C (at) void (at) SiC (at) SiO2 double-gradient structure lightweight wave-absorbing ceramic material and preparation method thereof

Abstract

The invention relates to the technical field of high-temperature-resistant wave-absorbing materials, in particular to a light wave-absorbing ceramic material with a C (at) void (at) SiC (at) SiO2 double-gradient structure and a preparation method of the light wave-absorbing ceramic material. The wave-absorbing ceramic material forms a double-gradient structure on a macro / micro level and comprises an inner core and a hole wall, the inner core is a C core, a nano gap layer is arranged between the C core and the hole wall, the hole wall is of a double-layer structure, the inner layer is a SiC layer, and the outer layer is a SiO2 layer. The porosity of the prepared light wave-absorbing ceramic material with the C (at) void (at) SiC (at) SiO2 double-gradient structure is 70%-85%, the lowest reflection loss at 8GHz-14GHz can reach-65dB, the highest compression strength can reach 12 + / -1MPa, the use temperature in an oxidizing atmosphere can reach 1100 DEG C, and the requirements of wide frequency domain, strong absorption, high temperature resistance, light weight, strong thinness and the like can be met; and an efficient electromagnetic protection solution is provided for high-precision radars, high-speed communication and new energy equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of high-temperature resistant wave-absorbing materials, and more specifically, to a C@voids@SiC@SiO2 dual-gradient structure lightweight wave-absorbing ceramic material and a preparation method thereof. Background Art

[0002] While electromagnetic waves drive technological advancement, their negative impacts on electronic equipment and human health are becoming increasingly prominent. This is particularly true in the military, where advances in radar detection technology have made stealth a critical requirement. As an important means of suppressing electromagnetic radiation and enhancing stealth, optimizing the performance of absorbing materials is crucial. However, traditional magnetically and electrically lossy absorbing materials are susceptible to failure due to decomposition, oxidation, and paramagnetization at high temperatures, limiting their application.

[0003] Silicon carbide (SiC) has become a research focus for high-temperature resistant absorbing materials due to its excellent properties such as high temperature resistance, oxidation resistance, and thermal shock resistance. However, SiC with a single morphology and component has problems such as low conductivity, single polarization, poor impedance matching, and narrow absorption bandwidth, making it difficult to meet actual needs. In recent years, researchers have improved the performance of SiC-based absorbing materials through multi-component and multi-structure composite strategies. Among them, the core-shell structure has attracted widespread attention due to its tunable impedance matching properties. At present, although SiC-based core-shell structure absorbing materials (such as C@SiC and SiC@SiO2) have made certain progress, their structure is simple and the performance improvement has reached a bottleneck. In addition, they are mainly dispersed in the resin matrix as absorbers, and the synergistic absorption effect between the core and shell has not been fully utilized.

[0004] In addition, gradient structures have become a research hotspot because they are easier to meet the "thin, light, wide, and strong" absorption requirements. However, there are currently few reports on dual-dielectric gradient structure absorbing materials. The design of dual-dielectric gradient absorbing materials based on the core-shell structure can combine the advantages of impedance gradient matching, multi-scale interface polarization, and pore gradient structure to break through the performance limitations of a single gradient structure, while giving the material excellent thermal insulation properties. Therefore, the development of SiC-based dual-dielectric gradient structure absorbing ceramic materials can not only promote the innovative development of high-temperature resistant absorbing materials, but also have important scientific value and application prospects for military stealth technology and civilian electromagnetic protection. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, one aspect of the present invention is to provide a lightweight absorbing ceramic material with a C@voids@SiC@SiO2 dual-gradient structure. The absorbing ceramic material has a dual-gradient structure at the macro / micro level, including a core and pore walls. The core is a C core, and a nano-void layer is formed between the C core and the pore wall. The pore wall has a double-layer structure, with an inner layer being a SiC layer and an outer layer being a SiO2 layer.

