A broadband high-temperature resistant ceramic-based microwave absorbing material and its preparation method

Abstract

This invention provides a broadband high-temperature resistant ceramic-based microwave absorbing material and its preparation method, belonging to the technical field of microwave absorbing materials. The microwave absorbing material uses silicon carbide powder with a particle size of 100-500 nm as the matrix material. Silicon carbide is mixed with acetylene black and polycarbosilane solution and ball-milled to prepare ceramic slurries containing different concentrations of acetylene black. The ceramic slurries are then poured into a steel mold and vibrated on a vibration table. The sample surface is then smoothed and dried in a vacuum freeze dryer. The dried green sample is then subjected to high-temperature pyrolysis under vacuum and bonded to obtain a silicon carbide ceramic-based composite material. This invention utilizes a concentration gradient multilayer structure to effectively improve the impedance matching of the material. Simultaneously, by utilizing the multiple reflection and scattering effects of electromagnetic waves between silicon carbide and acetylene black, as well as the interfacial polarization loss between silicon carbide and black, broadband high absorption of electromagnetic waves can be achieved under high-temperature conditions.

Description

Technical Field

[0001] This invention relates to the field of microwave absorbing materials technology, and in particular to a broadband high-temperature resistant ceramic-based microwave absorbing material and its preparation method. Background Technology

[0002] Radar wave absorbing materials are advanced materials that absorb incident electromagnetic waves and reduce the intensity of target echoes. They are widely used on the surfaces of equipment and special devices to achieve electromagnetic protection. With the emergence of high-tech reconnaissance and precision guidance technologies, higher demands are placed on the stealth capabilities of weapons and equipment. Radar wave absorbing materials used in special parts of airborne weapons and equipment such as fighter jets and cruise missiles operate at temperatures exceeding 700℃ or even 950℃. Room-temperature radar absorbing materials are no longer sufficient, necessitating the development of high-performance high-temperature radar absorbing materials.

[0003] Currently, commonly used radar wave absorbing materials are mainly composite materials containing carbon, metals, or metal oxides. However, with the development of high thrust-to-weight ratio aero engines, traditional high-temperature alloys and intermetallic compounds are no longer sufficient to meet the requirements of high service temperatures and lightweight construction. Silicon carbide ceramic matrix composites, on the other hand, possess advantages such as low density, high strength, high temperature resistance, and oxidation resistance, making them a new generation of thermal structural materials suitable for high thrust-to-weight ratio aero engines. Furthermore, they also exhibit good radar wave absorption performance.

[0004] However, existing silicon carbide ceramic matrix composites have poor impedance matching characteristics, resulting in a narrow radar wave absorption band and low absorption intensity. By bonding multiple layers of silicon carbide ceramic matrix composites containing different concentrations of absorbent to form a multilayer composite structure, the impedance matching characteristics of the material can be improved, promoting multiple scattering and reflection of electromagnetic waves, thereby enhancing the conductivity loss of the composite material and exhibiting superior radar absorption performance. Summary of the Invention

[0005] The main objective of this invention is to provide a broadband high-temperature resistant ceramic-based microwave absorbing material, which solves the shortcomings of existing microwave absorbing materials that are difficult to combine broadband high absorption, high temperature resistance and high strength.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A broadband high-temperature resistant ceramic-based microwave absorbing material includes multiple layers of silicon carbide ceramic layers with a gradient concentration of acetylene black and an adhesive layer, wherein the silicon carbide ceramic layers are bonded together by the adhesive layer.

[0008] This invention also provides a method for preparing the above-mentioned broadband high-temperature resistant ceramic-based microwave absorbing material, comprising the following steps:

[0009] S1. Mix silicon carbide, acetylene black of different masses, polycarbosilane and xylene to prepare acetylene black ceramic matrix mixtures of different concentrations; then place them in a ball mill jar, add zirconium balls and ball mill to obtain silicon carbide ceramic slurries containing different concentrations of acetylene black.

[0010] S2. Silicon carbide ceramic slurries containing different concentrations of acetylene black are placed in steel molds, vibrated and leveled on a vibrating platform, and then dried to obtain blocky silicon carbide ceramic blanks containing different concentrations of acetylene black.

