Zinc dissolution in electrolytes containing nickel

The anodic dissolution of zinc RDE and passive film formation were studied in NH4Cl+ NICl2 and NH4Cl+ NiCl2 + ZnCl2 electrolytes at pH 5.5. A passivat ion process of the Zn electrode was observed in these Ni-containing solutio ns, which was a result of cathodic reactions of the Ni and/or Zn-Ni alloy e lectrodeposition and zn(OH)(2) precipitation. XPS data indicated that the o uter part of the film (the film/electrolyte interface) was almost exclusive ly zinc hydroxide, while the bulk film was a metallic matrix with constant composition (cr-Zn-Ni alloy) and it incorporated zinc oxidation products. T hese results indicated that the composition of the film obtained under anod ic polarization or in open circuit conditions was not the same. The zinc dissolution reaction in Ni-containing electrolytes was determined by a diffusion stage; at high rotation speeds the Zn dissolution reaction b ecame controlled by the slow removal of zinc-oxygen containing, which were formed both at the open circuit potential and at anodic polarization and al so by the diffusion of the dissolution products within pores. (C) 1999 Else vier Science Ltd. All rights reserved.