CFRP surface double-gradient multifunctional protective coating and preparation method thereof

Abstract

The invention discloses a CFRP surface double-gradient multifunctional protective coating and a preparation method. The protective coating is characterized by being composed of fluoroplastic, ferromagnetic phase particles, a carbon wrapping layer of the ferromagnetic phase particles and a nano conductive particle double-gradient concentration structure. The double-gradient protective coating has the characteristics of electric conduction, magnetic conduction, heat conduction and corrosion resistance, the overall shielding performance is flexible and adjustable, and the cost is reduced while the multifunctional performance is improved.

Description

Technical Field

[0001] The present invention relates to a protective coating preparation technology, in particular to a protective coating that can take into account multiple performances, specifically a CFRP surface dual-gradient multifunctional protective coating and a preparation method thereof. Technical Background

[0002] In recent years, carbon fiber composites have been widely used in aerospace, military, and other fields due to their superior properties, such as high specific strength and low density. However, due to the growing use of electronic information equipment and the increasing frequency of electromagnetic interference, CFRP components inherently have poor electrical and magnetic permeability and cannot meet electromagnetic shielding performance requirements.

[0003] To enhance the electromagnetic shielding performance of CFRP components, single electromagnetic protective coatings are used that utilize metallization on the substrate surface to enhance overall electromagnetic shielding performance. While these coatings possess a certain level of electromagnetic protection, they are susceptible to wear or corrosion failure in complex environments, resulting in overall performance degradation and severely restricting the service life and effectiveness of CFRP components in these environments. Furthermore, single metal electromagnetic protective coatings are affected by impedance matching and are unable to simultaneously address performance requirements such as high electrical conductivity, high magnetic permeability, and a wide electromagnetic shielding band, resulting in limited electromagnetic wave attenuation. In summary, existing electromagnetic protective coatings exhibit poor electromagnetic shielding performance and corrosion resistance, making it difficult to achieve a balance between these two requirements. This makes them unable to effectively address the issue of CFRP components being simultaneously subject to electromagnetic interference and dielectric erosion in complex environments. Summary of the Invention

[0004] The purpose of the present invention is to address the problem that CFRP materials cannot meet the protection requirements of strong acids, strong bases, organic solvents and fluorides, as well as the shielding of interfering electromagnetic waves in the fields of aerospace, weapons and electronic equipment. A dual-gradient multifunctional protective coating on the CFRP surface and a preparation method are invented. The coating adopts a dual-concentration gradient structure design and introduces fluoroplastics, nano-conductive particles and carbon-encapsulated ferromagnetic phase particles to have high electrical conductivity, magnetic conductivity, thermal conductivity and corrosion resistance. It can achieve high corrosion resistance in complex environments and high electromagnetic shielding performance in a wide band, and is suitable for CFRP surface protection with complex service environments and electromagnetic shielding performance requirements.

[0005] One of the technical solutions of the present invention is:

[0006] A double-gradient multifunctional protective coating for CFRP surface, characterized in that it consists of a fluoroplastic 1 and ferromagnetic phase particles 2 and nano-conductive particles 4 regularly dispersed therein, the surface of the ferromagnetic phase particles 2 being coated with a carbon coating layer 3, and the ferromagnetic phase particles 2 and the nano-conductive particles 4 being respectively dispersed in the fluoroplastic 1 in an anti-gradient manner; the fluoroplastic 1 being one of PTFE, PFA, and FEP; the ferromagnetic phase particles 2 being metal particles formed of one or more of iron, nickel, and cobalt, and being dispersed in the fluoroplastic according to a set concentration gradient to improve the magnetic permeability and electromagnetic absorption loss of the matrix material; the carbon coating layer 3 being coated on the surface of the ferromagnetic phase particles, and being amorphous carbon layer formed by dispersion, coating, pyrolysis, and carbonization of one of glucose, sucrose, and fructose, isolating the ferromagnetic phase particles 2 from the environment, thereby improving the corrosion resistance of the ferromagnetic phase particles; the nano-conductive particles 4 being composed of one of silver, copper, and gold, and being dispersed in the fluoroplastic 1 according to a set concentration gradient to improve the thermal conductivity, electrical conductivity, and electromagnetic absorption loss of the matrix material.

