Composite coating for inhibiting microbial acid corrosion of sewer networks and method for its production

Abstract

The application discloses a composite coating for inhibiting microbial acid corrosion of a drainage pipe network and a preparation method thereof, and relates to the field of coatings. The coating comprises, from inside to outside, an anchoring bacteriostatic primer layer, an acid-base buffer intermediate layer and a super-hydrophobic self-repairing topcoat layer. In the application, the nano-zinc oxide in the primer layer continuously inhibits the activity of SRB and reduces the generation of H2S gas, thereby reducing the risk of microbial corrosion from the source. The basic copper carbonate in the intermediate layer and the heat-activated water supply sludge ash form an efficient acid-base buffer system, which can quickly neutralize the sulfuric acid that penetrates the coating and prevent it from reaching the surface of the concrete substrate, thereby solving the problem that traditional coatings can only passively block and lose effectiveness once damaged. The polydopamine microspheres in the topcoat layer have both photothermal response repair and pH response corrosion inhibitor release functions, can realize the rapid closure of coating micro-cracks and active protection in a corrosive environment, and the performance of the repaired coating can be restored to more than 80% of the original state.

Description

Technical Field

[0001] This invention belongs to the field of anti-corrosion coating technology, specifically relating to a composite coating and its preparation method for inhibiting corrosion caused by acid produced by microbial metabolism in drainage pipe networks. It is applicable to facilities such as drainage pipes, inspection wells, rainwater inlets and pumping stations made of concrete or metal. Background Technology

[0002] Urban drainage pipes and their ancillary facilities operate in complex and harsh environments for extended periods. The corrosion mechanism of concrete structures is generally considered to be a "microbial-induced corrosion" (MIC) process: First, sulfates in wastewater are reduced to hydrogen sulfide (H2S) by sulfate-reducing bacteria (SRB) under anaerobic conditions. Subsequently, the H2S gas diffuses into the unfilled spaces within the pipe walls, where it is oxidized to sulfuric acid by sulfur-oxidizing bacteria (SOBs, such as sulfate bacteria) under aerobic conditions. This bio-sulfuric acid continuously erodes the hydration products (calcium hydroxide, calcium silicate hydrate, etc.) in the concrete, generating gypsum and ettringite, leading to volume expansion, cracking, and even structural collapse. According to literature reports, the sulfate bacteria corrosion rate in concrete can reach 1-5 mm / year, and in severe cases, it can cause pipe failure within several years.

[0003] Currently, protective technologies for drainage pipes mainly include organic coatings (such as epoxy and polyurethane), cement-based coatings (such as polymer-modified cement mortar), and surface hydrophobic treatments. Existing technologies have the following shortcomings: (1) Although ordinary epoxy or polyurethane coatings can provide physical barriers, they cannot inhibit the activity of microorganisms attached to the coating surface. Once the corrosive medium penetrates, microbial reproduction and acid corrosion will still occur under the coating.

[0004] (2) Although cement-based repair materials are compatible with concrete substrates, they have poor acid resistance and will quickly fail in sulfuric acid environment.

[0005] (3) Some antibacterial coatings kill microorganisms by releasing heavy metal ions (such as silver and copper ions), but they have problems such as rapid release, short effective period, and potential secondary pollution of water bodies.

[0006] (4) Although a single superhydrophobic coating can reduce the adhesion of water and dirt, it has low mechanical strength and is easily damaged under the flushing of sewage, and has no neutralizing ability to penetrate acidic substances.

[0007] (5) Some self-healing coatings in the prior art use microcapsule-encapsulated repair agents, but the microcapsule preparation process is complicated, has poor compatibility with the matrix resin, and the repair can often only occur once, which is difficult to meet the long-term service requirements of drainage pipes.

[0008] Therefore, developing a coating material that can actively inhibit the metabolism of acid-producing microorganisms, buffer and neutralize the generated bio-sulfuric acid, and has a long-lasting self-healing function is of great significance for fundamentally solving the problem of microbial corrosion in drainage pipe networks. Summary of the Invention

[0009] To achieve the above objectives, this invention provides a composite coating for inhibiting acid corrosion caused by microorganisms in drainage pipe networks, comprising, from the inside out: an anchoring and antibacterial primer layer, an acid-base buffering intermediate layer, and a superhydrophobic self-healing topcoat layer. 1. Anchoring antibacterial primer layer: By weight, it includes: 45-65 parts epoxy resin, 3-8 parts nano zinc oxide, 2-6 parts silane-modified nano montmorillonite, 15-25 parts curing agent, and 20-35 parts solvent.

[0010] Among them, nano zinc oxide (particle size 20-80nm) has broad-spectrum antibacterial activity. It can generate reactive oxygen species (ROS) to destroy the cell membrane of sulfate-reducing bacteria (SRB), inhibit their metabolic activity, and reduce the generation of hydrogen sulfide from the source.

[0011] The preparation method of silane-modified nano-montmorillonite is as follows: First, sodium-based montmorillonite is organically intercalated with hexadecyltrimethylammonium bromide to increase the interlayer spacing; then, amino groups are grafted onto the surface of the montmorillonite sheets with γ-aminopropyltriethoxysilane (KH550).

