Development of multilayered nanocomposite Zn-Ni-Sio2 coatings for better corrosion protection

Abstract

Multilayer nanocomposite coatings of Zn-Ni-SiO<inf>2</inf> was deposited galvanostatically on mild steel (MS) from Zn-Ni bath, having Zn+2 and Ni+2 ions and uniformly dispersed nano-SiO<inf>2</inf> particles. The corrosion performances of multilayered nanocomposite (MNC) coatings were evaluated by electrochemical polarization and impedance methods. The deposition conditions such as, bath composition, cyclic cathode current densities (CCCD's) and number of layers were optimized for peak performance of coatings against corrosion. A significant improvement in the corrosion performance of MNC coatings was observed when coating is changed from monolayer to multilayer type. Corrosion rate (CR) of MNC coating decreased progressively with number of layers up to an optimal level, and then started increasing. The increase of CR at higher degree of layering is attributed to diffusion of layers due to very short deposition time, failing to give the enhanced corrosion protection. The formation of layers, inclusion of silicate particle in MNC coating matrix were confirmed by SEM and XRD study. At optimal current densities, i.e. at 3.0-5.0 A/cm2, the Zn-Ni-SiO<inf>2</inf> coating having 300 layers, represented as (Zn-Ni-SiO<inf>2</inf>)<inf>3.0/5.0/300</inf> is found to be about 107 times more corrosion resistant than monolayer Zn-Ni-SiO<inf>2</inf> coating, developed from same bath for same time. The reasons responsible for extended corrosion protection of MNC Zn-Ni-SiO<inf>2</inf> coatings, compared to corresponding monolayer Zn-Ni and (Zn-Ni-SiO<inf>2</inf>) coatings were analyzed, and results were discussed. © 2012 Penerbit UTM Press. All rights reserved.