Al2o3 fiber reinforced oxide composite material based on core-shell structure for regulating electromagnetic shielding performance and preparation method

Abstract

The application discloses an Al2O3 fiber reinforced oxide composite material based on core-shell structure regulation of electromagnetic shielding performance and a preparation method, and belongs to the field of ceramic matrix composites and electromagnetic shielding materials.The continuous Al2O3 fiber is used as a reinforcing body, and the Al2O3-3YSZ@SiOC core-shell structure ceramic particle is used as a functional matrix, wherein the core layer is an Al2O3 and 3YSZ composite oxide, and the shell layer is a SiOC carbon-containing ceramic phase; the core-shell structure ceramic particle is prepared through hydrolysis and polycondensation of an organic silicon precursor and high-temperature pyrolysis, and the electromagnetic performance is adjusted by regulating the carbon content; then, the slurry impregnation, laminated forming and hot-pressing sintering processes are adopted to prepare the composite material.The application realizes the synergistic effect of the electric conduction loss and the polarization loss through the construction of a multiphase interface, realizes the adjustable conversion of the electromagnetic absorption and shielding performance while the high-temperature stability and the mechanical performance of the material are maintained, and the material is suitable for the fields of aerospace high-temperature structures and electromagnetic shielding integration.

Description

Technical Field

[0001] This invention belongs to the field of ceramic matrix composites and electromagnetic protection materials, specifically relating to an Al2O3 fiber-reinforced oxide composite material and its preparation method based on core-shell structure to regulate electromagnetic protection performance. Background Technology

[0002] With the development of aerospace, advanced weaponry, and high-temperature protection technologies, the service environment of materials is becoming increasingly complex. They not only need to withstand extreme conditions such as high temperatures, oxidation, and thermal shock, but also need electromagnetic protection capabilities to meet application requirements such as electromagnetic stealth and resistance to electromagnetic interference. Therefore, developing structural-functional integrated materials that combine excellent structural properties with electromagnetic functionality has become a current research hotspot.

[0003] Continuous Al₂O₃ fiber-reinforced oxide composites have promising applications in hot-end structural components of aero-engines and high-temperature protection structures due to their excellent high-temperature stability, oxidation resistance, and low thermal conductivity and density. However, these composites are typically composed of electrically insulating oxides with low dielectric constants and low conductivity, resulting in limited electromagnetic wave loss capabilities and hindering effective electromagnetic wave absorption and shielding, thus limiting their application in integrated electromagnetic protection structures. Currently, the main method to improve the electromagnetic protection performance of materials is to introduce conductive phases or magnetic components to achieve electromagnetic wave attenuation through conductive or magnetic losses. However, this method generally suffers from the following problems: firstly, metal or magnetic fillers are prone to oxidation or performance degradation in high-temperature oxidizing environments, making it difficult to meet high-temperature service requirements; secondly, the large difference in thermal expansion coefficients between the added conductive phase and the oxide matrix can easily lead to interface failure and decreased structural stability. Furthermore, traditional fillers are often difficult to distribute uniformly within the material, making it difficult to construct effective multi-scale electromagnetic loss structures.

[0004] In recent years, research on the modulation of electromagnetic properties based on multiphase interfaces has gradually attracted attention. Studies have shown that electromagnetic wave loss mainly originates from the synergistic effect of conductivity loss and polarization loss (including interfacial polarization and dipole polarization). Constructing multiphase interface structures can effectively enhance electromagnetic wave attenuation capabilities. Among them, SiOC carbon-containing ceramics are considered a class of promising electromagnetic functional materials due to their good high-temperature stability and tunable conductivity. However, the distribution state and conductivity of a single SiOC phase in composite materials are difficult to precisely control, easily leading to a single electromagnetic loss mechanism and making it difficult to achieve synergistic optimization between absorption and shielding performance.

[0005] Therefore, how to achieve adjustable control of electromagnetic absorption and electromagnetic shielding performance through reasonable structural design while ensuring the high-temperature structural performance of continuous Al2O3 fiber reinforced oxide composites remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the problems of poor high-temperature stability and mechanical properties, and the inability to control electromagnetic absorption and shielding performance of existing electromagnetic shielding materials, this invention introduces core-shell structured ceramic particles containing SiOC into an oxide matrix and controls the shell composition to construct a multiphase interface structure in which the conductive shell and the insulating core are synergistically distributed. This achieves a synergistic enhancement of conductivity loss and polarization loss, thereby enabling an adjustable transition between electromagnetic wave absorption and electromagnetic shielding performance.

[0007] This invention relates to an Al2O3 fiber-reinforced oxide composite material for regulating electromagnetic protection performance based on a core-shell structure. The composite material comprises a continuous Al2O3 fiber reinforcement and an oxide matrix. The volume fraction of the Al2O3 fiber reinforcement is 35-45%. The Al2O3 fiber reinforcement is a fiber cloth with a ply spacing of 0.2-0.5 mm. In the composite material, the SiOC shell is a carbon-containing amorphous structure, where the carbon phase exists in the form of amorphous carbon or defective carbon. The carbon phase is used to construct a dielectric response structure in the composite material that synergistically enhances conductivity and polarization loss. By adjusting the Si, O, and C content in the SiOC shell, the composite material exhibits tunable dielectric loss characteristics in the 2-18 GHz frequency band. When the SiOC shell content is 12-20 wt%, the O content is 30%-34 wt%, and the C content is 45-50 wt%, the composite material exhibits good dielectric loss characteristics at room temperature. The composite material exhibits a minimum reflection loss of less than -20dB in the 2-18GHz frequency band, corresponding to an electromagnetic response structure dominated by dielectric loss. When the Si content in the SiOC shell of the composite material is 1-10wt%, the O content is 5-20wt%, and the C content is 70-90wt%, the electromagnetic shielding effectiveness of the composite material in the 2-18GHz frequency band at room temperature is greater than 10dB, corresponding to an electromagnetic response structure with enhanced conductivity loss. The electromagnetic shielding effectiveness is measured using the coaxial method, waveguide method, or bow method.

[0008] This invention relates to a continuous Al2O3 fiber-reinforced oxide composite material with core-shell structure for regulating electromagnetic protection performance, and is carried out according to the following steps:

[0009] Step 1: Heat-treat the Al2O3 fiber cloth by mixing Al2O3 powder and 3YSZ powder;

[0010] The mass ratio of Al2O3 powder to 3YSZ powder is 75-80:20-25;

[0011] The Al2O3 powder includes Al2O3 powder with a median particle size of 100 nm and Al2O3 powder with a median particle size of 500 nm; the mass ratio of the 100 nm Al2O3 powder to the 500 nm Al2O3 powder is 68-72:3-7.

[0012] Step 2: Preparation of ceramic slurry

[0013] ① Al2O3 powder and 3YSZ powder are mixed and dry ball-milled to obtain oxide powder. Then, the oxide powder is mixed with dimethyldimethoxysilane and tetraethoxysilane, and anhydrous ethanol, deionized water and ammonia are added. After stirring for 24-48 hours, an Al2O3-3YSZ@SiOC-nC precursor suspension is obtained. Resorcinol and formaldehyde aqueous solution are added to the Al2O3-3YSZ@SiOC-nC precursor suspension, and after stirring for 24-48 hours, centrifugation and washing are performed to obtain Al2O3-3YSZ@SiOC-nC precursor particles. The Al2O3-3YSZ@SiOCnC precursor particles are pyrolyzed to obtain Al2O3-3YSZ@SiOC-nC core-shell structured composite ceramic particles.

[0014] The ratio of the oxide powder to dimethyldimethoxysilane and tetraethoxysilane is 1.78-3.85 g: 9.1 mL: 1.82 mL;

[0015] The ratio of the oxide powder to anhydrous ethanol, deionized water and ammonia is 1.78-3.85g: 200mL-220mL: 27-30mL: 13-15mL;

[0016] The ratio of the oxide powder to the aqueous solution of resorcinol and formaldehyde is 1.78-3.85g: 2-6g: 2.8-8.4mL;

[0017] The pyrolysis process is as follows: heating at 1100-1300℃ for 1.5-3 hours in an argon atmosphere;

[0018] ② The Al2O3-3YSZ@SiOC-nC core-shell composite ceramic particles are mixed with a dispersant solution to obtain a ceramic slurry;

[0019] The dispersant solution is an aqueous solution of sodium polyacrylate with a mass fraction of 49-51%.