[0012] Its function is: ① Amino groups can undergo ring-opening reactions with epoxy groups in epoxy resins to form chemical crosslinks, which firmly anchor the nanosheets in the coating and improve the density of the coating. ② The layered structure is arranged parallel to the substrate surface during the coating curing process, forming a "maze effect" that effectively extends the diffusion path of corrosive media; ③ Montmorillonite itself has a certain cation exchange capacity and can adsorb some corrosive cations.

[0013] 2. Acid-base buffer intermediate layer: By weight, it includes: 50-70 parts waterborne epoxy resin, 10-25 parts thermally activated water supply sludge, 5-12 parts basic copper carbonate, 8-20 parts flake mica powder, and 10-20 parts amine curing agent.

[0014] This layer is one of the core innovations of this invention. The thermally activated water supply sludge ash is an activated pozzolanic material produced by dewatering, drying, and crushing aluminate coagulation sludge from municipal water supply plants, followed by calcination at 700-850℃ for 1.5-3 hours, and then ball milling to an average particle size ≤10μm. Its total mass content of amorphous silica and alumina is ≥65%. It reacts with H+ when exposed to acid. +The reaction consumes sulfuric acid and generates silica gel and aluminum glue, which neutralize and seal microcracks; simultaneously, its pozzolanic activity enhances the density of the coating. Basic copper carbonate (Cu2(OH)2CO3) is a unique pH-responsive alkaline inorganic filler: it is stable under normal neutral conditions; once sulfuric acid penetrates and comes into contact with the coating, basic copper carbonate immediately reacts with H2SO4 to neutralize it, producing copper sulfate, water, and carbon dioxide. The reaction equation is: Cu2(OH)2CO3 + 2H2SO4 → 2CuSO4 + CO2↑ + 3H2O, thus effectively neutralizing the acid, and the generated Cu... 2+ Ions themselves have antibacterial effects and can further inhibit SOB activity. Flake mica powder (flake diameter 10-60μm, aspect ratio ≥15) acts as a physical shielding filler, extending the diffusion path of corrosive media and forming a dual protection of "physical barrier-chemical neutralization" with the above-mentioned chemical neutralization mechanism.

[0015] 3. Superhydrophobic self-healing topcoat layer: By weight, it includes: 40-60 parts of fluorocarbon resin, 8-18 parts of hollow mesoporous polydopamine microspheres loaded with corrosion inhibitor, 5-15 parts of hydrophobic modified nano-silica, 10-20 parts of curing agent, and 30-50 parts of organic solvent.

[0016] The method for preparing the hollow mesoporous polydopamine microspheres loaded with corrosion inhibitors adopts the polystyrene (PS) microsphere sacrificial template method, specifically including the following steps: (a) Monodisperse polystyrene microspheres (particle size 200 nm-3 μm) were prepared by soap-free emulsion polymerization or dispersion polymerization. (b) Disperse polystyrene microspheres in Tris buffer (pH=8.5), add dopamine hydrochloride, and stir at room temperature for 12-24 hours to allow dopamine to undergo oxidative self-polymerization on the surface of polystyrene microspheres to form a polydopamine shell, thus obtaining polystyrene@polydopamine core-shell microspheres; (c) Disperse the core-shell microspheres in tetrahydrofuran or toluene, stir at room temperature or heat under reflux for 6-12 hours to dissolve and remove the internal polystyrene template, and obtain hollow mesoporous polydopamine microspheres (particle size 200nm-5μm, wall thickness 20-100nm) after centrifugation and washing. (d) Hollow mesoporous polydopamine microspheres are dispersed in an ethanol-water solution containing a corrosion inhibitor (benzotriazole BTA or sodium molybdate), vacuum impregnated for 12-24 hours, and centrifuged and dried to obtain microspheres loaded with the corrosion inhibitor. The corrosion inhibitor loading accounts for 15-40% of the total mass of the microspheres. Compared with the composite template method in the prior art, this method has a single template type, mild removal conditions, and easy control of shell thickness.

[0017] Polydopamine itself possesses excellent photothermal conversion properties. When microcracks appear in the topcoat layer, it can withstand near-infrared light irradiation (wavelength 808nm, power 1.5W / cm²). 2 Under conditions of 5-10 minutes, the polydopamine microspheres rapidly heat up to above 80°C, causing the surrounding fluorocarbon resin to soften and flow, filling the cracks. At the same time, the microspheres release the corrosion inhibitors they carry in an acidic environment (pH<5, i.e., an environment where microorganisms produce acid) or under photothermal stimulation, forming a protective film on the exposed metal or concrete surface, thus achieving active repair.

[0018] The hydrophobically modified nano-silica is obtained by surface grafting modification of silica particles with a particle size of 30-150 nm using perfluorooctyltriethoxysilane or heptadecafluorodecyltrimethoxysilane, resulting in a surface water contact angle ≥150°. Together with fluorocarbon resin, it constructs a micro-nano composite rough surface, achieving a coating water contact angle ≥150° and a roll-off angle ≤10°, thus imparting self-cleaning and antimicrobial adhesion functions to the surface and reducing biofilm formation.

