Galvanostatic Oxidation of Nickel in Borate Buffer Solution

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Abstract
Anodic oxide films formed on nickel in pH 7.65 borate buffer solution in both the passive potential and oxygen evolution regions have been analyzed by RHEED, Auger spectroscopy (in conjunction with argon ion sputtering), and O x‐ray emission spectroscopy. In the passive potential region, a highly epitaxed, single crystal film is formed with a limiting thickness of ∼12Å. In this potential range, even very long times of anodizing do not alter the oxide epitaxy or increase its thickness. In contrast, polarization in the potential range where oxygen is evolved results in the development of considerable oxide misorientation and a significant increase in oxide thickness. While long times of polarization (>20 hr) in this potential region produce oxide films hundreds of angstroms thick, the current efficiency for oxide growth is <1%. These thick anodic oxide films are quite different from thermally prepared, compact films of and appear to have an open‐cellular, sponge‐like structure with an oxygen:nickel ratio approaching 1.3. This oxide probably forms by a direct oxidation rather than a dissolution/precipitation reaction.
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