Preparation method of carbon-based wave-absorbing coating powder for plasma spraying, product and application thereof

Abstract

The application discloses a preparation method of carbon-based wave-absorbing coating powder for plasma spraying, a product and application thereof, and belongs to the technical field of functional materials. Lithium-aluminum-silicon gel powder, graphene oxide and N precursor are added into water and uniformly mixed, the obtained slurry is dried, and heat treatment is carried out in an inert atmosphere to obtain ceramic / graphene wave-absorbing powder; sodium silicate aqueous solution is added into the ceramic / graphene wave-absorbing powder, and stirring is uniformly carried out to obtain a wet mixed solid, and high-speed shearing is carried out to obtain a solid powder; the above operation is repeated, the finally obtained sample is dried and subjected to secondary heat treatment to obtain the carbon-based wave-absorbing coating powder for plasma spraying. Through a liquid sodium silicate foaming method, the outer layer of the ceramic / graphene wave-absorbing powder is coated with sodium silicate, the high-temperature resistance and oxidation resistance of the powder are improved, and the plasma spraying and the wave-absorbing coating are combined together, so that the application range of the coating is widened.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology, and particularly relates to a method for preparing carbon-based microwave absorbing coating powder for plasma spraying, as well as its products and applications. Background Technology

[0002] In the military field, with the rapid development of radar technology, weapons and military targets such as fighter jets have nowhere to hide. In order to improve the combat performance of military aircraft, it is necessary to make them stealthy to avoid radar detection. Electromagnetic absorbing coatings have become the most widely used stealth material on fighter jets and other aircraft due to their advantages such as simple process, convenient construction, low cost, significant effect and strong adaptability to target shape.

[0003] Magnetic absorbing materials are currently the most widely used electromagnetic absorbing materials in stealth fighters. While these materials offer advantages such as excellent absorption performance and low cost, their high density, poor high-temperature performance, and narrow absorption bandwidth limit their application. For high-speed fighters, after supersonic cruise, the compressed air causes the fuselage coating to remain at a consistently high temperature. According to a report by the UK Defence Assessment and Research Agency, as flight speeds exceed the speed of sound and continue to increase, the temperature of the fuselage coating begins to rise rapidly. At a cruise speed of Mach 2.2, the temperature of the fuselage coating can reach over 120 degrees Celsius, and can even reach a maximum of 207 degrees Celsius. Prolonged exposure to such high temperatures can cause demagnetization of the magnetic absorbing materials, leading to a decrease in absorption performance or even failure.

[0004] Therefore, the demagnetization problem of traditional magnetic loss materials makes them difficult to operate at high temperatures. Compared to magnetic loss materials, dielectric loss materials can maintain stable performance at high temperatures and have great research potential in high-temperature microwave absorbing materials. Graphene, as a popular dielectric loss material, also occupies a high proportion in microwave absorbing applications. However, unmodified graphene and its derivatives, as microwave absorbing materials, have poor electromagnetic wave loss performance due to their excessively high dielectric constant, which is mismatched with air impedance. Furthermore, graphene is easily oxidized at high temperatures, necessitating the improvement of graphene's performance through composite materials. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for preparing carbon-based microwave absorbing coating powder for plasma spraying, as well as its products and applications.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing a carbon-based microwave absorbing coating powder for plasma spraying includes the following steps:

[0008] Lithium aluminum silicon gel powder, graphene oxide and N precursor were added to water and mixed. The resulting slurry was dried and then subjected to a heat treatment in an inert atmosphere to obtain ceramic / graphene microwave absorbing powder.

[0009] A sodium silicate aqueous solution is added to the ceramic / graphene microwave absorbing powder, and the mixture is stirred until a moist solid is obtained. This mixture is then subjected to high-speed shearing to obtain a solid powder. The above operation (repeatedly adding the sodium silicate aqueous solution to the powder and performing high-speed shearing) is repeated. The final sample is then dried and subjected to a secondary heat treatment to obtain a carbon-based microwave absorbing coating powder for plasma spraying. The repetition is performed three times.