[0019] 4. Preparation method: The present invention also provides a method for preparing the above-mentioned composite coating, comprising the following steps: (1) Substrate pretreatment: Clean, grind or sandblast the concrete / metal inner wall of the drainage pipe or ancillary facilities to remove floating dust, oil stains and loose attachments, and keep the surface dry; (2) Primer layer construction: Weigh each component of the anchoring antibacterial primer layer according to the ratio, stir evenly, and apply it to the pretreated substrate surface by air spraying or airless spraying. Apply 1-2 coats, cure at room temperature for 12-24 hours, and the dry film thickness is 60-120μm. (3) Intermediate layer construction: Weigh each component of the acid-base buffer intermediate layer according to the ratio, mix them evenly with a high-speed disperser, then add amine curing agent, continue stirring for 5-10 minutes, and apply it to the surface of the primer layer by high-pressure airless spraying. Spray 2-3 coats, with an interval of 4-6 hours between each coat, cure at room temperature for 24-48 hours, and the dry film thickness is 150-300μm; (4) Topcoat layer construction: Mix the components of the superhydrophobic self-healing topcoat layer evenly, apply it to the surface of the intermediate layer by spraying, let it stand at room temperature for 20-40 minutes to allow the solvent to evaporate, and then place it in an oven to cure at 50-80℃ for 2-5 hours. The final total thickness of the composite coating is 250-450μm.

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) Source inhibition: The nano zinc oxide in the primer layer continuously inhibits SRB activity and reduces the generation of H2S gas, thereby reducing the risk of microbial corrosion from the source.

[0021] (2) Active neutralization: The basic copper carbonate and thermally activated sludge in the intermediate layer form an efficient acid-base buffer system, which can quickly neutralize the sulfuric acid that penetrates the coating and prevent it from reaching the concrete substrate surface. This solves the problem that traditional coatings can only passively block and become ineffective once damaged.

[0022] (3) Synergistic antibacterial effect: The copper ions released after the reaction of basic copper carbonate with sulfuric acid, and the zinc ions released by the nano zinc oxide in the primer layer, form Zn 2+ / Cu 2+ The synergistic antibacterial system has a long-lasting inhibitory effect on both SRB and SOB.

[0023] (4) Intelligent self-repair: The polydopamine microspheres in the topcoat layer have the dual functions of photothermal response repair and pH response corrosion inhibitor release, which can realize the rapid closure of microcracks in the coating and active protection in the corrosive environment. The performance of the repaired coating can be restored to more than 80% of the original state.

[0024] (5) Self-cleaning and anti-adhesion: The superhydrophobic surface effectively reduces the adhesion of water, dirt and microorganisms, reducing the possibility of biofilm formation and subsequent corrosion.

[0025] (6) Resource utilization of solid waste: The large-scale utilization of sludge ash, a by-product of water supply plants, not only reduces costs but also realizes the resource utilization of solid waste. Attached Figure Description

[0026] Figure 1 The cross-sectional structure diagram of the composite anti-corrosion coating provided by the present invention is shown, wherein: 1-concrete / metal substrate, 2-anchoring antibacterial primer layer, 3-acid-alkali buffer intermediate layer, and 4-superhydrophobic self-healing topcoat layer.

[0027] Figure 2 A bar chart comparing the mass loss rates of different coatings after immersion in a simulated microbial corrosion environment for 180 days. Detailed Implementation

[0028] The present invention will be further illustrated below through specific embodiments. Experimental methods not specifying specific conditions in the embodiments were performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0029] This invention provides a composite coating that inhibits acid corrosion caused by microorganisms in drainage pipe networks. The coating comprises, from the inside out, an anchoring antibacterial primer layer, an acid-base buffer intermediate layer, and a superhydrophobic self-healing topcoat layer.

[0030] 1. Anchoring antibacterial primer layer: The preferred components of the anchoring and antibacterial primer layer by weight are: 45-65 parts epoxy resin, 3-8 parts nano zinc oxide, 2-6 parts silane-modified nano montmorillonite, 15-25 parts curing agent, and 20-35 parts solvent. More preferably, 50-60 parts of epoxy resin, 4-7 parts of nano zinc oxide, 3-5 parts of silane-modified nano montmorillonite, 18-22 parts of curing agent, and 25-30 parts of solvent.

[0031] In this invention, the preferred particle size of nano zinc oxide is 20-80 nm; nano zinc oxide can be uniformly dispersed in the primer system, effectively inhibiting the growth of acid-producing microorganisms inside the pipeline network and blocking the corrosion at the source of microbial acid production.

[0032] In this invention, the interlayer spacing of the silane-modified nano-montmorillonite is preferably 2-5 nm; the layer thickness is preferably 10-50 nm. Silane-modified nano-montmorillonite can improve the anchoring adhesion between the primer and the substrate, while forming a physical barrier layer to prevent the penetration of acidic media.

