An ultra-high temperature ceramic composite material with broadband wave absorption and oxidation resistance and a preparation method thereof

Abstract

This invention discloses an ultra-high temperature ceramic composite material with both broadband microwave absorption and oxidation resistance, and its preparation method, belonging to the field of microwave absorbing materials technology. The ultra-high temperature ceramic composite material with both broadband microwave absorption and oxidation resistance is a ZrB2-BNNT / SiC-BNNT ceramic matrix composite material. By volume percentage, the ZrB2-BNNT / SiC-BNNT ceramic matrix composite material is prepared from 70-95% ZrB2-BNNT high-temperature pyrolysis products and 5-30% SiC-BNNT crosslinking products. Boron nitride nanotubes are intercalated into ZrB2 particles in the ZrB2-BNNT high-temperature pyrolysis products and SiC particles in the SiC-BNNT crosslinking products, with ZrB2 particles and SiC particles arranged alternately. The ZrB2-BNNT / SiC-BNNT ceramic matrix composite material contains heterogeneous interfaces, including BNNT / ZrB2 heterogeneous interfaces, BNNT / SiC heterogeneous interfaces, and ZrB2 / SiC heterogeneous interfaces. Based on ZrB2 and SiC prepared by polymer conversion method, boron nitride nanotube dielectric networks were constructed on them respectively and then mixed to obtain ZrB2-BNNT / SiC-BNNT ultra-high temperature ceramic composite material with both anti-oxidation and microwave absorption capabilities, which broadens the selection of microwave absorbing materials in high temperature and oxygen environment.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing materials technology, specifically relating to an ultra-high temperature ceramic composite material that combines broadband microwave absorption and oxidation resistance, and its preparation method. Background Technology

[0002] As future aircraft evolve towards higher speeds and higher operating temperatures, there is an urgent need to develop high-temperature absorbing materials that are lightweight and have a wide frequency range. Ceramics and ceramic composites are ideal choices for absorbing materials suitable for high-temperature environments due to their high thermal stability.

[0003] Ultra-high temperature ceramics (UHTC) are a class of ceramic materials with ultra-high melting points (above 3000℃) and excellent thermal stability and ablation resistance. UHTC typically includes transition metal borides, carbides, nitrides and their composites, which have great application potential in extreme environments and are ideal choices for microwave absorbing materials suitable for high-temperature environments. Although ZrB2, as a typical UHTC ceramic, has an ultra-high melting point, it is easily oxidized in high-temperature oxygen-containing environments. Adding SiC as an additive is an effective way to improve the oxidation resistance of ZrB2. ZrB2 / SiC is a typical UHTC ceramic system. Reference 1, "Yao X, Chen M, and Feng G. Antioxidant Behavior of La2O3 Modified ZrB2-SiCCoating for C / C Composites at Full Temperature[J]. Rare Metal Materials and Engineering, 2020, 49(1):241-246," mentions that in high-temperature oxygen-containing environments, SiC forms a SiO2 protective layer on the surface of the composite material, which can effectively inhibit the continuous entry of oxygen. However, neither ZrB2 nor SiC prepared at high temperatures via polymer-converted ceramics (PDC) are traditional microwave absorbing materials. Both possess high electrical conductivity, and the skin effect causes impedance mismatch, resulting in electromagnetic waves being reflected at the material surface and unable to penetrate the interior for dissipation. Therefore, developing microwave absorbing capabilities in polymer-converted ZrB2 / SiC composites has pioneering theoretical and practical significance for the research and application of high-temperature stealth materials in extreme environments. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention aims to provide an ultra-high temperature ceramic composite material with both broadband microwave absorption and oxidation resistance, and its preparation method. Based on ZrB2 and SiC prepared by polymer conversion method, boron nitride nanotube dielectric networks are constructed on them respectively and then mixed to obtain a ZrB2-BNNT / SiC-BNNT ultra-high temperature ceramic composite material with both oxidation resistance and microwave absorption capabilities, thus broadening the selection of microwave absorbing materials in high temperature and oxygen-containing environments.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] This invention provides an ultra-high temperature ceramic composite material that combines broadband microwave absorption and oxidation resistance. The ultra-high temperature ceramic composite material that combines broadband microwave absorption and oxidation resistance is a ZrB2-BNNT / SiC-BNNT ceramic matrix composite material.

[0007] The ZrB2-BNNT / SiC-BNNT ceramic matrix composite material is prepared from 70-95% of ZrB2-BNNT high-temperature pyrolysis products and 5-30% of SiC-BNNT crosslinking products by volume percentage.

[0008] Among them, boron nitride nanotubes are interspersed in ZrB2 particles in ZrB2-BNNT high-temperature pyrolysis products and SiC particles in SiC-BNNT crosslinking products, with ZrB2 particles and SiC particles arranged alternately.

