An electrochemical study of pH influences on corrosion and passivation for a Q235 carbon steel in HNO3–NaNO2, HAc–NaNO2 and HCl–NaNO2 solutions

Abstract

In this study, the influences of different pH values on the corrosion and passivation behaviors of a Q235 carbon steel in HNO₃–NaNO₂, HAc–NaNO₂ and HCl–NaNO₂ solutions were studied by electrochemical methods. The manifestations of the electrochemical characteristics were revealed and the variations in the electrochemical parameters were clarified. Moreover, for the Q235 steel in the three solutions with different pH values, the decrease in the corrosion current density (i_corr) and the increase in the charge transfer resistance (R_ct) in each solution, indicated a decrease in the corrosion rate. The decrease in the critical passivation current density (i_crit) and increase in the passive film resistance (R_f) suggested the reinforcement of passivation capability. On the other hand, in the three solutions at the same pH value, the corrosion rate increased and the passivation capability weakened in HNO₃–NaNO₂, HAc–NaNO₂ and HCl–NaNO₂ solutions. Simultaneously, the related electrochemical mechanisms of corrosion and passivation for Q235 carbon steel in acidic solutions containing nitrite anions (NO₂⁻) were also discussed.