Composite material as well as preparation method and application thereof

Abstract

The invention provides a composite material which comprises a porous silicon carbide matrix doped with 3-9wt% of zirconium boride and in-situ generated silicon carbide nanowires loaded on the surface of the pore wall of the porous silicon carbide matrix, and the silicon carbide nanowires are used for forming a heterogeneous interface with the pore wall of the porous silicon carbide matrix. The invention also provides a preparation method and application of the composite material.

Description

Technical Field

[0001] The present invention relates to the field of composite ceramic materials, and particularly to a SiC ceramic composite material, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid progress of social science and technology and the increasing demands, 5G and future communication technologies have developed rapidly, and the society's demand for the control and management of electromagnetic waves has become more urgent. In this context, the importance of wave-absorbing materials has become increasingly prominent. Wave-absorbing materials play a key role in improving the performance of communication systems, reducing interference and attenuation, enhancing signal quality, and expanding the coverage range. At the same time, the continuous demand for stealth technology in the military field has also promoted the in-depth research of wave-absorbing materials. These materials play an important role in the development of more advanced stealth technologies, helping to improve the concealment and battlefield survival ability of military equipment.

[0003] It is worth mentioning that the rapid development of nanotechnology has provided new ways for the design and preparation of wave-absorbing materials. By regulating the nanostructure and functionalization, more efficient wave-absorbing performance and multifunctional properties can be achieved, further broadening the application fields of wave-absorbing materials. In addition to the military and communication fields, wave-absorbing materials also show great application potential in many other fields. For example, in the fields of aerospace, medical equipment, automotive engineering, and construction engineering, the reduction of electromagnetic interference and noise is inseparable from the application of wave-absorbing materials. These materials can effectively reduce the potential hazards of electromagnetic radiation to equipment and the human body, and improve the performance and reliability of equipment.

[0004] Among many electromagnetic interference shielding materials, ceramic matrix composites stand out due to their unique advantages. It has excellent thermal stability and chemical stability, and can maintain stable performance in harsh environments such as high temperature. At the same time, ceramic matrix composites also have high mechanical strength and anti-microbial ability, enabling them to maintain excellent performance under various extreme conditions. Therefore, ceramic matrix composites have broad application prospects in the field of electromagnetic shielding and can meet the electromagnetic shielding requirements in various complex environments.

[0005] As one of the wave-absorbing ceramic materials, silicon carbide has attracted attention due to its unique physical and chemical properties. It has high chemical stability, oxidation resistance, and good dielectric properties, making it suitable for a variety of harsh environments. However, traditional single materials have problems such as impedance mismatch, low conductivity, and single loss mechanism in terms of electromagnetic wave absorption performance.

[0006] The Chinese patent application with the publication number CN103922776A discloses a microwave absorbing ceramic, which uses a silicon carbide fiber cloth composed of continuous silicon carbide fibers as a reinforcement, and connects the silicon carbide fiber cloth (preferably plain cloth) into a whole by means of carbon fiber Z-direction stitching; the introduction of Z-direction carbon fibers significantly improves the interlaminar shear strength of the microwave absorbing ceramic, so that the finally obtained microwave absorbing ceramic has excellent mechanical properties. However, this technical solution fails to solve the problems of impedance mismatch, low conductivity, and single loss mechanism in the electromagnetic wave absorption performance of single materials.

[0007] The Chinese patent application with the publication number CN114466580A discloses a heat-insulating and microwave-absorbing composite material, which uses a silicon carbide-coated reinforced graphene honeycomb as the matrix of the composite material, and effectively reduces the overall density of the composite material by utilizing the light weight and high strength characteristics of the silicon carbide-coated reinforced graphene honeycomb while ensuring the overall strength. In addition, the graphene honeycomb is also an excellent electromagnetic wave absorbing and shielding material, which can effectively improve the overall microwave absorption performance of the material. However, this technical solution fails to solve the problems of impedance mismatch, low conductivity, and single loss mechanism in the electromagnetic wave absorption performance of single materials. Summary of the Invention

[0008] The first object of the present invention is to provide a composite material with high microwave absorption performance.

[0009] The second object of the present invention is to provide a preparation method of the composite material.

[0010] The second object of the present invention is to provide an application of the composite material.

[0011] The present invention is realized through the following technical solutions:

[0012] A composite material, comprising a porous silicon carbide matrix doped with 2-4 wt% of zirconium boride; and

[0013] In-situ generated silicon carbide nanowires loaded on the pore wall surface of the porous silicon carbide matrix, and the silicon carbide nanowires are used to form a heterojunction interface with the pore wall of the porous silicon carbide matrix.

