Tin–zinc electrodeposition from sulphate–gluconate baths

The electrodeposition of tin–zinc alloys with 20–30% Zn by weight from sulphate–gluconate baths at pH 4 and different [Sn(II)], [Zn(II)] and [gluconate]/([Sn(II)]+[Zn(II)]) ratios was studied. The anodic stripping analysis of the deposits was correlated with their morphology, composition and phase structure. When [Zn(II)] is equal to or not much greater than [Sn(II)], a eutectic type Sn–Zn alloy is obtained, with a Zn content of around 20% by weight, which is greater than that of a thermal eutectic alloy. The morphology of the electrodeposited eutectic Sn–Zn alloy tends to disappear at high deposition charges and a second crystalline coating, richer in Sn, is obtained.