Effect of Chloride and Sulfate Ions on Electrodeposition and Surface Properties of Alloys Produced from Zinc-Nickel-Manganese Gluconate Baths

Abstract

Alloys were potentiostatically codeposited from gluconate baths containing zinc, nickel and manganese chlorides and/or sulfates. The electrodeposits were characterized in terms of their chemical (XRF, EDS) and phase (XRD, ASA) compositions, surface morphology (SEM), wettability (WCA, SFE) and corrosion resistance in neutral and acid media (linear polarization, immersion test). Morphology and composition of the alloys were mainly dependent on deposition potential, while effect of bath speciation was less emphasized. Multiphase ternary alloys were produced only at potentials more negative than −1.5 V (Ag/AgCl). Codeposition of the metals was anomalous and run according to instantaneous nucleation model, but at more electronegative potentials and in a presence of chloride ions transition progressive-instantaneous nucleation stages were observed. Comparison of surface wettability of as-plated and air-stored alloys showed improved (super)hydrophobicity caused by spontaneous oxidation of zinc-rich alloys. Surface free energies of the deposits were discussed. It was found that sulfate anions exhibited distinct effect on cathodic processes demonstrated by higher deposit masses, lower manganese percentages in the alloys, formation of more coarse and compact hydrophobic deposits of high corrosion resistance in neutral solution.