Organic-inorganic composite metal anticorrosive pigment and preparation method thereof

Abstract

The invention provides an organic-inorganic composite metal anti-corrosion pigment and a preparation method thereof, and relates to the technical field of anti-corrosion materials. Nitrogen-doped zinc oxide (N-ZnO) is prepared from zinc nitrate hexahydrate, urea and glycine through a calcination method, then the surfaces of N-ZnO nano particles (N-ZnO) are coated with a PDA film in situ through dopamine active monomers, the N-ZnO (at) PDA with the core-shell structure is successfully prepared, and the compatibility between the N-ZnO (at) PDA and epoxy resin is high; n-ZnO (at) PDA is introduced into water-borne epoxy resin to obtain the anticorrosive pigment, and the anticorrosive performance of the anticorrosive pigment can be greatly improved.

Description

Technical Field

[0001] This application relates to the field of anti-corrosion materials technology, and in particular to an organic-inorganic composite metal anti-corrosion pigment and its preparation method. Background Technology

[0002] Metal corrosion easily leads to the degradation of the performance and structural failure of metallic materials, seriously threatening industrial production and the safety of human life and property, and is a major economic and security problem facing the world. Among many anti-corrosion strategies, anti-corrosion coatings are recognized as one of the most direct and effective means of metal corrosion protection due to their low cost, simple construction, and wide applicability.

[0003] Nano-zinc oxide (ZnO), as an environmentally friendly, low-cost, and abundant wide-bandgap semiconductor material (bandgap of approximately 3.37 eV), has attracted much attention in the field of anti-corrosion coatings. Studies have shown that ZnO can not only physically shield against the penetration of corrosive media, but its photoelectric properties (photogenerated electrons) can also provide some cathodic protection for metals. However, ZnO nanoparticles have high surface energy and poor compatibility with organic epoxy resins. This not only leads to uneven dispersion of zinc oxide pigments in epoxy resins and weak interfacial bonding, but also introduces new defects, becoming channels for corrosive media penetration and affecting overall protective performance. Furthermore, ZnO only responds to ultraviolet light, with low utilization of visible light, which constitutes a larger proportion of sunlight, limiting its cathodic protection capabilities. Therefore, effectively modifying ZnO nanoparticles to improve their dispersion stability and interfacial bonding in epoxy resins is key to realizing their anti-corrosion potential.

[0004] Currently, ZnO is mainly modified through techniques such as ion doping and heterostructure construction to broaden its photoresponse range and promote the separation of photogenerated electrons and holes through heterostructures to improve its corrosion resistance. However, the problem of its poor compatibility with epoxy resin cannot be improved by this technology, and cracking and peeling are likely to occur after long-term use.

[0005] Therefore, there is currently a lack of zinc oxide anti-corrosion pigments that have excellent anti-corrosion properties and good compatibility with epoxy groups. Summary of the Invention

[0006] The purpose of this application is to address the shortcomings of existing technologies by providing an organic-inorganic composite metal anti-corrosion pigment and its preparation method. This application improves the compatibility between nitrogen-doped zinc oxide and epoxy resin by coating the zinc oxide with a polydopamine film. Adding this film to the epoxy resin anti-corrosion pigment helps to improve the density and impermeability of the coating, thereby enhancing the anti-corrosion performance of the pigment. Furthermore, this method is simple and easily scalable for industrial mass production.

[0007] To achieve the above objectives, the technical solution adopted in this application is as follows: According to one aspect of this application, a method for preparing an organic-inorganic composite metal anti-corrosion pigment is provided, comprising the following steps: S1. Zinc nitrate hexahydrate, urea and glycine are mixed and ground, and then heated to obtain the precursor. S2. The precursor is calcined, cooled to room temperature in the furnace, and then annealed to obtain nitrogen-doped zinc oxide powder N-ZnO. S3. Dissolve tris(hydroxymethyl)aminomethane (TRIS) in water and adjust the pH to 8.5 to obtain a TRIS-HCl buffer solution; S4. Disperse N-ZnO in TRIS-HCl buffer to obtain N-ZnO dispersion; S5. Disperse the active dopamine monomer in TRIS-HCl buffer to obtain a dopamine dispersion; S6. Under stirring, dopamine dispersion is added dropwise to N-ZnO dispersion. Stirring continues to produce a precipitate. The precipitate is then centrifuged, washed, dried, and ground to obtain N-ZnO@PDA. S7. Mix N-ZnO@PDA with epoxy resin until homogeneous, then add curing agent and mix well to obtain the final product.

