Zinc-nickel alloy whiskers electrodeposited from a sulfate bath

ZnNi alloy whiskers (20–50 μm) were grown from a sulfate bath by electrodeposition. The current density was 20–40 mA cm−2 and the pH was above 2. The structure of the whiskers was h.c.p. η-phase or cubic γ-phase. The Ni content in the whiskers was 2–7 wt.%, which was below that of the bath solution (8.5 wt.%), and anomalous co-deposition occurred. ZnO films covered the surface of the whiskers, but Zn(OH)2 films did not. When the oxide film disappeared, tip growth of the whiskers ceased, and granular particles (10–30 wt.% Ni) composed of η + γ phases deposited onto the surface of the whiskers; the electrodeposition mechanism changed from anomalous to normal co-deposition. When Ni2+ ions were not added to the sulfate solution, neither ZnO films nor whiskers were formed, and only Zn(OH)2 films grew. In order to grow ZnNi whiskers, ZnO films were necessary.