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    Home > Coatings News > Paints and Coatings Market > The development of metal anti-corrosion self-healing coatings

    The development of metal anti-corrosion self-healing coatings

    • Last Update: 2020-11-23
    • Source: Internet
    • Author: User
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    1 The importance of metal anti-corrosion self-healing coating
    metal in an unstable state will occur corrosion phenomenon, coating anti-corrosion coating on the metal surface is currently a common measure, but by various environmental factors or the effect of the coating's own performance, the coating surface will inevitably appear some small invisible micro-cracks, these micro-cracks exposed to the air will continue to spread and expand, resulting in the coating peeled off the substrate and reduce the protective life of the coating. Inspired by biological systems, intelligent coatings with certain self-healing capabilities have received wide attention from academia and industry. In July 2015, Dr. Ronan Daly, Head of the School of Advanced Manufacturing at the University of Cambridge, delivered a speech entitled "Self-Healing Smart Coatings - The Future of Materials"
    China
    .
    so-called self-healing coating refers to coatings that have self-healing function after the coating has been damaged, or have self-healing function under certain conditions. There have been literature on self-healing coatings since the 1980s. The early self-healing anti-corrosion coatings were based on hexavalent chromium forming a dense layer of γ-Fe
    2
    O 3

    and Cr
    2
    O
    3
    on the carbon steel surface in a humid environment, which played a good role in slowing corrosion on the substrate surface. However, hexavalent chromium compounds are not only toxic and easy to be absorbed by the human body, with carcinogenic effects, do not meet the requirements of health and environmental protection. Anti-corrosion coatings must meet the requirements of today's environmental protection laws and regulations, so energy-saving and environmentally friendly self-healing anti-corrosion coatings is a product with broad prospects.
    2 The development of self-healing anti-corrosion coatings
    According to Alicja and other statistics, from the 1980s to 2015, there were 542 literature reports on self-healing protective coatings, and the number of literature on self-healing coatings showed a rapid growth trend between 2010 and 2015, with more research on self-healing coatings in Asia and Europe, especially in Germany. According to the different self-healing process, metal anti-corrosion self-healing coating can be divided into microcapsules type self-healing coating, high-polymer type self-healing coating and load corrosion inhibitor type self-healing coating.
    2.1 microcapsules self-healing coating
    White and so on designed a typical microcapsue self-healing composite system, the specific design ideas are shown in Figure 1.
    Figure 1 Automatic Repair Concept Diagram
    As can be seen from Figure 1, the system wraps the repair agent in a microcapsules and loads the microcapsules into a composite structure containing a catalyst capable of polymerization of the repair agent. The specific self-healing process is: (a) cracks caused by damage to the coating, (b) cracks causing the microcapsules to rupture, releasing repair agents, and (c) polymerization reactions after contact with the catalyst to repair the cracks.
    method of preparing self-healing anti-corrosion coatings using the principle of microcapsules has been widely studied. Using different synthesis methods, the researchers selected various repair reagents to prepare self-healing antiseptic coatings. Cotting and others prepared polystyrene microcapsules using hinge siliconol and triethyl ions as nuclear materials, and then mixed the microcapsules into epoxy resins to prepare self-healing epoxy coatings. The self-healing effect of the system was studied by accelerated corrosion tests using electrochemical impedance spectrum (EIS), scanning vibration electrode technology (SVET) and salt spray chamber (SSC). For samples with artificial defects, after soaking 120h in a 0.05mol/L NaCl solution, the microcapsules formula coating performs better than the unprogrammed coating due to the release of inhibitors. SVET results are in good agreement with EIS results, showing corrosion inhibition of artificial defects in coating samples, showing significant self-healing effects. Acceleration tests in the salt mist chamber showed that after exposure of 144h, the coating made with microcapsules containing inhibitors, corrosion products and bruises around the foaming is less. It has been reported that microcapsue self-healing epoxy antiseptic coating containing repair agent is prepared by in-place polymerization legal system, and the anti-corrosion and self-healing effect of coating are studied. The results showed that the cracks were effectively healed after the microcapsules were broken.
    microcapsules self-healing coating theory research is more mature, but in the process of industrial use, there are some difficulties, containing repair agent microcapsules content is too little to repair the effect, too much content affects the mechanical properties of the coating. In the production of microcapsules coating process needs to be strictly controlled, in the construction process also needs special attention.
    2.2 Polymer-type self-healing anti-corrosion coatings
    High-polymer polymers used in polymer-type self-healing anti-corrosion coatings include thermosolytic polymers, thermoplastic polymers, elastomers, shape memory polymers, supermoleal polymers, composite polymers, etc. The repairing structure of polymer-type self-healing anti-corrosion coating is mainly to use the reversible properties of specific structural elements, and to achieve the purpose of self-healing by using the reversible co-price bonds or weak non-co-priced bonds in the molecular structure of these polymers. Natascha et al. used Diels-Alder reactions to study self-healing coatings based on reversible co-price bonds, and the Diels-Alder reaction was actually a ring-addition reaction of conjugated diolefins and pro-biolefins. The method of electroscopic scanning is used to record the self-healing process of coating using reversible reaction process, as shown in Figure 2. As can be seen from Figure 2, the coating film with scratches disappears after heating and reverts to a complete coating film, achieving the goal of self-healing.
