Corrosion-resistant coating and application thereof in aluminum alloy heat exchange tube

Abstract

The invention relates to the field of corrosion-resistant coatings, and discloses a corrosion-resistant coating and application of the corrosion-resistant coating in an aluminum alloy heat exchange tube, the corrosion-resistant coating comprises waterborne epoxy resin, modified silicon dioxide nanotubes, modified composite filler and auxiliaries; the modified silicon dioxide nanotube is prepared by carrying out acylating chlorination on a silicon dioxide nanotube by using 4-isocyanobenzoyl chloride and then reacting with an amination modifier; the amination modifier is prepared by synthesizing spirocyclic phosphate diacyl chloride by using pentaerythritol and phosphorus oxychloride, and then carrying out substitution on 2-aminobenzimidazole, 3, 5-diamino-1, 2, 4-triazole and the spirocyclic phosphate diacyl chloride; the modified composite filler is prepared by forming a polydopamine layer on the outer surface of mica through auto-polymerization of dopamine, then wrapping the outer layer of dopamine modified mica with zinc oxide through a sol-gel method and high-temperature calcination, and then modifying with KH550. The coating prepared by the invention has good mechanical properties, corrosion resistance, heat insulation performance, flame retardant effect and antibacterial effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of corrosion-resistant coatings, and in particular relates to a corrosion-resistant coating and an application thereof in an aluminum alloy heat exchange tube. Background Art

[0002] Aluminum alloys have good corrosion resistance, but are susceptible to pitting corrosion in marine salt spray environments, such as aluminum alloy heat exchange tubes. Heat exchange tube coating is a protective layer applied to the surface of heat exchange tubes to improve their corrosion resistance and mechanical properties. The coating prevents direct contact between the metal surface and the medium, thereby reducing corrosion and wear.

[0003] Epoxy resin coatings have good mechanical properties, thermal properties, and corrosion resistance, and are therefore widely used in the field of corrosion-resistant coatings. However, they also exhibit some shortcomings. For example, during the curing process, the volatilization of the solvent will produce some micropores and defects. Over time, the corrosive medium gradually penetrates and causes corrosion. Therefore, some inorganic nanofillers are often added to fill the epoxy resin to improve its performance. However, inorganic nanofillers are often difficult to disperse in the base material, which in turn has a certain impact on the mechanical properties. At the same time, existing epoxy resin coatings have deficiencies in thermal insulation, flame retardancy, and antibacterial properties, and their corrosion resistance needs to be further improved. Existing technologies improve their flame retardancy and antibacterial properties by adding inorganic flame retardants or antibacterial agents, but simple physical mixing is prone to precipitation, making it difficult to ensure the coating's long-lasting flame retardancy or antibacterial effect. Summary of the Invention

[0004] In order to address the deficiencies mentioned in the above background technology, the purpose of the present invention is to provide a corrosion-resistant coating and its application in aluminum alloy heat exchange tubes. By adding modified silica nanotubes and modified composite fillers, the coating is given good mechanical properties, corrosion resistance, thermal insulation, flame retardant effect and antibacterial effect.

[0005] The purpose of the present invention can be achieved through the following technical solutions: A corrosion-resistant coating comprising the following components in parts by weight: 45-70 parts of a waterborne epoxy resin, 7-16 parts of modified silica nanotubes, 4-9 parts of a modified composite filler, 5-12 parts of a curing agent, 0.5-2.5 parts of a wetting agent, 0.3-1 parts of a defoaming agent, 0.2-0.8 parts of a leveling agent, and 0.1-0.6 parts of a dispersant; The modified silica nanotubes are prepared by acylating silica nanotubes with 4-isocyanatobenzoyl chloride and then reacting them with an amidation modifier; the amidation modifier is prepared by synthesizing a spirocyclic phosphate dichloride using pentaerythritol and phosphorus oxychloride as raw materials, and then reacting 2-aminobenzimidazole and 3,5-diamino-1,2,4-triazole with the chlorine atoms at both ends of the spirocyclic phosphate dichloride to form a substitution reaction. The silica nanotubes are prepared by reacting toluene-2,4-diisocyanate with hydroxylated carbon nanotubes to obtain isocyanate-modified carbon nanotubes, which are then covalently grafted with polyethylene glycol to prepare modified carbon nanotubes. Subsequently, the modified carbon nanotubes are used as templates and tetraethyl orthosilicate is used as a raw material. A sol-gel method is used under alkaline conditions, and the template is removed by heat treatment. The modified composite filler is made by using silane coupling agent KH550 to modify the composite filler; the composite filler is made by using dopamine to self-polymerize on the outer surface of mica to form a polydopamine layer, and then using a sol-gel method and high-temperature calcination to wrap a layer of zinc oxide on the outer layer of the dopamine-modified mica.

