Nucleation and Growth of Zinc Electrodeposited onto Electropolished and Mechanically Polished Steel Surfaces

Nucleation and growth of zinc electrodeposition in acid sulphate bath on electropolished and mechanically polished low carbon steel surfaces was investigated. On both surfaces thin η-zine crystals were stacked on each other, although their orientation was different. Potentiostatic current-time plots and cyclic voltammetry were used to study the nucleation process. The results indicated that at pH 2 the nucleation process on both surfaces um instantaneous, and that the growth process was charge transfer controlled. The growth rate on the electropolished surface was higher than the mechanically polished surface under the same electrochemical conditions. Increasing temperature did not affect the nucleation mode; it only increased the growth rate. Increasing the pH from 2 to 4 caused deviation from instantaneous nucleation, so that on the mechanically polished surface the nucleation mode was fully progressive. The reason for this behavior was attributed to the number density of active nucleation sites on the steel surface. Cyclic voltammetry also confirmed the hydroxide layer formation model.