Barrel electroplating of Zn-Ni alloy coatings from a modified deep eutectic solvent

ABSTRACT

Here the authors report the electroplating of Zn-Ni alloy on mild steel components from a modified deep eutectic solvent (DES), Ethaline, through a combination of barrel-plating and pulse-plating processes. The Ethaline electrolyte, a eutectic mixture of choline chloride (ChCl) and ethylene glycol (EG), was modified with propylene carbonate (PC) as a co-solvent together with the addition of boric acid to control deposit morphology and to suit the barrel plating system. A coating of γ-phase Zn-Ni alloy with 12–16% Ni was formed uniformly on mild steel screws and small components and the coating performed well as a sacrificial anti-corrosion layer. These findings are reported as part of an Innovate UK funded collaboration between university and industry partners, and included here are also the results of a scale-up pilot demonstrator system installed at E.C. Williams Ltd. (UK). It is concluded that the barrel plating of components using these materials and methods is very effective on a medium-scale and that the specification and performance of the coating is comparable with that from aqueous media. However, further development of this process may be limited by low current efficiency and the high relative cost of DES media.

KEYWORDS:

• Deep eutectic solvent
• Zn-Ni coating
• barrel electroplating
• pulse electroplating
• scale-up

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

* Here the authors use the commercial, trivial names, Ethaline and Reline for DES electrolytes having the compositions ChCl:2Eg and ChCl:2Ur, respectively. Whilst these are the eutectic compositions, other compositions are also commonly used, for example ChCl:4Eg, which is designated Ethaline 400 (or E400).

* MgCl₂ was used here in preference to NaCl because it is more aggressive and yields a qualitative result more quickly.

Additional information

Funding

This project was co-funded by Innovate UK (project ref. #:74450-501442). We also gratefully acknowledge support from the Advanced Microscopy Facility, University of Leicester.