Electrodeposition of Zn-Zr oxide composite from dispersed particles-free solution

Electrodeposition of Zn-Zr oxide composite was examined from an unagitated sulfate solution containing Zn²⁺ and Zr ions at pH 1 to 2 and 313 K under galvanostatic conditions. Zr content in deposits was higher in pH 2 than that in pH 1, and decreased for the moment with increasing current density, but the further increase in current density brought about the increase in Zr content in deposits. This increase in Zr content in deposits is attributed to the acceleration of the hydrolysis of Zr ions by means of an increase in hydrogen evolution in the cathode layer. In solution containing Zr ions, Zn deposition was significantly polarized due to the film resistance of Zr oxide formed by the hydrolysis of Zr ions. The pH in the vicinity of the cathode, as measured by an Sb microelectrode, was approximately 2.2, which is close to the critical pH for the formation of ZrO₂. SEM and EDX point analysis of deposits revealed that the granular Zr oxide deposited at the surface of Zn platelet crystals and at the void between the Zn platelet crystals. It was found from the polarization curves in 3 mass% NaCl solution that the corrosion potential of deposited Zn-1.1 mass% Zr oxide films was more noble than that of pure Zn, and the corrosion current density of Zn-1.1 mass% Zr oxide films was lower than that of pure Zn.