In this work, a new approach is introduced to determine the kinetic constants of the elementary steps involved in the overall reaction of iron anodic dissolution. A procedure based on transient analysis is established, for the first time, that enables the estimation of a series of kinetic parameters that can be used for modeling the anodic potentiodynamics over a wide range of environmental conditions. The findings of the present research enhance the ability of explaining how different environmental factors (CO2 presence, pH, temperature, steel type, etc.) mechanistically affect the kinetics of iron dissolution.
Although extensive research has been carried out on modeling the cathodic potentiodynamic sweep during the corrosion of iron/steel, previous studies have not been able to layout a systematic approach to mechanistically describe the kinetics and model anodic dissolution. This study offers some insights into the mechanistic modeling of electrochemical anodic reactions at different experimental conditions. For iron dissolution, there are two well-known mechanisms valid for strong acid solutions (pH ≤ 4) in the literature; namely, the "catalytic mechanism" proposed by Heusler et al.,1 and the "consecutive mechanism" proposed by Bockris et al.2 In 1981 and 1986, Keddam, et al.,4-7 reported that multiple dissolution paths exist as several time constants were observed during EIS measurements under well controlled experimental conditions. They claimed that more than one single intermediate and three dissolution paths can be occurring in parallel during iron dissolution under certain experimental conditions. Hence, Keddam, et al., combined both consecutive and catalytic mechanisms into a single multipath scheme (Figure 1) to define a plausible explanation for such observations.4
In this scheme (Figure 1), the first and the second elementary steps (Path (1)) approximate the Bockris’ mechanism (non-catalytic path).2 In our previous research,8 thirty-eight different pathways were investigated for the mechanism of iron dissolution in strong acid and it was found that the experimental observations in the active range of dissolution were explainable only by relying on Bockris’ mechanism.2
In this scheme (Figure 1), the first and the second elementary steps (Path (1)) approximate the Bockris’ mechanism (non-catalytic path).2 In our previous research,8 thirty-eight different pathways were investigated for the mechanism of iron dissolution in strong acid and it was found that the experimental observations in the active range of dissolution were explainable only by relying on Bockris’ mechanism.2