[0010] Furthermore, the ratio of the lithium aluminum silicon gel powder, graphene oxide, N precursor and water is (1.5-2.5)g∶(2-3)g∶(0.5-1.5)g∶(70-90)mL.

[0011] Furthermore, the preparation method of the lithium aluminum silicon gel powder includes the following steps:

[0012] Ammonia was added dropwise to an aluminum salt aqueous solution until a boehmite sol was formed. Then, an aqueous lithium salt solution was added to the boehmite sol and stirred until homogeneous to obtain a lithium-aluminum solution.

[0013] Silica sol was added dropwise to the lithium-aluminum solution and stirred to obtain lithium-aluminum-silica sol. After drying and heat treatment, lithium-aluminum-silica gel powder was obtained.

[0014] Furthermore, the concentration of the aluminum salt aqueous solution is 1.5-2.5 mol / L, and the aluminum salt is Al(NO3)3·9H2O; the concentration of the lithium salt aqueous solution is 1.5-2.5 mol / L, and the lithium salt is LiNO3;

[0015] The mass molar ratio of the aluminum salt, lithium salt and silica sol is 1 mol: 1 mol: 400 mg;

[0016] The drying process refers to drying at 90-110℃ for 46-50 hours.

[0017] The heat treatment refers to heating at 750-850℃ for 10-14 hours.

[0018] Further, the preparation method of the graphene oxide is as follows: graphene multilayer sheets and conductive carbon black powder are mixed in a mass ratio of 2:1, and then 6-8 wt% sodium silicate aqueous solution is added to the mixture and stirred until homogeneous to obtain graphene oxide. The graphene multilayer sheets have a diameter of 3 μm and a thickness of 50-80 nm, and the conductive carbon black powder has a particle size of 200 nm.

[0019] The N precursor is urea or melamine.

[0020] Furthermore, the temperature of the primary heat treatment is 300-1300℃, and the inert gas is one or more of nitrogen, helium, neon and argon atmospheres; the secondary heat treatment refers to heating at 1000℃ for 8 hours.

[0021] Furthermore, the parameters for the high-speed shearing are: shearing rotor speed of 8000-30000 rpm and stirring time of 6-30 min.

[0022] The present invention also provides a carbon-based microwave absorbing coating powder for plasma spraying prepared by the above preparation method, wherein the particle size of the carbon-based microwave absorbing coating powder for plasma spraying is 30-70 μm.

[0023] This invention also provides a method for using carbon-based microwave absorbing coating powder for plasma spraying. The method involves spraying the carbon-based microwave absorbing coating powder using plasma spraying technology. The spraying parameters are as follows: powder feeding rate 10-30 g / min, actual plasma torch power 14-33 KW, spraying distance 3-12 cm, spraying speed and torch speed 10-25 cm / s, and solid-phase reaction temperature 650-1100℃.

[0024] The present invention also provides the application of a carbon-based microwave absorbing coating powder for plasma spraying in the preparation of microwave absorbing materials.

[0025] Compared with the prior art, the present invention has the following advantages and technical effects:

[0026] This invention prepares a composite electromagnetic absorbing material with a special ceramic / graphene coating structure, which alleviates the high impedance matching characteristics of reduced graphene oxide. By controlling the shear granulation linear velocity, the internal shear stress of the microparticles is adjusted, thereby controlling the number of graphene sheets in the coated microparticles and inducing slippage of the graphene sheets, resulting in changes in the size of the microparticles. This alleviates the high impedance matching characteristics of reduced graphene oxide, improves electromagnetic absorption performance, and thus adjusts the electromagnetic absorption performance of the material. Sodium silicate is coated onto the ceramic / graphene absorbing powder using a liquid sodium silicate foaming method, improving the powder's high-temperature resistance and oxidation resistance. Furthermore, combining plasma spraying with absorbing coatings broadens the application range of the coating.

