Effect of Thiocompounds on the Electrodeposition of Copper

The effect of different thiocompounds in the concentration range 4.10–7–2,5.10–4 M on the electrodeposition of copper from 0,63 M CuSO4/2,04 M H2SO4 solution at 50°C was investigated. Almost no influence was observed with thiazol. Thiourea, N,N'diethylthiourea, cystine and methionine strongly influence the current/overvoltage characteristics and the structure and surface roughness of copper electrodeposits. With these compounds a depolarisation was found at low concentrations while at higher concentrations an increase of the overvoltage is observed. Addition of thiocompounds decreases the surface roughness of deposits obtained at 50 mA/cm2 with respect to those deposited from the pure solution and generally results in a grain size refinement of the crystallites. Results are discussed in terms of the strong interaction of the thiocompounds with the electrode. It is proposed that at low concentrations thiourea and N,N'-diethylthiourea are desulfurated in preferred sites on the surface while at higher concentrations more uniform adsorption over the whole surface is predominant.