The corrosion behavior of 316L stainless steel in an Fe(II)EDTA-based liquid-phase denitrification system.

With the continuous tightening of marine exhaust emission standards, removing nitric oxide (NO) by Fe(II)EDTA solution complex adsorption is regarded as a promising method. In order to evaluate the feasibility and risk of the corrosion failure for candidate metal in the Fe(II)EDTA-based liquid-phase denitrification system, the corrosion behavior of 316L stainless steel (SS) in Fe(II)EDTA, Fe(III)EDTA, and Fe(II)EDTA-NO was investigated using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, Mott-Schottky method, and X-ray photoelectron spectroscopy (XPS). The experimental results reveal that 316L SS is applicable to the liquid-phase denitrification environment, because of a passive film produced on the 316L SS surface which can protect effectively itself from further corrosion. Thereinto, the homogeneity and thickness of the passive film formed in the Fe(III)EDTA secure the maximum value. Beyond all doubt, the corrosion rate of 316L SS in Fe(III)EDTA is minimum only 0.001 mm·year−1. Meanwhile, the passive film was found to have semiconductive characteristics. The XPS results provide strong evidences for the above electrochemical measurements that the different electrochemical properties including variation of n/p-type semiconductor behavior are attributed to its chemical component. The passive film mainly consists of Cr2O3, Fe3O4, and MoOx, and FeO, CrO3, NiO, and MoO2 are not detected in the passive film formed in Fe(III)EDTA. These phenomena reasonably explain why the Mott-Schottky plot in Fe(III)EDTA only showed one n/p-type transformation rather than two in Fe(II)EDTA and Fe(II)EDTA-NO. [ABSTRACT FROM AUTHOR]