Anti-corrosion coatings are one of the most important applications in the field of industrial coatings. Anti-corrosive fillers are usually added to anticorrosive coatings to achieve good anticorrosive function. Some nanomaterials, especially two-dimensional nanomaterials (e.g., graphene, boron nitride, etc.), have become popular research targets for anticorrosive fillers. In recent years, another new 2D nanomaterial, MXene, has emerged. MXene is a new family of materials with a rich variety of 2D layered transition metal carbides, nitrides, or carbon-nitrides, where M refers to the transition metal and X refers to the carbon or nitrogen, which was accidentally discovered by Yuri Gogochi and Michel Bassom of Drexel University in 2011. As a new type of 2D nanomaterials, compared with traditional 2D nanomaterials such as graphene, it not only has a large specific surface area and excellent electro-thermal properties, but also has a rich set of surface functional groups, which gives it better water dispersibility and electrical conductivity. In the field of coatings, it can be used as a filler in coatings such as electromagnetic shielding coatings, conductive and thermal conductive coatings, light and heat conversion coatings, marine anticorrosive coatings, fireproof coatings, anticorrosive coatings and other coatings.
Anti-corrosion mechanism
MXene has a two-dimensional layered structure with a surface rich in electron-rich heteroatoms and groups such as oxygen, nitrogen, fluorine and hydroxyl. The two-dimensional layered structure gives it high barrier properties, and the surface groups allow it to be adsorbed on metal surfaces and form coordination bonds, as well as react with water and oxygen to reduce the diffusion of invasive corrosive substances to metal surfaces.
Research progress at home and abroad
Epoxy resin is often used as the main resin material for anticorrosive coatings, and MXene composite coatings based on epoxy resin have been most widely studied at home and abroad. For pure MXene containing titanium, after compounding with the coating resin, water and oxygen may still enter into the coating through penetration and diffusion in the defective channels, the adsorbed oxygen and water are consumed through oxidation and degradation reactions, and the oxidation product titanium dioxide plays the role of a physical barrier, which blocks further advancement of the defective channels, and improves the corrosion-resistant stability of the coating. For solvent-based epoxy resin, the addition of MXene can reduce its micro-defects, the addition of 1% of MXene, the coating that has a better corrosion resistance, can effectively prevent the penetration of corrosive media. However, epoxy resin and MXene itself also has certain compatibility problems, can be improved through the interface, such as based on the MXene surface rich in hydroxyl groups introduced glycidyl ether propyltrimethoxysilane coupling agent, can significantly improve the compatibility between MXene and epoxy resin, the addition of 0.5% of modified MXene coating has the largest minimum frequency impedance, while the composite coating also has Better scratch resistance and higher adhesion.
For the waterborne epoxy resin, the hydroxyl group on the surface of MXene can be reacted with dopamine, and the interfacial interaction as well as the dispersion of the modified MXene with the waterborne epoxy resin can be improved, and the anticorrosive performance of the waterborne epoxy coating can be improved. For the possible defects of epoxy resin, the addition of carbon dots can provide passivation to further effectively prevent the spread of corrosion brought about by local damage, and enhance the durability and stability of the corrosion resistance of epoxy coatings. For epoxy zinc-rich coatings, modified MXene (e.g., polyaniline or polypyrrole modified) can form a network or conductive bridging effect with zinc powder to improve the utilization efficiency of zinc powder.
In addition to epoxy resin systems, the effective dispersion of MXene in waterborne polyurethane systems can also play the role of physical barrier to delay the intrusion of corrosive substances and improve the anti-corrosion performance. It has been shown that by adding 0.4% of MXene, the composite coating can show the best anti-corrosion performance. If titanium dioxide is used to modify MXene and introduced into the waterborne polyurethane coatings, only 0.1% of MXene composite filler needs to be added, the coating has the best corrosion resistance. This is due to a combination of good physical shielding, improved resin compatibility and increased hydrophobicity of the polyurethane coating.
If the modified surface negatively charged carbon nanotubes are utilized to compound with surface positively charged MXene, a complex three-dimensional shielding structure can be formed to slow down the ineffective accumulation of MXene in the system, the dispersion is improved, and the penetration distance of corrosive media into the coating is increased, and the anticorrosion performance is improved. If other effective functional materials are added, functionalized anti-corrosion coatings can be obtained. Such as adding silica can get wear-resistant anti-corrosion coatings, grafting anti-fouling polymers to the surface of MXene can get anti-corrosion and anti-fouling coatings.
Problems and development trends
The use of pure MXene in coatings has a tendency towards stacking and compatibility problems with different resins.MXene all need to be modified and functionalized to overcome the established deficiencies. Various new means of modification and functionalization are being developed. Also of concern is the oxidation of MXene in coatings, where oxidative degradation causes MXene to lose its two-dimensional structure and thus fail. To address this issue, researchers have designed ionic liquid functionalized MXene by taking advantage of the property that ionic liquids can trap oxygen atoms, effectively preventing the oxidative degradation of MXene materials and enabling them to maintain their two-dimensional nanostructures for a long period of time in water and polymer matrices. This provides a good idea to solve the oxidation problem of MXene. In addition, the large-volume industrialized preparation of MXene materials needs to be further developed.
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