[0009] The ZrB2-BNNT / SiC-BNNT ceramic matrix composite material contains heterogeneous interfaces, including BNNT / ZrB2 heterogeneous interfaces, BNNT / SiC heterogeneous interfaces, and ZrB2 / SiC heterogeneous interfaces.

[0010] In the specific implementation process, the ultra-high temperature ceramic composite material with both broadband wave absorption and oxidation resistance has a SiO2 protective layer on its surface.

[0011] This invention provides a method for preparing an ultra-high temperature ceramic composite material that combines broadband microwave absorption and oxidation resistance, comprising the following steps:

[0012] ZrB2 precursor and first group of boron nitride nanotubes were mixed and anhydrous ethanol was added. The mixture was ultrasonically treated and then stirred to remove the anhydrous ethanol to obtain a first homogeneous mixture. The first homogeneous mixture was subjected to first cross-linking and curing to obtain a first cross-linking product. The first cross-linking product was pretreated to obtain a pretreated product. The pretreated product was subjected to high-temperature pyrolysis treatment to obtain ZrB2-BNNT high-temperature pyrolysis product.

[0013] After mixing liquid polycarbosilane with the second group of boron nitride nanotubes, xylene was added, followed by ultrasonic treatment and stirring to remove xylene, resulting in a second homogeneous mixture; the second homogeneous mixture underwent a second crosslinking and curing process to obtain the SiC-BNNT crosslinked product;

[0014] The high-temperature pyrolysis products of ZrB2-BNNT and the crosslinking products of SiC-BNNT were mixed, ground, and then pressed into tablets to obtain a block solid. The block solid was subjected to high-temperature pyrolysis heat treatment to obtain a ZrB2-BNNT / SiC-BNNT ceramic matrix composite material.

[0015] In the specific implementation process, the mass fraction of the first group of boron nitride nanotubes is 0.5-20%; the mass ratio of anhydrous ethanol to ZrB2 precursor is 1:1.

[0016] In the specific implementation process, the temperature of the first cross-linking curing is 130-150℃, and the time of the first cross-linking curing is 2-3 hours.

[0017] In specific implementation, the preprocessing process is as follows:

[0018] The first crosslinking product is heated from room temperature to 400-600°C at a rate of 5-10°C / min and held at that temperature for 2-3 hours. Then, it is cooled to 300°C at a rate of 5°C / min and then cooled to room temperature in the furnace to obtain the pretreated product.

[0019] In specific implementation, the high-temperature pyrolysis process is as follows:

[0020] The pretreated product was heated from room temperature to 1500–1600°C at a rate of 5–10°C / min and held at that temperature for 1–2 hours. Then, it was cooled to 300°C at a rate of 4°C / min and then cooled to room temperature in the furnace to obtain the ZrB2-BNNT high-temperature pyrolysis product.

[0021] In the specific implementation process, the mass fraction of the second group of boron nitride nanotubes is 3-20%; the mass ratio of xylene to liquid polycarbosilane is 1:1.

[0022] In the specific implementation process, the second cross-linking curing process is as follows:

[0023] The second homogeneous mixture was crosslinked and cured at a rate of 5–10 °C / min from room temperature to 140–160 °C for 2–3 h to obtain the SiC-BNNT crosslinked product.

[0024] In specific implementation, the high-temperature pyrolysis heat treatment process is as follows:

[0025] The bulk solid was heated from room temperature to 1400–1600°C at a rate of 5–10°C / min and held at that temperature for 1–2 hours. Then, it was cooled to 300°C at a rate of 4°C / min and then cooled to room temperature in the furnace to obtain the ZrB2-BNNT / SiC-BNNT ceramic matrix composite material.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] This invention provides an ultra-high temperature ceramic composite material that combines broadband microwave absorption and oxidation resistance. This composite material possesses advantages such as high temperature resistance, oxidation resistance, broadband microwave absorption, and simple preparation process, making it an ideal candidate material for high-temperature microwave absorbing materials. While the high-temperature pyrolysis products of ZrB2-BNNT in the raw materials have ultra-high melting points and can be used in extreme thermal environments, they are easily oxidized in high-temperature aerobic environments. Therefore, the addition of SiC-BNNT composite material not only improves the material's oxidation resistance but also provides more heterogeneous interfaces, enabling greater dissipation of electromagnetic waves and enhanced microwave absorption capabilities. Furthermore, the BNNT introduced in this invention forms a network distribution in the ZrB2-BNNT / SiC-BNNT composite material, effectively preventing electron movement and transitions, reducing the composite material's conductivity, and improving the impedance mismatch issue currently encountered when using PDC-ZrB2 and high-temperature pyrolysis PDC-SiC polymers converted to ZrB2 / SiC ceramics as microwave absorbing materials. This optimizes the dielectric constant and improves its microwave absorption performance. Furthermore, the presence of numerous heterogeneous interfaces (BNNT / ZrB2, BNNT / SiC, ZrB2 / SiC, etc.) in composite materials leads to strong interfacial polarization losses, resulting in significant electromagnetic wave loss.

