The investigation of electronic conduction processes in anodic tantalum oxide films with electrolytic and solid contacts is generally hampered by parallel ionic conductivity at high fields and the uncertain contributions of flaws, even in the case of high‐purity materials. We found that electronic conductivity could be induced reproducibly and with homogeneous current densities in the presence of thin layers of semiconducting oxides, such as
Fe2O3
and
MnO2
which were deposited by reactive sputtering. Experiments were carried out with electrolyte contact. The electronic current was found to follow
logi normalprop.V½
in a wide range of current densities. A Poole‐Frenkel mechanism is proposed in which the current is controlled by thermionic emission at the
Ta2O5/normalMeO
‐interface. Electronic conductivity increases as a time dependent activation process lowers the emission barrier through ionic interface polarization. The contribution of flaws to the electronic conductivity was investigated by means of the anodic printing technique. The electronic current resulting from the activation process was found to be of uniform density and unrelated to any physical flaws in the anodic tantalum oxide.
The conditions under which anodic oxide films on tantalum showed electronic conductivity were studied using an electrochemical printing‐out technique with starch‐iodide as the redox indicator. The sensitivity for the detection of electronic charge was approximately 1 millicoulomb/cm2. The effect of alloying (contamination), thermal oxidation, plastic deformation, and surface topography were investigated with regard to their contribution to the electronic conductivity of anodic oxide films on mechanically treated (“rough”) tantalum surfaces. It was concluded that impurities alone were responsible for the electronic conductivity even in cases where supposedly clean tantalum had been abraded with tantalum. Roughness by itself was not a sufficient condition for electronic conductivity.
A printing method using iodide-starch as the redox indicator in a solidified electrolyte was developed for applications to various valve metals and their anodic oxide films. It was used to study the electronic conductivity of anodic oxide films on tantalum and niobium and to detect defective sites in oxide films on aluminum. Applied to titanium, zirconium, and silicon, as well as the other valve metals, the technique was used for an evaluation of the surface condition of the metal substrates. The technique also was useful in cases where the oxide films corroded under the influence of the printing electrolyte.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.210.126.199 Downloaded on 2015-06-18 to IP
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