Polyaniline Anti-Corrosion 100 Questions

Metal corrosion is a spontaneous, irreversible process. In nature, apart from a very small number of noble metals such as gold, platinum and palladium, the vast majority of metals readily react with corrosive media in the natural environment, undergoing chemical or electrochemical reactions and reverting from high-energy metallic elements or alloys into thermodynamically more stable compounds — completing the corrosion process. The factors that cause metal corrosion are complex, and typically include chemical corrosion, electrochemical corrosion, and galvanic corrosion between metals with different electrochemical potentials. Theoretically these reactions are difficult to eliminate completely, so metal corrosion is unavoidable; it can only be mitigated through anti-corrosion solutions in order to safeguard the service life of the metal.

Metal corrosion not only causes enormous economic losses but also creates serious safety hazards. Corrosion-related losses account for 4% of global GDP each year, amounting to roughly USD 2.5 trillion in direct economic losses worldwide annually. In China and abroad there have been many major safety accidents in which corrosion reduced the load-bearing capacity of bridges and tunnels and, without timely repair and maintenance, led to collapse.

Given the significant economic losses and safety risks caused by metal corrosion, metals must be protected against corrosion in order to extend the service life of metal structures and eliminate economic losses and safety hazards at the source.

There are many technical solutions for metal anti-corrosion. Adding nickel or chromium to produce corrosion-resistant alloys — stainless steel being the typical example — is convenient to use, but substantially increases cost and offers poor durability under extremely corrosive service conditions. Galvanizing processes such as electro-galvanizing and hot-dip galvanizing deliver good anti-corrosion performance, yet they still face high cost, high energy consumption and heavy pollution in manufacturing, as well as great difficulty in protecting large metal components. On-site application during maintenance is particularly difficult, which greatly limits their use. Applying a layer of anti-corrosion coating to the metal surface is currently the most cost-effective technical solution, being convenient for both application and maintenance — and it has therefore become the dominant technical approach in the field.

Metal anti-corrosion coatings are divided into conventional anti-corrosion coatings and heavy-duty anti-corrosion coatings. Conventional coatings protect metals in ordinary atmospheric environments, while heavy-duty coatings are those capable of delivering a longer protection period than conventional coatings in relatively harsh corrosive environments such as industrial and marine atmospheres.

Types of metal anti-corrosion coatings include lead- and chromium-based coatings, zinc-based coatings and polyaniline coatings. Although lead- and chromium-based coatings offer excellent anti-corrosion performance at low cost, their high toxicity poses major environmental hazards and they are being phased out. Today, zinc-based coatings that use zinc powder as the anti-corrosion material dominate the market. Polyaniline anti-corrosion coating is a zero-zinc, all-polymer product; thanks to its unique anti-corrosion mechanism and extremely long service life, it is rapidly becoming one of the most important options for metal anti-corrosion coatings.

Zinc-based anti-corrosion coatings comprise three major categories: organic zinc-rich, cold galvanizing (cold zinc spray) and inorganic zinc-rich coatings. Organic zinc-rich coatings are usually epoxy zinc-rich coatings, whose anti-corrosion life depends on the zinc powder content; with a zinc powder content above 80%, a service life of more than 10 years can be achieved. Cold galvanizing coating is a one-component zinc-rich coating with an even higher zinc powder content, with zinc in the dry film reaching as high as 96%.

Inorganic zinc-rich coatings include waterborne and solvent-borne types. They offer the advantages of resistance to 400 °C, fast drying and good anti-corrosion performance; however, their biggest drawbacks are difficult application, very high demands on substrate surface preparation, a requirement for high relative humidity during application, the need for continuous stirring, long recoat intervals and relatively poor film flexibility — all of which have limited their large-scale adoption.

The advantage of organic zinc-rich coatings is that their anti-corrosion performance is widely recognised in the industry, the mechanism is broadly accepted, and they are backed by a large number of verified field cases. Their preparation process is relatively simple, and a complete set of procedures covering application, quality inspection and acceptance has been established.

