Pulsed Current Plating of Zinc from Chloride and Zincate Baths

The effects of pulsed current on surface morphology, electrode potential, current efficiency, macrothrowing power and electrical power usage were studied by means of scanning electron microscopy, polarization measurement and Hull cell testing in ZnCl2-KCl and zincate baths, with and without additives. The grain size deposited from baths without additives decreased with increasing pulse current density and shorter duty-cycles under constant average current density, but bright deposits could not be obtained. In a chloride bath containing only a non-ionic surfactant (nonyl phenyl eicosa-ethylene glycol ether: NPEGE), however, a mirror bright surface was obtained under a wide range of current densities under appropriate pulse conditions. Pulsed plating had little effect on improving either current efficiency or macro-throwing power. At constant average current density, it was found that pulsed plating used more electrical power than direct current plating and this trend was more pronounced the shorter the duty-cycle. This is explained in terms of increased ohmic drop due to the electrical resistance of the solution.