“…By contrast, in acidic environments, the related investigations involving the effectiveness and mechanism of NO 2 − on the surface passivation of carbon steels are only just starting. In the previous works (Li et al , 2019; Zhou et al , 2019; Deng et al , 2020; Zhou and Yan, 2016; Zhou et al , 2019), the influences of NO 2 − on the electrochemical behavior of carbon steels in pure acidic solutions, such as HAc (Li et al , 2019), HCl (Zhou et al , 2019a, 2019b, 2019c, 2019d), HNO 3 (Deng et al .,2020) and CO 2 /H 2 CO 3 (Zhou and Yan, 2016), have been reported. The main results are summarized as follows: - The electrochemical behavior transfers from the activation (A) in acidic solutions without NO 2 − to the activation-passivation (A-P) transition in the corresponding solutions with NO 2 − .
- In pure acidic solutions containing NO 2 − , the acidity, oxidability and composition of the bulk acids show some degree of influence on the pH range for the occurrence of A-P transition.
- The presence of inhibitive species in pure acidic solutions is beneficial to the occurrence of A-P transition, but the presence of aggressive species shows the opposite effect.
Unfortunately, for the surface passivation of carbon steels in acidic environments, the detailed mechanism of NO 2 − is still not clear; besides, the present investigations concerning the effectiveness of NO 2 − are mainly focused on simple acidic solutions.…”