Formation and dissolution of the passive film on iron studied by a light reflectance technique

Journal Article · Tue Jul 01 04:00:00 EDT 1997 · Journal of the Electrochemical Society

DOI:https://doi.org/10.1149/1.1837809· OSTI ID:533110

Buechler, M; Schmuki, P; Boehni, H ^[1]

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1. Swiss Federal Inst. of Tech., Zuerich (Switzerland). Inst. of Material Chemistry and Corrosion

The formation, growth, and dissolution of the passive film on iron in neutral and alkaline solutions was investigated using a light reflectance technique. In this study, laser light of 325 nm was used to access the amount of light absorbed in the film and to evaluate the optical absorption coefficient. After calibration, this technique allows a fast, in situ determination of the film thickness. Cyclic voltammetry and potential-step experiments with simultaneous thickness monitoring were carried out in borate buffer and in 0.1 M NaOH. For the borate buffer, anodic film formation and cathodic film dissolution are reversible, i.e., repeated anodic/cathodic cycling leads to conditions identical to the initial state. In NaOH, cathodic reduction of the film does not lead to film dissolution but to the formation of an electrochemically active layer, which does not significant contribute to the potential drop in the metal/film/electrolyte system. Hence, repeated passivation and reduction leads to successive thickening of the film, consisting of a barrier layer of constant thickness and a porous layer having increased thickness with every passivation/reduction cycle. This layer does not contribute to the passivity of iron.

• Sponsoring Organization: USDOE
• OSTI ID: 533110
• Journal Information: Journal of the Electrochemical Society, Journal Name: Journal of the Electrochemical Society Journal Issue: 7 Vol. 144; ISSN JESOAN; ISSN 0013-4651
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CRYSTAL GROWTH
DEPOSITION
DISSOLUTION
IRON
MORPHOLOGY
PASSIVATION
PROTECTIVE COATINGS
SODIUM HYDROXIDES
THICKNESS