Photo-assisted anti-corrosion coating material based on metal coordination structure and preparation method of photo-assisted anti-corrosion coating material

Abstract

The invention discloses a photo-assisted anti-corrosion coating material based on a metal coordination structure and a preparation method, the photo-assisted anti-corrosion coating material is continuously coordinated with a metal coordination polymer Co (bpy) (dhbq) (bq) with photoelectric conversion capability on the basis of a traditional anti-corrosion metal zinc layer to form a coordination compound Co (bpy) (dhbq) (bq) (at) Zn. Due to the fact that the metal coordination polymer Co (bpy) (dhbq) (bq) can additionally generate photo-generated electrons and photo-generated currents after being illuminated, redundant charges are provided for the Zn layer, the Zn layer is made to be in a low potential, and the cathode protection function is enhanced. Through the mechanism, corrosion can be inhibited, the service life of the Zn layer can be prolonged, and efficient and green anti-corrosion protection is provided for steel and iron materials needing to be protected. In addition, by slowly releasing metal ions Co, the metal coordination light-assisted anticorrosion technology can inhibit marine organism adhesion, prevent biofilm formation, reduce microbial growth and prolong the service life of a protected material in a marine environment, and is also suitable for underwater organism induced corrosion and protection of stained metal structures.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of corrosion protection of marine equipment or coastal facilities, and particularly relates to a light-assisted corrosion protection coating material based on metal coordination structure and a preparation method thereof. BACKGROUND

[0002] The application background of light-assisted corrosion protection coating mainly comes from the protection demand of metal materials in corrosive environments, especially in the fields of marine, chemical industry and construction. Metal materials, especially steel, aluminum alloy and zinc, are easily oxidized and corroded when exposed to humid air, salt spray, acid and alkali for a long time, which leads to the decline of structural performance and increases the maintenance cost. Although traditional corrosion protection methods such as coating, cathodic protection and sacrificial anode method are effective, they may have problems such as environmental pollution and limited service life. Therefore, the surface of the coating must be protected to inhibit the corrosion of seawater and other corrosive media.

[0003] At present, the corrosion protection at home and abroad mainly forms the following three technologies: 1. organic corrosion protection coating technology, 2. cathodic protection technology, and 3. composite protection method of sacrificial anode and organic coating.

[0004] Technology 1, organic corrosion protection coating technology, is one of the most common corrosion protection methods, which mainly isolates the contact between metal and corrosive medium by coating a protective coating (such as epoxy resin, polyurethane, polyvinyl chloride, etc.) on the surface of the metal, so as to prevent corrosion. Coating corrosion protection technology is widely used and suitable for marine platforms, ships, offshore facilities and land metal structures. However, the coating may fall off, crack or age due to mechanical damage, ultraviolet radiation and chemical corrosion in the service environment (such as seawater), which reduces the corrosion protection effect. In addition, the effective protection period of the coating is limited, especially in marine environments, which requires a lot of manpower and material resources for regular maintenance and re-coating.

[0005] Technology 2, cathodic protection technology, connects the metal surface to a sacrificial anode (usually zinc, aluminum or magnesium) or an external current source (such as a current-driven cathodic protection system), so that the metal surface becomes a cathode, thereby avoiding anodic oxidation corrosion. This method is widely used in structures such as submarine pipelines and offshore platforms. However, an external power source is required, which increases the operating cost and system complexity. Alternatively, zinc blocks are welded as sacrificial anodes, but the metal anodes will gradually consume during use, which must be replaced regularly, increasing the complexity and cost of maintenance.

[0006] Technology three, the composite corrosion protection technology of sacrificing anode plus organic coating is a long-acting protection technology widely used in metal structures, especially suitable for facilities such as underground pipelines, storage tanks, ship hulls, steel piles, offshore platforms and the like which are exposed to corrosive environments for a long time. The coating acts as the first line of defense, isolating the metal surface from direct contact with corrosive media (such as water, electrolytes, oxygen), reducing the likelihood of corrosion. When the coating has defects or is aged and falls off, the metal anode loses electrons at a lower potential to prevent the protected steel metal from undergoing redox reactions, thereby inhibiting the corrosion process. The widely used composite coating system uses a coating with cathodic protection such as an epoxy zinc-rich coating, an inorganic zinc-rich coating, and a hot-dip zinc layer as a base coating, and a top coating with physical barrier, usually combined into a thick film protection, which increases the cost and causes the problem of cracking and falling off of the thick film, resulting in premature failure. SUMMARY