[0008] Furthermore, in step S1, the molar ratio of zinc nitrate hexahydrate, urea, and glycine is (4-5):(1-1.5):(2-3), for example, it can be 4:1:2, 4.1:1:2, 4.2:1:2, 4.3:1:2, 4.4:1:2, 4.5:1:2, 4.6:1:2, 4.7:1:2, 4.8:1:2, 4.9:1:2, 5:1:2, 4:1.1:2, or 4:1. 2:2, 4:1.3:2, 4:1.4:2, 4:1.5:2, 4.1:1.1:2, 4.1:1.2:2, 4.1:1.3:2, 4.1:1.4:2, 4.1:1.5:2, 4:1:2.5, 4:1.5:2.5, 4.5:1:2.5, 4:1.5:2.5, 4:1.5:2.5, 4:1.5:2.5, 4:1.5:3 or any range thereof.

[0009] This application uses urea as the main nitrogen source and employs a calcination method to prepare loose and porous nitrogen-doped zinc oxide, which exhibits improved dispersibility. Glycine is added during the preparation of nitrogen-doped zinc oxide. During rapid heating, glycine serves both as a fuel to provide heat and promote crystallization, and as a pore-forming agent to prevent particle agglomeration by releasing gas, passivating surface defects and improving the overall performance of nitrogen-doped zinc oxide.

[0010] Furthermore, in step S1, the heat treatment temperature is 150-160℃, and the heat treatment time is 2-3 hours. The heat treatment causes a preliminary complexation reaction between glycine and zinc nitrate.

[0011] Furthermore, in step S2, the calcination step is as follows: first, the temperature is raised to 400-450℃ at a heating rate of 8-10℃ / min, and held at this temperature for 0.5-1h; then, the temperature is rapidly raised to 600-620℃ at a heating rate of 15-20℃ / min, and calcined at this temperature for 1.5-2h.

[0012] This application first heats the nitrogen source to 400-450℃ at a relatively low heating rate to avoid excessive nitrogen source loss and uneven doping, and may also prevent grain agglomeration. Then, it rapidly heats the nitrogen source to 600-620℃ for calcination, which can ensure that the nitrogen source is fully decomposed and achieve rapid and uniform doping of nitrogen atoms, thereby maximizing the performance of nitrogen-doped zinc oxide.

[0013] Furthermore, in step S2, the cooling method is furnace-side cooling.

[0014] Further, in step S2, the annealing process is as follows: in a nitrogen atmosphere, the temperature is increased to 400-450℃ at a heating rate of 5-8℃ / min, and held at this temperature for 2-3 hours, then cooled to room temperature in the furnace to complete the annealing process.

[0015] The above annealing process can further reduce surface defects in nitrogen-doped zinc oxide and improve the uniformity and stability of the material.

[0016] Furthermore, in step S3, the mass-to-volume ratio of tris(hydroxymethyl)aminomethane to water is 1 g: (700-800) mL, for example, it can be 1 g: 700 mL, 1 g: 710 mL, 1 g: 720 mL, 1 g: 730 mL, 1 g: 740 mL, 1 g: 750 mL, 1 g: 760 mL, 1 g: 770 mL, 1 g: 780 mL, 1 g: 790 mL, 1 g: 800 mL or any range thereof.

[0017] Furthermore, in step S3, any pH adjuster known to those skilled in the art can be used during the pH adjustment process, and there are no special limitations. For example, it can be hydrochloric acid solution, nitric acid solution, etc.