[0007] The particle size of the ferromagnetic phase particles is distributed in the range of 1 to 2 μm.

[0008] The particle size distribution of the nano conductive particles is 40-70 nm.

[0009] The second technical solution of the present invention is:

[0010] A method for preparing a dual-gradient multifunctional protective coating on a CFRP surface, characterized in that it comprises the following steps:

[0011] Step 1: adding a carbon source to the solution prepared from the ferromagnetic phase particles, with the mass of the carbon source to the total mass of the metal salt in the solution being 1:1, adjusting the pH value to 8-9, and stirring at 300 r / min for 30 minutes to obtain a uniform mixed solution;

[0012] Step 2: transferring the mixed solution in step 1 into an autoclave, and performing a solvent thermal reaction at 160-200° C. for 6 hours to allow the metal particles to complex in the solvent to obtain a ferromagnetic phase particle precursor;

[0013] Step 3: Place the ferromagnetic phase particle precursor in step 2 in an inert gas, heat it to 600-700° C., maintain the temperature for 2 hours, form a uniform carbon coating layer 3 on the surface of the ferromagnetic phase particles, and collect the carbon-coated ferromagnetic phase particles 2 after cooling;

[0014] Step 4: Divide the 60wt% fluoroplastic aqueous dispersion into 5 to 7 parts, add carbon-coated ferromagnetic phase particles and nano-conductive particles to form a gradient spray solution with different particle concentrations, stir each layer with a magnetic stirrer at 400r / min for 20min, and ultrasonically disperse for 30min to ensure uniform particle dispersion;

[0015] Step 5: Grind the CFRP surface with 400-600 grit sandpaper for 10 minutes to remove surface impurities and improve the adhesion of the gradient spray liquid described in step 4;

[0016] Step 6: Spray the gradient spray liquid described in step 4 onto the CFRP surface through a pneumatic spray gun with a nozzle diameter of 0.2 to 0.4 mm and a distance of 12 to 16 cm from the nozzle to the material surface. Spray 2 to 3 times in a vertical cross direction, with a spray thickness of 4 to 5 μm per layer. The coating material is dried in hot air at 80°C for 8 to 10 minutes to prevent the lower gradient coating from being interfered with by the upper spray liquid. After each spraying, the spray liquid in the pneumatic spray gun needs to be replaced with the next concentration gradient spray liquid. This step is repeated the same number of times as the number of gradient spray liquids described in step 4.

[0017] In step seven, the sprayed CFRP material is cured at a certain temperature and under the protection of an inert gas to obtain a double-gradient multifunctional protective coating on the CFRP surface. The temperature rise is controlled at 5°C / min to prevent the nano-conductive particles from agglomerating.

[0018] When the fluoroplastic aqueous dispersion is a PTFE dispersion, the curing temperature is 380°C and the curing time is 30 minutes; when the fluoroplastic aqueous dispersion is a PFA dispersion, the curing temperature is 380°C and the curing time is 15 minutes; when the fluoroplastic aqueous dispersion is a FRP dispersion, the curing temperature is 300°C and the curing time is 10 minutes.

[0019] If the ferromagnetic phase particles are composed of a single metal, the composition of the solution prepared from the ferromagnetic phase particles is 0.06 to 0.07 mol / L of nitrate of the metal cations contained in the ferromagnetic phase particles; if the ferromagnetic phase particles are composed of multiple metals, the content of each nitrate in the solution prepared from the ferromagnetic phase particles is 0.06 to 0.07 mol / L, the solvent is deionized water, and the pH is adjusted to 8 to 9 using NaOH;

[0020] The outermost layer of the gradient spraying liquid has the highest content of ferromagnetic phase particles and the lowest content of nano-conductive particles; the gradient spraying liquid closest to the CFRP substrate has the lowest content of ferromagnetic phase particles and the highest content of nano-conductive particles, forming a dual-gradient structure with opposite concentration gradients of ferromagnetic phase particles and nano-conductive particles.

