In-situ construction method of high-temperature broadband wave-absorbing SiC periodic microtube ceramic

Abstract

The invention belongs to the technical field of preparation of high-temperature broadband wave-absorbing ceramics, and particularly relates to an in-situ construction method of high-temperature broadband wave-absorbing SiC periodic microtube ceramics. Comprising the following steps: 1, weaving 1K T300 carbon fibers into a carbon fiber preform; 2, SiC ceramic is deposited on the carbon fiber preform in situ through a chemical vapor deposition method, a layered structure is formed after the SiC ceramic is deposited multiple times, and a porous Cf / SiC composite material is obtained; and 3, carrying out oxidation treatment on the porous Cf / SiC composite material to obtain the hollow SiC periodic microtube ceramic structures with different oxidation degrees. Through the innovative preparation method and the unique structural design, the SiC micron hollow tube periodic structure is constructed in situ, the problem that SiC powder is difficult to form is successfully solved, broadband strong absorption in a high-temperature environment is achieved, a new way is opened up for application of the SiC micron hollow tube periodic structure in the field of additive manufacturing, and the SiC micron hollow tube periodic structure has good application prospects. Meanwhile, the method has wide application prospects in the fields of aerospace, military and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of high-temperature broadband wave-absorbing ceramics, and in particular relates to an in-situ construction method of high-temperature broadband wave-absorbing SiC periodic micro-tube ceramics. Background Art

[0002] In view of the urgent need for lightweight, high-temperature, broadband, and strong absorption materials in the hot end components of aerospace vehicles, it is necessary to carry out the preparation and electromagnetic property research of a series of SiC-based foam ceramics.

[0003] SiC ceramic is a typical dielectric lossy absorbing material with excellent properties such as light weight, high temperature resistance and high strength, and has broad application prospects in the field of high temperature absorbing. At present, SiC as a high temperature absorbing material can be optimized by preparing element-doped SiC ceramics, in-situ self-generated SiC nanowires, SiC foams, SiC fibers, etc., which can optimize the electromagnetic parameters and impedance matching performance of SiC absorbing materials.

[0004] Most of the existing SiC absorbing materials are powder materials. The absorbing materials prepared by compounding with a wave-transmitting matrix have a uniform and dense structure, which can achieve strong wave-absorbing performance in a certain frequency band. However, its dielectric constant increases with the increase of temperature, resulting in poor high-temperature wave-absorbing performance and a narrow effective wave-absorbing frequency band, which cannot meet the needs of practical applications. Song et al. from Zhengzhou University prepared porous SiC nanofibers and nanowire aerogel ceramics by freeze-drying, and used the multiple reflections and scattering of the porous structure in the foam ceramics to improve its polarization loss capacity, effectively improving its wave-absorbing performance, but there are no reports on its high-temperature wave-absorbing performance. The electrical properties of SiC fibers are closely related to their microstructures. SiC fibers from wave-absorbing to shielding can be obtained by regulating the preparation process. However, SiC fibers have a narrow wave-absorbing frequency band and a high modulus, and it is difficult to prepare broadband strong absorption composite materials by weaving and compounding with a wave-transmitting matrix.

[0005] Therefore, the structure of the SiC absorbing materials currently prepared is single, and it is difficult to achieve lightweight, broadband, and strong absorption of electromagnetic waves. How to prepare high-temperature, broadband, and efficient SiC absorbing materials through multi-scale structural design has become a key scientific problem that needs to be solved in the absorbing materials used in aerospace hot end components. Summary of the invention

[0006] In order to comprehensively solve the above problems, the present invention aims to develop a lightweight, high temperature resistant, wide-band, and highly absorbing ceramic structure to solve the problems of existing high temperature absorbing materials such as high density, thick thickness, unstable high temperature dielectric properties, and insufficient room temperature / high temperature absorbing performance.