[0033] The preferred method for preparing silane-modified nano-montmorillonite is as follows: sodium-based montmorillonite is dispersed in deionized water, hexadecyltrimethylammonium bromide is added for intercalation modification, and after centrifugation, washing and drying, organo-montmorillonite is obtained; then, organo-montmorillonite is dispersed in ethanol, γ-aminopropyltriethoxysilane is added, and the mixture is refluxed at 60-80℃ for 6-12 hours, centrifuged, washed and dried to obtain silane-modified nano-montmorillonite with amino groups grafted onto its surface; The reflux reaction temperature is more preferably 65-75℃, and the reflux reaction time is more preferably 8-10 hours.

[0034] This invention does not impose any special limitations on epoxy resin, curing agent, or solvent; commercially available conventional raw materials in the field of drainage and anti-corrosion coatings can be used.

[0035] 2. Acid-base buffer intermediate layer: By weight, the acid-base buffer intermediate layer preferably comprises: 50-70 parts of waterborne epoxy resin, 10-25 parts of thermally activated water supply sludge, 5-12 parts of basic copper carbonate, 8-20 parts of flake mica powder, and 10-20 parts of amine curing agent.

[0036] In this invention, the thermally activated water supply sludge ash is preferably an activated pozzolanic material obtained by dewatering, drying, and crushing aluminate coagulation sludge from municipal water supply plants, followed by calcination at 700-850℃ for 1.5-3 hours, and then ball milling to an average particle size ≤10μm. The calcination temperature is more preferably 750-800℃, and the calcination time is more preferably 2-2.5 hours. The total mass content of amorphous silica and alumina is preferably ≥65%. The thermally activated water supply sludge ash can sustainably buffer the acidic corrosive media of the pipe network, maintain the acid-base stability of the coating interface, and simultaneously achieve the resource utilization of solid waste.

[0037] In this invention, the sheet diameter of the flake mica powder is preferably 10-60 μm; the aspect ratio is preferably ≥15; the flake mica powder is stacked and arranged to form a labyrinthine barrier structure, which prolongs the penetration path of corrosive media.

[0038] In this invention, basic copper carbonate is in the form of nano-sized particles, with a preferred particle size of 100-500 nm. Nano-basic copper carbonate can synergistically inhibit the activity of acid-producing microorganisms such as sulfate-reducing bacteria, forming a synergistic protective effect with the primer antibacterial system.

[0039] This invention does not have any special limitations on water-based epoxy resins or amine curing agents; commercially available water-based anti-corrosion coating raw materials can be used.

[0040] 3. Superhydrophobic self-healing topcoat layer: The superhydrophobic self-healing topcoat layer preferably comprises, by weight, 40-60 parts of fluorocarbon resin, 8-18 parts of hollow mesoporous polydopamine microspheres loaded with corrosion inhibitor, 5-15 parts of hydrophobic modified nano-silica, 10-20 parts of curing agent, and 30-50 parts of organic solvent.

[0041] The preferred method for preparing hollow mesoporous polydopamine microspheres loaded with corrosion inhibitors in this invention is as follows: using polystyrene microspheres as sacrificial templates, polydopamine shells are formed by in-situ polymerization of dopamine on the template surface, and the template is then removed by dissolving it with an organic solvent to obtain hollow mesoporous polydopamine microspheres. Finally, under vacuum conditions, corrosion inhibitors benzotriazole or sodium molybdate are loaded into the mesoporous channels and hollow cavities of the microspheres.

[0042] The hollow mesoporous polydopamine microspheres loaded with corrosion inhibitors preferably have a particle size of 200 nm-5 μm and a wall thickness of 20-100 nm. The corrosion inhibitor loading is preferably 15-40% of the total mass of the microspheres. The polydopamine microspheres can release the loaded corrosion inhibitors under near-infrared light irradiation or acidic pH stimulation, thereby achieving self-repair of the coating damage.

[0043] In this invention, the hydrophobically modified nano-silica is preferably obtained by surface grafting modification of silica particles with a particle size of 30-150nm using perfluorooctyltriethoxysilane or heptadecafluorodecyltrimethoxysilane; the water contact angle of the modified surface is preferably ≥150°, thereby constructing a stable superhydrophobic surface layer and isolating sewage from direct contact with the coating.

[0044] This invention does not impose any special limitations on fluorocarbon resins, topcoat curing agents, or organic solvents; commercially available raw materials commonly used in anti-corrosion fluorocarbon coatings can be selected.

[0045] II. Description of Composite Coating Preparation Method: This invention also provides a method for preparing the above-mentioned composite coating, preferably comprising the following steps: (1) Substrate pretreatment: Clean, grind or sandblast the concrete / metal inner wall of the drainage pipe or ancillary facilities; remove surface laitance, rust and oil stains to ensure the coating anchoring bond; (2) Primer layer construction: Mix the components of the anchoring antibacterial primer layer evenly, apply it to the surface of the pretreated substrate, and cure at room temperature for 12-24 hours to form a primer layer with a thickness of 60-120μm. (3) Intermediate layer construction: Mix all components of the acid-base buffer intermediate layer evenly, apply it to the surface of the primer layer by spraying or brushing, and cure at room temperature for 24-48 hours to form an intermediate layer with a thickness of 150-300μm. (4) Topcoat layer construction: Mix the components of the superhydrophobic self-healing topcoat layer evenly, apply it to the surface of the intermediate layer by spraying, let it stand at room temperature for 20-40 minutes to allow the solvent to evaporate, and then cure it at 50-80℃ for 2-4 hours to form a composite coating with a total thickness of 250-450μm.

