Nanometer core-shell type CoFe2O4 coated SiO2 / polymer composite coating with electromagnetic shielding function and preparation method of nanometer core-shell type CoFe2O4 coated SiO2 / polymer composite coating

Abstract

The invention discloses a nano core-shell CoFe2O4-coated SiO2 / polymer composite coating with an electromagnetic shielding function and a preparation method thereof, and relates to the technical field of building functional materials, in particular to an electromagnetic shielding cement-based coating material. The polymer cement coating material with the electromagnetic shielding function comprises a component A and a component B, wherein the component A is prepared from 5.0 to 25.0 parts by weight of cement and 10.0 to 35.0 parts by weight of inorganic filler; the component B is prepared from the following components in parts by weight: 20.0 to 50.0 parts of polymer emulsion, 0.05 to 0.35 part of CoFe2O4 coated SiO2 magnetic nanoparticles and 10.0 to 40.0 parts of water. The CoFe2O4-coated SiO2 magnetic nanoparticles with the core-shell structure are introduced and cooperate with the polymer emulsion (PA / VAE) and the cement-based matrix, so that the problems that a traditional material is low in shielding effectiveness at a high frequency band (1-6 GHz) and poor in durability in an alkaline environment are solved. CoFe2O4 can be used as an electromagnetic loss body, and the SiO2 shell layer realizes passivation protection on magnetic particles in a molecular scale, so that the durability of the coating-resistant layer is improved. The coating adopts an A / B double-component separate storage design, mixed coating is performed during construction, the shielding effectiveness at the frequency band of 3.5 GHz reaches 38.2 dB or above, and the coating is suitable for high-electromagnetic-sensitivity buildings such as hospitals and laboratories. The technology provides a material science solution for high electromagnetic sensitivity buildings.

Description

Technical Field

[0001] This invention relates to the field of building functional materials technology, specifically to a polymer cement-based composite coating with broadband electromagnetic shielding function, and more particularly to the application of core-shell structured CoFe2O4@SiO2 magnetic nanoparticles in cement-based systems. Background Technology

[0002] As radio communication technology evolves towards higher frequencies and higher densities, with the 5G frequency band extending to 3.5-7.1 GHz, the electromagnetic field strength (EMF) in space is growing exponentially. ITU data shows that the global environmental EMF intensity will increase by more than 12% annually from 2020 to 2030. Electromagnetic waves interfere with the operation of medical equipment, threaten information security, and even affect human health.

[0003] Traditional building structures are insufficient for attenuating electromagnetic waves in the GHz band, necessitating the development of high-bandwidth, high-durability electromagnetic shielding coatings. While traditional polymer cement coatings (styrene-acrylic / epoxy modified, etc.) can improve flexibility and adhesion, they primarily serve basic needs such as corrosion and waterproofing, offering extremely low shielding effectiveness against electromagnetic waves. Some carbon-based / metallic conductive coatings exhibit poor dispersibility in cementitious matrices, and high addition amounts can impair mechanical properties.

[0004] While directly adding ferrites (such as Fe3O4 and CoFe2O4) can introduce magnetic properties, the high specific surface energy of nanoparticles makes them prone to agglomeration, leading to a deterioration in the rheological properties of the coating. In addition, the highly alkaline environment (pH≥12.5) of cement hydration products corrodes magnetic particles, causing a decrease in magnetic properties, and the volume expansion of corrosion products triggers coating cracking.

[0005] Ferrite absorbing materials are iron-based metal oxides or composite oxides, belonging to the subferromagnetic material category. Their microwave absorption performance derives from their ferromagnetic and dielectric properties. Both their relative permeability and relative permittivity are complex, generating both dielectric and magnetic losses, thus exhibiting excellent microwave absorption performance.

[0006] This invention utilizes a core-shell structure design to encapsulate CoFe2O4, forming a CoFe2O4@SiO2 core-shell structure. This achieves: (1) long-term stability of magnetic particles under highly alkaline conditions; (2) uniform dispersion of nanoparticles in the slurry; (3) Synergistic improvement of electromagnetic function and mechanical properties This invention resolves the technical contradictions of traditional electromagnetic shielding materials in terms of broadband response, alkaline environment durability, and construction compatibility by constructing a CoFe2O4@SiO2 / polymer cement-based composite coating. The SiO2 shell provides passivation protection for magnetic particles at the molecular scale, while the magnetic-dielectric dual-loss mechanism enables the coating to meet the Class A shielding standard specified in GB / T25471-2020 at a critical thickness of 0.8 mm. This technology provides a materials science solution for buildings with high electromagnetic susceptibility.

