Insights into the effects of Ni and Cu on improving corrosion resistance of low alloy steel in GMZ compacted bentonite infiltrated by simulated groundwater

The durability of overpacks used for geological disposal of high-level radioactive waste largely depends on the corrosion resistance of their manufacturing materials. The corrosion evolution behavior and corrosion kinetics of Q235 carbon steel and NiCu low alloy steels (1Ni and 3Ni) in compacted bentonite infiltrated by simulated deoxygenated Beishan groundwater were investigated using corrosion weight loss method, electrochemical tests, and several characterization techniques. Initially, the cathodic corrosion process transformed from the reduction of residual oxygen to the combined reduction of oxygen and rust, while the anodic process primarily involved the active dissolution of Fe. For Q235 steel, the Fe(II)-containing corrosion products were easily oxidized to Fe(III)-containing ones by residual oxygen, which promoted rust reduction. However, in the corrosion products of NiCu steels, the isomorphous substitution of Fe(II) in Fe 6 (OH) 12 CO 3 by Ni(II) enhanced the compound’s oxidation resistance and reduced the formation of Fe(III) corrosion products, thereby inhibiting the early-stage cathodic process. Over time, oxygen was gradually consumed and the cathodic process shifted to hydrogen evolution reaction (HER) and rust reduction. Subsequently, Fe(III) corrosion products were depleted due to continuous reduction, after which the cathodic process became controlled by HER. Following long-term embedment, both the cathodic and anodic polarization resistances of NiCu steels were significantly higher than those of Q235 steel. The role of Ni and Cu was to reduce the driving force of HER by increasing open circuit potential. Meanwhile, the formed Ni 4 Fe 2 (OH) 12 CO 3 , NiFe 2 O 4 , and CuFeO 2 improved both the stability of the rust layer and its protective properties.