Electrochemical studies of three - dimensional nucleation

A study has been made of the electrochemical three-dimensional nucleation of metals onto vitreous carbon electrodes from aqueous solution. A general review of the formulation of simple electrode processes as well as of the classical and atomistic theories of nucleation is presented. The metals investigated were copper, silver, cadmium and mercury. A wide range of potentiostatic current transients was recorded and analysed to obtain information about the number density of nuclei formed, their morphology and kinetics of growth. Under potentiostatic conditions, the growth was observed to be diffusion controlled and for the systems studied here the nuclei were hemispherical, except in the case of cadmium. This system presented several difficulties and no definite conclusions could be drawn. The effect of complexing agents and surfactants on the kinetics of nucleation has also been investigated. Double potential step measurements were perforniad to determine induction times, critical radii and other parameters of nucleus formation. Galvanostatic overpotential transients for the deposition of mercury were analysed and the multiple pulse potentiostatic-galvanostaticpotentiostatic method (PGP) was used to obtain a better understanding of the kinetics of nucleation. It was also made the basis of a new method for determining the charge transfer parameters of an electrode process. The description of this technique and of its shortcomings are extensively discussed. The last part of the thesis is devoted to the application of numerical methods and computer simulation to several problems in electrode processes and especially to the simulation of galvanostatic transients under conditions of diffusion control, charge transfer control and mixed control at planar and spherical electrodes. These methods were also applied to the case where the area of the electrode increases with time, which is one of the so-called Stefan problems.