[0020] The volume fraction of Al2O3-3YSZ@SiOC-nC core-shell structured composite ceramic particles in the ceramic slurry is 45-47%.

[0021] Step 3: Preheat the Al2O3 fiber cloth, then stack it, and impregnate the Al2O3 fiber cloth with ceramic slurry to obtain a preform; then dry and hot-press the preform to obtain an Al2O3 fiber reinforced oxide composite material.

[0022] The mass ratio of Al2O3 fiber cloth to Al2O3-3YSZ@SiOC-nC core-shell composite ceramic particles is 7-8:17-19.

[0023] The hot pressing sintering process is as follows: heating rate 5-20℃ / min, sintering temperature 1200-1350℃, pressure 5-30MPa, and holding time 1-4h.

[0024] Another continuous Al2O3 fiber-reinforced oxide composite material based on core-shell structure to regulate electromagnetic protection performance according to the present invention is carried out according to the following steps:

[0025] Step 1: Heat-treat the Al2O3 fiber cloth by mixing Al2O3 powder and 3YSZ powder;

[0026] The mass ratio of Al2O3 powder to 3YSZ powder is 75-80:20-25;

[0027] The Al2O3 powder includes Al2O3 powder with a median particle size of 100 nm and Al2O3 powder with a median particle size of 500 nm; the mass ratio of the 100 nm Al2O3 powder to the 500 nm Al2O3 powder is 68-72:3-7.

[0028] Step 2: Preparation of ceramic slurry

[0029] ① Al2O3 powder and 3YSZ powder are mixed and dry ball-milled to obtain oxide powder. Then, the oxide powder is mixed with dimethyldimethoxysilane and tetraethoxysilane, and anhydrous ethanol, deionized water and ammonia are added. After stirring for 24-48 hours, an Al2O3-3YSZ@SiOC-nC precursor suspension is obtained. Resorcinol and formaldehyde aqueous solution are added to the Al2O3-3YSZ@SiOC-nC precursor suspension, and after stirring for 24-48 hours, centrifugation and washing are performed to obtain Al2O3-3YSZ@SiOC-nC precursor particles.

[0030] The ratio of the oxide powder to dimethyldimethoxysilane and tetraethoxysilane is 1.78-3.85 g: 9.1 mL: 1.82 mL;

[0031] The ratio of the oxide powder to anhydrous ethanol, deionized water and ammonia is 1.78-3.85g: 200mL-220mL: 27-30mL: 13-15mL;

[0032] The ratio of the oxide powder to the aqueous solution of resorcinol and formaldehyde is 1.78-3.85g: 2-6g: 2.8-8.4mL;

[0033] ② The Al2O3-3YSZ@SiOC-nC precursor particles are mixed with a dispersant solution to obtain a ceramic slurry;

[0034] The dispersant solution is an aqueous solution of sodium polyacrylate with a mass fraction of 49-51%.

[0035] The volume fraction of Al2O3-3YSZ@SiOC-nC precursor particles in the ceramic slurry is 45-47%.

[0036] Step 3: Preheat the Al2O3 fiber cloth, then stack it, and impregnate the Al2O3 fiber cloth with ceramic slurry to obtain a preform; then dry and hot press sinter the preform. During the hot pressing sintering process, the organosilicon in the Al2O3-3YSZ@SiOC-nC precursor particles undergoes in-situ pyrolysis to form a SiOC shell on the core layer surface; thus obtaining an Al2O3 fiber-reinforced oxide composite material.

[0037] The mass ratio of the Al2O3 fiber cloth to the Al2O3-3YSZ@SiOC-nC precursor particles is 7-8:17-19.

[0038] The hot pressing sintering process is as follows: heating rate 5-20℃ / min, sintering temperature 1200-1350℃, pressure 5-30MPa, and holding time 1-4h.

[0039] The principle and beneficial effects of this invention are as follows:

[0040] 1. This invention constructs a rich, multi-scale, multi-phase interface network by introducing an oxide core / SiOC carbon-shell core-shell structure into an oxide matrix, achieving synergistic enhancement of various electromagnetic wave attenuation mechanisms, including conductivity loss, polarization loss, and multiple scattering. First, the uniformly distributed free carbon phase in the SiOC shell forms a local conductive network, generating electron migration and hopping conduction under the action of an alternating electromagnetic field, effectively converting electromagnetic energy into heat energy and achieving conductivity loss. Second, there are significant differences in conductivity and dielectric constant among the oxide core, SiOC ceramic phase, amorphous carbon phase, and composite matrix. Under the action of an electromagnetic field, charge accumulation easily occurs at the interface, forming a significant Maxwell-Wagner interface polarization effect. Simultaneously, the numerous carbon defects in the SiOC structure can induce dipole polarization loss. The core-shell particles and the oxide matrix together construct a complex heterogeneous interface system, causing the incident electromagnetic wave to continuously reflect, refract, and scatter during propagation, significantly extending the propagation path of the electromagnetic wave within the material and increasing its interaction time with the loss unit, thereby enhancing the electromagnetic energy dissipation efficiency. More importantly, the introduction of the carbon-containing shell in SiOC improves dielectric loss while avoiding impedance mismatch caused by excessive conductivity. This gives the material both good impedance matching characteristics and strong attenuation capabilities, allowing more electromagnetic waves to penetrate the material's interior rather than being directly reflected at the surface. The aforementioned conductivity loss, interface polarization loss, dipole polarization loss, and multiple scattering effects are coupled and work synergistically to enhance the material's absorption and dissipation of electromagnetic waves, thereby significantly improving the electromagnetic protection performance of the composite material.

[0041] 2. This invention enables the tunable transformation of the electromagnetic shielding mechanism of composite materials by adjusting the carbon content in the SiOC shell: Under low carbon content conditions, the material exhibits excellent electromagnetic wave absorption performance. When the Si content in the SiOC shell is 12-20 wt%, O is 30%-34 wt%, and C is 45-50 wt%, the minimum reflection loss of a 2.6 mm thick composite material is ≤-20 dB, and the effective absorption bandwidth can reach over 3.5 GHz. As the carbon content increases, a conductive network gradually forms, and the material changes from being dominated by electromagnetic wave absorption to being dominated by electromagnetic shielding. When the Si content is 1-10 wt%, O is 5-20 wt%, and C is 70-90 wt%, the electromagnetic shielding effectiveness of a 3.0 mm thick composite material in the 2-18 GHz frequency band is greater than 10 dB. In summary, the electromagnetic absorption and shielding performance can be controlled and adjusted. The carbon in the SiOC shell of this invention is amorphous carbon or a carbon phase with defective structures, and its Raman spectrum I... D / I G The value is 0.8-1.2;

[0042] 3. The composite material of this invention achieves electromagnetic protection while maintaining low density and good mechanical properties, with a density of approximately 2.05-2.24 g / cm³.3 With a Vickers hardness of approximately 500-690 MPa, it balances lightweight design with structural load-bearing capacity, making it suitable for high-temperature lightweight structural applications.

[0043] 4. By introducing a carbon-containing phase and multiphase interface structure into SiOC, this invention can effectively suppress phonon transmission and enhance interface scattering, keeping the thermal conductivity of the material in the range of approximately 1.55-1.82 W / (m·K) at room temperature. It has good thermal insulation performance and is suitable for high-temperature thermal protection environments.

[0044] 5. The core-shell structure design in this invention has good compatibility and high-temperature stability with the oxide matrix. The preparation method is based on the combination of precursor conversion and traditional composite molding process. The process route is simple and highly controllable. While ensuring the oxidation resistance and structural stability of the material, it realizes the integration of structure and electromagnetic function, and expands the application range of continuous Al2O3 fiber reinforced oxide composite materials in complex service environments. Attached Figure Description

[0045] Figure 1 SEM images and EDS images of the oxide raw materials used to prepare the composite materials in Examples 1-3;

[0046] Figure 2 SEM images of the oxide matrix in the composite materials prepared in Examples 1-3 and EDS images of the matrix in Example 1;

[0047] Figure 3 SEM and EDS images of the composite materials prepared in Examples 1-3;

[0048] Figure 4 The XRD patterns of the oxide matrix in the composite materials prepared in Examples 1-3 are shown.

