Preparation method of self-repairing hydrophobic coating based on porous structure of red mud

Abstract

The present application belongs to the technical field of self-repairing hydrophobic coating, and particularly relates to a preparation method of self-repairing hydrophobic coating based on porous structure of red mud, comprising the following steps: S1: red mud raw material pretreatment, S2: preparation of red mud-based porous structure, S3: preparation of self-repairing hydrophobic coating, S4: coating of hydrophobic coating and solidification forming, S5: detection and evaluation of coating performance, and S6: post-treatment, maintenance and repair of coating. The present application uses industrial bulk solid waste red mud as the main raw material to prepare functional coating, greatly improves the comprehensive utilization rate of red mud, relieves the environmental pressure and land occupation of stacking, realizes the reduction, harmlessness and high-value utilization of solid waste, and has remarkable ecological and social benefits. The triple synergistic repair mechanism of wax thermal phase transition, elastic polymer structure rebound and resin chain segment thermal motion can simultaneously repair the surface chemical composition and reconstruct the micro-nano multi-level structure, solve the problem that traditional coatings cannot be repaired after serious damage, and has high repair efficiency and long cycle service life.

Description

Technical Field

[0001] This invention belongs to the field of self-healing hydrophobic coating technology, specifically relating to a method for preparing a self-healing hydrophobic coating based on the porous structure of red mud. Background Technology

[0002] The core of preparing self-healing hydrophobic coatings is to construct a composite structure of "micro-nano rough structure + low surface energy component + self-healing system". It usually requires key steps such as raw material pretreatment, coating system formulation, coating and curing: First, select suitable raw materials to construct micro-nano rough skeleton, combine with low surface energy modifier to reduce surface energy, then introduce self-healing components (such as waxes, elastic polymers, etc.), and prepare a uniform coating by ultrasonic dispersion and stirring. Finally, apply it to the substrate by spraying, brushing or other methods, and form a coating with hydrophobic and self-healing functions after pre-curing and high-temperature curing. Its core goal is to solve the problem of easy failure of traditional hydrophobic coatings.

[0003] Existing self-healing superhydrophobic coatings generally suffer from a single repair mechanism, relying solely on the migration of low surface energy substances to repair the surface chemical composition. This fails to restore hydrophobic properties after severe damage to the micro / nano hierarchical structure. Furthermore, they exhibit drawbacks such as demanding repair conditions, short cycle life, environmentally unfriendly use of fluorinated modifiers, and weak adhesion between the coating and the substrate. Organically combining the porous structure of red mud with a self-healing hydrophobic system can not only facilitate the large-scale disposal of red mud solid waste but also construct a structurally stable, rapidly thermally repairable, wear-resistant, and corrosion-resistant hydrophobic coating. This effectively overcomes existing technological bottlenecks and offers significant environmental benefits and industrial application value. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a self-healing hydrophobic coating based on the porous structure of red mud, so as to solve the above-mentioned problems. This invention provides the following technical solution: A method for preparing a self-healing hydrophobic coating based on the porous structure of red mud, comprising the following steps: S1: Red mud raw material pretreatment: Red mud is sequentially screened and dried, coarsely ground and sieved, deeply dealkalized, dried and activated to obtain modified red mud powder; S2: Preparation of porous structure based on red mud: Modified red mud powder is mixed with fly ash, cement, foaming agent and wet ball milled, foamed and aged, dried and sintered at high temperature, crushed and graded and sieved to obtain porous red mud powder; S3: Formulation of self-healing hydrophobic coating: Powdered wax pretreated with wax, low surface energy modified elastic polymer, porous red mud powder, low surface energy resin, curing agent and organic solvent are mixed in proportion and then mixed through multi-stage dispersion to obtain self-healing hydrophobic coating. S4: Hydrophobic coating application and curing: After substrate pretreatment, the coating is applied to the substrate surface through a coating application operation, and a red mud-based self-healing hydrophobic coating is obtained after pre-curing and high-temperature curing. S5: Coating performance testing and evaluation: Hydrophobicity test, wear resistance repair performance test, mechanical impact repair test, chemical etching repair test, and adhesion test of the coating; S6: Coating post-treatment, maintenance and repair: The cured coating is subjected to gradient cooling treatment, surface cleaning treatment, standard maintenance conditions and on-site repair and long-term maintenance. When the coating is damaged, it can achieve self-repair through heating.

