Collect. Czech. Chem. Commun. 1992, 57, 2321-2330

Nature and Stability of Oxide Films Formed on Niobium in Acid Bromide Solution

Ahmed G. Gad Allah, Ali M. Bekheet, Said S. El-Egamy and Mohamed S. El-Basiouny

Department of Chemistry, Faculty of Science, Cairo University, Giza, Egypt


The formation and stability of the anodic oxide films formed on niobium in acid bromide solutions were studied using polarization and impedance measurements. The charging curves in all concentrations display the same general trend. The steady-state potential was found to depend on HBr concentration. The efficiency of oxide building is diminished owing to preferential adsorption of Br- ions on the oxide surface acting as depolarizer for the main anodic process. The dissolution behaviour of the anodized oxide niobium films is duplex in nature. The outer layer becomes more liable to dissolution with increasing film thickness or formation voltage. Also, the properties of the surface oxide film are greatly influenced by HBr concentration.