Corrosion-resistant phosphoric acid-based geopolymer coating and preparation method thereof

Abstract

The corrosion-resistant phosphoric acid-based geopolymer coating comprises metakaolin, an acid activator, a reaction medium, an organic modifier and an interfacial compatibilizer, the acid activator is a phosphoric acid solution, and the phosphorus-aluminum mass ratio of H3PO4 in the phosphoric acid solution to Al2O3 in the metakaolin is H3PO4 / Al2O3 = (1.2-1.4): 1; the organic modifier comprises simethicone, resin and a special curing agent for the resin; the dimethyl silicone oil and the epoxy resin respectively account for 1-9% and 10-30% of the mass of the metakaolin; the invention also discloses a preparation method. The hydrophobic performance, compactness and chloride ion corrosion resistance of the coating are improved, the corrosion inhibition efficiency reaches up to 96.45%, and a green and efficient protective coating is provided for a reinforced concrete structure in a highly corrosive environment such as ocean. The problems that a phosphoric acid-based geopolymer coating is relatively high in water absorption, relatively large in porosity, relatively weak in chloride ion penetration resistance and the like are solved.

Description

Technical Field

[0001] This invention belongs to the field of waterproof material manufacturing technology, and relates to a corrosion-resistant phosphate-based polymer coating and its preparation method. Background Technology

[0002] Reinforced concrete, as a major building structural system, is widely used in various construction projects for its excellent mechanical properties and economic benefits, particularly in the application of corrosion-resistant phosphate-based polymer coatings. However, its durability remains a persistent concern in the engineering community. Extensive engineering practice and research indicate that steel corrosion is a major factor leading to the deterioration of the durability of reinforced concrete structures, especially in marine environments. Seawater is rich in various corrosive ions, such as... , , etc., of which chloride ions ( Due to their small radius and strong permeability, chloride ions can penetrate deep into the structure through the pores and microcracks within concrete. When the chloride ion concentration reaches a critical threshold, it destroys the passivation film on the surface of the reinforcing steel, inducing electrochemical corrosion. This corrosion process not only reduces the effective cross-sectional area of ​​the reinforcing steel, but the volume expansion of its corrosion products also generates internal stress in the concrete cover, leading to a series of deterioration phenomena such as concrete cracking and spalling. Therefore, developing new anti-corrosion coatings to improve the service performance of reinforced concrete in corrosive environments is of significant practical importance.

[0003] Geopolymers, as a novel inorganic non-metallic material, possess potential advantages such as being environmentally friendly, having high-temperature resistance, and being corrosion-resistant. They show promising prospects for corrosion-resistant phosphate-based geopolymer coatings in protective coatings used in construction and chemical industries. Phosphate-based geopolymers, in particular, have become a research hotspot in coating materials due to their certain resistance to chemical corrosion. However, unmodified phosphate-based geopolymer coatings exhibit significant deficiencies in mechanical strength, hardness, and adhesion to the substrate, making them prone to damage and peeling during use. Furthermore, their limited hydrophobicity and high water absorption rate result in insufficient resistance to chloride ion corrosion, making them unsuitable for demanding engineering applications.

[0004] To improve the overall performance of phosphate-based polymer coatings, current research focuses primarily on composite modification techniques, mainly including organic-inorganic hybrid coatings and nanocomposite coatings. However, nanocomposite coatings suffer from complex dispersion processes and high costs; while in organic-inorganic hybrid coatings, the large polarity difference between the organic and inorganic components leads to poor compatibility and easy phase separation. Existing research shows that using tetraethyl orthosilicate as the inorganic precursor and dimethyl silicone oil as the organic component, a stable hybrid coating can be prepared under the action of a neutral catalyst. When the dimethyl silicone oil content is 43%, the coating contact angle can reach 102°, and the water absorption rate is reduced to 1.233%. On the other hand, the study "Research on Seawater Corrosion Resistance of Epoxy Resin-Geopolymer Composite Coating Materials" (ZEZE Armande Loraine Phalé, Xu Hongyan, Zhang Mo, Ma Guowei, Materials Reports, 2021-05-25) et al. used epoxy resin to modify geopolymers and found that incorporating 20% ​​and 30% epoxy resin could significantly improve the pore structure of the material, enhance its resistance to chloride ion penetration, and reduce corrosion current. However, there are currently no related studies on the composite modification of phosphate-based geopolymer coatings by simultaneously combining dimethyl silicone oil and epoxy resin.

[0005] Although the addition of dimethyl silicone oil alone can improve the hydrophobicity of the coating to some extent, its effect on improving the compressive strength, hardness, and adhesion of the coating is limited, making it difficult to achieve a synergistic improvement in mechanical properties and corrosion resistance. The study "Research on the Corrosion Resistance of Resin Geopolymers in Seawater" (Bian Wenrui, Dalian Jiaotong University, 2020-06-18) found that when epoxy resin is added as a toughening agent, this composite method can improve compressive strength and corrosion resistance in seawater environments, but it causes problems such as prolonged setting time and slow early strength development.