[0006] Preferably, the method for preparing the modified silica nanotubes comprises the following steps: A. Place pentaerythritol, chlorobenzene, phosphorus oxychloride, and 4-dimethylaminopyridine in a reactor, purify the reaction with nitrogen, and react at 60-70°C for 2-3 hours. Then, heat to 95-100°C and continue the reaction for 6-8 hours. After the reaction is complete, stop heating and allow to stand for 8-10 hours. Filter the product, wash with dichloromethane, and vacuum dry to obtain a spirocyclic phosphate diacyl chloride. B. Take spirocyclic phosphate dichloride and acetonitrile in a reactor, heat to 50-60° C. under a nitrogen atmosphere, take 2-aminobenzimidazole, 3,5-diamino-1,2,4-triazole and anhydrous methanol, stir and mix evenly, then add them to the reactor, place at 65-75° C. and stir to react for 6-8 hours. After the reaction is completed, filter, wash and dry to prepare an amino modifier; C. Ultrasonic dispersion of silica nanotubes in acetone solvent, then adding 4-isocyanatobenzoyl chloride and dibutyltin dilaurate, stirring and mixing, placing the mixture at 40-60° C. and stirring for 12-24 hours. After the reaction is completed, filtering, washing, and drying to prepare acyl chloride silica nanotubes; D. Ultrasonic dispersion of acyl chloride silica nanotubes in tetrahydrofuran solvent, then adding an amino modifier and pyridine, stirring and mixing, placing the mixture at 25-40° C., stirring and reacting for 6-18 hours. After the reaction is completed, filtering, washing, and drying to prepare modified silica nanotubes.

[0007] Preferably, the molar ratio of pentaerythritol to phosphorus oxychloride in step A is 1:2-2.5; and the molar ratio of spirocyclic phosphate dichloride, 2-aminobenzimidazole and 3,5-diamino-1,2,4-triazole in step B is 1:1-1.1:1-1.1.

[0008] Preferably, the method for preparing the silica nanotubes in step C comprises the following steps: C1. Dispersing hydroxylated carbon nanotubes in toluene-2,4-diisocyanate, reacting at 75-85°C for 70-72 hours under nitrogen protection, filtering, washing, and drying to obtain isocyanate-treated carbon nanotubes. C2. Place isocyanate-treated carbon nanotubes, polyethylene glycol, and toluene in a reactor, ultrasonically disperse the mixture at 55-70°C for 20-30 minutes under nitrogen protection, and then react at 90-100°C for 30-36 hours. After the reaction is complete, filter, wash, and dry the mixture to obtain modified carbon nanotubes. C3. Take the modified carbon nanotubes and ultrasonically disperse them in an ethanol solution. After adding ethyl orthosilicate, ultrasonically disperse them for another 20-30 minutes. Then, add ammonia water and stir the reaction at room temperature for 20-24 hours. Then, let it stand for aging. Then, filter, wash, and dry the obtained silica-coated modified carbon nanotubes. Place them at 480-520°C in an air atmosphere and calcine them for 5-7 hours to prepare silica nanotubes.

[0009] Preferably, in step D, the mass ratio of the acyl chloride silica nanotubes to the amino modifier is 1:0.5-1.

