Codeposition Behavior of Impurities during Electrogalvanization in Sulfate Baths in the Presence of Fe Ions

Abstract

The codeposition behavior of impurity Fe with Zn was investigated galvanostatically over the current density range 1–1000 A/m² at 40°C in zinc sulfate solutions of pH 3 containing 5000 ppm of Fe²⁺ and other organic or inorganic impurities. Fe showed hardly any codeposition with Zn in solutions containing Fe and either Mo or Ni as impurities. The codeposition of Fe is strongly suppressed in the presence of Zn²⁺ ions through preferential adsorption of Zn hydroxide on the cathode. In solutions containing Fe and Cu, Fe codeposited with Zn and the Fe content in the deposit decreased with increasing current density. Codeposited Cu promotes Fe deposition by providing active sites that are free of adsorbed Zn hydroxide. In solutions containing Fe and benzyl(dimethyl)(stearyl)ammonium chloride (C18-Benzyl) as an impurity, significant amounts of Fe were codeposited. The cathode potential for Zn deposition was greatly polarized by addition of C18-Benzyl, and the Fe content in deposits increased with increasing current density.