[0014] The porosity of the porous silicon carbide matrix is 30-35%

[0015] The diameter of the silicon carbide nanowires is 10-500 nanometers

[0016] A preparation method of the composite material, comprising the following steps:

[0017] Mix silicon carbide coarse powder, silicon carbide fine powder, zirconium boride powder, an aqueous solution of a binder, and a water-miscible organic solvent, then dry and sinter to obtain a porous silicon carbide matrix;

[0018] The porous silicon carbide matrix is immersed in a silicon carbide precursor solution containing a nickel-based catalyst for multiple times, and then dried and fired to obtain the product;

[0019] The average particle size of the silicon carbide coarse powder is 50-150 mesh;

[0020] The average particle size of the silicon carbide fine powder is 150-250 nm.

[0021] The aqueous solution of the binder includes an aqueous solution of PVA;

[0022] The water-miscible organic solvent includes ethanol;

[0023] The concentration of the aqueous solution of PVA is 5-4-6 wt%;

[0024] The addition amount of the aqueous solution of the binder is 3-5 wt% of the sum of the weights of the silicon carbide coarse powder, the silicon carbide fine powder and the zirconium boride powder;

[0025] The addition amount of the water-miscible organic solvent is 5-10 wt% of the sum of the weights of the silicon carbide coarse powder, the silicon carbide fine powder and the zirconium boride powder.

[0026] The sintering temperature is 2350°C-2450°C.

[0027] The firing temperature is 1350-1450°C.

[0028] The nickel-based catalyst includes nickel sulfamate;

[0029] The silicon carbide precursor solution includes a carbon source and a silicon source.

[0030] The carbon source includes glucose;

[0031] The silicon source includes tetraethyl orthosilicate.

[0032] The weight ratio of the carbon source to the silicon source is 1:2.5-3.5;

[0033] The addition amount of the nickel-based catalyst is 8-12 wt% of the sum of the weights of the carbon source and the silicon source.

[0034] The application of the composite material is for absorbing electromagnetic waves.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] The composite material provided by the present invention includes a porous silicon carbide matrix, in which silicon carbide nanowires are loaded. Since the silicon carbide nanowires are in-situ grown on the porous silicon carbide matrix, the silicon carbide nanowires will form a three-dimensional network structure. This three-dimensional network structure, combined with the high specific surface area of the silicon carbide nanowires, enhances the interfacial properties such as dipole polarization, multiple reflections, and electromagnetic wave scattering of the porous silicon carbide matrix, thereby enhancing the electromagnetic wave absorption ability. At the same time, in order to avoid the limitations of single materials in electromagnetic wave absorption performance, such as impedance mismatch, low conductivity, and single loss mechanism, the present invention dopes zirconium boride into the porous silicon carbide matrix. Zirconium boride can improve the thermal conductivity, electromagnetic properties, and thermal shock resistance of the silicon carbide matrix. These properties enable the silicon carbide ceramics provided by the present invention to perform excellently in high-temperature and harsh environments. At the same time, the doping of zirconium boride changes the elemental composition of the porous silicon carbide matrix. Since the elemental composition of the porous silicon carbide matrix is different from that of the silicon carbide nanowires, a heterojunction is formed at the interface between the porous silicon carbide matrix and the silicon carbide nanowires. The existence of the heterojunction will further improve the wave absorption performance of the silicon carbide ceramics.

[0037] The preparation method of the composite material provided by the present invention is simple, which is conducive to industrial production.

[0038] The composite material provided by the present invention has good electromagnetic wave absorption performance and can be applied to the field of electromagnetic wave absorption. Description of the Drawings

[0039] Figure 1 Shows the schematic diagram of the preparation process of the composite material provided by the present invention.

[0040] Figure 2 Shows the XRD patterns of the products obtained by firing the silicon carbide nanowire precursors prepared in Examples 6-7 and Comparative Example 3 at different firing temperatures.

[0041] Figure 3(a) TEM photo of the nanowires obtained by firing the silicon carbide nanowire precursor at 1600 °C.

[0042] Figure 3(b) TEM photo of the nanowires obtained by firing the silicon carbide nanowire precursor at 1650 °C.

[0043] Figure 3(c) TEM photo of the nanowires obtained by firing the silicon carbide nanowire precursor at 1550 °C.

[0044] Figure 4(a) shows the TEM photo of the composite material prepared in Example 6.

[0045] Figure 4(b) shows the TEM photo of the composite material prepared in Example 7.