[0005] As a method for preparing a self-healing hydrophobic coating based on the porous structure of red mud according to the present invention, preferably, in S1: raw material screening and drying: Bayer process red mud or sintering process red mud is selected as raw material, impurities such as stones and fibers are removed, and it is placed in a forced-air drying oven and dried at a constant temperature of 105°C for 12 hours until the moisture content drops to below 1%, so as to avoid the moisture affecting the subsequent ball milling and sintering effect. Coarse grinding and sieving: The dried red mud is put into a planetary ball mill and ball milled at 300 r / min for 4 hours. Then it is passed through a 200-mesh standard sieve to obtain red mud fine powder with uniform particle size. The coarse particles on the sieve are returned to the ball milling process for repeated processing to ensure the consistency of powder particle size. Deep dealkali treatment: Red mud powder and calcium ion replacement agent are mixed at a mass ratio of 10:1. Calcium chloride or calcium carbonate is selected as the calcium ion replacement agent. Deionized water is added to prepare a suspension with a solid-liquid ratio of 1:3. The suspension is placed in an 80℃ constant temperature water bath and mechanically stirred for 2 hours to fully replace the soluble sodium alkali and chemically bound alkali in the red mud. After the reaction is completed, vacuum filtration is performed, and the filter cake is repeatedly washed with deionized water until the pH value of the filtrate stabilizes at 7-8, eliminating the interference of alkalinity on the coating performance. Drying and activation modification: The dealkali-treated red mud filter cake was placed in a 60℃ oven and dried for 8 hours to obtain dealkali-treated red mud powder; the dealkali-treated red mud powder and silane coupling agent were mixed at a mass ratio of 100:3, with KH-550 or KH-570 selected as the silane coupling agent. The mixture was stirred at 800 r / min for 30 minutes using a high-speed mixer to ensure that the coupling agent uniformly coated the red mud particles; then it was transferred to a 100℃ activation furnace and kept at that temperature for 1 hour to complete the surface organic modification, which significantly improved the interfacial compatibility and bonding strength between the red mud and the resin and polymer.

[0006] As a method for preparing a self-healing hydrophobic coating based on the porous structure of red mud according to the present invention, preferably, the Bayer process red mud is made from high-alumina, low-silica bauxite, which is dissolved in concentrated sodium hydroxide solution at high temperature and high pressure to extract alumina, and the remaining strongly alkaline waste residue after separating the sodium aluminate solution; the sintering process red mud is made from high-silica bauxite combined with limestone and soda ash, which is sintered at high temperature to produce clinker, and then dissolved in dilute alkali solution to extract alumina, and the discharged waste residue with high calcium and silicon content is used.

[0007] As a method for preparing a self-healing hydrophobic coating based on the porous structure of red mud according to the present invention, preferably, in step S2: ingredient preparation and wet ball milling: accurately weigh 70-80 parts of modified red mud powder, 15-25 parts of fly ash, 5-10 parts of cement, and 0.5-1.5 parts of foaming agent by mass, wherein the foaming agent is selected from hydrogen peroxide or carbonate composite foaming agent; add deionized water to adjust the viscosity of the slurry, and place it in a ball mill jar for ball milling at 200 r / min for 2 h to fully mix and disperse the components and obtain a uniform and stable ceramic slurry; Foaming and aging molding: Add 0.3%~0.5% nonionic surfactant to the slurry and stir at 1200r / min for 10min to introduce a large number of uniform bubbles to form foam slurry; transfer the foam slurry to an aging tank and let it stand at room temperature for 30min to eliminate internal stress of bubbles and improve foam stability; then slowly pour it into a custom mold and let it flow naturally to complete the molding process. Drying and high-temperature sintering: After curing the shaped green body at room temperature for 24 hours, it is demolded and placed in a 50℃ oven to dry for 6 hours to remove free water. The dried green body is then sent to a high-temperature sintering furnace and heated at a uniform rate of 5℃ / min. It is first preheated at 350~450℃ for 30 minutes to remove residual organic foaming agent, and then heated to 1050~1150℃ and held for 60~90 minutes to sinter and combine the red mud and fly ash to form a through-porous structure. After sintering, it is naturally cooled to room temperature with the furnace to obtain a red mud-based porous ceramic block. Crushing and grading: The porous ceramic block is crushed in a high-speed crusher and passed through 100-mesh, 200-mesh and 300-mesh standard sieves in sequence. The 100-300 mesh range of red mud porous micro powder is collected. This micro powder has a multi-level pore structure with a pore size of 1-5 mm and a porosity of 60%-80%, which can be used as the core rough skeleton and functional carrier of the coating.