[0027] The method of this invention has good repeatability, low cost, environmental friendliness, cleanliness and non-toxicity, and is easy to mass-produce. The synthesized ceramic / graphene aerogel absorbing material has a structure and morphology that are conducive to electromagnetic wave absorption, making it an ideal composite electromagnetic absorbing material that can be practically applied. Attached Figure Description

[0028] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0029] Figure 1 XRD phase analysis of the carbon-based microwave absorbing coating powder for plasma spraying prepared in Example 4; where (a) is the X-ray diffraction pattern; (b) is the infrared spectrum.

[0030] Figure 2 The surface of the sphere viewed by SEM transmission electron microscope of the carbon-based microwave absorbing coating powder for plasma spraying prepared in Example 4;

[0031] Figure 3 The morphology of the carbon-based microwave absorbing coating powder for plasma spraying prepared in Example 4;

[0032] Figure 4 The effect of the carbon-based microwave absorbing coating powder for plasma spraying prepared in Example 4 on the target material after plasma spraying;

[0033] Figure 5 The diagrams show the microwave absorption performance of the carbon-based microwave absorbing coating powders for plasma spraying prepared in Examples 1-4, where (a) is a schematic diagram of the microwave absorption performance of Example 1, (b) is a schematic diagram of the microwave absorption performance of Example 2, (c) is a schematic diagram of the microwave absorption performance of Example 3, and (d) is a schematic diagram of the microwave absorption performance of Example 4. Detailed Implementation

[0034] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0035] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0036] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0037] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0038] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0039] This invention employs a liquid sodium silicate foaming method to coat ceramic / graphene microwave absorbing powder, specifically including the following steps:

[0040] (1) Add aluminum salt to water to obtain an aluminum salt solution, heat the aluminum salt solution at 160-200℃, and add ammonia water dropwise to the aluminum salt solution while stirring until a borosilicate sol is formed.

[0041] (2) Add lithium salt to water to obtain lithium salt solution, and add the lithium salt solution to the boehmite sol and stir evenly to obtain lithium aluminum solution;

[0042] (3) Add SiO2 sol dropwise to the lithium aluminum solution and stir to obtain lithium aluminum silicon sol;

[0043] (4) The lithium aluminum silicon sol is dried to obtain lithium aluminum silicon precursor powder; the drying refers to drying at 90-110℃ for 46-50h.

[0044] (5) The lithium aluminum silicon precursor powder is heat-treated to obtain the lithium aluminum silicon gel powder; the heat treatment refers to heating at 750-850℃ for 10-14h.

[0045] (6) Add lithium aluminum silicon gel powder and graphene oxide into a mixing device, and add solvent and N precursor to mix evenly into a slurry. Dry the slurry to obtain a solid precursor, and put it into a heating device. Heat treat it in an inert atmosphere at 300-1300℃ (preferably 300℃, 700℃, 1000℃ or 1300℃, more preferably 1300℃) for 3-8 hours to obtain ceramic / graphene absorbing powder. The ceramic / graphene absorbing powder is graphene isolated and encapsulated by a nano-scale lithium aluminum silicon mixture. The lithium aluminum silicon mixture seals the oxidation channels of graphene, making it less likely for graphene to oxidize and fail at high temperatures.

[0046] The inert gas is one or more of nitrogen, helium, neon, and argon atmosphere.

