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Electrochemical, ellipsometrical and surface analytical investigations of passive layers on binary Fe/Al alloys
Author(s) -
Schaepers Dirk,
Strehblow HansHenning,
Künzelmann Ulrich,
Schwarz Yvonne
Publication year - 1994
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.740210604
Subject(s) - x ray photoelectron spectroscopy , dielectric spectroscopy , analytical chemistry (journal) , ellipsometry , dissolution , alloy , electrochemistry , aluminium , materials science , oxide , chemistry , thin film , electrode , metallurgy , chemical engineering , nanotechnology , chromatography , engineering
X‐ray photoelectron spectroscopy, ISS, ellipsometry, electrochemical impedance spectroscopy and electrochemical methods have been used to investigate the passive layers (PAL) on iron/aluminium alloys with low contents of Al (2 up to 12 wt.%). Ellipsometric measurements were performed during the galvanostatic reduction of PAL formed on Fe/8Al in 0.5 M Na 2 SO 4 /H 2 SO 4 (pH 3.85) at various potentials. Combining the results of ellipsometric singlelayer model evaluations and of the electrochemical reduction curves it was found that the outer part of the PAL mainly consists of the relatively stable γ‐Fe 2 O 3 . Its fraction to the overall thickness of the PAL gives a maximum value when the alloy is passivated at +1 V SHE . At higher potentials, porous films with both decreasing capacities and polarization resistances, measured by impedance spectroscopy, are formed. The XPS and ISS sputter depth profiles of PAL on Fe4/12Al formed in phthalate buffer (pH 5) at +1 V SHE showed an Al enrichment in the centre of the layers. The reductive dissolution of the passive layer in close combination with XPS analysis at distinct states of this process yields similar depth profiles. These results suggest the formation of mixed Fe/Al oxides or oxide compounds.