[0006] Therefore, how to improve the hydrophobicity and corrosion resistance of phosphate-based polymer coatings while taking into account their mechanical properties and construction adaptability remains a key issue that needs to be addressed in current research. Summary of the Invention

[0007] To address the above shortcomings, this invention provides a corrosion-resistant phosphate-based polymer coating and its preparation method, solving the problems of high water absorption, large porosity, and weak resistance to chloride ion penetration in phosphate-based polymer coatings. By improving the hydrophobicity, density, and chloride ion corrosion resistance of the coating, the corrosion inhibition efficiency (IE) can reach up to 96.45%, providing a green and efficient protective coating for reinforced concrete structures in highly corrosive environments such as marine environments. The specific technical solution is as follows: One objective of this invention is to provide a corrosion-resistant phosphate-based polymer coating, comprising metakaolin, an acid activator, a reaction medium, an organic modifier, and an interface compatibilizer; The acid activator is a phosphoric acid solution, and the mass ratio of phosphorus and aluminum in the phosphoric acid solution (H3PO4 / Al2O3) to that in metakaolin is (1.2~1.4):1. The organic modifier includes dimethyl silicone oil, resin, and resin-specific curing agent; the dimethyl silicone oil accounts for 1% to 9% of the mass of metakaolin; the resin accounts for 10% to 20% of the mass of metakaolin; the resin is epoxy resin (E51 type) or phenolic resin.

[0008] Metakaolin serves as a precursor for geopolymerization, providing both silicon and aluminum sources. Phosphoric acid solution is used to dissolve the silica-alumina phase in the metakaolin, initiating the geopolymerization reaction. Preferably, the dimethyl silicone oil comprises 3%–6% of the metakaolin by mass, and its primary function is to provide hydrophobicity. Preferably, the epoxy resin (E51 type) comprises 15%–25% of the metakaolin by mass, and its primary function is to enhance density and adhesion.

[0009] Furthermore, the phosphoric acid solution has a mass fraction of 85%; the metakaolin contains 38.52% Al2O3.

[0010] Further, the reaction medium is water, and the mass ratio of water to metakaolin is (0.35–0.45):1. Preferably, the reaction medium is distilled water. The reaction medium provides the liquid phase environment required for the reaction.

[0011] Furthermore, the interface compatibilizer is a silane coupling agent, which accounts for 2% to 5% of the mass of dimethyl silicone oil. The silane coupling agent (such as KH-550) is used to improve the interfacial bonding between the organic modifier and the inorganic geopolymer matrix.

[0012] Furthermore, the mass ratio of the resin-specific curing agent to the resin is 1:1. The epoxy resin-specific curing agent is used to crosslink and cure the epoxy resin.

[0013] Furthermore, a second objective of this invention is to provide a method for preparing a corrosion-resistant phosphate-based polymer coating as described above, comprising the following steps: (1) Pre-prepared acid activation solution: Stir the reaction medium and phosphoric acid solution evenly, let stand and cool to room temperature to obtain the acid activation solution; (2) Organic modifier pre-emulsification: Dimethyl silicone oil, silane coupling agent, resin and resin-specific curing agent are added sequentially to the acid activation solution prepared in step (1), and stirred evenly to obtain organic-acid activation premix. (3) Preparation of geopolymer slurry: Under stirring, metakaolin powder is slowly added to the organic-acid activated premix prepared in step (2) to obtain geopolymer slurry; (4) Coating and curing: The geopolymer slurry obtained in step (3) is uniformly coated onto the pretreated clean substrate surface using a scraping method. After compaction, sealing and pre-curing, demolding and continuous curing, the corrosion-resistant phosphate-based geopolymer coating is obtained.

[0014] Further, in step (2), the stirring is carried out at room temperature and continuously stirred at a speed of 750-850 rpm for 25-35 minutes. Through the high-speed shearing action of pre-emulsification stirring, the organic modifier (especially hydrophobic dimethyl silicone oil) is fully emulsified and dispersed in the aqueous phase to form a relatively stable premix; the silane coupling agent is fully mixed with other substances during the pre-emulsification process, its silanol groups interact with dimethyl silicone oil or epoxy resin, and its amino and other functional groups prepare for subsequent bonding with the inorganic phase.

[0015] Further, in step (3), after adding the metakaolin powder, the stirring speed is adjusted to 280–320 rpm, and stirring continues for 8–12 minutes until a uniformly mixed geopolymer slurry with suitable fluidity is obtained. Phosphoric acid reacts with metakaolin, undergoing a depolymerization reaction and releasing silica-alumina species. The emulsified organic phase is uniformly incorporated into the entire inorganic reaction system.

[0016] Further, in step (4), the substrate is at least one of a ceramic plate, a concrete test block, or a mortar test block with reinforcing bars; the wet film thickness of the corrosion-resistant phosphate-based polymer coating is controlled to be 290-310 μm.

[0017] Further, in step (4), the compaction time is 5 minutes. The compaction involves vibrating the mold or coated specimen on a vibration table for 4 to 6 minutes to remove large air bubbles.

[0018] Further, in step (4), the sealing pre-curing involves placing the specimen, along with the mold, into a sealed bag and curing it in an oven at 48–52°C for 23.5–24.5 hours. During this stage, the geopolymerization reaction and the epoxy resin curing reaction begin simultaneously.

[0019] Further, in step (4), the demolding and continuous curing involves demolding the pre-cured specimen after the sealing pre-curing is completed, and then placing it in an oven at 48–52°C for continued sealing curing. After demolding and continuous curing, the coating is fully cured, forming the final organic-inorganic hybrid structure.

[0020] Furthermore, in step (4), the total curing time for the sealing pre-curing, demolding and continuous curing is 7 days.