[0046] Figure 4(c) shows the TEM photo of the composite material prepared in Comparative Example 3.

[0047] Figure 4(d) shows the XRD photographs of the composite materials prepared in Example 6-7 and Comparative Example 3.

[0048] Figure 5 Shows the X-ray energy spectrum of the nanowires in the composite material prepared in Example 6.

[0049] Figure 6 Shows the XRD patterns of the precursor powders with different carbon-silicon ratios sintered at 1600 °C.

[0050] Figure 7(a) shows the real part of the complex permittivity diagram of the composite materials prepared in Example 4-6.

[0051] Figure 7(b) shows the imaginary part of the complex permittivity diagram of the composite materials prepared in Example 4-6.

[0052] Figure 7(c) shows the loss tangent diagram of the composite materials prepared in Example 4-6.

[0053] Figure 8(a) shows the Cole-Cole diagram of the composite material prepared in Example 4.

[0054] Figure 8(b) shows the Cole-Cole diagram of the composite material prepared in Example 5.

[0055] Figure 8(c) shows the Cole-Cole diagram of the composite material prepared in Example 6.

[0056] Figure 8(d) shows the Cole-Cole diagram of the composite material prepared in Comparative Example 2.

[0057] Figure 9 Shows the electromagnetic wave absorption mechanism of the composite ceramic material. Detailed implementation mode

[0058] The materials involved in the specific embodiments of the present invention are as follows:

[0059] Glucose (analytical pure, Sinopharm Chemical Reagent Co., Ltd.), citric acid (analytical pure, Sinopharm Chemical Reagent Co., Ltd.), tetraethyl orthosilicate (analytical pure, Tianjin Kemiou Chemical Reagent Co., Ltd.), nickel sulfamate tetrahydrate (analytical pure, Shanghai Macklin Biochemical Co., Ltd.), ultrafine high-purity zirconium diboride (10 μm, Qinghe Enyi Metal Materials Co., Ltd.), silicon carbide powder (coarse powder: 100 mesh, fine powder: 200 nm, Changle Hongxin Grinding Materials Co., Ltd.).

[0060] The characterizations involved in the specific embodiments of the present invention are as follows:

[0061] The phase composition of the composite materials was analyzed using an X-ray diffractometer (XRD, Rigaku D / max 2550, Cu Kα radiation). The working parameters were as follows: tube voltage 40 kV, tube current 30 mA, scanning angle range 5 - 80°, sampling interval 0.02°, and scanning speed 5° / min. The morphology and microstructure were analyzed using a field emission scanning electron microscope (SEM, Tescan Mira4). The variable-temperature electromagnetic parameters in the range of 8.2 - 12.4 GHz were measured using a vector network analyzer (Agilent N5230A).

[0062] The present invention will be further described below in conjunction with specific embodiments.

[0063] Example 1

[0064] Preparation of a SiC matrix doped with 3% zirconium boride

[0065] After mixing 300 g of coarse silicon carbide powder (100 mesh) and 100 g of fine silicon carbide powder (200 nm), 3 wt% zirconium boride based on the total mass of the silicon carbide powder, 5 wt% PVA based on the total mass of the silicon carbide powder, and 500 g of absolute ethanol were added. After ball milling for 1 h and mixing evenly, it was dried at 45°C. It was pressed into a specimen with dimensions of 22.86 mm × 10.16 mm × 3 mm, and then sintered at 2400°C to prepare a porous SiC matrix (porosity 33%).

[0066] Example 2

[0067] Preparation of a SiC matrix doped with 6% zirconium boride

[0068] After mixing 300 g of coarse silicon carbide powder (100 mesh) and 100 g of fine silicon carbide powder (200 nm), 6 wt% zirconium boride based on the total mass of the silicon carbide powder, 5 wt% PVA based on the total mass of the silicon carbide powder, and 500 g of absolute ethanol were added. After ball milling for 1 h and mixing evenly, it was dried at 45°C. It was pressed into a specimen with dimensions of 22.86 mm × 10.16 mm × 3 mm, and then sintered at 2400°C to prepare a porous SiC matrix (porosity 33%).

[0069] Example 3

[0070] Preparation of a SiC matrix doped with 9% zirconium boride

[0071] After mixing 300 g of coarse silicon carbide powder (100 mesh) and 100 g of fine silicon carbide powder (200 nm), 9 wt% zirconium boride based on the total mass of the silicon carbide powder, 5 wt% PVA based on the total mass of the silicon carbide powder, and 500 g of absolute ethanol were added. After ball milling for 1 h and mixing evenly, it was dried at 45 °C. It was pressed into a test block with dimensions of 22.86 mm × 10.16 mm × 3 mm, and then sintered at 2400 °C to prepare a porous SiC matrix (porosity 33%).