[0007] The technical problem to be solved by the present application is: in view of the problems of high cost caused by the dependence on current supply and regular replacement of anodes in traditional corrosion protection technology, and the problems of weakened corrosion protection effect, high maintenance cost, environmental pollution, uneven protection, and biological attachment faced by traditional marine corrosion protection technology, the present application provides a light-assisted corrosion protection coating material based on metal coordination structure and a preparation method, which can provide continuous protection through photoelectric effect, reduce maintenance cost, use environmentally friendly materials, avoid pollution, uniformly protect the metal surface, inhibit marine biological attachment, and improve the corrosion protection effect and service life of a new type of light-assisted corrosion protection technology. And can be applied to the fouling management of the coating surface of marine equipment.

[0008] The technical solution adopted by the present application to solve the above technical problems is: A light-assisted corrosion protection coating material based on metal coordination structure, comprising raw materials of cobalt nitrate hexahydrate, 2,2'-bipyridine (2,2'-bpy), 2,5-dihydroxy-1,4-benzoquinone (DHBQ) and p-benzoquinone (BQ); the light-assisted corrosion protection coating material is a complex Co(bpy)(dhbq)(bq)@Zn. formed by the Co(bpy)(dhbq)(bq) film coordinated on the surface of a zinc plate or a metal zinc corrosion-resistant base coating, wherein the metal zinc corrosion-resistant base coating is a zinc plating layer or a zinc powder coating.

[0009] A preparation method of the above-mentioned light-assisted corrosion protection coating material, comprising the following steps: S1. Preparing a 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, a metal coordination polymer Co(bpy)(dhbq)(bq) is prepared by a precipitation method; S2. Preparation of Co(bpy)(dhbq)(bq) aqueous solution: The prepared metal coordination polymer Co(bpy)(dhbq)(bq) was dissolved in deionized water to obtain Co(bpy)(dhbq)(bq) aqueous solution; S3. Preparation of composite Co(bpy)(dhbq)(bq)@Zn: The Co(bpy)(dhbq)(bq) film was coordinated on the surface of zinc plate or zinc metal-containing anticorrosive primer by water bath method to obtain the composite Co(bpy)(dhbq)(bq)@Zn.

[0010] Preferably, the preparation method of the light-assisted anticorrosive coating material comprises the following steps: S11. 1.0 mmol of cobalt nitrate hexahydrate was added to a 100 ml round-bottom flask containing 10 ml of methanol.

[0011] S12. 1.0 mmol of 2,2'-bipyridine was dissolved in 10 ml of methanol and added dropwise to the above-mentioned round-bottom flask, then continuously stirred at 50 °C for 2 h.

[0012] S13. 2.0 mmol of 2,5-dihydroxy-1,4-benzoquinone and 4.0 mmol of triethylamine were dissolved in 10 ml of methanol, and the solution was added dropwise to the round-bottom flask of step S12 and stirred at 50 °C for 0.5 h.

[0013] S14. 1.0 mmol of p-benzoquinone was dissolved in 10 ml of methanol, and the solution was added dropwise to the round-bottom flask of step S13 and stirred at 50 °C for 0.5 h.

[0014] S15. After the mixture obtained from step S14 was cooled to room temperature, 2 / 3 of the solvent was removed by rotary evaporation, and 30 ml of diethyl ether was added thereto, and after 20 minutes, the solution was filtered to obtain a dark red precipitate, which was then dried in a vacuum at 80 °C for 12-16 h to assemble the metal coordination polymer Co(bpy)(dhbq)(bq).

[0015] S16. 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 °C water bath for 30 min.

[0016] S17. The polished zinc plate was immersed in the Co(bpy)(dhbq)(bq) aqueous solution after step S16 for 20 min, and kept in a 60 °C water bath, so that a Co(bpy)(dhbq)(bq) anticorrosive film was formed on the surface of the zinc plate to obtain Co(bpy)(dhbq)(bq)@Zn.

[0017] Preferably, the above-mentioned light-assisted anticorrosion coating material or the light-assisted anticorrosion coating material prepared by the above-mentioned preparation method can be applied to the surface of a metal structure to form a corrosion protection layer.

