Some peculiarities in the codeposition of zinc-nickel alloys

The electrodeposition of zinc-nickel alloys from ammonium chloride baths wa s studied at intermediate current densities, where some peculiarities were observed both during the deposition and during the oxidation of the alloys. In this interval, although the whole deposit had a composition correspondi ng to ct-phase zinc-nickel alloy, electrochemical and surface analyses indi cated that the deposition took place with the formation of two structures: a first nickel-like crystalline deposit followed by a second-stage typical a-phase microcrystalline structure deposit. The high hydrogen evolution on this second deposit promoted the inclusion of zinc oxidized species on the coating. During the potentiodynamic oxidation of the alloys obtained at the se current densities, a reduction process was observed that was attributed to the deposition of the ct-phase together with hydrogen evolution. (C) 200 1 Elsevier Science Ltd. All rights reserved.