[0010] Preferably, the preparation method of the modified composite filler comprises the following steps: (1) Tris(hydroxymethyl)aminomethane and deionized water were placed in a reactor, and the pH was adjusted to 8.5 using hydrochloric acid. Then, ground mica powder was added and dispersed evenly by ultrasonication. Then, dopamine hydrochloride was added under stirring, and the mixture was stirred and reacted at room temperature for 20 to 24 hours. After the reaction was completed, the mixture was filtered, washed, and dried to prepare dopamine-modified mica. (2) Dopamine-modified mica was ultrasonically dispersed in ethanol and deionized water, heated to 65-75°C, zinc nitrate hexahydrate and dispersant polyethylene glycol were added, stirred and reacted for 1-1.5 hours, and then a mixed solution of ammonia and deionized water was added dropwise. After the addition was completed, the reaction was continued for 1.5-2 hours. After the reaction was completed, the mixture was filtered, washed, dried, ground, and placed in a tube furnace. It was calcined at 950-1000°C for 2-2.5 hours to prepare a composite filler. (3) The composite filler was ultrasonically dispersed in a mixed solution of anhydrous ethanol and silane coupling agent KH550, and stirred at 55-70°C for 3-5 hours. Deionized water was then slowly added and stirred for 2-3 hours. After the reaction was completed, the modified composite filler was filtered, washed, and dried to obtain the modified composite filler.

[0011] Preferably, in step (2), the mass ratio of dopamine-modified mica to zinc nitrate hexahydrate is 0.07-0.08:2.4; and the heating rate of the tubular furnace is 8-10°C / min.

[0012] Preferably, the curing agent is an amine curing agent; the wetting agent is polydimethylsiloxane; the defoaming agent is one of fatty alcohol polyoxyethylene ether or alkylphenol polyoxyethylene ether; the leveling agent is sodium polyacrylate; and the dispersant is one of BYK-190 or BYK-191.

[0013] Preferably, the preparation method of the corrosion-resistant coating includes the following steps: weighing each raw material by weight, mixing the water-based epoxy resin and the dispersant evenly, then adding modified silica nanotubes, modified composite fillers, wetting agents, and leveling agents and stirring evenly, then adding curing agents and defoaming agents and continuing to stir evenly to prepare the corrosion-resistant coating.

[0014] An application of the corrosion-resistant coating is to coat the corrosion-resistant coating on the surface of an aluminum alloy heat exchange tube by a coating method.

[0015] Beneficial effects of the present invention: The present invention uses pentaerythritol and phosphorus oxychloride as raw materials to synthesize spirocyclic phosphate dichloride, then uses 2-aminobenzimidazole and 3,5-diamino-1,2,4-triazole to respectively undergo substitution reactions with chlorine atoms at both ends of the spirocyclic phosphate dichloride to prepare an amino modifier. Simultaneously, the present invention uses 4-isocyanatobenzoyl chloride to react with hydroxyl groups on the surface of silica nanotubes to prepare acyl chloride silica nanotubes, and then uses an amidation reaction to graft the amino modifier onto the surface of the silica nanotubes, thereby introducing antibacterial benzimidazole groups and synergistic flame-retardant phosphorus and nitrogen elements onto the surface of the silica nanotubes, thereby imparting good antibacterial effect and flame-retardant performance to the coating. Strong chemical bond bonding facilitates long-term action. In addition, the grafting reaction facilitates improving the surface lipophilicity of the silica nanotubes, allowing them to be relatively evenly dispersed in a matrix material, thereby avoiding performance defects caused by agglomeration of the silica nanotubes.

[0016] Among them, the present invention utilizes toluene-2,4-diisocyanate to react with hydroxylated carbon nanotubes to prepare isocyanate-treated carbon nanotubes, and then covalently grafts polyethylene glycol onto the surface of the isocyanate-treated carbon nanotubes to prepare modified carbon nanotubes with good dispersibility. Subsequently, the modified carbon nanotubes are used as templates and ethyl orthosilicate is used as raw material. A sol-gel method is adopted under alkaline conditions and the template is removed by heat treatment to prepare hollow silica nanotubes. The silica nanotubes have good thermal stability, mechanical properties and high temperature resistance, and their hollow structure can absorb stress, prevent crack propagation, improve the impact resistance of the coating, and have good thermal insulation effect.

