2019 Volume 60 Issue 2 Pages 297-305
Electrodeposition of a Zn–Zr oxide composite was performed under galvanostatic conditions from an unagitated sulfate solution containing Zn2+ and Zr ions, as well as additives, such as NO3− ions and polyethylene glycol (PEG), at pH 2 and 313 K. The effect of these additives on the codeposition of Zr oxide and its polarization behavior, as well as the microstructure of the deposits, was investigated. The Zr content in the deposits obtained at varying current densities increased significantly with the addition of 2.0 g·dm−3 of NaNO3. Zn–Zr oxide films deposited from the NaNO3-containing solution showed a massive structure composed of fine crystals without crystalline Zn platelets, although large cracks were observed between the large crystals. EDX analysis revealed that Zr codeposited on the massive crystals as a fine concave-convex oxide. The corrosion current density of the Zn–Zr oxide films deposited from the NaNO3-containing solution was almost the same as that of pure Zn deposits, showing that there is no improvement in corrosion resistance when Zn is codeposited with Zr oxide. Moreover, Zr content in the deposits obtained from the PEG-containing solution increased significantly along with increasing current density above 1000 A·m−2. With the addition of 1000 mg·dm−3 of PEG, the crystalline Zn platelets disappeared, and the deposits were instead composed of fine mesh-like crystals with a preferred orientation of the Zn plane, resulting in a smooth surface. The cathodic current density for the reduction of dissolved oxygen on the Zn–Zr oxide films deposited from the PEG-containing solution was smaller than that of the pure Zn deposits, and as a result, the corrosion current density of the Zn–Zr oxide films was smaller than that of the pure Zn deposits. The increase in Zr content in the deposits with NO3− ions and PEG is attributed to the acceleration of the hydrolysis of Zr ions.
This Paper was Originally Published in Japanese in J. Japan Inst. Metals 82 (2018) 366–374.