[0011] S3. The obtained blocky silicon carbide ceramic blanks containing different concentrations of acetylene carbon black were placed in xylene solution of polycarbosilane and impregnated and dried under reduced pressure.

[0012] S4. Place the sample obtained in step S3 in a tube furnace, and pyrolyze it under a nitrogen atmosphere. Record the weight gain rate of the sample. Repeat steps S3 and S4 until the weight gain rate is less than 1% to obtain silicon carbide ceramic samples with different acetylene black concentrations.

[0013] S5. Coat the upper and lower surfaces of silicon carbide ceramic samples with different acetylene black concentrations with aluminosilicate gel, and bond them according to the acetylene black concentration gradient. Allow the aluminosilicate gel to solidify at room temperature to obtain the broadband high-temperature resistant ceramic-based microwave absorbing material.

[0014] Preferably, in step S1, the silicon carbide is spherical.

[0015] Preferably, in step S1, the particle size of the silicon carbide is 100-500 nm.

[0016] More preferably, in step S1, the silicon carbide is one or more of the following: 100nm, 300nm, and 500nm.

[0017] More preferably, in step S1, the mixing mass ratio of the silicon carbide with particle sizes of 100nm, 300nm, and 500nm is 1-3:1-2:1.

[0018] Because ball milling results in random particle size control, this invention further improves the initial sample density by proportionally grading the initial silicon carbide particle size.

[0019] Preferably, in step S1, the acetylene black is ultrasonically treated. Acetylene black is prone to agglomeration, and ultrasonic treatment improves its dispersibility.

[0020] Preferably, in step S1, the mass of the zirconium ball is 1 to 3 times the total mass of silicon carbide and acetylene black.

[0021] Preferably, in step S1, the zirconium balls are zirconium balls with particle sizes of 1 mm, 3 mm, and 5 mm, mixed in a mass ratio of 5:3:2.

[0022] Preferably, in step S1, the ball milling speed is 150-250 r / min and the ball milling time is 6-12 h.

[0023] Preferably, in step S1, the particle size of the silicon carbide ceramic slurry is 40-60 nm.

[0024] Preferably, in step S2, the vibration scraping is to remove gas from inside the silicon carbide ceramic slurry, with a vibration frequency of 40-60Hz and a vibration time of 3-10min.

[0025] Preferably, in step S2, the drying is vacuum freeze drying, with a temperature of -50 to -40°C, a pressure of 10 to 30 Pa, and a drying time of 45 to 50 hours.

[0026] Preferably, in step S3, the concentration of the xylene solution of the polycarbosilane is 40wt% to 60wt%, the impregnation time is 20 to 40 min, the impregnation pressure is 15 to 25 Pa, the drying temperature is 50 to 80 °C, and the drying time is 1 to 3 h.

[0027] Preferably, the heating and pyrolysis conditions in step S4 are as follows: heating at a rate of 4-7°C / min to 140-160°C and holding for 2-5 hours, then heating at a rate of 2-4°C / min to 1100-1300°C and holding for 1-3 hours.

[0028] Preferably, in step S5, to further solidify the aluminosilicate gel and avoid shrinkage deformation of the sample, after being placed at room temperature for 22-26 hours, the temperature is increased to 85-100℃ at 4-7℃ / min and held for 0.75-1.5 hours, and then increased to 140-160℃ at 2-4℃ / min and held for 0.75-1.5 hours.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] 1. This invention utilizes a concentration gradient multilayer structure to effectively improve the impedance matching of materials. At the same time, by utilizing the multiple reflection and scattering effects of electromagnetic waves between silicon carbide powder and acetylene black, as well as the interfacial polarization loss between silicon carbide and carbon black, broadband high absorption of electromagnetic waves can be achieved.