[0017] The present invention utilizes the self-polymerization property of dopamine to coat a layer of polydopamine on the outer surface of mica to prepare dopamine-modified mica, and then adopts a sol-gel method and high-temperature calcination to grow a zinc oxide shell around the dopamine-modified mica to prepare a composite filler, wherein the mica forms a large-area protective layer with its flaky shape, which can delay the diffusion and penetration of corrosive media. At the same time, zinc oxide has a broad-spectrum antibacterial effect, and coating the outer layer of mica with a layer of zinc oxide greatly improves the mechanical properties and anti-corrosion properties of the coating. In addition, the composite filler is modified by the silane coupling agent KH550 to improve the hydrophobicity and improve the compatibility of the composite filler in the matrix material, thereby avoiding the aggregation of the composite filler. In addition, the grafted amino group can participate in the curing of the epoxy resin together with the curing agent, so that its comprehensive performance is fully exerted. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0019] Example 1 A method for preparing silicon dioxide nanotubes comprises the following steps: C1. Disperse 100 mg of hydroxylated carbon nanotubes in 50 mL of toluene-2,4-diisocyanate, and react at 80°C for 72 hours under nitrogen protection. After the reaction is completed, filter, wash, and dry to prepare isocyanate-treated carbon nanotubes. C2. 10 mg of isocyanate-modified carbon nanotubes, 400 mg of polyethylene glycol (Mn = 4000 g / mol), and 10 mL of toluene were placed in a reactor, ultrasonically dispersed at 60 ° C for 25 min under nitrogen protection, and then reacted at 100 ° C for 36 h. After the reaction was completed, the modified carbon nanotubes were prepared by filtration, washing, and drying. C3. Take 5 mg of modified carbon nanotubes and ultrasonically disperse them in 100 mL of 95% ethanol solution. Add 0.1 mL of ethyl orthosilicate and ultrasonically disperse them for 20 minutes. Then add 0.1 mL of 25% ammonia water. Stir the reaction at room temperature for 24 hours and then let it stand for aging. Then filter, wash and dry the obtained silica-coated modified carbon nanotubes. Place them at 500°C in air atmosphere and calcine for 6 hours to prepare silica nanotubes.

[0020] Example 2 A method for preparing modified silica nanotubes comprises the following steps: A. 27.2 g of pentaerythritol, 100 mL of chlorobenzene, 76.6 g of phosphorus oxychloride, and 0.1 g of 4-dimethylaminopyridine were placed in a reactor, the reaction was vented under nitrogen protection, the reaction was placed at 65° C. for 2 h, then the temperature was raised to 98° C. and the reaction was continued for 8 h. After the reaction was completed, heating was stopped and the reaction was allowed to stand for 10 h. The product was filtered, washed with dichloromethane, and vacuum dried to prepare a spirocyclic phosphate dichloride; B. Take 29.7g of spirocyclic phosphate dichloride and 100mL of acetonitrile in a reactor, heat to 60°C under a nitrogen atmosphere, take 13.4g of 2-aminobenzimidazole, 10g of 3,5-diamino-1,2,4-triazole and 50mL of anhydrous methanol, stir and mix evenly, then add them to the reactor, place at 70°C and stir to react for 8h. After the reaction is completed, filter, wash and dry to prepare an amino modifier; C. 1 g of the silica nanotubes prepared in Example 1 was ultrasonically dispersed in 50 mL of acetone solvent, and then 0.4 g of 4-isocyanatobenzoyl chloride and 0.01 g of dibutyltin dilaurate were added and stirred. The mixture was stirred at 50° C. for 12 h. After the reaction was completed, the mixture was filtered, washed, and dried to prepare chlorinated silica nanotubes. D. Take 1 g of acyl chloride silica nanotubes and ultrasonically disperse them in 80 mL of tetrahydrofuran solvent. Then, add 0.7 g of amino modifier and 0.02 g of pyridine and stir to mix. Place the mixture at 30°C and stir to react for 12 hours. After the reaction is completed, filter, wash, and dry to prepare modified silica nanotubes.

