Electrodeposition of Zn Alloys with Cu and Sn from Citrate Electrolytes

Abstract

The effect of Zn concentration on the electrodeposition of Zn, CuZn, SnZn, and CuSnZn was investigated using an upside down rotating disk electrode at pH 2. At a constant potential the alloys were both Cu- or Sn-rich at low Zn(II) ion electrolyte concentration and then jumped to Zn-rich at higher Zn (II) ion electrolyte concentration. The effect of codepositing Zn with Cu (or Sn) on the reaction order of Zn was studied by varying the Zn concentration in the electrolyte. A first order reaction order of Zn was found when Zn was singly deposited, but to capture the influence of the alloys the solid state activity was found to play an important role in the Tafel rate expression. When all three elements were present in the electrolyte at equimolar concentration the amount of Zn was between 18 - 44 wt %, in contrast to the upper and lower limits found with the binary alloys.