Application of polyphenylamine anti-corrosion coatings in metal protection

Metal material is the foundation of human material civilization, metal long-term exposure to the air, its interface is prone to chemical or electrochemical reactions, so that metal into oxidation or ion state, reduce the material's electrical properties. Metal corrosion has caused huge economic losses to the national economy. According to the survey, the economic losses caused by metal corrosion in the United States in 1975 were about $70 billion. The gross national product of the United States was $1677 billion in that year, and the losses caused by metal corrosion in one year accounted for about 4.17 per cent of that year's gross national product. According to statistics, China's annual economic losses caused by metal corrosion amounted to hundreds of billions of yuan. With the development of China's natural gas industry, especially the development of oil and gas fields containing hydrogen sulfide and carbon dioxide, the corrosion and protection of natural gas transmission equipment and pipelines have been paid more and more attention. At present, the most effective and commonly used method of metal corrosion protection is to apply
corrosive coatings
on the metal surface, such as ordinary organic
coatings
and coatings containing heavy metal corrosion inhibitors, etc., in order to isolate the corrosion medium from the metal substate, so as to achieve anti-corrosion effect. Most of these organic anti-corrosion coatings contain chromium and vanadium compounds that seriously pollute the environment, so research and development of environmentally friendly and economical anti-corrosion coatings has become a trend in the industry. Polyphenylamine, as a conductive polymer material, has the characteristics of low cost, simple preparation method and excellent anti-corrosion properties, and has been widely used in many fields in recent years. Since 1985, when De Berry first reported polyphenylamine as a new type of metal surface antiseptic coating and corrosion inhibitor, many scholars around the world have begun to study this aspect. A number of companies, including Dupont, IBM and Zipperling Kessler of Germany, are actively developing industrial applications of polyphenylamine. German Ormecon Chemie company has begun the production of conductive polyphenyl coatings, the domestic Hunan Ben Anya Daxin Materials Co., Ltd. has now formed a polyphenyl anti-corrosion coating 1000T / year production capacity, become the earliest polyphenylamine anti-corrosion coating production and sales enterprises. This paper summarizes the research progress and application results of polyphenylamine in metal corrosion prevention in recent years, and looks forward to the future research direction.
1. The anti-corrosion of polyphenylamine
Polyphenylamine is composed of two parts, and according to its degree of redox (0≤y≤1), can be a full reduction state (y-1, referred to as LEB), full oxidation state (y-0, PNB), and intermediate oxidation state (y-0.5, EB). MacDiarmid and others first gave the molecular structure of polyphenylamine (see Figure 1), where only intermediate oxidized polyphenylamines can be changed from insulators to conductors through proton acid doping.
Figure 1 Molecular Structure of Polyphenylamine
The excellent anti-corrosion properties of polyphenylamine have been confirmed by a large number of research institutes, and its anti-corrosion mechanism is completely different from traditional coatings, mainly through the conductive polyphenylamine-containing primer and metal substrate contact and interaction to form a special oxide film, thereby greatly delaying the corrosion of metals. The research on the anti-corrosion of polyphenylamine has been in-depth, and there are several the following statements:
1.1 shielding action
using coatings to separate the metal surface from the surrounding corrosive substances, prevent oxygen, water and other ions immersion, reduce the corrosion rate of metals. Wesling.B s electrochemical test found that as the thickness of the polyphenyl coating increased, the corrosion current of cast iron decreased, which he attributed to the shielding of polyphenylamine.
1.2 Polyphenylamine blunts metal surfaces
compared to traditional coatings that temporarily shield, polyphenylamine can blunt metal substrates and form a dense, stable oxide film on different metal surfaces (e.g. Fe2O3, Al2O3, etc.), which causes the electrochemical corrosion of the metal to move in positive position and protects the metal electrode inductive level in the passivation zone, the formation of the Fe2O3 membrane is shown in
Figure 2. The formation process of O3 membrane
polyphenylamine is a conjugated polymer with redox ability, because the reduction potential of polyphenylamine is at 0V/SCE, while the oxidizing potential of metal Fe is -0.7V/SCE, when When metal iron is in contact, a redox reaction occurs with the participation of water and oxygen, and a dense layer of metal oxide γ-Fe2O3 is formed at the interface, which prevents further oxidation of the metal, which blunts the metal to achieve corrosion protection.
1.3 Electric field action
Polyphenylamine produces an electric field on the metal surface in the opposite direction to electron transmission, which prevents electrons from being transmitted from the metal to the oxidant, equivalent to a barrier act of electron transmission, which cannot be formed by conventional coatings such as epoxy resin or polyurethane.
1.4 corrosion inhibition
aniline and aniline derivatives are effective corrosion inhibitors of iron-based metals, mainly because aniline N atoms have unsharing of electron pairs, metal iron has an empty d-track, when polyphenylamine is applied to the metal surface, isolated electrons and empty tracks easily form a mating bond, its molecules are adsorbed on the metal surface to form a layer of hydrophobic adsorption layer, reduce corrosion efficiency, play a role in corrosion. Wang Yangyong and others compared the corrosion effect of A3 steel in the introduction of 0.4% EB into the ordinary epoxy resin coating in 3.0% NaCl solution and 0.1MHCl solution, as shown in Figure 3. It can be seen that the introduction of a small number of EB can greatly improve the corrosion resistance of the coating, which is not available in traditional corrosion inhibitors, which is also easier to achieve large-scale industrial applications.
