A boron nitride nanotube dielectric network enhanced zrB2-based ultrahigh temperature ceramic wave-absorbing material and a preparation method thereof

Abstract

The application discloses a boron nitride nanotube dielectric network enhanced ZrB2-based ultrahigh-temperature ceramic wave-absorbing material and a preparation method thereof, and belongs to the technical field of wave-absorbing materials. The ultrahigh-temperature ceramic wave-absorbing material is prepared from a ZrB2 precursor and boron nitride nanotubes; the pyrolysis product of the ZrB2 precursor is spherical ZrB2 particles, and the spherical ZrB2 particles form a matrix; the boron nitride nanotubes are distributed in a network in the matrix. Part of the boron nitride nanotubes are inserted into the ZrB2 particles, and a hetero-interface exists between the boron nitride nanotubes and the matrix. The boron nitride nanotubes introduced in the application are distributed in a network in the matrix, effectively prevent the movement and transition of electrons, reduce the conductivity of the composite material, optimize the dielectric constant and impedance matching of the PDC-ZrB2, improve the wave-absorbing performance of the PDC-ZrB2, widen the selection of wave-absorbing materials in the high-temperature field, and solve the technical problem of impedance mismatching when the polymer converted ZrB2 ceramic is applied as a wave-absorbing material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wave-absorbing materials, and particularly relates to a boron nitride nanotube dielectric network enhanced ZrB2-based ultrahigh-temperature ceramic wave-absorbing material and a preparation method thereof. BACKGROUND

[0002] Future aircrafts develop towards higher speed and higher service temperature, which puts forward severe requirements and challenges for stealth materials resistant to extreme thermal environment. Ceramics and ceramic composites are ideal choices for wave-absorbing materials suitable for high-temperature environment due to their high thermal stability. In view of the research progress of high-temperature wave-absorbing ceramic materials, the research mainly focuses on composites with oxide ceramics and silicon-based compound ceramics as matrices, but the service temperature thereof is limited by the service temperature of oxide ceramics or silicon-based compound ceramics.

[0003] ZrB2 as a representative of ultrahigh-temperature ceramics (UHTC) has excellent thermal stability, oxidation resistance and ablation resistance, and the service temperature thereof is higher than that of oxide ceramics and silicon-based ceramics, so it is an ideal choice for wave-absorbing materials suitable for high-temperature environment. Since ZrB2 itself has high electrical conductivity, it is often used as a high-conductivity phase wave-absorbing agent to improve the wave-absorbing performance of the material. For example, the prior art prepared a ZrB2 / Al2O3 composite material, ZrB2 particles were added as wave-absorbing agents into the matrix Al2O3, and the ceramic with a ZrB2 content of 15wt.% had the best wave-absorbing performance, and achieved effective absorption in the frequency range of 10.3-12GHz when the thickness was 1.4mm, and the density of the composite material was 4.12g / cm 3 .

[0004] However, there are few studies on ZrB2 directly as a wave-absorbing material matrix, because the high electrical conductivity of ZrB2 will cause strong reflection of electromagnetic waves due to impedance mismatch in free space, resulting in that the material does not have wave-absorbing capacity, so how to make ZrB2 as a wave-absorbing material matrix have wave-absorbing capacity has a pioneering theoretical and practical significance for the research and application of extreme environment high-temperature stealth materials. SUMMARY

[0005] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a boron nitride nanotube dielectric network enhanced ZrB2-based ultrahigh-temperature ceramic wave-absorbing material and a preparation method thereof, so as to solve the technical problem of impedance mismatch when the polymer converted ZrB2 (PDC-ZrB2) ceramic is applied as a wave-absorbing material.

[0006] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] This invention provides a ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced by a boron nitride nanotube dielectric network, wherein the ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced by a boron nitride nanotube dielectric network is prepared from a ZrB2 precursor and boron nitride nanotubes.

[0008] The pyrolysis products of the ZrB2 precursor are spherical ZrB2 particles, and the spherical ZrB2 particles constitute the matrix.

[0009] The boron nitride nanotubes are distributed in a network within the matrix.

[0010] In the specific implementation process, some of the boron nitride nanotubes are interspersed within the ZrB2 particles.

[0011] In the specific implementation process, there is a heterogeneous interface between the boron nitride nanotubes and the matrix.

[0012] In specific implementation, the bulk density of the ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced by the boron nitride nanotube dielectric network is 1.03–1.26 g / cm³. 3 The lowest reflection loss is -49.1 to -56.7 dB, and the effective absorption bandwidth is 3.6 to 6.2 GHz.

