Corrosion Science and Protection Technology: The Latest Research Advances in Marine Anti-corrosion Coatings

1. Foreword
The oceans account for about 70% of the Earth's surface area, more than 90% of the world trade depends on the sea transport of cargo, marine resources and marine shipping industry has become an indispensable pillar in the development of the world economy. However, the marine environment has become an extremely harsh corrosive environment with re-impacts on metal components such as sea surface winds and waves, and corrosion of metal materials such as seawater, marine life and their metabolites. Submarines, ships, etc., both in seawater and on the sea surface, need to be made of high-strength, corrosion-resistant materials and protected by an anti-corrosion coating. Therefore, the search for the most suitable marine anti-corrosion coating has attracted widespread attention.
The 12th Five-Year Plan period, China is in the intensive low-carbon economic transition period, but also to the implementation of the ocean strategy of the key period, ocean transportation, deep-sea new energy development, coastal ports, ships and other industries of rapid development, marine anti-corrosion coatings have higher requirements, research and development of green harmless, long-life, economical marine anti-corrosion coatings is objectively necessary. With the rapid growth of the demand for marine anti-corrosion coatings in various industries, the marine anti-corrosion coatings industry will certainly get an unprecedented golden period of development, product types, performance and application range, scale and so on will be developed by great s. This paper introduces the current situation of marine anti-corrosion coatings, focusing on several types of marine anti-corrosion coatings with significant anti-corrosion properties.
2. Anti-corrosion Coatings Overview
Protection of marine metal substrates is mainly through the use of corrosion-resistant materials, the addition of corrosion inhibitors, metal surface changes, coating protection and electrochemical protection. Among them, coating protection is a traditional marine anti-corrosion technology: the use of corrosion-resistant coatings applied to the metal substrate surface, by high temperature or temperature curing into a film, to protect it. The anti-corrosion structure of anti-corrosion coating film includes: shielding, passivation, anti-rust filler protection, cathode protection, etc. Coating protection has the advantages of simple construction, obvious anti-corrosion effect and high economic benefits, and is widely used in the field of marine anti-corrosion.
coating performance determines the protective effect of the coating, in the field of marine heavy corrosion protection, should have the following advantages: good mechanical performance, rain resistance, seawater wash collision and even friction; In addition, the shielding, hydrophobic, anti-fouling and service life of the coating also have certain requirements.
the performance of the coating is not independent, mutual influence, closely related, the development of anti-corrosion coating with the above advantages is one of the most important work at present.
3. Types of marine anti-corrosion coatings
There are many types of corrosion of steel structures in marine engineering: electrolytic corrosion, cavitation, wear corrosion and impact corrosion, hydrogen corrosion, oxygen absorption corrosion, etc. The main applications of heavy anti-corrosion coatings are: epoxy anti-corrosion coatings, fluorocarbon anti-corrosion coatings, polyurethane anti-corrosion coatings, rubber anti-corrosion coatings, organic (inorganic) silicone resin coatings, polyurethane elastomer anti-corrosion coatings, glass scales heavy anti-corrosion coatings and organic (inorganic) zinc-rich coatings (Table 1).
below, the most widely used anti-corrosion coatings are briefly introduced:
3.1. Epoxy antiseptic coatings
Epoxy antiseptic coatings with epoxy resin as the main body, with pigments, dryers, additives and other modulation. Epoxy coating performance is excellent: high adhesion, high strength, chemical resistance and wear resistance is currently the field of marine heavy anti-corrosion applications, one of the most wide range of heavy anti-corrosion coatings.
variety of anti-corrosion coatings, mainly divided into bisphenol A epoxy resin and phenolic epoxy resin two categories. Bisphenol A epoxy resin (Figure 1) molecular structure contains hydroxyl, ether bonds and epoxy group, with strong adhesion to the substrate;
phenolic epoxy resin, due to the content of more epoxy group, corrosion resistance and adhesion is stronger, curing cross-linking is greater, more dense, while phenolic resin with high temperature and corrosion resistance. However, the increase of epoxy group makes the brittleness increase, which affects its application range. Bisphenol A instead of phenol synthetic biphenol A phenol epoxy resin (Figure 2), low free phenol content, narrow molecular weight distribution, the introduction of BPA makes the resin more technical performance, lower shrinkage, the increase of epoxy group makes the adhesion force is very strong, flexibility, thermal stability, insulation, water resistance and corrosion resistance and other performance is better.
