Fundamental aspects of pulse plating.

The fundamental aspects of pulse plating are reviewed mostly on the basis of theoretical and experimental results. The main features of pulse plating are due to the effect of pulse current on the mass transport process. A pulsed current produces a pulsating diffusion layer in which the concentration of the ionic species fluctuates periodically with time near the electrode surface. Mathematical analysis of mass transport revealed that there are mutual restrictions among the pulse parameters-pulse current density, pulse width and off-time-, although pulse current can be increased up to some ten times the d.c. limiting current. Results obtained in pulse plating of tin and zinc are in good agreement with this theoretical prediction. While the morphorogy of the deposits, such as unevenness and porosity, is mainly influenced by mass transport, their crystal structure -grain size, crystallinity and preferred orientation -is strongly affected by activation overpotential. The corrosion resistance, magnetic and electrical properties, and the residual stress of the deposits are sometimes improved by pulse plating. It is concluded that pulse plating has more potential than d.c. plating in obtaining electrodeposits having specific physicochemical properties.