[0006] Another aspect of the present invention is to provide a method for preparing a C@voids@SiC@SiO2 dual gradient structure lightweight absorbing ceramic material, the specific steps of the preparation method are: S1. A series of spherical carbons with a gradient particle size distribution were synthesized using a hydrothermal method using a carbon source; S2. A silicon source was used to deposit SiO2 onto the surface of a series of spherical carbon particles with a gradient distribution of particle size prepared in S1 using a low-temperature chemical vapor deposition process to form a SiO2 shell layer, thereby obtaining a series of C@SiO2 core-shell powder particles with a gradient distribution of particle size. S3. The C@SiO2 core-shell structure powder in S2 is dispersed in deionized water to form a C@SiO2 dispersion; S4. The dispersion in S3 is placed in a mold, and a C@SiO2 primary green body having a gradient structure is formed by density induction; S5. The primary green body in S4 is pressed into a C@SiO2 secondary green body by a pressing process; S6. The C@SiO2 green body prepared in S5 is sintered in an argon atmosphere to form a C@SiC@SiO2 intermediate; S7. The C@SiC@SiO2 intermediate prepared in S6 is heat-treated in an oxygen-containing atmosphere to oxidize the C core therein, thereby separating it from the shell, forming a C@void@SiC@SiO2 dual-gradient structure lightweight absorbing ceramic material.

[0007] Preferably, the carbon source in S1 is glucose, fructose, chitosan, sucrose, cellulose or starch, the hydrothermal temperature is 150° C. to 200° C., the time is 1 hour to 12 hours, and the diameter of the spherical carbon balls is 50 nm to 500 nm.

[0008] Preferably, the silicon source in S2 is methyl orthosilicate, ethyl orthosilicate, propyl orthosilicate, butyl orthosilicate, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane or ethyltriethoxysilane, and the low-temperature chemical vapor deposition process temperature is room temperature to 300°C, and the time is 1 hour to 48 hours.

[0009] Preferably, the thickness of the SiO2 shell in the S2 is 10nm~60nm.

[0010] Preferably, the solid content of the C@SiO2 dispersion in S3 is 10% to 90%.

[0011] Preferably, the induction time in S4 is 1 hour to 24 hours.

[0012] Preferably, the pressing pressure in S5 is 10 MPa to 200 MPa.

[0013] Preferably, the sintering temperature in S6 is 1500° C. to 1700° C., and the sintering time is 0.5 hour to 3 hours.

[0014] Preferably, the heat treatment temperature in S7 is 400° C. to 1000° C., the heat treatment time is 0.5 hour to 5 hours, and the oxygen partial pressure is 20 ppm to 200 ppm.

[0015] The beneficial effects of the present invention are as follows: Excellent Absorption Performance: A unique dielectric gradient (SiO2→SiC→C) achieves gradual impedance matching, effectively reducing electromagnetic wave reflection and enhancing absorption efficiency. The synergistic effect of multiple heterogeneous interface polarization (C / SiC / SiO2 interfaces) and the resonant cavity effect induced by the void layer create a "deep-diving wave absorption mechanism with no return" that achieves a minimum reflection loss of -65dB in the 8-14GHz frequency band, far exceeding that of traditional absorbers.

[0016] Excellent high temperature resistance and oxidation resistance: The SiO2 shell and SiC middle layer provide dual thermal protection for the C core, allowing the material to remain stable in an oxidizing atmosphere at 1100°C, overcoming the problem of traditional carbon-based materials being easily oxidized and failing at high temperatures.

[0017] Lightweight, High-Strength, and Broadband Absorption: With a porosity of 70% to 85%, the material is ultra-lightweight while maintaining a compressive strength of 12±1 MPa, offering excellent mechanical properties. The dual-gradient structural design (a macroscopic continuous interface + a microscopic core-shell heterogeneous interface) promotes cross-scale scattering and loss of electromagnetic waves, broadening the effective absorption bandwidth.

[0018] Strong controllability and wide applicability: By adjusting parameters such as SiC / SiO2 pore wall thickness, C core size, gradient layer ratio, etc., it can be precisely adapted to different military and civilian application needs (such as stealth coating, communication shielding, etc.).

[0019] Green and efficient preparation process: The method is easy to operate, free of solvent pollution, suitable for mass production, and promotes the practical application of high-performance absorbing materials.

[0020] In summary, the C@void@SiC@SiO2 dual-gradient structure lightweight absorbing ceramic material of this application breaks through the bottleneck of traditional absorbing materials that are difficult to achieve "wideband, strong absorption, high temperature resistance, lightness, strength and thinness", and provides an innovative solution for high-precision radar stealth, high-speed communication anti-interference and electromagnetic protection of new energy equipment.