    2 SEM in the self-healing
    Marcel and others studied self-healing polymer coatings using the principle of supermoleal interaction. Supermoons are complex, organized aggregates that are combined by two or more molecules that rely on molecular interactions. The action force between supermoleual molecules is a non-co-priced bond form, including electrostatic action, van der Huali, hydrogen bond, π-π key, etc. Although π-π bonds are less powerful than ion bonds or hydrogen bonds, they are important inter-molecular interactions in non-hydro-hydro environments. Some typical materials for self-healing systems π-π keys are shown in Figure 3. Wherein (a) represents a compound containing 2 to 4 π-π mutually accumulated nicomolide polymers (blue) and or clamp-typederivatives (red);
    Figure 3 π-π-key accumulation structure diagram
    There are more studies on the thermoplastic polyethylene methyl acrylates co-polymer as an elastic system for self-healing coatings. The elastomer self-healing process is shown in Figure 4. As can be seen from Figure 4, elastomer heating can be restored to its original shape when the coating film is hit and cracked.figure
    Figure 4 elastomer self-healing film self-healing schematic
    high-polypluoration coating in the production and construction process is not as difficult to control as microcapsules self-healing coating, but the mechanical properties of high-lying self-healing coatings are low, coating hardness and wear resistance is low, and in the self-healing process needs heating to complete.
    2.3 load corrosion inhibitor type self-healing coating
    adding metal corrosion inhibitor is a common method in metal corrosion protection. Although hexavalent chromium can effectively inhibit the corrosion of metal substrates, it does not meet environmental requirements due to its toxicity. In recent years, a number of environmentally friendly corrosion inhibitors, such as vanadium, vanadium, phosphoric acid and organic corrosion inhibitors, have been developed, which can effectively replace hexavalent chromium. Although corrosion inhibitors can effectively form a protective passivation film on the metal surface to inhibit further corrosion of the metal, but because of the corrosion inhibitors and coating compatible differences, if added directly to the coating will affect the anti-corrosion effect. And because of the mutual influence of chemical bonds, it is also quite difficult to spread the corrosion inhibitor evenly into the coating. In order to solve this problem, many scholars have designed a series of solutions.
    Karan and others studied the load of corrosion inhibitors into the kaolin nanotube structure, and then doped the substance into the epoxy coating system, through the nanotube release corrosion inhibitors to inhibit anode activity, thereby preventing further corrosion of the coating. The corrosion dynamics of coating defects are studied by scanning vibration electrode technology (SVET) and electrochemical impedance spectrum (EIS) analysis. The results show that the corrosion resistance of the coating has been improved obviously due to the release of corrosion inhibitors by nanotubes. Yuanwei and others developed an anti-corrosion self-healing coating, the talcum powder loaded with sodium tungsten acid corrosion inhibitor into the epoxy resin coating prepared into an anti-corrosion coating, using electrochemical impedance spectrum and salt spray test method to test the self-healing capacity of the coating, the results show that the coating film has a good anti-corrosion effect.
    loads corrosion inhibitors into the material of the porous structure and then adds the self-healing coating prepared in the resin to solve the problem of the complex production and construction process of the microcapsules and the mechanical performance of the polymer-type self-healing coatings. However, the coating in the self-healing process needs corrosion inhibitors released from the porous structure to achieve the purpose of repair, so in the repair process to quickly release corrosion inhibitors in order to achieve satisfactory results.
    3 Directions for the development of self-healing metal anti-corrosion coatings
    The use of self-healing performance to extend the life of anti-corrosion coatings has attracted wide interest in academia and industry. But there is still a gap between self-healing antiseptic coatings that are as ideal as biology. Self-healing anti-corrosion coatings will be developed in the following areas in the future.
    3.1 Simplify the process and improve operability
    from the practical point of view, the simpler the production formula and the production and construction process, the higher the practical application value, the more widely used. Such as the microcapsules now widely studied self-healing system on the production or use of microcapsules early rupture and can not achieve the goal of self-healing.
    3.2 Research room temperature self-healing high-polyseal intelligent coating
    using certain characteristics of high-polypics to achieve self-healing purposes of composite coatings, self-healing process generally need heating and heating, generally at a temperature of about 80 to 160 degrees C to achieve self-healing, such self-healing did not achieve the purpose of spontaneous. Therefore, the study of anti-corrosion coatings that can achieve self-healing at room temperature is the future development trend with industrial practical value.
    3.3 Expand the application of natural materials in protective coatings
    Natural materials are ideal industrial raw materials, such as natural polymer materials (including fiber, shell polysaccharies, natural rubber, etc.), natural mineral nanomaterials, etc. have been widely used in anti-corrosion coatings. U.S. patent US9683109B2 introduces a self-healing anti-corrosion coating that uses shell polysaccharides, silica particles, and epoxy resins to synthesize polycodyclic conductive compounds. Test quality loss and salt spray tests have shown that the epoxy coating of shell polysaccharose polymers with a load of 2.0% has excellent corrosion resistance in high corrosive environments. Continuous research on the properties of natural materials, and its application in self-healing anti-corrosion coating system is an important cause for the good of the country and the people.
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