[0008] As a method for preparing a self-healing hydrophobic coating based on the porous structure of red mud according to the present invention, preferably, in step S3: wax pretreatment: take 1-40 parts by mass of beeswax / palm wax / paraffin wax, add 10-40 parts of ethyl acetate, place in an 85°C water bath and stir in a sealed manner for 5 minutes to completely dissolve the wax and form a transparent solution; slowly add 20-50 parts of ethanol, the solution gradually turns into an emulsion, continue stirring until cooled to room temperature; then vacuum filter, place the filter cake in a 50°C oven to dry for 4 hours, grind through a 200-mesh sieve to obtain powdered wax, which serves as the core component for thermo-induced structural repair; Low surface energy modification of elastic polymer: Take 1-20 parts by mass of polyurethane / silicone rubber / fluororubber and grind them into powder; prepare a modification solution with a volume ratio of triethoxyperfluorosilane / stearic acid and ethyl acetate of 1:2, completely immerse the rubber powder in the modification solution, and immerse it at room temperature for 30 minutes; after taking it out, put it in an 80℃ oven to dry, wash it repeatedly with ethyl acetate and filter it to remove the unadsorbed modifier, and dry it again to obtain a low surface energy elastic polymer, which improves the coating's cushioning impact resistance and structural resilience; Multi-stage dispersion and mixing: First, add the porous red mud powder and low surface energy elastic polymer to an organic solvent, and then use a cell disruptor to strongly disperse the mixture using ultrasound for 30 minutes to ensure uniform particle dispersion without agglomeration; then add low surface energy resin and powdered wax, and continue to disperse the mixture using ultrasound for 5 minutes; finally, add the curing agent, and then transfer the mixture to an ultrasonic cleaner for low-intensity ultrasound for 10 minutes to obtain a self-healing hydrophobic coating with no sedimentation and uniform dispersion.

[0009] As a method for preparing a self-healing hydrophobic coating based on the porous structure of red mud according to the present invention, preferably, the coating formulation (parts by mass) in S3 is as follows: porous red mud powder: 10-25 parts, powdered wax: 5-20 parts, low surface energy elastic polymer: 5-15 parts, low surface energy resin: 50-100 parts (organosilicon epoxy resin / fluorosilicone resin / fluorocarbon resin), curing agent: 5-10 parts (aliphatic polyamine / isocyanate), organic solvent: 20-80 parts (acetone / ethyl acetate / tetrahydrofuran).

[0010] As a method for preparing a self-healing hydrophobic coating based on the porous structure of red mud according to the present invention, preferably, in step S4: substrate pretreatment: for metal substrates, aluminum plates or steel plates are selected, and oxide films and oil stains are removed by bidirectional sanding with 1000-grit sandpaper, and the substrates are cleaned three times alternately with ethanol and distilled water, and then dried at 80°C for later use; for concrete / stone substrates, dust removal and leveling are performed first, and floating dust is removed by wiping with ethanol, and then dried at 60°C; for glass substrates, piranha detergent is used for cleaning, and after rinsing with deionized water, the substrate surface is dried to ensure that it is clean and free of impurities. Coating application: Apply by vapor phase spraying, brushing or scraping. Control the air pressure to 4-6 bar during spraying, keep the distance between the spray gun and the substrate at 15-20 cm, and move the gun at a uniform speed to ensure a uniform coating. Control the thickness of a single layer to 50-100 μm. If a thicker layer is required, apply multiple layers with a 10-minute interval between layers to avoid sagging and bubbles. Pre-curing and high-temperature curing: After coating, the substrate is placed on a heating platform at 40~60℃ for pre-curing for 30 minutes to allow the solvent to evaporate initially and the coating to set. Then, it is placed in a forced-air drying oven and cured at 120~180℃ for 60~120 minutes to allow the low surface energy resin and curing agent to react completely and form a dense film-forming substance. At the same time, the wax and elastic polymer are evenly distributed inside the coating to obtain a red mud-based self-healing hydrophobic coating.

[0011] As a method for preparing a self-healing hydrophobic coating based on the porous structure of red mud according to the present invention, preferably, in step S5: hydrophobic performance test: using a Thetalite contact angle measuring instrument, take 10μL of deionized water droplet, and test the static water contact angle and roll-off angle of the coating. The static contact angle is required to be ≥150° and the roll-off angle is ≤10° to meet the superhydrophobic standard. Wear-resistant repair performance test: The coating was cyclically polished with a 500g load and 1000-grit sandpaper, and the hydrophobicity was tested every 100 cycles; the damaged coating was placed in a 120℃ oven and heated for 2 minutes, and the contact angle was tested again. It was required that the contact angle after repair should be restored to more than 150°, and the superhydrophobicity should still be maintained after 10 polishing-repair cycles. Mechanical impact repair test: Use a 500~1000g steel ball to drop freely from a height of 50~100cm to impact the coating surface and observe whether there are cracks or peeling in the coating; heat the impact-damaged coating at 70~120℃ and test the recovery of microstructure and hydrophobic properties. The requirements are that the dents are repaired, there are no cracks, and the contact angle is restored to the superhydrophobic level. Chemical etching repair test: The coating is etched using oxygen plasma to change it from superhydrophobic to superhydrophilic; the etched coating is then heated or irradiated with UV light to test the surface wettability recovery effect, requiring that the superhydrophobic properties can be restored. Adhesion test: The adhesion between the coating and the substrate is tested using a cross-cut tester and tape peeling method. The coating should not peel off or curl, and the adhesion strength should meet the standard.

