Composition estimation of Sn-Bi alloy electrodeposition using polarization curve

Methane sulfonic acid based tin-bismuth (Sn-Bi) plating baths containing hydroquinone and gelatin as electrolyte additives were characterized in this work. Potentiodynamic polarization curves were obtained using a potentio/galvanostat to study the polarization behavior in the Sn-Bi plating bath. Galvanostatic deposition was conducted in the Sn-Bi plating bath at applied current densities in the range of 10-30 mA cm(-2). The Bi content of the electrodeposits was found to decrease with increasing current density. A relationship between the limiting current density (i (lim) ), the applied current density (i (app) ) and the weight percent of deposited Bi was derived. The Bi weight percent in the electrodeposits was found to be given by . The composition of the electrodeposits obtained experimentally conforms to the estimated composition. This work therefore suggests a simple and practical way to estimate the composition of Sn-Bi alloys from polarization curves. This estimation method could be applied to similar regular alloy deposition systems with at least one limiting current density plateau shown on the polarization curve.