[0007] The technical solution of the present invention is to use two-dimensional woven carbon fiber cloth to provide a mesoscopic periodic structure skeleton, form a nano-scale SiC layered structure by chemical vapor deposition of highly crystallized SiC ceramics, and construct SiC micron tubes with multi-scale periodic structures in situ through multiple oxidations.

[0008] The process of the present invention is simple, and there are a large number of periodic pore structures, defects, cracks and dipoles in the periodic structure of SiC micron hollow tubes, and the thickness and number of SiC layers can be controlled. The laminated structure of the two-dimensional woven carbon fiber cloth provides a mesoscopic periodic structure for the SiC micron hollow tubes, while reducing the density of homogeneous SiC ceramics and improving its wave absorption performance, providing a new idea for the preparation of "thin, light, wide and strong" electromagnetic wave absorption materials.

[0009] By regulating the weaving structure of carbon fiber, the deposition time of SiC layer and the oxidation time of carbon fiber, the multi-scale periodic structure and SiC micron hollow tube structure can be optimized. The prepared SiC micron hollow tube periodic structure can achieve full-frequency RC≤-8dB in the 8.2-18.0GHz band, and the effective absorption band with electromagnetic wave absorption efficiency higher than 90% can reach 6.8GHz. The absorbing performance is stable under high temperature conditions, and it has high-temperature, broadband and high-efficiency electromagnetic wave absorption characteristics, making it a highly potential high-temperature absorbing material.

[0010] In order to achieve the above object, the specific technical solution of the present invention is:

[0011] An in-situ construction method of high-temperature broadband wave-absorbing SiC periodic micro-tube ceramics, comprising:

[0012] Step 1: Weave 1K T300 carbon fiber into a carbon fiber preform;

[0013] Step 2: SiC ceramics are deposited in situ on the carbon fiber preform by chemical vapor deposition. After multiple depositions of SiC ceramics, a layered structure is formed to obtain a porous C f / SiC composite materials;

[0014] Step 3: Place the porous C f / SiC composite materials were oxidized to obtain hollow SiC periodic micro-tube ceramic structures with different oxidation degrees.

[0015] Preferably, the carbon fiber preform in step 1 is anisotropic, has an elliptical periodic structure in cross section, and has a rectangular woven periodic structure with different periods on the surface.

[0016] Preferably, the diameter of the SiC micron hollow tube in step 3 is 5 to 8 μm, and the single layer thickness of the layered SiC on the hollow tube wall does not exceed 1 μm, forming a multi-scale layered SiC hollow tube structure.

[0017] Preferably, the porosity of SiC periodic microtube ceramics is greater than 68% and the density is less than 0.85 g / cm 3 .

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The present invention successfully solves the problem of difficult SiC powder molding through innovative preparation methods and unique structural design, and realizes broadband strong absorption under high temperature environment, which opens up a new path for its application in the field of additive manufacturing. At the same time, it has broad application prospects in aerospace, military and other fields.

[0020] 2. The present invention successfully prepared a multilayer SiC matrix by using carbon fiber preforms with different weaving structures as the skeleton and combining them with chemical vapor deposition (CVI) technology, thereby forming a C f / SiC composite material. Subsequently, the carbon fiber is removed by oxidation treatment, and a periodic structure of SiC micron hollow tubes is constructed in situ, in which the SiC tube wall is β-SiC. The high hardness and strength of SiC make it difficult to be compressed and shaped during the molding process, which increases the difficulty of traditional molding methods. However, the present invention cleverly circumvents this problem by adopting a carbon fiber preform and a CVI process, thereby achieving complex shape molding of SiC. More importantly, the SiC matrix prepared by the CVI method has a high purity, usually reaching more than 97%, which is due to the less damage to the fiber by the CVI method and the avoidance of impurities that may be introduced in the traditional preparation process. In addition, high-purity CVI SiC not only has high strength, but also good plasticity, which means that it can be processed into various special shapes to meet the needs of complex structural design. This feature gives CVI SiC a significant advantage in the field of additive manufacturing, and makes it possible to manufacture ceramic components with high precision and complex structures.