can expand its application by changing epoxy resin by filling and other means. Ghaffari and other modifiers, through the analysis methods such as infrared spectroscopy and thermal heavy analysis, studied the properties of suspended nanofillers and coatings in epoxy composites, and the research showed that the modifiers made the dispersion effect of suspended nanofillers better, and after adding 0.5% of the mass fraction of modified suspended nanofills, the coating had a significant effect during the immersion period. Paula and others analyzed the microstructure of water-based epoxy resins, and the results showed that the average pinhole size of the coating surface was well related to the permeability of chloride. Liu Jiangtao and others analyzed the water-based modified amine epoxy curing agent and liquid epoxy resin ratio, filler, additive selection and other issues, the results show that epoxy-based amine hydrogen equivalent ratio of 1:1, pigments, non-ion and cation wetting agent when used together, made of paint film properties and chemical resistance is excellent. Mukesh and other cashew phenols in place of BPA synthesis of new epoxy resin and infrared spectroscopy and MRI spectrum, the results show that the new epoxy resin cashew phenol only need the original epoxy resin BPA use of 40% to 60% to achieve the same performance.
these modified methods can only improve a certain characteristic of the resin, in the face of complex marine corrosion environment, the application advantage is not obvious. According to different areas of use, through mixing with various resins and fillers, combined with physical and chemical modified methods to develop hydration or high solidified epoxy anti-corrosion coatings is its development direction, such as we use BPA instead of BPA synthetic phenolic resin, and then oxidize it, the fluorine epoxy resin, not only has excellent adsorption properties on the substrate, but also greatly improves the anti-corrosion properties of epoxy resin, in the field of marine corrosion prevention. The performance of the coating depends on the characteristics of the resin, including the research and development of modifiers, the optimization of the coating process, etc. is also the future epoxy anti-corrosion coating research direction.
3.2. Fluorocarbon anti-corrosion coatings
Fluorocarbon anti-corrosion coatings with fluorine resin as the main film-forming substances, fluorine atomic electronegative negative, small radius, C-F key length, strong key energy, low polarization rate, these coatings show excellent weather resistance, heat resistance and chemical resistance, with excellent self-cleaning performance, anti-fouling properties and ultra-strong corrosion resistance. In 1965, the U.S. pennwalt company introduced PVDF (polydeflon) as a building coating as a symbol, fluorocarbon resin began to be used in the field of corrosion protection. In 1982, Asahi Nitro subsidiary developed FEED (fluoroolefin-vinyl ether co-polymer), achieved amblyother curing, greatly expanding the application of fluorocarbon coatings. Fluorocarbon coatings from the type of teflon to teflon, teflon, from high temperature curing to temperature curing, to water-based fluorocarbon emulsion resin is applied to fluorocarbon coatings, and gradually formed a variety of widely used fluorocarbon coating system, the application area has been greatly expanded.
years, through different ways of fluorocarbon coatings modified or a variety of paint mixing means to optimize the performance of fluorine-containing coatings, expand its application areas. Lu and others doped different amounts of sharp titanium TiO2 nanoparticles in fluorocarbon coatings, testing coating properties, the results show that the addition of TiO2 nanoparticles in fluorocarbon coatings, the resulting coating film has better heat resistance, weather resistance and excellent self-cleaning performance. Kim and others spray water-soluble fluorocarbon sealing materials with cryogenic spray coatings that show high corrosion current density and corrosion resistance. LL'darkhanova and others use carbon nanotubes and carbon nanofibers to modifie fluorocarbon resins, the nanostructure formed on the surface of the coating and fluorocarbon resin inherent hydrophobic synergy, so that the hydrophobicity of the coating has been greatly improved.
These changes only enhance or improve the performance of a coating, it is not possible to apply all the modified methods completely to a coating, so to change the status quo, it is necessary to design and synthesize new fluorine-containing resins in the structure, so that the resin body has a comprehensive excellent performance, and then through the modified means to improve some of its performance defects, is the focus of fluorocarbon resin research and development. In addition, the main factors affecting the promotion of fluorocarbon coatings are the high cost of coatings, coatings need high temperature baking, poor hardness, easy leakage and so on. In short, the use of new monomer co-polymerization, the introduction of fluorine elements in different types of resins, multi-polymerization and other means is the main way to prepare new fluorocarbon coatings and future research direction.
3.3. Rubber anticorrosive coatings
rubber coatings with natural rubber derivatives or synthetic rubber as the main film-forming substances. The main applications are chlorine sulfonate polyethylene anti-corrosion coatings and chlorinated rubber anti-corrosion coatings. Rubber coating non-toxic tasteless, non-irritating to the skin, coating film corrosion resistance, and substrate adhesion, at the same time has the advantages of fast drying, water resistance and wear resistance and anti-aging, rubber anti-corrosion coating is mainly used in ships, sluices, chemicals and other fields.