[0018] Compared with the prior art, the present application has the following beneficial effects: The photoelectric ocean corrosion protection technology generates electric charges through photoelectric effect, providing continuous charge protection for the metal surface and inhibiting the occurrence of corrosion. This corrosion protection mechanism does not require external power supply or frequent maintenance, continuously regenerates resources using natural sunlight, avoids the high cost of relying on current supply and regular replacement of anodes in traditional corrosion protection technology, and achieves long-term protection effect. Traditional technologies such as coating and sacrificial anode are prone to aging, falling off or consumption over time, resulting in gradually weakened corrosion protection effect, and must be recoated or replaced with sacrificial anodes. The photoelectric corrosion protection coating and the surface zinc layer form an integrated thin film protection layer, eliminating the risk of coating falling off, spontaneously activating under light, and stably functioning for a long time, reducing manual intervention and maintenance frequency, significantly reducing maintenance costs, and providing longer protection. The present application can be widely used in corrosion protection of marine ships, offshore platforms, submarine cables, nuclear power plant water pipelines and coastal facilities, and has high practical application value.

[0019] In addition, traditional corrosion protection technologies often have the problem of uneven surface protection, especially cathodic protection or sacrificial anode cannot provide sufficient protection in some positions, resulting in localized corrosion. The photoelectric coordination corrosion protection technology can uniformly provide electronic protection for the metal surface, ensuring omnidirectional corrosion protection effect. Furthermore, the photoelectric corrosion protection coating also has the function of inhibiting the attachment of marine organisms, which can effectively reduce the attachment of algae, shellfish and other organisms by releasing trace amounts of metal ions or changing the charge characteristics of the metal surface, avoiding the corrosion and increased sailing resistance problems caused by biological attachment, and further improving the efficiency and service life of the facility. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a schematic diagram of the light-assisted anticorrosion mechanism of the light-assisted anticorrosion coating material of the present application; Figure 2 is a synthetic characterization diagram of Co(bpy)(dhbq)(bq) with photoelectric conversion function of an embodiment of the present application; wherein, Figure 2 a is the Fourier transform infrared spectrum of DHBQ, Co(bpy) and Co(bpy)(dhbq); Figure 2b is Fourier transform infrared spectra of BQ, Co(bpy)(dhbq)(bq) and Co(bpy)(dhbq); 2c is a scanning electron microscope micrograph of Co(bpy)(dhbq)(bq) powder; 2d is a UV-Vis spectrum of Co(bpy)(dhbq)(bq) powder and a Torr plot of Co(bpy)(dhbq)(bq) powder (upper right inset); Figure 3 is a photoelectric performance response diagram of Co(bpy)(dhbq)(bq) of the embodiment of the present application; wherein, Figure 3 a is, in turn, a hole distribution equipotential map (value = 0.0009), an electron distribution equipotential map (value = 0.0009) and an electron-hole distribution equipotential map (value = 0.0009), with blue representing holes and green representing electrons; Figure 3 b is a heat map of the contribution of each molecule to electrons and holes, wherein 1 corresponds to bpy, 2 corresponds to the Co atom and 3 corresponds to DHBQ.

[0021] Figure 4 is a comparison diagram of Tafel curves of the corrosion protection effect of Example 1 and Comparative Example 1 of the present application. DETAILED DESCRIPTION Example 1

[0022] A light-assisted corrosion protection coating material based on a metal coordination structure, the raw materials of which comprise cobalt nitrate hexahydrate, 2,2'-bipyridine (2,2'-bpy), 2,5-dihydroxy-1,4-benzoquinone (DHBQ) and p-benzoquinone (BQ), the light-assisted corrosion protection coating material being a complex Co(bpy)(dhbq)(bq)@Zn formed by coordinating Co(bpy)(dhbq)(bq) film on a zinc plate or a metal zinc-containing corrosion protection primer coating. The metal zinc corrosion protection primer coating is a zinc plating layer or a zinc powder-containing coating. Specifically, the light-assisted corrosion protection coating material can be prepared by the following preparation steps: S11. 1.0 mmol of cobalt nitrate hexahydrate is added to a 100 ml round-bottom flask containing 10 ml of methanol.

[0023] S12. 1.0 mmol of 2,2'-bipyridine is dissolved in 10 ml of methanol and added dropwise to the above-mentioned round-bottom flask containing cobalt nitrate, followed by continuous stirring at 50 °C for 2 h.