[0028] Furthermore, SiC forms a SiO2 protective layer under a high-temperature oxygen atmosphere, which gives the composite material antioxidant properties.

[0029] Furthermore, the ZrB2-BNNT / SiC-BNNT composite material has an effective absorption bandwidth of 1.4-9.6 GHz, with the optimal effective absorption bandwidth being 9.6 GHz (8.4-18 GHz), covering almost the entire X-band and Ku-band, achieving a new breakthrough in the microwave absorption performance of monolithic ceramic materials.

[0030] This invention provides a method for preparing an ultra-high temperature ceramic composite material with both broadband microwave absorption and oxidation resistance. A boron nitride nanotube (BNNT) dielectric network is uniformly dispersed in a ZrB2 precursor and polycarbosilane, respectively. The high-temperature pyrolysis product of the ZrB2 precursor with added BNNT is mixed with the crosslinking product of the SiC precursor with added BNNT. After mixing at different volume fractions, the mixture is subjected to high-temperature pyrolysis heat treatment to obtain the ZrB2-BNNT / SiC-BNNT composite material. The introduction of BNNT improves the impedance mismatch in the current application of polymer-converted ZrB2 / SiC composite materials as microwave absorbing materials, optimizes the dielectric constant of the ZrB2 / SiC composite material, and improves its microwave absorption performance while retaining its oxidation resistance. Attached Figure Description

[0031] Figure 1 Scanning electron microscope images and energy dispersive spectroscopy (EDS) of the ZrB2-BNNT / SiC-BNNT composite material prepared in this invention;

[0032] Figure 2 The transmission electron microscope (TEM) image and energy dispersive spectroscopy (EDS) image of the ZrB2-BNNT / SiC-BNNT ultra-high temperature ceramic matrix composite material with a volume fraction of 20% prepared in this invention are shown in Figure (a), Figure (b) is the TEM image, and Figure (c) is the high-resolution image of the block region in Figure (b).

[0033] Figure 3 Figures (a), (b), (c), and (d) are RL two-dimensional diagrams of the ZrB2-BNNT / SiC-BNNT ultra-high temperature ceramic matrix composite materials of Examples 1, 2, 3, and 4 of the present invention, respectively. Detailed Implementation

[0034] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0035] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0036] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0037] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0038] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0039] This invention provides an ultra-high temperature ceramic composite material that combines broadband microwave absorption and oxidation resistance, and its preparation method.

[0040] The first aspect of this invention provides an ultra-high temperature ceramic composite material that combines broadband microwave absorption and oxidation resistance. This ultra-high temperature ceramic composite material is a ZrB2-BNNT / SiC-BNNT ceramic matrix composite material. By volume percentage, the ZrB2-BNNT / SiC-BNNT ceramic matrix composite material is prepared from 70-95% ZrB2-BNNT high-temperature pyrolysis products and 5-30% SiC-BNNT crosslinking products.

[0041] Boron nitride nanotubes are intercalated within ZrB2 particles in the high-temperature pyrolysis products of ZrB2-BNNT and SiC particles in the crosslinked products of SiC-BNNT, with ZrB2 and SiC particles arranged alternately. Furthermore, heterogeneous interfaces exist in the ZrB2-BNNT / SiC-BNNT ceramic matrix composite material, including BNNT / ZrB2, BNNT / SiC, and ZrB2 / SiC heterogeneous interfaces. This ultra-high temperature ceramic composite material, possessing both broadband microwave absorption and oxidation resistance, has a SiO2 protective layer on its surface.

[0042] BNNTs, interspersed within ZrB2 and SiC particles, form numerous heterogeneous interfaces that strongly dissipate electromagnetic waves. Simultaneously, the SiO2 protective layer formed by SiC under high-temperature oxygen atmosphere enhances the composite material's oxidation resistance.

[0043] The effective absorption bandwidth of the ZrB2-BNNT / SiC-BNNT composite material is 1.4-9.6 GHz, with the optimal effective absorption bandwidth being 9.6 GHz (8.4-18 GHz), covering the entire X-band and Ku-band.