[0021] The double-gradient multifunctional protective coating on the CFRP surface is used for protection against strong acids, strong alkalis, organic solvents and fluorides in aerospace, weapons and electronic equipment, as well as for shielding interfering electromagnetic waves.

[0022] The double-gradient multifunctional protective coating on the surface of CFRP has a shielding effectiveness of 80-90dB against electromagnetic waves in the 8-12GHz band; the self-corrosion current of the double-gradient multifunctional protective coating on the surface of CFRP in a neutral solution is 10 -8~10 -9 A.cm 2 .

[0023] The beneficial effects of the present invention are:

[0024] The fluoroplastic of the protective coating of the present invention is composed of one of PTFE, PFA, and FEP, and has good corrosion resistance and chemical stability to strong acids, strong bases, organic solvents and fluorides. At the same time, the surface has wear resistance, friction reduction and good hydrophobicity, which significantly extends the effective corrosion resistance time of the coating.

[0025] The nano-conductive particles of the protective coating of the present invention are composed of one of silver, copper and gold. Through their own high conductivity, they construct a conductive network in the coating, enhance the overall reflection of electromagnetic waves by the coating, and realize multiple scattering and reflection paths of electromagnetic waves under the concentration gradient structure.

[0026] The ferromagnetic phase particles of the protective coating of the present invention are metal particles formed by one or more of iron, nickel, and cobalt, which provide the protective coating with high magnetic permeability characteristics, enhance the ability to resist magnetic loss of electromagnetic waves, and at the same time realize a multi-scale magnetic conductive network under a concentration gradient structure, thereby enhancing the multiple absorption losses of electromagnetic waves.

[0027] The carbon coating of the protective coating of the present invention is an amorphous carbon layer formed by dispersion coating and pyrolysis carbonization using one of glucose, sucrose and fructose as a carbon source. It has good chemical stability and oxidation resistance, and forms a core-shell structure with ferromagnetic phase particles, effectively improving particle dispersion and metal interface corrosion, and enhancing the overall coating dielectric loss and long-term corrosion resistance.

[0028] The protective coating of the present invention organically combines fluoroplastics, nano-conductive particles, ferromagnetic phase particles and a carbon coating layer, and adopts a dual-concentration gradient structure of nano-conductive particles and carbon-coated ferromagnetic phase particles to construct a protective coating with efficient magnetic-electric synergistic electromagnetic shielding and long-lasting corrosion resistance, thereby solving the problems of the existing CFRP surface protective coating with a single structure, poor shielding performance and poor corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the double-gradient multifunctional protective coating on the CFRP surface of the present invention.

[0030] Figure 2 This is a comparison chart of the electromagnetic shielding effects of the double-gradient multifunctional protective coating on the CFRP surface and the PTFE protective coating on the CFRP surface. Specific implementation methods

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments. Obviously, the embodiments described are only a part of the present invention, rather than all of the embodiments.

[0032] like Figure 1 shown.

[0033] A method for preparing a dual-gradient multifunctional protective coating on a CFRP surface mainly includes preparing a ferromagnetic phase particle precursor solution, preparing carbon-coated ferromagnetic phase particles, preparing a gradient spraying solution, pre-treating the CFRP surface, and curing the protective coating. The structure obtained by the preparation is as follows: Figure 1 As shown, it is composed of fluoroplastic 1 and ferromagnetic phase particles 2 and nano-conductive particles 4 regularly dispersed therein. The surface of ferromagnetic phase particles 2 is coated with a carbon coating 3. Ferromagnetic phase particles 2 and nano-conductive particles 4 are respectively dispersed in the fluoroplastic 1 in an anti-gradient manner.

[0034] Example 1.

[0035] A dual-gradient multifunctional protective coating for CFRP surfaces comprises a fluoroplastic 1, ferromagnetic particles 2 and their carbon coating 3, and nano-conductive particles 4. The ferromagnetic particles are 1 μm iron spherical particles, the fluoroplastic is PTFE, and the nano-conductive particles are 40 nm silver spherical particles. The dual-gradient multifunctional protective coating for CFRP surfaces of this embodiment is prepared by the following steps:

[0036] 1. Preparation of ferromagnetic phase particle precursor. 0.07 mol / LFe was prepared using deionized water and Fe(NO3)3·9H2O reagent. 3+ The solution was prepared by adding 29 g / L glucose to adjust the pH to 8-9. The solution was stirred at 300 r / min with a magnetic stirrer for 30 min, and then transferred to an autoclave for thermal reaction at 160 ° C for 6 h to obtain a ferromagnetic phase particle precursor.

