Studies of galvanostatic pulse plating of copper from solution containing complexing ions

The first part of this research work was the investigation of Galvanostatic pulse plating of copper and copper(I) halides from acid copper(ir) halide solutions. The general stoichiometric equation for the reaction which occurs during the relaxation time was found to be Cu2+ + Cu° + 2x - → 2 CuX E(1--10, p24). Further study showed that the rate determining step of reaction E(1-10) involves CuCl+ in a first order reaction d(CuCl/dt = kCuCl + [CuCl+] E(3-38, p174). It is discovered here that the galvanostatic pulse plating technique has a great potential in the production of Cu°/CuCl electrodes. These electrodes can be used in sea-water batteries. Control of the pulse plating conditions can produce electrodes of almost any desired composition of CuCl in the deposit of any required thickness and discharged capacity. The presence of a small amount of copper in the layer gives the electrodes conductivity which is an advantage for such electrodes. The second part of the research involved studies of the electrodeposition of copper in electrolytes with and without 'addition agents'. It was found that the bright deposits obtained using solutions containing brighteners (dimethyl thiourea or thioglycolic acid) could consist of either small or large grains, instead of only small grains which had been frequently observed by others. It was also found that those addition agents which gave bright deposits were easily oxidised in sulphuric acid. In the same sweep range (-72mV to -350mV vs SCE) the addition agents which did not give bright deposits did not oxidise significantly. A postulation of the involvement of the brighteners is suggested. As the disulphide of dimethyl thiourea or thioglycolic acid could have been reduced during the deposition of copper, there are probably two electro-reduction processes taking place in solutions containing brighteners.