[0031] 2. This invention uses absorbent with a gradient concentration as filler, which improves the material's matching characteristics. It exhibits strong absorption of electromagnetic waves in the 1–18 GHz range. When the overall material thickness is 8 mm, the reflectivity can reach as low as -32 dB, and the effective bandwidth with a reflectivity less than -4 dB can reach 17 GHz. At the same time, the use of silicon carbide ceramic slurry with high solid content ensures the mechanical properties and high-temperature resistance of the material after molding and after pyrolysis. It still has good microwave absorption and mechanical properties in a thermal environment of 1200℃. In addition, the combination of impregnation pyrolysis process increases the density of the material, improves the bonding between the microwave absorbing filler and the matrix material, and is beneficial to the material's oxidation resistance. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of the broadband high-temperature resistant ceramic-based microwave absorbing material of the present invention. Detailed Implementation

[0033] The technical solution of the present invention will be further described and illustrated below through examples. All raw materials used in the examples are commercially available or prepared using conventional methods.

[0034] Example 1

[0035] A method for preparing a broadband high-temperature resistant ceramic-based microwave absorbing material includes the following steps:

[0036] S1. Silicon carbide powder with a particle size of 500 nm, acetylene black that has been ultrasonically dispersed, polycarbosilane and xylene are premixed in mass ratios of 10:0:9:9, 10:0.1:9:9, 10:0.2:9:9 and 10:0.3:9:9, respectively. The mixtures are placed in ball mill jars, and twice the mass of silicon carbide and carbon black powder are added. The ball milling beads are zirconium balls with a particle size of 1 mm, 3 mm and 5 mm mixed in a mass ratio of 5:3:2. The ball milling speed is 200 r / min and the ball milling time is 6 h. Silicon carbide ceramic slurries with acetylene black concentrations of 0, 0.36 wt%, 0.71 wt% and 1.1 wt% are obtained, respectively.

[0037] S2. The ball-milled slurry was placed in steel molds and vibrated on a vibration platform at a vibration frequency of 50Hz for 5 minutes. Then, it was vacuum freeze-dried at a temperature of -45℃ and a pressure of 20Pa for 48 hours to obtain blocky ceramic blanks with different concentrations after drying.

[0038] S3. The obtained ceramic green body is placed in a 50wt% xylene solution of polycarbosilane and impregnated at a pressure of 20 Pa for 30 min, and then dried at 60 °C for 2 h.

[0039] S4. Place the impregnated sample in a tube furnace and heat it to 150°C at a rate of 5°C / min under a nitrogen atmosphere and hold it for 3 hours. Then heat it to 1200°C at a rate of 3°C / min and hold it for 2 hours. Repeat steps S3 and S4 and record the weight gain rate of the sample until the weight gain rate is less than 1%. This will give you silicon carbide ceramic samples with different acetylene black concentrations. The thickness of each silicon carbide ceramic sample is 2 mm.

[0040] S5. Coat the upper and lower surfaces of the ceramic sample with sodium silicate aqueous solution and bond them according to the acetylene black concentration gradient. Place them at room temperature for 24 hours, then raise the temperature to 90℃ at 5℃ / min and hold for 1 hour. Then raise the temperature to 150℃ at 3℃ / min and hold for 1 hour to obtain a broadband high-temperature resistant ceramic-based microwave absorbing material with a multi-layer composite structure and a thickness of 8 mm.

[0041] Example 2

[0042] A method for preparing a broadband high-temperature resistant ceramic-based microwave absorbing material includes the following steps:

[0043] S1 First, silicon carbide powders with particle sizes of 100nm, 300nm, and 500nm are mixed in a mass ratio of 1:1:1 to obtain a premixed powder. Then, the premixed powder, acetylene black, polycarbosilane, and xylene are mixed in mass ratios of 10:0.1:9:9, 10:0.2:9:9, 10:0.3:9:9, and 10:0.4:9:9, respectively, and placed in a ball mill jar. Three times the mass of silicon carbide and carbon black powder are placed in the jar. The jar contains zirconium balls with particle sizes of 1mm, 3mm, and 5mm, mixed in a mass ratio of 5:3:2. The ball milling speed is 100r / min, and the ball milling time is 10h, respectively, to obtain silicon carbide ceramic slurries with acetylene black concentrations of 0.36wt%, 0.71wt%, 1.07wt%, and 1.43wt%, respectively.

