C@void@SiC@SiO2 dual-gradient structure lightweight wave-absorbing ceramic material and preparation method

Abstract

The application relates to the technical field of high-temperature-resistant wave-absorbing materials, in particular to a C@void@SiC@SiO2 double-gradient-structure light wave-absorbing ceramic material and a preparation method thereof. The wave-absorbing ceramic material is composed of a double-gradient structure at a macro / micro level, including a core and a hole wall, the core is a C core, a nano-void layer is arranged between the C core and the hole wall, the hole wall is a double-layer structure, the inner layer is an SiC layer, and the outer layer is an SiO2 layer. The C@void@SiC@SiO2 double-gradient-structure light wave-absorbing ceramic material prepared by the application has a porosity of 70% to 85%, the lowest reflection loss can reach -65 dB at 8 GHz to 14 GHz, the compression strength can be up to 12+ / -1 MPa, 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 + thin" can be met, so that the application provides an efficient electromagnetic protection solution for high-precision radars, high-speed communication and new energy equipment.

Description

Technical Field

[0001] This invention relates to the field of high-temperature resistant microwave absorbing materials technology, and more specifically, to a lightweight microwave absorbing ceramic material with a C@void@SiC@SiO2 dual-gradient structure and its preparation method. Background Technology

[0002] While electromagnetic waves drive technological progress, their negative impacts on electronic devices and human health are becoming increasingly prominent, especially in the military field, where the development of radar detection technology has made stealth capability a critical requirement for equipment. As an important means of suppressing electromagnetic radiation and improving stealth performance, the performance optimization of absorbing materials is crucial. However, traditional magnetic and electrical loss absorbing materials are prone to failure due to decomposition, oxidation, and paramagnetization at high temperatures, limiting their application range.

[0003] Silicon carbide (SiC) has become a key research focus in high-temperature 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 composition suffers from problems such as low electrical conductivity, single polarization, poor impedance matching, and narrow absorption bandwidth, making it difficult to meet practical needs. In recent years, researchers have improved the performance of SiC-based absorbing materials through multi-component and multi-structure composite strategies, among which core-shell structures have attracted widespread attention due to their tunable impedance matching characteristics. Currently, although SiC-based core-shell structure absorbing materials (such as C@SiC and SiC@SiO2) have made some progress, their simple structures have led to a bottleneck in performance improvement, and they are mainly dispersed as absorbing agents in a resin matrix, failing to fully utilize the synergistic absorption effect between the core and shell.

[0004] Furthermore, gradient structures have become a research hotspot due to their ability to better meet the requirements of "thin, light, wide, and strong" microwave absorption. However, there are currently few reports on dual-dielectric gradient structure microwave absorbing materials. Designing dual-dielectric gradient microwave absorbing materials based on core-shell structures can combine the advantages of impedance gradient matching, multi-scale interface polarization, and pore gradient structures, overcoming the performance limitations of single-gradient structures while simultaneously endowing the materials with excellent thermal insulation properties. Therefore, the development of SiC-based dual-dielectric gradient structure microwave absorbing ceramic materials can not only promote the innovative development of high-temperature resistant microwave absorbing materials but also has significant scientific value and application prospects for military stealth technology and civilian electromagnetic protection. Summary of the Invention

[0005] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, one aspect of the present invention is to provide a lightweight microwave absorbing ceramic material with a C@void@SiC@SiO2 dual gradient structure. The microwave 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 has a double-layer structure, with an inner SiC layer and an outer SiO2 layer.

[0006] Another objective of this invention is to provide a method for preparing a lightweight microwave absorbing ceramic material with a C@void@SiC@SiO2 dual-gradient structure, wherein the specific steps of the preparation method are as follows:

[0007] S1. A series of spherical carbon particles with a gradient size distribution were synthesized using a hydrothermal method with carbon source;

[0008] S2. Using a low-temperature chemical vapor deposition process, SiO2 is deposited onto a series of spherical carbon surfaces with a gradient particle size distribution prepared in S1 to form a SiO2 shell layer, thereby obtaining a series of C@SiO2 core-shell structure powders with a gradient particle size distribution.