[0018] Furthermore, in step S4, the mass-to-volume ratio of N-ZnO to TRIS-HCl buffer is 1 g: (400-500) mL, for example, it can be 1 g: 400 mL, 1 g: 410 mL, 1 g: 420 mL, 1 g: 430 mL, 1 g: 440 mL, 1 g: 450 mL, 1 g: 460 mL, 1 g: 470 mL, 1 g: 480 mL, 1 g: 490 mL, 1 g: 500 mL or any range thereof.

[0019] Further, in step S5, the active dopamine monomer is dopamine hydrochloride and / or norepinephrine hydrochloride; preferably, the active dopamine monomer is selected from dopamine hydrochloride and norepinephrine hydrochloride in a mass ratio of 1:(0.2-0.5), for example, the mass ratio can be 1:0.2, 1:0.21, 1:0.22, 1:0.23, 1:0.24, 1:0.25, 1:0.26, 1:0.27, 1:0.28, 1:0.29, 1:0.3, 1:0.4, 1:0.5 or any range therebetween.

[0020] Studies have found that when dopamine hydrochloride and norepinephrine hydrochloride are used as active monomers, the corrosion resistance of the resulting pigments is further improved, and their adhesion to the surface of metal substrates is also enhanced.

[0021] Furthermore, in step S5, the mass-to-volume ratio of the dopamine active monomer to the TRIS-HCl buffer is (1-0.45) g:50 mL, for example, it can be 0.1 g:50 mL, 0.11 g:50 mL, 0.12 g:50 mL, 0.13 g:50 mL, 0.14 g:50 mL, 0.15 g:50 mL, 0.16 g:50 mL, 0.17 g:50 mL, 0. 18g:50mL, 0.19g:50mL, 0.2g:50mL, 0.21g:50mL, 0.22g:50mL, 0.23g:50mL, 0.24g:50mL, 0.25g:50mL, 0.26g:50mL, 0.27g:50mL, 0.28g:50mL, 0.29g:50mL, 0.3g:50mL, or any range between these values.

[0022] Furthermore, the mass ratio of the dopamine active monomer to N-ZnO is (1-4.5):3, for example, it can be 1:3, 1.1:3, 1.2:3, 1.3:3, 1.4:3, 1.5:3, 1.6:3, 1.7:3, 1.8:3, 1.9:3, 2.0:3, 2.1:3, 2.2:3, 2.3:3, 2.4:3, 2.5:3, 2.6:3, 2.7:3, 2.8:3, 2.9:3, 3:3, 3.1:3, 3.2:3, 3.3:3, 3.4:3, 3.5:3, 3.6:3, 3.7:3, 3.8:3, 3.9:3, 4:3, 4.1:3, 4.2:3, 4.3:3, 4.4:3, 4.5:3 or any range between them.

[0023] Furthermore, in step S6, anhydrous ethanol and water are used alternately for washing during the washing process.

[0024] Furthermore, in step S6, the drying temperature is 55-60℃ and the drying time is 10-12h.

[0025] Further, in step S7, the mass ratio of N-ZnO@PDA, epoxy resin, and curing agent is (4-5):(80-85):(11-15); for example, it can be 4:81:15, 4:82:14, 4:83:13, 4:84:12, 4:85:11, 4.1:81:14.9, 4:82:13.9, 4:83:12.9, 4:84:11.9, 4.1:80.9:14.9, 4:81.9:14, 4:82.9:13, 4:83.9:12, 4:84.9:11, 5:80:15, 5:81:14, 5:82:13, 5:83:12, 5:84:11, or any range between them.

[0026] Preferably, the mass ratio of N-ZnO@PDA, epoxy resin, and curing agent is 4:82:14.

[0027] Optionally, the curing agent is a curing agent well known to those skilled in the art, such as a polyamide curing agent.

[0028] According to another aspect of this application, an organic-inorganic composite metal anti-corrosion pigment is provided, which is prepared by the above method.

[0029] Compared with the prior art, this application has the following beneficial effects: 1. This application obtains a core-shell structure N-ZnO@PDA by coating a polydopamine film on the surface of nitrogen-doped zinc oxide, which increases its compatibility with epoxy resin, improves the density and impermeability of the coating, enhances the anti-corrosion performance of the pigment, and the method is simple and easy to industrialize.