[0047] (7) Add sodium silicate aqueous solution to ceramic / graphene microwave absorbing powder and stir to mix evenly to obtain wet mixed solid A; the amount of sodium silicate aqueous solution added is 6-8% of the mass of ceramic / graphene microwave absorbing powder, preferably 7%;

[0048] (8) The mixed solid A is sheared at high speed and dried to obtain solid powder A;

[0049] (9) Add sodium silicate aqueous solution to the solid powder A again to obtain a moist mixed solid B; the amount of sodium silicate aqueous solution added is 6-8% of the mass of the solid powder A, preferably 7%;

[0050] (10) The mixed solid B is sheared at high speed and dried to obtain solid powder B;

[0051] (11) Add sodium silicate aqueous solution to the solid powder B again to obtain a moist mixed solid C; the amount of sodium silicate aqueous solution added is 6-8% of the mass of the solid powder B, preferably 7%;

[0052] (12) The mixed solid C is sheared at high speed to obtain a moist mixed solid C;

[0053] (13) The mixed solid C is dried to obtain solid powder C;

[0054] (14) The solid powder C is heat-treated to obtain a carbon-based microwave absorbing coating powder for plasma spraying with a particle size of 30-70 μm.

[0055] In steps (1)-(3) of some preferred embodiments of the present invention, the aluminum salt is Al(NO3)3·9H2O; the concentration of the aluminum salt solution is 1.5-2.5 mol / L; the lithium salt is LiNO3; and the concentration of the lithium salt solution is 1.5-2.5 mol / L. The molar ratio of the aluminum salt, lithium salt, and silica sol is 1 mol: 1 mol: 400 mg.

[0056] In step (6) of some preferred embodiments of the present invention, the ratio of the lithium aluminum silicon gel powder, graphene oxide, N precursor and water is (1.5-2.5)g∶(2-3)g∶(0.5-1.5)g∶(70-90)mL, preferably 2.5g∶2.5g∶1.5g∶90mL, 1.5g∶2.5g∶1.5g∶90mL or 2.5g∶2g∶1.5g∶90mL, more preferably 2.5g∶2.5g∶1.5g∶90mL.

[0057] The method for preparing the graphene oxide is as follows: graphene multilayer sheets and conductive carbon black powder are mixed in a mass ratio of 2:1, and then 6-8 wt% sodium silicate aqueous solution is added to the mixture and stirred until homogeneous to obtain graphene oxide. The graphene multilayer sheets have a diameter of 3 μm and a thickness of 50-80 nm, and the conductive carbon black powder has a particle size of 200 nm.

[0058] The N precursor is urea or melamine.

[0059] In steps (7) to (13) of some preferred embodiments of the present invention, all parameters for high-speed shearing are: shearing rotor speed of 8000-30000 rpm (preferably 18000 rpm, 10000 rpm or 8000 rpm, more preferably 18000 rpm), and stirring time of 6-30 min (preferably 15 min). All drying temperatures are 400℃ for 300-360 min.

[0060] In step (14) of some preferred embodiments of the present invention, the heat treatment refers to heating at 1000°C for 8 hours.

[0061] The graphene used as the raw material for graphene oxide in this invention can also be replaced with other carbon-based materials (such as graphite, activated carbon, acetylene black, mesoporous carbon, phenolic resin, furfural resin, epoxy resin, urea-formaldehyde resin, asphalt, citric acid, glucose, sucrose, polyvinyl chloride, or polyvinyl butyral). When replaced with other carbon-based materials, it is still necessary to mix it with conductive carbon black powder at a mass ratio of 2:1, and then add 6-8 wt% sodium silicate aqueous solution of the mixture and stir well. The resulting product can achieve similar effects to graphene oxide.

[0062] The carbon-based microwave absorbing coating powder for plasma spraying prepared by the above method has a particle size of 30-70 μm.

[0063] The method of using the carbon-based microwave absorbing coating powder for plasma spraying includes the following steps: spraying the carbon-based microwave absorbing coating powder for spraying using plasma spraying technology, with the following spraying parameters: powder feeding rate 10-30 g / min (preferably 20 g / min), actual plasma torch power 14-33 KW (preferably 23 KW), spraying distance 3-12 cm (preferably 7 cm), spraying speed and torch speed 10-25 cm / s (preferably 17 cm / s), and solid-phase reaction temperature 650-1100℃ (preferably 900℃).

