Electrochemical behaviour of SnZn-graphene oxide composite coatings

Electrochemical properties of pure SnZn and SnZn-graphene oxide composite coatings were determined and compared. Graphene oxide (GO) was synthesized by the modified Hummer's method. SnZn-GO composite coatings were electrodeposited over a mild steel substrate. Amount of GO in the composite coatings was varied by changing the concentration of the GO dispersed in the electrolyte bath used for the electrodeposition. Morphological and topographical characterization revealed that the relative smoothness and the compactness of the coatings increased with increase in the concentration of the graphene oxide in the coatings. Texture and the crystallite size, however, did not show any significant variation with the concentration of GO in the coatings. Corrosion behaviour of the coatings was examined through potentiodynamic polarization and electrochemical impedance spectroscopy methods. A significant improvement in the corrosion resistance in terms of reduction in corrosion current and corrosion rate and increase in polarization resistance was noted in the case of SnZn coating containing GO. Corrosion resistance of the coatings increased with increase in the GO content. Microstructural investigation conducted using transmission electron microscopy revealed that the pure SnZn coating contained large scale segregation of Zn-rich and Sn-rich phases. Whereas, the presence of graphene oxide facilitated relatively uniform distribution of Zn phase in the Sn-rich matrix. Uniform distribution of Zn-rich phase causes uniform formation of the corrosion product that is ZnO over the coating surface in case of SnZn-GO composite coating. This is responsible for greater corrosion resistance performance of the SnZn-GO coatings when compared to pure SnZn coating.