[0012] As a method for preparing a self-healing hydrophobic coating based on the porous structure of red mud according to the present invention, preferably, in step S6: gradient cooling treatment: after curing, the oven power is turned off, and the coating is slowly cooled to 60°C with the oven, and then taken out and naturally cooled to room temperature to avoid excessive internal stress, cracking, warping and other defects caused by sudden cooling. Surface cleaning treatment: Use a lint-free cloth dampened with anhydrous ethanol to gently wipe the coating surface to remove dust, uncured resin residue and impurities, keep the surface clean and do not damage the micro-nano rough structure; Standard curing conditions: Place the coating in a room temperature, ventilated, dry environment without direct sunlight and maintain a constant temperature for more than 24 hours to ensure complete cross-linking reaction and stable performance. Avoid contact with acid and alkali solutions, oil stains, and scratches from sharp objects during the curing period. On-site repair and long-term maintenance: When the coating is worn, scratched or dented during use, repair can be triggered by methods such as oven heating, hot air blowing, UV mercury lamp irradiation or heating platform baking. Heating at 70~120℃ for 1~30 minutes can complete the repair of micro-nano structure and hydrophobic properties. During long-term use, clean the surface dust regularly with ethanol to avoid contaminants clogging the pores and affecting the hydrophobicity and repair effect.

[0013] Compared with the prior art, the beneficial effects of the present invention are: This invention uses red mud, a major industrial solid waste, as the main raw material to prepare a functional coating, which greatly improves the comprehensive utilization rate of red mud, effectively alleviates the environmental pressure and land occupation problems caused by red mud stockpiling, and realizes the reduction, harmlessness and high-value utilization of solid waste, with significant ecological and social benefits.

[0014] This invention employs a triple synergistic repair mechanism involving wax thermal phase transformation, elastic polymer structure rebound, and resin chain segment thermal motion. It can not only repair the surface chemical composition but also reconstruct the damaged micro-nano hierarchical structure, solving the industry problem that traditional coating structures cannot be repaired after severe damage. It has high repair efficiency and long cycle life.

[0015] This invention utilizes the porous structure of red mud to construct a stable micro-nano rough framework, and combines it with a low surface energy system for modification, enabling the coating to possess excellent superhydrophobic properties. It also has good self-cleaning, anti-fouling, drag reduction, anti-icing, and anti-corrosion functions, which can significantly extend the service life of the substrate.

[0016] The elastic components inside the coating of this invention can effectively buffer external impacts and friction wear. The overall structure is dense and stable, and it has good wear resistance, impact resistance, chemical corrosion resistance and aging resistance. It can adapt to a variety of complex and harsh working conditions such as outdoor, industrial, construction and marine environments. Attached Figure Description

[0017] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the implementation process provided in the embodiments of this application. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Please see Figure 1 The present invention provides the following technical solution: a method for preparing a self-healing hydrophobic coating based on the porous structure of red mud, comprising the following steps; S1: Red mud raw material pretreatment Bayer process red mud was selected as raw material. First, impurities such as stones and fibers were manually removed. The red mud was then placed in a forced-air drying oven and dried at a constant temperature of 105℃ for 12 hours to reduce the moisture content to below 1%, preventing moisture from affecting subsequent ball milling and sintering. The dried red mud was then placed in a planetary ball mill and milled at 300 rpm for 4 hours. It was then passed through a 200-mesh standard sieve to obtain fine red mud powder with uniform particle size. Coarse particles on the sieve were returned to the ball milling process for repeated processing to ensure consistent particle size. A red mud powder to calcium chloride ratio of 10:1 was prepared by mixing red mud powder with deionized water to form a suspension with a solid-liquid ratio of 1:3. This suspension was mechanically stirred in an 80℃ constant-temperature water bath for 2 hours to fully displace the soluble sodium alkali and chemically bound alkali in the red mud. After the reaction, the mixture was vacuum filtered, and the filter cake was repeatedly washed with deionized water until the pH of the filtrate stabilized at 7-8. The dealkali-treated red mud filter cake was dried in a 60℃ oven for 8 hours to obtain dealkali-treated red mud powder. The dealkali-treated red mud powder and KH-550 silane coupling agent were mixed at a mass ratio of 100:3 and stirred at 800r / min for 30 minutes using a high-speed mixer to ensure that the coupling agent uniformly coated the red mud particles. Then, the mixture was transferred to an activation furnace at 100℃ and kept at that temperature for 1 hour to complete the surface organic modification and obtain modified red mud powder.