The disadvantage of organic zinc-rich coatings is that their anti-corrosion durability is about 10–15 years, far short of the 30-year anti-corrosion life required for large steel structures. Over the full life cycle, multiple large-scale repairs and maintenance interventions are needed, and maintenance costs exceed 5 times the initial construction cost. Another potential drawback is that zinc-rich coatings depend excessively on zinc ore resources. China holds only about 20% of world zinc reserves, and the industry faces excessive dependence on imports and the challenge of achieving an independent, controllable supply chain domestically.

Cold galvanizing coating is a high-zinc-content coating composed of zinc powder with a purity above 99.9%, volatile solvents and organic resins. Its advantage is relatively excellent anti-corrosion performance, with reports of a service life of more than 15 years; however, it also suffers from difficult application and requires continuous stirring, and its adhesion is only 3 MPa, with the risk of film detachment during service.

Taking the protection of iron by a zinc-rich coating as an example, the mechanism is that zinc powder acts as a sacrificial anode and is continuously consumed, while iron acts as the protected cathode and is spared from rusting. Specifically, the electrode potential of zinc is more negative than that of iron, so zinc is more active than iron and plays the role of sacrificial anode; iron is the cathode, current flows from zinc to iron, the anodic zinc is consumed and corroded away, and the cathodic iron is protected.

This mechanism therefore requires a sufficiently high zinc powder content to meet long-term anti-corrosion requirements. Its performance is positively correlated with zinc content, and for heavy-duty coatings with a service life of more than 15 years, the zinc powder content by weight must exceed 70%.

After nearly a century of development, inorganic zinc-rich coatings have evolved into organic zinc-rich coatings, and their anti-corrosion performance has gained recognition in the field. However, zinc powder is a sacrificial coating material, it cannot be recycled, and it faces the problem of rapidly depleting zinc ore resources. The sustainability of supply of zinc-based coatings has attracted major industry attention, and developing new anti-corrosion materials that can replace zinc powder is a research hotspot in academia and industry worldwide.

After nearly 40 years of sustained research, the anti-corrosion effectiveness and service life of polyaniline coatings have been fully verified by academia and industry. Polyaniline coating is one of the very few products that can replace zinc-based anti-corrosion coatings, and is currently the only zero-zinc metal anti-corrosion coating available worldwide.

Polyaniline is a long-chain conjugated polymer whose backbone consists of two repeating units, p-phenylenediamine and quinone diimine. Professor Alan G. MacDiarmid of Pennsylvania State University discovered in 1983 that polyaniline is an intrinsically conductive polymer; he shared the 2000 Nobel Prize in Chemistry for his innovative contributions to the field of conductive polymers.

The first to discover the anti-corrosion properties of polyaniline was the French scientist Deberry. In 1985, Deberry et al. synthesised a polyaniline film on a stainless steel surface by electrochemical methods; the film reduced the corrosion rate of stainless steel by two orders of magnitude, indicating potential anti-corrosion performance.

Academician Wang Fosong of the Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, was the first in China to carry out work on the synthesis, structure and application of polyaniline, as early as 1983. Subsequently, a research team led by Researcher Wang Xianhong (a doctoral student of Academician Wang Fosong) began applied basic research on polyaniline anti-corrosion in 1997. The team proved that the anti-corrosion mechanism of polyaniline stems from its unique reversible redox reaction, solved the key industrialisation technologies for polyaniline resin, and developed a high-solids polyaniline anti-corrosion coating (solid content >75 wt%).

In 2005, the Changchun Institute of Applied Chemistry cooperated with Hunan Ben'an Yada New Material Co., Ltd., moving polyaniline anti-corrosion coatings from the laboratory to industrialisation and establishing the world's first 10,000-tonne polyaniline anti-corrosion coating production line. In the process, it participated in the formulation of a number of industry technical standards for polyaniline anti-corrosion technology, and its products have been widely applied in bridges, highways, airport terminals, high-speed rail and petroleum storage tanks.

Polyaniline has a unique reversible redox property. Its electrode potential is higher than that of most metals such as iron and aluminium, so the metal surface in contact with it is slowly oxidised. This slow oxidation reaction forms a dense oxide film on the metal surface, preventing corrosive media from further attacking the steel structure.