Figure 3 3.0% NaCl solution in different samples of TFEl curve
2. Polyphenyl anticorrosive coating preparation method
Polyphenylamine has excellent corrosion resistance, due to polyphenyls hard to melt, with pure polyphenyls preparation paint is not realistic. At present, there are three main methods of preparing polyphenylamine anti-corrosion coating:
2.1 electrochemical polyinsurance legal
polyphenylamine anti-corrosion properties were first studied from the study of aniline electrochemical polymerization. Polyphenylamine coatings or powders are deposited directly on the surface of metal electrodes by electrochemical polymerization and the thickness of the membrane is controlled by controlling the charge. Common methods are constant current method, constant current method, cycling Vian method and so on. Shi Fusheng et al., in a solution containing aniline, alysate and sodium tungstenate, the synthetic polyphenylamine/sodium tungstenate composite film is synthesized on the stainless steel surface using the circulating voycation method. The results show that in the presence of chlorine ions, the composite film can raise the corrosion potentium of stainless steel by about 200mV and significantly reduce the corrosion current density. The film has excellent stability and barrier, and can provide long-term effective protection of stainless steel. Zhang Ailing and other s×. .× . . Although electrochemical polymerization of polyphenylamine synthesis and film-forming completion at once, the reaction conditions are mild, but from a practical point of view, limited by the operating process is difficult to be used in larger metal parts, it is difficult to apply on a large scale.
2.2 Polyphenylamine and solvent cosoluble
cosoluble method is the chemical polysynthetic synthesis of polyphenylamine and solvent formation cosoluble coating, to be evaporated solvent after the formation of a coating, the formation of polyphenyl coating on the metal has a certain anti-corrosion effect. The disadvantage is that adhesion is relatively poor, and due to the strong rigidity of the polyphenyl molecule chain skeleton, the interaction between molecules is large, it is difficult to dissolve in ordinary organic solvents, in other high boiling point solvents such as N-methyl Although there is a certain degree of solubility in pyridoxine, but these solvents are expensive, toxic to limit its application, so many domestic and foreign researchers through the polyphenylamine modified, such as synthetic polyphenylamine compound mixture to improve the processing performance of polyphenylamine.
2.3 Polyphenylamine mixed with
film-forming substanceBecause polyphenylamine is insoluble in conventional organic solvents, and pure polyphenyl film on steel bonding is very poor, the heavy use of pure polyphenylamine as anti-corrosion coating is not ideal either economically or from the comprehensive performance of coating film. Therefore, people try to use polyphenylamine as an additive of existing anti-corrosion coatings, mixed with conventional coating film substances (such as epoxy resin, polyimide, polyacrylic resin, etc.) to form a composite coating, polyphenylamine in accordance with the anti-corrosion mechanism of different materials, effectively play the anti-corrosion properties of each coating. Zhang Chun and others added the conductive polyphenyls from organophosphate doping to the water-based epoxy resin, prepared the water-based anti-corrosion coating of polyphenylamine, and studied their corrosion-resistant properties and corrosion-resistant properties. Changes in electrochemical impedance spectrum and open-circuit voltage show that the presence of polyphenylamine significantly improves the anti-corrosion effect of the coating. Qi Shengguang and other methods of interpolation polymerization were used to prepare the montage/polyphenylamine composite material, which was mixed with polyamide/epoxy cathode electrophoresis (CED) coatings to be made into polyphenylamine/epoxy composite cathode electrophoresis coatings. The study found that after soaking 10d in 3.5% NaCl solution, the corrosion medium could not reach the coating/base metal interface and the metal surface did not have a corrosion reaction. With the increase of polyphenylamine content, the impedance value of composite electrophoresis coating film increased, which has good anti-corrosion properties. A large number of studies show that polyphenylamine and resin mixed anti-corrosion coating not only has anode protection and adhesion is better than the first two methods, is currently the study of polyphenylamine anti-corrosion performance of the most used methods, in the development, production and application of a wide range of applications.
3. Application field and prospect
Polyphenylamine anticorrosive coatings have an incomparable anode protection and shielding effect on metals, whether it is the use of electrochemical methods deposited on the metal surface polyphenyl film, or polyphenylamine as an additive added to the resin, will produce excellent anti-corrosion effect. At present, people have not reached a consensus on the anti-corrosion mechanism of polyphenylamine anti-corrosion coatings, but the application of polyphenylamine anti-corrosion coatings has been studied a lot, and found that it in many fields such as chemical equipment, petroleum industry pipelines, railway bridges, ships, port terminal equipment and many other durable facilities anti-corrosion has broad application prospects, especially suitable for marine, aerospace and other harsh conditions of new metal corrosion protection.
Polyphenyl anti-corrosion coating as a new type of non-polluting coating, although a certain range of commercial applications have been achieved, but there are still many urgent problems to be solved: First, to explore the interaction between polyphenylamine and conventional film-forming substances, improve the degree of dispersion of polyphenylamine in the substation. Second, in the process of polyphenylamine compounding, select suitable film-forming substances to reduce environmental pollution, equipment investment and production costs. According to the current research status, the future research of polyphenyl anti-corrosion coatings will focus on the following aspects: (1) the study of polyphenyl anti-corrosion coatings in other metals such as magnesium alloy, aluminum alloy corrosion-proofing system; (2) the preparation of soluble polyphenylamine by doping and other means, the development of polyphenyl water-based anti-corrosion coatings; (3) Research and development of polyphenylamine composite anti-corrosion coating methods for direct polymerization in film-forming materials to simplify the existing preparation process and reduce costs. (4) Using the thermal stability of polyphenylamine, chemical stability to develop special anti-corrosion coatings.
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