[0049] Figure 5 The XRD patterns of the composite materials prepared in Examples 1-3 are shown below.

[0050] Figure 6 The thermal conductivity curves, thermal diffusivity curves, and heat capacity curves of the composite materials prepared in Examples 1-3 are shown.

[0051] Figure 7 Vickers hardness indentation maps of the composite materials prepared in Examples 1-3;

[0052] Figure 8 The Raman spectra of the oxide matrix of the composite materials prepared in Examples 1-3;

[0053] Figure 9 The Raman spectra of the composite materials prepared in Examples 1-3;

[0054] Figure 10 The FT-IR spectra of the composite materials prepared in Examples 1-3;

[0055] Figure 11 XPS spectra of the composite materials prepared in Examples 1-3;

[0056] Figure 12 The electromagnetic wave absorption performance of the composite materials prepared in Examples 1-3 includes reflection loss values, three-dimensional projection diagrams, and three-dimensional curves.

[0057] Figure 13 The electromagnetic wave shielding performance of the composite materials prepared in Examples 1-3 includes reflection shielding effectiveness, absorption shielding effectiveness, and total shielding effectiveness.

[0058] Figure 14 The real part of the relative complex permittivity, the imaginary part of the relative complex permittivity, and the nodal loss angle are for the composite materials prepared in Examples 1-3.

[0059] Figure 15 The impedance matching values ​​are those of the composite materials prepared in Examples 1-3.

[0060] Figure 16 The image shows the Debye relaxation Cole-Cole diagrams of the composite materials prepared in Examples 1-3. Detailed Implementation

[0061] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any reasonable combination of the specific embodiments.

[0062] Specific Implementation Method 1: This implementation method is based on the core-shell structure to regulate the electromagnetic protection performance of Al2O3 fiber-reinforced oxide composite material, which includes a continuous Al2O3 fiber reinforcement and an oxide matrix; the volume fraction of Al2O3 fiber reinforcement in the composite material is 35-45%; the Al2O3 fiber reinforcement is a fiber cloth with a fiber spacing of 0.2-0.5 mm.

[0063] This embodiment has the following beneficial effects:

[0064] 1. This embodiment introduces an oxide core / SiOC carbon-shell core-shell structure into an oxide matrix, constructing a rich multi-scale, multi-phase interface network, achieving synergistic enhancement of various electromagnetic wave attenuation mechanisms such as conductivity loss, polarization loss, and multiple scattering. First, the uniformly distributed free carbon phase in the SiOC shell forms a local conductive network, generating electron migration and hopping conduction under the action of an alternating electromagnetic field, effectively converting electromagnetic energy into heat energy and achieving conductivity loss. Second, there are significant differences in conductivity and dielectric constant among the oxide core, SiOC ceramic phase, amorphous carbon phase, and composite matrix. Under the action of an electromagnetic field, charge accumulation easily occurs at the interface, forming a significant Maxwell-Wagner interface polarization effect. Simultaneously, the numerous carbon defects in the SiOC structure can induce dipole polarization loss. The core-shell particles and the oxide matrix together construct a complex heterogeneous interface system, causing the incident electromagnetic wave to continuously reflect, refract, and scatter during propagation, significantly extending the propagation path of the electromagnetic wave within the material, increasing its interaction time with the loss unit, and thus enhancing the electromagnetic energy dissipation efficiency. More importantly, the introduction of the carbon-containing shell in SiOC improves dielectric loss while avoiding impedance mismatch caused by excessive conductivity. This gives the material both good impedance matching characteristics and strong attenuation capabilities, allowing more electromagnetic waves to penetrate the material's interior rather than being directly reflected at the surface. The aforementioned conductivity loss, interface polarization loss, dipole polarization loss, and multiple scattering effects are coupled and work synergistically to enhance the material's absorption and dissipation of electromagnetic waves, thereby significantly improving the electromagnetic protection performance of the composite material.

[0065] 2. This embodiment enables the tunable transformation of the electromagnetic shielding mechanism of the composite material by adjusting the carbon content in the SiOC shell: under low carbon content conditions, the material exhibits excellent electromagnetic wave absorption performance. When the Si content in the SiOC shell is 12-20wt%, O is 30%-34wt%, and C is 45-50wt%, the minimum reflection loss of the 2.6mm thick composite material is ≤-20dB, and the effective absorption bandwidth can reach over 3.5GHz. As the carbon content increases, a conductive network gradually forms, and the material changes from being dominated by electromagnetic wave absorption to being dominated by electromagnetic shielding. When the Si content is 1-10wt%, O is 5-20wt%, and C is 70-90wt%, the electromagnetic shielding effectiveness of the 3.0mm thick composite material in the 2-18GHz frequency band is greater than 10dB. In summary, the electromagnetic absorption and shielding performance can be controlled and adjusted. In this embodiment, the carbon in the SiOC shell is amorphous carbon or a carbon phase with defective structures, and its Raman spectrum I... D / I G The value is 0.8-1.2;

[0066] 3. The composite material in this embodiment achieves electromagnetic protection while maintaining low density and good mechanical properties; its density is approximately 2.05-2.24 g / cm³.3 With a Vickers hardness of approximately 500-690 MPa, it balances lightweight design with structural load-bearing capacity, making it suitable for high-temperature lightweight structural applications.

[0067] 4. By introducing the carbon-containing phase and multiphase interface structure of SiOC, this embodiment can effectively suppress phonon transmission and enhance interface scattering, so that the thermal conductivity of the material is maintained in the range of about 1.55-1.82 W / (m·K) at room temperature, which has good thermal insulation performance and is suitable for high-temperature thermal protection environments.

[0068] 5. In this embodiment, the core-shell structure design has good compatibility and high-temperature stability with the oxide matrix. The preparation method is based on the combination of precursor conversion and traditional composite molding process. The process route is simple and highly controllable. While ensuring the oxidation resistance and structural stability of the material, it realizes the integration of structure and electromagnetic function, and expands the application range of continuous Al2O3 fiber reinforced oxide composite materials in complex service environments.

[0069] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that: the oxide matrix is ​​a core-shell structured composite ceramic particle with a median particle size of 0.6-3.0 μm; the core layer of the core-shell structured composite ceramic particle is a composite oxide of Al2O3 and 3YSZ (3 mol% yttrium-stabilized zirconium oxide), with a mass ratio of Al2O3 to 3YSZ of 75-80:20-25, and the shell layer is SiOC; the Si content in the SiOC is 1-20 wt%, the C content is 45-50 wt% or 70-90 wt%, and O is the balance.

[0070] Specific Implementation Method 3: This implementation method: The preparation method of continuous Al2O3 fiber reinforced oxide composite material based on core-shell structure to regulate electromagnetic protection performance is carried out according to the following steps:

[0071] Step 1: Heat-treat the Al2O3 fiber cloth by mixing Al2O3 powder and 3YSZ powder;

[0072] The mass ratio of Al2O3 powder to 3YSZ powder is 75-80:20-25;

[0073] The Al2O3 powder includes Al2O3 powder with a median particle size of 100 nm and Al2O3 powder with a median particle size of 500 nm; the mass ratio of the 100 nm Al2O3 powder to the 500 nm Al2O3 powder is 68-72:3-7.

[0074] Step 2: Preparation of ceramic slurry

[0075] ① Al2O3 powder and 3YSZ powder are mixed and dry ball-milled to obtain oxide powder. Then, the oxide powder is mixed with dimethyldimethoxysilane and tetraethoxysilane, and anhydrous ethanol, deionized water and ammonia are added. After stirring for 24-48 hours, an Al2O3-3YSZ@SiOC-nC precursor suspension is obtained. Resorcinol and formaldehyde aqueous solution are added to the Al2O3-3YSZ@SiOC-nC precursor suspension, and after stirring for 24-48 hours, centrifugation and washing are performed to obtain Al2O3-3YSZ@SiOC-nC precursor particles. The Al2O3-3YSZ@SiOCnC precursor particles are pyrolyzed to obtain Al2O3-3YSZ@SiOC-nC core-shell structured composite ceramic particles.