[0046] The composite coating of this invention is composed of three functional layers: an anchoring and antibacterial primer layer to anchor the substrate and inhibit microbial sources; an acid-base buffer intermediate layer to continuously neutralize acidic corrosive media and block ion penetration; and a superhydrophobic self-healing topcoat layer to isolate sewage contact and possess stimulation-responsive self-healing capabilities. The three-layer system works synergistically to effectively inhibit microbial acid corrosion in drainage pipe networks. The coating's adhesion, acid resistance, antibacterial properties, and self-healing properties are all superior to traditional single-layer anti-corrosion coatings.

[0047] To further illustrate the technical solution of the present invention, the following examples and comparative examples are provided for detailed description. All raw materials used in the examples are commercially available conventional anti-corrosion coating raw materials. Silane-modified nano-montmorillonite, hollow mesoporous polydopamine microspheres loaded with corrosion inhibitors, thermally activated water supply sludge, and hydrophobically modified nano-silica are all prepared according to the preparation process specified in the present invention.

[0048] Example 1: This embodiment provides a composite coating for concrete drainage inspection wells.

[0049] (1) Preparation of silane-modified nano-montmorillonite: 10 g of sodium-based montmorillonite (cation exchange capacity of 90 mmol / 100 g) was dispersed in 500 mL of deionized water and stirred overnight. 3 g of hexadecyltrimethylammonium bromide was added, and the mixture was stirred at 80 °C for 6 hours. After centrifugation, the mixture was washed with deionized water until no bromide ions were detected (silver nitrate test), and dried at 50 °C to obtain organo-montmorillonite. 5 g of organo-montmorillonite was dispersed in 200 mL of ethanol, and 2 g of γ-aminopropyltriethoxysilane (KH550) was added. The mixture was refluxed at 70 °C for 8 hours under nitrogen protection, centrifuged, washed three times with ethanol, dried under vacuum at 50 °C, and ground to obtain silane-modified nano-montmorillonite with an interlayer spacing of approximately 3.2 nm and a sheet thickness of 20-40 nm.

[0050] (2) Preparation of hollow mesoporous polydopamine microspheres loaded with corrosion inhibitors (PS template method): a. Preparation of polystyrene template microspheres: A soap-free emulsion polymerization method was used. 100 mL of deionized water was added to a three-necked flask, and nitrogen gas was purged for 30 minutes to remove oxygen. 0.5 g of styrene monomer was added, and the temperature was raised to 70 °C. Then, 0.05 g of potassium persulfate was added, and the reaction was maintained at this temperature for 12 hours to obtain a monodisperse polystyrene microsphere emulsion with a particle size of approximately 300 nm. The microspheres were centrifuged, washed three times with ethanol, and dried under vacuum at 50 °C.

[0051] b. Polydopamine shell coating: Take 1g of dried polystyrene microspheres, sonicate them in 200mL Tris buffer (10mM, pH=8.5), add 0.5g of dopamine hydrochloride, and react magnetically at room temperature for 24 hours. Centrifuge, wash three times alternately with deionized water and ethanol, and dry at 50℃ to obtain polystyrene@polydopamine core-shell microspheres.

[0052] c. Template removal: The above core-shell microspheres were dispersed in 100 mL of tetrahydrofuran, stirred at room temperature for 12 hours, centrifuged, washed twice with fresh tetrahydrofuran, and finally washed with ethanol. The microspheres were then dried under vacuum at 50 °C to obtain hollow mesoporous polydopamine microspheres with a particle size of about 350 nm and a wall thickness of about 30-40 nm.

[0053] d. Corrosion inhibitor loading: 0.5 g of hollow mesoporous polydopamine microspheres were dispersed in 50 mL of 5 wt% benzotriazole (BTA) ethanol solution, immersed under vacuum (0.05 MPa) for 12 hours, centrifuged, the surface was quickly washed with a small amount of ethanol, and dried under vacuum at 50 °C to obtain BTA-loaded polydopamine microspheres with a BTA loading of approximately 28 wt%.

[0054] (3) Preparation of hydrophobically modified nano-silica: 10 g of fumed silica with a particle size of 50 nm was dispersed in 100 mL of anhydrous ethanol. 2 g of heptadecafluorodecyltrimethoxysilane and 0.3 g of water were added, and the mixture was refluxed and stirred at 70 °C for 8 hours. After centrifugation, the silica was washed three times with anhydrous ethanol and dried at 100 °C for 6 hours to obtain fluorosilane-modified silica. Its surface water contact angle is approximately 155°.

[0055] (4) Preparation of thermally activated water supply sludge: Dewatered sludge from a water treatment plant was dried at 105℃ for 24 hours, crushed, and passed through a 200-mesh sieve. It was then calcined in a muffle furnace at 800℃ for 2 hours, naturally cooled, and ball-milled to D50≈8μm. XRF analysis showed that the total content of amorphous SiO2+Al2O3 was approximately 72%.

