EN
The anodic oxide films were prepared on the niobium and tantalum in aqueous electrolyte mixtures containing 1 M CH₃COOH + 1 M H₃PO₄ or 1 M CH₃COOH + 1 vol.% HF or 1 M CH₃COOH + 1 M H₃PO₄ + 1 vol.% HF at 30 V for 30 min. The barrier films were obtained on both niobium and tantalum surfaces in all electrolyte mixtures except niobium oxide film formed in 1 M CH₃COOH + 1 vol.% HF which is porous in nature. The anodic oxide films were characterized by FESEM. Also, electrochemical impedance spectroscopy at open-circuit potential on Nb and Ta was applied and obtained data were analyzed by fitting with four different equivalent circuits.