[0021] In this invention, geopolymer refers to any three-dimensional network gel with amorphous and quasi-crystalline characteristics, prepared from natural minerals or solid waste and polymerized from silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra, wherein its three-dimensional network structure consists of [SiO4]. 4- With [AlO4] 5- Tetrahedrons are formed by alternating covalent bonds. Geopolymers possess advantages such as fire resistance, chemical corrosion resistance, high mechanical strength, and good durability. The acid-induced reaction process of geopolymers is divided into depolymerization and condensation. During depolymerization, H+ in phosphoric acid causes the Al-O layer to decompose, and excess H+ reacts with dissolved H+. 10 Si4O 13 Generate [Si4O] 13 H 11 The polycondensation process, specifically the depolymerization step, forms [Si4O]. 13 H 11 ] and Al formed by decomposition 3- H + And PO4 in phosphoric acid solution 3- The structures are connected to form structural units such as -Al-OPO- and -Si-O-Al-OPO-, and these structural units are connected by hydrogen bonds to form a three-dimensional network structure.

[0022] Dimethyl silicone oil is a stable, non-toxic, and highly adhesive hydrophobic organosilicon polymer with the chemical formula (C2H6OSi)n. Low-volume and low-viscosity dimethyl silicone oils are widely used in the market. Their low molecular weight and low viscosity effectively maintain the ability of composite sols to penetrate porous substrates. Dimethyl silicone oil has a siloxane structure, similar to the structure formed by the polymerization of alkoxysilanes. Furthermore, each atom in dimethyl silicone oil is linked to two methyl groups, giving it excellent elasticity and flexibility. The terminal hydroxyl groups in dimethyl silicone oil allow it to chemically bond with inorganic components, resulting in a good bond between the two. Dimethyl silicone oil is transparent and colorless, thus preventing color changes to the substrate.

[0023] The epoxy resin used in this invention is a thermosetting organic polymer containing two or more epoxy groups (three-membered epoxy ring structure, -COC-), which is a stable polymer material with good reactivity. Its molecular chain contains polar groups such as hydroxyl (-OH), exhibiting excellent adhesive properties and capable of cross-linking with various curing agents to form a three-dimensional network structure. Epoxy resin has good compatibility with inorganic materials; the polar groups in the molecule can bond with inorganic components through chemical bonds or hydrogen bonds, allowing the two to bond well together. Simultaneously, epoxy resin has excellent transparency, avoiding significant impact on the appearance of the substrate and meeting the appearance requirements of coating and other applications.

[0024] The present invention achieves at least the following beneficial effects: 1. In the compound modification process of this invention, in addition to epoxy resin, resins with good adhesive properties (such as phenolic resin) can also achieve the same effect. Phenolic resin also has good mechanical properties and adhesiveness, and when compounded with dimethyl silicone oil, it may also optimize the coating performance. Silane coupling agents can improve the bonding strength between dimethyl silicone oil and geopolymers and reduce interface defects.

[0025] 2. The purpose of this invention is to provide a modification scheme for phosphate-based polymer coatings. By simultaneously adding epoxy resin and dimethyl silicone oil to the phosphate-based polymer, and scientifically optimizing the compounding ratio of epoxy resin and dimethyl silicone oil, the compressive strength, hardness, adhesion, and setting time of the phosphate-based polymer coating are significantly improved. This enhances the hydrophobicity of the coating material and reduces its porosity, thereby reducing water absorption and improving chloride ion corrosion resistance. This achieves synergistic optimization of various coating properties, meeting the high performance requirements of coatings in more scenarios. It solves the problems of high water absorption, large porosity, and weak chloride ion penetration resistance in phosphate-based polymer coatings. By improving the hydrophobicity, density, and chloride ion corrosion resistance of the coating, it provides a green and efficient protective coating for reinforced concrete structures in highly corrosive environments such as marine environments.

[0026] 3. This invention optimizes the compounding ratio of epoxy resin and dimethyl silicone oil, limits the influence of preparation processes (such as stirring speed, time, molding temperature, pressure, curing time, etc.) on coating performance, and optimizes the parameter range. This not only significantly improves the compressive strength, hardness, and adhesion of the coating, but also further enhances its hydrophobic properties and reduces water absorption, thereby more effectively improving its resistance to chloride ion corrosion. It can more comprehensively and significantly solve the problems of insufficient mechanical properties, hydrophobic properties, and corrosion resistance of existing coatings, achieving synergistic optimization of various properties and better meeting the needs of practical applications.

[0027] 4. This invention employs an epoxy resin / dimethyl silicone oil composite modified coating. The epoxy resin, in the form of tiny particles, adheres to the surface of unreacted metakaolin particles and the voids in the geopolymer gel network, further filling the smaller pores that dimethyl silicone oil cannot fill. It also intertwines with the dimethyl silicone oil-rich areas. The epoxy resin groups may form Si-OC chemical bonds with the hydroxyl groups in the geopolymer, achieving more complete filling of the coating from the macroscopic to the microscopic scale, resulting in a denser structure (a leftward shift in the pore size distribution curve and a reduction in pore volume). The excellent adhesion and potential chemical bonding of the epoxy resin itself enhance the interfacial bonding between the organic and inorganic phases, improving the overall integrity and adhesion of the coating (achieving level 1 in the cross-cut adhesion test). This dense organic-inorganic composite layer formed on and inside the coating surface constitutes a highly efficient physicochemical barrier, effectively blocking the diffusion of chloride ions and oxygen. Electrochemical testing (Tafel curves) demonstrates a significant reduction in corrosion current density, with a corrosion inhibition efficiency (IE) reaching up to 96.45%. Detailed Implementation

[0028] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, not all of the embodiments, and do not limit the protection scope of this application. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this application. Any modifications, equivalent substitutions, etc., made within the spirit and scope of this invention should be included within the protection scope of this invention.

[0029] In the description of this application, "multiple" means two or more, unless otherwise expressly and specifically defined.