[0013] This invention also provides a method for preparing a ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced with a boron nitride nanotube dielectric network, comprising the following steps:

[0014] ZrB2 precursor was mixed with boron nitride nanotubes and then anhydrous ethanol was added. The mixture was ultrasonically treated and then stirred to remove the anhydrous ethanol, resulting in a homogeneous mixture.

[0015] The homogeneous mixture is cross-linked and cured to obtain a cross-linked product. The cross-linked product is then ground to obtain a powder, which is then pressed into a block solid.

[0016] Under a protective atmosphere, a bulk solid is pretreated to obtain a pretreated product, which is then subjected to high-temperature pyrolysis heat treatment to obtain a ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced with a boron nitride nanotube dielectric network.

[0017] In the specific implementation process, the anhydrous ethanol and the ZrB2 precursor are of equal mass.

[0018] In the specific implementation process, the mass fraction of the boron nitride nanotubes is 0.5% to 20%.

[0019] In the specific implementation process, the cross-linking curing is carried out in an oven at a temperature of 130-150°C for 2-3 hours.

[0020] In the specific implementation process, the protective atmosphere is an Ar atmosphere;

[0021] The pretreatment is carried out in a tubular heat treatment furnace;

[0022] The preprocessing process is as follows:

[0023] The solid block 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, and then cooled to 300°C at a rate of 5°C / min, and then cooled to room temperature in the tubular heat treatment furnace.

[0024] In the specific implementation process, the high-temperature pyrolysis heat treatment is carried out in a high-temperature tubular furnace;

[0025] The high-temperature pyrolysis heat treatment process is as follows:

[0026] The pretreated product was placed in a high-temperature tube furnace and heated from room temperature to 1500–1600°C at a rate of 5–10°C / min, held for 1–2 hours, and then cooled to 300°C at a rate of 4°C / min, before being cooled back to room temperature in the high-temperature tube furnace.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] This invention provides a ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced with a boron nitride nanotube dielectric network. The boron nitride nanotubes (BNNTs) introduced in this invention are distributed in a network within the ZrB2 matrix, effectively preventing electron movement and transitions, reducing the conductivity of the composite material, optimizing the dielectric constant and impedance matching of PDC-ZrB2, improving its microwave absorption performance, and broadening the selection of microwave absorbing materials in high-temperature applications. This composite material possesses advantages such as high temperature resistance, low density, excellent microwave absorption performance, and simple preparation process, making it an ideal candidate material for high-temperature microwave absorbing materials.

[0029] This invention provides a method for preparing a ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced with a boron nitride nanotube dielectric network. The crosslinked product, obtained by uniformly mixing a ZrB2 precursor and boron nitride nanotubes (BNNTs), is thoroughly ground and cold-pressed. The resulting composite material (ZrB2-BNNT) is obtained through low-temperature crosslinking and high-temperature pyrolysis heat treatment, where the BNNT dielectric network is reinforced. The boron nitride nanotube (BNNT) dielectric network is constructed within the ZrB2 matrix prepared by the polymer conversion method. Boron nitride nanotubes (BNNTs) possess 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. BNNTs belong to the boron nanotube (BN) material family, and the dielectric constant of BN materials does not change significantly with temperature; therefore, BNNTs also possess the ability to adjust the dielectric constant at high temperatures. To lower the ZrB2 transition temperature, this invention employs a polymer-converted ceramic method to prepare ZrB2-based ultra-high temperature ceramics. This invention introduces BNNT to improve the impedance mismatch in the current application of polymer-converted ZrB2 (PDC-ZrB2) ceramics as microwave absorbing materials, optimizes the dielectric constant of PDC-ZrB2, and improves its microwave absorption performance. Attached Figure Description

[0030] Figure 1 The XRD pattern of the ZrB2-BNNT ultra-high temperature ceramic matrix composite material prepared in this invention;

[0031] Figure 2 Figure (a) is a scanning electron microscope image of the ZrB2-BNNT ultra-high temperature ceramic matrix composite material with a boron nitride nanotube mass fraction of 1% prepared in this invention. Figure 2 Figure (b) is a detailed scanning electron microscope image of some boron nitride nanotubes interspersed in ZrB2 particles in the ZrB2-BNNT ultra-high temperature ceramic matrix composite material prepared in this invention;

[0032] Figure 3 Figure (a) shows the transmission electron microscope morphology of the ZrB2-BNNT ultra-high temperature ceramic matrix composite material with a boron nitride nanotube mass fraction of 1% prepared in this invention. Figure 3 Image (b) is a high-resolution image of the block region in Image (a);

[0033] Figure 4 Figures (a), (b), and (c) are RL two-dimensional diagrams of the ZrB2-BNNT ultra-high temperature ceramic matrix composite materials with boron nitride nanotubes of 0.5%, 1%, and 3% by mass, respectively, prepared in this invention. 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 a ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced with a boron nitride nanotube dielectric network. The ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced with a boron nitride nanotube dielectric network is prepared from a ZrB2 precursor and boron nitride nanotubes (BNNTs). The pyrolysis products of the ZrB2 precursor are spherical ZrB2 particles, which constitute the matrix. The boron nitride nanotubes (BNNTs) are distributed in a network in the matrix.

