Passive behaviour of zirconium

The title subject has been studied by quasi-steady and transient polarization measurements and dc capacitance determinations over potential from - 1 to 2 V (sce) in aqueous solutions of pH 0-13 at 250C. A few AES investigations of oxide films formed are also included. The quasi-steady data reveal an essentially potential and pH independent passive current and a superimposed current of oxygen evolution appearing already at rather low overvoltages for this reaction. The transients accord with the Cabrera-Mott equation and suggest charge transfer by Zr(IV) ions at sites of relatively fast responding field or current dependent density at the metal/oxide interface. The transient polarization fits with a value of about 1.5 A for the activation (half-jump) distance. The capacitance data largely satisfy a simple insular model, reveal the main charge distribution in the passive zirconium electrode, and combine with previous film thickness data to give about 28/r (r being the roughness factor) for the dielectric constant of the passive film. (author)