Anodization of Metals Through Thin Solid Electrolyte Films of Calcia Stabilized Zirconia

Abstract

This paper shows that anodic oxidation of the metals Nb, Ta, and Al through thin solid electrolyte films of calcia stabilized zirconia (CSZ) is possible. The metal oxides grown are stoichiometric and the CSZ behaves like pure anodic oxide, since the electric field in CSZ in the 0.1–10 mA cm−2current density range is comparable with those in anodic oxides. Anodization of Nb|Ta|CSZ or Al|CSZ|Nb|Ta systems shows that only oxygen movements take place in CSZ during oxide growth (i.e., transport number of cations t+=0 ), while both oxygen and cations take part in ionic current in the metal oxides underlying and overlying the CSZ layer (i.e., t+≠0 ). Thus the transport number of cations can be considered as an intrinsic property of an oxide layer, independent of the nature and of the position of the other layers. Possible microscopic transport mechanisms for oxygen and cations through superimposed oxide films are discussed.

Space Charge Effects on the Growth of Anodic Oxide Films on Zirconium Metal

“…In the presen6e of a mobile space charge and then of'an increasing electric field at the opposite injecting interface (26,27), the previous suggestion should mean that the oxygen transport occurs via a vacancy-type mechanism. Such a mechanism has been suggested for calcia stabilized zirconia (CSZ) (32) as welI as for ZrOz anodic films. By using the relationship i ~ A exp BE and Tafel plots of Fig.…”