[0021] 3. The structural unit size of the SiC hollow tube bundle is in the micron level, and the length of the SiC hollow tube is in the decimeter level. Since the SiC tube wall is composed of multiple layers of β-SiC with nanometer thickness, this nanometer size effect helps to enhance the absorption of electromagnetic waves. In addition, the high specific surface area of ​​SiC nanocrystals provides more electromagnetic wave scattering and absorption sites. The micron-level structural unit and the decimeter-level discontinuous hollow tube length together constitute a multi-scale gradient periodic structure with a density as low as 0.8g / cm 3 , the high thermal conductivity of SiC helps to dissipate heat quickly. At 600℃, the absorption bandwidth reaches 8.2GHz (covering most of the X-band and Ku-band), and the thickness is only 2.8mm. This excellent absorption performance and high temperature stability make SiC periodic microtube ceramics an ideal choice for lightweight, broadband, high-temperature absorbing ceramics. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0023] In the attached picture:

[0024] Figure 1 The structural unit morphology characteristics of SiC periodic microtube ceramics: Figure 1 (a) is the rectangular periodic morphology of the surface. Figure 1 (b) Cross-section of elliptical periodic units and inter-bundle holes;

[0025] Figure 2 Microstructure of SiC periodic microtube ceramics: Figure 2 (a) Discontinuous pores in the bundle, Figure 2 (b) micron hollow tube;

[0026] Figure 3 The microwave absorption performance of SiC periodic microtube ceramics at room temperature;

[0027] Figure 4 The microwave absorption performance of SiC periodic microtube ceramics under high temperature conditions;

[0028] Figure 5 The figure is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the technical solution of the present invention and to implement it, the following is a detailed description of the technical solution of the present invention in combination with the specific embodiments and the attached drawings. Figure 1-5 The present invention is further described below, but the embodiments are not intended to limit the present invention.

[0030] Example 1

[0031] An in-situ construction method of high-temperature broadband wave-absorbing SiC periodic micro-tube ceramics, comprising:

[0032] Step 1: Weave 1K T300 carbon fiber into a two-dimensional (2D) plain weave structure (the carbon fiber preform can also be in the form of plain weave, satin weave, 2.5D, three-dimensional four-way structure), and obtain a 2D carbon fiber preform with a thickness of (3-4mm) by laminating plain carbon fiber cloth. The prepared carbon fiber preform has anisotropy, an elliptical periodic structure in cross section, and a rectangular woven periodic structure with different periods on the surface.

[0033] Step 2: SiC ceramics are deposited in situ on the carbon fiber preform by chemical vapor deposition. After repeated deposition of SiC ceramics 4-5 times, a layered structure is formed. The thickness of the single layer of SiC does not exceed 1 μm. At this time, the bundle is evenly filled with SiC ceramics and there are large pores between the bundles, thus obtaining a porous C f / SiC composite materials;

[0034] Step 3: Place the porous C f The SiC / SiC composite material was oxidized at 800°C in an air-oxygen environment for about 12 hours. When the carbon fiber skeleton was oxidized to form a wedge shape, hollow SiC periodic microtube ceramic structures with different oxidation degrees were obtained.

[0035] The diameter of the hollow tube of the SiC periodic microtube ceramic structure is 5 to 8 μm, and the single layer thickness of the layered SiC on the hollow tube wall does not exceed 1 μm, forming a multi-scale layered SiC hollow tube structure.

[0036] The porosity of SiC periodic microtube ceramics is greater than 68% and the density is less than 0.85g / cm 3 .

[0037] Example 2

[0038] An in-situ construction method of high-temperature broadband wave-absorbing SiC periodic micro-tube ceramics, comprising:

[0039] Step 1: Weave 1K T300 carbon fiber into a two-dimensional (2D) plain weave structure (the carbon fiber preform can also be in the form of plain weave, satin weave, 2.5D, three-dimensional four-way structure), and obtain a 2D carbon fiber preform with a thickness of (3-4mm) by laminating plain carbon fiber cloth. The prepared carbon fiber preform has anisotropy, an elliptical periodic structure in cross section, and a rectangular woven periodic structure with different periods on the surface.

