A light-assisted anticorrosive coating material based on metal coordination structure and a preparation method thereof

Abstract

The application discloses a kind of light-assisted anticorrosion coating materials and preparation method based on metal coordination structure, the light-assisted anticorrosion coating material is on the basis of traditional anticorrosion metal zinc layer continue to be coordinated with the metal coordination polymer Co (bpy) (dhbq) (bq) with photoelectric conversion capability, and form coordination complex Co (bpy) (dhbq) (bq) @Zn.Because metal coordination polymer Co (bpy) (dhbq) (bq) itself can additionally generate photo-generated electron and photo-generated current after being illuminated, provide redundant charge for Zn layer, make it be in lower potential, strengthen the function of cathodic protection.Corrosion can be inhibited through this mechanism, prolong the service life of Zn layer, provide efficient, green anticorrosion protection for the steel material that needs to be protected.In addition, metal coordination light-assisted anticorrosion technology can also inhibit marine bioattachment by slowly releasing metal ions Co, prevent biofilm formation, reduce microbial growth, prolong the service life of protected material in marine environment, also applicable to underwater bioinduced corrosion and the protection of fouling metal structure.

Description

Technical Field

[0001] This invention belongs to the field of corrosion protection for marine equipment or coastal facilities, and specifically relates to a light-assisted anti-corrosion coating material based on metal coordination structure and its preparation method. Background Technology

[0002] The application of photo-assisted anti-corrosion coatings primarily stems from the need to protect metallic materials in corrosive environments, particularly in marine, chemical, and construction fields. Metallic materials, especially steel, aluminum alloys, and zinc, are prone to oxidation and corrosion when exposed to corrosive environments such as moisture, salt spray, and acids / alkalis for extended periods. This leads to a decline in structural performance and increased maintenance costs. While traditional anti-corrosion methods such as coatings, cathodic protection, and sacrificial anode methods are effective, they may present problems such as environmental pollution and limited service life. Therefore, it is essential to protect the coating surface to inhibit corrosion from seawater and other corrosive media.

[0003] Currently, corrosion protection technologies both domestically and internationally mainly fall into three categories: 1. Organic anti-corrosion coating technology; 2. Cathodic protection technology; and 3. Composite protection method using sacrificial anodes and organic coatings.

[0004] Technique 1: Organic anti-corrosion coatings are one of the most common anti-corrosion methods. They primarily work by applying a protective coating (such as epoxy resin, polyurethane, or polyvinyl chloride) to the metal surface to isolate the metal from corrosive media, thus preventing corrosion. Coating anti-corrosion technology is widely used and applicable to offshore platforms, ships, marine facilities, and land-based metal structures. However, in service environments (such as seawater), coatings may peel, crack, or age due to mechanical damage, ultraviolet radiation, and chemical corrosion, leading to a reduction in anti-corrosion effectiveness. Furthermore, the effective protection period of coatings is limited, especially in marine environments, where regular maintenance and recoating require significant manpower and resources.

[0005] Technique two, cathodic protection, involves connecting a metal surface to a sacrificial anode (typically zinc, aluminum, or magnesium) or an external current source (such as a current-driven cathodic protection system), making the metal surface the cathode and thus preventing anodic oxidation corrosion. This method is widely used in structures such as subsea pipelines and offshore platforms. However, it requires an external power source, increasing operating costs and system complexity. Alternatively, a zinc block can be welded as a sacrificial anode, but the metal anode gradually wears down during use and must be replaced periodically, increasing maintenance complexity and cost.

[0006] Technology 3, the composite corrosion protection technology of sacrificial anode plus organic coating, is a long-term protection technology widely used in metal structures, especially suitable for facilities such as underground pipelines, storage tanks, ship hulls, steel piles, and offshore platforms that are exposed to corrosive environments for a long time. The coating, as the first line of defense, isolates the metal surface from direct contact with corrosive media (such as water, electrolytes, and oxygen), reducing the possibility of corrosion. When the coating has defects or ages and peels off, the metal anode loses electrons at a lower potential to prevent the protected steel from undergoing redox reactions, thereby inhibiting its corrosion process. Widely used composite coating systems use coatings with cathodic protection, such as epoxy zinc-rich coatings, inorganic zinc-rich coatings, or hot-dip galvanized layers, as the base coat, topped with intermediate and top coats that provide physical barriers. This often results in thick-film protection, increasing costs and leading to problems such as cracking and peeling of the thick film, causing premature failure. Summary of the Invention