[0007] Chinese Patent Publication No. CN 105111913 B discloses a graphene / nanoferrite-based waterborne electromagnetic shielding coating and its preparation method. Ferrite nanoparticles are loaded onto the surface of graphene to prepare a graphene / ferrite nanocomposite material that combines the conductivity of graphene with the excellent magnetic properties of nanoferrite. This composite material is then combined with an aqueous film-forming resin and other additives to prepare a green and environmentally friendly waterborne electromagnetic shielding coating. This preparation method is characterized by its simple operation, high practicality, lack of harmful substances, and ability to produce electromagnetic shielding coatings suitable for different frequencies and applications with good shielding effect.

[0008] Although the above solution overcomes the shortcomings of existing electromagnetic shielding coatings, such as narrow absorption bandwidth and poor shielding effectiveness due to the use of a single conductive or magnetic material as filler, it has high production costs. Graphene sheets and nano-ferrites tend to agglomerate, resulting in uneven coating and affecting shielding effectiveness and coating performance. Summary of the Invention

[0009] This application provides a polymer cement-based composite coating with electromagnetic shielding function and its preparation method. By constructing a CoFe2O4@SiO2 / polymer cement-based composite coating, it solves the technical contradictions of traditional electromagnetic protection materials in terms of broadband response, alkaline environment durability, and construction adaptability.

[0010] In a first aspect, the present invention provides a polymer cement coating with electromagnetic shielding function, comprising two components, A and B. Component A comprises 5.0–25.0 parts by weight of cement and 10.0–35.0 parts by weight of inorganic filler; component B comprises 20.0–50.0 parts by weight of polymer emulsion, 0.05–0.35 parts by weight of CoFe2O4@SiO2 magnetic nanoparticles, and 10.0–40.0 parts by weight of water.

[0011] Furthermore, the electromagnetic shielding filler of the coating is a core-shell type CoFe2O4@SiO2 magnetic nanoparticle, with CoFe2O4 as the core and SiO2 as the shell. On the one hand, CoFe2O4 can act as an electromagnetic loss body, and on the other hand, the SiO2 shell achieves passivation protection of the magnetic particles at the molecular scale, thereby improving the durability of the coating.

[0012] Furthermore, the cement is rapid-hardening sulfoaluminate cement.

[0013] Furthermore, the polymer emulsion includes any one of vinyl acetate-ethylene copolymer emulsion (VAE), polyacrylate emulsion (PA), polyacrylate emulsion, and vinyl acetate-ethylene blend emulsion (VAE / PA). Optionally, the solid content of the polymer emulsion is 40-60%.

[0014] Furthermore, the inorganic filler includes silica fume, fly ash, ultrafine mineral powder, silica powder, talc powder, and mica. The inorganic filler can be any one of the following: powder, calcium carbonate powder, etc. In this invention, the combination of the inorganic filler and the polymer emulsion to form a three-dimensional network structure helps to simultaneously improve the strength and toughness of cement-based materials.

[0015] Furthermore, the CoFe2O4@SiO2 nanoparticles are experimentally prepared core-shell nanoscale magnetic particles. With CoFe2O4 as the core and SiO2 as the shell, CoFe2O4 can act as an electromagnetic loss medium, while the SiO2 shell provides passivation protection for the magnetic particles at the molecular scale, thus improving the durability of the coating.

[0016] Furthermore, the CoFe2O4@SiO2 nanoparticles are modified with silane coupling agent KH-560 and ultrasonically dispersed in a polymer emulsion.

[0017] Furthermore, the raw material composition also includes at least one of the following additives: 0.42-0.56 parts by weight of defoamer, 0.39-0.52 parts by weight of thickener, 0.12-0.16 parts by weight of water-reducing agent, and 0.06-0.08 parts by weight of dispersant.

[0018] Optionally, the defoamer includes any one of acetylenic diol, polyether, and tributyl phosphate. The main function of this defoamer in this invention is to eliminate air bubbles in the cement-based material layer, thereby improving the density and surface quality of the sprayed material layer.

