Role of Glycine as a Complexing Agent in Nickel Electrodeposition from Acidic Sulphate Bath

Abstract

Bright nickel coatings on copper substrates were successfully produced by electrodeposition using acidic glycine complexing baths. The investigation was conducted using electronic spectroscopy, potentiodynamic cathodic polarization, cyclic voltammetry, in situ-anodic linear stripping voltammetry and chronoamperometry techniques complemented with XRD analysis and SEM measurements. Such kinetic parameters as Tafel slope, transfer coefficient and exchange current density obtained from Tafel plots indicated that glycine had an accelerating effect on Ni2+ electroreduction. In the glycine-containing bath, SEM analysis revealed finer grains together with the appearance of fine microcracks. The XRD analysis showed an increase in noncrystallinity with increasing glycine concentration. The initial nucleation and growth of nickel followed the model of 3D instantaneous nucleation. The corrosion behaviour of the nickel coatings was studied using both anodic potentiodynamic polarization and open circuit potential tests in 3.5% NaCl solution, and the results indicated that glycine decreased the corrosion resistance of nickel deposits. The throwing power, as well as the throwing index, in the presence of glycine is lower than that observed in the absence of glycine.