[0021] Example 3 A method for preparing a modified composite filler comprises the following steps: (1) 0.5 g of tris(hydroxymethyl)aminomethane) and 300 mL of deionized water were placed in a reactor, and the pH was adjusted to 8.5 using 0.1 mol / L hydrochloric acid. Then, 0.3 g of ground mica powder was added and dispersed evenly by ultrasonication. Subsequently, 0.3 g of dopamine hydrochloride was added while stirring, and the mixture was stirred at room temperature for 24 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain dopamine-modified mica. (2) 75 mg of dopamine-modified mica was ultrasonically dispersed in 20 mL of ethanol and 50 mL of deionized water, and the temperature was raised to 70 °C. 2.4 g of zinc nitrate hexahydrate and 0.02 g of dispersant polyethylene glycol were added, and the mixture was stirred for 1 h. Then, a mixed solution of 2.5 mL of ammonia water and 30 mL of deionized water was added dropwise. After the addition was completed, the mixture was continued to react for 2 h. After the reaction was completed, the mixture was filtered, washed, dried, ground, and placed in a tube furnace. It was calcined at 1000 °C for 2 h at a heating rate of 10 °C / min to prepare a composite filler. (3) Take 50 mg of composite filler and ultrasonically disperse it in a mixed solution of 30 mL of anhydrous ethanol and 0.05 g of silane coupling agent KH550, place it at 70 ° C and stir to react for 3 hours, then slowly drop 30 mL of deionized water and stir to react for 3 hours. After the reaction is completed, filter, wash and dry to prepare a modified composite filler.

[0022] Example 4 A corrosion-resistant coating comprises the following components in parts by weight: 48 parts of water-based epoxy resin, 7.5 parts of modified silica nanotubes prepared in Example 2, 4.2 parts of modified composite filler prepared in Example 3, 5.5 parts of curing agent m-phenylenediamine, 0.8 parts of wetting agent polydimethylsiloxane, 0.4 parts of defoaming agent fatty alcohol polyoxyethylene ether, 0.3 parts of leveling agent sodium polyacrylate, and 0.2 parts of dispersant BYK-190.

[0023] The preparation method of the above-mentioned corrosion-resistant coating includes the following steps: weighing each raw material by weight, mixing the water-based epoxy resin and the dispersant evenly, then adding modified silica nanotubes, modified composite fillers, wetting agents, and leveling agents and stirring evenly, then adding curing agents and defoaming agents and continuing to stir evenly to prepare the corrosion-resistant coating.

[0024] Example 5 A corrosion-resistant coating comprises the following components in parts by weight: 60 parts of a water-based epoxy resin, 10 parts of modified silica nanotubes prepared in Example 2, 6.8 parts of a modified composite filler prepared in Example 3, 8.5 parts of a curing agent, m-phenylenediamine, 1.7 parts of a wetting agent, 0.7 parts of an alkylphenol polyoxyethylene ether defoaming agent, 0.5 parts of a leveling agent, and 0.4 parts of a dispersant, BYK-191.

[0025] The preparation method of the above-mentioned corrosion-resistant coating is the same as that of Example 4.

[0026] Example 6 A corrosion-resistant coating comprises the following components in parts by weight: 67 parts of water-based epoxy resin, 14 parts of modified silica nanotubes prepared in Example 2, 8.5 parts of modified composite filler prepared in Example 3, 10.5 parts of curing agent m-phenylenediamine, 2.1 parts of wetting agent polydimethylsiloxane, 0.8 parts of defoaming agent fatty alcohol polyoxyethylene ether, 0.7 parts of leveling agent sodium polyacrylate, and 0.5 parts of dispersant BYK-190.

[0027] The preparation method of the above-mentioned corrosion-resistant coating is the same as that of Example 4.

[0028] Comparative Example 1 A method for preparing a modified composite filler comprises the following steps: 20 mg of mica and 30 mg of zinc oxide were ultrasonically dispersed in a mixed solution of 30 mL of anhydrous ethanol and 0.05 g of silane coupling agent KH550, stirred and reacted at 70 ° C for 3 hours, and then 30 mL of deionized water was slowly added dropwise and stirred and reacted for 3 hours. After the reaction was completed, it was filtered, washed and dried to prepare a modified composite filler.