[0019] Optionally, the thickener includes any one of hydroxypropyl methylcellulose ether and polyvinylpyrrolidone. The main function of this thickener in this invention is to increase the viscosity of the slurry and improve the anti-sagging properties of the sprayed material.

[0020] Optionally, the water-reducing agent includes any one of polycarboxylate-based water-reducing agents and aliphatic water-reducing agents. The main function of this water-reducing agent in this invention is to reduce the water requirement of cement-based materials, thereby reducing the porosity formed by moisture in the cement-based materials.

[0021] Optionally, the dispersant includes any one of ultrafine quartz powder, sodium tripolyphosphate, and sodium pyrophosphate. The function of the dispersant in this invention is to enable the raw material components to mix more uniformly.

[0022] In a second aspect of the present invention, a method for preparing a cement-based composite coating with electromagnetic shielding function is provided, specifically comprising: S1. Preparation of core-shell magnetic nanoparticles (CoFe2O4@SiO2).

[0023] Preparation of S11. CoFe2O4 magnetic fluid.

[0024] Specifically: (a) Iron and cobalt sources were dissolved in deionized water according to a specific ratio and stirred uniformly at 70-90°C. This solution is denoted as solution a. (b) PEG (6000) was added as a dispersant to a certain amount of ammonia water (NH3·H2O) and stirred uniformly at 70-90°C. This solution is denoted as solution b. (c) Solution a was added dropwise to solution b and stirred for 1-2 h. This mixed solution was refluxed in a boiling water bath for 2-5 h. (d) The resulting black precipitate was rapidly separated by a magnetic field and washed with deionized water until neutral (pH=7). It was then vacuum dried at 80-100°C for 12 h and subsequently sintered at 350-550°C for 12-24 h to remove residual carbon. (e) The obtained CoFe2O4 magnetic nanoparticles (0.3-0.5 g) were ultrasonically dispersed in 200-500 mL of citric acid solution (200-500 mL). Citric acid-modified magnetic nanoparticles were collected by magnetic field separation, washed three times with alcohol, dispersed in a mixed solution of alcohol and deionized water (volume ratio 5:1, 4:1, 3:1), and sonicated for 2-5 h to obtain CoFe2O4 magnetic fluid. This fluid solution is labeled as solution c.

[0025] Silica coating of S12. CoFe2O4 nanoparticles Specifically, a certain amount of NH3·H2O was added to solution c to adjust the pH value. When the pH reached 7-9, TEOS (3-5 mL) was added dropwise to the suspension c under ultrasonic treatment. Subsequently, the mixture was stirred at room temperature for 12-24 h. The resulting powder was collected by a magnet, washed with deionized water until neutral (pH = 7), and vacuum dried at 80-100 °C for 12-24 h.

[0026] S13. Surface modification of core-shell materials; CoFe2O4@SiO2 nanoparticles were ultrasonically dispersed in an ethanol solution (2wt%) of silane coupling agent KH-560 for 30-60 min and then vacuum dried at 60 °C for 10-20 h.

[0027] S2. Preparation of cement-based composite coating with electromagnetic shielding function.

[0028] S21. Mix the cement and inorganic filler evenly to form component A, and set aside.

[0029] S22. The modified CoFe2O4@SiO2 nanoparticles and water described in step S13 are ultrasonically dispersed to form a suspension. The suspension is then added to the polymer emulsion and ultrasonically dispersed again. After completion, component B is obtained and set aside.

[0030] S23. Mix the components A and B evenly to obtain the electromagnetic shielding cement-based coating.

[0031] Furthermore, in step S21, component A further includes the auxiliary agent; Furthermore, in step S22, the ultrasonic power is 200~800W and the time is 25~55min.

[0032] Furthermore, in step S22, component B is sealed and stored before use to prevent the emulsion from failing.

[0033] It should be noted that steps S21 and S22 above do not have a specific order; that is, the A group can be prepared first. Alternatively, component B can be prepared first, followed by component A. The order of steps S21 and S22 described above is for ease of description only and does not constitute a specific arrangement.

