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

Electrodeposition of Zn-Zr oxide composite from an unagitated sulfate solution containing Zn²⁺ and Zr ions was investigated at pH 1-2 and at 313 K under galvanostatic conditions. The Zr content was higher in deposits formed from the solution at pH 2 than in those formed from the solution at pH 1 and initially decreased with increasing current density; however, when the current density was increased further, the Zr content in the deposits increased. This increase in Zr content was attributed to the acceleration of the hydrolysis of Zr ions by an increase in hydrogen evolution in the solution in the vicinity of cathode. In solutions containing Zr ions, Zn deposition was substantially polarized because of the electric resistance of film of the Zr oxide formed by the hydrolysis of Zr ions. The pH in the vicinity of the cathode, as measured using an Sb microelectrode, was approximately 2.2, which is similar to the critical pH for the formation of ZrO₂. Scanning electron microscopy and energy-dispersive X-ray spectroscopy point analysis of the deposits revealed that granular Zr oxide was deposited at the surfaces of the Zn platelet crystals and in the voids between the crystals. Polarization curves in 3 mass% NaCl solution revealed that the corrosion potential of the deposited Zn-1.1 mass% Zr oxide films was more noble than that of Zn films and that the corrosion current density of the Zn-1.1 mass% Zr oxide films was lower than that of Zn films.