| Stainless steel has an excellent corrosion resistance but it still faces a huge challenge of corrosion in various harsh environments.Electrochemical modification was verified to be able to enhance the corrosion resistance of stainless steel with advantages of higher efficiency and convenient application.How to further develop novel surface treatment and in-situ monitoring technique for stainless steel,and to further understand the mechanism of corrosion resistance of modified stainless steel have earned their high values in theoretical research and practical applications.Based on the advantages of electrochemical strategies and micro electrochemical analysis in our group,this thesis aims at optimizing the technological conditions to present a double-electrodes electrochemical modification,evaluating the corrosion protection properties via various techniques of corrosion electrochemistry,characterizing the electrochemically modified passive films through various kinds of advanced surface analysis,establishing a novel in-situ monitoring system combining electrochemical noise and scanning reference electrode technique to study the initiation and propagation of localized corrosion,and obtaining a comprehensive understanding of anti-corrosion mechanism of electrochemically modified passive film on the surface of stainless steel.The specific research contents were shown as follows:1.A "double-electrodes electrochemical modification" was developed,and its properties of corrosion resistance were assessed by various electrochemical techniques in 3.5 wt.%NaCl solution.It was indicated that after electrochemical modification,the open circuit potential of 304 stainless steel became more positive and kept stable for 2 hours.The charge transfer resistance was three orders higher in magnitude.The pitting potential of the electrochemically modified stainless steel increased form 316 mV to 1242 mV2.The anti-corrosion mechanism of electrochemically modified passive film was elucidated by using various advanced techniques of surface analysis.It was found that after electrochemical modification,the surface of stainless steel became flat,smooth,and homogeneous.The MnS inclusions and other physical defects were removed.The anion group including CrO42-,Cr2O72-,NO3-adhesive in the outermost layer of electrochemical modified passive film,which was able to block the attacks of aggressive ions.3.Simultaneous in situ ECN/SRET measurements were successfully made to provide direct correlation between ECN signals and corrosion behavior with spatial resolution,monitoring rapid pitting nucleation,capturing the delicate transformation of the pitting state from metastable micropitting to macropitting or repassivation(ceasing).The proposed approach was helpful in providing further insight into the physical significance of ECN current fluctuations and a deeper understanding of the pitting corrosion mechanism of stainless steel in chloride solution. |