[0029] Comparative Example 2 A corrosion-resistant coating comprises the following components in parts by weight: 67 parts of water-based epoxy resin, 14 parts of nano-silica, 8.5 parts of the modified composite filler prepared in Example 3, 10.5 parts of a curing agent, m-phenylenediamine, 2.1 parts of a wetting agent, polydimethylsiloxane, 0.8 parts of a defoaming agent, fatty alcohol polyoxyethylene ether, 0.7 parts of a leveling agent, sodium polyacrylate, and 0.5 parts of a dispersant, BYK-190.

[0030] The preparation method of the above-mentioned corrosion-resistant coating is the same as that of Example 4.

[0031] Comparative Example 3 A corrosion-resistant coating comprises the following components in parts by weight: 67 parts of a water-based epoxy resin, 14 parts of the silica nanotubes prepared in Example 1, 8.5 parts of the modified composite filler prepared in Example 3, 10.5 parts of a curing agent, m-xylenediamine, 2.1 parts of a wetting agent, polydimethylsiloxane, 0.8 parts of a defoaming agent, fatty alcohol polyoxyethylene ether, 0.7 parts of a leveling agent, sodium polyacrylate, and 0.5 parts of a dispersant, BYK-190.

[0032] The preparation method of the above-mentioned corrosion-resistant coating is the same as that of Example 4.

[0033] Comparative Example 4 A corrosion-resistant coating comprises the following components in parts by weight: 67 parts of a water-based epoxy resin, 14 parts of modified silica nanotubes prepared in Example 2, 8.5 parts of a modified composite filler prepared in Comparative Example 1, 10.5 parts of a curing agent, m-phenylenediamine, 2.1 parts of a wetting agent, polydimethylsiloxane, 0.8 parts of a defoaming agent, fatty alcohol polyoxyethylene ether, 0.7 parts of a leveling agent, sodium polyacrylate, and 0.5 parts of a dispersant, BYK-190.

[0034] The preparation method of the above-mentioned corrosion-resistant coating is the same as that of Example 4.

[0035] Performance testing The corrosion-resistant coatings prepared in Examples 4-6 and Comparative Examples 2-4 were coated on a polished AA2024 aluminum alloy substrate using a wire rod, and cured at room temperature for 24 hours and at 60° C. for 12 hours. Performance tests were then performed. (1) The impact resistance, adhesion and pencil hardness of the coating were tested according to the methods specified in GB / T 1732-2020, GB / T 9286-2021 and GB / T 6739-2022, respectively. The data results are shown in Table 1.

[0036] (2) Anti-corrosion performance test: The test was conducted in accordance with GB / T 9274-1988. The acid resistance was 10% sulfuric acid solution, the alkali resistance was 10% sodium hydroxide solution, and the salt water resistance was 5% sodium chloride solution. The end time was when the coating began to blister, rust, or become severely discolored. Slight discoloration was allowed. The data results are shown in Table 1.

[0037] (3) Thermal insulation performance test: The heat source temperature is 250 °C. After 60 min and 420 min of thermal insulation testing, the temperature difference between the heat source and the surface of the coating sample is measured. The data results are shown in Table 1.

[0038] (4) Flame retardant performance test: Through the limiting oxygen index test, the data results are shown in Table 1.

[0039] (5) Antibacterial performance test: The antibacterial rate test was carried out with reference to GB / T 21866-2008. The test bacteria was Staphylococcus aureus. The data results are shown in Table 1.

[0040] Table 1 Sample performance test results It can be seen from the data in Table 1 that the coatings prepared in Examples 4-6 of the present invention have strong adhesion, high impact strength and pencil hardness, and good corrosion resistance, heat insulation, flame retardant effect and antibacterial effect. In Comparative Example 2, the modified silica nanotubes were replaced with nano-silica in equal amounts, and in Comparative Example 3, the silica nanotubes were not modified. The mechanical properties, limiting oxygen index, and antibacterial rate of Comparative Examples 2-3 were lower than those of Examples 4-6. The possible reason was that the mechanical properties were reduced due to the agglomeration of nanoparticles. At the same time, the flame retardant properties and antibacterial effects were reduced due to the lack of introduction of antibacterial benzimidazole groups, synergistic flame retardant phosphorus and nitrogen elements. The impact strength and thermal insulation temperature difference of Comparative Example 2 were significantly lower than those of Examples 4-6, indicating that the addition of modified silica nanotubes can improve the mechanical properties, thermal insulation properties, flame retardant effects, and antibacterial effects of the coating. In Comparative Example 4, mica and zinc oxide were simply mixed, and the pencil hardness, impact strength, anti-corrosion properties, and thermal insulation temperature difference were lower than those of Examples 4-6, indicating that the addition of modified composite fillers improved the mechanical properties, anti-corrosion properties, and thermal insulation effects of the coating to a certain extent.