[0030] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0031] Geopolymers, as a novel type of inorganic non-metallic material, possess potential advantages such as being environmentally friendly, heat-resistant, and corrosion-resistant, showing promising application prospects in coating protection across various fields including construction and chemical engineering. Among them, phosphate-based geopolymers have attracted attention due to their certain chemical corrosion resistance, becoming an important direction in coating material research.

[0032] However, unmodified phosphate-based polymer coatings exhibit significant shortcomings in mechanical properties, hydrophobicity, and corrosion resistance in practical applications, limiting their large-scale adoption. Therefore, modifying phosphate-based polymer coatings to optimize their performance has become a research hotspot in order to expand their application range.

[0033] Existing methods for preparing composite coatings include organic-inorganic hybrid coatings and nanocomposite coatings. Nanocomposite coatings involve complex dispersion processes and are costly. Organic-inorganic hybrid coatings exhibit poor compatibility, with significant polarity differences between the organic and inorganic components, leading to easy phase separation.

[0034] It is evident that existing phosphate-based polymer coatings suffer from insufficient compressive strength, low hardness, and poor adhesion between the coating and the substrate, leading to easy damage and peeling during use. Furthermore, their limited hydrophobic properties and high water absorption rate make the coating susceptible to corrosion from moisture and chloride ions, requiring improved resistance to chloride ion corrosion and failing to meet the demands of some scenarios with high coating performance requirements.

[0035] Existing modification techniques for phosphate-based polymer coatings, when using dimethyl silicone oil as a single additive, can improve hydrophobicity to some extent, but the effect on improving the coating's compressive strength, hardness, and adhesion is not significant, making it difficult to achieve synergistic optimization of mechanical properties, hydrophobicity, and corrosion resistance.

[0036] To address the aforementioned shortcomings of existing technologies, the inventors have dedicated themselves to providing a phosphate-based polymer coating modification scheme. By scientifically optimizing the compounding ratio of epoxy resin and dimethyl silicone oil, the compressive strength, hardness, adhesion, and setting time of the phosphate-based polymer coating are significantly improved. The hydrophobicity of the coating material is enhanced, and its porosity is reduced, thereby decreasing water absorption. This, in turn, improves resistance to chloride ion corrosion, achieving synergistic optimization of various coating properties and meeting the high performance requirements of coatings in a wider range of scenarios. The specific scheme is as follows: As a preferred embodiment, a corrosion-resistant phosphate-based polymer coating comprises the following raw materials: Metakaolin: Al2O3 content is 38.52%; Phosphoric acid solution: mass fraction of 85%, the amount of which is controlled by the phosphorus-aluminum mass ratio (H3PO4 / Al2O3), preferably in the range of 1.2 to 1.4; Water: The amount used is controlled by the water-cement ratio (the mass ratio of water to metakaolin), with a preferred range of 0.35 to 0.45; Organic modifiers include dimethyl silicone oil, resin, and resin-specific curing agent; the dimethyl silicone oil accounts for 1% to 9% of the mass of metakaolin, preferably 3% to 6%; the epoxy resin (E51 type) accounts for 10% to 30% of the mass of metakaolin, preferably 15% to 25%; the mass ratio of the resin-specific curing agent to the resin is 1:1; the resin is epoxy resin (E51 type) or phenolic resin; Silane coupling agent (e.g., KH-550): 2%–5% of the mass of dimethyl silicone oil. As a further preferred embodiment, a method for preparing a corrosion-resistant phosphate-based polymer coating includes the following steps: (1) Pre-prepared acid activation solution: Mix the measured distilled water and phosphoric acid solution in a beaker, stir with a glass rod until uniform, and let stand and cool to room temperature (about 25°C). (2) Organic modifier pre-emulsification: The measured dimethyl silicone oil, silane coupling agent, resin, and resin-specific curing agent are added sequentially to the acid-activated liquid prepared in step (1). The mixture is placed under a mechanical stirrer and stirred continuously at a speed of 750-850 rpm for 25-35 minutes at room temperature. The purpose is to fully emulsify and disperse the organic modifier (especially the hydrophobic dimethyl silicone oil) in the aqueous phase through high-speed shearing to form a relatively stable premixed liquid. This allows the silane coupling agent to be fully mixed with other substances in the process. Its silanol groups interact with dimethyl silicone oil or epoxy resin, while its amino and other functional groups prepare for subsequent bonding with the inorganic phase. (3) Preparation of geopolymer slurry: The metered metakaolin powder is slowly added to the organic-acid activated premixed liquid obtained in step (2). Stirring is maintained during the addition process. After the addition is completed, the stirring speed is adjusted to 280-320 rpm and stirring is continued for 8-12 minutes until a uniformly mixed and fluid geopolymer slurry is obtained. This allows phosphoric acid to come into contact with metakaolin and undergo a depolymerization reaction, releasing silicon and aluminum species. The emulsified organic phase is uniformly introduced into the entire inorganic reaction system. (4) Coating and curing: The geopolymer slurry obtained in step (3) is uniformly coated onto the surface of a pre-treated clean substrate (such as a ceramic plate, concrete block or mortar block with steel reinforcement) using a scraping method. The wet film thickness is controlled to be 290-310 μm. Then, the following steps are followed for curing: Vibration compaction: The mold or coated specimen is vibrated on a vibrating table for 4-6 minutes to remove large air bubbles; Sealing and pre-curing: The specimen and the mold are placed in a sealed bag and placed in an oven at 48-52℃ for 23.5-24.5 hours to allow the geopolymer reaction and the epoxy resin curing reaction to start simultaneously; Demolding and continuous curing: After the sealing and pre-curing is completed, the initially cured specimen is demolded and placed in an oven at 48-52℃ for a total of 7 days for sealing and curing. The coating is fully cured, forming the final organic-inorganic hybrid structure, namely the corrosion-resistant phosphate-based geopolymer coating.