[0064] This invention utilizes shear stirring to coat reduced graphene oxide with sodium lithium aluminum silicon silicate ceramic, thereby adjusting its impedance matching performance. The synergistic effect of conductivity loss and polarization loss effectively improves the microwave absorption performance. Furthermore, the outer coating with sodium silicate significantly enhances the material's microwave absorption performance and effective time at high temperatures. This invention offers good repeatability, low cost, environmental friendliness, cleanliness, non-toxicity, and ease of large-scale production. The proposed application of plasma spraying to this material makes it an ideal and practically applicable high-temperature resistant composite electromagnetic absorbing material.

[0065] The carbon-based microwave absorbing coating powder used in plasma spraying can be used as a microwave absorbing material.

[0066] The reduced graphene oxide used in the following embodiments and comparative examples of the present invention was purchased from AP-3 type reduced graphene oxide from Luobei Yunshan Carbon Industry.

[0067] All raw materials used in the following embodiments and comparative examples of the present invention are commercially available products.

[0068] The following embodiments of the present invention describe the preparation method of graphene oxide: graphene multilayer sheets (sheet diameter of 3μm, thickness of 50-80nm) and conductive carbon black powder (particle size of 200nm) are mixed in a mass ratio of 2:1, and then 7wt% sodium silicate aqueous solution of the mixture is added and stirred until homogeneous to obtain graphene oxide.

[0069] The technical solution of the present invention will be further illustrated by the following embodiments.

[0070] Example 1

[0071] 1) Add 1 mol of Al(NO3)3·9H2O to water to obtain an aluminum salt solution with a concentration of 2 mol / L. Heat the aluminum salt solution to 180℃ and add ammonia water dropwise to the aluminum salt solution while stirring until a borosilicate sol is formed.

[0072] 1 mol of LiNO3 was added to water to obtain a lithium salt solution with a concentration of 2 mol / L;

[0073] A lithium salt solution was added to boehmite sol and stirred until homogeneous to obtain a lithium-aluminum solution;

[0074] 400 mg of SiO2 sol was added dropwise to a lithium aluminum solution and stirred to obtain lithium aluminum silica sol;

[0075] The lithium aluminum silicon sol was dried at 100℃ for 50 h to obtain lithium aluminum silicon precursor powder;

[0076] Lithium aluminum silicon precursor powder was heat-treated at 800℃ for 12 hours to obtain lithium aluminum silicon gel powder.

[0077] 2) Add 2.5g of lithium aluminum silicon gel powder and 2.5g of graphene oxide to a mixing device, add 90mL of water and 1.5g of urea and mix evenly to form a slurry. Dry the slurry to obtain a solid precursor, and then put it into a heating device and heat treat it in a nitrogen atmosphere at 300℃ for 5h to obtain ceramic / graphene microwave absorbing powder.

[0078] 3) Add 7 wt% sodium silicate aqueous solution of ceramic / graphene microwave absorbing powder to the ceramic / graphene microwave absorbing powder, stir and mix evenly to obtain a moist mixed solid A; granulate the mixed solid A by high-speed shearing, with a rotor speed of 18000 r / min, stirring time of 15 min, and dry at 400℃ to obtain solid powder A.

[0079] 4) Add 7 wt% sodium silicate aqueous solution of solid powder A to solid powder A again to obtain wet mixed solid B; granulate wet mixed solid B by high-speed shearing, with rotor speed of 18000 r / min, stirring time of 15 min, and drying at 400℃ to obtain solid powder B.

[0080] 5) Add 7 wt% sodium silicate aqueous solution of solid powder B to solid powder B again to obtain wet mixed solid C; granulate wet mixed solid C by high-speed shearing, rotor speed 18000 r / min, stirring time 15 min, and dry at 400℃ to obtain solid powder C.

