The effect of Cl^- on the 316L stainless steel in simulated cooling water has been studied using polarization curves, electrochemical impedance spectroscopy （EIS）, Mott- Schottky plot and scanning electron microscopy （SEM） techniques. Cl^- concentrations vary from 200 to 900 mg/L. Results reveal that the corrosion resistance increases with the decrease of Cl^- concentration in simulated cooling water. The increase of Cl^- concentration leads to the shift of the corrosion potential towards the positive direction. Mott-Schottky curves show that in the passive film, Cr2Oa and FeO at the inner layer exhibit P-type but Fe2O3 and CrOa （CrO4^2-） N-type semiconductive properties. The SEM/EDX data demonstrate that elements such as Fe, O, C, Si and Cl as well as the presence of calcium and aluminum are presented on the surface of the metal.
Pitting corrosion of 316L stainless steel （316L S S） under various stress was studied by potentiodynamic polarization, electrochemical impedance spectroscopy （EIS） and Mott-Schottky （M-S） analysis in 3.5% NaC1 solution. The results of polarization curves show that, with the increase of the stress, the pitting potentials and the passive current density markedly decrease firstly （180 MPa）, and then increase greatly （200 MPa）. The corresponding surface morphologies of the samples after the polarization test well correspond to the results. Mott-Schottky analysis proved the least C1- adsorbed to the surface of passive film with more positive flat potential, indicating that a moderate stress could increase the pitting corrosion resistance of 316L SS in 3.5% NaC1 solution.
The corrosion behaviors of alloy 690 in 1 wt pct sodium hydroxide aqueous solutions with and without PbO were characterized by electrochemical measurements, including potentiodynamic polarization, electrochemical impedance spectroscopy and Mott-Schottky measurement. The results reveal that there is a great difference between the corrosion behaviors of alloy 690 in the two tested solutions. The corrosion current density in PbO-containing solution is higher than that in the solution without PbO, which may be attributed to the anodic dissolution of metallic lead deposited at the early stage of polarization. The electrochemical impedance of the specimen in PbO-free solution is higher than that in the solution containing PbO. The slope of the Mott-Schottky curve in Pb-containing solution decreases notably compared with that in the Pb-free solution, which can be interpreted by the chromium depletion in the duplex structure of passive films.
The passive film formed on 2205 duplex stainless steel（DSS） in 0.5 M NaHCO3＋0.5 M NaCl aqueous solution was characterized by electrochemical measurements,including potentiodynamic anodic polarization and dynamic electrochemical impedance spectroscopy（DEIS）.The results demonstrate that there is a great difference between the passive film evolutions of ferrite and austenite.The impedance values of ferrite are higher than those of austenite.The impedance peaks of ferritic and austenitic phases correspond to the potential of 0.15 and 0.25 V in the low potential range and correspond to 0.8 and 0.75 V in the high potential range.The evolutions of the capacitance of both phases are reverse compared to the evolutions of impedance.The thickness variations obtained from capacitance agree well with those of impedance analysis.The results can be used to explain why pitting corrosion occurs more easily in austenite phase than in ferrite phase.
Xue-qun ChengCheng-tao LiChao-fang DongXiao-gang Li