[0040] Step 2: SiC ceramics are deposited in situ on the carbon fiber preform by chemical vapor deposition. After repeated deposition of SiC ceramics 4-5 times, a layered structure is formed. The thickness of the single layer of SiC does not exceed 1 μm. At this time, the bundle is evenly filled with SiC ceramics and there are large pores between the bundles, thus obtaining a porous C f / SiC composite materials;

[0041] Step 3: Place the porous C f The SiC / SiC composite material was oxidized at 850°C in an air-oxygen environment for about 5 to 12 hours. When the carbon fiber skeleton was oxidized to form a wedge shape, hollow SiC periodic microtube ceramic structures with different oxidation degrees were obtained.

[0042] The diameter of the hollow tube of the SiC periodic microtube ceramic structure is 5 to 8 μm, and the single layer thickness of the layered SiC on the hollow tube wall does not exceed 1 μm, forming a multi-scale layered SiC hollow tube structure.

[0043] The porosity of SiC periodic microtube ceramics is greater than 68% and the density is less than 0.85g / cm 3 .

[0044] Example 3

[0045] An in-situ construction method of high-temperature broadband wave-absorbing SiC periodic micro-tube ceramics, comprising:

[0046] Step 1: Weave 1K T300 carbon fiber into a carbon fiber preform with a thickness of 3-4 mm (the carbon fiber preform can be in the form of plain weave, satin weave, 2.5D, three-dimensional four-way and three-dimensional five-way structures). The prepared carbon fiber preform has anisotropy, an elliptical periodic structure in cross section, and a rectangular braided periodic structure with different periods on the surface.

[0047] Step 2: SiC ceramics are deposited in situ on the carbon fiber preform by chemical vapor deposition. After repeated deposition of SiC ceramics 4-5 times, a layered structure is formed. The thickness of the single layer of SiC does not exceed 1 μm. At this time, the bundle is evenly filled with SiC ceramics and there are large pores between the bundles, thus obtaining a porous C f / SiC composite materials;

[0048] Step 3: Place the porous C f The / SiC composite material was oxidized at 900°C in an air-oxygen environment for about 12 hours. The carbon fiber preform skeleton was completely oxidized to form SiC, and hollow SiC periodic microtube ceramic structures with different oxidation degrees were obtained.

[0049] The diameter of the hollow tube of the SiC periodic microtube ceramic structure is 5 to 8 μm, and the single layer thickness of the layered SiC on the hollow tube wall does not exceed 1 μm, forming a multi-scale layered SiC hollow tube structure.

[0050] The porosity of SiC periodic microtube ceramics is greater than 68% and the density is less than 0.85g / cm 3 .

[0051] Multi-scale and multiple electromagnetic wave loss mechanisms are formed in SiC periodic microtube ceramics, which is conducive to the coordinated absorption of high-temperature and broadband electromagnetic waves.

[0052] The microstructure of the wave-absorbing SiC micron hollow tube periodic structure obtained in this embodiment is as follows Figure 1 and Figure 2 As shown, the room temperature and high temperature reflection coefficients are Figure 3 and Figure 4 shown.

[0053] There are millimeter-scale periodic structures in SiC periodic microtube ceramics, such as Figure 1 (a), the surface of SiC microtube ceramics presents a regular plain weave structure. The cross-sectional morphology of the ceramics is shown in Figure 1As shown in (b), since the porosity of SiC is about 68%, it can be seen that there are micron to millimeter-scale macropores between the fiber bundles. The fiber bundles are elliptical in size and there are pores of different sizes in the fiber bundles, showing a cross-scale periodic structure. SiC periodic microtube ceramics also have micro / nanoscale hollow tubular structures. This structure not only significantly reduces the weight of the ceramic material, but also helps to improve the thermal stability and broadband absorption performance of the material. The cross-sectional morphology of SiC periodic microtube ceramics is shown in Figure 2. Figure 2 As shown by Figure 2 (a) It can be seen that the SiC microtubes are arranged in an orderly manner and the SiC tube wall is relatively thin; Figure 2 From the local enlarged view of the cross section of SiC periodic microtubes in (b), it can be seen that SiC ceramics present a hollow gradient layered distribution (the inner SiC layer is thinner and the outer SiC layer is thicker).

