Ni Alloy Electrodeposition Research Articles

Study of initial layer formation of Zn–Ni alloy electrodeposition by in situ ellipsometry

Initial layers of Zn, Ni, and Zn–Ni alloy electrodeposition on Au electrode in sulfate baths are detected in a nm thickness range by in situ ellipsometry. The thin layer deposits are also analyzed by Auger electron spectroscopy (AES), and ICP atomic emission spectroscopy. The preferential deposition of Zn, in the initial thin layer of Zn–Ni alloy deposition, is confirmed by the analysis. From the ellipsometric measurements, the underpotential deposition (UPD) of Zn is observed; i.e. the Zn deposition starts at a potential more positive by 0.5 V than the redox potential of Zn 2+ /Zn, while noticeable UPD of Ni cannot be observed. For Zn–Ni alloy deposition, the thin layer of Zn formed in the UPD potential region greatly inhibits the Ni deposition. It is speculated that the preferential Zn deposition in Zn–Ni alloy electroplating is caused by the inhibition of Ni nuclei growth due to a thin layer of Zn on the deposited Zn–Ni alloy.

Nature of the passive film formed at a zinc anode in zinc–nickel containing solutions

Abstract The main aim of this study was to obtain information about the nature of the passive film formed on the zinc anode surface in Ni-containing solutions by chronopotentiometry, SEM, X-ray microanalysis, XPS and SIMS. It was shown that, with an external anodic current, passive film formation was a result of space-sharing anodic and cathodic reactions due to local Ni or Zn–Ni alloy electrodeposition. As a result, a film of two layers was formed on the Zn anode: Zn substrate|2Ni x Zn ( x >1)+Zn(OH) 2 |NiZn+Zn(OH) 2 . At the rest potential a one-layer film was formed consisting of Zn substrate|2Ni 2 Zn+Zn(OH) 2 .

Hydrogen Permeation Inhibition by Thin Layer Zn–Ni Alloy Electrodeposition

The inhibition of hydrogen permeation by zinc-nickel electrodeposited alloy was investigated using the Devanathan–Stachurski permeation technique. The hydrogen evolution and hydrogen permeation rates for the zinc–nickel alloy electrodeposits on iron are compared with the rates for bare iron, zinc electroplated on iron, and nickel electroplated on iron. Hydrogen evolution rates and hydrogen permeation rates were followed as functions of time at different applied potentials. The hydrogen permeation inhibition for thin zinc–nickel electroplates (20s at 10mAcm−2 and 10s at 20mAcm−2) averaged 80% and intermediate to that of nickel and zinc. This inhibition was considered to be mostly due to kinetic effects. Zinc–nickel electroplated for 20 and 40min. at 10mAcm−2 inhibited the hydrogen permeation greater than 95% as compared to bare iron. This inhibition was due to both kinetics and the barrier effect caused by the diffusion resistance of the membrane.

The effects of substrate material on the microstructure of pulse-plated Zn–Ni alloys

The effect of substrate material on the microstructure (surface morphology, phases present and preferred orientation) and chemical composition of Zn–Ni alloy electrodeposits, produced from a chloride-based electrolyte using the square-wave pulse-plating technique, has been investigated. Steel and commercial-purity, cold-rolled copper substrates were considered. The results indicated that changing from a steel to copper substrate does not have a significant influence on the deposit characteristics, except for the variations in the chemical composition. These variations were attributed to a number of factors including; (1) the different initial electrode potential (open circuit potential); (2) differences in cell voltages due to different electrical resistivity of the two metals; and (3) possibly to surface energy considerations. Because of the similar microstructure obtained, these coatings should have similar properties.