CYSTINE AS AN ADDITION AGENT IN THE ELECTRODEPOSITION OF COPPER

Abstract

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.