[0021] Additional aspects and advantages of the invention will become apparent from the description which follows, or may be learned by practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which: Figure 1 Schematic diagram of the formation principle of the C@voids@SiC@SiO2 dual gradient structure lightweight absorbing ceramic material of the present invention; Figure 2 Schematic diagram of the macro / micro multi-scale interface of the C@void@SiC@SiO2 dual gradient structure lightweight absorbing ceramic material according to an embodiment of the present invention; Figure 3 This is the XRD spectrum of the C@voids@SiC@SiO2 dual gradient structure lightweight absorbing ceramic material according to an embodiment of the present invention; Figure 4 This is the Raman spectrum of the C@voids@SiC@SiO2 dual gradient structure lightweight absorbing ceramic material according to the embodiment of the present invention; Figure 5 This is a graph showing how the reflectivity of the lightweight absorbing ceramic material with a dual gradient structure of C@voids@SiC@SiO2 changes with frequency in an embodiment of the present invention; Figure 6 2. This is a stress-strain curve of a lightweight microwave-absorbing ceramic material with a dual-gradient structure of C@voids@SiC@SiO2 according to an embodiment of the present invention; Figure 7 This is an isothermal oxidation curve of the C@voids@SiC@SiO2 dual gradient structure lightweight absorbing ceramic material according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, in the absence of conflict, the embodiments of the present application and the features therein can be combined with each other.

[0024] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from the description. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0025] like Figure 1 The figure shows the formation principle of the C@voids@SiC@SiO2 dual gradient structure lightweight absorbing ceramic material of the present invention. Figure 2 Schematic diagram of the macro / micro multi-scale interface of the C@void@SiC@SiO2 dual gradient structure lightweight absorbing ceramic material according to an embodiment of the present invention.

[0026] Example 1 Take 10g of glucose, dissolve it in 100mL of deionized water, and carry out hydrothermal reaction at 180℃ for 8 hours. Centrifuge, wash and dry to obtain spherical carbon powder with a micro-gradient particle size distribution (mainly distributed in the range of 100nm~200nm). 5 g of the spherical carbon powder prepared above was placed in a low-temperature chemical vapor deposition apparatus using tetraethyl orthosilicate as the silicon source at 100°C for 24 hours. After natural cooling, a C@SiO2 core-shell structure powder with a uniform SiO2 shell (approximately 30 nm thick) and a gradient particle size distribution was obtained. Take 20g of the C@SiO2 core-shell structure powder prepared above, disperse it in 80g of deionized water, and stir it magnetically for 2 hours to form a C@SiO2 dispersion with a solid content of 20%; The dispersion was slowly injected into a polytetrafluoroethylene mold and allowed to stand for 12 hours to allow the C@SiO2 core-shell spheres of different particle sizes to settle and stratify according to their density under the action of gravity, forming a primary green body with a continuous gradient structure. The primary green body was placed in a cold isostatic press and held at 100 MPa for 5 minutes to form a C@SiO2 secondary green body. The secondary green body was placed in an atmosphere sintering furnace, high-purity argon was introduced, and the temperature was raised to 1600°C at a rate of 5°C / min and kept at this temperature for 1 hour to form a C@SiC@SiO2 intermediate. The sintered C@SiC@SiO2 intermediate was transferred to a tubular furnace with air (oxygen partial pressure of about 100 ppm), heated to 600°C at a rate of 3°C / min, and kept warm for 2 hours to form a C@void@SiC@SiO2 dual-gradient structure lightweight absorbing ceramic material.

[0027] Example 2 15 g of sucrose was dissolved in 150 mL of deionized water and subjected to hydrothermal reaction at 200°C for 4 hours. After centrifugation, washing, and drying, spherical carbon powder with a bimodal particle size gradient distribution (main peaks around 80 nm and 300 nm) was obtained. 6 g of the spherical carbon powder prepared above was placed in a low-temperature chemical vapor deposition apparatus using methyltriethoxysilane as the silicon source at 110°C for 18 hours to obtain a C@SiO2 core-shell structure powder with a uniform SiO2 shell (approximately 40 nm thick) and a gradient particle size distribution. 30 g of the C@SiO2 powder prepared above was mixed with 70 g of deionized water, and ultrasonically dispersed for 30 minutes, followed by magnetic stirring for 3 hours to form a dispersion with a solid content of 30%; The above dispersion was injected into a rectangular mold and induced for 6 hours to form a primary green body with a distinct two-layer structure: the lower layer was mainly composed of small-size (~80nm) C@SiO2 spheres, and the upper layer was mainly composed of large-size (~300nm) C@SiO2 spheres. The primary green body was subjected to unidirectional molding at a pressure of 50 MPa and maintained at this pressure for 2 minutes to obtain a C@SiO2 secondary green body with a dual gradient structure. Under argon protection, the green body was heated to 1550℃ at a rate of 10℃ / min and kept at this temperature for 1.5 hours for sintering to obtain a C@SiC@SiO2 intermediate. In an atmosphere with an oxygen partial pressure of about 50 ppm, the C@SiC@SiO2 intermediate is heated to 800°C and kept warm for 1 hour to form a C@voids@SiC@SiO2 dual-gradient structure lightweight absorbing ceramic material.

