Department of Chemistry, Aristotle University of Thessaloniki, 54 124 Thessaloniki, Greece.
Phys Chem Chem Phys. 2009 Oct 21;11(39):8841-54. doi: 10.1039/b906488e. Epub 2009 Jul 24.
This work analyses the nature of temporal patterning of the anodic potential induced by chlorides during polarization of iron under current-controlled conditions in acid solutions. It is shown that potential oscillations emerged as a result of the local chloride attack of a thin oxide layer, which covers the iron surface in its passive state. The mechanism by which both the local oxide breakdown and the subsequent localized active dissolution (pitting) occur is explained by considering a point defect model (PDM) developed to describe the oxide growth and breakdown. According to the PDM, chlorides occupy oxygen vacancies resulting in the inhibition of oxide growth and autocatalytic generation of cation vacancies that destabilize the oxide layer. Simultaneous transformation of the outer surface of the inner oxide layer to non-adherent ferrous chloride or oxo-chloride species leads to a further thinning of the oxide layer and its lifting-on from the iron surface. The process repeats again yielding sustained oscillations of the anodic potential. Analysis of the oscillatory response obtained under current-controlled conditions as a function of either the current or the time allows the suggestion of a set of alternate diagnostic criteria, which might be used to characterize localized corrosion of iron in acid solutions.
这项工作分析了在酸性溶液中电流控制条件下铁极化时氯离子引起的阳极电位时间模式的性质。结果表明，由于覆盖铁表面的薄氧化层受到局部氯化物的攻击，出现了电位振荡。通过考虑开发的点缺陷模型（PDM）来解释局部氧化物击穿和随后局部活性溶解（点蚀）发生的机制，该模型用于描述氧化物的生长和击穿。根据 PDM，氯化物占据氧空位，从而抑制氧化物的生长并自动催化产生阳离子空位，使氧化物层不稳定。内层氧化物外层同时转化为不附着的二价氯化亚铁或氧氯化物物种，导致氧化物层进一步变薄，并从铁表面抬起。该过程再次重复，导致阳极电位持续振荡。根据电流或时间，对电流控制条件下获得的振荡响应进行分析，可以提出一组交替的诊断标准，这些标准可能用于表征酸性溶液中铁的局部腐蚀。