[0007] The technical problem this invention aims to solve is the high cost associated with traditional anti-corrosion technologies that rely on current supply and periodic anode replacement, as well as the reduced anti-corrosion effect, high maintenance costs, environmental pollution, uneven protection, and biofouling issues faced by traditional marine anti-corrosion technologies. This invention provides a novel light-assisted anti-corrosion coating material and its preparation method based on metal coordination structures. This material provides continuous protection through the photoelectric effect, reduces maintenance costs, uses environmentally friendly materials to avoid pollution, uniformly protects the metal surface, inhibits marine biofouling, and improves anti-corrosion effect and service life. Furthermore, it can be applied to the treatment of fouling on the coating surfaces of marine equipment.

[0008] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0009] A photo-assisted anti-corrosion coating material based on a metal coordination structure comprises cobalt nitrate hexahydrate, 2,2'-bipyridine (2,2'-bpy), 2,5-dihydroxy-1,4-benzoquinone (DHBQ), and p-benzoquinone (BQ). The photo-assisted anti-corrosion coating material is a composite Co(bpy)(dhbq)(bq)@Zn formed by coordinating a Co(bpy)(dhbq)(bq) film onto the surface of a zinc plate or a zinc-containing anti-corrosion primer. The zinc-containing anti-corrosion primer is a zinc plating layer or a zinc powder coating.

[0010] A method for preparing the above-mentioned light-assisted anti-corrosion coating material includes the following steps:

[0011] S1. Preparation of metal coordination polymer Co(bpy)(dhbq)(bq): Using cobalt nitrate hexahydrate, 2,2'-bipyridine (2,2'-bpy), 2,5-dihydroxy-1,4-benzoquinone (DHBQ) and p-benzoquinone (BQ) as raw materials, metal coordination polymer Co(bpy)(dhbq)(bq) was prepared by precipitation method;

[0012] S2. Preparation of Co(bpy)(dhbq)(bq) aqueous solution: Dissolve the prepared metal coordination polymer Co(bpy)(dhbq)(bq) in deionized water to obtain Co(bpy)(dhbq)(bq) aqueous solution;

[0013] S3. Preparation of composite Co(bpy)(dhbq)(bq)@Zn: Co(bpy)(dhbq)(bq) film is coordinated onto the surface of zinc plate or zinc-containing anti-corrosion primer by water bath method to obtain composite Co(bpy)(dhbq)(bq)@Zn.

[0014] Preferably, the preparation method of the light-assisted anti-corrosion coating material includes the following steps:

[0015] S11. Add 1.0 mmol of cobalt nitrate hexahydrate to a 100 ml round-bottom flask containing 10 ml of methanol.

[0016] S12. Dissolve 1.0 mmol of 2,2'-bipyridine in 10 ml of methanol and add it dropwise to the round-bottom flask mentioned above, then stir continuously at 50 °C for 2 h.

[0017] S13. Dissolve 2.0 mmol of 2,5-dihydroxy-1,4-benzoquinone and 4.0 mmol of triethylamine in 10 ml of methanol, and add the solution dropwise to the round-bottom flask of step S12, and stir at 50 °C for 0.5 h.

[0018] S14. Dissolve 1.0 mmol of p-benzoquinone in 10 ml of methanol, and add the solution dropwise to the round-bottom flask of step S13, and stir at 50 °C for 0.5 h.

[0019] S15. After cooling the mixture obtained in step S14 to room temperature, remove 2 / 3 of the solvent by rotary evaporation, add 30 ml of diethyl ether, filter the solution after 20 minutes to obtain a dark red precipitate, and then dry it in vacuum at 80 °C for 12-16 h to assemble the metal coordination polymer Co(bpy)(dhbq)(bq).

[0020] S16. Dissolve the obtained Co(bpy)(dhbq)(bq) in an appropriate amount of deionized water to prepare a 20 g / L Co(bpy)(dhbq)(bq) aqueous solution, and keep it in a 60℃ water bath for 30 min.

