Corrosion Behaviour of Various Nickel Layers Electroplated from Watts Bath

Abstract

Three layers of semibright nickel (SB–Ni), bright nickel (B–Ni) and dispersed SiO₂-containing nickel (D–Ni) have been prepared from a Watts electroplating bath with some organic additives. The influence of the bath additives on the free corrosion potential of each as-plated nickel layer have been examined in 5 mass% NaCl and 6 mass% Na₂SO₄ solutions. Exposure time in the air after nickel layer preparation assisted more oxide film formation on semi-bright than on bright nickel surfaces. The anodic and cathodic polarization curves of as-plated nickel layers in chloride and sulphate solutions were investigated by using the potentiodynamic technique. In the chloride solution, all of these nickel layers exhibited pitting corrosion and the critical pitting potential, E_pit, shifts less noble in the order: D–Ni>B–Ni>SB–Ni, while in the sulphate solution the nickel layers were passivated.