[0040] Among them, such as Figure 1 The XRD pattern of the ZrB2-BNNT ultra-high temperature ceramic matrix composite material prepared in this invention shows that the ZrB2-BNNT ultra-high temperature ceramic matrix composite material contains ZrB2 phase and boron nitride nanotubes (BNNT) as additives, and has no other impurity phases.

[0041] In the specific implementation process, the pyrolysis products of the ZrB2 precursor are spherical ZrB2 particles, and some boron nitride nanotubes are interspersed in the spherical ZrB2 particles; there is a heterogeneous interface between the boron nitride nanotubes (BNNT) and the matrix.

[0042] from Figure 2 Figures (a) and (b) show a matrix composed of spherical ZrB2 particles and a network of BNNTs. Some BNNTs are interspersed within the ZrB2 particles. The boron nitride nanotubes (BNNTs) introduced in this invention are distributed in a network within the matrix, effectively preventing the movement and transition of electrons, reducing the conductivity of the composite material, improving the impedance mismatch in the current application of PDC-ZrB2 ceramics as microwave absorbing materials, optimizing the dielectric constant of PDC-ZrB2, and improving its microwave absorption performance.

[0043] from Figure 3 Figures (a) and (b) show that boron nitride nanotubes (BNNTs) are distributed in a cross pattern, and some BNNTs are interspersed in spherical ZrB2 particles, indicating that there is a heterogeneous interface between the boron nitride nanotubes (BNNTs) and the matrix.

[0044] Another aspect of the present invention provides a method for preparing a ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced with a boron nitride nanotube dielectric network. Boron nitride nanotubes (BNNTs) are uniformly dispersed in a ZrB2 precursor, and a BNNT-reinforced ZrB2-based ultra-high temperature ceramic composite material is prepared by low-temperature crosslinking and high-temperature pyrolysis heat treatment.

[0045] A method for preparing a ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced with a boron nitride nanotube dielectric network includes the following steps:

[0046] The ZrB2 precursor was mixed with boron nitride nanotubes with a mass fraction of 0.5-20%, and then anhydrous ethanol of equal mass to the ZrB2 precursor was added. The mixture was then subjected to ultrasonic treatment and stirred to remove the anhydrous ethanol, resulting in a homogeneous mixture.

[0047] The homogeneous mixture is cross-linked and cured in an oven at 130-150°C for 2-3 hours to obtain a cross-linked product. The cross-linked product is then ground to obtain a powder, which is then pressed into a block solid.

[0048] Under a flowing Ar protective atmosphere, a bulk solid is pretreated to obtain a pretreated product. The pretreated product is then subjected to high-temperature pyrolysis heat treatment to obtain a ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced with a boron nitride nanotube dielectric network. In this invention, the crosslinked product of a uniformly mixed ZrB2 precursor and boron nitride nanotubes (BNNT) is thoroughly ground and cold-pressed, then pyrolyzed at high temperature to obtain a ZrB2-BNNT composite material.

[0049] In the specific implementation process, the pretreatment is carried out in a tubular heat treatment furnace. The pretreatment process is as follows: the blocky solid is placed in the tubular heat treatment furnace and heated from room temperature to 400-600℃ at a rate of 5-10℃ / min, held for 2-3 hours, and then cooled to 300℃ at a rate of 5℃ / min, and then cooled to room temperature with the tubular heat treatment furnace.

[0050] In the specific implementation process, the high-temperature pyrolysis heat treatment is carried out in a high-temperature tube furnace. The process of high-temperature pyrolysis heat treatment is as follows: the pretreated product 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, and then cooled to room temperature with the high-temperature tube furnace.

[0051] Based on the above parameters, the specific preparation process is as follows:

[0052] 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.

[0053] Step 2: Place the homogeneous mixture obtained in Step 1 in an oven and cross-link it at 130-150℃ for 2-3 hours. Then, grind the cross-linked solid (cross-linked product) thoroughly in a mortar to obtain powder.