During this reaction, the polyaniline molecule is reduced to a reduced form whose electrode potential is lower than that of oxygen, and is then re-oxidised back to its original state by oxygen in the atmosphere, completing a “reversible polyaniline cycle”. Polyaniline is not consumed throughout the process, yet it enables a dense oxide film to form on the metal surface. A small amount of polyaniline is therefore sufficient to give the coating long-term anti-corrosion performance.

The principle of polyaniline anti-corrosion coatings lies in polyaniline's unique reversible redox property: polyaniline is not consumed during the process, yet a dense oxide film forms on the metal surface. Polyaniline can therefore “activate” the steel's own defence, generating a dense protective oxide film on its surface to achieve anti-corrosion performance, and the polyaniline content does not decrease during service.

Zinc-rich paint protects steel by “continuously sacrificing the zinc powder itself”. As time goes on the zinc powder diminishes, and once it is exhausted the anti-corrosion performance disappears. The effective film thickness of zinc-rich paint therefore decreases as the zinc is consumed, and eventually the coating loses its protective function. In one sentence: zinc-rich paint is “sacrificial” anti-corrosion, polyaniline is “activating” anti-corrosion — the two are fundamentally different.

Market research reports show that polyaniline anti-corrosion coating technology is already mature. Germany's Ormecon launched Corrpassive-brand polyaniline anti-corrosion coatings as early as 1996. In China, mass production began in 2005 and commercial products are available. For example, Hunan Ben'an Yada New Material Co., Ltd. operates a 10,000-tonne polyaniline anti-corrosion coating production line, and its products have been applied extensively in major landmark projects in China, making it a leading enterprise in this field.

Polyaniline has a higher electrode potential than the vast majority of metals. In addition to iron, it also provides anti-corrosion protection for most metals and alloys, including zinc, aluminium, copper, magnesium, aluminium alloys and magnesium alloys. This is precisely the universality of polyaniline anti-corrosion coatings — a property verified not only academically but also in actual applications such as copper/iron bolts and iron/galvanized layers.

Zinc-rich coatings work on the sacrificial anode principle and protect only iron; for metals more active than zinc, such as aluminium, zinc and magnesium alloys, they provide no protection.

Concrete structures show serious deterioration after 10–15 years of service, far short of the 50–100 year design life, and the cost of repair and reinforcement is 3 times the original construction cost. The most important source of concrete corrosion is corrosion of the reinforcing steel. Once the alkaline environment around embedded steel in the concrete is disrupted or chloride ions penetrate, numerous micro-corrosion cells form on the steel surface; iron loses electrons and gradually forms Fe(OH)₃, which accumulates between the steel surface and the concrete, generating large expansion stresses that cause the concrete cover to crack and spall continuously.

Polyaniline anti-corrosion coatings provide dual protection for both the concrete and the embedded steel: the film-forming resin component penetrates the porous concrete and seals it, protecting the concrete, while the polyaniline component that enters through the porous structure protects the embedded steel, forming a dense oxide layer that blocks the penetration of chloride ions and other corrosive media — addressing the root cause of concrete corrosion at its source. Polyaniline anti-corrosion coatings therefore do provide anti-corrosion protection for concrete.

Polyaniline anti-corrosion coatings include four major product categories: high-solids polyaniline anti-corrosion coatings (solid content >75 wt%), waterborne polyaniline anti-corrosion coatings, polyaniline powder coatings and UV-curable polyaniline anti-corrosion coatings. They contain no lead or chromium heavy metals and cause no heavy-metal pollution to the environment; with VOC below 350 g/L, they are a green and environmentally friendly coating.

Polyaniline anti-corrosion coatings can be applied to the protection of metals, alloys and concrete structures, including but not limited to bridges, highway guardrails, rail transit, large architectural steel structures, pipelines, heavy machinery, ships and port facilities.

According to the performance requirements for heavy-duty anti-corrosion coatings, the zinc powder content by weight in a zinc-rich coating must exceed 80% to meet anti-corrosion needs. Polyaniline anti-corrosion coatings have a lower density; at the same film thickness, the coverage area of a polyaniline coating is more than 1.5 times that of a zinc-rich coating. Combined with its long anti-corrosion life, this greatly reduces maintenance costs during operation. Polyaniline anti-corrosion coatings therefore offer very high cost-effectiveness — without increasing coating costs, they can reduce maintenance costs by more than 50%.