[0021] S17. Immerse the polished zinc plate in the Co(bpy)(dhbq)(bq) aqueous solution obtained in step S16 for 20 min, and maintain a water bath at 60°C to form a Co(bpy)(dhbq)(bq) anti-corrosion film on the surface of the zinc plate, thus obtaining Co(bpy)(dhbq)(bq)@Zn.

[0022] Preferably, the above-mentioned light-assisted anti-corrosion coating material or the light-assisted anti-corrosion coating material prepared by the above preparation method can be applied to the surface of metal structures to form a corrosion protection layer.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] Photoelectric marine corrosion protection technology generates electrical charges through the photoelectric effect, providing continuous charge protection to metal surfaces and inhibiting corrosion. This corrosion protection mechanism requires no external power source or frequent maintenance, utilizing the continuously regenerating resources of sunlight, thus avoiding the high costs of traditional corrosion protection technologies that rely on current supply and periodic anode replacement, while achieving long-term protection. Traditional technologies such as coatings and sacrificial anodes are prone to aging, peeling, or consumption over time, leading to a gradual weakening of the corrosion protection effect, requiring recoating or replacement of sacrificial anodes. In contrast, the photoelectric anti-corrosion coating coordinates with the surface zinc layer to form an integrated thin-film protective layer, eliminating the risk of coating peeling. It is spontaneously activated under sunlight, providing long-term stable performance, reducing manual intervention and maintenance frequency, significantly lowering maintenance costs, and providing longer-lasting protection. This invention can be widely used for corrosion protection of marine vessels, offshore platforms, submarine cables, nuclear power plant water pipelines, and coastal facilities, possessing extremely high practical application value.

[0025] Furthermore, traditional anti-corrosion technologies often suffer from uneven surface protection, especially since cathodic protection or sacrificial anodes may fail to provide sufficient protection in certain areas, leading to localized corrosion. In contrast, photoelectric coordination anti-corrosion technology can uniformly provide electronic protection to the metal surface, ensuring comprehensive anti-corrosion effects. Moreover, the photoelectric anti-corrosion coating also inhibits the attachment of marine organisms. By releasing trace amounts of metal ions or altering the charge characteristics of the metal surface, it effectively reduces the attachment of algae, shellfish, and other organisms, avoiding corrosion and increased navigation drag caused by biofouling, thereby further improving the efficiency and service life of facilities. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the photo-assisted anti-corrosion mechanism of the photo-assisted anti-corrosion coating material of the present invention;

[0027] Figure 2 This is a characterization diagram of the synthesis of Co(bpy)(dhbq)(bq) with photoelectric conversion function according to an embodiment of the present invention; wherein, Figure 2 a is the Fourier transform infrared spectrum of DHBQ, Co(bpy) and Co(bpy)(dhbq); Figure 2 b is the Fourier transform infrared spectrum of BQ, Co(bpy)(dhbq)(bq), and Co(bpy)(dhbq). 2c is a scanning electron microscope image of Co(bpy)(dhbq)(bq) powder; 2d is the UV-Vis spectrum of Co(bpy)(dhbq)(bq) powder and the Dow plot of Co(bpy)(dhbq)(bq) powder (top right inset).

[0028] Figure 3 This is the photoelectric performance response diagram of Co(bpy)(dhbq)(bq) according to an embodiment of the present invention; wherein, Figure 3 a represents the hole distribution equipotential diagram (value = 0.0009), electron distribution equipotential diagram (value = 0.0009), and electron-hole distribution equipotential diagram (value = 0.0009), respectively. Blue represents holes and green represents electrons. Figure 3 b is a heatmap showing the contribution of each molecule to electrons and holes, where 1 corresponds to bpy, 2 corresponds to the Co atom, and 3 corresponds to DHBQ.

[0029] Figure 4 This is a comparison chart of the anti-corrosion effects of Embodiment 1 and Comparative Example 1 of the present invention using Tafel curves. Detailed Implementation Example 1

[0030] A photo-assisted anti-corrosion coating material based on a metal coordination structure is disclosed. The raw materials include cobalt nitrate hexahydrate, 2,2'-bipyridine (2,2'-bpy), 2,5-dihydroxy-1,4-benzoquinone (DHBQ), and p-benzoquinone (BQ). This photo-assisted anti-corrosion coating material is a composite material Co(bpy)(dhbq)(bq)@Zn formed by coordinating a Co(bpy)(dhbq)(bq) film onto a zinc plate or a zinc-containing anti-corrosion primer. The zinc-containing anti-corrosion primer is a zinc plating layer or a zinc powder coating. Specifically, this photo-assisted anti-corrosion coating material can be prepared through the following steps:

[0031] S11. Add 1.0 mmol of cobalt nitrate hexahydrate to a 100 ml round-bottom flask containing 10 ml of methanol.