[0009] S3. Disperse the C@SiO2 core-shell structure powder in S2 into deionized water to form a C@SiO2 dispersion;

[0010] S4. Place the dispersion from S3 into a mold and use density induction to form a C@SiO2 primary green body with a gradient structure;

[0011] S5. The primary green body in S4 is pressed into a C@SiO2 secondary green body using a pressing molding process;

[0012] S6. The C@SiO2 green body prepared in S5 is sintered in an argon atmosphere to form a C@SiC@SiO2 intermediate;

[0013] S7. The C@SiC@SiO2 intermediate prepared in S6 is heat-treated in an oxygen-containing atmosphere to oxidize the C core, thereby separating it from the shell and forming a lightweight microwave absorbing ceramic material with a C@void@SiC@SiO2 dual-gradient structure.

[0014] Preferably, the carbon source in S1 is glucose, fructose, chitosan, sucrose, cellulose, or starch, the hydrothermal method is performed at a temperature of 150℃ to 200℃ for 1 hour to 12 hours, and the diameter of the spherical carbon spheres is 50nm to 500nm.

[0015] 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 is carried out at a temperature of room temperature to 300°C for a time of 1 hour to 48 hours.

[0016] Preferably, the SiO2 shell thickness in S2 is 10nm~60nm.

[0017] Preferably, the solid content of the C@SiO2 dispersion in S3 is 10%~90%.

[0018] Preferably, the induction time in S4 is 1 hour to 24 hours.

[0019] Preferably, the pressing pressure in S5 is 10MPa~200MPa.

[0020] Preferably, the sintering temperature in S6 is 1500℃~1700℃, and the sintering time is 0.5 hours~3 hours.

[0021] Preferably, the heat treatment temperature in S7 is 400℃~1000℃, the heat treatment time is 0.5 hours~5 hours, and the oxygen partial pressure is 20ppm~200ppm.

[0022] The beneficial effects of this invention are as follows:

[0023] Superior absorption performance: The unique gradient dielectric distribution (SiO2→SiC→C) achieves impedance gradient matching, effectively reducing electromagnetic wave reflection and enhancing absorption efficiency. The synergistic effect of multi-heterojunction polarization (C / SiC / SiO2 interface) and the resonant cavity effect induced by the void layer forms a wave absorption mechanism of "inducing deep penetration + no return," achieving a minimum reflection loss of -65dB in the 8~14GHz frequency band, far exceeding that of traditional wave absorbing materials.

[0024] Excellent high temperature resistance and oxidation resistance: The SiO2 shell and SiC intermediate layer provide double thermal protection for the C core, which makes the material stable in an oxidizing atmosphere at 1100℃, overcoming the problem of easy oxidation failure of traditional carbon-based materials at high temperatures.

[0025] Lightweight, high-strength, and broadband absorption: With a porosity of 70%~85%, the material achieves ultra-lightweight properties while maintaining a compressive strength of 12±1MPa, thus possessing excellent mechanical properties. The dual-gradient structural design (macroscopic continuous interface + microscopic core-shell heterogeneous interface) promotes cross-scale scattering and loss of electromagnetic waves, broadening the effective absorption bandwidth.

[0026] Highly adjustable and widely applicable: By adjusting parameters such as SiC / SiO2 pore wall thickness, C core size, and gradient layer ratio, it can be precisely adapted to different military and civilian application needs (such as stealth coatings, communication shielding, etc.).

[0027] Green and efficient preparation process: The method is simple to operate, has no solvent pollution, is suitable for mass production, and promotes the practical application of high-performance microwave absorbing materials.

[0028] In summary, the lightweight absorbing ceramic material with a C@void@SiC@SiO2 dual gradient structure in this application breaks through the bottleneck of traditional absorbing materials that are difficult to balance in terms of "wide bandwidth, strong absorption, high temperature resistance, and lightweight, strong and thin", providing an innovative solution for high-precision radar stealth, high-speed communication anti-interference and electromagnetic protection of new energy equipment.