[0030] 2. This application successfully broadens the photoresponse range of zinc oxide into the visible light region through nitrogen doping, improving the utilization rate of sunlight and enabling the material to generate more photogenerated electrons under natural light, thus providing more effective cathodic protection.

[0031] 3. The organic-inorganic composite anti-corrosion pigment of this application has a dense core-shell structure. The amine groups on its PDA surface can form crosslinks with organic coating matrices such as epoxy resin, which improves the dispersibility and interfacial bonding of the pigment in the resin, increases the density of the coating, effectively inhibits the transmission of corrosive media, and optimizes the physical barrier effect of the coating.

[0032] 4. The preparation method of this application is simple, requiring only conventional grinding and high-temperature calcination equipment. The polydopamine modification process is carried out in an aqueous phase at room temperature. The reaction conditions are mild, the operation is simple, the process flow is short, the equipment requirements are low, and it has good prospects for industrial scale-up. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is the FT-IR spectrum of N-ZnO and N-ZnO@PDA in Example 2 of this application. Detailed Implementation

[0035] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of this application, but do not limit this application in any way. The following content is merely an exemplary description of the scope of protection claimed in this application, and those skilled in the art can make various changes and modifications to the invention based on the disclosed content, which should also fall within the scope of protection claimed in this application.

[0036] Unless otherwise specified, all chemical reagents used in the embodiments of this application were obtained through conventional commercial channels. Where specific conditions are not specified in the embodiments, they were carried out under conventional conditions or conditions recommended by the manufacturer. In the following specific embodiments and comparative examples, the epoxy resin is epoxy resin E20, and the polyamide curing agent is 650 low molecular weight polyamide curing agent. This does not constitute a limitation of this application. It is understood that replacing them with other epoxy resins and polyamide curing agents well known in the art can achieve the same technical effects as this application.

[0037] The present application will be further described below by way of specific embodiments. Example

[0038] S1. Weigh 37.7 g of zinc nitrate hexahydrate (0.12 mol), 1.8 g of urea (0.03 mol), and 4.5 g of glycine (0.06 mol) and grind them thoroughly in an agate mortar until a transparent, particle-free mixture is obtained. Heat the mixture at 160 °C for 2 h to obtain the precursor.

[0039] S2. The precursor is placed in a muffle furnace and heated to 400°C at a rate of 8°C / min in air atmosphere. It is held at this temperature for 1 hour, then heated to 600°C at a rate of 15°C / min and calcined at this temperature for 1.5 hours. After calcination, it is cooled to room temperature in the furnace. Then, in a nitrogen atmosphere, it is heated to 400°C at a rate of 5°C / min and held at this temperature for 2 hours. It is then cooled to room temperature in the furnace to complete the annealing treatment and obtain nitrogen-doped zinc oxide (N-ZnO) product, named NZ.

[0040] S3. Weigh 0.18 g of tris(hydroxymethyl)aminomethane (TRIS) into a beaker, add 150 mL of ultrapure water to the beaker, and stir thoroughly on a magnetic stirrer until completely dissolved. Add 1 M hydrochloric acid (HCl) solution to adjust the pH to 8.5.

[0041] S4. Weigh 0.3g of the above NZ and place it in 150ml of TRIS-HCl solution to disperse it thoroughly, so as to obtain a uniform and stable NZ dispersion.

[0042] S5. Weigh 0.1 g of dopamine hydrochloride (DA) and place it in 50 mL of the above TRIS-HCl buffer solution. Stir rapidly until DA is evenly dispersed to obtain a DA dispersion.

[0043] S6. Under continuous stirring, the DA dispersion was added dropwise to the above NZ dispersion. After stirring for 12 h, a precipitate was obtained. The precipitate was then washed multiple times by centrifugation, anhydrous ethanol and ultrapure water, dried at 60°C for 12 h, and ground to obtain an organic-inorganic composite N-ZnO@PDA product, denoted as product I. Example

[0044] S1. Weigh 59.5 g of zinc nitrate hexahydrate (0.2 mol), 1.80 g of urea (0.03 mol), and 4.50 g of glycine (0.06 mol) and grind them thoroughly in an agate mortar until a transparent, particle-free mixture is obtained. Heat the mixture at 150 °C for 3 h to obtain the precursor.

