Incorporation of Zinc Hydroxide Sulphate (ZHS) Nanoplates into Epoxy Resin to Improve Its Corrosion Protection

Abstract

Zinc hydroxide sulphate (ZHS) nanoplates were synthesized and then characterized by various methods, including field-emission electron microscopy (FESEM), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron microscopy (XPS), thermal gravimetric analysis (TGA), and the Brunauer–Emmett–Teller (BET) theory. Then, the synthesized ZHS nanoplates were incorporated into the epoxy coating on a ST 37 steel alloy. No change in the morphology of the epoxy coating was observed after incorporating 1 wt. % ZHS nanoplates. Uniform distribution of the incorporated ZHS nanoplates inside the epoxy coating was confirmed by transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). Atomic force microscopy (AFM) images showed that the surface roughness (Sa) of the neat epoxy coating was about 1.1 µm, which was increased to about 2.1 µm by the incorporation of the ZHS nanoplates. The water contact angle on the coating was changed from 82.1 to 90.8° after incorporating the ZHS nanoplates, which may be attributed to the surface roughness. Electrochemical impedance spectroscopy (EIS) experiments showed that the polarization resistance of the epoxy coating in a 3.5 wt. % NaCl solution after 28 days of immersion was about 2.03 MΩ cm2, and increased to about 9.47 MΩ cm2 after adding the ZHS nanoplates. In addition, the capacitance of the ZHS-containing epoxy coating after 28 days of immersion in the corrosive solution was about 0.07 nsnΩ−1cm−2. The obtained value was more than four times lower than the value obtained for the neat epoxy coating (0.32 nsnΩ−1cm−2). The results of the EIS measurements indicated a significant increase in the corrosion resistance of the epoxy coating after the addition of the ZHS nanoplates. The improvement in the corrosion was explained by the filling of the possible defects and trapping of the aggressive agents by the incorporated ZHS nanoplates. FESEM and EDS analyses at the end of the immersion period confirmed the results of the corrosion tests.