Formation of Zirconium Oxide Film on Zr Substrate by Micro-Arc-Technology in Electrolytic Aqueous Solution

Abstract

The objective of this study was to form a polycrystalline oxide film on a Zr substrate using micro-arc-technology, and to identify the mechanism by which micro-arc occurs with valve metal. Polycrystalline oxide film was able to form on the Zr substrate. The polycrystalline oxide film generated on the Zr substrate had a mixed phase with tetragonal ZrO2, of which monoclinic ZrO2 was the main constituent. The choice of electrolytic aqueous solution for making micro-arc occur with Zr is wide in comparison with that in Al or Ti. The reason for this can be explained as follows: Among oxide films that consist of a two-layer structure, in Al and Ti, micro-arc occurs in the second layer due to the large resistance caused by anions mixed in the electrolytic aqueous solution. In Zr, micro-arc occurs in the first layer because the resistance of the first layer becomes large due to film thickness. Whether micro-arc occurs in the first layer or in the second layer of the valve metal depends on the value of the transport number of cation in the oxide film for the substrate metal.