[0037] Example 1

[0038] A corrosion-resistant phosphate-based polymer coating comprises metakaolin, an acid activator, a reaction medium, an organic modifier, and an interface compatibilizer; The Al2O3 content in metakaolin is 38.52%; The acid activator is a phosphoric acid solution with a mass fraction of 85%. The mass ratio of phosphoric acid aluminum (H3PO4 in the phosphoric acid solution to Al2O3 in metakaolin) is H3PO4 / Al2O3 = 1.2:1. The reaction medium is water, and the mass ratio of water to metakaolin is 0.35:1; The organic modifiers include dimethyl silicone oil, epoxy resin, and epoxy resin curing agent; the dimethyl silicone oil accounts for 1% of the mass of metakaolin; the epoxy resin accounts for 10% of the mass of metakaolin; and the mass ratio of epoxy resin curing agent to epoxy resin is 1:1. The interface compatibilizer is a silane coupling agent, which accounts for 2% of the mass of dimethyl silicone oil.

[0039] A method for preparing a corrosion-resistant phosphate-based polymer coating as described above includes the following steps: (1) Pre-prepared acid activation solution: Stir the reaction medium and phosphoric acid solution evenly, let stand and cool to room temperature to obtain the acid activation solution; (2) Organic modifier pre-emulsification: Dimethyl silicone oil, silane coupling agent, epoxy resin and epoxy resin curing agent are added to the acid activation solution prepared in step (1) in sequence. The mixture is stirred continuously at 750 rpm for 25 min at room temperature to obtain organic-acid activation premix. (3) Preparation of geopolymer slurry: Under stirring, metakaolin powder is slowly added to the organic-acid activated premixed liquid obtained in step (2). After adding metakaolin powder, the stirring speed is adjusted to 280 rpm and stirring is continued for 8 minutes until a uniformly mixed slurry with suitable fluidity is obtained, thus obtaining geopolymer slurry. (4) Coating and curing: The geopolymer slurry obtained in step (3) is uniformly coated onto the pretreated clean substrate surface using a scraping method. The wet film thickness is controlled to be 290 μm. First, the mold or coated specimen is vibrated on a vibrating table for 4 min to remove large air bubbles. Then, the specimen and the mold are placed in a sealed bag and cured in an oven at 48°C for 23.5 h. After the sealing and pre-curing is completed, the initially cured specimen is demolded and placed in an oven at 48°C for a total of 7 days for sealing and curing. The coating is fully cured to form the final organic-inorganic hybrid structure, and the corrosion-resistant phosphate-based geopolymer coating is obtained. The substrate is a ceramic plate.

[0040] Example 2

[0041] A corrosion-resistant phosphate-based polymer coating comprises metakaolin, an acid activator, a reaction medium, an organic modifier, and an interface compatibilizer; The Al2O3 content in metakaolin is 38.52%; The acid activator is a phosphoric acid solution with a mass fraction of 85%. The mass ratio of phosphorus aluminum in the phosphoric acid solution (H3PO4 / Al2O3) to that in metakaolin is H3PO4 / Al2O3 = 1.4:1. The reaction medium is water, and the mass ratio of water to metakaolin is 0.45:1; The organic modifiers include dimethyl silicone oil, phenolic resin, and a special curing agent for phenolic resin; dimethyl silicone oil accounts for 9% of the mass of metakaolin; epoxy resin accounts for 15% of the mass of metakaolin; and the mass ratio of the special curing agent for phenolic resin to phenolic resin is 1:1. The interface compatibilizer is a silane coupling agent, which accounts for 5% of the mass of dimethyl silicone oil.

[0042] A method for preparing a corrosion-resistant phosphate-based polymer coating as described above includes the following steps: (1) Pre-prepared acid activation solution: Stir the reaction medium and phosphoric acid solution evenly, let stand and cool to room temperature to obtain the acid activation solution; (2) Organic modifier pre-emulsification: Dimethyl silicone oil, silane coupling agent, phenolic resin and phenolic resin curing agent are added to the acid activation solution prepared in step (1) in sequence. The mixture is stirred continuously at 850 rpm for 35 min at room temperature to obtain organic-acid activation premix. (3) Preparation of geopolymer slurry: Under stirring, metakaolin powder is slowly added to the organic-acid activated premixed liquid obtained in step (2). After adding metakaolin powder, the stirring speed is adjusted to 320 rpm and stirring is continued for 12 min until a uniformly mixed slurry with suitable fluidity is obtained, thus obtaining geopolymer slurry. (4) Coating and curing: The geopolymer slurry obtained in step (3) is uniformly coated onto the pretreated clean substrate surface using a scraping method. The wet film thickness is controlled to be 310 μm. First, the mold or coated specimen is vibrated on a vibrating table for 6 min to remove large air bubbles. Then, the specimen and the mold are placed in a sealed bag and cured in an oven at 52℃ for 24.5 h. After the sealing and pre-curing is completed, the initially cured specimen is demolded and placed in an oven at 52℃ for a total of 7 days for sealing and curing. The coating is fully cured, forming the final organic-inorganic hybrid structure, and the corrosion-resistant phosphate-based geopolymer coating is obtained. The substrate is a concrete specimen.