[0041] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0042] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.

Claims

1. A corrosion-resistant coating, characterized in that: The invention comprises the following components in parts by weight: 45-70 parts of waterborne epoxy resin, 7-16 parts of modified silica nanotubes, 4-9 parts of modified composite fillers, 5-12 parts of curing agent, 0.5-2.5 parts of wetting agent, 0.3-1 parts of defoaming agent, 0.2-0.8 parts of leveling agent and 0.1-0.6 parts of dispersant; The modified silica nanotubes are prepared by acylating silica nanotubes with 4-isocyanatobenzoyl chloride and then reacting them with an amidation modifier; the amidation modifier is prepared by synthesizing a spirocyclic phosphate dichloride using pentaerythritol and phosphorus oxychloride as raw materials, and then reacting 2-aminobenzimidazole and 3,5-diamino-1,2,4-triazole with the chlorine atoms at both ends of the spirocyclic phosphate dichloride to form a substitution reaction. The silica nanotubes are prepared by reacting toluene-2,4-diisocyanate with hydroxylated carbon nanotubes to obtain isocyanate-modified carbon nanotubes, which are then covalently grafted with polyethylene glycol to prepare modified carbon nanotubes. Subsequently, the modified carbon nanotubes are used as templates and tetraethyl orthosilicate is used as a raw material. A sol-gel method is used under alkaline conditions, and the template is removed by heat treatment. The modified composite filler is made by using silane coupling agent KH550 to modify the composite filler; the composite filler is made by using dopamine to self-polymerize on the outer surface of mica to form a polydopamine layer, and then using a sol-gel method and high-temperature calcination to wrap a layer of zinc oxide on the outer layer of the dopamine-modified mica.

2. The corrosion-resistant coating according to claim 1, characterized in that The preparation method of the modified silica nanotubes comprises the following steps: A. Place pentaerythritol, chlorobenzene, phosphorus oxychloride, and 4-dimethylaminopyridine in a reactor, purify the reaction with nitrogen, and react at 60-70°C for 2-3 hours. Then, heat to 95-100°C and continue the reaction for 6-8 hours. After the reaction is complete, stop heating and allow to stand for 8-10 hours. Filter the product, wash with dichloromethane, and vacuum dry to obtain a spirocyclic phosphate diacyl chloride. B. Take spirocyclic phosphate dichloride and acetonitrile in a reactor, heat to 50-60° C. under a nitrogen atmosphere, take 2-aminobenzimidazole, 3,5-diamino-1,2,4-triazole and anhydrous methanol, stir and mix evenly, then add them to the reactor, place at 65-75° C. and stir to react for 6-8 hours. After the reaction is completed, filter, wash and dry to prepare an amino modifier; C. Ultrasonic dispersion of silica nanotubes in acetone solvent, then adding 4-isocyanatobenzoyl chloride and dibutyltin dilaurate, stirring and mixing, placing at 40-60° C. for 12-24 hours, filtering, washing, and drying after the reaction is complete to prepare acyl chloride silica nanotubes; D. Ultrasonic dispersion of acyl chloride silica nanotubes in tetrahydrofuran solvent, then adding an amino modifier and pyridine, stirring and mixing, placing the mixture at 25-40° C., stirring and reacting for 6-18 hours. After the reaction is completed, filtering, washing, and drying to prepare modified silica nanotubes.

3. The corrosion-resistant coating according to claim 2, characterized in that The molar ratio of pentaerythritol to phosphorus oxychloride in step A is 1:2-2.5; the molar ratio of spirocyclic phosphate dichloride, 2-aminobenzimidazole and 3,5-diamino-1,2,4-triazole in step B is 1:1-1.1:1-1.