[0024] S13. 2.0 mmol of 2,5-dihydroxy-1,4-benzoquinone and 4.0 mmol of triethylamine are dissolved in 10 ml of methanol, and the solution thereof is added dropwise to the round-bottom flask of step S12, and stirred at 50 °C for 0.5 h.

[0025] 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.

[0026] S15. After the mixture obtained from step S14 is cooled to room temperature, remove 2 / 3 of the solvent by rotary evaporation, and add 30 ml of diethyl ether thereto, and after 20 min, filter the solution to obtain a dark red precipitate, and then dry in a vacuum at 80 °C for 12-16 h to assemble the metal coordination polymer Co(bpy)(dhbq)(bq).

[0027] 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 in a 60 °C water bath for 30 min.

[0028] S17. Immerse the polished zinc plate into the Co(bpy)(dhbq)(bq) aqueous solution after step S16 for 20 min, and keep in a 60 °C water bath, so that a Co(bpy)(dhbq)(bq) corrosion protection film is formed on the surface of the zinc plate to obtain Co(bpy)(dhbq)(bq)@Zn.

[0029] Comparative Example 1 Directly use the sacrificial anode protection method by installing zinc as an anode on the metal structure.

[0030] The application will be further described below according to specific embodiments and in conjunction with the accompanying drawings: The application provides a light-assisted corrosion protection coating material based on a metal coordination structure; the light-assisted corrosion protection mechanism or working principle thereof is as shown in Figure 1 which utilizes the photoelectric conversion capability of the metal coordination polymer to generate additional photo-generated electrons and photo-generated current after being irradiated. The excess charge is provided for the Zn layer, so that it is at a lower potential, and the occurrence of corrosion is inhibited. Further, the required surface is effectively protected, the oxygen and corrosive ions in seawater are prevented from directly contacting the metal, the corrosion speed is reduced, and the purpose of inhibiting metal corrosion is achieved.

[0031] Figure 2 Fig. 2a shows the FTIR spectrum of the prepared complex, it can be seen that the characteristic peak at 1016 cm -1 belongs to the symmetric stretching ν(Co-N) vibration mode, indicating the establishment of Co-N coordination. The characteristic peak at 1441 cm -1The 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.

[0032] 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 3a-b is the equipotential map of the intramolecular electron and hole distribution of Co(bpy)(dhbq)(bq) and the corresponding fragment charge transfer hotspot map. It is found that a large number of electrons fall on DHBQ. The corresponding holes are distributed on 2,2'-bipyridine, Co and BQ. After the introduction of light, Co(bpy)(dhbq)(bq) generates photoelectrons and holes, and effectively separates them. In turn, it provides excess charge to the Zn layer, making it at a lower potential, inhibiting the occurrence of corrosion; at the same time, the photoelectrons generated are injected into the metal Zn layer, and the electron density of the Zn layer increases, causing the Zn layer surface to be more prone to electrochemical reaction, making the Zn layer reversible consumption, and in turn effectively and long-acting protection of the required metal surface, preventing oxygen and corrosive ions in seawater from directly contacting the metal, reducing the corrosion rate, and achieving the purpose of inhibiting metal corrosion.

[0033] The corrosion protection effect is as shown in Figure 4 . The polarization (Tafel) curve test was performed on the metal material with attached metal coordination complex Co(bpy)(dhbq)(bq)@Zn light-assisted corrosion protection and the metal material with pure traditional Zn layer corrosion protection, see Figure 4 . The polarization curve is one of the important methods for studying metal corrosion. From the polarization curve, information such as corrosion potential and corrosion current can be obtained, so as to judge the corrosion degree of the metal. The corrosion potential (Ecorr) and the corrosion current (Icorr) can be estimated by extrapolating the linear Tafel region on the cathode and anode branches. In the Tafel curve, the smaller the Ecorr, the less likely the metal is to corrode. The specific data of the polarization curves of Example 1 and Comparative Example 1 are shown in Table 1. Among them, Ecorr and Icorr represent the corrosion voltage and corrosion current, respectively, and β a and β b represent the anode polarization curve slope and the cathode polarization curve slope, respectively.