[0072] Comparative Example 1

[0073] Preparation of SiC matrix without doped zirconium boride

[0074] After mixing 300 g of coarse silicon carbide powder (100 mesh) and 100 g of fine silicon carbide powder (200 nm), 5 wt% PVA based on the total mass of the silicon carbide powder and 500 g of absolute ethanol were added. After ball milling for 1 h and mixing evenly, it was dried at 45 °C. It was pressed into a test block with dimensions of 22.86 mm × 10.16 mm × 3 mm, and then sintered at 2400 °C to prepare a porous SiC matrix (porosity 33%).

[0075] Example 4

[0076] Preparation of silicon carbide absorbing material

[0077] First, a silicon carbide precursor was prepared by the sol-gel method.

[0078] Using glucose as the carbon source and tetraethyl orthosilicate as the silicon source, the carbon source and the silicon source were mixed at a mass ratio of 1:1. Then, 10 wt% nickel aminosulfonate based on the total mass of the carbon source and the silicon source was added as a catalyst. Then, 50 wt% absolute ethanol and citric acid based on the total mass of the carbon source and the silicon source were added to adjust the pH value (4 - 5). Then, an appropriate amount of deionized water was added to promote the hydrolysis of tetraethyl orthosilicate to form a saturated sol. Secondly, the matrix prepared in Example 1 was put into the sol under vacuum for impregnation for 30 minutes and then dried, and this was repeated 3 times. Finally, the dried sample was put into a tubular furnace and fired under an argon atmosphere. The heating rate was 5 ° / min, the holding time was 4.5 h, and the firing temperature was 1600 °C.

[0079] Example 5

[0080] Preparation of silicon carbide absorbing material

[0081] First, a silicon carbide precursor was prepared by the sol-gel method.

[0082] Using glucose as the carbon source and tetraethyl orthosilicate as the silicon source, the carbon source and the silicon source are mixed at a mass ratio of 1:1. Then, nickel aminosulfonate accounting for 10 wt% of the total mass of the carbon source and the silicon source is added as a catalyst. Next, absolute ethanol and citric acid accounting for 50 wt% of the total mass of the carbon source and the silicon source are added to adjust the pH value (4 - 5), and an appropriate amount of deionized water is added to promote the hydrolysis of tetraethyl orthosilicate to form a saturated sol. Secondly, the substrate prepared in Example 2 is put into the sol under vacuum for impregnation for 30 minutes and then dried, and this is repeated 3 times. Finally, the dried sample is put into a tubular furnace and fired under an argon atmosphere. The heating rate is 5 ° / min, the holding time is 4.5 h, and the firing temperature is 1600 °C.

[0083] Example 6

[0084] Preparation of Silicon Carbide Absorbing Material

[0085] First, a silicon carbide precursor is prepared by the sol - gel method. Using glucose as the carbon source, tetraethyl orthosilicate as the silicon source, and nickel aminosulfonate (10 wt% of the total mass of the carbon source and the silicon source) as the catalyst, the carbon source and the silicon source are mixed at a mass ratio of 1:1. Absolute ethanol is added to promote the hydrolysis of tetraethyl orthosilicate and citric acid is added to adjust the pH value (4 - 5), and an appropriate amount of deionized water is added to form a saturated sol. Secondly, the substrate prepared in Example 3 is put into the sol under vacuum for impregnation for 30 minutes and then dried, and this is repeated 3 times. Finally, the dried sample is put into a tubular furnace and fired under an argon atmosphere. The heating rate is 5 ° / min, the holding time is 4.5 h, and the firing temperature is 1600 °C.

[0086] Comparative Example 2

[0087] Preparation of Silicon Carbide Absorbing Material

[0088] First, a silicon carbide precursor is prepared by the sol - gel method. Using glucose as the carbon source, tetraethyl orthosilicate as the silicon source, and nickel aminosulfonate (10 wt% of the total mass of the carbon source and the silicon source) as the catalyst, the carbon source and the silicon source are mixed at a mass ratio of 1:1. Absolute ethanol is added to promote the hydrolysis of tetraethyl orthosilicate and citric acid is added to adjust the pH value (4 - 5), and an appropriate amount of deionized water is added to form a saturated sol. Secondly, the substrate prepared in Comparative Example 1 is put into the sol under vacuum for impregnation for 30 minutes and then dried, and this is repeated 3 times. Finally, the dried sample is put into a tubular furnace and fired under an argon atmosphere. The heating rate is 5 ° / min, the holding time is 4.5 h, and the firing temperature is 1600 °C.

