Codeposition of Zinc and Copper in Gluconate-Sulfate Solutions

• Published in: Journal of the Electrochemical Society 2013-01, Vol.160 (10), p.D428-D433
• Main Authors: Survila, Arvydas, Mockus, Zenius, Kanapeckaitė, Stasė, Stalnionis, Giedrius, Juškėnas, Remigijus, Jasulaitienė, Vitalija
• Format: Article
• Language: English
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/2.005310jes

RDE voltammetry combined with SEM, EDS, XPS and XRD measurements was applied to study partial and net processes occurring in Cu(II) and Zn(II) gluconate solutions containing an excess of sulfate. Optimal plating baths contain sufficiently high gluconate concentrations ranging up to 0.1 M. To suppress hydrogen evolution, weakly acid or neutral media should be created. Compact brass coatings containing ∼10-40% of Zn can be obtained over a fairly wide potential region (-0.97 < E -0.6 V) where the current efficiency ranges from 80 to 100%. At -0.86 < E -0.6 V, the underpotential deposition of zinc is observed. Brass coatings obtained at -0.9 < E < -0.7 V contain two main phases: α-CuZn and pure Cu. The former phase is homogeneous and shows large-scale crystallites, whereas the pure Cu phase is nearly nanocrystalline. At a higher cathodic polarization, extra ɛ and γ phases are also formed. Besides, an admixture of ZnO (∼3 at%) was detected in the coatings. Codeposition of copper and zinc is accompanied by chemisorption of gluconate with its further partial destruction and incorporation of ligand fragments into the deposits. The molar ratio of carbon and oxygen in the coatings was found to be approximately the same as that in gluconic acid.