[0034] Table 1: Electrochemical parameters obtained from the polarization curves of Example 1 and Comparative Example 1

[0035] As shown in Figure 4As shown, the red curve represents the polarization curve of the light-assisted corrosion protection, and the black curve represents the polarization curve of the pure traditional Zn layer corrosion protection. When the light-assisted corrosion protection is performed, the voltage Ecorr of the red curve is obviously reduced, from-0.777 V of the traditional zinc anode protection in the comparative example to-1.073 V of the light-assisted corrosion protection in the present application, and the reduction is 296 mV. The reduction of Ecorr indicates that the Co(bpy)(dhbq)(bq) provides a large number of photoelectrons for the Zn layer and the protected material, so that the protected material is at a lower potential, and the corrosion of seawater to the Zn and the protected material is better inhibited. The current Icorr is increased, from 11.02 μA of the traditional zinc anode protection in the comparative example to 546.8 μA of the light-assisted corrosion protection in the present application, and the increase is 535.78 μA. This is because the electrons generated by the Co(bpy)(dhbq)(bq) light-assisted technology are injected into the Zn layer, the overall electron density is increased, the electrochemical reaction of the Zn is more likely to occur, which also indicates that the Co(bpy)(dhbq)(bq)@Zn effectively protects the metal material, and the purpose of inhibiting the metal corrosion is achieved.

[0036] The present application is not limited to the above specific embodiments, and various modifications made by those skilled in the art without creative labor, based on the above concept, all fall within the protection scope of the present application.

Claims

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

2. A light assisted corrosion protection coating material based on metal coordination structure according to claim 1, characterized in that, The anticorrosive primer coating containing metallic zinc is a zinc plating layer or a zinc powder-containing coating layer.

3. A method of preparing a photo-assisted anticorrosive coating material according to claim 1, characterized by, The method comprises the following steps: S1. Preparing a 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, a metal coordination polymer Co(bpy)(dhbq)(bq) is prepared by a precipitation method; S2. Preparing a Co(bpy)(dhbq)(bq) aqueous solution: dissolving the prepared metal coordination polymer Co(bpy)(dhbq)(bq) in deionized water to obtain a Co(bpy)(dhbq)(bq) aqueous solution; S3. Preparing a complex Co(bpy)(dhbq)(bq)@Zn: coordinating Co(bpy)(dhbq)(bq) film on a zinc plate or an anticorrosive primer coating containing metallic zinc by a water bath method to obtain a complex Co(bpy)(dhbq)(bq)@Zn.

4. The production method according to claim 3, characterized by, The step S1 of preparing the metal coordination polymer Co(bpy)(dhbq)(bq) comprises the following steps: S11. Adding 1.0 mmol of cobalt nitrate hexahydrate into a 100 ml round-bottom flask containing 10 ml of methanol; S12. Dissolving 1.0 mmol of 2,2'-bipyridine in 10 ml of methanol and adding it dropwise into the above-mentioned round-bottom flask, and then continuously stirring at 50°C for 2 h; S13. Dissolving 2.0 mmol of 2,5-dihydroxy-1,4-benzoquinone and 4.0 mmol of triethylamine in 10 ml of methanol, and adding the solution dropwise into the round-bottom flask of step S12, and stirring at 50°C for 0.5 h; S14. Dissolving 1.0 mmol of p-benzoquinone in 10 ml of methanol, and adding the solution dropwise into the round-bottom flask of step S13, and stirring at 50°C for 0.5 h; S15. After cooling the mixture obtained in step S14 to room temperature, removing 2 / 3 of the solvent by rotary evaporation, and adding 30 ml of diethyl ether into the mixture, filtering the solution after 20 min to obtain a dark red precipitate, and then drying the precipitate in a 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 of preparing the Co(bpy)(dhbq)(bq) aqueous solution comprises the following steps: Dissolving the obtained Co(bpy)(dhbq)(bq) in a proper amount of deionized water to prepare a 20 g / L Co(bpy)(dhbq)(bq) aqueous solution, and keeping the solution in a 60°C water bath for 30 min.

6. The production method according to claim 5, wherein The step S3 is to prepare the complex Co(bpy)(dhbq)(bq)@Zn by immersing the polished zinc plate into the Co(bpy)(dhbq)(bq) aqueous solution kept at 60 ℃ water bath for 30 min for 20 min, and keeping the 60 ℃ water bath, so that the zinc plate surface forms a Co(bpy)(dhbq)(bq) corrosion protection film, to obtain Co(bpy)(dhbq)(bq)@Zn.

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

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