[0089] Example 7

[0090] Preparation of Silicon Carbide Absorbing Material

[0091] First, a silicon carbide precursor was prepared by the sol-gel method. Using glucose as the carbon source, tetraethyl orthosilicate as the silicon source, and nickel aminosulfonate (10 wt% of the total mass of the carbon source and silicon source) as the catalyst, the carbon source and silicon source were mixed at a mass ratio of 1:1. Anhydrous ethanol was added to promote the hydrolysis of tetraethyl orthosilicate, and citric acid was used to adjust the pH value (4 - 5). Then, an appropriate amount of deionized water was added to form a saturated sol. Secondly, the substrate prepared in Example 3 was placed in the sol under vacuum for impregnation for 30 minutes and then dried, and this was repeated 3 times. Finally, the dried sample was placed in a tubular furnace and fired under an argon atmosphere. The heating rate was 5 ° / min, the holding time was 4.5 h, and the firing temperature was 1650 °C respectively.

[0092] Comparative Example 3

[0093] The difference from Example 6 is that the firing temperature is 1550 °C.

[0094] Comparative Example 4

[0095] Preparation of Silicon Carbide Absorbing Material

[0096] First, a silicon carbide precursor was prepared by the sol-gel method. Using glucose as the carbon source, tetraethyl orthosilicate as the silicon source, and nickel aminosulfonate (10 wt% of the total mass of the carbon source and silicon source) as the catalyst, the carbon source and silicon source were mixed at a mass ratio of 1:2. Anhydrous ethanol was added to promote the hydrolysis of tetraethyl orthosilicate, and citric acid was used to adjust the pH value (4 - 5). Then, an appropriate amount of deionized water was added to form a saturated sol. Secondly, the substrate prepared in Example 3 was placed in the sol under vacuum for impregnation for 30 minutes and then dried, and this was repeated 3 times. Finally, the dried sample was placed in a tubular furnace and fired under an argon atmosphere. The heating rate was 5 ° / min, the holding time was 4.5 h, and the firing temperature was 1600 °C respectively.

[0097] Comparative Example 5

[0098] Preparation of Silicon Carbide Absorbing Material

[0099] First, a silicon carbide precursor was prepared by the sol-gel method. Using glucose as the carbon source, tetraethyl orthosilicate as the silicon source, and nickel aminosulfonate (10 wt% of the total mass of the carbon source and silicon source) as the catalyst, the carbon source and silicon source were mixed at a mass ratio of 2:1. Anhydrous ethanol was added to promote the hydrolysis of tetraethyl orthosilicate, and citric acid was used to adjust the pH value (4 - 5). Then, an appropriate amount of deionized water was added to form a saturated sol. Secondly, the substrate prepared in Example 3 was placed in the sol under vacuum for impregnation for 30 minutes and then dried, and this was repeated 3 times. Finally, the dried sample was placed in a tubular furnace and fired under an argon atmosphere. The heating rate was 5 ° / min, the holding time was 4.5 h, and the firing temperature was 1600 °C respectively.

[0100] The present invention is further illustrated below by the characterization results of the products prepared in the examples.

[0101] The key of the present invention lies in that the interface between the porous silicon carbide matrix doped with ZrB2 and the silicon carbide nanowires is a heterojunction interface, and this heterojunction interface can improve the impedance matching and attenuation constant of the silicon carbide ceramic.

[0102] In order to form a heterojunction interface at the interface between the porous silicon carbide matrix and the silicon carbide nanowires, the present invention uses the sol-gel carbothermal reduction method to in-situ grow silicon carbide nanowires on the SiC / ZrB2 composite ceramic material, and at the same time compares the growth of silicon carbide nanowires at different temperatures, the influence of the addition amount of zirconium boride doping and the content of silicon carbide nanowires on the electromagnetic wave absorption performance of the composite ceramic material. Obviously, other methods that can form a heterojunction interface at the interface between the porous silicon carbide matrix and the silicon carbide nanowires can also achieve the present invention.

