Improving the throwing power of acidic zinc sulfate electroplating baths

Abstract

The effect of some plating parameters, such as Zn2+ ion concentration, pH, current density, temperature and duration on the throwing power, as well as on the throwing index of acidic zinc sulfate baths has been investigated. The addition of p-anisidine (PA) and/or sodium dodecylbenzenesulfonate (DBS) has been examined as a possible means of improving the uniformity of deposit distribution. The additives cause a substantial increase in the overpotential for the reduction of Zn2+ ions and consequently improve the throwing power of the baths. The throwing power increases by a factor of four in the presence of DBS and a factor of one-and-a-half in the presence of PA. The inhibition of zinc reduction was assumed to occur via adsorption of the PA or DBS molecules on the cathode surface and the adsorption followed the Langmuir adsorption isotherm. The surface morphology of the zinc plated with and without the additives was examined by using scanning electron microscopy (SEM).