[0020] S2: Preparation of porous structures based on red mud Accurately weigh the following components by weight: 75 parts modified red mud powder, 20 parts fly ash, 5 parts cement, and 1 part hydrogen peroxide foaming agent. Add deionized water to adjust the slurry viscosity, and place it in a ball mill jar for 2 hours at 200 rpm to obtain a uniform and stable ceramic slurry. Add 0.4% by weight of nonionic surfactant to the slurry and stir at 1200 rpm for 10 minutes to introduce a large number of uniform bubbles to form a foam slurry. Transfer the foam slurry to an aging tank and allow it to age at room temperature for 30 minutes to eliminate internal stress in the bubbles and improve foam stability. Then, slowly pour it into a custom mold and allow it to level naturally to complete the molding process. After curing at room temperature for 24 hours, the molded green body was demolded and dried in a 50℃ oven for 6 hours to remove free water. The dried green body was then sent to a high-temperature sintering furnace and heated at a uniform rate of 5℃ / min. It was first preheated at 400℃ for 30 minutes to remove residual organic foaming agent, and then heated to 1100℃ and held for 75 minutes to sinter and bond the red mud and fly ash, forming a through-hole porous structure. After sintering, the green body was naturally cooled to room temperature in the furnace to obtain a red mud-based porous ceramic block. The porous ceramic block was crushed in a high-speed pulverizer and passed through 100-mesh, 200-mesh, and 300-mesh standard sieves in sequence. The red mud porous micro powder in the 100-300 mesh range was collected as the core rough skeleton and functional carrier of the coating.

[0021] S3: Formulation of self-healing hydrophobic coating Take 15 parts of beeswax, add 25 parts of ethyl acetate, and place in an 85℃ water bath with sealed stirring for 5 minutes to completely dissolve the wax and form a transparent solution; slowly add 35 parts of ethanol, and the solution gradually turns into an emulsion, continuing to stir until cooled to room temperature; then vacuum filter, place the filter cake in a 50℃ oven to dry for 4 hours, grind through a 200-mesh sieve to obtain a powdered waxy substance. Take 10 parts of silicone rubber powder, prepare a modification solution of triethoxyperfluorosilane:ethyl acetate = 1:2, completely immerse the rubber powder in the modification solution, and impregnate and adsorb at room temperature for 30 minutes; after removal, place in an 80℃ oven to dry, repeatedly wash with ethyl acetate and filter to remove unadsorbed modifier, and dry again to obtain a low surface energy elastic polymer. Weigh the following by mass: 15 parts of porous red mud powder, 8 parts of powdered waxy substance, 8 parts of low surface energy elastic polymer, 75 parts of fluorosilicone resin, 7 parts of aliphatic polyamine curing agent, and 45 parts of acetone. First, add the porous red mud powder and low surface energy elastic polymer to acetone and disperse them by strong ultrasonication for 30 minutes using a cell disruptor; then add fluorosilicone resin and powdered wax and continue ultrasonic dispersion for 5 minutes; finally add curing agent and transfer to an ultrasonic cleaner for low-intensity ultrasonication for 10 minutes to obtain a self-healing hydrophobic coating with no precipitation and uniform dispersion.

[0022] S4: Hydrophobic coating application and curing An aluminum plate was selected as the substrate. The oxide film and oil stains were removed by bidirectional sanding with 1000-grit sandpaper. The plate was then cleaned three times alternately with ethanol and distilled water, and dried at 80℃ for later use. Vapor phase spraying was employed, with the spray pressure controlled at 5 bar, the distance between the spray gun and the substrate at 18 cm, and the spray gun moved at a uniform speed to ensure a uniform coating. The thickness of each coating layer was controlled at 80 μm. After coating, the substrate was placed on a 50℃ heating platform for pre-curing for 30 minutes to allow the solvent to initially evaporate and the coating to set. Subsequently, it was placed in a forced-air drying oven and cured at 150℃ for 90 minutes to allow the low surface energy resin and curing agent to fully react and form a dense film-forming substance. Simultaneously, wax and elastic polymers were evenly distributed within the coating, resulting in a red mud-based self-healing hydrophobic coating.

[0023] S5: Coating Performance Testing and Evaluation Using a Thetalite contact angle meter, a 10μL droplet of deionized water was used for testing. The coating's static contact angle was ≥150° and roll-off angle was ≤10°, meeting the superhydrophobic standard. Hydrophobicity was tested every 100 cycles of cyclic polishing with 500g weight and 1000-grit sandpaper. Heating the damaged coating in a 120℃ oven for 2 minutes restored the contact angle to over 150°, and it remained superhydrophobic after 10 polishing-repair cycles. A 500g steel ball was dropped from a height of 50cm onto the coating surface; no cracks or peeling were observed. After heating at 100℃, dents were completely repaired and hydrophobicity was restored. Oxygen plasma etching converted the coating to superhydrophilicity; UV light irradiation followed by heat treatment restored its superhydrophobic properties. The cross-cut adhesion test with adhesive tape showed no peeling or lifting, and the bonding strength met the standard.

