The oxide film consists of an inner defect rich \(\) forms at the electrode. Iron can form a stable oxide film by anodic polarization in neutral and basic solution 7, 8 (passivation in acidic solution is also possible but follows different mechanisms 9, 10, 11 and thus is not considered in this manuscript). Therefore, in this paper, iron oxide film growth is modeled and compared to experiments to bring general insights into passive film growth mechanism and correlations between external potential and internal reactions. Thus, for a deeper understanding of the basic mechanisms during the onset of passivation, stable growth and film dissolution, the less complex iron oxide can deliver deeper insights into passivity, also for complex alloys. In our daily life, passivity of stainless steel plays a more important role compared to the passivity of iron nevertheless, it is assumed that many general mechanisms during oxide film growth are comparable between stainless steel alloys and pure iron. Even though the research on the passivity of iron has a long history, it is still a very topical issue, and not all underlying mechanisms are fully understood. ![]() Faraday was the one who suggested that the altered behavior of the iron can be deducted to a surface film that forms on the electrodes’ surface and, together with Schönbein, brought the research on passivity to the forefront of electrochemistry at their time and started the following scientific progress in this field 5, 6. The name passivity first occurred in a correspondence between Schönbein and Faraday, who also studied the passivity of iron 4. In 1782, the German scientist Wenzel described the same observations but a more detailed study of the phenomena, followed by Keir in 1790 3. In 1738, Lomonosov reported the seemingly paradox behavior of fast iron dissolution in diluted nitric acid and a very low reaction rate in concentrated acid 2. Early work on the oxidation of iron laid the foundation for the broad research field of passivity. Without the phenomenon of passivity, which describes the formation of a stable oxide film on a metal or alloy surface, our metal-based civilization would not be possible 1.
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