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Behaviour of copper and generation of oxygen during anodizing of Nb–Cu alloys
Author(s) -
Mato S.,
Skeldon P.,
Thompson G. E.,
Masheder D.,
Sproule G. I.,
Graham M. J.,
Habazaki H.,
Shimizu K.
Publication year - 2000
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 - 10.1002/1096-9918(200012)29:12<895::aid-sia944>3.0.co;2-w
Subject(s) - anodizing , copper , alloy , oxygen , metallurgy , materials science , anode , anodic oxidation , chemical engineering , chemistry , aluminium , electrode , organic chemistry , engineering
The anodic oxidation behaviour of two compositions of Nb–Cu alloy is examined with particular reference to the oxidation of copper at the alloy/film interface and the generation of oxygen within the anodic film. Anodizing of an Nb–3 at.% Cu alloy results in a uniform, niobia‐based anodic film, with copper species, which migrate faster than Nb 5+ ions, distributed throughout the film. The oxidation of copper proceeds without significant enrichment of copper in the alloy. Further, the film is free of bubbles of oxygen, which is not generated in significant amounts during film growth to relatively high voltages. In contrast, copious amounts of oxygen are generated during anodizing of an Nb–30 at.% Cu alloy, with the consequential development of a highly flawed anodic film of non‐uniform thickness. The oxygen is present mainly in numerous bubbles located within the niobia‐based film material. Bursting of the bubbles, with release of trapped oxygen, leads to a highly damaged film. The continuous generation of oxygen consumes much of the current and limits the anodizing voltage to a low value. The large‐scale generation of oxygen for the more concentrated alloy is suggested to be associated with the distribution of copper in the alloy, with copper having a tendency to form copper‐rich clusters, which are enhanced in size by an initial brief period of uniform film growth. Oxygen is then generated, probably following oxidation of such clusters. Copyright © 2000 John Wiley & Sons, Ltd.