Electrodeposition of ZnNi Alloys from Ethylene Glycol for Corrosion Protection

Zn rich ZnNi alloys electrodeposition have recently attracted the attention of researchers due to their interesting corrosion properties [1]. In particular, alloys containing Ni in the 15 - 25 % range find application in a number of industrial fields, like automotive and constructions. ZnNi is normally electrodeposited from aqueous solutions, in which plating takes place following a typical anomalous mechanism [2]. In the last few years, however, new deposition approaches have been attempted to improve ZnNi plating performances. Specifically, III generation deep eutectic solvents comprising choline chloride have been tested [3]. The present work investigates the use of non-aqueous ethylene glycol based electrolytes for the deposition of Zn rich ZnNi alloys. The use of ethylene glycol as solvent introduces many advantages with respect to aqueous solutions: low oxygen contamination, high deposits purity and no pH dependance [4]. ZnNi codeposition was studied employing cyclic voltammetry and layers were deposited under potentiostatic control. Deposition potential was varied and its influence on final composition and morphology was determined. Addition of an additive (NH 4 Cl) to enhance surface morphology was attempted as well [3]. Phase composition was investigated using XRD to determine the possible presence of a metastable γ-ZnNi phase, which has already been observed in the case of ZnNi plated from alkaline aqueous solution [5]. Finally, corrosion behavior of layers obtained from ethylene glycol was assessed and compared with equivalent coatings deposited from commercial aqueous solutions. [1] M. Gavrila et al.; Surface and Coatings Technology, 123 (2-3), 164-172 (2000) [2] G. Roventi et al.; Journal of Applied Electrochemistry 30 (2), 173–179 (2000) [3] S Fashu et al.; Transactions of Nonferrous Metals Society of China 25 (6), 2054-2064 (2015) [4] G. Panzeri et al.; Electrochimica Acta 271 (1), 576-581 (2018) [5] S. Ieffa et al.; Transactions of the IMF 94, 321-324 (2014)