High-temperature-resistant antioxidant BN f Method for preparing wave-transparent composite material of / SiBN and product thereof

Abstract

The application discloses a high-temperature-resistant and oxidation-resistant BN f / SiBN wave-transparent composite material preparation method and product thereof, and belongs to the technical field of high-temperature wave-transparent composite material preparation. The application adopts the impregnation-pyrolysis process to obtain a BN f / SiBN wave-transparent composite material by taking a BN prefabricated body as a reinforcing body after degassing treatment and taking polysilicon borazine as a precursor, and the application has the advantages of safety, low preparation temperature, small damage to fibers and unique near-net forming advantage. f / SiBN prefabricated body is repeatedly subjected to the impregnation-pyrolysis process, and then is placed into a pyrolysis furnace, vacuumized, dried and obtained. f The application discloses a high-temperature-resistant and oxidation-resistant BN / SiBN wave-transparent composite material.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature microwave-transparent composite material preparation technology, and particularly relates to a high-temperature resistant and antioxidant BN. f Preparation method and products of / SiBN microwave transparent composite materials. Background Technology

[0002] With the advancement of aerospace and electronic technologies, increasingly higher demands are being placed on the performance of wave-transparent materials. High-temperature wave-transparent materials are multifunctional dielectric materials used to protect the communication, telemetry, guidance, and detonation systems of spacecraft under harsh environmental conditions. They are widely used in the antenna electrical systems of launch vehicles, spacecraft, missiles, and recoverable satellites. Currently, there is no material, domestically or internationally, that possesses ideal comprehensive properties including heat resistance, wave transmission, and oxidation resistance. Therefore, the lagging development of high-temperature wave-transparent composite material preparation technology has become a bottleneck in the development of next-generation spacecraft technology.

[0003] Boron nitride (BN) does not have a fixed melting point and is a high-temperature resistant insulating material. SiBN ceramics combine the advantages of Si3N4 ceramics and BN ceramics, exhibiting excellent high-temperature resistance, mechanical properties, and dielectric properties. This meets the multifunctional requirements of aerospace applications for high-temperature resistance, load-bearing capacity, and wave transmission, making it a promising candidate for applications in high-tech fields such as aerospace. Therefore, nitride fiber-reinforced nitride-based wave-transparent composite materials prepared from the above materials inherit excellent dielectric properties and high-temperature ablation resistance, as well as good high-temperature mechanical properties and thermal shock resistance. They are currently a key research focus both domestically and internationally, representing the development direction of a new generation of high-temperature wave-transparent materials.

[0004] Existing related research, such as Chen Zhaofeng et al. [Application No. CN02114501.6]'s method for preparing a fiber-reinforced silica-based composite material for microwave transmission, uses chemical vapor infiltration to treat oxide-woven fibers and organosilicon alkoxides as precursors to prepare the fiber-reinforced silica-based composite material for microwave transmission. However, the prepared composite material contains some organic matter, and the silica composite material crystallizes at high temperatures, leading to a sharp decrease in mechanical properties, reducing the composite material's use at high temperatures and limiting its application in harsh environments.

[0005] Patent CN112898038A discloses a method for preparing silicon nitride-based fiber ceramic microwave-transparent materials. The method involves impregnating and sintering Si3N4 fibers, then weaving them, mixing acrylamide and silicon nitride powder to form a gel, uniformly coating the prepared gel onto a silicon nitride preform, sintering, and removing the gel to obtain the silicon nitride-based fiber ceramic microwave-transparent material. Compared to vacuum slurry impregnation, the coated gel cannot effectively penetrate into the interior of the woven body due to the surface tension of the micropores, which has a significant impact on the density and mechanical properties of the material. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a high-temperature resistant and antioxidant BN f Preparation method and products of / SiBN microwave transparent composite materials.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A high-temperature resistant and antioxidant BN f The preparation method of / SiBN microwave-transparent composite material includes the following steps:

[0009] After debinding the BN preform, it was used as a reinforcement. Using polysiloxane as a precursor, an impregnation-pyrolysis process was employed to obtain BN. f / SiBN preform; the BN f The SiBN preform undergoes a repeated impregnation-pyrolysis process, followed by placement in a pyrolysis furnace, vacuuming, and drying to obtain high-temperature resistant and oxidation-resistant BN. f / SiBN wave-transparent composite material.

[0010] Furthermore, the debinding process specifically refers to: holding the product at 400-1000℃ for 0.5-10 hours in air or an inert gas atmosphere, and then allowing it to cool naturally to room temperature with the furnace.