1.

4. The corrosion-resistant coating according to claim 2, characterized in that The method for preparing the silicon dioxide nanotubes in step C comprises the following steps: C1. Dispersing hydroxylated carbon nanotubes in toluene-2,4-diisocyanate, reacting at 75-85°C for 70-72 hours under nitrogen protection, filtering, washing, and drying to obtain isocyanate-treated carbon nanotubes. C2. Place isocyanate-treated carbon nanotubes, polyethylene glycol, and toluene in a reactor, ultrasonically disperse the mixture at 55-70°C for 20-30 minutes under nitrogen protection, and then react at 90-100°C for 30-36 hours. After the reaction is complete, filter, wash, and dry the mixture to obtain modified carbon nanotubes. C3. Take the modified carbon nanotubes and ultrasonically disperse them in an ethanol solution. After adding ethyl orthosilicate, ultrasonically disperse them for another 20-30 minutes. Then, add ammonia water and stir the reaction at room temperature for 20-24 hours. Then, let it stand for aging. Then, filter, wash, and dry the obtained silica-coated modified carbon nanotubes. Place them at 480-520°C in an air atmosphere and calcine them for 5-7 hours to prepare silica nanotubes.

5. The corrosion-resistant coating according to claim 2, characterized in that: In the step D, the mass ratio of the acyl chloride silica nanotubes to the amino modifier is 1:0.5-1.

6. The corrosion-resistant coating according to claim 1, characterized in that The preparation method of the modified composite filler comprises the following steps: (1) Tris(hydroxymethyl)aminomethane and deionized water were placed in a reactor, and the pH was adjusted to 8.5 using hydrochloric acid. Then, ground mica powder was added and dispersed evenly by ultrasonication. Then, dopamine hydrochloride was added under stirring, and the mixture was stirred and reacted at room temperature for 20 to 24 hours. After the reaction was completed, the mixture was filtered, washed, and dried to prepare dopamine-modified mica. (2) Dopamine-modified mica was ultrasonically dispersed in ethanol and deionized water, and the temperature was raised to 65-75°C. Zinc nitrate hexahydrate and dispersant polyethylene glycol were added, and the mixture was stirred for 1-1.5 hours. Then, a mixed solution of ammonia water and deionized water was added dropwise. After the addition was completed, the mixture was continued to react for 1.5-2 hours. After the reaction was completed, the mixture was filtered, washed, dried, ground, and placed in a tube furnace. It was calcined at 950-1000°C for 2-2.5 hours to prepare a composite filler. (3) The composite filler was ultrasonically dispersed in a mixed solution of anhydrous ethanol and silane coupling agent KH550, and stirred at 55-70°C for 3-5 hours. Deionized water was then slowly added and stirred for 2-3 hours. After the reaction was completed, the modified composite filler was filtered, washed, and dried to obtain the modified composite filler.

7. The corrosion-resistant coating according to claim 6, characterized in that In the step (2), the mass ratio of dopamine-modified mica to zinc nitrate hexahydrate is 0.07-0.08:2.4; and the heating rate of the tubular furnace is 8-10°C / min.

8. The corrosion-resistant coating according to claim 1, characterized in that The curing agent is an amine curing agent; the wetting agent is polydimethylsiloxane; the defoaming agent is one of fatty alcohol polyoxyethylene ether or alkylphenol polyoxyethylene ether; the leveling agent is sodium polyacrylate; and the dispersant is one of BYK-190 or BYK-191.

9. The corrosion-resistant coating according to claim 1, characterized in that: The preparation method of the corrosion-resistant coating comprises the following steps: weighing each raw material by weight, mixing the water-based epoxy resin and the dispersant evenly, then adding the modified silica nanotubes, the modified composite filler, the wetting agent, and the leveling agent and stirring evenly, then adding the curing agent and the defoaming agent and continuing to stir evenly to prepare the corrosion-resistant coating.

10. The use of the corrosion-resistant coating according to claim 1, characterized in that: The corrosion-resistant coating is coated on the surface of the aluminum alloy heat exchange tube by a coating method.

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