[0024] S6: Post-coating treatment, maintenance, and repair. After curing, turn off the oven power and allow it to cool slowly to 60°C. Then remove it and allow it to cool naturally to room temperature to avoid internal stress, cracking, or warping caused by sudden cooling. Use a lint-free cloth dampened with anhydrous ethanol to gently wipe the coating surface to remove dust, uncured resin residue, and impurities, maintaining the integrity of the micro-nano rough structure. Place the coating in a well-ventilated, dry environment away from direct sunlight for at least 24 hours to ensure complete internal cross-linking and stable performance. During curing, avoid contact with acidic or alkaline solutions, oil, and scratches from sharp objects. When the coating shows wear, scratches, or impact dents, repair can be triggered by oven heating, hot air blowing, UV mercury lamp irradiation, or baking on a heated platform. Heating at 70-120°C for 1-30 minutes can complete the repair of the micro-nano structure and hydrophobic properties. During long-term use, regularly clean the surface with ethanol to prevent contaminants from clogging the pores and ensure stable hydrophobicity and repair effects.

[0025] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a self-healing hydrophobic coating based on the porous structure of red mud, characterized in that, Includes the following steps: S1: Red mud raw material pretreatment: Red mud is screened and dried, coarsely ground and sieved, deeply dealkalized, dried and activated to obtain modified red mud powder. S2: Preparation of porous structure based on red mud: Modified red mud powder is mixed with fly ash, cement, foaming agent and wet ball milled, foamed and aged, dried and sintered at high temperature, crushed and graded and sieved to obtain porous red mud powder; S3: Formulation of self-healing hydrophobic coating: Powdered wax pretreated with wax, low surface energy modified elastic polymer, porous red mud powder, low surface energy resin, curing agent and organic solvent are mixed in proportion and then mixed through multi-stage dispersion to obtain self-healing hydrophobic coating. S4: Hydrophobic coating application and curing: After substrate pretreatment, the coating is applied to the substrate surface through a coating application operation, and a red mud-based self-healing hydrophobic coating is obtained after pre-curing and high-temperature curing. S5: Coating performance testing and evaluation: Hydrophobicity test, wear resistance repair performance test, mechanical impact repair test, chemical etching repair test, and adhesion test of the coating; S6: Coating post-treatment, maintenance and repair: The cured coating is subjected to gradient cooling treatment, surface cleaning treatment, standard maintenance conditions and on-site repair and long-term maintenance. When the coating is damaged, it can achieve self-repair through heating.

2. The method for preparing a self-healing hydrophobic coating based on the porous structure of red mud according to claim 1, characterized in that: In S1: Raw material screening and drying: Bayer process red mud or sintering process red mud is selected as raw material, impurities such as stones and fibers are removed, and the raw material is placed in a forced-air drying oven and dried at a constant temperature of 105℃ for 12 hours until the moisture content drops to below 1% to avoid moisture affecting the subsequent ball milling and sintering effect. Coarse grinding and sieving: The dried red mud is put into a planetary ball mill and ball milled at 300 r / min for 4 hours. Then it is passed through a 200-mesh standard sieve to obtain red mud fine powder with uniform particle size. The coarse particles on the sieve are returned to the ball milling process for repeated processing to ensure the consistency of powder particle size. Deep dealkali treatment: Red mud powder and calcium ion replacement agent are mixed at a mass ratio of 10:

1. Calcium chloride or calcium carbonate is selected as the calcium ion replacement agent. Deionized water is added to prepare a suspension with a solid-liquid ratio of 1:

3. The suspension is placed in an 80℃ constant temperature water bath and mechanically stirred for 2 hours to fully replace the soluble sodium alkali and chemically bound alkali in the red mud. After the reaction is completed, vacuum filtration is performed, and the filter cake is repeatedly washed with deionized water until the pH value of the filtrate stabilizes at 7-8, eliminating the interference of alkalinity on the coating performance. Drying and activation modification: The dealkali-treated red mud filter cake was placed in a 60℃ oven and dried for 8 hours to obtain dealkali-treated red mud powder; the dealkali-treated red mud powder and silane coupling agent were mixed at a mass ratio of 100:3, with KH-550 or KH-570 selected as the silane coupling agent. The mixture was stirred at 800 r / min for 30 minutes using a high-speed mixer to ensure that the coupling agent uniformly coated the red mud particles; then it was transferred to a 100℃ activation furnace and kept at that temperature for 1 hour to complete the surface organic modification, which significantly improved the interfacial compatibility and bonding strength between the red mud and the resin and polymer.