First, long-term anti-corrosion: polyaniline anti-corrosion coatings typically last more than 30 years, whereas zinc-rich paint typically lasts 10–15 years.

Second, an independent and controllable supply chain: the core material of polyaniline anti-corrosion coatings, polyaniline, is derived from aniline, and domestic capacity is self-sufficient and controllable, whereas zinc-rich paint depends on zinc ore resources, 80% of which come from overseas, raising concerns about security of supply.

Third, maintenance cost: over the full service life of a steel structure, polyaniline coatings require fewer than 2 maintenance interventions, while zinc-rich paint typically requires 3–4. Polyaniline anti-corrosion coatings therefore reduce later-stage maintenance costs and offer a clear competitive advantage.

Polyaniline anti-corrosion coatings already have relevant industry technical standards in several application fields, including three industry standards: JT/T 722-2026 Technical Conditions for Anti-Corrosion Coating of Highway Bridge Steel Structures, JT/T 600-2025 Anti-Corrosion Powder Coatings and Coating Layers for Highway Use, and JT/T 695-2026 Anti-Corrosion Coating of Highway Bridge Concrete Structures.

The anti-corrosion material in polyaniline anti-corrosion coatings is polyaniline; they contain no zinc powder.

The polyaniline content in polyaniline anti-corrosion coatings is 1–5%.

The polyaniline content in polyaniline anti-corrosion coatings can be tested in accordance with the local standard DB43/T 2421-2022 Determination of Polyaniline Content in Polyaniline Anti-Corrosion Coatings.

Polyaniline content has a major influence on anti-corrosion performance. To achieve the long-term anti-corrosion required by the design life, the polyaniline content in the coating should be 1–5 wt%, and the average polyaniline particle size should be between 0.5 and 10 microns.

High-solids polyaniline anti-corrosion coatings and waterborne polyaniline anti-corrosion coatings are both two-component and must be mixed on site immediately before use. Thermosetting polyaniline powder coatings and UV-curable polyaniline anti-corrosion coatings are one-component.

China's heavy-duty anti-corrosion coating volume exceeded 4.6 million tonnes in 2025, with a market size of more than RMB 180 billion. The industry is currently transitioning from “quantity” to “quality”, and polyaniline anti-corrosion coatings are in line with China's trend towards environmentally friendly, high-performance development, with broad market prospects.

Germany's Ormecon Chemical Company developed the Corrpassive series of marine polyaniline anti-corrosion products as early as 1999, and the United States, Japan and other countries subsequently developed related polyaniline anti-corrosion products, though on relatively small production scales.

In China, Hunan Ben'an Yada New Material Co., Ltd., through more than 20 years of long-term cooperation with the Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, has built the world's first 10,000-tonne polyaniline anti-corrosion coating production line. Its polyaniline anti-corrosion coating products have been widely applied in major projects of national importance in China, including bridges, expressways and airport terminals.

Verification of steel structure anti-corrosion is a lengthy process. As a completely new anti-corrosion technology, polyaniline anti-corrosion coatings have been validated through more than 20 years of actual anti-corrosion engineering. With tightening environmental regulations and growing demand for long-term anti-corrosion, more and more customers are gradually accepting polyaniline anti-corrosion coatings and beginning to actively seek polyaniline anti-corrosion solutions. In particular, in recent years polyaniline anti-corrosion coatings have attracted widespread attention in extreme service fields with harsh corrosive environments, such as offshore facilities, wind power, marine engineering and sea-crossing bridges.

The position of zinc-rich primer as an anti-corrosion coating is beyond doubt, and it remains the main competing product for polyaniline anti-corrosion coatings. Over the next 3–5 years the two product categories will coexist; as polyaniline anti-corrosion coatings become better known in the industry and their performance is understood, they will gradually replace zinc-rich primers and their usage will rise rapidly.

