission pipeline.In this paper,the Y₂O₃ and ZrO₂ nanoparticles were added into the plating bath,and the composite electrodeposition technology was used to study the electrodeposition mechanism and corrosion resistance of the composite coating containing Y₂O₃ and ZrO₂ in the Ni-W system,in order to obtain a dual nanocomposite coating with good overall performance and resistance to CO₂ corrosion.This work could provide a new solution to CO₂ corrosion problem in petrochemical industry and ensure the safety of field pipeline and equipment operation by slowing down the corrosion,which has important benefits to the economic and social dimension.Firstly,based on the first-principle,a model of CO₂ adsorption on the surface of the coating was established to study the horizontal and vertical adsorption characteristics of CO₂ molecules on the surface of different nanoparticles,and the structure of the nano-alloy coating with better CO₂ corrosion resistance was obtained.The study found that CO₂ was difficult to chemisorb on the surface of Y₂O₃ and ZrO₂,indicating that Y₂O₃ and ZrO₂ were nanoparticle additives that make the alloy coating had CO₂ corrosion resistance potential.When Y₂O₃ and ZrO₂ nanoparticles were simultaneously added to the coating,the adsorption energy of CO₂ on the surface was smaller than that on the surface of Y₂O₃ or ZrO₂,indicating that the composite coating containing Y₂O₃ and ZrO₂ nanoparticles had more excellent corrosion resistance.Therefore,the structure of the nano-alloy plating layer with the best corrosion resistance was:Ni-W alloy with Y₂O₃ and ZrO₂ nano-particles dopped.Then,electrochemical test methods?e.g.cyclic voltammetry,linear polarization method,AC impedance spectroscopy test,etc?were used to investigate the electrodeposition mechanism and crystallization kinetics process of nanoparticles containing Y₂O₃ and ZrO₂.It was found that the nucleation process of the nanocomposite coating occurd during deposition and met the three-dimensional continuous nucleation process under diffusion control.When the addition amount of Y₂O₃ and ZrO₂ nanoparticles in the plating bath was 10 g/L respectively,the nucleation overpotential reached the most positive value,which was propitious to nucleation during co-deposition.The effects of current density,temperature,nano-particle concentration and other process parameters on electrode potential of electrode surface were obtained though chronopotentiometry.It was found that the coating could be more stable and free of crack when the addition amount of Y₂O₃ and ZrO₂ nanoparticles was 10 g/L respectively,the current density of electrodeposition was 1.5 A/dm²,and the temperature of plating bath was 60°C.Thirdly,the effects of current density,temperature and nanoparticle concentration on the properties of Y₂O₃ and ZrO₂ nanocomposite coatings were studied based on theoretical findings through SEM analysis,EDS analysis,microhardness test and electrochemical test.The correctness of the theoretical results was verified.Then,the effects of deposition time,duty cycle,stirring method and ultrasonic power on the properties of the coatings were studied by using the same characterization methods.Finally established a set of method of nanocomposite coating qualified with best microstructure and corrosion resistance:adding Y₂O₃ and ZrO₂ nanoparticles 10 g/L respectively,using ultrasonic agitation to disperse nanoparticles,keeping ultrasonic power at 300 W,current density of electrodeposition at 1.5A/dm²,temperature of plating bath constant at 60?,pulse duty cycle at 0.4 and depositing for 2 h.Finally,based on the above-mentioned optimal preparation process,a nanocomposite coating was successfully prepared.High-temperature and high-pressure reactors and electrochemical tests were used to study the CO₂ corrosion resistance of the nanocomposite coatings.It was found that after corrosion for a certain time at high CO₂ partial pressure,high temperature and certain flow rate,the surface was smooth and no small pits and cracking of the coating were found,indicating that the nanocomposite coating has good CO₂ corrosion resistance.The results of electrochemical studies of coatings with corrosion product films shows that the coatings still exhibited good corrosion resistance after a certain period of time in the CO₂ environment.