Advances in the research of graphene water-based composite anti-corrosion coatings

Graphene is the world's thinnest corrosion-resistant material, can be used for metal protection, graphene in the field of corrosion prevention research has attracted the attention of researchers around the world. A large number of research results show that graphene's oversized surface area, excellent barrier, high chemical stability and good conductivity and other properties, for the comprehensive performance of anti-corrosion coatings have a strong role in improving, such as enhancing the coating on the substrate adhesion, improve the paint wear resistance and corrosion resistance, at the same time has environmental safety, no secondary pollution and other characteristics.
recent years, research on anti-corrosion applications based on graphene has focused on pure graphene anti-corrosion coatings and graphene composite anti-corrosion coatings
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. Pure graphene coating generally covers pure graphene to the surface of copper, nickel and other metal substrates by chemical vapor deposition (CVD) method, mechanical transfer method, spray method, etc., and protects the metal by using the dense isolation layer formed by layering the layer of graphene's own two-dimensional sheet layer. However, the simple use of graphene anti-corrosion coating has many limitations: high quality requirements for graphene, once the film has a slight defect will aggravate metal corrosion, can only provide a short period of antioxidant corrosion efficiency; Compared with pure graphene anti-corrosion coatings, graphene composite anti-corrosion coatings can take into account graphene's excellent chemical stability, rapid conductivity, outstanding electrical properties and polymer resin strong adhesion, film-forming properties, can be combined to improve the comprehensive performance of the coating. In addition, graphene composite anti-corrosion coating preparation methods and coating process can be based on the traditional coating production process, in industrial synthesis and industrialization applications show good controllability and construction. Therefore, graphene composite anti-corrosion coatings will be the new anti-corrosion coating materials in the future.
present, the research of graphene composite anti-corrosion coating mainly focuses on solvent-based composite materials, because it contains a large number of toxic heavy metals and volatile organic substances (VOCs), the development of solvent-based anti-corrosion coatings is more and more limited. With the continuous improvement of people's awareness of environmental protection, the world has put forward more and more requirements for the development of anti-corrosion coatings, anti-corrosion coatings are moving towards high-performance, functional, green direction, especially the development of water-based coatings has become an important development direction of heavy anti-corrosion coatings. China's paint industry "12th Five-Year Plan" clearly pointed out that the water-based anti-corrosion coatings to the field of heavy anti-corrosion promotion, the paint industry "13th Five-Year Plan" will also vigorously develop high solid and water-friendly coatings as a key research and development projects. Therefore, speeding up the application of graphene in water-based anti-corrosion coatings, the development of low-cost, high-performance, green new graphene water-based composite anti-corrosion coatings, to speed up the transformation of water-based coatings, promote the development process of environmentally friendly heavy anti-corrosion coatings, has far-reaching strategic significance and broad prospects for development. Therefore, this paper will focus on the anti-corrosion mechanism of graphene, the research progress of graphene water-based composite anti-corrosion coatings, and the difficulties faced by graphene in the practical application of water-based coatings.
1 graphene corrosion protection
graphene itself has a unique structural properties, making it physically and electrochemically resistant to corrosion. Graphene's layer structure is layered and staggered, and a "maze-like" shielding structure can be formed in the coating, which can effectively inhibit the immersion, penetration and diffusion of corrosive media and improve the physical barrier of the coating. At the same time, due to its small size effect, graphene can be filled with coating defects, reducing coating pore rate, enhancing coating tightness, further delaying or preventing corrosion factors from dipping into the base surface. Graphene layer and layer between the good lubrication, graphene layer structure can be divided into many small intervals, can effectively reduce the internal stress of the coating, consumption of break energy, and thus improve the flexibility of the coating, impact resistance and wear resistance. In addition, graphene conjugate structure makes it have a high electron migration rate, showing good conductivity, at the same time, its layer structure can also ensure better electrochemical contact between coatings, the formation of a conductive network, to provide better electrochemical protection.
2 Graphene in water-based composite anti-corrosion coatings
water-based coatings due to low pollution, easy to purify, no stimulation and so on, has become the paint industry vigorously developed green and environmentally friendly coatings. At present, all over the country is speeding up the process of oil-to-water, but the protective effect of water-based coatings is still not comparable to its corresponding solvent-based coatings, resulting in its application in the field of heavy anti-corrosion is still not high. There are some technical problems in water-based coatings: due to the different mechanism of film formation, compared with solvent-based coatings, water-based anti-corrosion coatings are difficult to form a high-quality coating with a high degree of erration and a highly complete structure, and their film-forming properties and abrasive resistance are not good; Residual water-based group makes its shielding ability of water, oxygen and other corrosive media is poor, because the surface of water is too strong, water-based coating is difficult to achieve a high degree of immersion and dispersion of pigment fillers, so improving the corrosion resistance of water-based coatings has become the focus of the development of environmentally friendly coatings. Graphene's unique properties provide new ways to improve the tightness, barrier, mechanical properties and corrosion resistance of water-based coatings. In recent years, the research progress of graphene preparation, functional correction and graphene polymer nanocomposite materials has been remarkable, and the effects of solvent-based composite anti-corrosion coatings prepared by solution or melting, in-place polymerization and other methods have also been proved feasible, which provides a research basis for the application and development of graphene water-based composite anti-corrosion coatings, and brings new possibilities.
