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The influence of the surface structure on the mechanism of the active dissolution of iron

Authors
Journal
Electrochimica Acta
0013-4686
Publisher
Elsevier
Publication Date
Volume
35
Issue
1
Identifiers
DOI: 10.1016/0013-4686(90)85054-q

Abstract

Abstract The active dissolution and the surface morphology of single-crystalline and polycrystalline iron in acid'aqueous solutions were studied by using potentiostatic and microscopic techniques. The anodic dissolution of the hydroxylated metal species yields steady-state metal surfaces containing more or less etch pits depending on the applied potential, the crystallographic orientation of the surface and the deformation structure. The nucleation and growth of the pits are impeded by the presence of higher-index faces or numerous crystal edges and corners whereas it is markedly enhanced by the presence of low-index planes with discrete dislocations emerging on the metal surface. Apparently distinct pits whose walls consist of close packed stepped faces dissolve via atoms at kink sites with the assistance of two hydroxyl ions and give Tafel slopes of ≈30 mV and reaction orders with respect to hydroxyl ions of ≈2, whereas atomically roughened surfaces cause uniform dissolutin with the co-operation of one hydroxyl ion per iron atom and Tafel slopes of ≈40 mV and reaction orders of ≈1.

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