Ammonium-grafted graphene oxide for enhanced corrosion resistance of waterborne epoxy coatings

This study reports an eco-friendly waterborne epoxy (WBE) coating with excellent corrosion resistance by adding ammonium grafted graphene oxide (AGO) as co-dispersant. AGO, as a co-dispersant, addresses the problem of a lot of micro-defects caused by the intrinsic mismatch between epoxy resin and amine curing agents during the formation of aqueous epoxy resin. Also, the compatibility of GO in the epoxy resin matrix is also improved by the ammonium modification. The ammonium modification process was systematically studied using Fourier transform infrared (FT-IR) spectra, X-ray diffraction (XRD) spectra, UV–vis spectra, Raman spectra and X-ray photoelectron spectra (XPS). Scanning electron microscope (SEM) images show that AGO sheets has successfully inhibited the formation of micro-pores and micro-defects, forming a more compact WBE/AGO composite coating . As a result, the corrosion resistance of the coating has been greatly improved as investigated by the potentiodynamic polarization test. The corrosion rate of WBE/AGO is decreased by three orders of magnitude compared to pure WBE coating. The corrosion protection mechanism of the WBE/AGO coating is studied via Electrochemical impedance spectroscopy (EIS) test, and equivalent electrical circuits are applied to fitting the EIS results and reveal the effect of AGO in the composite coating.