Abstract
In this paper, the flow injection (FI) technique combined with a partially-closed electrode (PCE) was used to manipulate the physicochemical microenvironment at the electrode/electrolyte interface so as to study the effects of chloride ions (Cl− ions) and nitrate ions (NO3− ions) on the anodic dissolution of the Fe/0.5 mol dm−3 H2SO4 system. The anodic dissolution is modified by injecting various composition-containing solutions into the vicinity of the PCE, and then, the electrodissolution processes are analyzed by comparing the j–t curves before and after the injections. At the initial stage of the passive region, it is found that NO3− ions promote the anodic dissolution of iron by creating more active sites on the surface of the electrode when CNO3−/CCl− = 1:1; however, they inhibit the anodic dissolution by making the film more compact for the strong oxidized characteristics of NO3− ions when CNO3−/CCl− = 10:1.
Highlights
Pitting may cause tremendous losses and damages for its unpredictable nature and rapid propagation
The oscillatory region (III) was an active–passive transition region, and a relaxation type of current oscillations was observed if the potential was constantly controlled at E < EF
In the passive region (IV), the current was low and stable due to a protective passive film formed on the surface of the electrode
Summary
Pitting may cause tremendous losses and damages for its unpredictable nature and rapid propagation. Chloride ions (Cl− ions) usually induce pitting by breaking down the passive film for its aggressiveness to metallic materials [1,2,3,4,5,6,7,8,9,10], so the study on the mechanisms of chloride corrosion is of theoretical and practical significance. Since Cl− ions and other ions often coexist in the corrosive environment, and it is necessary to study the combined effects of possibly coexisting ions on the corrosion processes of metals [14,15,16,17,18,19,20,21]. Leckie et al [14] suggested that the inhibitive effects of NO3 − ions on the corrosion induced by Cl− ions could be explained by the competitive adsorption theory
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