Natural passivation and chloride corrosion resistance of Inconel 625 in OPC and CSA concrete pore solutions with different pH

Abstract

This study considers the different engineering application environments for normal use and emergency repair of reinforced concrete structures. The natural passivation and chloride corrosion resistance of Inconel 625 in Ordinary Portland cement (OPC) and Calcium Sulfoaluminate cement (CSA) was first evaluated through electrochemical measurement and surface analysis techniques. OPC and CSA related to different pH values of pore solutions were selected while low carbon (LC) steel and 304 stainless steels (304SS) were also investigated as reference. The electrochemical test results showed that the passivation ability of 304SS and Inconel 625 in CSA solution was as well as or better than that in OPC solution, while LC steel could hardly be passivated in CSA solution. In addition, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) results indicated that the thickness and integrity of the Inconel 625 passivation film were lower than that of 304SS. Notably, the thicknesses of Inconel 625 and 304SS in CSA solution are 4.6 nm and 5.2 nm, respectively. However, the corrosion resistance of Inconel 625 in chloride environments was significantly better than that of 304SS, which was attributed to the presence of highly corrosion-resistant Cr, Ni, and Mo compounds on the surface of Inconel 625 passivation film. Finally, based on the research results, the passivation and chloride corrosion resistance mechanism of Inconel 625 in OPC and CSA solutions was proposed, which may provide a reference and theoretical basis for the application of Inconel 625 in cement-based materials. In particular, the introduction of Inconel 625 is of great significance in improving the durability of concrete structures for emergency construction projects using CSA in complex and harsh environments.