Effect of hydroxyl-containing additives on the codeposition of Cu–Zn–Sn alloys

Abstract

The electrodeposition of Cu–Zn–Sn ternary alloys on stainless steel from a cyanide-free alkaline electrolyte containing hydroxyethylidene diphosphonic acid (HEDP) was investigated. Four hydroxyl-containing additives, namely methanol (MET), ethylene glycol (EG), glycerol (GLY), and mannitol (MAN), were added to an HEDP bath, and the effects of the number of hydroxyl groups on the codeposition of Cu–Zn–Sn ternary alloys were compared. Cu–Zn–Sn codeposition occurred at − 0.53 Vvs.Hg|HgO. The hydroxyl-containing additives were beneficial to promote the codeposition of Cu–Zn–Sn, since they can complex with metal ions and act as auxiliary complexing agents. The scanning electron microscopy (SEM) analysis showed that the smallest grain size of 0.1 μm was obtained from the bath containing MAN. In addition to being smaller than the others, these coatings had uniform particle sizes. The energy-dispersive X-ray spectroscopy (EDS) analysis indicated that the composition of the Cu–Zn–Sn coatings obtained from the bath containing MAN was 73.293 wt% Cu, 26.079 wt% Zn, and 0.629 wt% Sn, and these coatings were golden in color. X-ray diffraction (XRD) showed that the Cu–Zn–Sn coatings were crystalline and were composed of a mixture of Cu, Zn, Cu5Zn8, Cu20Sn6, and Cu39Sn11 phases, indicating the formation of Cu–Zn–Sn ternary alloys. These results may provide theoretical guidance for an electrodeposition technology of Cu–Zn–Sn ternary alloys from a new cyanide-free alkaline electrolyte.