[0037] 2. Preparation of carbon-coated ferromagnetic phase particles. The ferromagnetic phase particle precursor was placed in a N2 environment, heated to 600℃, and maintained at this temperature for 2 hours to carbonize the glucose and reduce the Fe 3+ The Fe particles are uniformly coated with a carbon layer 3, and carbon-coated ferromagnetic phase particles are obtained after cooling.

[0038] III. Preparation of Gradient Spray Fluid. A 60wt% aqueous PTFE dispersion was divided into five portions, each containing 20wt% nanosilver spheres; 15wt% nanosilver spheres and 5wt% carbon-coated ferromagnetic particles; 10wt% nanosilver spheres and 10wt% carbon-coated ferromagnetic particles; 5wt% nanosilver spheres and 15wt% carbon-coated ferromagnetic particles; and 20wt% carbon-coated ferromagnetic particles. Each portion was stirred at 400 rpm for 20 minutes using a magnetic stirrer, followed by ultrasonic dispersion for 30 minutes to obtain five gradient spray fluids.

[0039] 4. CFRP surface pretreatment: Use 400-grit sandpaper to polish the CFRP surface for 10 minutes to remove impurities on the material surface and improve the coating bonding performance.

[0040] V. Curing of the CFRP Surface Protective Coating. A spray solution containing 20 wt% nanosilver spherical particles, a spray solution containing 15 wt% nanosilver spherical particles and 5 wt% carbon-coated ferromagnetic particles, a spray solution containing 10 wt% nanosilver spherical particles and 10 wt% carbon-coated ferromagnetic particles, a spray solution containing 5 wt% nanosilver spherical particles and 15 wt% carbon-coated ferromagnetic particles, and a spray solution containing 20 wt% carbon-coated ferromagnetic particles were sequentially sprayed onto the CFRP surface using a pneumatic spray gun. The nozzle diameter was 0.3 mm, and the distance between the nozzle and the material surface was 14 cm. Two passes were applied in a perpendicular, cross-directional direction, with each layer sprayed to a thickness of 4 μm. After each layer was applied, the entire material was dried in hot air at 80°C for 8 minutes. Finally, the entire material was placed in an N2 environment and maintained at 380°C for 30 minutes, with a temperature rise controlled at 5°C / min, completing the protective coating curing process. This resulted in a CFRP substrate with a dual-gradient multifunctional protective coating on its surface, ready for subsequent use.

[0041] Example 2.

[0042] A dual-gradient multifunctional protective coating for CFRP surfaces, comprising fluoroplastics, ferromagnetic phase particles and their carbon coating, and nano-conductive particles. The ferromagnetic phase particles are 1μm iron-nickel alloy spherical particles, the fluoroplastic is PFA, and the nano-conductive particles are 60nm copper spherical particles. The preparation process includes:

[0043] Preparation of ferromagnetic phase particle precursor: 0.07 mol / L Fe 3+ and 0.07 mol / L Ni 3+ The solution was mixed and 29 g / L sucrose was added to adjust the pH to 8-9. The solution was stirred at 300 r / min with a magnetic stirrer for 30 minutes, and then transferred to an autoclave for thermal reaction at 180° C. for 6 hours to obtain a ferromagnetic phase particle precursor.

[0044] Preparation of carbon-coated ferromagnetic phase particles: The ferromagnetic phase particle precursor is placed in a N2 environment, heated to 700°C, and maintained at this temperature for 2 hours to uniformly form a carbon coating layer on the ferromagnetic phase particles. After cooling, carbon-coated ferromagnetic phase particles are obtained.