3. The method for preparing a self-healing hydrophobic coating based on the porous structure of red mud according to claim 2, characterized in that: The Bayer process red mud is made from high-alumina, low-silica bauxite. After the alumina is dissolved in a concentrated sodium hydroxide solution at high temperature and pressure, the remaining strongly alkaline waste residue after separating the sodium aluminate solution is produced. The sintering process red mud is made from high-silica bauxite combined with limestone and soda ash. After high-temperature sintering to produce clinker, the alumina is dissolved in a dilute alkali solution, and the discharged waste residue has a high calcium and silicon content.

4. The method for preparing a self-healing hydrophobic coating based on the porous structure of red mud according to claim 1, characterized in that: In step S2: Ingredient preparation and wet ball milling: Accurately weigh 70-80 parts of modified red mud powder, 15-25 parts of fly ash, 5-10 parts of cement, and 0.5-1.5 parts of foaming agent by mass. The foaming agent is selected from hydrogen peroxide or carbonate composite foaming agent. Add deionized water to adjust the viscosity of the slurry, and place it in a ball mill jar to ball mill at 200 r / min for 2 hours to fully mix and disperse the components and obtain a uniform and stable ceramic slurry. Foaming and aging molding: Add 0.3%~0.5% nonionic surfactant to the slurry and stir at 1200r / min for 10min to introduce a large number of uniform bubbles to form a foam slurry; The foam slurry is transferred to an aging tank and aged at room temperature for 30 minutes to eliminate internal stress in the bubbles and improve foam stability. Then it is slowly poured into a custom mold and allowed to flow naturally to complete the molding process. Drying and high-temperature sintering: After curing the shaped green body at room temperature for 24 hours, it is demolded and placed in a 50℃ oven to dry for 6 hours to remove free water. The dried green body is then sent to a high-temperature sintering furnace and heated at a uniform rate of 5℃ / min. It is first preheated at 350~450℃ for 30 minutes to remove residual organic foaming agent, and then heated to 1050~1150℃ and held for 60~90 minutes to sinter and combine the red mud and fly ash to form a through-porous structure. After sintering, it is naturally cooled to room temperature with the furnace to obtain a red mud-based porous ceramic block. Crushing and grading: The porous ceramic block is crushed in a high-speed crusher and passed through 100-mesh, 200-mesh and 300-mesh standard sieves in sequence. The 100-300 mesh range of red mud porous micro powder is collected. This micro powder has a multi-level pore structure with a pore size of 1-5 mm and a porosity of 60%-80%, which can be used as the core rough skeleton and functional carrier of the coating.

5. The method for preparing a self-healing hydrophobic coating based on the porous structure of red mud according to claim 1, characterized in that: In S3: wax pretreatment: take 1-40 parts by mass of beeswax / palm wax / paraffin wax, add 10-40 parts of ethyl acetate, place in an 85℃ water bath and stir in a sealed manner for 5 minutes to completely dissolve the wax and form a transparent solution; slowly add 20-50 parts of ethanol, the solution gradually turns into an emulsion, continue stirring until cooled to room temperature; then vacuum filter, place the filter cake in a 50℃ oven to dry for 4 hours, grind through a 200-mesh sieve to obtain powdered wax, which serves as the core component for thermo-induced structural repair; Low surface energy modification of elastic polymer: Take 1-20 parts by mass of polyurethane / silicone rubber / fluororubber and grind them into powder; prepare a modification solution with a volume ratio of triethoxyperfluorosilane / stearic acid and ethyl acetate of 1:2, completely immerse the rubber powder in the modification solution, and immerse it at room temperature for 30 minutes; after taking it out, put it in an 80℃ oven to dry, wash it repeatedly with ethyl acetate and filter it to remove the unadsorbed modifier, and dry it again to obtain a low surface energy elastic polymer, which improves the coating's cushioning impact resistance and structural resilience; Multi-stage dispersion and mixing: First, add the porous red mud powder and low surface energy elastic polymer to an organic solvent, and then use a cell disruptor to strongly disperse the mixture using ultrasound for 30 minutes to ensure uniform particle dispersion without agglomeration; then add low surface energy resin and powdered wax, and continue to disperse the mixture using ultrasound for 5 minutes; finally, add the curing agent, and then transfer the mixture to an ultrasonic cleaner for low-intensity ultrasound for 10 minutes to obtain a self-healing hydrophobic coating with no sedimentation and uniform dispersion.

