Carbon nanocapsules doped separately with epoxy and polyamine were used to fabricate an epoxy nanocomposite coating. Carbon nanospheres with dual-encapsulated epoxy/polyamine were dispersed uniformly in the epoxy resin at concentrations of 2, 5, and 10 wt %. The mechanical properties of the nanocomposites were studied by tensile testing and scratch hardness measurements. Furthermore, nanocomposites were applied on mild steel substrates, and their corrosion protection and barrier performance were evaluated using electrochemical impedance spectroscopy (EIS). Adhesion loss measurements of coatings after 240 h exposure to 3.5 wt % NaCl solution were performed by pull-off adhesion testing. Also, the buried steel/polymer interface was studied in situ using attenuated total reflection Fourier transform infrared spectroscopy in the Kretschmann geometry. The results showed that both mechanical and corrosion protection properties of the prepared nanocomposites are enhanced as compared to the baseline epoxy coating and improved with the concentration of doped carbon nanocapsules. Maximum mechanical and corrosion protection properties were achieved in the case of 10 wt % doped carbon nanocapsules as a result of active intermolecular interactions between the epoxy and polyamine chains of the coating matrix and amine groups grafted on the surface of carbon capsules.

The ability of an active protective organic coating to restore its protection functionality in case of a coating defect is of pivotal importance to ensure durable performance under demanding corrosive conditions. In this paper, a self-healing epoxy system is fabricated by separate encapsulation of epoxy and polyamine in carbon hollow spheres (CHSs) and the autonomous healing performance of the system applied on mild steel is investigated. CHSs were synthesized via a silica templating method using carbonization of polysaccharide shells formed on the surface of silica templates. Consequently, epoxy and polyamine were loaded in separate capsules by dispersion of CHSs into the dilute solutions of epoxy/acetone and polyamine/acetone respectively, under vacuum conditions. The synthesized CHSs were characterized before and after the silica removal using field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The CHSs loaded with the film forming agents were assessed using thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. Furthermore, the protective and self-healing properties of the coatings fabricated were studied using electrochemical impedance spectroscopy (EIS), scanning vibrating electrode technique (SVET) and salt spray testing. The results showed that scribe defects in epoxy coatings with 10 wt % epoxy and polyamine capsules were healed effectively upon efficient release and subsequent recombination of the epoxy and polyamine agents reforming a protective layer at the damaged region.

In this work, we synthesized carbon hollow spheres (CHSs) using the silica templating method, encapsulated 2-mercaptobenzimidazole (MBI) inhibitor in the CHSs and evaluated their corrosion inhibition performance upon exposure of mild steel to a saline solution containing the released inhibitor. The effects of silica template surface modification on the CHS structure was evaluated, while the structure and morphology of the synthesized CHS was analyzed using field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), Raman spectroscopy and X-ray diffraction (XRD) spectroscopy. Furthermore, thermogravimetric analysis (TGA), energy-dispersive X-ray spectroscopy mapping (EDS-mapping) and UV–vis were employed to evaluate the MBI release from carbon capsules at different pH values. Corrosion protection performance of the doped CHS was evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results showed tunability of the shell structure between an amorphous carbon and graphene structure using surface modification of the silica templates. Moreover, the MBI release from the CHSs showed to be pH-dependent allowing smart protection of mild steel when exposed to corrosive conditions.