Potentiostatic and AFM Morphological Studies of Zn Electrodeposition in the Presence of Surfactants

Abstract

Zinc electrodeposition onto a steel substrate in the presence of surfactants with different charged head groups, namely, anionic sodium dodecylsulfate (SDS), cationic dodecyltrimethylammonium bromide (CTAB), and nonionic , (Triton X-100), was studied by both chronoamperometric and atomic force microscopy (AFM) techniques. AFM analysis shows that Zn electrodeposition, in the absence of surfactants, begins in the underpotential deposited (UPD) region with the formation of different-sized circular aggregates with a random distribution, which indicates that progressive nucleation takes place. In the presence of SDS, CTAB, and Triton X-100 no change of the electrodeposit morphology is observed as a function of the surfactant presence. The Zn UPD deposition is confirmed by chronoamperometric measurements performed in this potential region. In what concerns the bulk deposition region, where the hydrogen evolution that goes together with the zinc deposition, the analysis of the current–time transients indicates that the Zn electrodeposition occurs by instantaneous nucleation and three-dimensional growth controlled by diffusion in the surfactant-free solution and in the presence of SDS. When the CTAB and Triton X-100 were added to the bath, change from instantaneous to progressive nucleation arises as a consequence of the simultaneous adsorption of the surfactant that inhibits the nucleation sites. The kinetic parameters values obtained from the Heerman and Tarallo model are in accordance with the dimensionless analysis of the transients. AFM confirms the effect of surfactants on the zinc bulk deposition.