Perminder Singh Bindra

Mechanisms of electroless metal plating. III: Mixed potential theory and the interdependence of partial reactions

Electroless plating reactions are classified according to four overall reaction schemes in which each partial reaction is either under diffusion control or electrochemical control. The theory of a technique based on the observation of the mixed potential as a function of agitation, concentration of the reducing agent and concentration of metal ions is presented. Using this technique it is shown that in electroless copper plating the copper deposition reaction is diffusion-controlled while the formaldehyde decomposition reaction is activation-controlled. Values of the kinetic and mechanistic parameters for the partial reactions obtained by this method and by other electrochemical methods indicate that the two partial reactions are not independent of each other.

THE EFFECT OF PH ON THE ELECTROCATALYTIC PROPERTIES OF ADSORBED METAL IONS

The electrocatalytic behavior of adsorbed lead atoms on mercury towards O2 reduction in neutral electrolyte at ambient temparature is examined. The results shows that O2 reduction on these modified surfaces proceeds through the series mechanism and that the enhancement is mainly due to hydrogen peroxide elimination through reduction and/or heterogeneous chemical decomposition. Measurements performed as a function of pH in the range pH = 4 to pH = 10 indicate that the hydrogen peroxide decomposition reaction slows down as the pH increases. Using cyclic voltammetry and rotating ring-disk techniques, it is demonstrated that for the PbHg system the catalytic species is lead oxide or lead hydroxide.