Studies of phase composition of Zn-Ni alloy obtained in acetate-chloride electrolyte by using XRD and potentiodynamic stripping

The phase composition of Zn-Ni alloy electrodeposited in acetate-chloride electrolyte has been studied as a function of ZnCl2 concentration and cathodic current density (i(c)) by the potentiodynamic stripping and XRD methods. It appeared to be dependent only on the Zn/Ni ratio in the alloy, irrespective of whether the result was attained by varying the cathodic current density or by changing the [Zn2+]/[Ni2+] ratio in electrolyte. A Zn-Ni alloy dissolving in the potential range of i(a) peak D can be obtained by the method of cyclic voltammetry. This phase is a compact black coating. It has been determined by potentiodynamic stripping that pure Ni oxidizes only in the range of positive potentials, while Zn-Ni alloy containing some quantity of Zn oxidizes in the range of negative potentials. It was determined that the preciser data of potentiodynamic stripping were obtained in electrolyte containing Cl- ions. Zn-Ni alloy can be chromated only in the case when the eta-phase makes up a sufficiently large portion of Zn-Ni alloy. (C) 2004 Elsevier Ltd. All rights reserved.