[0032] S12. Dissolve 1.0 mmol of 2,2'-bipyridine in 10 ml of methanol and add it dropwise to the round-bottom flask containing cobalt nitrate. Then stir continuously at 50 °C for 2 h.

[0033] S13. Dissolve 2.0 mmol of 2,5-dihydroxy-1,4-benzoquinone and 4.0 mmol of triethylamine in 10 ml of methanol, and add the solution dropwise to the round-bottom flask of step S12, and stir at 50 °C for 0.5 h.

[0034] S14. Dissolve 1.0 mmol of p-benzoquinone in 10 ml of methanol, and add the solution dropwise to the round-bottom flask of step S13, and stir at 50 °C for 0.5 h.

[0035] S15. After cooling the mixture obtained in step S14 to room temperature, remove 2 / 3 of the solvent by rotary evaporation, add 30 ml of diethyl ether, filter the solution after 20 minutes to obtain a dark red precipitate, and then dry it in vacuum at 80 °C for 12-16 h to assemble the metal coordination polymer Co(bpy)(dhbq)(bq).

[0036] S16. Dissolve the obtained Co(bpy)(dhbq)(bq) in an appropriate amount of deionized water to prepare a 20 g / L Co(bpy)(dhbq)(bq) aqueous solution, and keep it in a 60℃ water bath for 30 min.

[0037] S17. Immerse the polished zinc plate in the Co(bpy)(dhbq)(bq) aqueous solution obtained in step S16 for 20 min, and maintain a water bath at 60°C to form a Co(bpy)(dhbq)(bq) anti-corrosion film on the surface of the zinc plate, thus obtaining Co(bpy)(dhbq)(bq)@Zn.

[0038] Comparative Example 1

[0039] The sacrificial anode protection method is directly adopted by installing zinc as the anode on the metal structure.

[0040] The present invention will be further described below with reference to specific embodiments and accompanying drawings:

[0041] This invention provides a photo-assisted anti-corrosion coating material based on a metal coordination structure; its photo-assisted anti-corrosion mechanism or working principle is as follows: Figure 1As shown, it utilizes the photoelectric conversion capability of metal coordination polymers to generate additional photoelectrons and photocurrents upon exposure to light. This provides excess charge to the Zn layer, placing it at a lower potential and inhibiting corrosion. This effectively protects the desired surface, preventing oxygen and corrosive ions in seawater from directly contacting the metal, reducing the corrosion rate, and thus achieving the goal of inhibiting metal corrosion.

[0042] Figure 2 The following diagram illustrates the synthesis and characterization of Co(bpy)(dhbq)(bq) with photoelectric conversion function according to an embodiment of the present invention. Figure 2a shows the FTIR spectrum of the prepared composite, indicating that the peak value is located at 1016 cm⁻¹. -1 The characteristic peak at 1441 cm⁻¹ belongs to the symmetric stretching ν(Co-N) vibration mode, indicating the establishment of Co-N coordination. -1 The peak at 100 cm⁻¹ is attributed to C=N, and then shifts to 1400 cm⁻¹ after the coordination reaction of ligand DHBQ with Co(bpy). -1 Furthermore, after the coordination reaction, C=O at 1670 cm⁻¹ -1 The peak shifted to 1659 cm. -1 Therefore, the successful synthesis of Co(bpy)(dhbq) can be concluded. Based on this, from... Figure 2 b. It can be observed that with the addition of the new ligand BQ, the position at 1659 cm⁻¹... -1 The intensity of the C=O characteristic peak at the point of induction was further enhanced, thus horizontally verifying the successful preparation of Co(bpy)(dhbq)(bq). Figure 2c shows a scanning electron microscope (SEM) image of the Co(bpy)(dhbq)(bq) powder. The Co coordination polymer exhibits a roughly spherical, closely packed morphology with a wide variation in particle size, mostly in the 200-500 nm range. All these observations demonstrate the successful stepwise synthesis of Co(bpy)(dhbq)(bq). The UV-Vis spectrum given in Figure 2d shows strong absorption and prominent peaks at wavelengths of 300 and 355 nm, confirming the suitability and significant trend of Co(bpy)(dhbq)(bq) for photoelectric activity. The corresponding Tauc plot (i.e., Tauc plot, see the upper right inset of Figure 2d) shows a band gap (Eg) of 2.34 eV, indicating higher conductivity and laying a material foundation for subsequent composite with Zn, as well as subsequent self-healing and corrosion-resistant properties.

