Galvanic corrosion of electroplated nickel coupled electrodes in chloride and sulphate solutions

ABSTRACT

The free corrosion potential of the as-plated pure nickel [P-Ni], semi bright nickel [SB-Ni], bright nickel [B-Ni] and dispersed nickel [D-Ni] electrodes were measured in 5 percent NaCl and in 6 percent Na[2]SO[4] solutions. It has been found that there are a potential difference in the free corrosion potential of these electrodes when they are immersed in chloride or sulphate solution. The galvanic current and the coupled potential [mixed potential] for the couples of different as-plated nickel electrodes were determined in chloride and sulphate solutions. The value of the galvanic current depended on the mixed potential, type of nickel couples as well as on the solution type. SEM observation confirmed the presence of pitting corrosion attack on the more active member of the as-plated nickel couples in chloride solution. Impedance spectroscopy of as-plated nickel electrodes in chloride and sulphate solution under potentiostatic showed that the charge transfer resistance of the as-plated nickel electrodes indicated the presence of pitting corrosion attack in chloride solution while passivation occurred on the electrodes in the sulphate solution