High speed electroplating in low-concentrate colloid-electrolyte baths

Abstract

We define colloid-electrolytes as those plating baths where metal deposits are formed by reducing not only metal ions but also colloids and fine dispersions of metal compounds. Such dispersions in the field of the cathode (ie in the part of the diffusion layer where the rate of stirring usually tends to zero) may be treated in certain optimal cases as systems of mobile pores, giving rise to equilibrium and nonequilibrium electrokinetic phenomena, (electroosmosis, electrophoresis, diffusiophoresis and so on) and thus to efficient stirring. This results in reducing or eliminating the diffusion control and in an essential rise of the limiting current densities. Dispersions may arise by anode dissolution and by secondary cathodic processes (hydrogen evolution, dissociation of complexes). Adsorbed polyelectrolyte compounds may be good dispersion stabilizers, also giving rise to Marangoni instability, interphase convection and (or) turbulence and thus supplementing