[0034] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages: Firstly, the natural resonant frequency of the magnetic nanoparticles CoFe2O4 is located in the 1-6 GHz range, perfectly covering the core frequency bands of 5G / Bluetooth / WiFi. With an addition of 0.35 parts, the coating achieves a shielding effectiveness of 38.2 dB at 3.5 GHz, a 50% improvement over traditional Fe3O4 coatings. Its electromagnetic shielding mechanism is achieved through synergistic magnetic-dielectric loss, and the SiO2 shell enhances interfacial polarization, expanding the absorption bandwidth.

[0035] Secondly, the SiO2 shell forms a ≡Si-O-Si≡ passivation layer in a pH=12.5 environment, which prevents Ca(OH)2 from penetrating during cement hydration, prevents CoFe2O4 from being corroded by alkali, and can also inhibit cracking. The -OH on the surface forms a hydrogen bond network with the polymer, enhancing the durability of the coating.

[0036] Thirdly, nanomaterials have high surface energy and are easy to aggregate. This invention modifies the surface of CoFe2O4@SiO2 nanoparticles and forms ≡Si-O-Si(CH2)3OCH3 covalent bonds on the SiO2 surface through KH-560, thereby enhancing compatibility with polymer emulsions.

[0037] Fourthly, this invention first uses cement and inorganic fillers as the base materials as component A, which have good durability and high tensile strength, ensuring the mechanical properties of the resulting cement-based material. Then, this invention introduces a polymer emulsion modified with magnetic core-shell CoFe2O4@SiO2 nanoparticles as component B to increase the functionality of the cement-based material. Thus, the cement-based material of this invention has excellent electromagnetic shielding performance while maintaining good durability and tensile strength. Moreover, the two-component design (A / B separate storage) avoids the consumption of magnetic particles during cement hydration, allowing for on-site mixing and construction. Attached Figure Description

[0038] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Hereinafter, embodiments of the invention will be described in detail with reference to the accompanying drawings, wherein: Figure 1 This is a SEM image of magnetic core-shell CoFe2O4@SiO2 nanoparticles in an embodiment of the present invention; Figure 2 This is a TEM image of magnetic core-shell CoFe2O4@SiO2 nanoparticles in an embodiment of the present invention; Figure 3 This is a flowchart illustrating the preparation process of the electromagnetic shielding coating prepared in Example 1 of the present invention. Detailed Implementation

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0040] Example 1 1. A method for preparing silane-modified magnetic core-shell nanoparticles CoFe2O4@SiO2, comprising the following steps: (1) Preparation of CoFe2O4 magnetic nanoparticles: (a) Iron source and cobalt source were dissolved in 100 mL of deionized water at a ratio of 2:1 and stirred uniformly at 70 °C. This solution is denoted as solution a. (b) PEG (6000) was added as a dispersant to a certain amount of ammonia water (NH3·H2O) and stirred uniformly at 70 °C. This solution is denoted as solution b. (c) Solution a was added dropwise to solution b and stirred for 1 h. This mixed solution was refluxed in a boiling water bath for 2 h. (d) The obtained black precipitate was rapidly separated by a magnetic field and washed with deionized water until neutral (pH = 7). It was then vacuum dried at 80 °C for 12 h and sintered at 350 °C for 12 h to remove residual carbon.

[0041] (2) Silica coating of CoFe2O4 nanoparticles: The CoFe2O4 magnetic nanoparticles (0.3 g) obtained in step (1) were ultrasonically dispersed in 200 mL of citric acid solution. The citric acid-modified magnetic nanoparticles were collected by magnetic field separation, washed three times with alcohol, dispersed in a mixed solution of alcohol and deionized water (volume ratio 4:1), and ultrasonicated for 2 h to obtain a CoFe2O4 dispersion, which was labeled as solution c. A certain amount of NH3·H2O was added to solution c to adjust the pH value of the solution. When the pH reached 9, TEOS (3 mL) was added dropwise to the above suspension c under ultrasonic action. Subsequently, the above mixture was stirred at room temperature for 12 h. The obtained powder was collected by magnet, washed with deionized water until neutral (pH = 7), and vacuum dried at 80 °C for 12 h.

[0042] Surface modification of core-shell material: CoFe2O4@SiO2 nanoparticles were ultrasonically dispersed in an ethanol solution (2wt%) of silane coupling agent KH-560 for 30 min and then vacuum dried at 60 °C for 12 h.