[0076] The ratio of the oxide powder to dimethyldimethoxysilane and tetraethoxysilane is 1.78-3.85 g: 9.1 mL: 1.82 mL;

[0077] The ratio of the oxide powder to anhydrous ethanol, deionized water and ammonia is 1.78-3.85g: 200mL-220mL: 27-30mL: 13-15mL;

[0078] The ratio of the oxide powder to the aqueous solution of resorcinol and formaldehyde is 1.78-3.85g: 2-6g: 2.8-8.4mL;

[0079] The pyrolysis process is as follows: heating at 1100-1300℃ for 1.5-3 hours in an argon atmosphere;

[0080] ② The Al2O3-3YSZ@SiOC-nC core-shell composite ceramic particles are mixed with a dispersant solution to obtain a ceramic slurry;

[0081] The dispersant solution is an aqueous solution of sodium polyacrylate with a mass fraction of 49-51%.

[0082] The volume fraction of Al2O3-3YSZ@SiOC-nC core-shell structured composite ceramic particles in the ceramic slurry is 45-47%.

[0083] Step 3: Preheat the Al2O3 fiber cloth, then stack it, and impregnate the Al2O3 fiber cloth with ceramic slurry to obtain a preform; then dry and hot-press the preform to obtain an Al2O3 fiber reinforced oxide composite material.

[0084] The mass ratio of Al2O3 fiber cloth to Al2O3-3YSZ@SiOC-nC core-shell composite ceramic particles is 7-8:17-19.

[0085] The hot pressing sintering process is as follows: heating rate 5-20℃ / min, sintering temperature 1200-1350℃, pressure 5-30MPa, and holding time 1-4h.

[0086] 1. This embodiment introduces an oxide core / SiOC carbon-shell core-shell structure into an oxide matrix, constructing a rich multi-scale, multi-phase interface network, achieving synergistic enhancement of various electromagnetic wave attenuation mechanisms such as conductivity loss, polarization loss, and multiple scattering. First, the uniformly distributed free carbon phase in the SiOC shell forms a local conductive network, generating electron migration and hopping conduction under the action of an alternating electromagnetic field, effectively converting electromagnetic energy into heat energy and achieving conductivity loss. Second, there are significant differences in conductivity and dielectric constant among the oxide core, SiOC ceramic phase, amorphous carbon phase, and composite matrix. Under the action of an electromagnetic field, charge accumulation easily occurs at the interface, forming a significant Maxwell-Wagner interface polarization effect. Simultaneously, the numerous carbon defects in the SiOC structure can induce dipole polarization loss. The core-shell particles and the oxide matrix together construct a complex heterogeneous interface system, causing the incident electromagnetic wave to continuously reflect, refract, and scatter during propagation, significantly extending the propagation path of the electromagnetic wave within the material, increasing its interaction time with the loss unit, and thus enhancing the electromagnetic energy dissipation efficiency. More importantly, the introduction of the carbon-containing shell in SiOC improves dielectric loss while avoiding impedance mismatch caused by excessive conductivity. This gives the material both good impedance matching characteristics and strong attenuation capabilities, allowing more electromagnetic waves to penetrate the material's interior rather than being directly reflected at the surface. The aforementioned conductivity loss, interface polarization loss, dipole polarization loss, and multiple scattering effects are coupled and work synergistically to enhance the material's absorption and dissipation of electromagnetic waves, thereby significantly improving the electromagnetic protection performance of the composite material.

[0087] 2. This embodiment enables the tunable transformation of the electromagnetic shielding mechanism of the composite material by adjusting the carbon content in the SiOC shell: under low carbon content conditions, the material exhibits excellent electromagnetic wave absorption performance. When the Si content in the SiOC shell is 12-20wt%, O is 30%-34wt%, and C is 45-50wt%, the minimum reflection loss of the 2.6mm thick composite material is ≤-20dB, and the effective absorption bandwidth can reach over 3.5GHz. As the carbon content increases, a conductive network gradually forms, and the material changes from being dominated by electromagnetic wave absorption to being dominated by electromagnetic shielding. When the Si content is 1-10wt%, O is 5-20wt%, and C is 70-90wt%, the electromagnetic shielding effectiveness of the 3.0mm thick composite material in the 2-18GHz frequency band is greater than 10dB. In summary, the electromagnetic absorption and shielding performance can be controlled and adjusted. In this embodiment, the carbon in the SiOC shell is amorphous carbon or a carbon phase with defective structures, and its Raman spectrum I... D / I GThe value is 0.8-1.2;

[0088] 3. The composite material in this embodiment achieves electromagnetic protection while maintaining low density and good mechanical properties; its density is approximately 2.05-2.24 g / cm³. 3 With a Vickers hardness of approximately 500-690 MPa, it balances lightweight design with structural load-bearing capacity, making it suitable for high-temperature lightweight structural applications.

[0089] 4. By introducing the carbon-containing phase and multiphase interface structure of SiOC, this embodiment can effectively suppress phonon transmission and enhance interface scattering, so that the thermal conductivity of the material is maintained in the range of about 1.55-1.82 W / (m·K) at room temperature, which has good thermal insulation performance and is suitable for high-temperature thermal protection environments.

[0090] 5. In this embodiment, the core-shell structure design has good compatibility and high-temperature stability with the oxide matrix. The preparation method is based on the combination of precursor conversion and traditional composite molding process. The process route is simple and highly controllable. While ensuring the oxidation resistance and structural stability of the material, it realizes the integration of structure and electromagnetic function, and expands the application range of continuous Al2O3 fiber reinforced oxide composite materials in complex service environments.

[0091] Specific Implementation Method Four: This implementation method differs from Specific Implementation Method Three in that the heat treatment process of the Al2O3 fiber cloth in step one is: heating in an air atmosphere at 600-800℃ for 1-4 hours.

[0092] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Three in that:

[0093] Step 2① The ball milling process is as follows: the rotation speed is 400 rpm, and the ball milling time is 2 hours;

[0094] Step 2① The concentration of the ammonia solution is 25-28 wt.%;

[0095] Step 2① The concentration of the formaldehyde aqueous solution is 35-40 wt.%.

[0096] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Three in that:

[0097] The interlayer spacing of the Al2O3 fiber cloth stacked in step three is 0.2-0.5 mm;

[0098] The preheating process described in step three is as follows: heating at 700℃ for 1-2 hours;

[0099] The drying process described in step three is as follows: drying at 90℃ for 18-24 hours.

[0100] Specific Implementation Method Seven: The preparation method of the continuous Al2O3 fiber-reinforced oxide composite material based on core-shell structure to regulate electromagnetic protection performance in this implementation method is carried out according to the following steps:

[0101] Step 1: Heat-treat the Al2O3 fiber cloth by mixing Al2O3 powder and 3YSZ powder;

[0102] The mass ratio of Al2O3 powder to 3YSZ powder is 75-80:20-25;

[0103] The Al2O3 powder includes Al2O3 powder with a median particle size of 100 nm and Al2O3 powder with a median particle size of 500 nm; the mass ratio of the 100 nm Al2O3 powder to the 500 nm Al2O3 powder is 68-72:3-7.

[0104] Step 2: Preparation of ceramic slurry

[0105] ① Al2O3 powder and 3YSZ powder are mixed and dry ball-milled to obtain oxide powder. Then, the oxide powder is mixed with dimethyldimethoxysilane and tetraethoxysilane, and anhydrous ethanol, deionized water and ammonia are added. After stirring for 24-48 hours, an Al2O3-3YSZ@SiOC-nC precursor suspension is obtained. Resorcinol and formaldehyde aqueous solution are added to the Al2O3-3YSZ@SiOC-nC precursor suspension, and after stirring for 24-48 hours, centrifugation and washing are performed to obtain Al2O3-3YSZ@SiOC-nC precursor particles.

[0106] The ratio of the oxide powder to dimethyldimethoxysilane and tetraethoxysilane is 1.78-3.85 g: 9.1 mL: 1.82 mL;

[0107] The ratio of the oxide powder to anhydrous ethanol, deionized water and ammonia is 1.78-3.85g: 200mL-220mL: 27-30mL: 13-15mL;

[0108] The ratio of the oxide powder to the aqueous solution of resorcinol and formaldehyde is 1.78-3.85g: 2-6g: 2.8-8.4mL;

[0109] ② The Al2O3-3YSZ@SiOC-nC precursor particles are mixed with a dispersant solution to obtain a ceramic slurry;

[0110] The dispersant solution is an aqueous solution of sodium polyacrylate with a mass fraction of 49-51%.

