Characterization of zinc-cobalt electrodeposits

The structure and morphology of electrodeposits depend on many factors including temperature, current density, time of deposition and composition of the bath. The properties of an electrodeposit depend on its micro structure. For example corrosion and wear resistance, hardness, internal stress, strength, brightness, electrical conductivity, magnetic properties and leveling are all affected by structure. The relationships between electroplating parameters such as current density, temperature, bath agitation and electrolyte composition have been investigated for the zinc-cobalt system. It was found that electrolyte composition and temperature affect both deposit composition and morphology. The cathodic current efficiency decreased with current density and hardness was raised with increasing cobalt content in the deposit. Three powerful techniques were used to access the microstructure of zinc-cobalt deposits: scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The results show that the alloy is constituted of a single phase of a solid solution of cobalt dissolved in zinc within an hexagonal crystal system. The deposit is porous and changes from dendritic to nodular with increasing cobalt content.