Zinc-Cobalt alloy electrodeposition and characterisation

Abstract

Zinc-Cobalt electrodeposits offer enhanced corrosion protection to steel, compared to zinc deposits. A near neutral zinc-cobalt alloy sulfate bath was developed. In the absence of b-naphthol and sodium lauryl sulfate (SLS), only a light grey and non-uniform deposit was obtained. Addition of boric acid yielded a grey and uniform deposit. To obtain the grey uniform alloy deposit, the optimum bath composition was: 0.5 M ZnSO4, 0.5 M CoSO4, 40 g/L H3BO3, 0.865 g/L SLS and 0.345 b-naphthol. The current efficiency for alloy deposition was 50% in the current density range 0.5-2.5 A/dm2. X-ray fluorescene studies on the alloy deposit formed on steel revealed 58-75% zinc on the surface. Anodic stripping voltammetris studies were carried out on zinc-cobalt alloy films formed on glassy carbon to identify the phases formed in the alloy. Zn-Co alloy film dissolution peaks suggested the existence of b, b1 and r phases of the alloy