The anodic oxidation of superimposed metallic layers: theory

• Published in: Electrochimica acta 1980-11, Vol.25 (11), p.1423-1437
• Main Author: Pringle, J.P.S.
• Format: Article
• Language: English
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/0013-4686(80)87157-X

The anodic oxidation of one metal superimposed upon another is governed by several factors, the most important being the resistivity difference between the two oxides. When the oxide of the superimposed metal is the less resistive, the metal order is conserved, the oxygen order is conserved, and the final voltage under constant current conditions is just the sum of the component potentials across the two oxide layers. When the superimposed oxide is the more resistive, however, fingers of the substrate oxide force their way through it after the manner of the Rayleigh-Taylor effect in superimposed liquid layers; the metal order is then partially inverted, the oxygen order likewise, and the final voltage is less than the sum of the components. These phenomena, however, will be modified by the effects of transport number, relative metal migration rate, oxide structure and Pilling-Bedworth ratio; the nature and possible interactions of these factors are discussed. Experimental evidence on the anodization of superimposed layers is then reviewed, and all observations can be accounted for.