Passive film structure of supersaturated Al-Mo alloys

Reflection-extended X-ray absorption fine-structure spectroscopy has been used to probe the local atomic structure of the passive film of supersaturated Al--Mo alloys polarized in KCl. These alloys (with 7-11 at.% Mo) exhibit resistance to localized attack with an increase in the pitting potential o...

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Bibliographic Details
Published in:Journal of the Electrochemical Society 1991-11, Vol.138 (11), p.3194-3199
Main Authors: DAVIS, G. D, MOSHIER, W. C, LONG, G. G, BLACK, D. R
Format: Article
Language:English
Subjects:
360102 - Metals & Alloys- Structure & Phase Studies
400101 - Activation, Nuclear Reaction, Radiometric & Radiochemical Procedures
664200 - Spectra of Atoms & Molecules & their Interactions with Photons- (1992-)
664400 - Experimentally Derived Information on Atomic & Molecular Properties- (1992-)
ALLOYS
ALUMINIUM ALLOYS
Applied sciences
ATOMIC AND MOLECULAR PHYSICS
CHEMICAL REACTIONS
CORROSION
CRYSTAL STRUCTURE
ELECTRON SPECTROSCOPY
Electronics
Exact sciences and technology
FINE STRUCTURE
INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
Materials
MATERIALS SCIENCE
MICROSTRUCTURE
MOLYBDENUM ALLOYS
PASSIVATION
PHOTOELECTRON SPECTROSCOPY
PITTING CORROSION
SPECTRA
SPECTROSCOPY
THIN FILMS
X-RAY SPECTRA
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Summary:Reflection-extended X-ray absorption fine-structure spectroscopy has been used to probe the local atomic structure of the passive film of supersaturated Al--Mo alloys polarized in KCl. These alloys (with 7-11 at.% Mo) exhibit resistance to localized attack with an increase in the pitting potential of approx 600 mV relative to pure Al. Measurements show that the structure of the Al--Mo passive films resembles that of alpha -Al sub 2 O sub 3 /AlOOH, whereas an oxide film grown on pure Al in tartaric acid, which does not possess enhanced passivity, is more like gamma -Al sub 2 O sub 3 /AlOOH. Complementary X-ray photoelectron spectroscopy measurements indicate the Al--Mo passive film composition to be near that of AlOOH and the tartaric-acid film to be Al sub 2 O sub 3 . Because corundum ( alpha -Al sub 2 O sub 3 ) and diaspore ( alpha -AlOOH), which contain only octahedrally coordinated Al atoms, are very stable and inert while gamma -Al sub 2 O sub 3 , which contains both octahedral and tetrahedral sites, is reactive, the change in structure of the passive film suggests that improved passivity may be correlated with a reduction in the density of tetrahedrally coordinated atoms. This structural change likely results from the incorporation of oxidized Mo into the passive film; only as this Mo is hydrated with a presumed change in local structure does the alloy pit.
ISSN:0013-4651
1945-7111
DOI:10.1149/1.2085392