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Ellipsometry of passive oxide films on nickel in acidic sulfate solution

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Title: Ellipsometry of passive oxide films on nickel in acidic sulfate solution
Authors: Iida, Masahede Browse this author
Ohtsuka, Toshiaki Browse this author →KAKEN DB
Keywords: B. Ellipsometry
B. Nickel
C. Passivation
C. Oxide film
C. Thickness
Issue Date: Mar-2007
Publisher: Elsevier Inc.
Journal Title: Corrosion Science
Volume: 49
Issue: 3
Start Page: 1408
End Page: 1419
Publisher DOI: 10.1016/j.corsci.2006.08.002
Abstract: Nickel passive film has been studied in acidic sulfate solutions at pH 2.3 and 3.3 by ellipsometry. During anodic passivation followed by cathodic reduction, the roughness increases with dissolution of nickel, being indicated by gradual decrease of reflectance. However, the ellipsometric parameters, Ψ (arctan of relative amplitude ratio) and Δ (relative retardation of phase), are relatively insensitive to the roughness increase. From the change of Ψ and Δ, δΨ and δΔ, during the anodic passivation and reduction, thickness of the passive oxide film was estimated with assumption of refractive index of nf = 2.3 of the film. The thickness estimated is a range between 1.4 and 1.7 nm in the passive potential region from 0.8 to 1.4 V vs. RHE, having a tendency of thickening with increase of potential. Cathodic reduction at constant potential induces a change of the oxide film to an oxide film with lower refractive index of nf = 1.7, accompanied by thickening of the film about 30% more in the initial stage of reduction for 30 s. The gradual decrease of thickness takes place for the oxide with the lower refractive index in the latter stage. The potential change from the passive region to cathodic hydrogen evolution region may initially cause hydration of the passive oxide of NiO, i.e., NiO + H2O = Ni(OH)2, and during the latter stage of reduction, the hydrated nickel oxide gradually dissolves.
Type: article (author version)
Appears in Collections:工学院・工学研究院 (Graduate School of Engineering / Faculty of Engineering) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 大塚 俊明

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