[0056] (5) Primer application: Weigh out 55 parts by weight of E51 epoxy resin, 5 parts by weight of 40nm nano zinc oxide, 3 parts by weight of the above-mentioned silane-modified nano montmorillonite, 20 parts by weight of polyamide curing agent (type 650), and 30 parts by weight of xylene / n-butanol mixed solvent (volume ratio 7:3). After mixing evenly, spray the mixture onto the surface of a sandblasted (Sa2.5 grade) concrete slab (C40, size 150mm×70mm×20mm). Control the wet film thickness to 120μm, cure at room temperature for 24 hours, and the dry film thickness is about 80μm.

[0057] (6) Intermediate layer construction: Weigh out 60 parts by weight of waterborne epoxy emulsion (55% solids content), 18 parts of the above-mentioned thermally activated water supply sludge, 8 parts of nano-basic copper carbonate (300nm), 15 parts of flake mica powder (40μm diameter), 15 parts of waterborne amine curing agent (epoxy equivalent 220), 20 parts of deionized water, and 1.5 parts of BYK-190 dispersant. After high-speed dispersion for 20 minutes, add the waterborne amine curing agent and continue stirring for 5 minutes. Use high-pressure airless spraying at a spraying pressure of 15MPa, a wet film thickness of 250μm, and cure at room temperature for 36 hours, resulting in a dry film thickness of approximately 200μm.

[0058] (7) Topcoat layer application: Weigh out 50 parts by weight of FEVE fluororesin (trifluorochloroethylene-vinyl ether copolymer, solid content 50%), 12 parts of the above-mentioned BTA-loaded polydopamine microspheres, 10 parts of the above-mentioned hydrophobically modified nano-silica, 15 parts of isocyanate curing agent (N3390), 35 parts of methyl ethyl ketone (MEK), and 0.5 parts of BYK-066 defoamer. After mixing evenly, apply the mixture to the surface of the intermediate layer by spraying, with a wet film thickness of 80 μm. After standing at room temperature for 30 minutes, cure in an 80℃ oven for 3 hours. The final total thickness of the composite coating is approximately 320 μm.

[0059] Example 2: The difference between this embodiment and Embodiment 1 is that the ratio of basic copper carbonate and thermally activated water supply sludge in the intermediate layer was adjusted, and a different corrosion inhibitor (sodium molybdate) was used.

[0060] (1) Preparation of silane-modified nano-montmorillonite: Same as in Example 1.

[0061] (2) Preparation of hollow mesoporous polydopamine microspheres loaded with corrosion inhibitor: The corrosion inhibitor was replaced with sodium molybdate (Na2MoO4), and the loading method was the same as in Example 1. The concentration of sodium molybdate aqueous solution was 5wt%, and it was vacuum impregnated for 12 hours, with a loading amount of about 25wt%.

[0062] (3) Preparation of hydrophobic modified nano silica: Same as in Example 1.

[0063] (4) Preparation of thermally activated water supply sludge: Same as in Example 1.

[0064] (5) Primer application: Same as in Example 1.

[0065] (6) Intermediate layer construction: Weigh out 55 parts of waterborne epoxy emulsion, 22 parts of thermally activated water supply sludge, 10 parts of nano-basic copper carbonate, 12 parts of flake mica powder, 18 parts of waterborne amine curing agent, and other additives as in Example 1. The dry film thickness is 220 μm.

[0066] (7) Topcoat layer construction: 15 parts of polydopamine microspheres loaded with sodium molybdate were used, and the rest were the same as in Example 1. The total dry film thickness was about 340 μm.

[0067] Example 3: The difference between this embodiment and Embodiment 1 is that the amount of silane-modified nano-montmorillonite used in the primer layer is different, and the hydrophobic modified nano-silica is omitted in the topcoat layer, relying only on fluorocarbon resin and polydopamine microspheres to construct a rough structure.

[0068] (1) Preparation of silane-modified nano-montmorillonite: Same as in Example 1.

[0069] (2) Preparation of hollow mesoporous polydopamine microspheres loaded with corrosion inhibitor: Same as in Example 1 (BTA loading).

[0070] (3) Preparation of hydrophobic modified nano silica: This step is omitted in this embodiment.

[0071] (4) Preparation of thermally activated water supply sludge: Same as in Example 1.

[0072] (5) Primer layer construction: The amount of silane-modified nano-montmorillonite was changed to 5 parts, and the rest was the same as in Example 1. The dry film thickness was 80 μm.

[0073] (6) Intermediate layer construction: Same as in Example 1.

[0074] (7) Topcoat application: Weigh 60 parts by weight of FEVE fluororesin, 12 parts by weight of BTA-loaded polydopamine microspheres (without hydrophobic modified nano-silica), 15 parts by weight of isocyanate curing agent, and 35 parts by weight of methyl ethyl ketone, and mix and spray. The total dry film thickness after curing is approximately 310 μm.