[0044] The boron nitride nanotubes (BNNTs) used possess low dielectric properties, high electrical insulation, strong oxidation resistance, and thermal stability, making them ideal dielectric materials for reducing the dielectric constant of composite materials and improving impedance matching. Reference 2, "Jia Y, Ajayi TD and Xu C. Dielectric properties of polymer-derived ceramic reinforced with boron nitride nanotubes[J]. Journal of the American Ceramic Society, 2020, 103(10): 5731-5742," mentions that the real part of the dielectric constant of SiCN continuously decreases with increasing BNNT content. Furthermore, BNNT belongs to the BN material family, and the dielectric constant of BN materials does not change significantly with temperature; therefore, BNNT also possesses the ability to adjust the dielectric constant of materials at high temperatures.

[0045] The second aspect of this invention provides a method for preparing an ultra-high temperature ceramic composite material that combines broadband microwave absorption and oxidation resistance. The method involves mixing the high-temperature pyrolysis product of a ZrB2 precursor with added boron nitride nanotubes (BNNT) with the crosslinking product of a SiC precursor with added boron nitride nanotubes (BNNT), grinding thoroughly, cold pressing, and then obtaining a polymer-converted ceramic composite material (ZrB2-BNNT / SiC-BNNT) with a BNNT dielectric network reinforced by high-temperature pyrolysis heat treatment.

[0046] The ZrB2 precursor and the first group of boron nitride nanotubes were mixed and then anhydrous ethanol was added. The mixture was ultrasonically treated and stirred to remove the anhydrous ethanol, resulting in a first homogeneous mixture. The first homogeneous mixture was subjected to a first cross-linking and curing process to obtain a first cross-linked product. The first cross-linked product was pretreated to obtain a pretreated product. The pretreated product was subjected to high-temperature pyrolysis to obtain a ZrB2-BNNT high-temperature pyrolysis product. The mass fraction of the first group of boron nitride nanotubes was 0.5-20%, and the mass ratio of anhydrous ethanol to ZrB2 precursor was 1:1.

[0047] After mixing liquid polycarbosilane with the second group of boron nitride nanotubes, xylene is added, followed by ultrasonic treatment and stirring to remove xylene, resulting in a second homogeneous mixture. The second homogeneous mixture undergoes a second crosslinking and curing process to obtain a SiC-BNNT crosslinked product. The mass fraction of the second group of boron nitride nanotubes is 3-20%, and the mass ratio of xylene to liquid polycarbosilane is 1:1.

[0048] The high-temperature pyrolysis products of ZrB2-BNNT and the crosslinking products of SiC-BNNT were mixed, ground, and then pressed into tablets to obtain a block solid. The block solid was subjected to high-temperature pyrolysis heat treatment to obtain a ZrB2-BNNT / SiC-BNNT ceramic matrix composite material.

[0049] The volume fraction of ZrB2-BNNT high-temperature pyrolysis products is 70-95%, and the volume fraction of SiC-BNNT crosslinking products is 5-30%.

[0050] The specific steps of the above preparation method are as follows:

[0051] Step 1: Mix ZrB2 precursor with boron nitride nanotubes (BNNT) with a mass fraction of 0.5-20%, then add anhydrous ethanol of the same mass as ZrB2 precursor, sonicate in an ultrasonic machine for 4 hours, and then place in a magnetic stirrer and stir at 80°C for 4 hours to remove anhydrous ethanol, to obtain the first homogeneous mixture.

[0052] Step 2: Place the first homogeneous mixture obtained in Step 1 in an oven and perform cross-linking curing at 130-150℃ for 2-3 hours to obtain the first cross-linked product;

[0053] Step 3: Under a flowing Ar atmosphere, the first crosslinking product obtained in step 2 is placed in a tubular heat treatment furnace and heated from room temperature to 400-600°C at a rate of 5-10°C / min, held for 2-3 hours, then cooled to 300°C at a rate of 5°C / min, and then cooled to room temperature with the furnace to obtain the pretreated product.

[0054] Step 4: Under a flowing Ar atmosphere, the pretreated product obtained in Step 4 is placed in a high-temperature tube furnace and heated from room temperature to 1500-1600℃ at a rate of 5-10℃ / min, held for 1-2 hours, and then cooled to 300℃ at a rate of 4℃ / min. The product is then cooled to room temperature with the furnace to obtain the ZrB2-BNNT ultra-high temperature ceramic matrix composite material, i.e., the ZrB2-BNNT high-temperature pyrolysis product, which is then ground into powder.

[0055] Step 5: Mix liquid polycarbosilane (PCS) with boron nitride nanotubes (BNNT) at a mass fraction of 3-20%, add xylene of the same mass as the precursor, sonicate in an ultrasonic machine for 4 hours, then place in a magnetic stirrer and stir at 80°C for 8 hours to remove xylene and obtain a second homogeneous mixture.

[0056] Step 6: Under a flowing Ar atmosphere, the second homogeneous mixture obtained in step 5 is placed in a tubular heat treatment furnace and crosslinked and cured at a rate of 5-10°C / min from room temperature to 140-160°C for 2-3 hours to obtain the SiC-BNNT crosslinked product.