[0081] 6) Solid powder C is heat-treated at 1000℃ for 8 hours to obtain carbon-based microwave absorbing coating powder for plasma spraying.

[0082] Example 2

[0083] Same as Example 1, except that the heat treatment temperature in step 2) is 700°C.

[0084] Example 3

[0085] Same as Example 1, except that the heat treatment temperature in step 2) is 1000℃.

[0086] Example 4

[0087] Same as Example 1, except that the heat treatment temperature in step 2) is 1300℃.

[0088] Example 5

[0089] Same as Example 4, except that in step 2), the amount of lithium aluminum silicon gel powder added is 1.5g, that is, the amount of lithium aluminum silicon gel powder, graphene oxide, N precursor and water is 1.5g:2.5g:1.5g:90mL.

[0090] Example 6

[0091] Same as Example 4, except that the amount of graphene oxide added in step 2) is 2g, that is, the amount of lithium aluminum silicon gel powder, graphene oxide, N precursor and water is 2.5g:2g:1.5g:90mL.

[0092] Example 7

[0093] Same as Example 4, except that in steps 3)-5), the rotor speed is 10,000 rpm and the stirring time is 15 min during high-speed shear granulation.

[0094] Example 8

[0095] Same as Example 4, except that in steps 3)-5), the rotor speed is 8000 rpm and the stirring time is 15 min during high-speed shear granulation.

[0096] Example 9

[0097] Same as Example 4, except that the raw material for graphene oxide in step 2) is activated carbon.

[0098] Comparative Example 1

[0099] Same as Example 4, except that in steps 3)-5), the rotor speed is 1000 rpm and the stirring time is 60 min during high-speed shear granulation.

[0100] Comparative Example 2

[0101] Same as Example 4, except that in steps 3)-5), the rotor speed is 3000 rpm and the stirring time is 50 min during high-speed shear granulation.

[0102] Comparative Example 3

[0103] Same as Example 4, except that in steps 3)-5), the rotor speed is 5000 rpm and the stirring time is 40 min during high-speed shear granulation.

[0104] Comparative Example 4

[0105] Same as Example 4, except that in steps 3)-5), the rotor speed is 7000 rpm and the stirring time is 30 min during high-speed shear granulation.

[0106] Figure 1 XRD phase analysis of the carbon-based microwave absorbing coating powder for plasma spraying prepared in Example 4; as can be seen from the figure, the material mainly contains graphene nanosheets and quartz.

[0107] Figure 2 The surface of the sphere viewed by SEM transmission of the carbon-based microwave absorbing coating powder for plasma spraying prepared in Example 4; based on the transmission results of the electron microscope, its particle size can be roughly estimated to be 30-70 μm.

[0108] The carbon-based microwave absorbing coating powder prepared in Example 4 was sprayed onto a copper plate using plasma spraying technology. The specific parameters were: powder feeding rate 20 g / min, actual plasma torch power 23 KW, spraying distance 7 cm, spraying speed and torch speed 17 cm / s, and solid-phase reaction temperature 900℃.

[0109] Figure 3 The morphology of the carbon-based microwave absorbing coating powder for plasma spraying prepared in Example 4; Figure 4 The effect of the carbon-based microwave absorbing coating powder for plasma spraying prepared in Example 4 on the target material after plasma spraying.

[0110] Effect verification:

[0111] 1. To verify the high-temperature microwave absorption performance of the products obtained in this invention, microwave absorption tests were conducted at 200°C on the products of Examples 1-9 and Comparative Examples 1-4. The test method is as follows: The electromagnetic wave absorption performance test mainly involves determining the complex permittivity and complex permeability of the material using the following formula:

[0112]

[0113]

[0114] Where ε' is the real part of the dielectric constant of the material; ε” is the imaginary part of the dielectric constant of the material; δE is the electrical loss angle; μ' is the real part of the permeability; μ” is the imaginary part of the permeability; and δM is the magnetic loss angle.