[0054] Step 3: Press the ground powder into solid blocks using a dry press;

[0055] Step 4: Under a flowing Ar atmosphere, the block solid pressed in Step 3 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.

[0056] Step 5: 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 furnace is then cooled to room temperature to obtain ZrB2-BNNT ultra-high temperature ceramic matrix composite material.

[0057] The BNNT-enhanced PDC-ZrB2 obtained by this invention can effectively improve the impedance mismatch of PDC-ZrB2 ceramics when used as microwave absorbing materials.

[0058] 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.

[0059] 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.

[0060] Example 1

[0061] 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.

[0062] Step 2: Place the homogeneous mixture obtained in Step 1 in an oven and cross-link it at 130°C for 3 hours. Then, grind the cross-linked solid thoroughly in a mortar to obtain powder.

[0063] Step 3: Press the ground powder into solid blocks using a dry press;

[0064] Step 4: Under a flowing Ar atmosphere, the block solid pressed in Step 3 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 5: 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.

[0066] Example 2

[0067] 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.

[0068] Step 2: Place the homogeneous mixture obtained in Step 1 in an oven and cross-link it at 140°C for 2.5 hours. Then, grind the cross-linked solid thoroughly in a mortar to obtain powder.

[0069] Step 3: Press the ground powder into solid blocks using a dry press;

[0070] Step 4: Under a flowing Ar atmosphere, the block solid pressed in Step 3 is placed in a tubular heat treatment furnace and heated from room temperature to 500°C at a rate of 7°C / min, held at that temperature 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.

[0071] Step 5: 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 7℃ / 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.

[0072] Example 3

[0073] Step 1: Mix ZrB2 precursor with 3% 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.

[0074] Step 2: Place the homogeneous mixture obtained in Step 1 in an oven and cross-link it at 150°C for 2 hours. Then, grind the cross-linked solid thoroughly in a mortar to obtain powder.

[0075] Step 3: Press the ground powder into solid blocks using a dry press;

[0076] Step 4: Under a flowing Ar atmosphere, the block solid pressed in Step 3 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.

[0077] Step 5: 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 5℃ / 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.

[0078] Furthermore, Examples 1, 2, and 3 are described in sequence as follows: Figure 4As shown in Figures (a), (b), and (c), the ZrB2-BNNT ultra-high temperature ceramic absorbing material (ZrB2-based ultra-high temperature ceramic absorbing material reinforced with boron nitride nanotube dielectric network) prepared in this invention has a bulk density of 1.03–1.26 g / cm³. 3 The lowest reflection loss is -49.1 to -56.7 dB, and the effective absorption bandwidth is 3.6 to 6.2 GHz.

[0079] Example 4

[0080] Step 1: Mix ZrB2 precursor with 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.

[0081] Step 2: Place the homogeneous mixture obtained in Step 1 in an oven and cross-link it at 130°C for 3 hours. Then, grind the cross-linked solid thoroughly in a mortar to obtain powder.

[0082] Step 3: Press the ground powder into solid blocks using a dry press;

[0083] Step 4: Under a flowing Ar atmosphere, the block solid pressed in Step 3 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.

[0084] Step 5: 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.

[0085] Example 5

[0086] Step 1: Mix ZrB2 precursor with 10% 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.

[0087] Step 2: Place the homogeneous mixture obtained in Step 1 in an oven and cross-link it at 140°C for 2.5 hours. Then, grind the cross-linked solid thoroughly in a mortar to obtain powder.

[0088] Step 3: Press the ground powder into solid blocks using a dry press;

[0089] Step 4: Under a flowing Ar atmosphere, the block solid pressed in Step 3 is placed in a tubular heat treatment furnace and heated from room temperature to 500°C at a rate of 7°C / min, held at that temperature 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.

[0090] Step 5: 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 7℃ / 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.

[0091] Example 6

[0092] 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.

[0093] Step 2: Place the homogeneous mixture obtained in Step 1 in an oven and cross-link it at 150°C for 2 hours. Then, grind the cross-linked solid thoroughly in a mortar to obtain powder.

[0094] Step 3: Press the ground powder into solid blocks using a dry press;

[0095] Step 4: Under a flowing Ar atmosphere, the block solid pressed in Step 3 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.

[0096] Step 5: 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 5℃ / 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.

[0097] Example 7

[0098] 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.

[0099] Step 2: Place the homogeneous mixture obtained in Step 1 in an oven and cross-link it at 150°C for 2 hours. Then, grind the cross-linked solid thoroughly in a mortar to obtain powder.