[0045] S2. The precursor is placed in a muffle furnace and heated to 450°C at a heating rate of 10°C / min in air atmosphere. It is held at this temperature for 0.5 h, then heated to 620°C at a heating rate of 20°C / min and calcined at this temperature for 2 h. After calcination, it is cooled to room temperature with the furnace. Then, in a nitrogen atmosphere, it is heated to 450°C at a heating rate of 8°C / min and held at this temperature for 3 h. It is then cooled to room temperature with the furnace to complete the annealing treatment and obtain nitrogen-doped zinc oxide (N-ZnO) product, named NZ.

[0046] S3. Weigh 0.18g of tris(hydroxymethyl)aminomethane (TRIS) into a beaker, add 150 mL of ultrapure water to the beaker, and stir thoroughly on a magnetic stirrer until completely dissolved. Add 1 M hydrochloric acid (HCl) solution to adjust the pH to 8.5.

[0047] S4. Weigh 0.3g of the above NZ and place it in 150ml of LTS-HCl solution to disperse it thoroughly to obtain a uniform and stable NZ dispersion.

[0048] S5. Weigh 0.45g of dopamine hydrochloride (DA) and place it in 50 mL of the above TRIS-HCl buffer solution. Stir rapidly until DA is evenly dispersed to obtain a DA dispersion.

[0049] S6. Under continuous stirring, the DA dispersion was added dropwise to the above NZ dispersion. After stirring for 12 h, a precipitate was obtained. The precipitate was then washed multiple times by centrifugation, anhydrous ethanol and ultrapure water, dried at 55°C for 10 h, and ground to obtain the organic-inorganic composite N-ZnO@PDA product, which was designated as product II.

[0050] The FT-IR spectra of N-ZnO and N-ZnO@PDA in this embodiment are as follows: Figure 1 As shown, the N-ZnO curve exhibits distinct absorption peaks at 489 cm⁻¹, 1634 cm⁻¹, and 3445 cm⁻¹. The absorption peak at 489 cm⁻¹ is attributed to the asymmetric stretching vibration of the Zn-O bond, while the absorption peak at 1634 cm⁻¹ is related to the bending vibration of the Zn-O bond. Compared to the N-ZnO curve, the N-ZnO@PDA curve shows a significant absorption peak at 1514 cm⁻¹. -1 1634 cm -1 The presence of a characteristic absorption peak at this location is attributed to the stretching vibration of the benzene ring structure of PDA, indicating that PDA has been successfully modified onto the surface of the N-ZnO material. Example

[0051] S1. Weigh 37.70 g of zinc nitrate hexahydrate (0.12 mol), 1.80 g of urea (0.03 mol), and 4.50 g of glycine (0.06 mol) and grind them thoroughly in an agate mortar until a transparent, particle-free mixture is obtained. Heat the mixture at 160 °C for 2 h to obtain the precursor.

[0052] S2. The precursor is placed in a muffle furnace and heated to 400°C at a rate of 8°C / min in air atmosphere. It is held at this temperature for 1 hour, then heated to 600°C at a rate of 15°C / min and calcined at this temperature for 1.5 hours. After calcination, it is cooled to room temperature in the furnace. Then, in a nitrogen atmosphere, it is heated to 400°C at a rate of 5°C / min and held at this temperature for 2 hours. It is then cooled to room temperature in the furnace to complete the annealing treatment and obtain nitrogen-doped zinc oxide (N-ZnO) product, named NZ.

[0053] S3. Weigh 0.18 g of tris(hydroxymethyl)aminomethane (TRIS) into a beaker, add 150 mL of ultrapure water to the beaker, and stir thoroughly on a magnetic stirrer until completely dissolved. Add 1 M hydrochloric acid (HCl) solution to adjust the pH to 8.5.

[0054] S4. Weigh 0.3g of the above NZ and place it in 150mL of TRIS-HCl solution to disperse it thoroughly to obtain a uniform and stable NZ dispersion.