[0111] The volume fraction of Al2O3-3YSZ@SiOC-nC precursor particles in the ceramic slurry is 45-47%.

[0112] Step 3: Preheat the Al2O3 fiber cloth, then stack it, and impregnate the Al2O3 fiber cloth with ceramic slurry to obtain a preform; then dry and hot press sinter the preform. During the hot pressing sintering process, the organosilicon in the Al2O3-3YSZ@SiOC-nC precursor particles undergoes in-situ pyrolysis to form a SiOC shell on the core layer surface; thus obtaining an Al2O3 fiber-reinforced oxide composite material.

[0113] The mass ratio of the Al2O3 fiber cloth to the Al2O3-3YSZ@SiOC-nC precursor particles is 7-8:17-19.

[0114] The hot pressing sintering process is as follows: heating rate 5-20℃ / min, sintering temperature 1200-1350℃, pressure 5-30MPa, and holding time 1-4h.

[0115] 1. This embodiment introduces an oxide core / SiOC carbon-shell core-shell structure into an oxide matrix, constructing a rich multi-scale, multi-phase interface network, achieving synergistic enhancement of various electromagnetic wave attenuation mechanisms such as conductivity loss, polarization loss, and multiple scattering. First, the uniformly distributed free carbon phase in the SiOC shell forms a local conductive network, generating electron migration and hopping conduction under the action of an alternating electromagnetic field, effectively converting electromagnetic energy into heat energy and achieving conductivity loss. Second, there are significant differences in conductivity and dielectric constant among the oxide core, SiOC ceramic phase, amorphous carbon phase, and composite matrix. Under the action of an electromagnetic field, charge accumulation easily occurs at the interface, forming a significant Maxwell-Wagner interface polarization effect. Simultaneously, the numerous carbon defects in the SiOC structure can induce dipole polarization loss. The core-shell particles and the oxide matrix together construct a complex heterogeneous interface system, causing the incident electromagnetic wave to continuously reflect, refract, and scatter during propagation, significantly extending the propagation path of the electromagnetic wave within the material, increasing its interaction time with the loss unit, and thus enhancing the electromagnetic energy dissipation efficiency. More importantly, the introduction of the carbon-containing shell in SiOC improves dielectric loss while avoiding impedance mismatch caused by excessive conductivity. This gives the material both good impedance matching characteristics and strong attenuation capabilities, allowing more electromagnetic waves to penetrate the material's interior rather than being directly reflected at the surface. The aforementioned conductivity loss, interface polarization loss, dipole polarization loss, and multiple scattering effects are coupled and work synergistically to enhance the material's absorption and dissipation of electromagnetic waves, thereby significantly improving the electromagnetic protection performance of the composite material.

[0116] 2. This embodiment enables the tunable transformation of the electromagnetic shielding mechanism of the composite material by adjusting the carbon content in the SiOC shell: under low carbon content conditions, the material exhibits excellent electromagnetic wave absorption performance. When the Si content in the SiOC shell is 12-20wt%, O is 30%-34wt%, and C is 45-50wt%, the minimum reflection loss of the 2.6mm thick composite material is ≤-20dB, and the effective absorption bandwidth can reach over 3.5GHz. As the carbon content increases, a conductive network gradually forms, and the material changes from being dominated by electromagnetic wave absorption to being dominated by electromagnetic shielding. When the Si content is 1-10wt%, O is 5-20wt%, and C is 70-90wt%, the electromagnetic shielding effectiveness of the 3.0mm thick composite material in the 2-18GHz frequency band is greater than 10dB. In summary, the electromagnetic absorption and shielding performance can be controlled and adjusted. In this embodiment, the carbon in the SiOC shell is amorphous carbon or a carbon phase with defective structures, and its Raman spectrum I... D / I G The value is 0.8-1.2;

[0117] 3. The composite material in this embodiment achieves electromagnetic protection while maintaining low density and good mechanical properties; its density is approximately 2.05-2.24 g / cm³. 3 With a Vickers hardness of approximately 500-690 MPa, it balances lightweight design with structural load-bearing capacity, making it suitable for high-temperature lightweight structural applications.

[0118] 4. By introducing the carbon-containing phase and multiphase interface structure of SiOC, this embodiment can effectively suppress phonon transmission and enhance interface scattering, so that the thermal conductivity of the material is maintained in the range of about 1.55-1.82 W / (m·K) at room temperature, which has good thermal insulation performance and is suitable for high-temperature thermal protection environments.

[0119] 5. In this embodiment, the core-shell structure design has good compatibility and high-temperature stability with the oxide matrix. The preparation method is based on the combination of precursor conversion and traditional composite molding process. The process route is simple and highly controllable. While ensuring the oxidation resistance and structural stability of the material, it realizes the integration of structure and electromagnetic function, and expands the application range of continuous Al2O3 fiber reinforced oxide composite materials in complex service environments.

[0120] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that the heat treatment process of the Al2O3 fiber cloth in step one is: heating in an air atmosphere at 600-800℃ for 1-4 hours.

[0121] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Seven in that:

[0122] Step 2① The ball milling process is as follows: the rotation speed is 400 rpm, and the ball milling time is 2 hours;

[0123] Step 2① The concentration of the ammonia solution is 25-28 wt.%;

[0124] Step 2① The concentration of the formaldehyde aqueous solution is 35-40 wt.%.

[0125] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method Seven in that:

[0126] The interlayer spacing of the Al2O3 fiber cloth stacked in step three is 0.2-0.5 mm;

[0127] The preheating process described in step three is as follows: heating at 700℃ for 1-2 hours;

[0128] The drying process described in step three is as follows: drying at 90℃ for 18-24 hours.

[0129] Example 1

[0130] This embodiment describes the continuous Al2O3 fiber-reinforced oxide composite material with core-shell structure for regulating electromagnetic protection performance, following the steps below:

[0131] Step 1: Heat-treat the Al2O3 fiber cloth (AF18) by mixing Al2O3 powder and 3YSZ powder;

[0132] The mass ratio of Al2O3 powder to 3YSZ powder is 75:25;

[0133] The Al2O3 powder includes Al2O3 powder with a median particle size of 100 nm and Al2O3 powder with a median particle size of 500 nm; the mass ratio of the 100 nm Al2O3 powder to the 500 nm Al2O3 powder is 70:5.

[0134] The heat treatment process for the Al2O3 fiber cloth is as follows: heating at 700°C in air for 2 hours; heat treatment in air can remove surface organic impurities and improve interfacial bonding performance.

[0135] Step 2: Preparation of ceramic slurry

[0136] ① Al2O3 powder and 3YSZ powder were mixed and dry ball-milled to obtain oxide powder. Then, 1.78 g of oxide powder was mixed with 9.1 mL of dimethyldimethoxysilane and 1.82 mL of tetraethoxysilane, followed by the addition of 200 mL of anhydrous ethanol, 28 mL of deionized water, and 14 mL of ammonia. After stirring for 24 h, an Al2O3-3YSZ@SiOC-nC precursor suspension was obtained. 2 g of resorcinol and 2.8 mL of formaldehyde aqueous solution were added to the Al2O3-3YSZ@SiOC-nC precursor suspension, and after stirring for another 24 h, the mixture was centrifuged and washed to obtain Al2O3-3YSZ@SiOC-nC precursor particles. The shell of the Al2O3-3YSZ@SiOC-nC precursor particles was SiOC, with Si comprising 19.63 wt%, O 33.70 wt%, and C 46.67 wt%.

[0137] The ball milling process is as follows: the rotation speed is 400 rpm, and the ball milling time is 2 hours;

[0138] The concentration of the ammonia solution was 27 wt.%.

[0139] The concentration of the formaldehyde aqueous solution is 38 wt.%;

[0140] ② The Al2O3-3YSZ@SiOC-nC precursor particles are mixed with a dispersant solution to obtain a ceramic slurry;

[0141] The dispersant solution is an aqueous solution of sodium polyacrylate with a mass fraction of 49 wt.%.