[0115] The quality of wave absorption performance can be intuitively represented by the reflection loss (RL) value, which, according to transmission line theory, can be expressed by the following formula:

[0116]

[0117]

[0118] Where f, d, and c are the frequency, absorber thickness, and speed of light in free space, respectively; Z in —Input impedance; j is mass flux density; μr is relative permittivity; εr is relative permeability.

[0119] A reflection loss RL value < -10dB indicates 90.00% effective absorption, a reflection loss RL value < -20dB indicates 99.00% effective absorption, and a reflection loss RL value < -30dB indicates 99.90% effective absorption. The attenuation of electromagnetic waves in a material can be expressed by the following formula:

[0120]

[0121] The reflection loss value of the material was calculated. The electromagnetic wave absorption performance of the samples was studied using an Agilent Technologies VNA N5245A network vector analyzer. The powder samples were prepared by uniformly mixing the sample powders from the embodiments and comparative examples of this invention with paraffin wax at a mass ratio of 40%:60% while the paraffin wax was molten. The mixture was then pressed into a mold with an inner diameter of 3.04 mm and an outer diameter of 7 mm to obtain the desired hollow coaxial cylinder. Within the frequency range of 2-18 GHz, 201 sampling points were used. The real and imaginary parts of the complex permittivity and complex permeability of the samples were retained. The dielectric loss tangent and magnetic loss tangent were equal to the ratio of the real to the imaginary parts. The test results are shown in Table 1.

[0122] Table 1 Microwave Absorption Test

[0123]

[0124] As shown in Table 1, Example 4 exhibits the best microwave absorption performance. The electromagnetic absorption performance of this plasma-sprayed carbon-based microwave absorbing coating powder is a reflection loss RL value of -38.236 dB, with the minimum reflection loss RL value corresponding to an electromagnetic wave frequency of 11.44 GHz and an effective absorption bandwidth of 6.08 GHz. A comparison of Example 4 with Examples 1-3 shows that the heat treatment temperature of the solid precursor affects the microwave absorption performance. Only when the heat treatment temperature is relatively high can the graphene and lithium aluminum silicon gel powder be better anchored, resulting in ceramic / graphene microwave absorbing powder and improving the material's microwave absorption performance. A comparison of Examples 4 and 5-6 shows that the ratio of lithium aluminum silicon gel powder to graphene oxide has a certain impact on the microwave absorption performance of the material. However, when the ratio varies within a certain range, the material still has good microwave absorption performance. A comparison of Examples 4 and 7-8, as well as with Comparative Examples 1-4, shows that the rotor speed and time during high-speed shear granulation have a significant impact on the microwave absorption performance of the material. Only when the rotor speed and stirring time are within a certain range can the material be guaranteed to have reliable microwave absorption performance. A comparison of Examples 4 and 9 shows that the material still has microwave absorption performance after the carbon source is changed.

[0125] 2. To verify the microwave absorption performance of the product obtained in this invention at different frequencies, the return loss of the carbon-based microwave absorbing coating powder for plasma spraying prepared in Examples 1-4 was tested in the frequency range of 2-18 GHz. The test method was the coaxial loop method using a vector network analyzer. The return loss test mainly involved determining the complex permittivity and complex permeability of the material and calculating the reflection loss value of the material using the aforementioned formulas (1-5). The electromagnetic wave absorption performance of the samples was studied using a VNA, N5245A vector network analyzer from Agilent Technologies, USA. 20 wt.% of the sample powder was added to the molten paraffin and mixed uniformly. The mixture was then pressed into a mold with an inner diameter of 3.04 mm and an outer diameter of 7 mm to obtain the desired hollow coaxial cylinder. 201 sampling points were used in the 2-18 GHz frequency range. The real and imaginary parts of the complex permittivity and complex permeability of the samples were retained. The dielectric loss tangent and magnetic loss tangent were equal to the ratio of the real to the imaginary parts. The test results are as follows: Figure 5 As shown.