[0103] In order to explore the optimal growth temperature of the silicon carbide nanowires, the silicon carbide nanowire precursors in Example 6 of the present invention were sintered at 1550 °C, 1600 °C and 1650 °C respectively, and their phase compositions were analyzed. Figure 2 The XRD patterns of the silicon carbide nanowire precursors at different temperatures are shown. The XRD patterns show that the sample mainly contains silicon carbide. As the sintering temperature increases, the characteristic peaks of silicon carbide first increase and then decrease, and the characteristic peaks of carbon gradually decrease. The characteristic peaks of silicon carbide appear at 35.73°, 41.49°, 60.13°, 71.95°, 75.69°, corresponding to the (111), (200), (220), (311), (222) crystal planes of SiC (NO.73-1665) respectively. According to the PDF card NO.73-1665, the type of the silicon carbide nanowires (SiCnws) is 3C-SiC, belonging to the cubic crystal system, and the cubic SiCnws has better microwave absorption performance. At 1600 °C, the characteristic peaks of carbon almost disappear, showing excellent crystallinity and purity of silicon carbide. It can be seen that it is appropriate to prepare silicon carbide nanowires at a temperature of about 1600 °C.

[0104] In order to further determine the sintering temperature, the morphology and microstructure of the samples were characterized. Figure 3 shows the morphologies of the silicon carbide nanowires obtained by firing the silicon carbide nanowire precursors in Example 6 of the present invention at 1550 °C, 1600 °C and 1650 °C respectively.

[0105] Figure 4 is a TEM photograph of the composite materials prepared in Examples 6-7 and Comparative Example 3. At a temperature of 1600 °C, a large number of nanowires were observed on the outer surface and the inner surface of the sample, and the nanowires grew more uniformly at 1600 °C. At 1650 °C, no nanowires were observed on the inner and outer surfaces of the sample.

[0106] X-ray energy spectrum analysis was performed on the nanowires in the composite material prepared in Example 6, as shown in Figure 5. Figure 5 It shows that the elemental composition of the nanowires is carbon, silicon, and nickel. Combining with the XRD pattern analysis, it can be known that the phase of the nanowires is silicon carbide. According to Figure 5 it can be known that the nanowires are silicon carbide nanowires, and there are nickel droplets in the nanowires. The nickel droplets can be used as the growth points for the nucleation of silicon carbide nanowires. This indicates that the growth of silicon carbide nanowires conforms to the vapor-liquid-solid growth mechanism. The interface between the catalyst alloy droplet and the solid material follows the principle of minimum energy, promoting the growth of anisotropic crystals and preferentially growing under the catalysis of the catalyst droplet to obtain nanowires. Comparing the microscopic morphology diagrams at different temperatures, at 1600 °C, the growth of silicon carbide nanowires on the inner and outer surfaces of the matrix is relatively uniform. Therefore, the synthesis temperature of silicon carbide nanowires is about 1600 °C at the best.

[0107] After determining the firing temperature, explore the optimal carbon and silicon source ratio for the growth of silicon carbide nanowires. Figure 6 Figure 9 shows the XRD patterns of the precursor powders with different carbon-silicon ratios sintered at 1600 °C. From Figure 6 it can be known that when the mass ratio of the carbon source to the silicon source is 1:1, the sample has fewer miscellaneous peaks and is mainly silicon carbide peaks. When the mass ratio of the carbon source to the silicon source is 1:2, with the increase of the silicon source, more Ni2Si peaks appear in the sample. When the mass ratio of the carbon source to the silicon source is 2:1, with the increase of the carbon source, the carbon peaks in the sample increase. When the mass ratio of the carbon source to the silicon source is 1:1, it shows excellent crystallinity and purity of silicon carbide.

[0108] According to the prior art, the dielectric silicon carbide ceramic material is non-magnetic (μ′ = 1, μ″ = 0), so its electromagnetic wave absorption performance mainly depends on the complex dielectric constant. The complex dielectric constant (ε r = ε′ - jε″) and the loss tangent (tanδ = ε″ / ε′) are two key factors determining the electromagnetic wave absorption performance of the material. The real part of the complex dielectric (ε′) represents the ability of the material to store electromagnetic wave energy, and the imaginary part of the complex dielectric (ε″) represents the ability of the material to dissipate electromagnetic wave energy. The loss tangent is one of the key parameters for evaluating the electromagnetic wave absorption and attenuation characteristics. Generally, the larger the imaginary part of the complex dielectric, the higher the loss tangent value, the greater the dielectric loss, and the stronger the electromagnetic wave loss ability of the material.

[0109] Figure 7 shows the complex dielectric constant and conductivity diagrams of the composite materials prepared in Examples 4-6 and Comparative Example 2 in the frequency range of 8.2 - 12.4 GHz. As shown in Figure 7, with the increase of frequency, the value shows a downward trend and is accompanied by certain fluctuations. This is due to the frequency scattering effect, the formation of nanoparticle-induced interfaces and dipoles, resulting in the hysteresis of the frequency scattering effect under the alternating electromagnetic field.

