Investigation into the Effect of Cr2O3 Nanoparticles on the Protective Properties of Epoxy Coatings on Carbon Steel in 3.5% NaCl Solution by Scanning Electrochemical Microscopy

Abstract

The effect of introducing chromium oxide (Cr₂O₃) nanoparticles in the epoxy coatings on carbon steel was analyzed using Scanning Electrochemical Microscopy (SECM) and Electrochemical Impedance Spectroscopy (EIS). Localized measurements such as oxygen consumption and iron dissolution were observed using SECM in 3.5% NaCl in the epoxy coated sample. Line profile and topographic image analysis were measured by applying –0.70 and +0.60 V as the tip potential for the cathodic and anodic reactions, respectively. The tip current at –0.70 V for the epoxy coated sample with Cr₂O₃ nanoparticles decreased rapidly, which is due to cathodic reduction of dissolved oxygen. The EIS measurements were conducted in 3.5% NaCl after wet and dry cyclic corrosion test. The increase in the film resistance (R_f) and charge transfer resistance (R_ct) values was confirmed by the addition of Cr₂O₃ nanoparticles in the epoxy coating. SEM/EDX analysis showed that Cr₂O₃ was enriched in corrosion products at a scratched area of the coated steel after corrosion testing. FIB-TEM analysis confirmed the presence of the nanoscale oxide layer of Cr₂O₃ in the rust of the steel, which had a beneficial effect on the corrosion resistance of coated steel by forming protective corrosion products in the wet/dry cyclic test.