[0126] Depend on Figure 5 It can be seen that the products of Examples 1-4 have the best microwave absorption in the C-band and X-band. Therefore, it can be concluded that the absorption range of the products prepared in the embodiments of the present invention covers the current main electromagnetic detection frequency bands.

[0127] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing a carbon-based wave-absorbing coating powder for plasma spraying, characterized in that, It comprises the following steps: adding lithium aluminum silicon gel powder, graphene oxide and N precursor into water, mixing uniformly, drying the obtained slurry, and then performing a heat treatment in an inert atmosphere to obtain ceramic / graphene absorbing powder; the temperature of the heat treatment is 300-1300℃; the N precursor is urea or melamine; adding sodium silicate aqueous solution into the ceramic / graphene absorbing powder, stirring uniformly to obtain a wet mixed solid, and then performing high-speed shearing to obtain a solid powder; repeating the above operation, drying the finally obtained sample, and then performing a secondary heat treatment to obtain a carbon-based absorbing coating powder for plasma spraying; the secondary heat treatment is heating at 1000℃ for 8h; the parameters of the high-speed shearing are: shearing rotor rotating speed 8000-30000rpm, and stirring time 6-30min; the amount ratio of the lithium aluminum silicon gel powder, graphene oxide, N precursor and water is (1.5-2.5)g:(2-3)g:(0.5-1.5)g:(70-90)mL; the preparation method of the lithium aluminum silicon gel powder comprises the following steps: adding ammonia water dropwise into an aluminum salt aqueous solution until a boehmite sol is formed, then adding a lithium salt aqueous solution into the boehmite sol, and stirring to obtain a lithium aluminum solution; adding a silica sol dropwise into the lithium aluminum solution, stirring to obtain a lithium aluminum silicon sol, drying, and then performing a heat treatment to obtain a lithium aluminum silicon gel powder.

2. The method of claim 1, wherein the carbon-based wave-absorbing coating powder for plasma spraying is prepared by the steps of: preparing a carbon-based wave-absorbing coating precursor; and mixing the carbon-based wave-absorbing coating precursor with a solvent to obtain the carbon-based wave-absorbing coating powder for plasma spraying. the concentration of the aluminum salt aqueous solution is 1.5-2.5mol / L, and the aluminum salt is Al(NO3)3·9H2O; the concentration of the lithium salt aqueous solution is 1.5-2.5mol / L, and the lithium salt is LiNO3; the mass molar ratio of the aluminum salt, lithium salt and silica sol is 1mol:1mol:400mg; the drying is drying at 90-110℃ for 46-50h; the heat treatment is heating at 750-850℃ for 10-14h.

3. The method of claim 1, wherein the carbon-based wave-absorbing coating powder for plasma spraying is prepared by the steps of: preparing a carbon-based wave-absorbing coating precursor; and mixing the carbon-based wave-absorbing coating precursor with a binder to obtain the carbon-based wave-absorbing coating powder for plasma spraying. the inert gas is one or more of nitrogen, helium, neon and argon.

4. A carbon-based wave-absorbing coating powder for plasma spraying, obtainable by the production process according to any one of claims 1 to 3, characterized in that the particle size of the carbon-based absorbing coating powder for plasma spraying is 30-70μm.

5. A method of using a carbon-based wave-absorbing coating powder for plasma spraying as claimed in claim 4, characterized in that, the carbon-based absorbing coating powder for plasma spraying is sprayed by using a plasma spraying technology, and the spraying parameters are: powder feeding rate 10-30g / min, plasma torch actual power 14-33KW, spraying distance 3-12cm, spraying speed and torch walking speed 10-25cm / s, and solid phase reaction temperature 650-1100℃.

6. Application of the carbon-based absorbing coating powder for plasma spraying in claim 4 in preparing an absorbing material.

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