6. The method for preparing a self-healing hydrophobic coating based on the porous structure of red mud according to claim 5, characterized in that: The coating formulation (parts by weight) in S3 is as follows: porous red mud powder: 10-25 parts, powdered wax: 5-20 parts, low surface energy elastic polymer: 5-15 parts, low surface energy resin: 50-100 parts (organosilicon epoxy resin / fluorosilicone resin / fluorocarbon resin), curing agent: 5-10 parts (aliphatic polyamine / isocyanate), organic solvent: 20-80 parts (acetone / ethyl acetate / tetrahydrofuran).

7. The method for preparing a self-healing hydrophobic coating based on the porous structure of red mud according to claim 1, characterized in that: In S4: Substrate pretreatment: For metal substrates, aluminum plates or steel plates are selected. The oxide film and oil stains are removed by bidirectional sanding with 1000-grit sandpaper. The substrates are cleaned three times with alternating ethanol and distilled water, and then dried at 80°C for later use. For concrete / stone substrates, dust removal and leveling are performed first. The substrates are wiped with ethanol to remove floating dust and then dried at 60°C. For glass substrates, the substrates are cleaned with piranha detergent, rinsed with deionized water, and then dried to ensure that the substrate surface is clean and free of impurities. Coating application: Apply by vapor phase spraying, brushing or scraping. Control the air pressure to 4~6 bar during spraying, keep the distance between the spray gun and the substrate at 15~20 cm, and move at a constant speed to ensure uniform coating. The thickness of a single coating layer should be controlled at 50~100μm. If a thicker layer is required, multiple coating layers can be applied with a 10-minute interval between layers to avoid sagging and air bubbles. Pre-curing and high-temperature curing: After coating, the substrate is placed on a heating platform at 40~60℃ for pre-curing for 30 minutes to allow the solvent to evaporate initially and the coating to set. Then, it is placed in a forced-air drying oven and cured at 120~180℃ for 60~120 minutes to allow the low surface energy resin and curing agent to react completely and form a dense film-forming substance. At the same time, the wax and elastic polymer are evenly distributed inside the coating to obtain a red mud-based self-healing hydrophobic coating.

8. The method for preparing a self-healing hydrophobic coating based on the porous structure of red mud according to claim 1, characterized in that: In S5: Hydrophobicity test: Using a Thetalite contact angle measuring instrument, take a 10μL deionized water droplet and test the static water contact angle and roll-off angle of the coating. The static contact angle is required to be ≥150° and the roll-off angle is ≤10° to meet the superhydrophobic standard. Wear-resistant repair performance test: The coating was cyclically polished with a 500g load and 1000-grit sandpaper, and the hydrophobicity was tested every 100 cycles; the damaged coating was placed in a 120℃ oven and heated for 2 minutes, and the contact angle was tested again. It was required that the contact angle after repair should be restored to more than 150°, and the superhydrophobicity should still be maintained after 10 polishing-repair cycles. Mechanical impact repair test: Use a 500~1000g steel ball to drop freely from a height of 50~100cm to impact the coating surface and observe whether there are cracks or peeling in the coating; heat the impact-damaged coating at 70~120℃ and test the recovery of microstructure and hydrophobic properties. The requirements are that the dents are repaired, there are no cracks, and the contact angle is restored to the superhydrophobic level. Chemical etching repair test: The coating is etched using oxygen plasma, which transforms the coating from superhydrophobic to superhydrophilic. The etched coating is heated or irradiated with UV light to test the surface wettability recovery effect, and the superhydrophobic properties must be restored. Adhesion test: The adhesion between the coating and the substrate is tested using a cross-cut tester and tape peeling method. The coating should not peel off or curl, and the adhesion strength should meet the standard.

9. The method for preparing a self-healing hydrophobic coating based on the porous structure of red mud according to claim 1, characterized in that: In S6: Gradient cooling treatment: After curing, turn off the oven power and slowly cool it to 60°C with the oven, then take it out and let it cool naturally to room temperature to avoid excessive internal stress in the coating due to sudden cooling, resulting in defects such as cracking and warping. Surface cleaning treatment: Use a lint-free cloth dampened with anhydrous ethanol to gently wipe the coating surface to remove dust, uncured resin residue and impurities, keep the surface clean and do not damage the micro-nano rough structure; Standard curing conditions: Place the coating in a room temperature, ventilated, dry environment without direct sunlight and maintain a constant temperature for more than 24 hours to ensure complete cross-linking reaction and stable performance. Avoid contact with acid and alkali solutions, oil stains, and scratches from sharp objects during the curing period. On-site repair and long-term maintenance: When the coating is worn, scratched or dented during use, repair can be triggered by methods such as oven heating, hot air blowing, UV mercury lamp irradiation or heating platform baking. Heating at 70~120℃ for 1~30 minutes can complete the repair of micro-nano structure and hydrophobic properties. During long-term use, clean the surface dust regularly with ethanol to avoid contaminants clogging the pores and affecting the hydrophobicity and repair effect.

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