[0055] S5. Weigh 0.45g of dopamine hydrochloride and norepinephrine hydrochloride in a mass ratio of 1:0.2 and disperse them evenly in 50 mL of the above TRIS-HCl buffer solution to obtain a dispersion.

[0056] S6. Under continuous stirring, the DA dispersion was added dropwise to the above NZ dispersion. After stirring for 12 h, a precipitate was obtained. The precipitate was washed multiple times by centrifugation, anhydrous ethanol and ultrapure water, dried at 60°C for 12 h, and ground. The resulting product was designated as Product III. Example

[0057] S1. Weigh 37.70 g of zinc nitrate hexahydrate (0.12 mol), 1.80 g of urea (0.03 mol), and 4.50 g of glycine (0.06 mol) and grind them thoroughly in an agate mortar until a transparent, particle-free mixture is obtained. Heat the mixture at 160 °C for 2 h to obtain the precursor.

[0058] S2. The precursor is placed in a muffle furnace and heated to 400°C at a rate of 8°C / min in air atmosphere. It is held at this temperature for 1 hour, then heated to 600°C at a rate of 15°C / min and calcined at this temperature for 1.5 hours. After calcination, it is cooled to room temperature in the furnace. Then, in a nitrogen atmosphere, it is heated to 400°C at a rate of 5°C / min and held at this temperature for 2 hours. It is then cooled to room temperature in the furnace to complete the annealing treatment and obtain nitrogen-doped zinc oxide (N-ZnO) product, named NZ.

[0059] S3. Weigh 0.18 g of tris(hydroxymethyl)aminomethane (TRIS) into a beaker, add 150 mL of ultrapure water to the beaker, and stir thoroughly on a magnetic stirrer until completely dissolved. Add 1 M hydrochloric acid (HCl) solution to adjust the pH to 8.5.

[0060] S4. Weigh 0.3g of the above NZ and place it in 150ml of TRIS-HCl solution to disperse it thoroughly, so as to obtain a uniform and stable NZ dispersion.

[0061] S5. Weigh 0.45g of dopamine hydrochloride and norepinephrine hydrochloride in a mass ratio of 1:0.5 and disperse them evenly in 50 mL of the above TRIS-HCl buffer solution to obtain a dispersion.

[0062] S6. Under continuous stirring, the DA dispersion was added dropwise to the above NZ dispersion. After stirring for 12 h, a precipitate was obtained. The precipitate was then washed multiple times by centrifugation, anhydrous ethanol and ultrapure water, dried at 60°C for 12 h, and ground. The resulting product was designated as product IV. Example

[0063] S1. Weigh 37.70 g of zinc nitrate hexahydrate (0.12 mol), 1.80 g of urea (0.03 mol), and 4.50 g of glycine (0.06 mol) and grind them thoroughly in an agate mortar until a transparent, particle-free mixture is obtained. Heat the mixture at 160 °C for 2 h to obtain the precursor.

[0064] S2. The precursor is placed in a muffle furnace and heated to 400°C at a rate of 8°C / min in air atmosphere. It is held at this temperature for 1 hour, then heated to 600°C at a rate of 15°C / min and calcined at this temperature for 1.5 hours. After calcination, it is cooled to room temperature in the furnace. Then, in a nitrogen atmosphere, it is heated to 400°C at a rate of 5°C / min and held at this temperature for 2 hours. It is then cooled to room temperature in the furnace to complete the annealing treatment and obtain nitrogen-doped zinc oxide (N-ZnO) product, named NZ.

[0065] S3. Weigh 0.18 g of tris(hydroxymethyl)aminomethane (TRIS) into a beaker, add 150 mL of ultrapure water to the beaker, and stir thoroughly on a magnetic stirrer until completely dissolved. Add 1 M hydrochloric acid (HCl) solution to adjust the pH to 8.5.

[0066] S4. Weigh 0.3g of the above NZ and place it in 150mL of TRIS-HCl solution to disperse it thoroughly to obtain a uniform and stable NZ dispersion.

