Rust evolution and electrochemical properties of field-exposed carbon steel in a tropical marine environment

Abstract

The corrosion behavior of carbon steel (CS) exposed in a tropical marine atmosphere for 2 years was studied by the weight loss, scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and electrochemical impedance spectroscopy techniques. The results show that the corrosion layer became more loose and thick with increasing exposure time, and after 2 years exposure, the rust layer developed into the dual-layer structure. The XRD and Raman analyses confirmed that the corrosion products contained γ-FeOOH, a-FeOOH, γ-Fe2O3, and Fe3O4. The polarization curves show that the corrosion potentials (Ecorr) and corrosion current densities (Icorr) changed with increasing exposure duration. Furthermore, an equivalent circuit is proposed for modeling the impedance data, and the charge transfer resistance (R2) decreased with exposure time during 6 months and increased from 6 months to 24 months, demonstrating that the corrosion rate increased first and then decreased with exposure time.