[0043] Example 3

[0044] A corrosion-resistant phosphate-based polymer coating comprises metakaolin, an acid activator, a reaction medium, an organic modifier, and an interface compatibilizer; The Al2O3 content in metakaolin is 38.52%; The acid activator is a phosphoric acid solution with a mass fraction of 85%. The mass ratio of phosphorus aluminum in the phosphoric acid solution (H3PO4 / Al2O3) to that in metakaolin is H3PO4 / Al2O3 = 1.3:1. The reaction medium is water, and the mass ratio of water to metakaolin is 0.4:1; The organic modifiers include dimethyl silicone oil, epoxy resin, and epoxy resin curing agent; dimethyl silicone oil accounts for 6% of the mass of metakaolin; epoxy resin accounts for 20% of the mass of metakaolin; and the mass ratio of epoxy resin curing agent to epoxy resin is 1:1. The interface compatibilizer is a silane coupling agent, which accounts for 4% of the mass of dimethyl silicone oil.

[0045] A method for preparing a corrosion-resistant phosphate-based polymer coating as described above includes the following steps: (1) Pre-prepared acid activation solution: Stir the reaction medium and phosphoric acid solution evenly, let stand and cool to room temperature to obtain the acid activation solution; (2) Organic modifier pre-emulsification: Dimethyl silicone oil, silane coupling agent, epoxy resin and epoxy resin curing agent are added to the acid activation solution prepared in step (1) in sequence. The mixture is stirred continuously at 800 rpm for 30 min at room temperature to obtain organic-acid activation premix. (3) Preparation of geopolymer slurry: Under stirring, the metakaolin powder calcined at 800°C is slowly added to the organic-acid activated premixed liquid prepared in step (2). After adding the metakaolin powder, the stirring speed is adjusted to 300 rpm and stirring is continued for 10 min until a uniformly mixed slurry with suitable fluidity is obtained, thus obtaining the geopolymer slurry. (4) Coating and curing: The geopolymer slurry obtained in step (3) is uniformly coated onto the pretreated clean substrate surface using a scraping method. The wet film thickness is controlled to be 300 μm. First, the mold or coated specimen is vibrated on a vibrating table for 5 min to remove large air bubbles. Then, the specimen and the mold are placed in a sealed bag and cured in an oven at 50°C for 24 h. After the sealing and pre-curing is completed, the initially cured specimen is demolded and placed in an oven at 50°C for a total of 7 days for sealing and curing. The coating is fully cured, forming the final organic-inorganic hybrid structure, and the corrosion-resistant phosphate-based geopolymer coating is obtained. The substrate is a mortar block with reinforcing steel bars.

[0046] Example 4: Epoxy resin content is 10% (dimethyl silicone oil is fixed at 3%). The difference from Example 3 is that a corrosion-resistant phosphate-based polymer coating is made from the following raw materials: Metakaolin: Al2O3 content is 38.52%, 100g; Phosphoric acid solution: mass fraction is 85%, and the amount used is calculated based on the phosphorus-aluminum mass ratio H3PO4 / Al2O3 = 1.3, which is 56.6g; Distilled water: water-to-ash ratio = 0.4, 31.51g; Dimethyl silicone oil: 3% of the mass of metakaolin, which is 3g; Epoxy resin (E51): 10% of the mass of metakaolin, which is 10g; Epoxy resin curing agent: 10g, with a mass ratio of 1:1 to epoxy resin; Silane coupling agent (KH-550): 4% of the mass of dimethyl silicone oil, 0.12g. Other conditions remain unchanged.

[0047] A method for preparing a corrosion-resistant phosphate-based polymer coating as described above includes the following steps: Example 5: Epoxy resin content is 20%. The difference from Example 4 is that the epoxy resin accounts for 20% of the mass of metakaolin, while other conditions remain unchanged.

[0048] Comparative Example 1: Epoxy resin content is 30%. The difference from Example 4 is that the epoxy resin accounts for 30% of the mass of metakaolin, while other conditions remain unchanged.

[0049] Comparative Example 2: Dimethyl silicone oil content was 1%. A phosphate-based polymer coating is made from the following raw materials: Metakaolin: Al2O3 content is 38.52%, 100g; Phosphoric acid solution (H3PO4): The amount needed is 56.6g, calculated based on a phosphorus-aluminum mass ratio (H3PO4 / Al2O3) of 85% by mass. Distilled water: water-cement ratio (mass ratio of water to metakaolin) = 0.4, totaling 31.51g; Dimethyl silicone oil: 1% of the mass of metakaolin, which is 1g; Silane coupling agent (KH-550): accounts for 4% of the mass of dimethyl silicone oil, which is 0.04g.

[0050] A method for preparing a phosphate-based polymer coating as described above includes the following steps: (1) Pre-prepared acid activation solution: Mix distilled water and phosphoric acid solution evenly, let stand and cool to room temperature (25℃) to obtain acid activation solution; (2) Add dimethyl silicone oil and silane coupling agent to the acid activation solution in step (1), and stir at 800 rpm for 30 minutes at room temperature to perform pre-emulsification; (3) Slowly add the metakaolin powder calcined at 800°C, adjust the stirring speed to 300 rpm, and continue stirring for 10 minutes to obtain a uniform slurry; (4) Apply the slurry to the surface of the pretreated ceramic plate or concrete test block, and control the wet film thickness to be 300 μm; (5) Vibrate for 5 minutes, seal and place in a 50℃ oven for 24 hours for pre-curing. After demolding, continue to seal and cure for a total of 7 days to obtain a phosphate-based polymer coating.