[0067] S5. Weigh 0.45g of dopamine hydrochloride and norepinephrine hydrochloride in a mass ratio of 1:1 and disperse them evenly in 50 mL of the above TRIS-HCl buffer solution to obtain a dispersion.

[0068] S6. Under continuous stirring, the DA dispersion was added dropwise to the above NZ dispersion. After stirring for 12 h, a precipitate was obtained. The precipitate was then washed multiple times by centrifugation, anhydrous ethanol and ultrapure water, dried at 60°C for 12 h, and ground. The resulting product was denoted as product V. Example

[0069] The difference from Example 2 is that, during the calcination process, the temperature was directly raised to 620°C at a heating rate of 20°C / min, and then calcined at this temperature for 2.5 hours; the resulting product is referred to as Product VI. Example

[0070] The difference from Example 2 is that, during the calcination process, the temperature was directly increased to 620°C at a heating rate of 10°C / min, and then calcined at this temperature for 2.5 hours; the resulting product is referred to as Product VII.

[0071] The difference from Example 2 is that glycine was not added in step S1; the resulting product is referred to as product VIII.

[0072] The difference from Example 2 is that no annealing treatment was performed in step S2; the resulting product is denoted as product IX.

[0073] The difference from Example 2 is that the nitrogen-doped zinc oxide (N-ZnO) product obtained in step S2 is used as the final product, which is denoted as product X.

[0074] To verify the performance of the above product, 0.3 g of product IX was mixed evenly with 6.00 g of epoxy resin E20, and then 1.00 g of polyamide curing agent was added. The mixture was stirred for another 15 min to obtain composite coatings 1#-10#. It should be noted that only one ratio (4.1:82.2:13.7) is given here as a sample to verify its effect. It can be understood that any ratio within the range of (4-5):(80-85):(11-15) can achieve the effect of this application.

[0075] Using epoxy resin E20 and polyamide curing agent prepared coating 11# as a blank control, the above composite coating was uniformly applied to the surface of steel (40 mm × 10 mm × 5 mm) using a one-time dip coating method and cured at room temperature for 7 days. Then, the following tests were conducted. The steel was pretreated as follows: First, the surface of the steel (40 mm × 10 mm × 5 mm) was successively polished with 180 grit, 360 grit, and 600 grit silicon carbide sandpaper, and then cleaned and dried with anhydrous ethanol.

[0076] Corrosion resistance test: During the test, a saturated calomel electrode (SCE) was used as the reference electrode, coated steel was used as the working electrode, and a platinum sheet electrode was used as the auxiliary electrode. Electrochemical impedance spectroscopy (EIS) was performed on an IM6e electrochemical workstation (Zahner GmbH, Germany, model AUTOLAB G1).

[0077] To investigate the long-term protective behavior of the coating in sodium chloride medium, the working electrode was immersed in a 3.5 wt% NaCl solution to a depth of approximately 10 mm before testing, with four immersion time points set at 6 h, 24 h, 48 h, and 72 h. The EIS test frequency scan range was 100 kHz to 0.1 Hz, and the applied sinusoidal perturbation signal amplitude was 10 mV. The measured total impedance values ​​are shown in Table 1 below.

[0078] Table 1. Total Impedance Values

[0079] As shown in the table, compared to the coating formed by coating 11# (pure epoxy resin coating), the coating formed by adding N-ZnO to coating 10# showed an increase in total impedance after immersion for 72 hours. The coating formed by adding N-ZnO@PDA showed an even greater increase in total impedance, with an increase of up to 120%. This indicates that the N-ZnO@PDA prepared in this application significantly improves the anti-corrosion performance of epoxy resin. In the N-ZnO preparation process of coatings 8# and 9# (i.e., Comparative Examples 1 and 2), no glycine was added or annealing treatment was performed. The resulting coatings showed significantly lower total impedance values ​​after 72 hours compared to Example 2. This may be because the addition of glycine and annealing treatment during the N-ZnO preparation process affects its structure, thereby influencing its performance.

[0080] The adhesion of the coating was tested according to GB / T 5210-2006, and the test results are shown in Table 2 below.