[0043] 2. A method for preparing a cement-based composite coating with electromagnetic shielding function, comprising the following steps: (1) Prepare the following raw materials: 20 parts by weight of rapid hardening sulfoaluminate cement, 25 parts by weight of calcium carbonate powder, 40 parts by weight of polyacrylate emulsion / vinyl acetate-ethylene (PA / VAE) blend emulsion (mass ratio 3:1), 0.25 parts by weight of silane-modified CoFe2O4@SiO2 magnetic nanoparticles, 25 parts by weight of water, 0.15 parts by weight of polycarboxylate superplasticizer, and 0.45 parts by weight of hydroxypropyl methylcellulose ether.

[0044] (2) Mix the cement and calcium carbonate powder and stir mechanically for 10 min to form component A for later use.

[0045] (3) The silane-modified CoFe2O4@SiO2 and water were mixed and ultrasonically dispersed for 10 min at an ultrasonic power of 500 W. After cooling to room temperature, a suspension was obtained. The suspension was then added to the ethylene-vinyl acetate emulsion and ultrasonically dispersed for 30 min at an ultrasonic power of 300 W, so that the CoFe2O4@SiO2 was uniformly dispersed in the emulsion and reacted with the polymer particles. After completion, component B was obtained and set aside.

[0046] (4) Add the components A and B to the mixer and stir at 1200 r / min for 10 minutes to obtain the cement-based coating material.

[0047] (5) Apply the coating from step (4) to a concrete test block with a thickness of 3 mm and cure it at 23 °C for 3, 7 and 28 days.

[0048] The properties of the cement-based coating material prepared in this embodiment were tested, and the results are shown in the table below. Specifically: elongation at break and tensile strength were measured according to ASTM D638; bond strength was measured according to GB / T 23445-2009; 3.5GHz shielding effectiveness was measured according to ASTM D4935; and surface drying time was measured according to GB / T1728.

[0049]

[0050] Example 2 1. A method for preparing silane-modified magnetic core-shell nanoparticles CoFe2O4@SiO2, comprising the following steps: (1) Preparation of CoFe2O4 magnetic nanoparticles: (a) Iron source and cobalt source were dissolved in 80 mL of deionized water at a ratio of 1.6:1 and stirred uniformly at 100 °C. This solution is denoted as solution a. (b) PEG (6000) was added as a dispersant to a certain amount of ammonia water (NH3·H2O) and stirred uniformly at 100 °C. This solution is denoted as solution b. (c) Solution b was added dropwise to solution a and stirred for 1 h. This mixed solution was refluxed in a boiling water bath for 2 h. (d) The obtained black precipitate was rapidly separated by a magnetic field and washed with deionized water until neutral (pH = 7). It was then vacuum dried at 100 °C for 12 h and sintered at 350 °C for 12 h to remove residual carbon.

[0051] (2) Silica coating of CoFe2O4 nanoparticles: The CoFe2O4 magnetic nanoparticles (0.2 g) obtained in step (2) were ultrasonically dispersed in 150 mL of citric acid solution. The citric acid-modified magnetic nanoparticles were collected by magnetic field separation, washed three times with alcohol, dispersed in a mixed solution of alcohol and deionized water (volume ratio 4:1), and ultrasonicated for 2 h to obtain a CoFe2O4 dispersion, which was labeled as solution c. A certain amount of NH3·H2O was added to solution c to adjust the pH value of the solution. When the pH reached 9, TEOS (3 mL) was added dropwise to the above suspension c under ultrasonic action. Subsequently, the above mixture was stirred at room temperature for 12 h. The obtained powder was collected by magnet, washed with deionized water until neutral (pH = 7), and vacuum dried at 100 °C for 12 h.

[0052] (3) Surface modification of core-shell material: CoFe2O4@SiO2 nanoparticles were ultrasonically dispersed in an ethanol solution (concentration 2wt%) of silane coupling agent KH-560 for 30 min and vacuum dried at 60 °C for 12 h.

[0053] 2. A method for preparing a cement-based composite coating with electromagnetic shielding function, comprising the following steps: (1) Prepare the following raw materials: 10 parts by weight of ordinary silicate cement, 35 parts by weight of fly ash, 50 parts by weight of vinyl acetate-ethylene copolymer emulsion (VAE, solid content 40%), 0.05 parts by weight of silane-modified CoFe2O4@SiO2, and 40 parts by weight of water.

[0054] (2) Mix the cement and fly ash and then mechanically stir for 10 min to form component A for later use.

