Understanding the role of alloyed Ni and Cu on improving corrosion resistance of low alloy steel in the simulated Beishan groundwater

Abstract

• The addition of Ni and Cu elements significantly inhibited the cathodic and anodic processes of steel corrosion. • Ni and Cu alloy elements were obviously enriched in the inner rust layer, which could improve the compactness of rust layer. • Fe 6 (OH) 12 SO 4 stably existed in the corrosion products of NiCu steel because Ni(Ⅱ) or Cu(Ⅱ) could substitute Fe(Ⅱ) of Fe 6 (OH) 12 SO 4 and increase its oxidation resistance. • Ni and Cu made Fe3O4 ionic selective by doping, which could repel the aggressive anions and improve the corrosion resistance. The corrosion behavior of NiCu low alloy steel and Q235 low carbon steel as the candidate materials for geological disposal containers of high-level radioactive waste in the simulated Beishan groundwater was comparatively studied by weight loss test, electrochemical measurements, scanning electron microscope (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), Raman spectrum and X-ray photoelectron spectroscopy (XPS). The electrochemical results showed that the corrosion potential of NiCu steel and Q235 steel gradually increased with the immersion time. Simultaneously, the cathodic process transited from hydrogen evolution reaction (HER) control to the rust reduction control, while the anodic process was always dominated by the active dissolution of iron. By comparison, both the cathodic resistance and the anodic dissolution resistance of NiCu steel corrosion were apparently higher than that of Q235 steel. The results of rust layer characterization indicated that Ni and Cu elements could be enriched in the inner rust layer of NiCu steel and the rust layer was more compact. As the main corrosion products, the content of α-FeOOH in the rust layer of NiCu steel was obviously increased more than that of Q235 steel. Fe 6 (OH) 12 SO 4 stably existed in the corrosion products of NiCu steel because Ni(II) or Cu(II) could substitute Fe(II) of Fe 6 (OH) 12 SO 4 and increased its oxidation resistance. Moreover, Ni and Cu could also make Fe 3 O 4 ionic selective by doping. After the long-term immersion, the corrosion mass loss of NiCu steel was significantly lower than Q235 steel, which further confirmed the benefits of Ni and Cu alloying on improving the steel corrosion resistance.