[0028] Example 3 8 g of microcrystalline cellulose was dispersed in 120 mL of deionized water and subjected to hydrothermal reaction at 190 ° C for 12 hours to obtain spherical carbon powder with a particle size range of 50 nm to 400 nm and a continuous gradient distribution; 7 g of the spherical carbon powder prepared above was placed in a low-temperature chemical vapor deposition apparatus, using methyl orthosilicate as the silicon source, and deposited at 200°C for 36 hours to obtain a wide gradient C@SiO2 powder with a SiO2 shell thickness of about 50 nm.

[0029] 45 g of the C@SiO2 powder prepared above was mixed with 55 g of deionized water and stirred vigorously to form a dispersion with a solid content of 45%. The dispersion is injected into the mold and allowed to stand for 24 hours to ensure that the particles with a wide range of particle sizes are fully settled and stratified, forming a primary green body with a continuous change in particle size from small to large from bottom to top; Cold isostatic pressing was performed at 200 MPa and the pressure was maintained for 3 minutes to obtain a C@SiO2 secondary green body; Under argon atmosphere, the temperature was raised to 1700°C at 8°C / min and kept at this temperature for 0.5 hours to obtain a C@SiC@SiO2 intermediate. In an air atmosphere with strictly controlled oxygen partial pressure (about 30ppm), the temperature is raised to 450℃ and kept for 5 hours to separate the C core from the pore wall, forming a C@void@SiC@SiO2 dual-gradient structure lightweight absorbing ceramic material.

[0030] Example 4 5 g of soluble starch was dissolved in 100 mL of deionized water and subjected to hydrothermal reaction at 150 ° C for 10 hours. After treatment, spherical carbon powder with a small particle size and a narrow gradient distribution (mainly in the range of 50 nm to 150 nm) was obtained. 4 g of the spherical carbon powder prepared above was deposited at 180°C for 12 hours using ethyltriethoxysilane as the silicon source to obtain a very uniform, ultra-thin SiO2 shell with a precisely controlled thickness of 20 nm, resulting in C@SiO2 powder with a nano-gradient particle size. 15 g of the C@SiO2 powder prepared above was dispersed in 135 g of deionized water to form a dispersion with a solid content of 10%; The dispersion was injected into the mold and allowed to stand for 4 hours to form a primary green body with a gradient structure; The C@SiO2 gradient structure secondary green body was obtained by light pressing at 10 MPa and holding the pressure for 1 minute. The temperature was raised to 1500°C at a rate of 3°C / min and kept at that temperature for 3 hours for sintering to obtain a C@SiC@SiO2 intermediate. In air with an oxygen partial pressure of about 150ppm, the temperature is raised to 1000℃ at a rate of 5℃ / min and kept at that temperature for 0.5 hours for rapid oxidation treatment to form a C@voids@SiC@SiO2 dual-gradient structure lightweight absorbing ceramic material.

[0031] Detection test Porosity tests were conducted on Examples 1 to 4 of the present invention, and the test results showed that the porosity of the C@voids@SiC@SiO2 dual-gradient structure lightweight absorbing ceramic material can be adjusted to 70%~85%.

[0032] XRD analysis was performed on Examples 1 to 4 of the present invention, and the results are as follows Figure 3 As shown; Raman spectroscopy analysis was performed on Examples 1 to 4 of the present invention, and the results were as follows: Figure 4 As shown; Electromagnetic simulations were performed on the first to fourth embodiments of the present invention, and the simulation results are as follows: Figure 5 As shown; The compressive strength test of Examples 1 to 4 of the present invention was carried out, and the test results are as follows: Figure 6 As shown; Isothermal oxidation tests were performed on Examples 1 to 4 of the present invention, and the test results were as follows: Figure 7 shown.