[0075] Comparative Example 1: The difference between this comparative example and Example 1 is that: no basic copper carbonate is added to the acid-base buffer intermediate layer, and the missing amount is made up by aqueous epoxy emulsion; otherwise, it is the same as Example 1.

[0076] Comparative Example 2: The difference between this comparative example and Example 1 is that no nano zinc oxide is added to the anchoring antibacterial primer layer, and the missing amount is made up by epoxy resin. The rest is the same as in Example 1.

[0077] Comparative Example 3: The difference between this comparative example and Example 1 is that no hollow mesoporous polydopamine microspheres loaded with corrosion inhibitors are added to the superhydrophobic self-healing topcoat layer, and the missing amount is made up by fluorocarbon resin. The rest is the same as in Example 1.

[0078] Performance testing: The coatings prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to the following performance tests, and the results are shown in Table 1.

[0079] (1) Adhesion test: Performed according to GB / T5210-2006 (pull-off method), using a hydraulic adhesion tester, and take the average value of at least 5 points.

[0080] (2) Water contact angle and roll-off angle test: According to GB / T30693-2014, a contact angle measuring instrument was used to test the water droplet volume of 5μL, and the roll-off angle test was conducted using the tilt table method.

[0081] (3) 180-day simulated microbial corrosion test: A simulated sewage pipeline reactor was constructed in the laboratory and inoculated with sulfate-reducing bacteria (SRB, 1×10⁻⁶). 6 (cFU / mL) and sulfur-oxidizing bacteria (SOB, 1×10⁻⁶) 5 The activated sludge was prepared using an artificial wastewater formula containing: glucose 2000 mg / L, sodium sulfate 500 mg / L, ammonium chloride 300 mg / L, potassium dihydrogen phosphate 100 mg / L, and pH 7.0-7.5. H2S gas (concentration 80 ppm) was continuously introduced at 30°C and humidity >95%. The coated specimens were placed in the reactor and run for 180 days. After removal, the pH value of the concrete specimen surface was tested (using precision pH test paper), and the mass loss rate (%) of the specimens was measured.

[0082] (4) Evaluation of coating appearance: Observe the blistering, peeling, discoloration and other conditions on the coating surface after 180 days of corrosion test.

[0083] (5) Self-healing performance test: Use a blade to make a scratch about 2 cm long and 50 μm wide on the coating surface, and then place the sample under near-infrared light (wavelength 808 nm, power 1.5 W / cm). 2 Irradiated for 5 minutes, and the healing of the scratches was observed using an optical microscope. The sample was then placed in a simulated wastewater reactor and run for 180 days. After removal, an indicator containing potassium ferrocyanide (to detect iron ion leaching) was added to the scratches, or corrosion products were observed to determine whether the scratches were effectively repaired. The test results are as follows: Table 1 Performance test results of each embodiment and comparative example As can be seen from the data in Table 1: Examples 1-2 exhibited the best overall performance, especially the specimens with basic copper carbonate in the intermediate layer (Examples 1 and 2), whose surface pH remained above 8 after 180 days of microbial corrosion, with an extremely low mass loss rate (<0.25%), proving that the acid-base buffer layer effectively neutralized the biological sulfuric acid. Example 2, due to the increased amount of basic copper carbonate and sludge ash, achieved even better neutralization (surface pH 8.5, mass loss rate 0.18%).

[0084] In Example 3, the hydrophobicity of the topcoat layer decreased (water contact angle 136°) because no hydrophobic modified nano-silica was added, but it was still better than that of ordinary coatings. Its corrosion resistance was slightly lower than that of Example 1, but much better than that of the comparative examples, indicating that even if the hydrophobic effect was reduced, the intermediate layer and primer layer still provided good protection.

[0085] In Comparative Example 1 (without basic copper carbonate), the intermediate layer lost its ability to actively neutralize acid, suffered severe corrosion, had a surface pH of 3.1, a mass loss rate as high as 8.7%, and the coating showed large-area blistering and peeling, indicating that basic copper carbonate is the core functional component of the intermediate layer of this invention.

[0086] Comparative Example 2 (without nano zinc oxide) showed a lack of antibacterial ability in the primer layer, with vigorous SRB metabolism and the generation of a large amount of H2S, leading to increased overall corrosion, a mass loss rate of 4.2%, and a surface pH drop to 5.8, demonstrating the importance of inhibiting microorganisms at the source.

[0087] Comparative Example 3 (without polydopamine microspheres) showed that the topcoat layer lost its self-healing ability, the scratches could not be healed, and the corrosive medium penetrated from the scratches, resulting in localized corrosion aggravation (surface pH 7.2, mass loss rate 2.5%, slight corrosion at the scratches), proving that the self-healing function plays an important role in maintaining the long-term integrity of the coating.

[0088] In summary, this invention achieves effective inhibition of microbial acid-producing corrosion in drainage pipe networks through the synergistic function of a three-layer structure, particularly by using silane-modified nano-montmorillonite as the physical shielding material of the primer layer, constructing an acid-base buffer system in the intermediate layer using basic copper carbonate, and constructing a self-healing function for the topcoat layer using polydopamine microspheres. This invention has significant technological advancements and industrial application value.

