CORROSION BEHAVIOR OF VARIOUS NICKEL LAYERS ELECTROPLATED FROM WATTS BATH

Three layers of semibright nickel (SB-Ni), bright nickel (B-Ni) and di spersed 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 nicke l layer have been examined in 5 mass% NaCl and 6 mass% Na2SO4 solution s. Exposure time in the air after nickel layer preparation assisted mo re oxide film formation on semi-bright than on bright nickel surfaces. The anodic and cathodic polarization curves of as-plated nickel layer s in chloride and sulphate solutions were investigated by using the po tentiodynamic 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 th e sulphate solution the nickel layers were passivated.