[0043] To more clearly observe the transfer process of electrons and holes after light absorption and to theoretically verify that Co(bpy)(dhbq)(bq) can effectively separate electrons and holes, a Gaussian 09 simulation was performed to visualize the distribution of electrons and holes more intuitively. Multiwfn analysis following excited-state calculations determined the dominant excited states at 365 nm, and a visualization simulation was then conducted based on these states. Figure 3 ). Figure 3 ab is an equipotential diagram of the electron and hole distribution within the Co(bpy)(dhbq)(bq) molecule and a corresponding fragment charge transfer hotspot diagram. A large number of electrons were found to land on DHBQ. Holes were correspondingly distributed on 2,2'-bipyridine, Co, and BQ. After illumination, Co(bpy)(dhbq)(bq) generated photogenerated electrons and holes, which were effectively separated. This provided excess charge to the Zn layer, placing it at a lower potential and inhibiting corrosion. Simultaneously, the generated photogenerated electrons were injected into the metallic Zn layer, increasing the electron density and making the Zn layer surface more susceptible to electrochemical reactions. This led to reversible Zn layer consumption, effectively and sustainably protecting the required metal surface, preventing direct contact between oxygen and corrosive ions in seawater and the metal, reducing the corrosion rate, and achieving the goal of inhibiting metal corrosion.

[0044] Anti-corrosion effect such as Figure 4 As shown. Polarization (Tafel) curve tests were performed on metal materials with photo-assisted corrosion protection using the attached metal coordination complex Co(bpy)(dhbq)(bq)@Zn and metal materials with corrosion protection using a simple traditional Zn layer. Figure 4 Polarization curves are an important method for studying metal corrosion. Information such as corrosion potential and corrosion current can be obtained from polarization curves, thus determining the degree of corrosion. Corrosion potential (Ecorr) and corrosion current (Icorr) can be estimated by extrapolating the linear Tafel regions on the cathode and anodic branches. In the Tafel curve, the smaller the Ecorr, the less susceptible the metal is to corrosion. Specific data for the polarization curves of Example 1 and Comparative Example 1 are shown in Table 1. Here, Ecorr and Icorr represent corrosion voltage and corrosion current, respectively, and β... a and β b These represent the slopes of the anodic polarization curve and the cathodic polarization curve, respectively.

[0045] Table 1: Electrochemical parameters obtained from the polarization curves of Example 1 and Comparative Example 1

[0046]

[0047] like Figure 4As shown, the red curve represents the polarization curve for photo-assisted corrosion protection, while the black curve represents the polarization curve for traditional Zn layer corrosion protection. When photo-assisted corrosion protection is performed, the voltage Ecorr of the red curve decreases significantly, from -0.777 V in the comparative traditional zinc anodic protection to -1.073 V in the photo-assisted corrosion protection of this case, a decrease of 296 mV. This decrease in Ecorr indicates that Co(bpy)(dhbq)(bq) provides a large number of photogenerated electrons to the Zn layer and the protected material, resulting in the protected material being at a lower potential and better inhibiting seawater corrosion of Zn and the protected material. The current Icorr increased from 11.02 μA in the comparative traditional zinc anode protection to 546.8 μA in the photo-assisted corrosion protection of this case, an increase of 535.78 μA. This is because after the electrons generated by the Co(bpy)(dhbq)(bq) photo-assisted technology are injected into the Zn layer, the overall electron density increases, making Zn more susceptible to electrochemical reactions. This also demonstrates the effective protection of metal materials by Co(bpy)(dhbq)(bq)@Zn, achieving the purpose of inhibiting metal corrosion.