[0057] Step 7: Mix the SiC-BNNT crosslinking product and the ZrB2-BNNT high-temperature pyrolysis product at a volume fraction of 5% to 30%, grind thoroughly, and then compress into tablets to obtain a block solid.

[0058] Step 8: Under a flowing Ar atmosphere, the blocky solid obtained in step 7 is placed in a high-temperature tube furnace and heated from room temperature to 1400-1600℃ at a rate of 5-10℃ / min, held for 1-2 hours, and then cooled to 300℃ at a rate of 4℃ / min, and then cooled to room temperature with the furnace to obtain ZrB2-BNNT / SiC-BNNT ceramic matrix composite material.

[0059] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0060] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0061] Example 1:

[0062] Step 1: Mix ZrB2 precursor with 0.5% boron nitride nanotubes (BNNT) and add anhydrous ethanol of the same mass as ZrB2 precursor. Place the mixture in an ultrasonic machine and sonicate for 4 hours. Then place it in a magnetic stirrer and stir at 80°C for 4 hours to remove anhydrous ethanol, and obtain the first homogeneous mixture.

[0063] Step 2: Place the first homogeneous mixture obtained in Step 1 in an oven and perform cross-linking curing at 130°C for 3 hours to obtain the first cross-linked product;

[0064] Step 3: Under a flowing Ar atmosphere, the first crosslinking product obtained in step 2 is placed in a tubular heat treatment furnace and heated from room temperature to 400°C at a rate of 10°C / min, held for 3 hours, then cooled to 300°C at a rate of 5°C / min, and then cooled to room temperature with the furnace to obtain the pretreated product.

[0065] Step 4: Under a flowing Ar atmosphere, the pretreated product obtained in Step 4 is placed in a high-temperature tube furnace and heated from room temperature to 1500℃ at a rate of 10℃ / min, held for 1 hour, and then cooled to 300℃ at a rate of 4℃ / min. The product is then cooled to room temperature with the furnace to obtain the ZrB2-BNNT ultra-high temperature ceramic matrix composite material, i.e., the ZrB2-BNNT high-temperature pyrolysis product, which is then ground into powder.

[0066] Step 5: After mixing liquid polycarbosilane (PCS) with boron nitride nanotubes (BNNT) at a mass fraction of 3%, add xylene of the same mass as the precursor, place in an ultrasonic machine and sonicate for 4 hours, then place in a magnetic stirrer and stir at 80°C for 8 hours to remove xylene and obtain a second homogeneous mixture.

[0067] Step 6: Under a flowing Ar atmosphere, the second homogeneous mixture obtained in Step 5 is placed in a tube heat treatment furnace and crosslinked and cured at a rate of 10℃ / min from room temperature to 140℃ for 3 hours to obtain the SiC-BNNT crosslinked product.

[0068] Step 7: Mix the SiC-BNNT crosslinking product and the ZrB2-BNNT high-temperature pyrolysis product at a volume fraction of 15%, grind thoroughly, and then compress into tablets to obtain a block solid.

[0069] Step 8: Under a flowing Ar atmosphere, the blocky solid obtained in step 7 is placed in a high-temperature tube furnace and heated from room temperature to 1400°C at a rate of 10°C / min, held for 1 hour, and then cooled to 300°C at a rate of 4°C / min, and then cooled to room temperature with the furnace to obtain ZrB2-BNNT / SiC-BNNT ceramic matrix composite material.

[0070] It was machined into a ring with an inner diameter of 3.04 mm and an outer diameter of 7 mm, placed in a coaxial cavity, and its wave absorption performance was measured as follows: Figure 3 As shown in Figure (a), the effective absorption bandwidth is 7.7 GHz when the thickness of the ZrB2-BNNT / SiC-BNNT ceramic matrix composite is 4.8 mm.

[0071] Example 2:

[0072] Step 1: Mix ZrB2 precursor with 1% boron nitride nanotubes (BNNT) and add anhydrous ethanol of the same mass as ZrB2 precursor. Place the mixture in an ultrasonic machine and sonicate for 4 hours. Then place it in a magnetic stirrer and stir at 80°C for 4 hours to remove anhydrous ethanol, and obtain the first homogeneous mixture.

[0073] Step 2: Place the first homogeneous mixture obtained in Step 1 in an oven and perform cross-linking curing at 150°C for 2 hours to obtain the first cross-linked product;

[0074] Step 3: Under a flowing Ar atmosphere, the first crosslinking product obtained in step 2 is placed in a tubular heat treatment furnace and heated from room temperature to 600°C at a rate of 5°C / min, held for 2 hours, then cooled to 300°C at a rate of 5°C / min, and then cooled to room temperature with the furnace to obtain the pretreated product.

