The influence of sulfate ions on the electrodeposition of Ni–Sn alloys from acidic chloride–gluconate baths

• Electrodeposition of Ni–Sn alloys from acidic gluconate baths is described.
• Effect of sulfate ions on the plating was studied.
• pH-dependent equilibrium distribution of species in all solutions was calculated.
• A nucleation model was identified.
• Correlation between phase composition and anodic stripping results was found.

Codeposition of nickel and tin from acidic gluconate baths of various compositions was investigated. It was found that cathodic process was seriously affected by sulfate ions resulting in lower nickel percentages in the deposits, changes in the phase composition as well as improved surface morphology of the alloys. Partial cathodic polarization curves have shown that tin ions were reduced under limiting current. Chronoamperometric studies indicated nucleation of the alloys according to the instantaneous mechanism. Anodic stripping analysis confirmed phase composition of the alloys – NiSn and Ni3Sn4 were formed in the chloride bath, while NiSn phase was produced in the presence of sulfate anions. It was accordant with thermodynamic predictions. Equilibrium speciation of the baths was also calculated.