Passivation behavior and surface chemistry of 316 SS in the environment containing Cl− and NH4+

Abstract

Abstract The passivation behavior and surface chemistry of 316 stainless steel (316 SS) in the environment containing NH4+ and Cl- are studied systematically in this paper. The influence of NH4+ on the passive film formed on 316 SS in the presence of Cl- was studied by electrochemical testing, point defect model (PDM), and X-ray photoelectron spectroscopy (XPS). The results show that NH4+ is favorable for the passive film formed on 316 SS. According to the PDM, it is concluded that the film performance is affected by the defect density and the defect diffusion coefficient, while the addition of low concentration NH4+ has little influence on the defect density but reduces the defect diffusion coefficient to delay the dissolution of the passive film, increasing the corrosion resistance of the passive film. In addition, the XPS results show that the addition of NH4+ does not have much influence on the double-layer structure, but increases the contents of Fe(III) and Cr(OH)3 in the surface layer of the passive film, making the surface layer of the passive film denser and resistant to erosive ions.