[0029] Additional aspects and advantages of the invention will become apparent from the description which follows, or may be learned by practice of the invention. Attached Figure Description

[0030] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0031] Figure 1 This is a schematic diagram illustrating the formation principle of the lightweight microwave absorbing ceramic material with a C@void@SiC@SiO2 dual gradient structure of the present invention;

[0032] Figure 2 This is a schematic diagram of the macro / micro multi-scale interface of the lightweight microwave absorbing ceramic material with a C@void@SiC@SiO2 dual gradient structure according to an embodiment of the present invention;

[0033] Figure 3 This is the XRD pattern of the lightweight microwave absorbing ceramic material with a C@void@SiC@SiO2 dual-gradient structure according to an embodiment of the present invention;

[0034] Figure 4 This is the Raman spectrum of the lightweight microwave absorbing ceramic material with a C@void@SiC@SiO2 dual-gradient structure according to an embodiment of the present invention;

[0035] Figure 5 This is a graph showing the reflectivity of the lightweight microwave absorbing ceramic material with a C@void@SiC@SiO2 dual-gradient structure as a function of frequency, according to an embodiment of the present invention.

[0036] Figure 6 This is a stress-strain curve of the lightweight microwave absorbing ceramic material with a C@void@SiC@SiO2 dual-gradient structure according to an embodiment of the present invention;

[0037] Figure 7 This is an isothermal oxidation curve of the lightweight microwave absorbing ceramic material with a C@void@SiC@SiO2 dual-gradient structure according to an embodiment of the present invention. Detailed Implementation

[0038] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0039] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0040] like Figure 1 The diagram shown illustrates the formation principle of the lightweight microwave absorbing ceramic material with a C@void@SiC@SiO2 dual-gradient structure according to the present invention. Figure 2This is a schematic diagram of the macro / micro multi-scale interface of the lightweight microwave absorbing ceramic material with a C@void@SiC@SiO2 dual gradient structure according to an embodiment of the present invention.

[0041] Example 1

[0042] Take 10g of glucose, dissolve it in 100mL of deionized water, carry out hydrothermal reaction at 180℃ for 8 hours, centrifuge, wash and dry to obtain spherical carbon powder with micro-gradient particle size distribution (mainly distributed in 100nm~200nm).

[0043] Take 5g of the spherical carbon powder prepared above and place it in a low-temperature chemical vapor deposition device. Use tetraethyl orthosilicate as the silicon source, set the temperature to 100℃, and deposit for 24 hours. After natural cooling, C@SiO2 core-shell structure powder with uniform SiO2 shell (about 30nm thick) and gradient particle size distribution is obtained.

[0044] Take 20g of the C@SiO2 core-shell structure powder prepared above, disperse it in 80g of deionized water, and stir magnetically for 2 hours to form a C@SiO2 dispersion with a solid content of 20%.

[0045] The above dispersion was slowly injected into a polytetrafluoroethylene mold and allowed to stand for 12 hours to induce the C@SiO2 core-shell spheres of different particle sizes to settle and stratify under gravity according to their own density, forming a primary green body with a continuous gradient structure.

[0046] The primary green billet is placed in a cold isostatic press and held at 100 MPa for 5 minutes to form a C@SiO2 secondary green billet.

[0047] The secondary green blank is placed in an atmosphere sintering furnace, high-purity argon gas is introduced, and the temperature is raised to 1600℃ at a rate of 5℃ / min. It is then held at this temperature for 1 hour to sinter and form a C@SiC@SiO2 intermediate.

[0048] The sintered C@SiC@SiO2 intermediate was transferred to a tube furnace filled with air (oxygen partial pressure of about 100ppm), heated to 600℃ at 3℃ / min, and held for 2 hours to form a lightweight microwave absorbing ceramic material with a C@void@SiC@SiO2 dual gradient structure.

[0049] Example 2

[0050] Take 15g of sucrose, dissolve it in 150mL of deionized water, and hydrothermally react it at 200℃ for 4 hours. After centrifugation, washing and drying, spherical carbon powder with a bimodal gradient particle size distribution (main peaks around 80nm and 300nm) is obtained.

[0051] Take 6g of the spherical carbon powder prepared above and place it in a low-temperature chemical vapor deposition device. Use methyltriethoxysilane as the silicon source and set the temperature to 110℃. Deposit for 18 hours to obtain C@SiO2 core-shell structure powder with a uniform SiO2 shell layer (about 40nm thick) and a gradient distribution of particle size.

[0052] Take 30g of the C@SiO2 powder prepared above and mix it with 70g of deionized water. After ultrasonic dispersion for 30 minutes, stir magnetically for 3 hours to form a dispersion with a solid content of 30%.

