Anodic Oxidation of Tantalum in Formic Acid Electrolytes

Duplex films formed anodically on tantalum in formic acid and other organic electrolytes have both low capacity and low optical thickness per unit formation voltage. 1/c vs . curves show a "break point," values being lower at higher voltages. The film adjacent to the metal has the characteristics of normal and grows simultaneously with the outer more rapidly soluble film suggesting oxygen ion mobility in this outer film. Evidence from sequential formations in organic and aqueous electrolytes indicates also tantalum ion mobility and the growth of some new oxide in the pre‐existing outer layer. Conditions at the electrolyte interface may exert some control on the number of oxygen ions entering the film. Other anions influence the film structure which is thought to contain voids.