Metallic materials directly exposed to air, water or other corrosive media are susceptible to damage due to various physical and chemical changes, resulting in huge waste of resources and environmental problems. A protective layer can effectively slow down the corrosion of the matrix material by isolating the metal from the environmental medium, and its compactness and corrosion resistance are two key factors for the final protective effect.
Compared with inorganic coatings such as enamel and ceramics, organic coatings are more likely to form a denser coverage on the metal surface, with a wide range of sources and good corrosion resistance, have been widely used from our days. But a critical fact is that microcracks easily form on the surface of the organic coating under different natural application conditions, allowing water and other corrosive media to penetrate.
To solve this problem, the scientific research team of Zhifeng Lin and Weihua Li from Sun Yat-sen University prepared an epoxy-based coating (thickness about 200 μm) with Fe3O4 nanoparticles and tetradecanol which exhibited self-healing ability under solar irradiation and could protect the underlying carbon steel (CS) substrate from erosion. This study has just been published in Frontiers of chemical science and engineering.
Self-Healing Coating (SHC) is a new type of coating that has an extended lifespan by repairing micro-cracks or damage to form a repairable physical barrier, first reported only 20 years ago. Although several methods can be applied to obtain the self-healing coatings, including the addition of external repair/corrosion inhibitors, self-dynamic bonding of the polymer resin, and the use of thermoplasticity/shape memory materials, the UV irradiation or high temperature conditions are required to induce chemical reactions, thus self-healing coatings obtained under mild conditions are in urgent demand.
They found that the SHC coating could be heated to 70°C in just 200 s under simulated solar irradiation due to the photothermal effect of Fe3O4 nanoparticles, which far exceeded the melting point of tetradecanol at 37.6°C. And the punctures and scratches caused by the scalpel on the surface of the coating were only repaired after the simulated solar irradiation for 3 minutes. Its wettability has also been proven to increase with the addition ratio of tetradecanol, attributed to a large number of polar hydroxyl groups. To testify the performance of the SHC coating in real natural environment, the researchers also carried out the coating healing experiment under natural outdoor light and finally obtained ideal results.
The corrosion protection effectiveness of the SHC coating on the underlying metal substrate is verified and can be maintained above 99% regardless of the repair. It can effectively prevent the infiltration of O2H2O and Cl–and exhibits good stability and protective performance even after immersion in 3.5 wt% NaCl solution for 168 hours.
By selecting suitable liquefied phase change materials, photothermal particles and mixing them with suitable content, scientists have achieved new self-healing of the anti-corrosion coating under sunlight in a simple way. SHC coating has good photothermal property and can turn into liquid flow under sunlight to fill defects. Its impermeability and anti-corrosion property are comparable to commercial coatings, intended to be mass-produced and used for corrosion protection in outdoor installations.
Reference: Zhentao Hao et al (2022). Self-healing composite anti-corrosion coating activated by solar irradiation, Frontiers of chemical science and engineering DOI: 10.1007/s11705-022-2147-1
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On Frontiers of chemical science and engineering
Frontiers of chemical science and engineering presents the latest developments in chemical science and engineering, with an emphasis on emerging and multidisciplinary fields and international trends in research and development. The journal promotes communication and exchanges between scientists around the world. Content includes original reviews, research papers and short communications. Coverage includes reaction catalysis and engineering, clean energy, functional materials, nanotechnology and nanoscience, biomaterials and biotechnology, particle technology and multiphase processing, separation science and technology, sustainable technologies and green processing. The editors are Academician Jingkang Wang of Tianjin University, Academician Qunji Xue of Ningbo Institute of Industrial Technology and Academician Jiongtian Liu of Zhengzhou University. The journal has been indexed by SCI, Ei, CA, ChemWeb, INSPEC, SCOPUS, Source Journals for Chinese Scientific and Technical Papers and Citations, CSCD, etc.
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Self-healing composite anti-corrosion coating activated by solar irradiation
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