[0142] The volume fraction of Al2O3-3YSZ@SiOC-nC precursor particles in the ceramic slurry is 45%.

[0143] Step 3: Preheat the Al2O3 fiber cloth, then stack it, and impregnate the Al2O3 fiber cloth with ceramic slurry to obtain a preform; then dry and hot-press the preform to obtain an Al2O3 fiber reinforced oxide composite material, denoted as AF18 / Al2O3-3YSZ@SiOC-1C; the obtained Al2O3 fiber reinforced oxide composite material is composed of Al2O3 fiber cloth (AF18) and oxide matrix (Al2O3-3YSZ@SiOC-1C), and the oxide matrix is ​​a core-shell structured composite ceramic particle;

[0144] The interlayer spacing of the Al2O3 fiber cloth stacked is 0.2 mm;

[0145] The preheating process is as follows: heating at 700℃ for 2 hours;

[0146] The drying process is as follows: drying at 90℃ for 24 hours;

[0147] The mass ratio of the Al2O3 fiber cloth to the Al2O3-3YSZ@SiOC-nC precursor particles is 7:17.

[0148] The hot pressing sintering process is as follows: heating rate 10℃ / min, sintering temperature 300℃, pressure 10MPa, and holding time 2h.

[0149] Example 2

[0150] This embodiment describes the continuous Al2O3 fiber-reinforced oxide composite material with core-shell structure for regulating electromagnetic protection performance, following the steps below:

[0151] Step 1: Heat-treat the Al2O3 fiber cloth (AF18) by mixing Al2O3 powder and 3YSZ powder;

[0152] The mass ratio of Al2O3 powder to 3YSZ powder is 75:25;

[0153] The Al2O3 powder includes Al2O3 powder with a median particle size of 100 nm and Al2O3 powder with a median particle size of 500 nm; the mass ratio of the 100 nm Al2O3 powder to the 500 nm Al2O3 powder is 70:5.

[0154] The heat treatment process for the Al2O3 fiber cloth is as follows: heating at 700°C in air for 2 hours; heat treatment in air can remove surface organic impurities and improve interfacial bonding performance.

[0155] Step 2: Preparation of ceramic slurry

[0156] ① Al2O3 powder and 3YSZ powder were mixed and dry ball-milled to obtain oxide powder. Then, 1.78 g of oxide powder was mixed with 9.1 mL of dimethyldimethoxysilane and 1.82 mL of tetraethoxysilane, followed by the addition of 200 mL of anhydrous ethanol, 28 mL of deionized water, and 14 mL of ammonia. After stirring for 24 h, an Al2O3-3YSZ@SiOC-nC precursor suspension was obtained. 2 g of resorcinol and 2.8 mL of formaldehyde aqueous solution were added to the Al2O3-3YSZ@SiOC-nC precursor suspension, and after stirring for another 24 h, the mixture was centrifuged and washed to obtain Al2O3-3YSZ@SiOC-nC precursor particles. The shell of the Al2O3-3YSZ@SiOC-nC precursor particles was SiOC, with Si accounting for 6.53 wt%, O for 16.13 wt%, and C for 77.34 wt%.

[0157] The ball milling process is as follows: the rotation speed is 400 rpm, and the ball milling time is 2 hours;

[0158] The concentration of the ammonia solution was 28 wt.%.

[0159] The concentration of the formaldehyde aqueous solution is 35 wt%;

[0160] ② The Al2O3-3YSZ@SiOC-nC precursor particles are mixed with a dispersant solution to obtain a ceramic slurry;

[0161] The dispersant solution is an aqueous solution of sodium polyacrylate with a mass fraction of 49 wt.%.

[0162] The volume fraction of Al2O3-3YSZ@SiOC-nC precursor particles in the ceramic slurry is 45%.

[0163] Step 3: Preheat the Al2O3 fiber cloth, then stack it, and impregnate the Al2O3 fiber cloth with ceramic slurry to obtain a preform; then dry and hot-press the preform to obtain an Al2O3 fiber reinforced oxide composite material, denoted as AF18 / Al2O3-3YSZ@SiOC-2C; the obtained Al2O3 fiber reinforced oxide composite material is composed of Al2O3 fiber cloth (AF18) and oxide matrix (Al2O3-3YSZ@SiOC-2C), and the oxide matrix is ​​a core-shell structured composite ceramic particle;

[0164] The interlayer spacing of the Al2O3 fiber cloth stacked is 0.25 mm;

[0165] The preheating process is as follows: heating at 700℃ for 2 hours;

[0166] The drying process is as follows: drying at 90℃ for 24 hours;

[0167] The mass ratio of the Al2O3 fiber cloth to the Al2O3-3YSZ@SiOC-nC precursor particles is 7:16;

[0168] The hot pressing sintering process is as follows: heating rate 10℃ / min, sintering temperature 300℃, pressure 10MPa, and holding time 2h.

[0169] Example 3

[0170] This embodiment describes the continuous Al2O3 fiber-reinforced oxide composite material with core-shell structure for regulating electromagnetic protection performance, following the steps below:

[0171] Step 1: Heat-treat the Al2O3 fiber cloth (AF18) by mixing Al2O3 powder and 3YSZ powder;

[0172] The mass ratio of Al2O3 powder to 3YSZ powder is 75:25;

[0173] The Al2O3 powder includes Al2O3 powder with a median particle size of 100 nm and Al2O3 powder with a median particle size of 500 nm; the mass ratio of the 100 nm Al2O3 powder to the 500 nm Al2O3 powder is 70:5.

[0174] The heat treatment process for the Al2O3 fiber cloth is as follows: heating at 700°C in air for 2 hours; heat treatment in air can remove surface organic impurities and improve interfacial bonding performance.

[0175] Step 2: Preparation of ceramic slurry

[0176] ① Al2O3 powder and 3YSZ powder were mixed and dry ball-milled to obtain oxide powder. Then, 1.78 g of oxide powder was mixed with 9.1 mL of dimethyldimethoxysilane and 1.82 mL of tetraethoxysilane, and then 200 mL of anhydrous ethanol, 28 mL of deionized water and 14 mL of ammonia were added. After stirring for 24 h, an Al2O3-3YSZ@SiOC-nC precursor suspension was obtained. 2 g of resorcinol and 2.8 mL of formaldehyde aqueous solution were added to the Al2O3-3YSZ@SiOC-nC precursor suspension, and after stirring for another 24 h, the mixture was centrifuged and washed to obtain Al2O3-3YSZ@SiOC-nC precursor particles. The shell of the Al2O3-3YSZ@SiOC-nC precursor particles is SiOC, where Si is 2.52 wt%, O is 7.94 wt%, and C is 89.54 wt%.

[0177] The ball milling process is as follows: the rotation speed is 400 rpm, and the ball milling time is 2 hours;

[0178] The concentration of the ammonia solution is 25 wt.%.

[0179] The concentration of the formaldehyde aqueous solution is 40 wt.%.

[0180] ② The Al2O3-3YSZ@SiOC-nC precursor particles are mixed with a dispersant solution to obtain a ceramic slurry;

[0181] The dispersant solution is an aqueous solution of sodium polyacrylate with a mass fraction of 50 wt.%.

[0182] The volume fraction of Al2O3-3YSZ@SiOC-nC precursor particles in the ceramic slurry is 45%.

[0183] Step 3: Preheat the Al2O3 fiber cloth, then stack it, and impregnate the Al2O3 fiber cloth with ceramic slurry to obtain a preform; then dry and hot-press the preform to obtain an Al2O3 fiber reinforced oxide composite material, denoted as AF18 / Al2O3-3YSZ@SiOC-3C; the obtained Al2O3 fiber reinforced oxide composite material is composed of Al2O3 fiber cloth (AF18) and oxide matrix (Al2O3-3YSZ@SiOC-3C), and the oxide matrix is ​​a core-shell structured composite ceramic particle;

[0184] The interlayer spacing of the Al2O3 fiber cloth stacked is 0.3 mm;

[0185] The preheating process is as follows: heating at 700℃ for 2 hours;

[0186] The drying process is as follows: drying at 90℃ for 24 hours;

[0187] The mass ratio of the Al2O3 fiber cloth to the Al2O3-3YSZ@SiOC-nC precursor particles is 7:19.