2.1 graphene water-based polyurethane anti-corrosion coating
water-based polyurethane (WPU) has solvent-based polyurethane performance, but also overcome solvent volatile environmental pollution. However, the thermal stability, solvent resistance and technical properties of WPU are poor, affecting its application range, so in order to provide the comprehensive performance of WPU, it is usually necessary to cross-link the modified, epoxy resin modified, silicone modified and inorganic nanomaterials (SiO2, TiO2, CNTs) modified. Graphene as a new high-performance nano-enhancer, so that polyurethane water resistance, thermal properties, the performance of the force has been improved to varying degrees. Yoon and others used a hybrid method to composite isocyanate acrylic modified graphene oxide (iGO) with WPU, and the extrusion strength, glass transition temperature and thermal stability of the compound were significantly improved. Yang et al. added graphene oxide (GO), prototype graphene oxide (RGO) and functional graphene derivatives as inorganic nanofillers to water-based polyurethane (PU) anti-corrosion coatings, combined with salt spray testing, electrochemical impedance (EIS) phenidation, and examined in detail the effects of graphene's surface chemistry, dispersion and dosing on the corrosion resistance of PU composite coatings. The results show that RGO with a mass score of 0.2% has the best effect on the corrosion resistance of PU composite coating. Chen et al. found that after adding a small amount of sulfur fossil ink to the thermoplastic polyurethane (TPU), the Yang's mod of the composite material increased by 120%.
considering the compatibility and stability of the composite coating, Li and so on use titaniumate coupled agent to function fossil ink, so that it is evenly dispersed in water-based polyurethane. Wang and others used sol-gel method to silane functional graphene and WPU composite, the results found that the addition of 2.0% graphene can increase the coating's Yang's mod by 86%, the strength of 71%.
Ding Jianning and others used ampicillin triethyloxysilane (KH550) to functionally modify the surface of GO, improve the dispersion of GO in acetone, DMF organic solvents, and use the chemical reaction between the -NH2 group on GO and the WPU polymer monomer, through in-place polymerization legal system to prepare GO/WPU composite materials, improve GO's compatible in the WPU substitut. Li Youliang and so on through in-place poly-legal, in the preparation of water-based polyurethane water emulsification reaction process to add graphene oxide solution, deionized water and ethyl amine, and then add vitamin C for in-place reduction, and finally made graphene / water-based polyurethane nanocomposite. Zhu Ke and others through the gradual polymerization reaction of isocyanate functional fossil ink (IGN) to the water-based polyurethane (WPU) chain segment, prepared to obtain water-based isocyanate modified graphene / polyurethane nanocomposite emulsion (IGN/WPU), and applied to the field of metal anti-corrosion coating. The results show that with the increase of IGN content, the hardness of the coating increases, the rate of water vapor through decreases, and the anti-corrosion efficiency increases.
2.2 Graphene water-based epoxy anti-corrosion coatings
After years of efforts by researchers, water-based epoxy coatings have overcome the disadvantages of poor water resistance/corrosion resistance and are gradually being applied to the heavy anti-corrosion areas involved in solvent-based coatings. To further improve its corrosion resistance, the researchers combined graphene into a water-based epoxy coating to develop a new composite coating.
