Surface analytical investigations of electrochemically formed passive layers on binary Fe/Al alloys

Journal Article · Sat Jul 01 00:00:00 EDT 1995 · Journal of the Electrochemical Society

DOI:https://doi.org/10.1149/1.2044277· OSTI ID:99613

Schaepers, D; Strehblow, H H ^[1]

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1. Heinrich-Heine-Universitat Duesseldorf (Germany). Institut fuer Physikalische Chemie und Elektrochemie

Passive layers have been formed on Fe/Al alloys under well-controlled electrochemical conditions. These layers were studied by X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) without any exposure to the laboratory atmosphere during the specimen transfer from the electrolyte to the ultrahigh vacuum. The presence of aluminum reduces the active dissolution of the alloys in weakly acidic electrolytes such as phthalate buffer. This leads to lower anodic current densities compared to pure iron. The passive layer thickness due to the preparation conditions varies from 3 to 6 nm. Both components (Al and Fe) enter the passive layer, but Al is significantly enriched. XPS and especially ISS depth profiles show an Al concentration maximum at a depth of 2 nm which is roughly in the center of the passive layer. Apparently the passive film is a mixed oxide with a pronounced concentration gradient of both cationic species. Galvanostatic reduction and dissolution of the passive layers in combination with XPS permits the determination of an electrochemical depth profile which confirms the results of the sputter depth profiles. A clearly separated sublayer structure of different oxidation states [Fe(II) and Fe(III)] was only found in the passive layers on pure iron. Its existence in the passive layers on Fe/Al alloys could not be confirmed. The preparation parameters, especially the passivation time. cause changes in the concentration gradients. Closer examinations of these effects by time-resolved measurements provide kinetic information on the growth and chemical changes of the passive layer. A model describing the observed effects during the layer formation is presented.

• Sponsoring Organization: USDOE
• OSTI ID: 99613
• Journal Information: Journal of the Electrochemical Society, Journal Name: Journal of the Electrochemical Society Journal Issue: 7 Vol. 142; ISSN JESOAN; ISSN 0013-4651
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM ALLOYS
ALUMINIUM OXIDES
ELECTROCHEMICAL CORROSION
IRON BASE ALLOYS
IRON OXIDES
MATHEMATICAL MODELS
MECHANICAL STRUCTURES
PASSIVATION
SURFACE PROPERTIES
THICKNESS