[0044] S2 placed the ball-milled slurry in a steel mold and vibrated it on a vibration platform at a vibration frequency of 60Hz for 10 minutes. Then, it was vacuum freeze-dried at a temperature of -40℃ and a pressure of 30Pa for 45 hours to obtain blocky ceramic blanks with different concentrations after drying.

[0045] S3 The obtained ceramic green body was placed in a xylene solution of 60 wt% polycarbosilane and impregnated at a pressure of 20 Pa for 40 min, and then dried at 80 °C for 1.5 h.

[0046] S4. The impregnated sample was placed in a tube furnace and heated to 140℃ at a rate of 4℃ / min under a nitrogen atmosphere and held for 5 hours. Then, it was heated to 1100℃ at a rate of 2℃ / min and held for 3 hours. Steps S3 and S4 were repeated, and the weight gain rate of the sample was recorded until the weight gain rate was less than 1%, thus obtaining ceramic samples with different concentrations of acetylene black. The thickness of each silicon carbide ceramic sample was 2 mm.

[0047] S5 The upper and lower surfaces of the ceramic sample were coated with potassium silicate gel and bonded according to the acetylene black concentration gradient. The sample was placed at room temperature for 22 hours. Then, the temperature was increased to 85℃ at 4℃ / min and held for 1.5 hours. Finally, the temperature was increased to 140℃ at 2℃ / min and held for 1.5 hours to obtain a broadband high-temperature resistant ceramic-based microwave absorbing material with a multilayer composite structure with a thickness of 8 mm.

[0048] Example 3

[0049] A method for preparing a broadband high-temperature resistant ceramic-based microwave absorbing material includes the following steps:

[0050] In step S1 of this embodiment, silicon carbide powders with particle sizes of 100nm, 300nm, and 500nm are mixed in a mass ratio of 1:2:1 to obtain a premixed powder. Then, the premixed powder, acetylene black, polycarbosilane, and xylene are mixed in mass ratios of 10:0.1:9:9, 10:0.2:9:9, 10:0.3:9:9, and 10:0.4:9:9, respectively. The mixture is then placed in a ball mill jar, with a volume of twice the amount of silicon carbide and carbon black powder. The grinding balls were zirconium balls with particle sizes of 1 mm, 3 mm and 5 mm mixed in a mass ratio of 5:3:2. The grinding speed was 200 r / min and the grinding time was 12 h. Silicon carbide ceramic slurries with carbon black concentrations of 0.36 wt%, 0.71 wt%, 1.07 wt% and 1.43 wt% were obtained respectively. Other steps were the same as in Example 1 to prepare a broadband high-temperature resistant ceramic-based microwave absorbing material with a multilayer composite structure and a thickness of 8 mm.

[0051] Example 4

[0052] A method for preparing a broadband high-temperature resistant ceramic-based microwave absorbing material includes the following steps:

[0053] In step S1 of this embodiment, silicon carbide powders with particle sizes of 100nm, 300nm, and 500nm are mixed in a mass ratio of 3:2:1 to obtain a premixed powder. Then, the premixed powder, acetylene black, polycarbosilane, and xylene are mixed in mass ratios of 10:0.2:9:9, 10:0.3:9:9, 10:0.4:9:9, and 10:0.5:9:9, respectively. The mixture is then placed in a ball mill jar, with a volume of twice the amount of silicon carbide and carbon black powder. The grinding balls were zirconium balls with particle sizes of 1 mm, 3 mm and 5 mm mixed in a mass ratio of 5:3:2. The grinding speed was 200 r / min and the grinding time was 12 h. Silicon carbide ceramic slurries with carbon black concentrations of 0.71 wt%, 1.07 wt%, 1.43 wt% and 1.78 wt% were obtained respectively. Other steps were the same as in Example 1 to prepare a broadband high-temperature resistant ceramic-based microwave absorbing material with a multilayer composite structure and a thickness of 8 mm.

