Electrodeposition of Nanocrystalline Zinc from Sulfate and Sulfate-Gluconate Electrolytes in the Presence of Additives

This study investigated electrodeposition of zinc from sulfate and sulfate-gluconate electrolytes in the presence and absence of additives such as Polyethylene glycol (PEG), hexadecyltrimethylammonium bromide (CTAB) and thiourea.Equilibrium distribution of zinc (II) species revealed that in both sulfate and sulfate-gluconate electrolytes, ZnSO 4 was the predominant species at the pH range of 1 to 6. Voltammetric analysis and potentiostatic experiments showed that although ZnSO 4 had higher concentration in both sulfate and sulfate-gluconate electrolytes, zinc-gluconate (Zn(GH 4 ) + ) species played a significant role in the reduction process.Due to strong effects of (Zn(GH 4 ) + ) species on the deposition process a negative shift in reduction potential and a decrease in zinc diffusion coefficient was observed.Effects of gluconate complex agent on the deposition of zinc was confirmed by evaluation of the surface morphology and the texture of electrodeposited zinc on mild steel substrate.Two distinct microstructures with different preferred orientations were produced from sulfate and sulfate-gluconate electrolytes under the same deposition conditions.Synergistic effects of additives resulted in the formation of zinc coatings with nano grain sizes for both sulfate and sulfate-gluconate electrolytes with the same preferred orientation.X-ray diffraction results indicated that the effects of ligands from which zinc deposition occurred became negligible in the presence of all additives.