[0053] The above dispersion was injected into a rectangular mold and allowed to stand for 6 hours to induce the formation of a primary green body with a distinct two-layer structure: the lower layer is mainly composed of small-diameter (~80nm) C@SiO2 spheres, and the upper layer is mainly composed of large-diameter (~300nm) C@SiO2 spheres.

[0054] The primary green body was subjected to unidirectional molding at a pressure of 50 MPa for 2 minutes to obtain a secondary green body with a dual-gradient structure of C@SiO2.

[0055] Under argon protection, the green compact was heated to 1550℃ at 10℃ / min and held for 1.5 hours for sintering to obtain C@SiC@SiO2 intermediate;

[0056] In an atmosphere with an oxygen partial pressure of approximately 50 ppm, the C@SiC@SiO2 intermediate is heated to 800℃ and held for 1 hour to form a lightweight microwave absorbing ceramic material with a C@void@SiC@SiO2 dual gradient structure.

[0057] Example 3

[0058] Take 8g of microcrystalline cellulose, disperse it in 120mL of deionized water, and perform a hydrothermal reaction at 190℃ for 12 hours to obtain spherical carbon powder with a particle size range of 50nm~400nm and a continuous gradient distribution.

[0059] Take 7g of the spherical carbon powder prepared above and place it in a low-temperature chemical vapor deposition apparatus. Using methyl orthosilicate as the silicon source, deposit at 200℃ for 36 hours to obtain a wide gradient C@SiO2 powder with a SiO2 shell thickness of about 50nm.

[0060] Take 45g of the C@SiO2 powder prepared above and mix it with 55g of deionized water, stir vigorously to form a dispersion with a solid content of 45%;

[0061] Inject the dispersion into the mold and let it stand for 24 hours to ensure that the particles with a wide range of particle sizes settle and stratify fully, forming a primary green body with a continuous change in particle size from bottom to top.

[0062] Cold isostatic pressing was performed at 200 MPa and held for 3 minutes to obtain C@SiO2 secondary green blank;

[0063] Under an argon atmosphere, the temperature was increased to 1700℃ at 8℃ / min and held for 0.5 hours for sintering to obtain C@SiC@SiO2 intermediate;

[0064] In an air atmosphere with strictly controlled oxygen partial pressure (approximately 30 ppm), the temperature is raised to 450°C and held for 5 hours to separate the C core from the pore wall, forming a lightweight microwave absorbing ceramic material with a C@void@SiC@SiO2 dual gradient structure.

[0065] Example 4

[0066] Take 5g of soluble starch, dissolve it in 100mL of deionized water, and perform a hydrothermal reaction at 150℃ for 10 hours. After treatment, spherical carbon powder with small particle size and narrow gradient distribution (mainly in the range of 50nm~150nm) is obtained.

[0067] Take 4g of the spherical carbon powder prepared above, use ethyltriethoxysilane as the silicon source, and deposit it at 180℃ for 12 hours to obtain a very uniform and precisely controlled ultrathin SiO2 shell with a thickness of 20nm, and obtain C@SiO2 powder with a nano-gradient particle size.

[0068] Take 15g of the C@SiO2 powder prepared above and disperse it in 135g of deionized water to form a dispersion with a solid content of 10%.

[0069] The dispersion was injected into the mold and allowed to stand for 4 hours to induce the formation of a primary green body with a gradient structure.

[0070] Lightly press at 10MPa and hold for 1 minute to obtain a secondary green blank with a C@SiO2 gradient structure.

[0071] The temperature was increased to 1500℃ at 3℃ / min and held for 3 hours for sintering to obtain C@SiC@SiO2 intermediate;

[0072] Rapid oxidation is performed in air with an oxygen partial pressure of approximately 150 ppm, heating to 1000 °C at a rate of 5 °C / min and holding for 0.5 hours to form a lightweight microwave absorbing ceramic material with a C@void@SiC@SiO2 dual gradient structure.

[0073] Testing and Experiment

[0074] Porosity tests were conducted on embodiments one to four of the present invention, and the test results showed that the porosity of the lightweight microwave absorbing ceramic material with the C@void@SiC@SiO2 dual gradient structure can be adjusted to 70%~85%.