[0054] The electromagnetic absorption properties of SiC periodic microtube ceramics are as follows Figure 3 As shown in the figure, the effective absorption band is the widest at a thickness of 2.6 mm, reaching 6.8 GHz (from 11.2 GHz to 18.0 GHz), indicating that SiC periodic microtube ceramics have a wide frequency response range. At a thickness of 2.4 mm and a frequency of 15.65 GHz, the minimum reflection coefficient of SiC periodic microtube ceramics reaches -56.36 dB. The high-temperature dielectric constant of SiC microtube ceramics shows significant stability with temperature changes. It is particularly noteworthy that when the temperature rises to 600 ° C, the maximum effective absorption bandwidth of SiC microtube ceramics reaches 8.2 GHz. Figure 4 What is more outstanding is that the electromagnetic reflection coefficient of SiC microtube ceramics is kept below -7dB in the entire X-band and Ku-band. SiC periodic microtube ceramics are undoubtedly a high-temperature absorbing material with great potential due to its wide-band electromagnetic absorption capability, high-temperature stability and excellent performance in the X-band and Ku-band.

[0055] In addition, the carbon fiber preforms prepared in the three embodiments of the present invention all exhibit anisotropy.

[0056] This is due to the properties of the carbon fiber itself and the weaving method. There are significant differences in the properties of carbon fiber along the fiber direction and perpendicular to the fiber direction. This anisotropy is retained after weaving into a preform and in-situ deposition of CVI SiC. Since the preform is composed of two-dimensional woven carbon fiber bundles, it presents a periodic structure on a macro scale. This periodic structure is determined by the arrangement and interweaving of the carbon fiber bundles during the weaving process. Different weaving methods will result in different arrangements and interweaving patterns of the carbon fiber bundles, resulting in different rectangular periodic structures on a macro scale.

[0057] 1K T300 carbon fiber refers to a bundle of 1,000 carbon fibers. Due to its dense fiber arrangement, the cross section appears as an elliptical periodic structure on a macro scale. This structure is determined by the number of fibers, the arrangement method, and the weaving process.

[0058] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. An in-situ construction method for high-temperature broadband wave-absorbing SiC periodic micro-tube ceramics, characterized in that: include: Step 1: Weave 1K T300 carbon fiber into a carbon fiber preform; Step 2: SiC ceramics are deposited in situ on the carbon fiber preform by chemical vapor deposition. After multiple depositions of SiC ceramics, a layered structure is formed to obtain a porous C f / SiC composite materials; Step 3: Place the porous C f / SiC composite materials were oxidized to obtain hollow SiC periodic microtube ceramic structures with different oxidation degrees.

2. The in-situ construction method of a high-temperature broadband wave-absorbing SiC periodic micro-tube ceramic according to claim 1, characterized in that: The carbon fiber preform in step 1 is anisotropic, with an elliptical periodic structure in cross section and a rectangular woven periodic structure with different periods on the surface.

3. The in-situ construction method of a high-temperature broadband wave-absorbing SiC periodic micro-tube ceramic according to claim 2, characterized in that: The diameter of the SiC micron hollow tube in step 3 is 5 to 8 μm, and the single layer thickness of the layered SiC on the hollow tube wall does not exceed 1 μm, forming a multi-scale layered SiC hollow tube structure.

4. The in-situ construction method of a high-temperature broadband wave-absorbing SiC periodic micro-tube ceramic according to claim 3, characterized in that: The porosity of SiC periodic microtube ceramics is greater than 68% and the density is less than 0.85g / cm 3 .

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