X-ray photoelectron spectroscopic examinations of electrochemically formed passive layers on Ni-Cr alloys

Journal Article · Tue Apr 01 04:00:00 EST 1997 · Journal of the Electrochemical Society

DOI:https://doi.org/10.1149/1.1837577· OSTI ID:509378

Jabs, T; Borthen, P; Strehblow, H H ^[1]

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1. Heinrich-Heine-Univ. Duesseldorf (Germany). Inst. fuer Physikalische Chemie und Elektrochemie

The structure and composition of passive films electrochemically formed on Ni-Cr alloys in 1 M NaOH and 0.5 M H{sub 2}SO{sub 4} has been studied with x-ray photoelectron spectroscopy. The passivation potential was varied within the passive range up to the transpassive range and the time of passivation from 10 ms to 1,000 s. With angular-resolved x-ray photoelectron spectroscopy, the passive film was found to have a two-layer structure with an inner oxide part formed directly at the metal surface and an outer hydroxide part in contact with the electrolyte. The metal surface underneath is enriched in Ni compared to the metal bulk composition. Except for potentials approaching the transpassive range, the hydroxide layer forms the dominant part of the passive film. Above 0.3 V in NaOH and 1.2 V in H{sub 2}SO{sub 4}, Cr(VI) ions are found within the hydroxide layer. The maximum thickness of the passive layer is about 6 nm in NaOH and 3.5 nm in H{sub 2}SO{sub 4}. The growth and the pronounced changes of the composition of the passive layers reflect the electrochemical behavior of the pure metal components. The results are in agreement with the thermodynamic data.

• Sponsoring Organization: Deutsche Forschungsgemeinschaft, Bonn (Germany)
• OSTI ID: 509378
• Journal Information: Journal of the Electrochemical Society, Journal Name: Journal of the Electrochemical Society Journal Issue: 4 Vol. 144; ISSN JESOAN; ISSN 0013-4651
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CHEMICAL COMPOSITION
CHROMIUM ALLOYS
CORROSION PRODUCTS
ELECTROCHEMICAL CORROSION
MORPHOLOGY
NICKEL ALLOYS
PASSIVATION
PROTECTIVE COATINGS
SODIUM HYDROXIDES
SULFURIC ACID