The Passivation Behavior of Mild Steel in CO₂Saturated Solution Containing Nitrite Anions

Abstract

The passivation behavior of mild steel in CO 2 saturated solution was studied with electrochemical methods and XPS. In CO 2 saturated solution at the open circuit potential, NO 2 − may accelerate corrosion of mild steel to some extent. By addition of NO 2 − in CO 2 saturated solution, the polarization behavior of mild steel changes from active dissolution to passivation. With the increase of NO 2 − concentration, during anodic polarization the current density increases faster and the active-passive transition potential moves to the negative direction. The passivation of mild steel is attributed to the formation of a protective Fe 2 O 3 passive film on the mild steel substrate under the FeCO 3 layer. NO 2− is a good corrosion inhibitor and passivation accelerator for carbon steels in alkaline and neutral environments, and the corrosion behavior of carbon steels can be obviously affected by the presence of NO 2 − in corrosion environments. 1-9 Reffass et al. 5 studied the effects of NO 2 − on localized corrosion behavior of carbon steel in NaHCO 3 + NaCl solution with the scanning vibrating electrode technique (SVET) and chronoamperometry. The authors found that the breakdown potential (E b ) of the steel moved positively from -15 ± 5 mV SCE up to 400 ± 50 mV SCE by addition of 0.1 M NO 2 − , and NO 2 − accelerated repassivation of the carbon steel surface and made the localized active sites lose their activity. Dong et al. 6,7 studied the relationship between the corrosion susceptibility and the semiconductive characteristics of the passive film on Q345 carbon steel in simulated carbonated concrete pore solution with the electrochemical noise (ECN) method. NO 2 − decreased the donor density in the passive film and caused E b to move toward the positive direction. The authors explained the effects of NO 2 − in two aspects: NO 2 − can promote repassivation of the localized active sites and repair the defective air-formed passive film. Valcarce et al. 8 investigated the effects of NO 2 − on the passivation behavior of steel bar in a mixed alkaline solution (KOH + NaOH + Ca(OH) 2 ) containing Cl − . NO 2 − was found to restrain the initiation and growth of localized corrosion and accelerate repassivation of the steel surface. The effect of NO 2 − in alkaline and neutral environments is attributed to the following reaction:The generated γ-Fe 2 O 3 by reaction 1 can repair the defective airformed passive film on the carbon steel surface, which strengthens the protection capacity of the passive film. [5][6][7][8][9][10] On the other hand, studies concerning the corrosion behavior of carbon steels in CO 2 environments have been carried out by many researchers. [11][12][13][14][15][16] The corrosion behavior of carbon steels is closely related to the composition and structure of the corrosion product layers, which depend mainly on the temperature of CO 2 environment. When the temperature is less than 60 • C, there is a thin and poorly adherent FeCO 3 layer, and uniform corrosion occurs in this temperature range. When the t...

The Comparative Investigation of Corrosion and Passivation for X65 Carbon Steel in pH 1 to 5 HNO3 Solutions without and with 0.01 mol L–1 NaNO2

“…However, in the pH 4 to 5 solutions without NaNO 2 , the presence of two capacitive semicircles and the absence of inductive semicircle are observed on the two Nyquist plots. From the previous discussion, for the two capacitive semicircles, one is attributed to the deposition of corrosion product on the X65 surface and the other one is due to the process of charge transfer between double electron layer; 29 the presence of inductive semicircle is attributed to the adsorption relaxation process of H + , 20 and the disappearance of inductive semicircle further confirms the different cathodic reaction: H + reduction (equation 2) in the pH 1 to 3 solutions without NaNO 2 and O 2 reduction (equation 4) in the pH 4 to 5 solutions without NaNO 2 . From Figure 5a, the radius of capacitive semicircle enlarges significantly with the raise of pH value, indicating the decrease of corrosion rate.…”

“…17 However, for the surface passivation of carbon steels in acidic environments, the effectiveness of NO 2 is very few reported, and the detailed mechanism of NO 2 is still not completely clear. Zhou et al [19][20][21] systemically investigated the influences of NaNO 2 addition and its concentration on the corrosion and passivation of Q235 carbon steel in CO 2 saturated solution (pH 3.7). The electrochemical behavior of Q235 carbon steel transferred from the activation in CO 2 saturated solution free of NaNO 2 to the passivation in the same solution containing NaNO 2 ; 19 with the increase of NaNO 2 concentration, the passivation capability of Q235 carbon steel was strengthened obviously until the NaNO 2 concentration was up to 0.05 mol L -1 ; 20 the mechanism of NO 2 on the surface passivation was very closely associated with the formation of Fe 2 O 3 passive film under FeCO 3 corrosion product layer.…”

“…As summarized above, until by now, the reports involving the effectiveness of NO 2 on the surface passivation of carbon steels in CO 2 saturated solution (a weak and non-oxidizing acid environment) 20 and in pH 1 to 6 HCl solutions (a strong and non-oxidizing acid environment) 22 have been published. However, in strong and oxidizing acid environments, such as HNO 3 solutions, the related investigations are absent.…”

The inhibitive mechanisms of nitrite and molybdate anions on initiation and propagation of pitting corrosion for mild steel in chloride solution

“…Under the standard state the equilibrium potential of the above reaction (5) (0.715 V SCE ) is more positive than that of the above reaction (6) (0.527 V SCE ), hence Fe 2+ could be oxidized to Fe 3+ with the presence of NO 2 − , even the oxygen concentration is very little within pits [40]. The hydrolysis reaction of Fe 3+ would occur as follows:…”

The Effects of pH Values on Functional Mechanisms of Nitrite Anions for Q235 Carbon Steels in 0.01 mol L-1 NaNO2-HCl Solutions

“…8,11,13 However, in acidic media, the related studies involving NO 2 − are relatively few, and the present studies are summarized as follows. In carbon dioxide (CO 2 ) corrosion environments, Zhou et al [15][16][17][18] studied the influence of NO 2 − on the corrosion / passivation behavior of Q235 carbon steel in CO 2 saturated solution (pH 3.7) in detail.The Q235 steel presented the electrochemical behavior of activation in CO 2 saturated solution without NO 2 − ; 15 after the addition of NO 2 − , the electrochemical behavior transferred from activation to anodic passivation, and the critical NO 2 − concentration for the stable passivation was approximately 0.05 mol L -1 ; 16 intergranular corrosion (IGC) was observed on the surface of Q235 carbon steel when the Q235 steel was polarized into activation-passivation potential region with a low potential scanning rate; 17 the occurrence of IGC was very closely associated with the electrochemical behavior of activation-passivation transition, which was resulted from the synergetic mechanisms of CO 2 and ΝΟ 2 − . 18 In other 19 studied the combined influences of NO 2 − and thioureido imidazoline (TAI) on the passivation behavior and the pitting corrosion (PC) of X70 carbon steels in acidic NaCl solution (pH 5.5) and reported that the mechanisms of NO 2 − and TAI were both interactive and superimposed, and the addition of NO 2 − was beneficial to restrain the initiation and propagation of PC.…”