Synergistic effect of ninhydrin and iodide ions during electrodeposition of zinc at steel electrodes

• Synergistic effect between Nin and I− ions was observed during deposition of zinc.
• CV and i/E measurements showed that the additives increased the nucleation potential.
• Adsorption of additives on cathode surface during zinc deposition obeys Langmuir isotherm.
• The initial nucleation of zinc on steel followed the model of 3D instantaneous nucleation.
• TP and TI improved in the presence of either Nin and/or I− ions in a synergistic way.

The addition of Nin and /or iodide ions to the sulfate bath for zinc electrodeposition onto steel substrates has been examined as a possible means of improving the quality and uniformity of deposit distribution. The investigation was carried out using potentiodynamic polarization, cyclic voltammetry and anodic linear stripping voltammetry techniques, complemented with XRD analysis and SEM measurements. The synergistic effect between Nin and iodide ions is proved using the data obtained from the polarization curves, throwing power, throwing index, Wagner number, cyclic voltammetry and anodic stripping voltammetry. On the other hand, addition of Nin or iodide ions increases the TP% by about five times, however, addition of the combination of both of them increases TP% by more than seven times. The inhibition of zinc reduction in the presence of Nin and/or iodide ions was assumed to occur via adsorption which followed the Langmuir adsorption isotherm. The initial nucleation and growth of zinc on steel followed the model of 3D instantaneous nucleation.