Electrodeposition of tin-zinc-bismuth alloys from aqueous citrate-EDTA baths

Abstract

Sn–Zn–Bi alloys layers were, for the first time, successfully produced by electrodeposition from stable and homogeneous aqueous electrolytes based on citric (Cit) and ethylenediaminetetraacetic (EDTA) acids. The optimal conditions for electrodeposition of Sn–Zn–Bi alloys from Cit-EDTA baths are in the narrow pH range of between 3.5 and 4.5. The possible process of the Bi(III) complexes reduction by Sn(II) complexes is inhibited by the specific structure of the Bi(III) complex with EDTA, which ensures the kinetic stability of the bath. Cyclic voltammetry with rotating disc electrode and construction of partial polarization curves, based on potentiostatic deposition in coulostatic conditions, allowed to determine the mechanism of co-deposition of Sn, Zn, and Bi. The achievable tin contents in the electrolytic layers are in the range of approx. 50 to 100 wt%, zinc in the range up to approx. 40 wt%, and bismuth in the range up to 12 wt%, with current efficiency of the electrodeposition process up to 95%.