[0081] Table 2. Adhesion Group Adhesion (MPa) Group Adhesion (MPa) Paint #1 8.2 Paint #7 7.8 Paint #2 8.5 Paint #8 7.5 Paint #3 9.2 Paint #9 7.2 Paint #4 9.2 Paint #10 6.5 Paint #5 8.8 Paint #11 6.7 Paint #6 7.5 —— —— The results showed that, compared to alcohol epoxy resin coating 11#, the addition of nitrogen-doped zinc oxide 10# did not improve the adhesion of the coating to the metal substrate, while the addition of N-ZnO@PDA improved the adhesion. This indicates that the N-ZnO@PDA prepared in this application also helps to improve the adhesion of epoxy resin coatings. Compared to coating 2#, the adhesion of coatings 3# and 43 was further improved, indicating that the combined use of the two dopamine active monomers also helps to improve the adhesion of the coating to the metal substrate, thereby helping to extend the service life.

[0082] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, this application is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of this application without departing from the scope of this application should be within the protection scope of this application.

Claims

1. A method for preparing an organic-inorganic composite metal anti-corrosion pigment, characterized in that, Includes the following steps: S1. Zinc nitrate hexahydrate, urea and glycine are mixed and ground, and then heated to obtain the precursor. S2. The precursor is calcined, cooled to room temperature in the furnace, and then annealed to obtain nitrogen-doped zinc oxide powder N-ZnO. S3. Dissolve tris(hydroxymethyl)aminomethane in water and adjust the pH to 8.5 to obtain TRIS-HCl buffer solution; S4. Disperse N-ZnO in TRIS-HCl buffer to obtain N-ZnO dispersion; S5. Disperse the active dopamine monomer in TRIS-HCl buffer to obtain a dopamine dispersion; S6. Under stirring, dopamine dispersion is added dropwise to N-ZnO dispersion. Stirring continues to produce a precipitate. The precipitate is then centrifuged, washed, dried, and ground to obtain N-ZnO@PDA. S7. Mix N-ZnO@PDA with epoxy resin until homogeneous, then add curing agent and mix well to obtain the final product.

2. The preparation method according to claim 1, characterized in that, In step S1, the molar ratio of zinc nitrate hexahydrate, urea and glycine is (4-5):(1-1.5):(2-3).

3. The preparation method according to claim 1, characterized in that, In step S2, the calcination step is as follows: first, the temperature is raised to 400-450℃ at a heating rate of 8-10℃ / min, and held at this temperature for 0.5-1h; then, the temperature is rapidly raised to 600-620℃ at a heating rate of 15-20℃ / min, and calcined at this temperature for 1.5-2h.

4. The preparation method according to claim 1, characterized in that, In step S2, the annealing process is as follows: in a nitrogen atmosphere, the temperature is increased to 400-450℃ at a heating rate of 5-8℃ / min, and held at this temperature for 2-3 hours. The furnace is then cooled to room temperature to complete the annealing process.

5. The preparation method according to claim 1, characterized in that, In step S3, the mass-to-volume ratio of tris(hydroxymethyl)aminomethane to water is 1 g: (700-800) mL.

6. The preparation method according to claim 1, characterized in that, In step S4, the mass-to-volume ratio of N-ZnO to TRIS-HCl buffer is 1 g: (400-500) mL; in step S5, the mass-to-volume ratio of dopamine active monomer to TRIS-HCl buffer is (0.1-0.45) g: 50 mL.

7. The preparation method according to claim 1, characterized in that, In step S5, the dopamine active monomer is dopamine hydrochloride and / or norepinephrine hydrochloride; preferably, the dopamine active monomer is selected from dopamine hydrochloride and norepinephrine hydrochloride in a mass ratio of 1:(0.2-0.5).

8. The preparation method according to claim 6, characterized in that, The mass ratio of dopamine active monomer to N-ZnO is (1-4.5):

3.

9. The preparation method according to claim 1, characterized in that, In step S7, the mass ratio of N-ZnO@PDA, epoxy resin, and curing agent is (4-5):(80-85):(11-15).

10. An organic-inorganic composite metal anti-corrosion pigment, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

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