Codeposition of copper and tin from acid sulphate solutions containing gluconic acid

Abstract

RDE voltammetry, XPS and XRD techniques were applied to investigate the codeposition of copper and tin from acid gluconate solutions. Voltammograms contain two plateaus of limiting current of diffusive nature which obeys Levich equation. Underpotential deposition of tin occurs at potentials 0.3 V higher than the equilibrium potential of Sn|Sn(II) electrode. Cu–Sn deposits contain carbon and oxygen that prevail at the surface and are found in the deeper layers of coatings. Chemosorption of gluconic acid with its partial destruction is supposed to take place. Bright Cu–Sn coatings are obtained when the quantity of inclusions is sufficiently high. Cu–Sn coatings obtained in the UPD area consist of α phase or solid solution of tin in copper and a small amount of pure copper. The β-CuSn and δ-CuSn phases as well as a small amount of η phase were detected at −0.31 V. At a more negative potential (−0.4 V) Cu–Sn coatings contain the pure Sn phase, η phase and a small amount of β-CuSn.