The effect of complex ion formation on the polarisation potential and nature of electrodeposits of copper, with particular reference to benzotriazole

• Main Author: Prall, John Karel
• Published: University of Surrey 1962
• Subjects: 669
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.751576

A critical review of the literature pertaining to acid copper sulphate electrodeposition preceded the following two paths of research:- 1. A study of electrode kinetic factors using plating solutions without addition agents. A new experimental polarisation technique (called the Reproducible Substrate method) was developed which ensured, in particular, that the cathode had no significant time-dependent properties. This enabled reproducible and linear Tafel plots to be obtained even for those solutions that, with classical polarisation methods, did not previously conform to Tafel behaviour. Special solution preparation methods enabled the properties of super-pure solutions (virtually free of chloride ions) to be studied. The marked effect of trace amounts of chloride ions was shown. The super-pure solutions possessed linear Tafel behaviour, but each plot of n a versus log i showed a change in slcpe at n a = 0.1V - these results were the first to directly confirm a previous prediction made that a change in the cathodic rate-step should occur at this overpotential. 2. A study of addition agent action. Initial trials of many active addition agents were effected in order to select only those that were sufficiently stable and marked in effect to warrant further study. In particular, benzotriazole was studied in detail since it markedly raised n a and affected electrodeposit stuctures(in some cases fully bright coherent deposits were obtained). A mechanism of its action was proposed based on the formation of insoluble cuprous benzotriazolate arising from the formation of cuprous ions in the normal discharge process. A physical model was proposed to explain the phenomenon of banding. Analysis showed that the cuprous benzotriazolate inclusions could be quantitatively retrieved by dissolving up the electrodeposits in acidified silver sulphate. The analysis of trace amounts of these inclusions was carried out by"Polarisation Analysis".