Investigations on the repassivation of carbon steel in consequence of cathodic polarization: Fid-Bau Portal

Investigations on the repassivation of carbon steel in consequence of cathodic polarization

Isecke, Bernd / Eichler, Thorsten / Burkert, Andreas

Pitting corrosion of carbon steel and iron in chloride containing alkaline environment is already well investigated, although a couple of questions are not clarified satisfactorily. The critical chloride content for steel in concrete and the critical chloride to hydroxide ion ratio for steel in alkaline solutions is still a major concern, considering chloride induced corrosion problems of steel in concrete. Another not satisfactorily clarified point is the repassivation of carbon steel in consequence of cathodic polarization. In the recent literature some indications are shown that repassivation occurs after a certain time of polarization. Therefore, the investigations discussed in this paper aim to clarify, to what extend the repassivation of carbon steel due to cathodic polarization occurs, and if the ennoblement of OCP is a sufficient indication for repassivation. In a first step the corrosion state of five nominal equal test specimens was determined by electrochemical techniques, i.e. electrochemical noise measurements (ENM) and electrochemical impedance spectroscopy (EIS). After determining the initial corrosion state by evaluating the charge transfer resistance and the polarization resistance respectively as well as evaluating potential and current noise signals, the specimens were polarized cathodically. Impedance data were recorded previous to, during and after polarization. The impedance data were evaluated by equivalent circuit fitting with special attention to charge transfer resistances and diffusion properties. The results show that reduction of oxides and oxygen diffusion during cathodic polarization has strong impact on the system's behavior.