Fabrication of Poly(o/m-Toluidine)–SiC/Zinc Bilayer Coatings and Evaluation of Their Corrosion Resistances

Chuanbo Hu,Jiawei Zhang,Wenlong Huang,Ying Li

doi:10.3390/coatings8050180

Abstract

The purpose of this research was to study the structure and corrosion resistance of poly(o/m-toluidine)-SiC/zinc (Zn) bilayer coatings. Poly(o/m-toluidine) films, such as poly(o-toluidine) (POT) and poly(m-toluidine) (PMT), were chemically deposited on the surface of composite SiC/Zn coating using the solution evaporation method. The structures of poly(o/m-toluidine) were characterized by various optic techniques and the electrochemical behavior was studied by cyclic voltammetry (CV). The structures and morphologies of the SiC/Zn coating were detected by Fourier transformation infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), and scanning electron microscopy (SEM). Thereafter, the corrosion resistances of electrodeposited and bilayer coatings were investigated in 3.5% NaCl solution by electrochemical corrosion techniques and an accelerated immersion test. The results showed that the outer POT film exhibits a lower corrosion behavior with respect to PMT, which significantly reduces the corrosion rate of SiC/Zn coating and prolongs the service life of the zinc matrix. The conclusion demontrates that the stronger adsorptive POT film ensures the formed POT–SiC/Zn bilayer coatings possess a compact and low-defect surface, which facilitates POT film to develop its excellent barrier and passivation properties against corrosion.

Highlights

Zinc (Zn) coatings are widely used on the surface of steel and iron, with the Zn coating acting as a sacrificial anode and cathodically protecting the underlying metal against corrosion [1]
In our recent investigations [20], we found that the corrosion protection effect of poly(o-ethylaniline) on composite silicon carbide (SiC)/Zn coating is stronger than that of poly(o-ethylaniline)/SiC composite to pure Zn coating, which indicates that the corrosion resistance of bilayer coating is dependent on the interaction between the inner/outer coating films
Compared to the electrodeposited coatings, the protection efficiencies of bilayer coatings have been improved significantly. These results indicate that the assembled outer polymer films can effectively protect the SiC/Zn surface and that the POT film is more protective

Summary

Introduction

Zinc (Zn) coatings are widely used on the surface of steel and iron, with the Zn coating acting as a sacrificial anode and cathodically protecting the underlying metal against corrosion [1]. An excellent coating must be defect free and compact enough to endure the attack of a corrosive environment [2]. The presence of different types of inorganic nanoparticles in the zinc matrix has been reported to increase the coating compactness and improve the corrosion behavior of the Zn coating [4,5,6]. Praveen et al [7] found that the incorporation of TiO2 nanoparticles in the zinc matrix led to improvement in the crystal size and enhanced the corrosion resistance, microhardness, and wear resistance properties of the composite coating. Zn and its composite coatings have excellent surface and corrosion characteristics, Zn substrate in humid environments is susceptible to the formation of white-rust corrosion products which significantly reduce the zinc-matrix lifetime

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Results

Conclusion