[0033] In summary, the C@void@SiC@SiO2 dual-gradient structure lightweight absorbing ceramic material prepared by the method provided by the present invention can simultaneously have the following performance indicators: porosity 70%~85%, the minimum reflection loss can reach -65dB at 8GHz~14GHz, the maximum compressive strength can reach 12±1MPa, and the operating temperature in an oxidizing atmosphere can reach 1100℃. It can meet the requirements of "wide frequency range + strong absorption + high temperature resistance + light, strong and thin", and provide efficient electromagnetic protection solutions for high-precision radar, high-speed communications and new energy equipment.

[0034] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A C@voids@SiC@SiO2 dual-gradient structure lightweight microwave-absorbing ceramic material, characterized by: The absorbing ceramic material forms a dual gradient structure at the macro / micro level, including a core and a pore wall. The core is a C core, and there is a nano-void layer between the C core and the pore wall. The pore wall is a double-layer structure, with an inner layer being a SiC layer and an outer layer being a SiO2 layer.

2. The method for preparing a C@voids@SiC@SiO2 dual gradient structure lightweight microwave-absorbing ceramic material according to claim 1, characterized in that: The specific steps of the preparation method are: S1. A series of spherical carbons with a gradient particle size distribution were synthesized using a hydrothermal method using a carbon source; S2. A silicon source was used to deposit SiO2 onto the surface of a series of spherical carbon particles with a gradient distribution of particle size prepared in S1 using a low-temperature chemical vapor deposition process to form a SiO2 shell layer, thereby obtaining a series of C@SiO2 core-shell powder particles with a gradient distribution of particle size. S3. The C@SiO2 core-shell structure powder in S2 is dispersed in deionized water to form a C@SiO2 dispersion; S4. The dispersion in S3 is placed in a mold, and a C@SiO2 primary green body having a gradient structure is formed by density induction; S5. The primary green body in S4 is pressed into a C@SiO2 secondary green body by a pressing process; S6. The C@SiO2 green body prepared in S5 is sintered in an argon atmosphere to form a C@SiC@SiO2 intermediate; S7. The C@SiC@SiO2 intermediate prepared in S6 is heat-treated in an oxygen-containing atmosphere to oxidize the C core therein, thereby separating it from the shell, forming a C@void@SiC@SiO2 dual-gradient structure lightweight absorbing ceramic material.

3. The method for preparing a C@voids@SiC@SiO2 dual gradient structure lightweight microwave absorbing ceramic material according to claim 2, characterized in that: The carbon source in S1 is glucose, fructose, chitosan, sucrose, cellulose or starch. The hydrothermal method temperature is 150° C. to 200° C., the time is 1 hour to 12 hours, and the diameter of the spherical carbon balls is 50 nm to 500 nm.

4. The method for preparing a C@voids@SiC@SiO2 dual gradient structure lightweight microwave absorbing ceramic material according to claim 2, characterized in that: The silicon source in S2 is methyl orthosilicate, ethyl orthosilicate, propyl orthosilicate, butyl orthosilicate, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane or ethyltriethoxysilane, and the low-temperature chemical vapor deposition process temperature is room temperature to 300°C, and the time is 1 hour to 48 hours.

5. The method for preparing a C@voids@SiC@SiO2 dual gradient structure lightweight microwave absorbing ceramic material according to claim 2, characterized in that: The thickness of the SiO2 shell in the S2 is 10nm~60nm.

6. The method for preparing a C@voids@SiC@SiO2 dual gradient structure lightweight microwave absorbing ceramic material according to claim 2, characterized in that: The solid content of the C@SiO2 dispersion in S3 is 10% to 90%.

7. The method for preparing a C@voids@SiC@SiO2 dual gradient structure lightweight microwave absorbing ceramic material according to claim 2, characterized in that: The induction time in S4 is 1 hour to 24 hours.

8. The method for preparing a C@voids@SiC@SiO2 dual gradient structure lightweight microwave absorbing ceramic material according to claim 2, characterized in that: The pressing pressure in S5 is 10 MPa to 200 MPa.

9. The method for preparing a C@voids@SiC@SiO2 dual gradient structure lightweight microwave absorbing ceramic material according to claim 2, characterized in that: In the S6, the sintering temperature is 1500° C. to 1700° C., and the sintering time is 0.5 hour to 3 hours.

10. The method for preparing a C@voids@SiC@SiO2 dual gradient structure lightweight microwave absorbing ceramic material according to claim 2, characterized in that: In the step S7, the heat treatment temperature is 400° C. to 1000° C., the heat treatment time is 0.5 hour to 5 hours, and the oxygen partial pressure is 20 ppm to 200 ppm.

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