[0048] This invention is not limited to the specific embodiments described above. For those skilled in the art, all modifications made based on the above concept without creative effort fall within the protection scope of this invention.

Claims

1. A light-assisted anti-corrosion coating material based on metal coordination structure, characterized in that, The raw materials include cobalt nitrate hexahydrate, 2,2'-bipyridine (bpy), 2,5-dihydroxy-1,4-benzoquinone (DHBQ), and p-benzoquinone (BQ); the photo-assisted anti-corrosion coating material is a composite Co(bpy)(dhbq)(bq)@Zn formed by coordinating a Co(bpy)(dhbq)(bq) film onto the surface of a zinc plate or a zinc-containing anti-corrosion primer.

2. The photo-assisted anti-corrosion coating material based on metal coordination structure according to claim 1, characterized in that, The zinc anti-corrosion primer is a zinc-plated layer or a zinc-containing powder coating.

3. A method for preparing a light-assisted anti-corrosion coating material according to claim 1, characterized in that, Includes the following steps: S1. Preparation of metal coordination polymer Co(bpy)(dhbq)(bq): Using cobalt nitrate hexahydrate, 2,2'-bipyridine (bpy), 2,5-dihydroxy-1,4-benzoquinone (DHBQ) and p-benzoquinone (BQ) as raw materials, metal coordination polymer Co(bpy)(dhbq)(bq) was prepared by precipitation method. S2. Preparation of Co(bpy)(dhbq)(bq) aqueous solution: Dissolve the prepared metal coordination polymer Co(bpy)(dhbq)(bq) in deionized water to obtain Co(bpy)(dhbq)(bq) aqueous solution; S3. Preparation of the composite Co(bpy)(dhbq)(bq)@Zn: Co(bpy)(dhbq)(bq) film is coordinated onto zinc plate or zinc-containing anti-corrosion primer by water bath method to obtain the composite Co(bpy)(dhbq)(bq)@Zn.

4. The preparation method according to claim 3, characterized in that, The preparation of the metal coordination polymer Co(bpy)(dhbq)(bq) in step S1 includes the following steps: S11. Add 1.0 mmol of cobalt nitrate hexahydrate to a 100 ml round-bottom flask containing 10 ml of methanol; S12. Dissolve 1.0 mmol of 2,2'-bipyridine in 10 ml of methanol and add it dropwise to the round-bottom flask mentioned above, then stir continuously at 50°C for 2 h; S13. Dissolve 2.0 mmol of 2,5-dihydroxy-1,4-benzoquinone and 4.0 mmol of triethylamine in 10 ml of methanol, and add the solution dropwise to the round-bottom flask of step S12, and stir at 50 °C for 0.5 h; S14. Dissolve 1.0 mmol of p-benzoquinone in 10 ml of methanol, and add the solution dropwise to the round-bottom flask of step S13, and stir at 50 °C for 0.5 h; S15. After cooling the mixture obtained in step S14 to room temperature, remove 2 / 3 of the solvent by rotary evaporation, add 30 ml of diethyl ether, filter the solution after 20 minutes to obtain a dark red precipitate, and then dry it in vacuum at 80 °C for 12-16 h to assemble the metal coordination polymer Co(bpy)(dhbq)(bq).

5. The preparation method according to claim 4, characterized in that, The step S2, preparing the Co(bpy)(dhbq)(bq) aqueous solution, is as follows: The obtained Co(bpy)(dhbq)(bq) was dissolved in an appropriate amount of deionized water to prepare a 20 g / L Co(bpy)(dhbq)(bq) aqueous solution, and kept in a 60℃ water bath for 30 min.

6. The preparation method according to claim 5, characterized in that, The step S3 for preparing the composite Co(bpy)(dhbq)(bq)@Zn is as follows: the polished zinc plate is immersed in the Co(bpy)(dhbq)(bq) aqueous solution that has been kept in a 60°C water bath for 30 min for 20 min, and the water bath is kept at 60°C to form a Co(bpy)(dhbq)(bq) anti-corrosion film on the surface of the zinc plate, thus obtaining Co(bpy)(dhbq)(bq)@Zn.

7. The light-assisted anti-corrosion coating material according to any one of claims 1-2 or the light-assisted anti-corrosion coating material prepared by the preparation method according to any one of claims 3-6 is applied to the surface of a metal structure to achieve corrosion protection.

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