[0045] Gradient spray solution preparation: A 60wt% PFA aqueous dispersion was divided into five portions and added with: 20wt% nano-copper spherical particles; 15wt% nano-copper spherical particles and 5wt% carbon-coated ferromagnetic particles; 10wt% nano-copper spherical particles and 10wt% carbon-coated ferromagnetic particles; 5wt% nano-copper spherical particles and 15wt% carbon-coated ferromagnetic particles; and 20wt% carbon-coated ferromagnetic particles. Each portion was stirred at 400 rpm for 20 minutes using a magnetic stirrer and then ultrasonically dispersed for 30 minutes to obtain five gradient spray solutions.

[0046] CFRP surface pretreatment: Grind the CFRP surface with 600-grit sandpaper for 10 minutes to remove impurities on the material surface and improve the coating bonding performance.

[0047] Curing of the CFRP surface protective coating: A spray solution containing 20 wt% nano-copper spherical particles, a spray solution containing 15 wt% nano-copper spherical particles and 5 wt% carbon-coated ferromagnetic phase particles, a spray solution containing 10 wt% nano-copper spherical particles and 10 wt% carbon-coated ferromagnetic phase particles, a spray solution containing 5 wt% nano-copper spherical particles and 15 wt% carbon-coated ferromagnetic phase particles, and a spray solution containing 20 wt% carbon-coated ferromagnetic phase particles were sequentially sprayed onto the CFRP surface using a pneumatic spray gun. The nozzle diameter was 0.3 mm, and the distance between the nozzle and the material surface was 14 cm. The spraying was carried out in three perpendicular cross-directions, with each layer sprayed with a thickness of 4.5 μm. After each layer was sprayed, the entire material was dried in hot air at 80°C for 9 minutes. Finally, the entire material was placed in a nitrogen atmosphere with a temperature rise controlled at 5°C / min and maintained at 380°C for 15 minutes to complete the protective coating curing process. This resulted in the CFRP substrate with a dual-gradient multifunctional protective coating on the surface of this example for subsequent use.

[0048] Example 3.

[0049] A dual-gradient multifunctional protective coating for CFRP surfaces, comprising fluoroplastics, ferromagnetic phase particles and their carbon coating, and nano-conductive particles. The ferromagnetic phase particles are 2μm cobalt alloy spherical particles, the fluoroplastic is FEP, and the nano-conductive particles are 70nm gold spherical particles. The preparation process includes:

[0050] Preparation of ferromagnetic phase particle precursor: 0.07 mol / L Fe 3+ and 0.07 mol / L Ni 3+ The solution was mixed and 29 g / L fructose was added to adjust the pH to 8-9. The solution was stirred at 300 r / min with a magnetic stirrer for 30 minutes, and then transferred to an autoclave for thermal reaction at 200° C. for 6 hours to obtain a ferromagnetic phase particle precursor.

[0051] Preparation of carbon-coated ferromagnetic phase particles: The ferromagnetic phase particle precursor is placed in a N2 environment, heated to 650°C, and maintained at this temperature for 2 hours to uniformly form a carbon coating layer on the ferromagnetic phase particles. After cooling, carbon-coated ferromagnetic phase particles are obtained.

[0052] Preparation of a gradient spray solution: Divide a 60wt% aqueous FEP dispersion into 5-7 portions (5 portions are used as an example). Add 20wt% nanogold spherical particles; 15wt% nanogold spherical particles and 5wt% carbon-coated ferromagnetic particles; 10wt% nanogold spherical particles and 10wt% carbon-coated ferromagnetic particles; 5wt% nanogold spherical particles and 15wt% carbon-coated ferromagnetic particles; and 20wt% carbon-coated ferromagnetic particles, respectively. Each portion was stirred at 400 rpm for 20 minutes using a magnetic stirrer and then ultrasonically dispersed for 30 minutes to obtain five gradient spray solutions.

[0053] CFRP surface pretreatment: Grind the CFRP surface with 500-grit sandpaper for 10 minutes to remove impurities on the material surface and improve the coating bonding performance.