[0110] The average values of ε′ of the four composite materials prepared in Examples 4-6 and Comparative Example 2 were 8.3, 8.5, 14.0, and 7.3, respectively, indicating that after doping with zirconium boride, the composite materials have strong microwave storage capabilities.

[0111] The average ε″ values of the four composite materials prepared in Examples 4-6 and Comparative Example 2 were 6.3, 7.8, 12.4, and 3.3, respectively. The ε″ curves of the three composite materials prepared in Examples 4-6 all had resonance peaks near 9, 9.5, 11 GHz, which were caused by dipole polarization caused by dipole rotation and interfacial polarization caused by heterogeneous interfaces. The average tanδ values of the four composite materials prepared in Examples 4-6 and Comparative Example 2 were 0.39, 0.56, 0.93, and 0.15, respectively, indicating that the composite materials doped with zirconium boride had high dielectric loss performance.

[0112] According to Debye theory, and can be represented by specific expressions as follows:

[0113] ε′ = ε ∞ +(ε s -ε ∞ ) / (1 + (ωτ) 2 )

[0114] ε″ = (ε s -ε ∞ )ωτ / (1 + (ωτ) 2 ) + σ / ωε0

[0115] where ε ∞ is the optical frequency dielectric constant, and ε s is the static dielectric constant. ω (ω = 2πf) is the angular frequency, τ, σ, and ε0 are the polarization relaxation time, conductivity, and free space dielectric constant, respectively, ε′ is the real part of the complex dielectric, and ε″ is the imaginary part of the complex dielectric.

[0116] As can be seen from the above formulas, the value of the real part of the complex dielectric constant is mainly related to the polarization phenomenon, and the imaginary part of the complex dielectric constant is positively correlated with the conduction loss. Compared with the unfired samples, both the complex dielectric constant and the loss tangent increased to a certain extent. The addition of silicon carbide nanowires increased the heterogeneous interfaces, and the interfacial polarization between the interfaces increased significantly, resulting in an increase in the imaginary part of the complex dielectric of the composite material.

[0117] Silicon carbide is a wide-bandgap semiconductor, and one-dimensional silicon carbide nanomaterials have unique electrical properties. Therefore, the addition of silicon carbide nanowires will affect the conductivity of the composite material, and the residual C phase in the grown silicon carbide nanowires will also increase the conductivity of the composite material. The increase in the conductivity of the composite material leads to a corresponding increase in the imaginary part of the complex dielectric. Moreover, the network structure formed by silicon carbide nanowires increases the carrier transport channels, further improving the imaginary part of the complex dielectric of the composite material.

[0118] The average conductivity values of the four composite materials prepared in Examples 4-6 and Comparative Example 2 are 2.39, 2.97, 3.73, and 6.30, respectively. The conductivity in the material affects the conduction loss, and the conduction loss also has a certain impact on the dielectric loss. The greater the conductivity of the material, the greater the conduction loss. Since the conductivity of the composite material increases after adding zirconium boride, the conduction loss of the composite material is better after adding zirconium boride.

[0119] Multiple resonance peaks appear in the ε″ curve, indicating the existence of multiple polarization relaxation processes. The Cole-Cole semicircle can be used to analyze the polarization relaxation process of the composite material. According to the formula, the Cole-Cole equation can be derived as follows:

[0120]

[0121] ε′ is the real part of the complex permittivity, ε″ is the imaginary part of the complex permittivity, ε ∞ is the optical frequency permittivity, ε s is the static permittivity.

[0122] When the relationship between ε′ and ε″ can be depicted as a semicircle, it can be considered a Cole-Cole semicircle. Each Cole-Cole semicircle can represent a relaxation mechanism. The Cole-Cole diagram of the composite material is shown in Figure 8. The number of semicircles in the composite materials prepared in Examples 4-6 is significantly more than that in the composite material prepared in Comparative Example 2. More semicircles indicate an enhanced polarization relaxation process. When silicon carbide nanowires are added, the silicon carbide nanowires will form a large number of defects and nanoheterointerfaces with the silicon carbide matrix doped with zirconium boride. The defects can act as the centers of dipole polarization, and there is interfacial polarization at the nanoheterointerfaces, such as the SiCnws / SiC nanoheterointerfaces. The 3D network structure formed by the silicon carbide nanowires and the composite material will generate cross polarization, which will further promote the Debye relaxation process.

