アルカリジンケート浴からの Zn − Ni 合金電析挙動に及ぼすエピクロルヒドリン−イミダゾール反応物の影響

Electrodeposition of Zn-Ni alloy was performed on a Cu electrode at a current density of 10-5000 A·m⁻² and a charge of 5 × 10⁴ C·m⁻² in an unagitated zincate solution at 293 K containing the reaction product of epichlorohydrin and imidazole as brightener. The effect of brightener on the deposition behavior of Zn-Ni alloy was investigated. The transfer current density at which the deposition behavior shifts from the normal type to anomalous was 50 to 100 A·m⁻² in brightener-free solution, while it became 10 to 20 A·m⁻² with an addition of brightener, indicating that the brightener greatly decreased the transfer current density. The transfer current density corresponded to the current density at which the potential of total polarization curve significantly shifted from the more noble region than the equilibrium potential of Zn to less noble region. With an addition of brightener, the decrease in transfer current density is attributed to suppression of hydrogen evolution, and the current efficiency for alloy deposition at high current density region decreased due to suppression of both Zn and Ni deposition. The Ni content of deposited films decreased with brightener, indicating that Ni deposition was more suppressed with brightener. With increasing current density, the crystals of films deposited from the solution containing brightener became smooth and showed the significant brightness. The oxidation reaction of films deposited from the solution containing brightener is suppressed, as a result, the corrosion potential shifted to noble direction.