[0075] Step 4: Under a flowing Ar atmosphere, the pretreated product obtained in Step 4 is placed in a high-temperature tube furnace and heated from room temperature to 1600℃ at a rate of 5℃ / min, held for 2 hours, and then cooled to 300℃ at a rate of 4℃ / min. The product is then cooled to room temperature with the furnace to obtain the ZrB2-BNNT ultra-high temperature ceramic matrix composite material, i.e., the ZrB2-BNNT high-temperature pyrolysis product, which is then ground into powder.

[0076] Step 5: After mixing liquid polycarbosilane (PCS) with boron nitride nanotubes (BNNT) at a mass fraction of 5%, add xylene of the same mass as the precursor, place in an ultrasonic machine and sonicate for 4 hours, then place in a magnetic stirrer and stir at 80°C for 8 hours to remove xylene and obtain a second homogeneous mixture.

[0077] Step 6: Under a flowing Ar atmosphere, the second homogeneous mixture obtained in Step 5 is placed in a tube heat treatment furnace and crosslinked and cured at a rate of 5°C / min from room temperature to 150°C for 2 hours to obtain the SiC-BNNT crosslinked product.

[0078] Step 7: Mix the SiC-BNNT crosslinking product and the ZrB2-BNNT high-temperature pyrolysis product at a volume fraction of 20%, grind thoroughly, and then compress into tablets to obtain a block solid.

[0079] Step 8: Under a flowing Ar atmosphere, the blocky solid obtained in step 7 is placed in a high-temperature tube furnace and heated from room temperature to 1600°C at a rate of 5°C / min, held for 2 hours, and then cooled to 300°C at a rate of 4°C / min, and then cooled to room temperature with the furnace to obtain ZrB2-BNNT / SiC-BNNT ceramic matrix composite material.

[0080] It was machined into a ring with an inner diameter of 3.04 mm and an outer diameter of 7 mm, placed in a coaxial cavity, and its wave absorption performance was measured as follows: Figure 3 As shown in Figure (b), the effective absorption bandwidth is 9.6 GHz when the thickness of the ZrB2-BNNT / SiC-BNNT ceramic matrix composite is 3.7 mm.

[0081] Example 3:

[0082] Step 1: Mix ZrB2 precursor with 15% boron nitride nanotubes (BNNT) and add anhydrous ethanol of the same mass as ZrB2 precursor. Place the mixture in an ultrasonic machine and sonicate for 4 hours. Then place it in a magnetic stirrer and stir at 80°C for 4 hours to remove anhydrous ethanol, and obtain the first homogeneous mixture.

[0083] Step 2: Place the first homogeneous mixture obtained in Step 1 in an oven and perform cross-linking curing at 150°C for 3 hours to obtain the first cross-linked product;

[0084] Step 3: Under a flowing Ar atmosphere, the first crosslinking product obtained in step 2 is placed in a tubular heat treatment furnace and heated from room temperature to 500°C at a rate of 5°C / min, held for 2.5 hours, then cooled to 300°C at a rate of 5°C / min, and then cooled to room temperature with the furnace to obtain the pretreated product.

[0085] Step 4: Under a flowing Ar atmosphere, the pretreated product obtained in Step 4 is placed in a high-temperature tube furnace and heated from room temperature to 1600℃ at a rate of 5℃ / min, held for 2 hours, and then cooled to 300℃ at a rate of 4℃ / min. The product is then cooled to room temperature with the furnace to obtain the ZrB2-BNNT ultra-high temperature ceramic matrix composite material, i.e., the ZrB2-BNNT high-temperature pyrolysis product, which is then ground into powder.

[0086] Step 5: After mixing liquid polycarbosilane (PCS) with boron nitride nanotubes (BNNT) at a mass fraction of 15%, add xylene of the same mass as the precursor, place in an ultrasonic machine and sonicate for 4 hours, then place in a magnetic stirrer and stir at 80°C for 8 hours to remove xylene and obtain a second homogeneous mixture.

[0087] Step 6: Under a flowing Ar atmosphere, the second homogeneous mixture obtained in step 5 is placed in a tube heat treatment furnace and crosslinked and cured at a rate of 5°C / min from room temperature to 160°C for 2 hours to obtain the SiC-BNNT crosslinked product.

[0088] Step 7: Mix the SiC-BNNT crosslinking product and the ZrB2-BNNT high-temperature pyrolysis product at a volume fraction of 25%, grind thoroughly, and then compress into tablets to obtain a block solid.

[0089] Step 8: Under a flowing Ar atmosphere, the blocky solid obtained in step 7 is placed in a high-temperature tube furnace and heated from room temperature to 1600°C at a rate of 5°C / min, held for 1-2 hours, and then cooled to 300°C at a rate of 4°C / min, and then cooled to room temperature with the furnace to obtain ZrB2-BNNT / SiC-BNNT ceramic matrix composite material.

