ANODIC GROWTH OF PASSIVE FILMS ON ZIRCONIUM AND HAFNIUM

Galvanostatic potential-time curves on passive zirconium and hafnium electrodes are recorded and analysed in the light of the Cabrera-Mott equation and the high-field ion migration equation. For both metals, the kink-site density in the reacting metal surface (s) and the oxygen vacancy density in the passive film at the metal-oxide interface (No) appear to attain steady values which depend on the current density of metal oxidation (j) according to d log s/d log j ≈ 1/2 and d log No/d log j ≈ 3/4. Possible effects of space charge in the passive film are considered and found to be negligible under the conditions covered. Comparisons are made to the corresponding behaviour of some other passive metals and to the anodic dissolution of some active metals. © 1990.