[0100] Step 3: Press the ground powder into solid blocks using a dry press;

[0101] Step 4: Under a flowing Ar atmosphere, the block solid pressed in Step 3 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.

[0102] Step 5: 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 5℃ / 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.

[0103] This invention proposes constructing a boron nitride nanotube (BNNT) dielectric network within a ZrB2 matrix prepared by polymer conversion. This invention provides an ultra-high temperature ceramic-based microwave absorbing material and its preparation method, broadening the selection of microwave absorbing materials in high-temperature applications. The resulting BNNT-reinforced PDC-ZrB2 can effectively improve the impedance mismatch currently encountered when using PDC-ZrB2 ceramics as microwave absorbing materials.

[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 ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced with a boron nitride nanotube dielectric network, characterized in that, The ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced by the boron nitride nanotube dielectric network is prepared from ZrB2 precursor and boron nitride nanotubes. The pyrolysis products of the ZrB2 precursor are spherical ZrB2 particles, and the spherical ZrB2 particles constitute the matrix. The boron nitride nanotubes are distributed in a network within the matrix; some of the boron nitride nanotubes are intercalated within ZrB2 particles; and there is a heterogeneous interface between the boron nitride nanotubes and the matrix. The preparation method of the ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced by boron nitride nanotube dielectric network includes the following steps: ZrB2 precursor was mixed with boron nitride nanotubes and then anhydrous ethanol was added. The mixture was ultrasonically treated and then stirred to remove the anhydrous ethanol, resulting in a homogeneous mixture. The homogeneous mixture is cross-linked and cured to obtain a cross-linked product. The cross-linked product is then ground to obtain a powder, which is then pressed into a block solid. Under a protective atmosphere, a bulk solid is pretreated to obtain a pretreated product, which is then subjected to high-temperature pyrolysis heat treatment to obtain a ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced with boron nitride nanotube dielectric network. The protective atmosphere is an Ar atmosphere; The pretreatment is carried out in a tubular heat treatment furnace; The preprocessing process is as follows: The solid block 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, and then cooled to 300°C at a rate of 5°C / min, and then cooled to room temperature with the tubular heat treatment furnace. The high-temperature pyrolysis heat treatment is carried out in a high-temperature tubular furnace; The high-temperature pyrolysis heat treatment process is as follows: The pretreated product was 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, and then cooled to room temperature in the high-temperature tube furnace.

2. The ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced by boron nitride nanotube dielectric network according to claim 1, characterized in that, The bulk density of the ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced by the boron nitride nanotube dielectric network is 1.03~1.26 g / cm³. 3 The lowest reflection loss is -49.1~-56.7dB, and the effective absorption bandwidth is 3.6~6.2GHz.

3. A method for preparing a ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced by a boron nitride nanotube dielectric network according to any one of claims 1 to 2, characterized in that, Includes the following steps: ZrB2 precursor was mixed with boron nitride nanotubes and then anhydrous ethanol was added. The mixture was ultrasonically treated and then stirred to remove the anhydrous ethanol, resulting in a homogeneous mixture. The homogeneous mixture is cross-linked and cured to obtain a cross-linked product. The cross-linked product is then ground to obtain a powder, which is then pressed into a block solid. Under a protective atmosphere, a bulk solid is pretreated to obtain a pretreated product, which is then subjected to high-temperature pyrolysis heat treatment to obtain a ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced with boron nitride nanotube dielectric network. The protective atmosphere is an Ar atmosphere; The pretreatment is carried out in a tubular heat treatment furnace; The preprocessing process is as follows: The solid block 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, and then cooled to 300°C at a rate of 5°C / min, and then cooled to room temperature with the tubular heat treatment furnace. The high-temperature pyrolysis heat treatment is carried out in a high-temperature tubular furnace; The high-temperature pyrolysis heat treatment process is as follows: The pretreated product was 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, and then cooled to room temperature in the high-temperature tube furnace.

4. The method for preparing the ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced by boron nitride nanotube dielectric network according to claim 3, characterized in that, The anhydrous ethanol and the ZrB2 precursor have the same mass.

5. The method for preparing the ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced by boron nitride nanotube dielectric network according to claim 3, characterized in that, The boron nitride nanotubes have a mass fraction of 0.5-20%.

6. The method for preparing the ZrB2-based ultra-high temperature ceramic microwave absorbing material reinforced by boron nitride nanotube dielectric network according to claim 3, characterized in that, The cross-linking and curing are carried out in an oven at a temperature of 130-150°C for 2-3 hours.

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