Wang Yuqiong and others used sodium polyacrylic acid to distribute graphene slurry evenly and steadily into the aqueous solution, and then physically mixed to obtain graphene water-based epoxy resin coating, through polarization curve, AC impedance spectrum and neutral salt spray test to explore the corrosion resistance of the coating. The results show that after adding graphene, the composite coating shows good water isolation performance, the diffusion rate of water molecules in the coating is obviously reduced, at the same time, the anti-corrosion effect of the coating is obviously improved, and the electrochemical test results show that the self-corrosion current density of the composite coating with graphene is added, and the coating resistance and charge transfer resistance are increased. Zhang Lanhe and other use of in-place polymerization-chemical reduction method to aggregate the aniline layer to the surface and sheet layer of graphene, the preparation of polyphenylamine / graphene composite materials, and the use of mechanical mixing to obtain polyphenylamine / graphene - water-based epoxy resin composite anti-corrosion coating. The results show that the polyphenyls doped with graphene have a higher surface area than polyphenylene, and maintain the original sheet layer structure of graphene, and the composite coatings prepared show impermeability, corrosion resistance and corrosion resistance, which are better than the protective properties of polyphenyls and pure epoxy resins. In order to make the dispersion and stability of graphene composite coating better, Zhang and so on in the graphene oxide GO reduction process to add polyethylene pyridoxine PVP, with the help of the non-common price bond π-π interaction between the two to obtain a high stability of PVP-rGO dispersion, the use of in-place synthesis method PVP-rGO and water-based epoxy resin composite preparation graphene-epoxy coating, and detailed investigation of the effects of different graphene coating. Compared with pure epoxy coating, the thermal decomposition temperature, Yang's mod and anti-corrosion properties of graphene-epoxy coating with PVP-rGO were added, and the graphene dosing was optimal. Yu Haibin and other use of aniline low-polylymer derivatives and graphene between the formation of π-π key, so that graphene in the water solubility is greater than 1 mg/ mL, conductivity of 1.5 S/cm. High Yanmin and other use of GO surface oxygen-containing functional group and amino reactions in the amino silane coupled agent, prepared a functional modification of the aminosilane coupled GO, greatly improving GO's hydrophobic and its affinity with epoxy resin, improve the water-based epoxy corrosion coating wear resistance and corrosion resistance.
2.3 Graphene water-based acrylic anti-corrosion coatings
water-based acrylic anti-corrosion coatings are cheap, with safety and environmental protection, excellent aging resistance, good alkaline resistance, simple synthetic processing and so on, but due to the residual hydrophobic group, its water resistance is poor, easy to flash erosion. Blue Xijian et al. used graphene in water-based acrylic antiseptic coatings, through the use of the corresponding dispersants or even agents, improve the dispersion of graphene in the coating, and further through stirring, sanding, filtration and other processes, to achieve the preparation of water-based graphene coatings. The results show that the water-based graphene coating has outstanding water-resistant and salt-spray-resistant properties, and its anti-corrosion effect is significantly better than that of other carbon-based materials filled with water-based coatings. Lu Shenghua and others used the solution to mix graphene oxide / acrylic / cement composite coating, the study found that the oxygen-containing group on the GO surface can effectively regulate the growth of cement hydration products, so that the composite coating's impermeability, stretch strength and fracture elongation performance has been significantly improved, and the coating is environmentally friendly and pollution-free.
2.4 Graphene water-based inorganic zinc-rich
water-based inorganic zinc-rich primer is a silicate solution as an important film-forming substance, with high content of zinc powder (to improve the performance of the coating film, can be mixed with some flaky aluminum powder, mica powder, phosphorus iron powder, phosphorus iron-zinc silicon powder, etc.) as anti-corrosion pigment water-based heavy anti-corrosion paint. Due to the high zinc content, zinc powder in the air is prone to whitening, reducing the adhesion of the coating, the coating in the process of use easy to foam and dry cracking, corrosion performance is reduced. Yuan Gaobing and others added graphene as a corrosion inhibitor to the water-based inorganic zinc-rich coating silicate liquid system, the results show that the coating plate with no graphene antiseptic additives after the salt spray test 1500 h began to appear spot embroidery, bubbles and other abnormal changes, and containing trace amounts of graphene antiseptic additives coating plate salt spray test 2000 h still no changes, indicating that the addition of graphene increased the film resistance.
Synthesis of the previous content, domestic and foreign corrosion protection workers in graphene water-based composite anti-corrosion coating performance research has done a lot of work, graphene water-based composite anti-corrosion coating showed the effect, indicating that the water-based paint by graphene modified, performance has improved. However, most of the research is laboratory results, research content fragmentation, and the research focus on how to prepare graphene composite protective coating and verify the corrosion resistance of graphene, ignoring the graphene selection, graphene water-based composite coating supporting system research, especially graphene on the water-based coating corrosion resistance between the structure of the relationship and graphene and coating dispersion, interface problems and other lack of understanding.
3 Difficulties in the application of graphene in the field of water-based corrosion
3.1 to solve the selection of graphene materials and water-based coatings
As shown in Figure 1, graphene oxide GO, reduced graphene graphene RGO structure is similar to graphene GNP, but due to the impact of chemical modification, its surface has a large number of structural defects, resulting in its conductivity, machinery, mechanics and other properties are not as good as GNP.
In terms of hydrophobicity, affected by the surface effect, GNP's immersion of water is very poor, showing good hydrophobicity, compared to GNP, GO, RGO surface because it contains a large or small amount of oxygenated organic organs, showing good hydrophobicity. When GNP and GO are added to the resin as fillers, hydrophobic GNP will prevent or delay the penetration of corrosive media such as water and oxygen, while hydrophobic GO will promote the penetration of corrosive media to some extent.
in terms of dispersion and compatibility, GO, RGO because the surface contains some organic