The Effects of Halides on Copper Deposition in the Presence of Gelatin

Abstract

In the electrodeposition of copper from acid copper sulfate electrolytes, the steady state cathode polarization was found to be independent of initial surface in the presence of 25 mg/l of gelatin and higher. Chloride, bromide, and iodide ions in presence of gelatin yielded polarization‐halide concentration curves with minima, while fluoride ions had no effect. These minima were independent of acid concentration and shifted to higher halide concentrations and higher polarization with increase in current density or gelatin concentration. An increase in temperature shifted the minimum of the polarization‐chloride concentration curve to lower values. The general trends in polarization with changes in halide concentration were shown to be independent of the method of measurement and the geometry of the cells. Excess weights (i.e., weight of deposit in excess of that obtained in a coulometer in series with pure copper sulfate electrolyte) increased to constant values with increasing chloride concentration. The gelatin content of the deposits was constant over a large range of chloride concentrations, while the chloride content passed through a maximum. The various observations have been explained on the basis of formation of crystal imperfections on the cathode by the halides, in conjunction with addition agent effects of gelatin and cuprous halide.