Polyaniline anti-corrosion coatings deliver excellent anti-corrosion performance in marine corrosive environments, marine atmospheric environments and high- and low-temperature environments, meeting anti-corrosion requirements under extreme service conditions, whereas conventional anti-corrosion coatings have relatively poor durability.

Based on this performance differentiation, demand for polyaniline anti-corrosion coatings is growing rapidly in harsh environments such as sea-crossing bridges, marine engineering, petrochemicals and new energy (photovoltaics, wind power).

China has already formed a complete and mature industrial chain covering polyaniline anti-corrosion coatings, from coating production and engineered anti-corrosion design to engineering anti-corrosion application. International demand for environmentally friendly anti-corrosion materials is strong, and because polyaniline coatings contain no heavy metals, they have very promising export prospects.

Polyaniline anti-corrosion coating applications include metal anti-corrosion and concrete anti-corrosion. Metal anti-corrosion is not limited to steel: it can efficiently protect most metals and alloys such as zinc, aluminium, magnesium and copper, and it also delivers excellent anti-corrosion results on concrete components.

Polyaniline anti-corrosion coatings have excellent cathodic disbondment resistance, and their comprehensive anti-corrosion performance is even more evident in marine environments and harsh corrosive conditions. Application fields include but are not limited to bridges, tunnels, highways, airport terminals, offshore equipment and wind power — across many sectors of national importance.

Polyaniline anti-corrosion coatings are suitable for all contact surfaces of bridge steel structures, including exposed external surfaces, enclosed internal surfaces of box sections, the underside of bridge decks, the top surface of uncovered steel bridge decks, the top surface of covered steel bridge decks, and unenclosed internal surfaces of box sections.

Sea-crossing bridges are located in harsh environments with high environmental protection requirements, and polyaniline anti-corrosion coatings offer significant advantages for the construction and maintenance of such bridges.

Polyaniline anti-corrosion coatings contain no heavy metals and are environmentally friendly: neither during bridge construction nor during on-site maintenance in later operation will they pollute the sea or rivers. More importantly, polyaniline anti-corrosion coatings have excellent anti-corrosion performance and outstanding resistance to acids, alkalis and salts, enabling long-term anti-corrosion protection for sea-crossing bridges.

Bridge piers of sea-crossing bridges are permanently exposed to high salinity and wave impact; whether stainless steel, alloy or concrete, they corrode and powder easily and are a “corrosion hotspot”. Polyaniline coatings have excellent salt-water resistance and can effectively prevent chloride ion attack, delivering very good anti-corrosion results on piers.

Wind turbine towers and blades are exposed to the marine atmospheric environment, where corrosion is severe and repair and maintenance are particularly difficult, usually requiring work at height and greatly increasing later O&M costs. Polyaniline anti-corrosion coatings resist high-humidity, high-salinity marine atmospheres and provide excellent anti-corrosion performance on offshore wind equipment, improving protection while substantially reducing later maintenance costs.

USVs are mainly made of aluminium alloy. Zinc-rich primers provide no anti-corrosion protection for this material, whereas polyaniline anti-corrosion coatings protect aluminium alloy very well and can meet demanding anti-corrosion requirements.

Offshore equipment and facilities, as well as sea-crossing bridges and tunnels, are permanently exposed to harsh marine corrosive environments with high salinity and high humidity, and short anti-corrosion life is an industry-wide pain point. Polyaniline anti-corrosion coatings offer excellent high-temperature, humid-heat and salt resistance, meeting anti-corrosion requirements under such harsh conditions and ensuring long-term protection for the related equipment.

Ports and wharves are permanently exposed to high salinity, high humidity and intense ultraviolet radiation, and the related equipment corrodes easily, requiring coatings with very good salt resistance.

Polyaniline anti-corrosion coatings strongly hinder the penetration of chloride ions and provide excellent anti-corrosion performance. Combined with a polyaniline anti-corrosion intermediate coat and a fluorocarbon topcoat to form a composite coating, they can effectively address both corrosion and UV-aging resistance.

Germany's Ormecon Chemical Company launched its Corrpassive series as early as 1994, dedicated to anti-corrosion in the marine sector. It was found that the anti-corrosion life of polyaniline anti-corrosion coatings on ships is 5 times that of traditional zinc-rich anti-corrosion paint.