[0090] It was machined into a ring with an inner diameter of 3.04 mm and an outer diameter of 7 mm, placed in a coaxial cavity, and its wave absorption performance was measured as follows: Figure 3 As shown in Figure (c), the effective absorption bandwidth is 7.1 GHz when the thickness of the ZrB2-BNNT / SiC-BNNT ceramic matrix composite is 2.9 mm.

[0091] Example 4:

[0092] Step 1: Mix ZrB2 precursor with 20% boron nitride nanotubes (BNNT) and add anhydrous ethanol of the same mass as ZrB2 precursor. Place the mixture in an ultrasonic machine and sonicate for 4 hours. Then place it in a magnetic stirrer and stir at 80°C for 4 hours to remove anhydrous ethanol, and obtain the first homogeneous mixture.

[0093] Step 2: Place the first homogeneous mixture obtained in Step 1 in an oven and perform cross-linking curing at 130°C for 2 hours to obtain the first cross-linked product;

[0094] Step 3: Under a flowing Ar atmosphere, the first crosslinking product obtained in step 2 is placed in a tubular heat treatment furnace and heated from room temperature to 400°C at a rate of 10°C / min, held for 2 hours, then cooled to 300°C at a rate of 5°C / min, and then cooled to room temperature with the furnace to obtain the pretreated product.

[0095] Step 4: Under a flowing Ar atmosphere, the pretreated product obtained in Step 4 is placed in a high-temperature tube furnace and heated from room temperature to 1500℃ at a rate of 10℃ / min, held for 2 hours, and then cooled to 300℃ at a rate of 4℃ / min. The product is then cooled to room temperature with the furnace to obtain the ZrB2-BNNT ultra-high temperature ceramic matrix composite material, i.e., the ZrB2-BNNT high-temperature pyrolysis product, which is then ground into powder.

[0096] Step 5: After mixing liquid polycarbosilane (PCS) with boron nitride nanotubes (BNNT) at a mass fraction of 20%, add xylene of the same mass as the precursor, place in an ultrasonic machine and sonicate for 4 hours, then place in a magnetic stirrer and stir at 80°C for 8 hours to remove xylene and obtain a second homogeneous mixture.

[0097] Step 6: Under a flowing Ar atmosphere, the second homogeneous mixture obtained in Step 5 is placed in a tube heat treatment furnace and crosslinked and cured at a rate of 10℃ / min from room temperature to 160℃ for 2 hours to obtain the SiC-BNNT crosslinked product.

[0098] Step 7: Mix the SiC-BNNT crosslinking product and the ZrB2-BNNT high-temperature pyrolysis product at a volume fraction of 30%, grind thoroughly, and then compress into tablets to obtain a block solid.

[0099] Step 8: Under a flowing Ar atmosphere, the blocky solid obtained in step 7 is placed in a high-temperature tube furnace and heated from room temperature to 1400°C at a rate of 10°C / min, held for 2 hours, and then cooled to 300°C at a rate of 4°C / min. The furnace is then cooled to room temperature to obtain the ZrB2-BNNT / SiC-BNNT ceramic matrix composite material.

[0100] It was machined into a ring with an inner diameter of 3.04 mm and an outer diameter of 7 mm, placed in a coaxial cavity, and its wave absorption performance was measured as follows: Figure 3 As shown in Figure (d), the effective absorption bandwidth is 1.4 GHz when the thickness of the ZrB2-BNNT / SiC-BNNT ceramic matrix composite is 4.4 mm.

[0101] like Figure 1 As shown, BNNTs are interspersed within ZrB2 and SiC particles, with the ZrB2 and SiC particles arranged alternately. This microstructure provides numerous heterojunctions to dissipate electromagnetic waves. Due to the difference in conductivity, charge redistribution occurs at the heterojunctions, forming numerous dipoles and strongly dissipating electromagnetic waves.

[0102] like Figure 2 As shown in Figures (a) and (b), the ZrB2 and SiC phases are interspersed, as follows: Figure 2 As shown in Figure (c), ZrB2 and SiC have a heterogeneous interface.

[0103] like Figure 3 As shown in Figures (a), (b), (c), and (d), the effective absorption bandwidth is 1.4–9.6 GHz, with the optimal effective absorption bandwidth being 9.6 GHz (8.4–18 GHz), covering almost the entire X-band and Ku-band.

