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Nucleation and growth of anodic oxide films on bismuth—I. Cyclic voltammetry

✍ Scribed by D.E. Williams; G.A. Wright

Publisher
Elsevier Science
Year
1976
Tongue
English
Weight
597 KB
Volume
21
Category
Article
ISSN
0013-4686

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✦ Synopsis

The early stages in the formation of a continuous anodic layer of bismuth oxide on a solid bismuth electrode, in the pH range 5-14, were studied. The oxide covered the surface by the simultaneous thickening and spreading of patches. The metal surface was classified into two different areas with different overvoltage for oxide nucleation . The ratio of the two areas varied according to the history of the surface .

The thickening of the newly formed layer (final thickness -20nm) followed the high-field growth law i = Amp(BE) where E is the field in the oxide layer, with B = (2 .0 ± 0 .5) x 10 -6 V -r cm. This value of B gives an activation distance for high-field ion transport of 0.2 nm, comparable to the radius of a lattice site and much smaller than that obtained previously, for much thicker films .

Dissolution of the film, giving breakdown of the oxide layer and pitting of the metal, occurred for pH a 8 . The thickness of the anodic film was thus limited to only 4 nor at pH 5 .

Cathodic reduction of the anodic oxide resulted in a porous metal surface . The current-voltage curve for the reduction often had a complex shape, which was related to the morphology of the original anodic layer-1. 1NTRODUMON

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