THE EFFECT OF ADDITIVES ON THE NUCLEATION AND GROWTH OF COPPER ONTO STAINLESS-STEEL CATHODES

A potentiostatic technique has been used to study the effects of chloride ion, glue, and thiourea on the initial electrodeposition of copper. A stainless steel (AISI 304) rotating disc electrode (RDE) with an electrolyte containing 40 g/l Cu2+ and 180 g/l H2SO4 at 40-degrees-C was employed. The current transients from the potential step measurements for the additive-free electrolyte could be fitted to a model that assumed progressive nucleation followed by growth of three-dimensional (3-D) centers under diffusion control. The growth mechanism and the type of nuclei were also confirmed by scanning electron microscopy (SEM) of the deposit. Chloride ions (40 ppm) affect the rate of the reaction, decrease the number of nuclei, and enhance the growth process. The particular glue (TPC 69, 5 ppm) used in this work is a polarizer and increases the number of nuclei formed on the surface. For the experimental parameters used in this research, the nucleation and growth mechanism is not changed by the presence of chloride ion or glue in the electrolyte. However, thiourea (0.5 ppm) additions caused the mechanism to change to instantaneous nucleation with 3-D growth under kinetic control, and a large number of equal sized nuclei are observed on the SEM micrographs, tending to verify the proposed mechanism.