[0188] The hot pressing sintering process is as follows: heating rate 10℃ / min, sintering temperature 300℃, pressure 10MPa, and holding time 2h.

[0189] Figure 1 SEM images and EDS images of the oxide raw materials used to prepare the composite materials in Examples 1-3 are shown; a1 and a2 correspond to large-particle-size (500nm) Al2O3 powder, b1 and b2 correspond to small-particle-size (100nm) Al2O3 powder; c1 and c2 correspond to 3YSZ; through Figure 1 It can be seen that the oxide raw materials used in the embodiments have uniform particle distribution and multi-scale particle size distribution characteristics, which provides a foundation for the subsequent construction of core-shell structures.

[0190] Figure 2 SEM images (ai) of the oxide matrix in the composite materials prepared in Examples 1-3 and EDS images (j) of the matrix in Example 1; where k is an energy dispersive spectroscopy (EDS) overlay. Figure 3 The images shown are SEM images (aj) and EDS images (j) of the composite materials prepared in Examples 1-3; where k is the energy dispersive spectroscopy (EDS) overlay. Figure 2 It can be seen that a uniform coating layer is formed on the surface of the oxide matrix particles in the core-shell structures prepared in Examples 1-3. EDS results show that Si, O, and C elements are uniformly distributed on the particle surface, proving that the SiOC shell layer was successfully constructed. Figure 3 It can be seen that the composite materials prepared in Examples 1-3 have a dense overall structure, with the fibers tightly bonded to the matrix, and no obvious pores or interface debonding phenomena were observed.

[0191] Figure 4 The XRD patterns of the oxide matrix in the composite materials prepared in Examples 1-3 are shown. Figure 5 The XRD patterns of the composite materials prepared in Examples 1-3 are shown; Figure 4 and Figure 5 It can be seen that no obvious impurity phases appeared in the SiOC shell and the composite material as a whole. The main phases were Al2O3 and 3YSZ crystal phases. At the same time, SiOC showed amorphous characteristics, indicating that the core-shell structure was successfully constructed and the phase composition was stable.

[0192] Figure 6 The thermal conductivity curve (a), thermal diffusivity curve (b), and heat capacity curve (c) of the composite materials prepared in Examples 1-3 are shown. Figure 6 It can be seen that the composite materials prepared in Examples 1-3 have low thermal conductivity at room temperature, with a thermal conductivity of about 1.6-1.8 W / (m·K), exhibiting good thermal insulation performance.

[0193] Figure 7 These are Vickers hardness indentation images of the composite materials prepared in Examples 1-3 under 5 kgf; from left to right, they are AF18 / Al2O3-3YSZ@SiOC-1C, AF18 / Al2O3-3YSZ@SiOC-2C, and AF18 / Al2O3-3YSZ@SiOC-3C. Figure 7 It can be seen that the composite materials prepared in Examples 1-3 formed regular Vickers indentations under a 5 kgf load, and no obvious crack propagation was observed, indicating that the material has good mechanical properties, and its Vickers hardness is about 500-690 MPa.

[0194] Figure 8 The Raman spectra of the oxide matrix of the composite materials prepared in Examples 1-3; Figure 9 The Raman spectra of the composite materials prepared in Examples 1-3; by Figure 8 and Figure 9 It can be seen that the Raman spectra of the SiOC shell and the composite material as a whole in Examples 1-3 all have obvious D and G peaks, and their I D / I G A value in the range of 0.8-1.2 indicates that the carbon in the shell mainly exists in the form of amorphous carbon or defective structures, which is beneficial to enhancing electromagnetic loss capability.

[0195] Figure 10 The FT-IR spectra of the composite materials prepared in Examples 1-3; Figure 11 XPS spectra of the composite materials prepared in Examples 1-3; by Figure 10 and Figure 11It can be seen that the SiOC shell in Examples 1-3 contains chemical bond structures such as Si-O-Si and Si-C, and XPS analysis shows that Si, O and C elements coexist and form stable chemical bonds, further verifying the successful construction of the SiOC shell.

[0196] Figure 12 The electromagnetic wave absorption performance of the composite materials prepared in Examples 1-3 is shown in the reflection loss values ​​(a, d, g), three-dimensional projection diagrams (b, e, h), and three-dimensional curves (c, f, i). Figure 12 It can be seen that the composite materials prepared in Examples 1-3 have excellent electromagnetic wave absorption performance in the 2-18 GHz frequency band, with a minimum reflection loss of about -40 dB and a wide effective absorption bandwidth in a certain frequency band.

[0197] Figure 13 The electromagnetic wave shielding performance of the composite materials prepared in Examples 1-3 is shown in the following figures: reflection shielding effectiveness (a), absorption shielding effectiveness (b), and total shielding effectiveness (c). Figure 13 It can be seen that the composite materials prepared in Examples 1-3 also have a certain electromagnetic shielding capability, and their total shielding effectiveness can reach more than 10 dB in the 2-18 GHz frequency band, indicating that the material has electromagnetic protection capability.

[0198] Figure 14 The real part (a), imaginary part (b), and nodal loss angle (c) of the relative complex permittivity of the composite materials prepared in Examples 1-3 are shown. Figure 14 It can be seen that the AF18 / Al2O3-3YSZ@SiOC-1C composite materials prepared in Examples 1-3 have moderate real and imaginary parts of complex permittivity, and their dielectric loss capability is strong, which is beneficial to the absorption and dissipation of electromagnetic waves. In contrast, AF18 / Al2O3-3YSZ@SiOC-2C and AF18 / Al2O3-3YSZ@SiOC-3C have higher real and imaginary parts of complex permittivity, and their conductivity loss capability is strong, which is beneficial to the reflection of electromagnetic waves.

[0199] Figure 15 The impedance matching values ​​are for the composite materials prepared in Examples 1-3. (The rest of the text appears to be a fragment and requires further context for accurate translation.) Figure 15 It can be seen that the AF18 / Al2O3-3YSZ@SiOC-1C composite material has good impedance matching performance, which is conducive to the entry of electromagnetic waves into the material interior, thereby improving absorption efficiency. However, there is a significant impedance mismatch between AF18 / Al2O3-3YSZ@SiOC-2C and AF18 / Al2O3-3YSZ@SiOC-3C, which is conducive to the reflection of electromagnetic waves.

[0200] Figure 16 The image shows the Debye relaxation Cole-Cole diagrams of the composite materials prepared in Examples 1-3. (The text is incomplete and requires further context.) Figure 16 It can be seen that the composite materials prepared in Examples 1-3 exhibit multiple relaxation arcs in the Cole-Cole diagram, indicating that there are multiple polarization relaxation processes in the material, including interfacial polarization and dipole polarization, which is beneficial to improving the electromagnetic wave attenuation capability.

[0201] In summary, the Al2O3-3YSZ@SiOC core-shell structure constructed by this invention forms a multi-scale, multi-phase interface structure within the composite material, achieving a synergistic effect between conductive loss and interface polarization loss. While maintaining the material's low thermal conductivity and good mechanical properties, it significantly improves its electromagnetic wave absorption and electromagnetic shielding performance, realizing adjustable control of electromagnetic protection performance.

Claims

1. An Al2O3 fiber-reinforced oxide composite material with core-shell structure for regulating electromagnetic protection performance, characterized in that: Al2O3 fiber-reinforced oxide composites based on core-shell structure for regulating electromagnetic protection performance include continuous Al2O3 fiber reinforcement and oxide matrix; The volume fraction of Al2O3 fiber reinforcement in the composite material is 35-45%; The Al2O3 fiber reinforcement is a fiber cloth with a ply spacing of 0.2-0.5 mm.

2. The Al2O3 fiber-reinforced oxide composite material with core-shell structure for regulating electromagnetic protection performance according to claim 1, characterized in that: The oxide matrix is ​​a core-shell structured composite ceramic particle with a median particle size of 0.6-3.0 μm; the core layer of the core-shell structured composite ceramic particle is a composite oxide of Al2O3 and 3YSZ, with a mass ratio of Al2O3 to 3YSZ of 75-80:20-25, and the shell layer is SiOC. The SiOC contains 1-20 wt% Si, 45-50 wt% or 70-90 wt% C, and the balance is O.