[0055] (3) The silane-modified CoFe2O4@SiO2 and water were mixed and ultrasonically dispersed for 10 min at an ultrasonic power of 500 W. After cooling to room temperature, a suspension was obtained. The suspension was then added to the vinyl acetate-ethylene copolymer emulsion and ultrasonically dispersed for 30 min at an ultrasonic power of 300 W, so that the CoFe2O4@SiO2 was uniformly dispersed in the emulsion and reacted with the polymer particles. After completion, component B was obtained and set aside.

[0056] (4) Add the components A and B to the mixer and stir at 1200 r / min for 10 minutes to obtain the cement-based material.

[0057] The properties of the cement-based coating prepared in this embodiment were tested. The shielding effectiveness at 1.0 GHz was 18.5 dB, while the shielding effectiveness of the cement-based coating without magnetic core-shell particles was less than 5 dB. Regarding alkali resistance, the coating without magnetic core-shell particles exhibited chalking.

[0058] Example 3 1. A method for preparing silane-modified magnetic core-shell nanoparticles CoFe2O4@SiO2, comprising the following steps: (1) Preparation of CoFe2O4 magnetic nanoparticles: (a) Iron source and cobalt source were dissolved in 100 mL of deionized water at a ratio of 1.8:1 and stirred uniformly at 80 °C. This solution is denoted as solution a. (b) PEG (6000) was added as a dispersant to a certain amount of ammonia water (NH3·H2O) and stirred uniformly at 80 °C. This solution is denoted as solution b. (c) Solution b was added dropwise to solution a and stirred for 1 h. This mixed solution was refluxed in a boiling water bath for 2 h. (d) The obtained black precipitate was rapidly separated by a magnetic field and washed with deionized water until neutral (pH = 7). It was then vacuum dried at 80 °C for 12 h and sintered at 550 °C for 12 h to remove residual carbon.

[0059] (2) Silica coating of CoFe2O4 nanoparticles: The CoFe2O4 magnetic nanoparticles (0.2 g) obtained in step (2) were ultrasonically dispersed in 100 mL of citric acid solution. The citric acid-modified magnetic nanoparticles were collected by magnetic field separation, washed three times with alcohol, dispersed in a mixed solution of alcohol and deionized water (volume ratio 4:1), and ultrasonicated for 2 h to obtain a CoFe2O4 dispersion, which was labeled as solution c. A certain amount of NH3·H2O was added to solution c to adjust the pH value of the solution. When the pH reached 9, TEOS (3 mL) was added dropwise to the above suspension c under ultrasonic action. Subsequently, the above mixture was stirred at room temperature for 12 h. The obtained powder was collected by magnet, washed with deionized water until neutral (pH = 7), and vacuum dried at 80 °C for 12 h.

[0060] Surface modification of core-shell material: CoFe2O4@SiO2 nanoparticles were ultrasonically dispersed in an ethanol solution (2wt%) of silane coupling agent KH-560 for 30 min and then vacuum dried at 60 °C for 12 h.

[0061] 2. A method for preparing a cement-based composite coating with electromagnetic shielding function, comprising the following steps: (1) Prepare the following raw materials: 15 parts by weight of rapid hardening sulfoaluminate cement, 20 parts by weight of silica fume, 35 parts by weight of VAE / PA blend (mass ratio 1:1) emulsion, 0.35 parts by weight of silane-modified CoFe2O4@SiO2 magnetic nanoparticles, 30 parts by weight of water, 0.08 parts by weight of sodium tripolyphosphate dispersant, and 0.56 parts by weight of polyether defoamer.

[0062] (2) Mix the cement and silica fume and then mechanically stir for 10 min to form component A for later use.

[0063] (3) The silane-modified CoFe2O4@SiO2 and water were mixed and ultrasonically dispersed for 10 min at an ultrasonic power of 500 W. After cooling to room temperature, a suspension was obtained. The suspension was then added to the VAE / PA blend emulsion and ultrasonically dispersed for 30 min at an ultrasonic power of 300 W, so that the CoFe2O4@SiO2 was uniformly dispersed in the emulsion and reacted with the polymer particles. After completion, component B was obtained and set aside.

[0064] (4) Add the components A and B to the mixer and stir at 1200 r / min for 10 minutes to obtain the cement-based material.