[0051] Comparative Example 3: Dimethyl silicone oil content was 2%. The difference from Comparative Example 1 is that dimethyl silicone oil accounts for 2% of the mass of metakaolin, while other conditions remain unchanged.

[0052] Comparative Example 4: Dimethyl silicone oil content was 3%. The difference from Comparative Example 1 is that dimethyl silicone oil accounts for 3% of the mass of metakaolin, while other conditions remain unchanged.

[0053] Comparative Example 5: Dimethyl silicone oil content was 4%. The difference from Comparative Example 1 is that dimethyl silicone oil accounted for 4% of the mass of metakaolin, while other conditions remained unchanged.

[0054] Comparative Example 6: Dimethyl silicone oil content was 5%. The difference from Comparative Example 1 is that dimethyl silicone oil accounts for 5% of the mass of metakaolin, while other conditions remain unchanged.

[0055] Comparative Example 7: Dimethyl silicone oil content was 6%. The difference from Comparative Example 1 is that dimethyl silicone oil accounts for 6% of the mass of metakaolin, while other conditions remain unchanged.

[0056] Comparative Example 8: No Additive Group (Control Group) The difference from Comparative Example 1 is that the dimethyl silicone oil content is 0%, there is no silane coupling agent, step (2) is removed during the preparation process, and other conditions remain unchanged.

[0057] Performance testing: The performance of the phosphate-based polymer coatings prepared by the methods of Examples 4-5 and Comparative Examples 1-8 was tested. Compressive strength (MPa): GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)" was used to test the compressive strength using an electronic universal testing machine (model ETM105D) manufactured by Shenzhen WanCe Testing Equipment Co., Ltd. Contact angle: The static contact angle of the liquid was measured using the seated drop method. The contact angle measuring instrument used was a DSA100E model manufactured by KYUSS GmbH, Germany. Pencil hardness: GB / T 6379-2006 "Paints and Varnishes - Pencil Method for Testing Hardness of Paint Films"; Adhesion rating: ISO 16276-2:2007 standard; The testing methods for corrosion current density (mA / cm²), corrosion inhibition efficiency (IE), corrosion rate (mm / year), and corrosion potential (mV) are as follows: First, a localized area of ​​the specimen is pretreated to ensure that only the working electrode portion is exposed to the electrolyte. Specifically, epoxy resin is used to seal the area where the steel and reinforcing bars at the top of the cylindrical specimen connect to the specimen module, preventing electrolyte penetration into non-working areas. Only a certain length of the top of the reinforcing bars is retained as the connection point for the working electrode to ensure accurate and reliable electrochemical signals. To construct a complete electrochemical circuit, the pretreated sample is immersed in a 3.5% NaCl solution. A sodium chloride solution of a certain concentration can be used as an electrolyte to form a stable electrochemical circuit between the electrodes of the sample, thus enabling subsequent corrosion tests to proceed smoothly. The electrochemical workstation was set to an initial potential of -0.2V, a final potential of 0.2V, and a scan rate of 0.001V / s to measure the Tafel curve of the sample corrosion. During the scan, the workstation recorded the current response of the sample at different potentials and plotted the Tafel curves. To accurately analyze the corrosion behavior, data within the voltage range of 60~120mV in the Tafel curves were selected for fitting. The voltage value obtained from the intersection of the fitted cathode voltage range curve and the anode voltage range curve is the corrosion potential E. corr The current value is i corr The coating corrosion rate CR is calculated using the following formula: Corrosion rate (mm / year) CR = (3270 × i) corr (×M) / (n×d) Among them, i corr (A / cm) 2 ) — Corrosion current density; M (g / mol) — Molar mass of the metal; n — Charge transfer number; d (g / cm³) 3 —Metal density; for reinforcing steel, M is generally taken as 55.85 g / mol; n is taken as 2 (Fe - →Fe 2+ +2e - ); d is 7.87 g / cm 3 ; The corrosion inhibition rate E of the coating is calculated using the following formula: Corrosion inhibition rate IE (%) = (i 0 corr -i corr ) / i 0 corr ×100%; Among them, i 0 corr (A / cm) 2 — Corrosion current density of the uncoated area; i corr (A / cm) 2— Corrosion current density of the coating; Water absorption rate: GB / T 41767-2022 "Test Method for Hygroscopic Properties and Equilibrium Conditioning of Polymer-Based Composite Materials". Pre-prepared samples were immersed in deionized water. First, each sample was accurately weighed before immersion, and its initial dry mass (m0) was recorded. When recording the mass, attention should be paid to any obvious defects or cracks on the sample surface to provide a reference for subsequent result analysis. The weighed samples were then placed in containers of deionized water, ensuring that all surfaces of the samples were completely covered by water during immersion. The immersion time was set at 24 hours. During immersion, the room temperature and water temperature were kept constant to ensure that each sample absorbed water under the same conditions. Stirring was not required during this period, but the water quality must be stable and there must be no significant circulation in the container to prevent uneven water contact from causing deviations in the water absorption rate measurement results. After 24 hours, the samples were removed from the deionized water, and the sample surface was gently wiped with a lint-free cloth to remove surface moisture. Subsequently, each sample was accurately weighed again, and its mass after immersion (m0) was recorded. w Additionally, observe and record changes in the appearance and morphology of the samples, such as the presence of cracks, surface peeling, or other abnormalities. This observation data provides a direct basis for analyzing the potential changes in physical properties of the material after water absorption. The formula for calculating the water absorption rate is: η = (m) w -m0) / m0×100%.

[0058] The experimental results are shown in Table 1 below.

