Amine functionalization of graphene oxide (AFGO) and corrosion behavior of epoxy-AFGO nanocomposites

Graphene oxide (GO) was amine-functionalized with benzidine. Amine Functionalized graphene oxide (AFGO) was characterized by Fourier Transform Infrared Spectrum (FT-IR), X-ray powder diffraction (XRD), Energy Dispersive X-ray Spectroscopy (EDS), and Thermogravimetric Analysis (TGA) techniques, and also the morphology of AFGO was determined by field-emission scanning electron microscopy (FESEM). AFGO was dispersed in an epoxy-based coating. The nano-composite coating was applied on tricationic phosphate normal steel substrates (20 cm × 10 cm × 0.8 cm). The coating was cured at 165 °C for 20 min and the final film thickness was 20 ± 2 μm. The corrosion resistance was investigated by electrochemical impedance spectroscopy (EIS) and salt spray test. The corrosion resistance improved significantly compared to the blank sample. Corrosion resistance in the salt spray test raised about 1200 h. The creepage at the scratched area was ≤ 3 mm. The EIS results showed that after 4 weeks of immersion in 3.5 wt % NaCl, the |Z | value dropped sharply and reached 104Ωcm2 in GO and neat samples, while in AFGO sample coating, the |Z | value was equivalent to 106Ωcm2. Also, The addition of graphene oxide to the epoxy resin mixture caused the hydroxyl and acidic groups on GO to react with the epoxy resin. The resulting three-dimensional grid formed a resistant layer in the paint film. In the FAGO sample, the elongation of the sub-branches and the activation of the amine functional group resulted in easier bonding, greater reactivity, and stronger flexibility in the final film.