[0065] The properties of the cement-based material prepared in this embodiment were tested, and the results are shown in the table below. After adding the dispersant and allowing the slurry to stand for 2 hours, the settling rate was less than 3%, while the settling rate without the dispersant was greater than 15%. The coating achieved a high-frequency shielding effectiveness of 31.8 dB for 6.0 GHz, demonstrating a significant shielding effect against broadband electromagnetic waves.

[0066] Example 4 1. A method for preparing CoFe2O4, comprising the following steps: (a) Iron and cobalt sources were dissolved in 100 mL of deionized water at a ratio of 2:1 and stirred uniformly at 70 °C. This solution is denoted as solution a. (b) PEG (6000) was added as a dispersant to a certain amount of ammonia water (NH3·H2O) and stirred uniformly at 70 °C. This solution is denoted as solution b. (c) Solution b was added dropwise to solution a and stirred for 1 h. This mixed solution was refluxed in a boiling water bath for 2 h. (d) The resulting black precipitate was rapidly separated by a magnetic field and washed with deionized water until neutral (pH = 7). It was then vacuum dried at 80 °C for 12 h and subsequently sintered at 350 °C for 12 h to remove residual carbon.

[0067] 2. A method for preparing a cement-based composite coating with electromagnetic shielding function, the same as in Example 1, comprising the following steps: (1) Prepare the following raw materials: 20 parts by weight of rapid hardening sulfoaluminate cement, 25 parts by weight of calcium carbonate powder, 40 parts by weight of polyacrylate emulsion / vinyl acetate-ethylene (PA / VAE) blend emulsion (mass ratio 3:1), 0.25 parts by weight of CoFe2O4 magnetic nanoparticles, 25 parts by weight of water, 0.15 parts by weight of polycarboxylate superplasticizer, and 0.45 parts by weight of hydroxypropyl methylcellulose ether.

[0068] (2) Mix the cement and calcium carbonate powder and stir mechanically for 10 min to form component A for later use.

[0069] (3) The CoFe2O4 magnetic nanoparticles were mixed with water and then ultrasonically dispersed for 10 min at an ultrasonic power of 500 W. After cooling to room temperature, a suspension was obtained. The suspension was then added to the ethylene-vinyl acetate emulsion and ultrasonically dispersed for 30 min at an ultrasonic power of 300 W. Component B was obtained after the process and was ready for use.

[0070] (4) Add the components A and B to the mixer and stir at 1200 r / min for 10 minutes to obtain the cement-based coating material.

[0071] (5) Apply the coating from step (4) to a concrete test block with a thickness of 3 mm and cure at 23 °C for 28 days.

[0072] The properties of the cement-based coating material prepared in this embodiment were tested. After 28 days, the electromagnetic shielding effectiveness decreased by ≥40%, while the electromagnetic shielding effectiveness of the CoFe2O4@SiO2 group decreased by ≤5%. This indicates that the silica coating provides excellent protection and effectively prevents Ca(OH)2 from penetrating and corroding the magnetic core.

[0073] The effect of the amount of different magnetic core-shell CoFe2O4@SiO2 nanoparticles added on the electromagnetic shielding effectiveness is shown in the table below:

[0074] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A nano-core-shell type CoFe2O4@SiO2 / polymer cement-based composite coating material with electromagnetic shielding function, characterized in that, This cement-based coating comprises two separately stored components, A and B; wherein: Component A comprises: 5.0 to 25.0 parts by weight of cement and 10.0 to 35.0 parts by weight of inorganic filler; Component B comprises: 20.0-50.0 parts by weight of polymer emulsion, 0.05-0.35 parts by weight of experimentally prepared surface-modified CoFe2O4@SiO2 magnetic nanoparticles, and 10.0-40.0 parts by weight of water; The CoFe2O4@SiO2 nanoparticles are core-shell magnetic nanoparticles with CoFe2O4 as the core and SiO2 as the shell, prepared in the laboratory. After surface modification with silane coupling agent KH-560, they are mixed with water to form a suspension. Then, the suspension is added to the polymer emulsion and ultrasonically dispersed to obtain component B.

2. The core-shell type CoFe2O4@SiO2 / polymer cement-based composite coating according to claim 1, characterized in that, The polymer emulsion is a vinyl acetate-ethylene copolymer emulsion (VAE), a polyacrylate emulsion (PA), or a blend of the two (PA / VAE), with a solid content of 40-60%.