[0059] Table 1

[0060] The unmodified geopolymer coating has a typical three-dimensional network geopolymer gel structure, encapsulating unreacted metakaolin flakes. The internal structure contains numerous micron- and nano-sized pores, providing permeation channels for water molecules and chloride ions. The structure changes after epoxy resin / dimethyl silicone oil composite modification: the epoxy resin adheres as tiny particles to the surface of the unreacted metakaolin particles and into the voids of the geopolymer gel network. Specifically, it further fills the smaller pores that dimethyl silicone oil cannot fill and interweaves with dimethyl silicone oil-rich areas. FTIR analysis indicates that the epoxy resin groups may form Si-OC chemical bonds with the hydroxyl groups in the geopolymer.

[0061] As shown in Table 1, the combined effect of epoxy resin and dimethyl silicone oil achieves more complete filling of the coating from the macroscopic to the microscopic scale, resulting in a denser structure (the pore size distribution curve shifts to the left, and the pore volume decreases). The excellent adhesion and potential chemical bonding of epoxy resin enhance the interfacial bonding between the organic and inorganic phases, improving the overall integrity and adhesion of the coating (achieving level 1 in the cross-cut adhesion test). This dense organic-inorganic composite layer formed on and within the coating surface constitutes a highly efficient physicochemical barrier, effectively blocking the diffusion of chloride ions and oxygen. Electrochemical testing (Tafel curves) demonstrates a significant reduction in corrosion current density, with an corrosion inhibition efficiency (IE) reaching up to 96.45%.

[0062] This invention innovatively employs a compounding of epoxy resin and dimethyl silicone oil, and by optimizing the compounding ratio of epoxy resin and dimethyl silicone oil, the synergistic effect of the two not only significantly improves the compressive strength, hardness, and adhesion of the coating, but also further enhances its hydrophobic properties and reduces water absorption, thereby more effectively improving its resistance to chloride ion corrosion. From the perspective of the technical problems solved, this invention more comprehensively and significantly addresses the deficiencies in mechanical properties, hydrophobic properties, and corrosion resistance of existing coatings, achieving synergistic optimization of each property and better meeting practical application requirements.

[0063] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A corrosion-resistant phosphate-based polymer coating, characterized in that, Including metakaolin, acid activator, reaction medium, organic modifier, and interface compatibilizer; The acid activator is a phosphoric acid solution, and the mass ratio of phosphorus and aluminum in the phosphoric acid solution (H3PO4 / Al2O3) to that in metakaolin is (1.2~1.4):

1. The organic modifier includes dimethyl silicone oil, resin, and resin-specific curing agent; the dimethyl silicone oil accounts for 1% to 9% of the mass of metakaolin; the resin accounts for 10% to 20% of the mass of metakaolin; and the resin is epoxy resin or phenolic resin.

2. The corrosion-resistant phosphate-based polymer coating according to claim 1, characterized in that, The phosphoric acid solution has a mass fraction of 85%; the metakaolin contains 38.52% Al2O3; the reaction medium is water, and the mass ratio of water to metakaolin is (0.35~0.45):

1.

3. The corrosion-resistant phosphate-based polymer coating according to claim 1, characterized in that, The interface compatibilizer is a silane coupling agent, and the silane coupling agent accounts for 2% to 5% of the mass of dimethyl silicone oil.

4. The corrosion-resistant phosphate-based polymer coating according to claim 1, characterized in that, The mass ratio of the resin-specific curing agent to the resin is 1:

1.

5. A method for preparing a corrosion-resistant phosphate-based polymer coating as described in any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Pre-prepared acid activation solution: Stir the reaction medium and phosphoric acid solution evenly, let stand and cool to room temperature to obtain the acid activation solution; (2) Organic modifier pre-emulsification: Dimethyl silicone oil, silane coupling agent, resin and resin-specific curing agent are added sequentially to the acid activation solution prepared in step (1), and stirred evenly to obtain organic-acid activation premix. (3) Preparation of geopolymer slurry: Under stirring, metakaolin powder is slowly added to the organic-acid activated premix prepared in step (2) to obtain geopolymer slurry; (4) Coating and curing: The geopolymer slurry obtained in step (3) is uniformly coated onto the pretreated clean substrate surface using a scraping method. After compaction, sealing and pre-curing, demolding and continuous curing, the corrosion-resistant phosphate-based geopolymer coating is obtained.

6. The preparation method according to claim 5, characterized in that, In step (2), the stirring is carried out at room temperature and the stirring speed is continuously stirred for 25 to 35 minutes at 750 to 850 rpm.

7. The preparation method according to claim 5, characterized in that, In step (3), after adding the metakaolin powder, adjust the stirring speed to 280-320 rpm and continue stirring for 8-12 minutes until a uniformly mixed and fluid geopolymer slurry is obtained.

8. The preparation method according to claim 5, characterized in that, In step (4), the substrate is at least one of ceramic plate, concrete block or mortar block with steel reinforcement; the wet film thickness of the corrosion-resistant phosphate-based polymer coating is controlled to be 290-310 μm.

9. The preparation method according to claim 5, characterized in that, In step (4), the compaction time is 5 minutes; the sealing pre-curing is to put the specimen together with the mold into a sealed bag and place it in an oven at 48-52℃ for curing for 23.5-24.5 hours; the demolding and continuous curing is to demold the initially cured specimen after the sealing pre-curing is completed and continue to place it in an oven at 48-52℃ for sealing curing.

10. The preparation method according to claim 5, characterized in that, In step (4), the total curing time for sealing pre-curing, demolding and continuous curing is 7 days.

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