[0075] XRD analysis was performed on embodiments one through four of the present invention, and the results are as follows. Figure 3 As shown;

[0076] Raman spectroscopy analysis was performed on Examples 1 to 4 of the present invention, and the results are as follows. Figure 4 As shown;

[0077] Electromagnetic simulations were performed on embodiments one through four of the present invention, and the simulation results are as follows: Figure 5 As shown;

[0078] The compressive strength of embodiments one to four of the present invention was tested, and the test results are as follows: Figure 6 As shown;

[0079] Isothermal oxidation tests were performed on Examples 1 to 4 of the present invention, and the test results are as follows: Figure 7 As shown.

[0080] In summary, the C@void@SiC@SiO2 dual-gradient lightweight absorbing ceramic material prepared by the method provided in this invention can simultaneously possess the following performance indicators: porosity of 70%~85%, minimum reflection loss of -65dB in the 8GHz~14GHz range, maximum compressive strength of 12±1MPa, and operating temperature of up to 1100℃ in an oxidizing atmosphere. It can meet the requirements of "wide frequency range + strong absorption + high temperature resistance + lightweight, strong and thin", providing an efficient electromagnetic protection solution for high-precision radar, high-speed communication and new energy equipment.

[0081] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A method for preparing a lightweight microwave absorbing ceramic material with a C@void@SiC@SiO2 dual-gradient structure, characterized in that: The core is a C core, and a nanogap layer is between the C core and the hole wall. The preparation method comprises the following specific steps: S1. Taking a carbon source, a series of spherical carbon with gradient distribution of particle size is synthesized by a hydrothermal method; S2. Taking a silicon source, SiO2 is deposited onto the surface of the series of spherical carbon with gradient distribution of particle size prepared in S1 by a low-temperature chemical vapor deposition process to form a SiO2 shell layer, and a series of C@SiO2 core-shell structure powder with gradient distribution of particle size is obtained; S3. The C@SiO2 core-shell structure powder in S2 is dispersed into deionized water to form a C@SiO2 dispersion liquid; S4. The dispersion liquid in S3 is placed into a mold, and a C@SiO2 primary green body with 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 forming 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, so that the C core is oxidized to separate from the shell layer, and a C@gap@SiC@SiO2 double-gradient structure light-weight wave-absorbing ceramic material is formed.

2. The preparation method of the C@gap@SiC@SiO2 double gradient structure lightweight wave-absorbing ceramic material according to claim 1, characterized in that: The carbon source in S1 is glucose, fructose, chitosan, sucrose, cellulose or starch, the hydrothermal method has a temperature of 150-200 DEG C and a time of 1-12 hours, and the spherical carbon has a particle size of 50-500 nm.

3. The preparation method of the C@gap@SiC@SiO2 double gradient structure lightweight wave-absorbing ceramic material according to claim 1, characterized in that: The silicon source in S2 is tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate, tetrabutyl orthosilicate, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane or ethyltriethoxysilane, the low-temperature chemical vapor deposition process has a temperature of room temperature-300 DEG C and a time of 1-48 hours.

4. The preparation method of the C@gap@SiC@SiO2 double gradient structure lightweight wave-absorbing ceramic material according to claim 1, characterized in that: The thickness of the SiO2 shell layer in S2 is 10-60 nm.

5. The preparation method of the C@gap@SiC@SiO2 double gradient structure lightweight wave-absorbing ceramic material according to claim 1, characterized in that: The solid content of the C@SiO2 dispersion liquid in S3 is 10-90%.

6. The preparation method of the C@gap@SiC@SiO2 double-gradient structure lightweight wave-absorbing ceramic material according to claim 1, characterized in that: The induction time in S4 is 1-24 hours.

7. The preparation method of the C@gap@SiC@SiO2 double-gradient structure lightweight wave-absorbing ceramic material according to claim 1, characterized in that: The pressing forming pressure in S5 is 10-200 MPa.

8. The preparation method of the C@gap@SiC@SiO2 double-gradient-structure lightweight wave-absorbing ceramic material according to claim 1, characterized in that: The sintering temperature in S6 is 1500-1700 DEG C, and the sintering time is 0.5-3 hours.

9. The preparation method of the C@gap@SiC@SiO2 double-gradient-structure lightweight wave-absorbing ceramic material according to claim 1, characterized in that: The heat treatment temperature in S7 is 400-1000 DEG C, the heat treatment time is 0.5-5 hours, and the oxygen partial pressure is 20-200 ppm.

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