Ballast water tanks are enclosed, alternate between wet and dry, and face highly corrosive seawater — they are a “corrosion hotspot” on ships. Thanks to their excellent water, salt, chemical and humid-heat resistance, polyaniline coatings can effectively extend the anti-corrosion performance of equipment in this area.

Highway corrugated guardrails are exposed to JC3–JC4 atmospheric conditions. Polyaniline anti-corrosion coatings fully meet the anti-corrosion requirements for highway guardrails and can more than triple anti-corrosion performance.

Concrete components of roads and bridges in severely cold regions suffer more serious deterioration. One reason is that a large amount of chloride ions from de-icing salt spread on the road surface in winter penetrates the porous structure of the concrete, accelerating the saturation of water in the pores; under freeze-thaw action, the expansion and contraction of the water damages the concrete structure. Another main reason is that chloride ions from the de-icing salt that penetrate the cement cause pitting corrosion of the reinforcing steel in the concrete, causing rapid corrosion from the inside out.

Polyaniline anti-corrosion coatings are excellent at preventing the damage caused by chloride-induced pitting, and polyaniline penetrates to the reinforcing steel within the porous cement, providing very good protection for embedded steel. Polyaniline anti-corrosion coatings can therefore solve anti-corrosion problems in concrete components of roads and bridges in severely cold, high-salinity regions, including bridge deck expansion joints, drainage holes and crash barriers.

Train carriages are mostly made of iron, aluminium and magnesium alloys. Polyaniline anti-corrosion coatings protect these metals very well, and are especially effective on aluminium-magnesium alloys with excellent adhesion, ensuring there is no risk of paint loss during high-speed operation — of great value for improving railway operating safety and reducing whole-life costs.

Polyaniline anti-corrosion coatings can certainly be used. Thermal power plants and chemical plants are permanently exposed to acidic and alkaline industrial atmospheres, which corrode steel components severely; polyaniline anti-corrosion coatings have excellent chemical resistance, protect steel components well in this sector and provide long-term protection.

Polyaniline anti-corrosion coatings can certainly be used. Their excellent environmental tolerance ensures that the coating protects steel pipework well in the complex environment of buried pipelines, achieving a long service life for the pipework.

These large construction projects require good anti-corrosion durability and aesthetics, and particularly high fire safety and environmental performance. Polyaniline anti-corrosion coatings offer good anti-corrosion performance and excellent compatibility with fire-retardant coatings and topcoats; they have passed rigorous toxicity testing and fully comply with relevant standards, and there are already many construction cases of this type.

High-voltage transmission towers and photovoltaic mounting structures made of aluminium alloy, stainless steel, galvanized steel or concrete are permanently exposed to intense ultraviolet light, wind-blown sand and industrial atmospheres. A composite coating of a polyaniline anti-corrosion primer, a polyaniline epoxy intermediate coat and a fluorocarbon topcoat can address the anti-corrosion and aging problems of these long-term outdoor installations.

Polyaniline anti-corrosion coatings can certainly be used. They offer scratch resistance, vibration resistance and long anti-corrosion life, reducing the maintenance frequency of outdoor working equipment and lowering operating costs.

Polyaniline powder coatings can be used for anti-corrosion protection of highway corrugated guardrails, and there are already relevant application cases; the related technology is reflected in the industry standard JT/T 600-2025 Anti-Corrosion Powder Coatings and Coating Layers for Highway Use.

For the repair and maintenance of corrugated guardrails, high-solids polyaniline anti-corrosion coatings can be used to meet on-site application requirements, and application is more convenient; for details refer to the technical standard JT/T 722-2026 Technical Conditions for Anti-Corrosion Coating of Highway Bridge Steel Structures.

The corrosive environment of hydraulic steel gates is far less severe than a marine corrosive environment. Polyaniline anti-corrosion coatings fully meet the anti-corrosion requirements of equipment in this environment and provide very good protection for hydraulic steel gates.

Waterborne polyaniline anti-corrosion coatings can be used and fully meet the anti-corrosion performance requirements for shipping containers.