[0054] Curing of the CFRP surface protective coating: A spray solution containing 20 wt% nano-gold spherical particles, a spray solution containing 15 wt% nano-gold spherical particles and 5 wt% carbon-coated ferromagnetic phase particles, a spray solution containing 10 wt% nano-gold spherical particles and 10 wt% carbon-coated ferromagnetic phase particles, a spray solution containing 5 wt% nano-gold spherical particles and 15 wt% carbon-coated ferromagnetic phase particles, and a spray solution containing 20 wt% carbon-coated ferromagnetic phase particles were sequentially sprayed onto the CFRP surface using a pneumatic spray gun. The nozzle diameter was 0.4 mm, and the distance between the nozzle and the material surface was 16 cm. The spraying was carried out in three perpendicular cross-directions, with each layer sprayed to a thickness of 5 μm. After each layer was sprayed, the entire material was dried in hot air at 80°C for 10 minutes. Finally, the entire material was placed in a nitrogen environment with a temperature rise controlled at 5°C / min and maintained at 300°C for 10 minutes to complete the protective coating curing process. This resulted in a CFRP substrate with a dual-gradient multifunctional protective coating on the surface for subsequent use.

[0055] Comparative Example 1.

[0056] The PTFE protective coating on the surface of ordinary CFRP is manufactured by the following steps:

[0057] 1. Substrate pretreatment: First, use sandpaper to polish the contaminants attached to the CFRP substrate surface, and then use anhydrous ethanol to ultrasonically clean the residual particles on the substrate surface until there are no obvious particles and contaminants on the substrate surface.

[0058] 2. PTFE aqueous solution spraying: Use the air pressure spraying process of PTFE aqueous solution to spray a 10μm thick aqueous solution layer on the pre-treated CFRP surface, and spray in a vertical cross direction.

[0059] 3. Curing of the PTFE protective coating: The sprayed substrate is cured at high temperature to form a 6μm thick PTFE surface coating on the CFRP surface. Curing must be carried out under inert gas protection.

[0060] The electromagnetic shielding effect of the obtained ordinary CFRP surface PTFE protective coating is similar to that of Example 1. Figure 2 shown.

[0061] The parts not involved in the present invention are the same as the existing technology or can be implemented by using the existing technology.

Claims

1. A dual-gradient multifunctional protective coating on a CFRP surface, characterized in that: The invention comprises a fluoroplastic (1) and ferromagnetic phase particles (2) and nano-conductive particles (4) regularly dispersed therein. The surface of the ferromagnetic phase particles (2) is coated with a carbon coating layer (3). The ferromagnetic phase particles (2) and the nano-conductive particles (4) are respectively dispersed in the fluoroplastic (1) in an anti-gradient manner. The fluoroplastic (1) is one of PTFE, PFA and FEP. The ferromagnetic phase particles (2) are metal particles formed by one or more of iron, nickel and cobalt, and are dispersed in the fluoroplastic according to a set concentration gradient to improve the magnetic permeability and electromagnetic absorption loss of the base material. The carbon coating layer (3) is coated on the surface of the ferromagnetic phase particles, and is made of one of glucose, sucrose and fructose as a carbon source. The amorphous carbon layer formed by dispersion, coating and pyrolysis carbonization isolates the ferromagnetic phase particles (2) from the environment, thereby improving the corrosion resistance of the ferromagnetic phase particles. The nano-conductive particles (4) are made of one of silver, copper and gold, and are dispersed in the fluoroplastic (1) according to a set concentration gradient to improve the thermal conductivity, electrical conductivity and electromagnetic absorption loss of the base material.

2. The CFRP surface dual-gradient multifunctional protective coating according to claim 1, characterized in that: The particle size of the ferromagnetic phase particles is distributed in the range of 1 to 2 μm.

3. The CFRP surface dual-gradient multifunctional protective coating according to claim 1, characterized in that: The particle size distribution of the nano conductive particles is 40-70 nm.

