Corrosion protection of carbon steel by water-borne resin modified by reduced-graphene oxide

Abstract

A significant constraint concerning the utilisation of reduced graphene oxide (rGO) as pigment in water-based resins resides in its pronounced tendency to agglomerate. The present study proposes the employment of sodium cholate (NaCh) not solely as a dispersant but also as a green reducing agent of graphene oxide. The stability of the suspension was validated through zeta potential measurements, and functionalised rGO nanosheets with an approximative size of 500 nm were confirmed.

The barrier properties of the doped films were evaluated by electrochemical impedance spectroscopy, both on the free films and on those applied on carbon steel. The results obtained from both experiments demonstrated a consistent pattern. Very high impedance values were obtained for undoped resin and when doped with 0.05 wt%, 0.1 wt% and 0.2 wt% rGO, confirming the uniform dispersion of the particles within the resin. A model was developed to analyse the electrolyte uptake in the free films, which accounted for the heterogeneity of the films, with two clearly differentiated kinetics. When these films were applied on carbon steel, they also exhibited good barrier properties in 0.6 M NaCl during long immersion periods. In a more aggressive medium, a 5 M HNO₃ solution, the best performance was observed for the resin doped with 0.1 wt% and 0.2 wt% rGO, presumably due to the chemical resistance of the rGO.

The highest concentration, 0.5 wt% rGO, exhibited a rapid decrease in impedance values from the initial immersion time. This behaviour was attributed to the disruption of the polymeric network formation by the high amount of particles, resulting in a defective film. To facilitate the interpretation of the impedance spectra recorded for 0.5 wt% rGO, the Distribution of Relaxation Times (DRT) approach was employed, resulting in the proposal of a novel electrical equivalent circuit.