The effects of TiO2 addition on the anticorrosion performance of ECTFE coating under lighting

Abstract

In this study, TiO2 particles were dispersed into ethylene-chlorotrifluoroethylene copolymers (ECTFE), and TiO2/ECTFE composite coating was prepared with the TiO2/ECTFE mixture via electrostatic spraying and low temperature thermal processing. The prepared coating was soaked in 3.5 wt% NaCl solution under lighting or dark for anticorrosion performance study. The microstructure of the treated coating was characterized with XRD, Raman, FT-IR and SEM. The results indicate that the low frequency impedance (|Z| 0.01 Hz) of the TiO2/ECTFE coating maintained above the 109 orders of magnitude after 90-day soaking. It is evident that the addition of TiO2 enhances the protective performance of the coating on steel, while simultaneously compromising its own integrity. With increasing soaking time, C-H groups in ECTFE coating would be exposed gradually and lighting would speed this process, making the surface roughness of coating reduced. This is because halogens in the polymer chain of ECTFE would be stretched gradually. TiO2 would also change the bond length of C-H groups and make the C-H groups oxidized under lighting. The strengthening effect of TiO2 can be ascribed to the filler and barrier effects of TiO2 particles together with the prior consumption of dissolved oxygen by photo-generated electrons. However, the fast degradation of TiO2/ECTFE coating under lighting is the result of local agglomeration of TiO2 particles, and oxidation of the C-H groups by photo-generated holes.