4. A method for preparing a dual-gradient multifunctional protective coating on a CFRP surface according to claim 1, characterized in that: It includes the following steps: Step 1: adding a carbon source to the solution prepared from the ferromagnetic phase particles, with the mass of the carbon source to the total mass of the metal salt in the solution being 1:1, adjusting the pH value to 8-9, and stirring at 300 r / min for 30 minutes to obtain a uniform mixed solution; Step 2: transferring the mixed solution in step 1 into an autoclave, and performing a solvent thermal reaction at 160-200° C. for 6 hours to allow the metal particles to complex in the solvent to obtain a ferromagnetic phase particle precursor; Step 3: placing the ferromagnetic phase particle precursor described in step 2 in an inert gas, heating it to 600-700° C., maintaining the temperature for 2 hours, forming a uniform carbon coating layer (3) on the surface of the ferromagnetic phase particles (2), and collecting the carbon-coated ferromagnetic phase particles after cooling; Step 4: Divide the 60wt% fluoroplastic aqueous dispersion into 5 to 7 parts, add carbon-coated ferromagnetic phase particles and nano-conductive particles to form a gradient spray solution with different particle concentrations, and stir the gradient spray solution with different particle concentrations using a magnetic stirrer at 400r / min for 20 minutes and ultrasonically disperse for 30 minutes to ensure uniform particle dispersion; Step 5: Grind the CFRP surface with 400-600 grit sandpaper for 10 minutes to remove surface impurities and improve the adhesion of the gradient spray liquid described in step 4; Step 6: Spray the gradient spray liquid described in step 4 onto the CFRP surface through a pneumatic spray gun. The nozzle diameter is 0.2-0.4 mm, the distance between the nozzle and the material surface is 12-16 cm, and the spraying is performed 2-3 times in a vertical cross direction. The thickness of each layer is 4-5 μm. The coating material is dried in hot air at 80°C for 8-10 minutes to prevent the lower gradient coating from being interfered with by the upper spray liquid. After each spraying is completed, the next concentration gradient spray liquid needs to be replaced. This step is repeated the same number of times as the number of gradient spray liquids described in step 4. In step seven, the sprayed CFRP material is cured at a certain temperature and under the protection of an inert gas to obtain a double-gradient multifunctional protective coating on the CFRP surface. The temperature rise is controlled at 5°C / min to prevent the nano-conductive particles from agglomerating.

5. The preparation method according to claim 4, characterized in that When the fluoroplastic aqueous dispersion is a PTFE dispersion, the curing temperature is 380°C and the curing time is 30 minutes; when the fluoroplastic aqueous dispersion is a PFA dispersion, the curing temperature is 380°C and the curing time is 15 minutes; when the fluoroplastic aqueous dispersion is a FRP dispersion, the curing temperature is 300°C and the curing time is 10 minutes.

6. The preparation method according to claim 4, characterized in that If the ferromagnetic phase particles (2) are composed of a single metal, the composition of the solution prepared from the ferromagnetic phase particles is 0.06-0.07 mol / L of nitrate of the metal cations contained in the ferromagnetic phase particles (2); if the ferromagnetic phase particles (2) are composed of multiple metals, the content of each nitrate in the solution prepared from the ferromagnetic phase particles is 0.06-0.07 mol / L, the solvent is deionized water, and NaOH is used to adjust the pH to 8-9.

7. The preparation method according to claim 4, characterized in that The content of ferromagnetic phase particles (2) in the gradient spraying liquid of the outermost layer is the highest, and the content of nano-conductive particles (4) is the lowest; the content of ferromagnetic phase particles (2) in the gradient spraying liquid closest to the CFRP substrate layer is the lowest, and the content of nano-conductive particles (4) is the highest, forming a double gradient structure with opposite concentration gradients of ferromagnetic phase particles (2) and nano-conductive particles (4).

8. The CFRP surface double-gradient multifunctional protective coating according to any one of claims 1 to 4, characterized in that: The double-gradient multifunctional protective coating on the CFRP surface is used in aerospace, weapons and electronic equipment to protect against strong acids, strong alkalis, organic solvents and fluorides, as well as to shield interfering electromagnetic waves.

9. The CFRP surface double-gradient multifunctional protective coating according to any one of claims 1 to 4, characterized in that: The double-gradient multifunctional protective coating on the surface of CFRP has a shielding effectiveness of 80-90dB for electromagnetic waves in the 8-12GHz band; the self-corrosion current of the double-gradient multifunctional protective coating on the surface of CFRP in a neutral solution is 10 -8 ~10 -9 A.cm 2 .

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