ELECTROCHEMICAL AND SPECTROSCOPIC STUDIES OF THE INFLUENCE OF THIOUREA ON COPPER DEPOSITION FROM ACID SULFATE-SOLUTION

The effect of thiourea (TU, CS(NH2)(2)) on the charge transfer control led and mixed controlled kinetics of copper deposition, from an acid s ulphate electrolyte, has been studied via steady state current vs. pot ential curves at a relating disc electrode. Pure charge transfer data are extracted and thiourea addition is shown to result in a complex re lationship between the exchange current density for copper deposition and the additive concentration. This behaviour can be contrasted with that shown by two other additives, benzotriazole (BTA, C6H5N3) and 4,5 -dithiaoctane-1,8-disulphonic acid (DTODSA, (HO3SCH2CH2CH2S-)(2)). Val ues of the product of mass transport coefficient and active electrode area (k(m)A) during cupric ion decay studies at a rotating cylinder el ectrode have been shown to be dependent on the electrode potential and on the concentration of TU. Limiting current studies have indicated a potential-dependent adsorption of TU at the electrode surface. In-sit u FTIR spectroscopic studies have confirmed the potential-dependent na ture of the adsorption of TU at a copper electrode and have also shown that the co-ordination to the metal surface is via the sulphur atom.