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| ELECTROCHEMICAL BEHAVIOR OF PASSIVE FILMS FORMED ON X80 PIPELINE STEEL IN VARIOUS CONCENTRATED NaHCO3 SOLUTIONS |
| FAN Lin,LI Xiaogang,DU Cuiwei,LIU Zhiyong |
| Corrosion and Protection Center, University of Science and Technology Beijing, Beijing 100083 |
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Abstract The electrochemical behavior of the passive films formed on X80 pipeline steel in various concentrated NaHCO3 solutions was studied using potentiodynamic polarization curves, potentiostatic polarization curves, electrochemical impedance spectroscopy (EIS) as well as Mott-Schottky plots. The electrochemical test results indicated n-type semiconducting characters of the passive film, which was composed of two layers, with γ-Fe2O3 as the outer layer, and Fe3O4 as the inner layer. The properties of the passive films were influenced by the concentration of NaHCO3 solutions. The thickness of the inner layer merely remained constant, which was supposed to be dominated by the film forming polarization, whereas the thickness of the outer layer decreased with the increase of the concentration of NaHCO3 solution, which suggested that the outer layer plays a more important role to the corrosion resistance and stability of the passive film. According to the point defect model (PDM), higher donor density and lower thickness of the passive films was affected by the enhanced conductivity of the solution and the intensified adsorption of HCO3- at local defect sites with higher HCO3- concentration.
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Received: 28 June 2011
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Corresponding Authors:
FAN Lin
E-mail: violin_fl@163.com
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