[0054] Example 5

[0055] A method for preparing a broadband high-temperature resistant ceramic-based microwave absorbing material includes the following steps:

[0056] In step S1 of this embodiment, silicon carbide powders with particle sizes of 100nm, 300nm, and 500nm are mixed in a mass ratio of 2:2:1 to obtain a premixed powder. Then, the premixed powder, acetylene black, polycarbosilane, and xylene are mixed in mass ratios of 10:0.1:9:9, 10:0.2:9:9, 10:0.3:9:9, and 10:0.4:9:9, respectively, and placed in a ball mill jar with an equal volume of silicon carbide and carbon black powder. The grinding balls were zirconium balls with particle sizes of 1 mm, 3 mm and 5 mm mixed in a mass ratio of 5:3:2. The grinding speed was 200 r / min and the grinding time was 12 h. Silicon carbide ceramic slurries with carbon black concentrations of 0.36 wt%, 0.71 wt%, 1.07 wt% and 1.43 wt% were obtained respectively. Other steps were the same as in Example 1 to prepare a broadband high-temperature resistant ceramic-based microwave absorbing material with a multilayer composite structure and a thickness of 8 mm.

[0057] Comparative Example 1

[0058] A method for preparing a broadband high-temperature resistant ceramic-based microwave absorbing material is the same as that in Example 1, except that in steps S3 to S4 of this comparative example, only one vacuum impregnation and drying are performed.

[0059] Comparative Example 2

[0060] A ceramic-based microwave absorbing material is prepared by the following method:

[0061] The preparation method is the same as in Example 1, except that in step S1 of this comparative example, the particle size of silicon carbide powder is 80 nm.

[0062] Comparative Example 3

[0063] A ceramic-based microwave absorbing material is prepared in the same way as in Example 1, except that the silicon carbide powder has a particle size of 550 nm in step S1 of this comparative example.

[0064] Comparative Example 4

[0065] A ceramic-based microwave absorbing material is prepared in the same way as in Example 3, except that in step S1 of this comparative example, the premixed powder, acetylene black, polycarbosilane and xylene are mixed in a mass ratio of 10:(0.1-0.4):2:9.

[0066] Comparative Example 5

[0067] A ceramic-based microwave absorbing material is prepared in the same way as in Example 3. The difference is that in step S1 of this comparative example, the premixed powder, acetylene black, polycarbosilane and xylene are mixed in a mass ratio of 10:(0.1-0.4):15:9.

[0068] Test and Results Analysis

[0069] The bending strength of the broadband high-temperature resistant ceramic-based microwave absorbing materials prepared in the examples and comparative examples, as well as the broadband high-temperature resistant ceramic-based microwave absorbing materials prepared in the examples and comparative examples after heat treatment at 1200℃ for 1 hour, was determined in accordance with GB / T 1456-2021 "Test Method for Bending Performance of Sandwich Structures".

[0070] According to GJB 2038A-2011 "Test Method for Reflectivity of Radar Absorbing Materials", the average vertical reflectivity of the broadband high-temperature resistant ceramic-based absorbing materials prepared in the examples and comparative examples, as well as the broadband high-temperature resistant ceramic-based absorbing materials prepared in the examples and comparative examples after heat treatment at 1200℃ for 1h, was measured from 1 to 18 GHz.

[0071] Table 1. Performance data of the samples prepared in the examples and comparative examples.

[0072]

[0073] As can be seen from the experimental data in Table 1, when the particle size of silicon carbide is between 100 and 500 nm, it can ensure that the absorbing material has good mechanical and absorbing properties at high temperatures. If the particle size of silicon carbide is too large, the penetration amount of polycarbosilane will be small, the density will be poor, and the strength of the material cannot be guaranteed. If the particle size of silicon carbide is too small, it will be difficult to disperse in the system. When silicon carbide with particle sizes of 100 nm, 300 nm, and 500 nm is used in combination, the performance of the material can be better guaranteed. In addition, the density of the material can be improved by repeatedly impregnating polycarbosilane. By bonding ceramic samples containing different concentrations of acetylene black together, the impedance matching of the material can be effectively improved. At the same time, by utilizing the multiple reflection and scattering effects of electromagnetic waves between silicon carbide powder and acetylene black, as well as the interfacial polarization loss between silicon carbide and acetylene black, broadband high absorption of electromagnetic waves under high temperature conditions and good mechanical strength can be achieved. The broadband high-temperature resistant ceramic-based absorbing material provided by this invention still maintains high bending strength and good absorbing performance even after high-temperature heat treatment at 1200℃, making it suitable for radar absorbing applications that need to operate in high-temperature environments, such as the aerospace field.