[0123] Impedance matching and attenuation constant are two important parameters in the design of electromagnetic wave absorbing materials. High impedance matching can minimize the reflection of electromagnetic waves on the material surface and allow as many electromagnetic waves as possible to enter the material. Generally, when the impedance matching of an ideal electromagnetic wave absorbing material approaches 1, the surface reflection is less when the electromagnetic wave enters the material. The impedance matching can be calculated by the formula

[0124] In the formula, Z, Z in and Z0 represent impedance matching, input impedance, and free space impedance, respectively; f, d, and c are the average frequency of light, the thickness of the sample, and the speed of light in vacuum, respectively; ε r and μ r represent the complex permittivity and complex permeability of the material, respectively. j is the imaginary unit.

[0125] A high attenuation constant indicates that the material can effectively convert electromagnetic wave energy into heat energy or other forms of energy, thereby reducing the propagation depth of electromagnetic waves within the material. The attenuation constant can be calculated using the formula

[0126] where α is the attenuation constant, f and c are the average frequency of light and the speed of light in vacuum respectively, ε′ is the real part of the complex permittivity, ε″ is the imaginary part of the complex permittivity, μ′ is the real part of the complex permeability, and μ″ is the imaginary part of the complex permeability. Silicon carbide is a non-magnetic material, and its μ' and μ” are close to 1 and 0 respectively.

[0127] In summary, in the present invention, silicon carbide nanowires are in-situ grown on the SiC porous ceramic material by the sol-gel carbothermal reduction method. By growing silicon carbide nanowires in the silicon carbide porous ceramic, the electromagnetic wave absorption performance can be effectively improved. The high specific surface area of the silicon carbide nanowires and the three-dimensional network structure formed with the porous ceramic optimize the electromagnetic wave absorption interface of the porous ceramic, enhance the impedance matching ability, establish an electromagnetic wave attenuation path, and jointly promote the electromagnetic wave absorption performance.

Claims

1. A composite material, characterized in that: A porous silicon carbide substrate comprising 3-9 wt % of zirconium boride; and The in-situ generated silicon carbide nanowires are supported on the pore wall surface of the porous silicon carbide substrate, and the silicon carbide nanowires are used to form a heterogeneous interface with the pore wall of the porous silicon carbide substrate.

2. The composite material according to claim 1, characterized in that: The porosity of the porous silicon carbide substrate is 30-35%.

3. The composite material according to claim 1, characterized in that: The diameter of the silicon carbide nanowire is 10-500 nanometers.

4. The method for preparing the composite material according to claim 1, characterized in that: The steps include: Silicon carbide coarse powder, silicon carbide fine powder, zirconium boride powder, an aqueous solution of a binder, and an organic solvent miscible with water are mixed, dried, and sintered to obtain a porous silicon carbide matrix; The porous silicon carbide substrate is immersed in a silicon carbide precursor solution including a nickel-based catalyst for multiple times, and then dried and sintered to obtain a porous silicon carbide substrate; The average particle size of the silicon carbide coarse powder is 50-150 mesh; The average particle size of the silicon carbide fine powder is 150-250nm; The weight ratio of the coarse silicon carbide powder to the fine silicon carbide powder is 3:0.5-1.

5.

5. The method for preparing the composite material according to claim 4, characterized in that: The aqueous solution of the binder includes an aqueous solution of PVA; The water-miscible organic solvent includes ethanol; The concentration of the aqueous solution of PVA is 5-4-6wt%; The amount of the aqueous solution of the binder added is 3-5wt% of the total weight of the coarse silicon carbide powder, the fine silicon carbide powder and the zirconium boride powder; The amount of the water-miscible organic solvent added is 5-10 wt % of the total weight of the coarse silicon carbide powder, the fine silicon carbide powder and the zirconium boride powder.

6. The method for preparing silicon carbide ceramics according to claim 4, characterized in that: The sintering temperature is 2350°C-2450°C; The sintering temperature is 1350-1450°C.

7. The method for preparing a composite material according to claim 4, characterized in that: The nickel-based catalyst includes nickel sulfamate; The silicon carbide precursor solution includes a carbon source and a silicon source.

8. The method for preparing a composite material according to claim 7, characterized in that: The carbon source includes glucose; The silicon source includes tetraethyl orthosilicate.

9. The method for preparing a composite material according to claim 7, characterized in that: The weight ratio of the carbon source to the silicon source is 1:2.5-3.5; The amount of the nickel-based catalyst added is 8-12 wt % of the sum of the weight of the carbon source and the silicon source.

10. The use of the composite material according to claim 1, characterized in that: Used to absorb electromagnetic waves.

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