Cathodic deposition of copper in the presence of aqueous sulfurous acid, bivalent aquacobalt ion, or both using a stainless steel cathode and a graphite anode

Abstract

A study on cathodic deposition of copper in acidic aqueous sulfate solution has been carried out using a stainless steel cathode and a graphite anode. The individual and the combined effects of added [H(2)SO(3)(.)aq] and [Co(2+.)aq] on cathode potential, current efficiency, crystal orientations, and deposit morphology have been investigated and are compared. The maximum decrease of congruent to50 pct in cathode potential is more pronounced in the presence of congruent to10.25 g/L of H2SO3 alone in the electrolyte than that (congruent to30 pct) in the presence of congruent to100 ppm of added Co2+ (aq) alone; however, the presence of added Co2+ (aq) along with H2SO3 (aq) does not cause further decrease in cathode potential in comparison to that observed in the presence of only H2SO3 (aq) in the electrolyte. The current efficiency is found to decrease in the presence of [H(2)SO(3)(.)aq] in the range of 1.32 to 30.75 g/L or in the presence of added [Co(2+.)aq] in the range of congruent to10 ppm to 600 ppm, while the decrease of about 4 pct in current efficiency is more pronounced in the presence of only H2SO3 (aq) in the electrolyte, it is about 2 pct in the presence of only added Co2+ (aq) in the same electrolyte. The addition of Co2+ (aq) to the electrolyte containing H2SO3 (aq) does not alter the current efficiency (94 pct) of copper at the cathode. The linear sweep voltammetry (LSV) method was used to study the effect of added [H(2)SO(3)(.)aq], [Co(2+.)aq], or both, on the copper deposition at the cathode. The presence of each of these two additives or both causes a depolarization effect; the extent of the depolarization depends on the concentration of H2SO3 (aq), Co2+ (aq), and the current density. X-ray diffraction (XRD) data suggest that there is a change in the order of the preferred crystal orientations (viz., from the (220) plane in the absence of added H2SO3 (aq) and Co2+ (aq) to the (111) plane in the presence of added H2SO3 (aq) and Co2+ (aq) in the electrolyte solution) due to a change in the preferred plane of relative crystal growth. Results of scanning electron microscopy (SEM) indicate that cathode deposits of better surface morphology due to small-sized crystallites are found in the presence of added H2SO3 (aq) + Co2+ (aq) in the electrolyte solution.