[0089] The above description is only a preferred embodiment of the present invention, but the present invention is not limited to the scope of implementation shown. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent changes, shall be within the protection scope of the present invention as long as they do not exceed the spirit covered by the specification.

Claims

1. A composite coating for inhibiting microbial acid production corrosion in a sewer network, characterised in that, The coating consists of, from the inside out: an anchoring antibacterial primer layer, an acid-base buffer intermediate layer, and a superhydrophobic self-healing topcoat layer; The anchoring antibacterial primer layer comprises, by weight, 45-65 parts epoxy resin, 3-8 parts nano zinc oxide, 2-6 parts silane-modified nano montmorillonite, 15-25 parts curing agent, and 20-35 parts solvent. The acid-base buffer intermediate layer comprises, by weight, 50-70 parts of waterborne epoxy resin, 10-25 parts of thermally activated water supply sludge, 5-12 parts of basic copper carbonate, 8-20 parts of flake mica powder, and 10-20 parts of amine curing agent. The superhydrophobic self-healing topcoat layer comprises, by weight: 40-60 parts of fluorocarbon resin, 8-18 parts of hollow mesoporous polydopamine microspheres loaded with corrosion inhibitor, 5-15 parts of hydrophobic modified nano-silica, 10-20 parts of curing agent, and 30-50 parts of organic solvent.

2. The composite coating of claim 1, wherein, The particle size of the nano zinc oxide is 20-80 nm.

3. The composite coating of claim 1, wherein, The preparation method of the silane-modified nano-montmorillonite includes: dispersing sodium-based montmorillonite in deionized water, adding hexadecyltrimethylammonium bromide for intercalation modification, centrifuging, washing and drying to obtain organo-montmorillonite; then dispersing the organo-montmorillonite in ethanol, adding γ-aminopropyltriethoxysilane, refluxing at 60-80℃ for 6-12 hours, centrifuging, washing and drying to obtain silane-modified nano-montmorillonite with amino groups grafted on the surface.

4. The composite coating of claim 1, wherein, The interlayer spacing of the silane-modified nano-montmorillonite is 2-5 nm, and the layer thickness is 10-50 nm.

5. The composite coating of claim 1, wherein, The thermally activated water supply sludge ash is an active pozzolanic material made from aluminum salt coagulated sludge from municipal water supply plants. After dewatering, drying, and crushing, the sludge is calcined at 700-850℃ for 1.5-3 hours and then ball-milled to an average particle size of ≤10μm. The total mass content of amorphous silica and aluminum oxide is ≥65%.

6. The composite coating according to claim 1, characterized in that, The flaky mica powder has a flake diameter of 10-60 μm and an aspect ratio of ≥15; the basic copper carbonate is made of nano-sized particles with a particle size of 100-500 nm.

7. The composite coating according to claim 1, characterized in that, The method for preparing the hollow mesoporous polydopamine microspheres loaded with corrosion inhibitors includes: using polystyrene microspheres as sacrificial templates, forming a polydopamine shell by in-situ polymerization of dopamine on the template surface, then dissolving and removing the template with an organic solvent to obtain hollow mesoporous polydopamine microspheres, and finally loading the corrosion inhibitor benzotriazole or sodium molybdate into its mesoporous channels and hollow cavities under vacuum conditions.

8. The composite coating according to claim 7, characterized in that, The hollow mesoporous polydopamine microspheres loaded with corrosion inhibitor have a particle size of 200nm-5μm and a wall thickness of 20-100nm, with the corrosion inhibitor loading accounting for 15-40% of the total mass of the microspheres; the polydopamine microspheres release the loaded corrosion inhibitor under near-infrared light irradiation or acidic pH stimulation.

9. The composite coating according to claim 1, characterized in that, The hydrophobically modified nano-silica is obtained by surface grafting modification of silica particles with a particle size of 30-150nm using perfluorooctyltriethoxysilane or heptadecafluorodecyltrimethoxysilane, and its surface water contact angle is ≥150°.

10. A method for preparing a composite coating according to any one of claims 1-9, characterized in that, Includes the following steps: (1) Substrate pretreatment: Cleaning, grinding or sandblasting roughening treatment of the concrete / metal inner wall of drainage pipes or ancillary facilities; (2) Primer layer construction: Mix the components of the anchoring antibacterial primer layer evenly, apply it to the surface of the pretreated substrate, and cure at room temperature for 12-24 hours to form a primer layer with a thickness of 60-120μm. (3) Intermediate layer construction: Mix all components of the acid-base buffer intermediate layer evenly, apply it to the surface of the primer layer by spraying or brushing, and cure at room temperature for 24-48 hours to form an intermediate layer with a thickness of 150-300μm. (4) Topcoat layer construction: Mix the components of the superhydrophobic self-healing topcoat layer evenly, apply it to the surface of the intermediate layer by spraying, let it stand at room temperature for 20-40 minutes to allow the solvent to evaporate, and then cure it at 50-80℃ for 2-4 hours to form a composite coating with a total thickness of 250-450μm.

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