Study Of The Anodic Dissolution Processes Of Inconel 600 With Digital Holography

Inconel 600,a nickel-based alloy,can be used under high temperature and pressure conditions.Because the oxide film is easily formed on the surface of Inconel600,it has good corrosion resistance,which is often used as the heat transfer tube of the steam generator of the nuclear power plant.However,with the presence of the aggressive ions,such as Cl^-and SCN^-,it is corroded easily.Therefore,it is nessary to study the anodic dissolution of Inconel 600 nickel-based alloy,which can provide theoretical basis for preventing corrosion of Inconel 600.In this paper,the on-line digital holography technology is combined with the electrochemical method,the scanning electrochemical microscope,and SEM are used to realize the complementary advantages of different experimental methods.The dynamic processes at the electrode|solution interface and the electrode surface were observed in situ during the anodic dissolution of 600 alloy.The effects of solution composition and external magnetic field（MF）on the anodic dissolution of Inconel600 are studied to reveal the MF effects on the occurrence and development of localized corrosion,meanwhile,EDS,SEM and other surface physical analysis methods were used.This work provides a new way to in situ monitor the corrosion of nickel based materials and develops a new environment-friendly corrosion inhibitor,which provides a theoretical basis for reducing the damage caused by corrosion of metallic material.The main contents of this paper are as follows.1.The inhibitve effects of PASP on the anodic dissolution of Inconel 600 in HCl solutionThe electrochemical method combined with digital holography was used to study the inhibitory effect of the environmentally friendly inhibitor polyaspartic acid（PASP）on the anodic dissolution of Inconel 600 in 0.04 mol dm^-3 HCl solution.The results proved that the inhibition efficiency increased with the increase of PASP concentration.When the PASP concentration was 6.66 g/L,the inhibition efficiency was as high as 84.13%.By using digital holography,the hydrolysis of M²⁺（M=Ni,Fe）near the electrode surface was observed in situ during the anodic dissolution process,which indicated that M（OH）₂ film was formed on the electrode surface.The inhibitory effect of PASP on the Inconel 600 electrode is caused by the adsorption of PASP and the surface film mixed with PASP-M complex.2.Effects of magnetic field on the anodic dissolution processes of Inconel600|H₂SO₄+KSCN systemThe effects of MF on the anodic dissolution of Inconel 600 in H₂SO₄+KSCN solutions were investigated by digital holography and electrochemical methods.The results shows as follows:in the active region,no matter whether the solution contains SCN^–or not,in the presence of magnetic field（MF）,Lorentz force may drive some active intermediate（such as Ni SCNH⁺）away from the interface.Because this active intermediate helps to dissolve the electrode,so MF decreased the anodic current.In the passive region,the dissolution of the passive film is a rate-determining step,and the MF promotes the dissolution of the film.Therefore,MF promotes the anodic dissolution processes whether the solution contains SCN^–or not.In this potential range,SCN^–can induce intergranular corrosion and pitting of Inconel 600,and MF promoted uniform corrosion,but inhibited intergranular corrosion and pitting.3.Effects of magnetic field on the anodic dissolution processes of Inconel600|Na Cl+KSCN systemIn the presence or absence of MF,the anodic dissolution of Inconel 600 in neutral and alkaline Na Cl solutions containing SCN^–was studied by electrochemical methods combined with digital holography.On the basis of the experimental results of digital holography,electrochemical methods,and SEM,it shows that the MF always inhibited the anodic dissolution processes of Inconel 600,because the Lorentz force driven some active intermediates（such as Ni Cl H⁺）away from interface in the solution containing a large number of chloride ions,whether the solution containing SCN^–or not.Because SCN^–was easy to form complexes with metal ions,the oxide film on the electrode surface is not easy to form,so it promoted the anodic dissolution processes.Becasuse the oxide film were easier to form on the electrode surface in the alkaline solution containing SCN^–,the higher the p H was,the lower the current was.