[0104] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A high-temperature ceramic composite material that combines broadband microwave absorption and oxidation resistance, characterized in that, The ultra-high temperature ceramic composite material that combines broadband wave absorption and oxidation resistance is a ZrB2-BNNT / SiC-BNNT ceramic matrix composite material. The ZrB2-BNNT / SiC-BNNT ceramic matrix composite material is prepared from 70-95% ZrB2-BNNT high-temperature pyrolysis products and 5-30% SiC-BNNT crosslinking products by volume percentage. The method for preparing the ultra-high temperature ceramic composite material with both broadband microwave absorption and oxidation resistance involves mixing the high-temperature pyrolysis product of ZrB2 precursor with 0.5-20% by mass of boron nitride nanotubes with the crosslinking product of SiC precursor with 3-20% by mass of boron nitride nanotubes, grinding and cold pressing, and obtaining ZrB2-BNNT / SiC-BNNT ceramic matrix composite material through high-temperature pyrolysis heat treatment. Among them, boron nitride nanotubes are interspersed in ZrB2 particles in ZrB2-BNNT high-temperature pyrolysis products and SiC particles in SiC-BNNT crosslinking products, with ZrB2 particles and SiC particles arranged alternately. The ZrB2-BNNT / SiC-BNNT ceramic matrix composite material contains heterogeneous interfaces, including BNNT / ZrB2 heterogeneous interfaces, BNNT / SiC heterogeneous interfaces, and ZrB2 / SiC heterogeneous interfaces.

2. A method for preparing an ultra-high temperature ceramic composite material with both broadband microwave absorption and oxidation resistance according to claim 1, characterized in that, Includes the following steps: ZrB2 precursor and first group of boron nitride nanotubes were mixed and then anhydrous ethanol was added. The mixture was ultrasonically treated and stirred to remove the anhydrous ethanol, resulting in a first homogeneous mixture. The first homogeneous mixture was then subjected to a first cross-linking curing process to obtain a first cross-linked product. The first crosslinking product is pretreated to obtain a pretreated product; The pretreated product is subjected to high-temperature pyrolysis to obtain ZrB2-BNNT high-temperature pyrolysis product; the mass fraction of the first group of boron nitride nanotubes is 0.5~20%; the mass ratio of anhydrous ethanol to ZrB2 precursor is 1:1; after mixing the second group of boron nitride nanotubes with liquid polycarbosilane, xylene is added, and the mixture is subjected to ultrasonic treatment and then stirred to remove xylene to obtain a second homogeneous mixture; the second homogeneous mixture is subjected to a second cross-linking and curing to obtain SiC-BNNT cross-linked product; The second group of boron nitride nanotubes has a mass fraction of 3-20%; the mass ratio of xylene to liquid polycarbosilane is 1:

1. The high-temperature pyrolysis products of ZrB2-BNNT and the crosslinking products of SiC-BNNT were mixed, ground, and then pressed into tablets to obtain a block solid. The block solid was subjected to high-temperature pyrolysis heat treatment to obtain a ZrB2-BNNT / SiC-BNNT ceramic matrix composite material.

3. The method for preparing the ultra-high temperature ceramic composite material with both broadband microwave absorption and oxidation resistance according to claim 2, characterized in that, The first cross-linking curing temperature is 130~150℃, and the first cross-linking curing time is 2~3h.

4. The method for preparing the ultra-high temperature ceramic composite material with both broadband microwave absorption and oxidation resistance according to claim 2, characterized in that, The preprocessing process is as follows: The first crosslinking product is heated from room temperature to 400-600°C at a rate of 5-10°C / min and held at that temperature for 2-3 hours. Then, it is cooled to 300°C at a rate of 5°C / min and then cooled to room temperature in the furnace to obtain the pretreated product.

5. The method for preparing the ultra-high temperature ceramic composite material with both broadband microwave absorption and oxidation resistance according to claim 2, characterized in that, The high-temperature pyrolysis process is as follows: The pretreated product was heated from room temperature to 1500-1600℃ at a rate of 5-10℃ / min and held for 1-2 hours. Then, it was cooled to 300℃ at a rate of 4℃ / min and then cooled to room temperature in the furnace to obtain the ZrB2-BNNT high-temperature pyrolysis product.

6. The method for preparing the ultra-high temperature ceramic composite material with both broadband microwave absorption and oxidation resistance according to claim 2, characterized in that, The second cross-linking and curing process is as follows: The second homogeneous mixture was crosslinked and cured at a rate of 5-10℃ / min from room temperature to 140-160℃ for 2-3 hours to obtain the SiC-BNNT crosslinked product.

7. The method for preparing the ultra-high temperature ceramic composite material with both broadband microwave absorption and oxidation resistance according to claim 2, characterized in that, The high-temperature pyrolysis heat treatment process is as follows: The bulk solid was heated from room temperature to 1400-1600℃ at a rate of 5-10℃ / min and held for 1-2 hours. Then it was cooled to 300℃ at a rate of 4℃ / min and then cooled to room temperature in the furnace to obtain ZrB2-BNNT / SiC-BNNT ceramic matrix composite material.

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