3. The core-shell type CoFe2O4@SiO2 / polymer cement-based composite coating with electromagnetic shielding function as described in claim 1, characterized in that, The cement includes any one of ordinary silicate cement and rapid-hardening sulfoaluminate cement.

4. The core-shell type CoFe2O4@SiO2 / polymer cement-based composite coating with electromagnetic shielding function as described in claim 1, characterized in that, The inorganic filler includes any one of calcium carbonate powder, silica fume, and fly ash.

5. The core-shell type CoFe2O4@SiO2 / polymer cementitious composite coating according to claim 1, characterized in that, It also includes at least one of the following additives: defoamer (0.42-0.56 parts by weight), thickener (0.39-0.52 parts by weight), water reducer (0.12-0.16 parts by weight), and dispersant (0.06-0.08 parts by weight).

6. A method for preparing the core-shell type CoFe2O4@SiO2 / polymer cement-based composite coating according to any one of claims 1-5, characterized in that, Specific preparation methods include: S1. Preparation of core-shell magnetic nanoparticles (CoFe2O4@SiO2); Preparation of S11. CoFe2O4 magnetic fluid; Specifically: (a) Iron and cobalt sources were dissolved in deionized water according to a specific ratio and stirred uniformly at 70-90°C; this solution is denoted as solution a. (b) PEG (6000) was added as a dispersant to a certain amount of ammonia water (NH3·H2O) and stirred uniformly at 70-90°C; this solution is denoted as solution b. (c) Solution a was added dropwise to solution b and stirred for 1-2 h. This mixed solution was refluxed in a boiling water bath for 2-5 h. (d) The resulting black precipitate was rapidly separated by a magnetic field and washed with deionized water until neutral (pH = 7). It was then vacuum dried at 80-100°C for 12 h, followed by sintering at 350-550°C for 12-24 h to remove residual carbon. (e) The obtained CoFe2O4 magnetic nanoparticles (0.3-0.5 g) were ultrasonically dispersed in a solution of 200-500 g. The magnetic nanoparticles modified with citric acid were collected by magnetic field separation in mL of citric acid solution. After being washed three times with alcohol, they were dispersed in a mixed solution of alcohol and deionized water (volume ratio 5:1, 4:1, 3:1) and sonicated for 2 to 5 h to obtain CoFe2O4 magnetic fluid. This fluid solution was labeled as solution c. S12. CoFe2O4 nanoparticles coated with silica; Specifically, a certain amount of NH3·H2O is added to solution c to adjust the pH value of the solution. When the pH reaches 7 to 9, TEOS (3 to 5 mL) is added dropwise to the above suspension c under ultrasonic action. Subsequently, the above mixture is stirred at room temperature for 12 to 24 h. The obtained powder is collected by a magnet, washed with deionized water until neutral (pH = 7), and vacuum dried at 80 to 100 °C for 12 to 24 h. Surface modification of S13. CoFe2O4@SiO2 magnetic nanoparticles; CoFe2O4@SiO2 nanoparticles were ultrasonically dispersed in an ethanol solution (2wt%) of silane coupling agent KH-560 for 30-60 min and then vacuum dried at 60 °C for 10-20 h. S2. Preparation of cement-based composite coating with electromagnetic shielding function; The cement and inorganic filler in the cement-based material with electromagnetic shielding function according to any one of claims 1-5 are mixed evenly to form component A, which is then set aside. The magnetic nanoparticles in the cement-based material with electromagnetic shielding function according to any one of claims 1-5 are mixed evenly with water to form a suspension. Then, the suspension is added to the polymer emulsion and ultrasonically dispersed. After completion, component B is obtained and set aside. Before use, mix components A and B evenly to obtain the cement-based material.

7. The method for preparing cement-based coatings according to claim 6, characterized in that, The A component further includes the additives of the cement-based coating as described in claim 6; the ultrasonic power is 200-800W and the time is 25-55min.

8. The cement-based coating obtained by the preparation method according to any one of claims 7 to 8 is used for brushing on concrete surfaces.

9. The application according to claim 7, characterized in that, The cement-based coating is used as a surface coating for concrete in sensitive locations such as hospitals, laboratories, and data centers.

10. The application according to claim 8, characterized in that, The coating thickness is 3~5mm.

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