Copper Sulfate Electrolyte Research Articles

CYSTINE AS AN ADDITION AGENT IN THE ELECTRODEPOSITION OF COPPER

The steady state polarization of 100 mv. in acid copper sulphate electrolyte, at 2 amp./dm.2, appears to consist of 45 to 50 mv. activation overpotential to deposit aquo–copper complexes, 20 to 25 mv. concentration polarization, and about 30 mv. polarization due to hydrogen ion interference. The presence of cystine in the electrolyte gave rise to polarization–time curves similar to those observed previously with gelatine. The increase of polarization caused by cystine appears to be due to an obstructive effect of adsorbed cystine (or its copper complex), together with an increase of concentration polarization. Cystine alone probably does not affect the activation overpotential. Addition of sufficient chloride virtually eliminated the polarization due to obstruction by cystine, possibly by acting as an electron bridge or by forming more readily dischargeable chloro–cystine–copper complexes. Chloride also eliminated the increment in concentration polarization caused by cystine. Attainment of a minimum total steady state polarization of about 40 mv. in the presence of cystine and chloride appeared to reflect an increase of surface, hence a decrease of true current density with time of deposition. The addition agent behavior of methionine was, in most respects, similar to that of cystine. The behavior of thiourea at low concentrations appeared to be complicated, but the effects of chloride were similar to those observed with gelatine.

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

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.