3. The preparation method of continuous Al2O3 fiber-reinforced oxide composite material based on core-shell structure for regulating electromagnetic protection performance as described in claim 1, characterized in that: Follow these steps: Step 1: Heat-treat the Al2O3 fiber cloth by mixing Al2O3 powder and 3YSZ powder; The mass ratio of Al2O3 powder to 3YSZ powder is 75-80:20-25; The Al2O3 powder includes Al2O3 powder with a median particle size of 100 nm and Al2O3 powder with a median particle size of 500 nm; the mass ratio of the 100 nm Al2O3 powder to the 500 nm Al2O3 powder is 68-72:3-7. Step 2: Preparation of ceramic slurry ① Al2O3 powder and 3YSZ powder are mixed and dry ball-milled to obtain oxide powder. Then, the oxide powder is mixed with dimethyldimethoxysilane and tetraethoxysilane, and anhydrous ethanol, deionized water and ammonia are added. After stirring for 24-48 hours, an Al2O3-3YSZ@SiOC-nC precursor suspension is obtained. Resorcinol and formaldehyde aqueous solution are added to the Al2O3-3YSZ@SiOC-nC precursor suspension, and after stirring for 24-48 hours, centrifugation and washing are performed to obtain Al2O3-3YSZ@SiOC-nC precursor particles. The Al2O3-3YSZ@SiOCnC precursor particles are pyrolyzed to obtain Al2O3-3YSZ@SiOC-nC core-shell structured composite ceramic particles. The ratio of the oxide powder to dimethyldimethoxysilane and tetraethoxysilane is 1.78-3.85 g: 9.1 mL: 1.82 mL; The ratio of the oxide powder to anhydrous ethanol, deionized water and ammonia is 1.78-3.85g: 200mL-220mL: 27-30mL: 13-15mL; The ratio of the oxide powder to the aqueous solution of resorcinol and formaldehyde is 1.78-3.85g: 2-6g: 2.8-8.4mL; The pyrolysis process is as follows: heating at 1100-1300℃ for 1.5-3 hours in an argon atmosphere; ② The Al2O3-3YSZ@SiOC-nC core-shell composite ceramic particles are mixed with a dispersant solution to obtain a ceramic slurry; The dispersant solution is an aqueous solution of sodium polyacrylate with a mass fraction of 49-51%. The volume fraction of Al2O3-3YSZ@SiOC-nC core-shell structured composite ceramic particles in the ceramic slurry is 45-47%. Step 3: Preheat the Al2O3 fiber cloth, then stack it, and impregnate the Al2O3 fiber cloth with ceramic slurry to obtain a preform; then dry and hot-press the preform to obtain an Al2O3 fiber reinforced oxide composite material. The mass ratio of Al2O3 fiber cloth to Al2O3-3YSZ@SiOC-nC core-shell composite ceramic particles is 7-8:17-19. The hot pressing sintering process is as follows: heating rate 5-20℃ / min, sintering temperature 1200-1350℃, pressure 5-30MPa, and holding time 1-4h.

4. The method for preparing continuous Al2O3 fiber-reinforced oxide composite material based on core-shell structure for regulating electromagnetic protection performance according to claim 3, characterized in that: The heat treatment process of the Al2O3 fiber cloth in step one is as follows: heating in an air atmosphere at 600-800℃ for 1-4 hours.

5. The method for preparing continuous Al2O3 fiber-reinforced oxide composite material based on core-shell structure for regulating electromagnetic protection performance according to claim 3, characterized in that: Step 2① The ball milling process is as follows: the rotation speed is 400 rpm, and the ball milling time is 2 hours; Step 2① The concentration of the ammonia solution is 25-28 wt.%; Step 2① The concentration of the formaldehyde aqueous solution is 35-40 wt.%.

6. The method for preparing continuous Al2O3 fiber-reinforced oxide composite material based on core-shell structure for regulating electromagnetic protection performance according to claim 3, characterized in that: The interlayer spacing of the Al2O3 fiber cloth stacked in step three is 0.2-0.5 mm; The preheating process described in step three is as follows: heating at 700℃ for 1-2 hours; The drying process described in step three is as follows: drying at 90℃ for 18-24 hours.

7. The preparation method of continuous Al2O3 fiber-reinforced oxide composite material based on core-shell structure for regulating electromagnetic protection performance as described in claim 1, characterized in that: This method is performed according to the following steps: Step 1: Heat-treat the Al2O3 fiber cloth by mixing Al2O3 powder and 3YSZ powder; The mass ratio of Al2O3 powder to 3YSZ powder is 75-80:20-25; The Al2O3 powder includes Al2O3 powder with a median particle size of 100 nm and Al2O3 powder with a median particle size of 500 nm; the mass ratio of the 100 nm Al2O3 powder to the 500 nm Al2O3 powder is 68-72:3-7. Step 2: Preparation of ceramic slurry ① Al2O3 powder and 3YSZ powder are mixed and dry ball-milled to obtain oxide powder. Then, the oxide powder is mixed with dimethyldimethoxysilane and tetraethoxysilane, and anhydrous ethanol, deionized water and ammonia are added. After stirring for 24-48 hours, an Al2O3-3YSZ@SiOC-nC precursor suspension is obtained. Resorcinol and formaldehyde aqueous solution are added to the Al2O3-3YSZ@SiOC-nC precursor suspension, and after stirring for 24-48 hours, centrifugation and washing are performed to obtain Al2O3-3YSZ@SiOC-nC precursor particles. The ratio of the oxide powder to dimethyldimethoxysilane and tetraethoxysilane is 1.78-3.85 g: 9.1 mL: 1.82 mL; The ratio of the oxide powder to anhydrous ethanol, deionized water and ammonia is 1.78-3.85g: 200mL-220mL: 27-30mL: 13-15mL; The ratio of the oxide powder to the aqueous solution of resorcinol and formaldehyde is 1.78-3.85g: 2-6g: 2.8-8.4mL; ② The Al2O3-3YSZ@SiOC-nC precursor particles are mixed with a dispersant solution to obtain a ceramic slurry; The dispersant solution is an aqueous solution of sodium polyacrylate with a mass fraction of 49-51%. The volume fraction of Al2O3-3YSZ@SiOC-nC precursor particles in the ceramic slurry is 45-47%. Step 3: Preheat the Al2O3 fiber cloth, then stack it, and impregnate the Al2O3 fiber cloth with ceramic slurry to obtain a preform; then dry and hot press sinter the preform. During the hot pressing sintering process, the organosilicon in the Al2O3-3YSZ@SiOC-nC precursor particles undergoes in-situ pyrolysis to form a SiOC shell on the core layer surface; thus obtaining an Al2O3 fiber-reinforced oxide composite material. The mass ratio of the Al2O3 fiber cloth to the Al2O3-3YSZ@SiOC-nC precursor particles is 7-8:17-19. The hot pressing sintering process is as follows: heating rate 5-20℃ / min, sintering temperature 1200-1350℃, pressure 5-30MPa, and holding time 1-4h.

8. The method for preparing continuous Al2O3 fiber-reinforced oxide composite material based on core-shell structure for regulating electromagnetic protection performance according to claim 7, characterized in that: The heat treatment process of the Al2O3 fiber cloth in step one is as follows: heating in an air atmosphere at 600-800℃ for 1-4 hours.

9. The method for preparing continuous Al2O3 fiber-reinforced oxide composite material based on core-shell structure for regulating electromagnetic protection performance according to claim 7, characterized in that: Step 2① The ball milling process is as follows: the rotation speed is 400 rpm, and the ball milling time is 2 hours; Step 2① The concentration of the ammonia solution is 25-28 wt.%; Step 2① The concentration of the formaldehyde aqueous solution is 35-40 wt.%.

10. The method for preparing continuous Al2O3 fiber-reinforced oxide composite material based on core-shell structure for regulating electromagnetic protection performance according to claim 7, characterized in that: The interlayer spacing of the Al2O3 fiber cloth stacked in step three is 0.2-0.5 mm; The preheating process described in step three is as follows: heating at 700℃ for 1-2 hours; The drying process described in step three is as follows: drying at 90℃ for 18-24 hours.

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