Study On The Corrosion Behaviors Of Iron And 304 Stainless Steel In Neutral Cl~- Solution By Electrochemical Scanning Probe Microscopy

As one of the main forms of local corrosion, pitting corrosion usually leads to safety problems and cause enormous economic losses. It is of great significance to investigate the mechanisms and kinetic of pitting initiation and growth of metals and alloys such as iron and stainless steels. Scanning electrochemical microscopy (SECM) has advantages compared with conventional electrochemical techniques which can only provide bulk and average electrochemical information. Especially, SECM can be used to characterize the topography and redox activity of the solid/liquid interface and obtain the information about electrode reactions. Due to its unique characteristics, SECM has been widely employed for investigating the corrosion processes, such as the growth and the local breakdown of the passive films on the metals, the pitting initiation, metastable pitting, stable pitting and so on.In this paper, the pure iron and 304 stainless steel were used as the working electrodes, the corrosive solution is 0.1 M NaCl aqueous solution. Pitting corrosion of the pure iron and 304 stainless steel in 0.1 M NaCl aqueous solution was studied by cyclic voltammetry, polarization curves, current-time curves, line scans and area scans, etc. The electrochemical surface activity of iron in 0.1 M NaCl aqueous solution was obtained. Also, the pitting corrosion of 304 stainless steel in 0.1 M NaCl aqueous solution was studied as a function of immersion times, applied currents and potentials. In addition, the concentration profiles and local electrochemical activity of the corrosion products of 304 stainless steel were investigated by generation/collection mode with I^-/I₃^- redox.The main work is as follows:1. Determine the experiment parameterThe appropriate tip potential and distance between the tip and substrate were determined by line scan experiments.2. The behaviors of pure iron in 0.1M NaCl aqueous solutionThe surface activity of iron at open circuit potential and applied potentials in 0.1M NaCl aqueous solution was obtained by line scan and area scan experiments. 3. The behaviors of 304 stainless steel in 0.1M NaCl aqueous solutionThe effect of immersed time on the pitting potential of 304 stainless steel was investigated. Also, the dependences of surface activity and pitting corrosion on immersion times and applied currents and potentials have been studied.4. The study of electrochemical activity of corrosion productThe cyclic voltammograms of 304 stainless steel in 0.1M NaCl and 0.1MNaCl+10mMKI aqueous solution were obtained to study the effect of I" ion on pitting corrosion. The distribution of corrosion product was obtained by tip's cyclic voltammogram with different distances between the tip and the pit. The species of corrosion products and their electrochemical activity have been studied by area scan experiments in 0.1M NaCl and 0.1MNaCl+10mMKI aqueous solutions.