Ce(SO4)2 as an efficient corrosion inhibitor for cold rolled steel in citric acid solution

The inhibition effect of rare earth salt of Ce(SO4)2 on the corrosion of cold rolled steel (CRS) in 0.50 M citric acid (H3C6H5O7) solution was studied by weight loss, electrochemical technique and surface analysis methods for the first time. The results reveal that Ce(SO4)2 behaves as an efficient inhibitor, and the maximum inhibition efficiency reaches a pleasant value of 97.2% at 20 °C with a little concentration of 0.25 mM. The adsorption of Ce(SO4)2 on CRS surface completely obeys Langmuir adsorption isotherm at 20 - 50°C. Ce(SO4)2 is arranged as a mixed-type inhibitor while mainly retards the cathodic reaction. Electrochemical impedance spectroscopy (EIS) has two time constants. Nyquist diagram contains a depressed capacitive loop at high frequencies followed by an inductive loop at low frequencies. The inhibition of CRS surface by Ce(SO4)2 is evidenced through scanning electron microscope (SEM), atomic force microscope (AFM) and confocal laser scanning microscope (CLSM). The inhibitive mechanism can be mainly attributed to the complexes of cerium (IV) ion with citric anions.