Abstract
The corrodability of thin oxide films formed on niobium either naturally or anodically was investigated in NaOH solutions of different concentrations (0.05–3.0 M) using impedance and potential measurements. Naturally formed films were found to thicken in NaOH solutions of concentrations ≤0.1 M, while they were subjected to dissolution in NaOH solutions of concentrations≥1.0 M. The dissolution behaviour of anodically formed oxide films on niobium was found to depend on the thickness and alkali concentration. Anodically formed thin films (≅4 nm resist dissolution in NaOH solutions of concentrations≤0.1 M, partially dissolve at [NaOH]≅0.5 and 1.0 M and are subject to aggressive dissolution at higher concentrations. Thick films (≅50 nm) resist dissolution at [NaOH]≤1.0 M, while they dissolve at higher alkali concentrations. The corrosion potential was found to depend on the alkali concentration and the oxide film thickness. The impedance of the oxide film was found to be purely capacitive and to increase with increasing film thickness.
Published Version
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