sulfurized polyethylene anti-corrosion coatings to chlorine-sulfurized polyethylene rubber as the main film-forming substances, not oil-friendly, non-hydroploric, flame retardant, weather-resistant, heat-resistant and low-temperature performance is excellent. Disadvantages are: with the substrate adhesion force is not high, need to mix with other resins (such as epoxy resin) or modified to improve adhesion;
anti-corrosion coating of chlorinated rubber is made of carbon tetrachloride as a solvent, which is refined by natural rubber and entered into chlorine gas. There is no active chemical group, excellent chemical resistance, water resistance, fog resistance and weather resistance. Mix with other coatings, more corrosive resistance, increased service life, single use and substrate adhesion is not high, anti-aging, non-ultraviolet performance is not strong. In recent years, some researchers have improved the defects of traditional rubber anti-corrosion coatings by changing them or mixing them with other coatings. Hwang and other rubber and epoxy resin, with different amounts of scale-shaped graphene microchip modified end amine-based rubber, the test results show that the impact resistance strength and toughness of modified composite coatings are greatly improved. Bulgakov and others modified chlorine polyethylene rubber with amino compounds to increase their bonding strength by 2 to 5 times. Li Shi and other use of medium and long oil alcoholic acid resin, epoxy resin and other chlorinated rubber modified, applied to offshore platforms, ships and other equipment, the results show that the coating adhesion, anti-aging, etc. have been greatly enhanced. However, although these modified methods improve the performance of the coating, but still use carbon tetrachloride as a solvent, its own toxic and ozone layer damage, so that its application is limited, the development of low VOC chlorinated rubber coating is the future direction of development. For example, the use of water phase method synthetic chlorinated rubber, research and development of water-based chlorinated rubber coatings, etc. for us to provide solutions, but the stability or practical effect of product quality can not meet the technical requirements of the marine harsh environment, the development of new solvents to replace carbon tetrachloride production of chlorinated rubber is still the rubber coating industry research and development hot spots and difficulties.
3.4. Silicone resin coating
silicone resin coating is silicone resin or modified silicone resin as the main film-forming material of an elemental organic coating, mainly divided into pure silicone resin coating and modified silicone resin coating, strong heat and cold resistance, insulation, adhesion, flexibility, mold resistance and other excellent performance. Modified silicone resins are used in a wide range of applications, including mechanical mixing and amerent types, and can be modified by adding different fillers or pigments to enhance their heat, insulation and weather resistance.
and abroad have adopted different ways to modifie silicone resin coatings, and achieved remarkable results. Lee and other self-healing agents of methamphetylsiloxane and methamphetylhydroxane double emulsion were introduced into the core of the nuclear shell nanofiber coating, and the results showed that the protective coating had high transparency (90% light transmission), self-healing ability and strong corrosion resistance. Balgude and other silane modified, research its corrosion protection of carbon steel, and four different silane content (5%, 10%, 15% and 20%) of the coating to sample and structure analysis, the results show that: compared to other preparations, 20% of the silane modified coating in the metal coating interface to form more metallic silica co-price bonds, its overall performance is stronger.
Although silicone resin coatings have excellent high and low temperature resistance and weather resistance, chemical resistance, wear resistance and other outstanding advantages, but its low strength, and low adhesion to the substrate and other shortcomings also limit its application range. Later work is mainly to adopt different methods of change, such as inorganic-organic mixing technology, so that it has the best characteristics of both organic and inorganic, through the exploration of silicone resin coating film-forming process, a variety of polymers such as acrylic resin, epoxy resin, etc. Obtaining more superior performance silicone modified coatings, preparing cross-linked silicone resin coatings to enhance their tightness, improve water resistance, solvent resistance and heat resistance, so that silicone resin coatings to low pollution, health and environmental protection direction is also the focus of future research and development.
3.5. Polyurethane anticorrosive coatings
Polyurethane coatings are a common class of coatings, and epoxy coatings have similar properties, divided into two-group and single-group polyurethane coatings. In addition to the presence of urethane bonds, there are many - OH, NCO and unsaturated double bonds, coating acid and alkali, oil resistance, corrosion resistance, high and low temperature and wear resistance and other excellent performance. Polyurethane coating belongs to the high-solid low VOC coating, environmental pollutant emissions are very low, polyurethane coating and substrate adhesion is strong, physical and mechanical performance is excellent, decorative performance is also very strong, can be used in the field of heavy anti-corrosion paint.
present, there are many methods of water-based polyurethane anti-corrosion coatings at home and abroad, including: epoxy resin modified, silicone copolymeration, nano-modified, composite modified. The performance of water-based polyurethane anti-corrosion coating has been greatly improved after the change, but there are still problems such as water resistance is not strong, demanding construction conditions and higher product prices.
Research and development of new water-based polyurethane anti-corrosion coating modified method is the main direction of water-based polyurethane anti-corrosion coating research, such as the use of emulsification agents or the introduction of hydrophobic groups such as niobine, hydroxyl and other hydrophobic groups to prepare water-based polyurethane coatings, the focus of the study is how to improve its water resistance and shorten the curing time and other directions; In short, the development of high-performance water-based, high solid content polyurethane