Characterization of Nano-kaolin and its enhancement of the mechanical and corrosion resistance of epoxy coatings

Abstract

This study compares the effects of varying concentrations of nano-kaolin and titanium dioxide on the mechanical and corrosion resistance of epoxy coatings. Characterization techniques such as TEM, XRD, Raman, FTIR, XPS, and AFM revealed surface features of nano-kaolin: the particle size reached the nanoscale, the XRD diffraction peak at 2θ = 25.3° disappeared, Raman peaks broadened with decreased intensity, and a blue shift occurred in the FTIR spectra for various functional groups. Compared to pure epoxy coatings, the composite epoxy coating with 10 wt% nano-kaolin showed an 83.87 % increase in adhesion, an 81.82 % improvement in impact resistance, and a 61.42 % reduction in friction coefficient; while a 20 wt% titanium dioxide composite coating showed a 74.19 % increase in adhesion, a 75.76 % improvement in impact resistance, and a 46.9 % reduction in friction coefficient. Electrochemical tests indicated that a composite coating with 10 wt% nano-kaolin, after soaking in 3.5 wt% NaCl solution for 960 hours, achieved a corrosion efficiency of 98.87 % and an impedance modulus of 10Ω.cm which was three orders of magnitude higher than that of pure epoxy resin, increasing corrosion resistance by 57.14 %; whereas a 20 wt% titanium dioxide composite coating reached a corrosion efficiency of 89.29 % and an impedance modulus of 10Ω.cm after the same conditions, increasing corrosion resistance by 17.86 % compared to the pure epoxy resin. The composite coating with 10 wt% nano-kaolin exhibited superior mechanical and corrosion resistance, outperforming the 20 wt% titanium dioxide coating. Mechanical and corrosion mechanisms suggest that the uniformly dispersed nano-kaolin inhibits interactions between epoxy resin molecules and carries the external load, thereby enhancing intermolecular cohesion. Improved adhesion and impact resistance indirectly extend the coating's lifespan by prolonging the path of corrosion media through the coating to the substrate. The novel coating modification method proposed in this study effectively replaces titanium dioxide and enhances the coating's mechanical and corrosion resistance, offering a new solution for corrosion prevention in metal materials.