[0074] It should be understood that the above embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A broadband high-temperature resistant ceramic-based microwave absorbing material, characterized in that, It includes multiple silicon carbide ceramic layers with a gradient concentration of acetylene black and an adhesive layer, wherein the silicon carbide ceramic layers are bonded together by the adhesive layer; The preparation method of the broadband high-temperature resistant ceramic-based microwave absorbing material includes the following steps: S1. Silicon carbide, acetylene black of different masses, polycarbosilane, and xylene are mixed to prepare acetylene black ceramic matrix mixtures of different concentrations; the silicon carbide powder has a particle size of 100~500nm, and is a graded powder with particle sizes of 100nm, 300nm, and 500nm mixed in a mass ratio of 1~3:1~2:1; then it is placed in a ball mill jar, and zirconium balls are added to it for ball milling to obtain silicon carbide ceramic slurries containing different concentrations of acetylene black; S2. Silicon carbide ceramic slurries containing different concentrations of acetylene black are placed in steel molds and vibrated and leveled on a vibrating platform, and then dried to obtain blocky silicon carbide ceramic blanks containing different concentrations of acetylene black; the drying is vacuum freeze drying, the temperature of vacuum freeze drying is -50~-40℃, the pressure is 10~30Pa, and the drying time is 45~50h. S3. The obtained blocky silicon carbide ceramic blanks containing different concentrations of acetylene carbon black were placed in xylene solution of polycarbosilane and impregnated and dried under reduced pressure. S4. Place the sample obtained in step S3 in a tube furnace and, under a nitrogen atmosphere, heat it to 140-160℃ at a rate of 4-7℃ / min and hold it for 2-5 hours. Then, heat it to 1100-1300℃ at a rate of 2-4℃ / min and hold it for 1-3 hours for pyrolysis. Record the weight gain rate of the sample. Repeat steps S3 and S4 until the weight gain rate is less than 1% to obtain silicon carbide ceramic samples with different acetylene black concentrations. S5. Coat the upper and lower surfaces of silicon carbide ceramic samples with different acetylene black concentrations with aluminosilicate gel, and bond them according to the acetylene black concentration gradient. Allow the aluminosilicate gel to solidify at room temperature to obtain the broadband high-temperature resistant ceramic-based microwave absorbing material.

2. The broadband high-temperature resistant ceramic-based microwave absorbing material according to claim 1, characterized in that, In step S1, the silicon carbide is spherical.

3. The broadband high-temperature resistant ceramic-based microwave absorbing material according to claim 1, characterized in that, In step S1, the acetylene black is ultrasonically treated.

4. The broadband high-temperature resistant ceramic-based microwave absorbing material according to claim 1, characterized in that, In step S1, the mass of the zirconium balls is 1 to 3 times the total mass of silicon carbide and acetylene black; the zirconium balls are zirconium balls with particle sizes of 1 mm, 3 mm and 5 mm mixed in a mass ratio of 5:3:2; the ball milling speed is 150 to 250 r / min and the ball milling time is 6 to 12 h; the particle size of the silicon carbide ceramic slurry is 40 to 60 nm.

5. The broadband high-temperature resistant ceramic-based microwave absorbing material according to claim 1, characterized in that, In step S2, the vibration frequency is 40~60Hz and the vibration time is 3~10min.

6. The broadband high-temperature resistant ceramic-based microwave absorbing material according to claim 1, characterized in that, In step S3, the concentration of the xylene solution of polycarbosilane is 40wt%~60wt%, the impregnation time is 20~40min, the impregnation pressure is 15~25Pa, the drying temperature is 50~80℃, and the drying time is 1~3h.

7. The broadband high-temperature resistant ceramic-based microwave absorbing material according to claim 1, characterized in that, In step S5, after being placed at room temperature for 22-26 hours, the temperature is increased to 85-100℃ at a rate of 4-7℃ / min and held for 0.75-1.5 hours. Then, the temperature is increased to 140-160℃ at a rate of 2-4℃ / min and held for 0.75-1.5 hours.

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