Codeposition Behavior of Impurity during Electrogalvanizing in Sulfate Bath in the Presence of Fe Ions

Abstract

The codeposition behavior of impurity Fe with Zn was investigated galvanostatically over the current density range from 1 to 1000 A/m² at 40°C in zinc sulfate solution of pH 3 containing 5000 ppm of Fe²⁺ and the other organic or inorganic impurity. Fe hardly codeposited with Zn in the solution containing both Fe and Mo or Ni as impurity. The codeposition of Fe seems to be strongly suppressed in the presence of Zn²⁺ ions due to the adsorption of Zn hydroxide preferentially formed on the cathode. However, in the solution containing Fe and Cu, Fe evidently codeposited with Zn. The Fe content in deposit decreased with increasing the current density. The role of codeposited Cu is considered to promote Fe deposition by providing an active sites free from adsorbed Zn hydroxide. On the other hand, in the solution containing Fe and stearyle benzyl ammonium chloride (C18-Benzyl) as impurities, the codeposition of Fe was significantly recognized. The cathode potential for Zn deposition was greatly polarized by addition of C18-Benzyl and the Fe content in deposit increased with increasing the current density.