[0011] Furthermore, the impregnation-pyrolysis process specifically includes the following steps:

[0012] The BN preform is placed in an impregnation tank, which is then evacuated to a vacuum level of -0.05 to -0.50 MPa. The precursor polysiloxane is then placed inside for impregnation to obtain BN. f / SiBN preform;

[0013] The obtained BN f The SiBN preform is transferred to an autoclave, and high-purity nitrogen is introduced into the autoclave until the pressure reaches 2-15 MPa. The inlet valve is then closed, and the autoclave is heated according to the curing temperature regime.

[0014] BN heat treatment f The SiBN preform is placed in a pyrolysis furnace and kept under a vacuum of -0.01 to -0.20 MPa for 20-30 minutes. Then, high-purity nitrogen is introduced at a flow rate of 200-5000 mL / min. When the absolute pressure inside the furnace reaches 100 kPa, the gas valve is opened to allow for heating and pyrolysis. The preform is then allowed to cool down naturally with the furnace.

[0015] Furthermore, the curing temperature regime is as follows: the room temperature is raised to 150-200℃, the heating time is 0.5-2h, the temperature is maintained for 2-20h, and then the temperature is lowered to room temperature.

[0016] Furthermore, the impregnation-pyrolysis process is repeated 2-10 times. The impregnation time is 3-10 hours.

[0017] Furthermore, during the pyrolysis process, the furnace temperature is raised from room temperature to 600-1000℃ in 1-3 hours, and then held at 600-1000℃ for 1-6 hours.

[0018] The principle of this invention is as follows: the SiBN matrix provides anti-oxidation and high-temperature protection for BN fibers, and also serves as a good transition layer between the fibers and the matrix. This is because, at high temperatures, the SiBN matrix partially liquefies B2O3 into a fluid state. The fluid B2O3 fills the voids on the material surface, thereby preventing oxygen from entering and further oxidizing the material. This results in a composite material with excellent high-temperature resistance, anti-oxidation, and oxidation resistance.

[0019] The present invention also provides a high-temperature resistant and antioxidant BN prepared by the above preparation method. f / SiBN wave-transparent composite material.

[0020] Compared with the prior art, the present invention has the following advantages and technical effects:

[0021] This invention uses BN fibers as reinforcement and introduces SiBN through a precursor impregnation-pyrolysis process, using it as an interface phase. It fully utilizes the excellent mechanical properties, thermal stability, and thermal shock resistance of both BN and Si3N4 nitride ceramics, resulting in a superior BN... f / SiBN wave-transparent composite materials possess stable mechanical properties.

[0022] The method provided by this invention is safe, uses a low preparation temperature, causes minimal damage to the fibers, and offers unique near-net-shape forming advantages. The organic precursor impregnation-curing-pyrolysis process involves impregnating the fiber braid with a liquid organic precursor, followed by low-temperature in-situ curing and then high-temperature in-situ pyrolysis in an atmospheric environment to form a SiBN ceramic matrix. Compared to traditional hot-pressing sintering processes, this method protects the structural integrity of the fiber braid and allows for the weaving of specific structures according to requirements. The in-situ impregnation-curing-pyrolysis process thus offers unique near-net-shape forming advantages. Attached Figure Description

[0023] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0024] Figure 1 The high-temperature resistant and antioxidant BN prepared in Example 1 of this invention f Image of the appearance of SiBN wave-transparent composite material;

[0025] Figure 2 The high-temperature resistant and antioxidant BN prepared in Example 1 of this invention f Microstructure of SiBN wave-transparent composite material observed under SEM; (a) BN f (a) Cross-sectional scan image of SiBN composite material; (b) Enlarged local image of cross-sectional scan; (c) Scan image of composite material after high-temperature oxidation; (d) Enlarged local image of composite material after high-temperature oxidation. Detailed Implementation

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0028] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0029] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0030] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0031] Unless otherwise specified, "room temperature" in this invention refers to 20-30℃.

[0032] All raw materials used in this invention were purchased from the market.

[0033] This invention provides a high-temperature resistant and antioxidant BNf The preparation method of / SiBN microwave-transparent composite material includes the following steps:

[0034] 1) BN fibers are woven into a preform, then desizing is performed on it. Next, using polysiloxane borazane (PBSZ) as a precursor, the BN preform undergoes a precursor impregnation-pyrolysis (PIP) process to introduce a SiBN matrix, thus obtaining BN. f / SiBN preform;

[0035] 2) Take the BN obtained in step 1). f The SiBN preform undergoes repeated impregnation-pyrolysis processes, then is placed in a pyrolysis furnace, vacuumed, and pyrolyzed to obtain high-temperature resistant and oxidation-resistant BN. f / SiBN wave-transparent composite material.

[0036] In step 1) of some preferred embodiments of the present invention, the conditions for the glue removal process are as follows: the glue removal temperature is 400-1000℃ (preferably 600℃), the atmosphere is air or an inert gas, preferably an air atmosphere, the temperature is maintained for 0.5-10h (preferably 1-2h, such as 1h or 2h), and then the material is naturally cooled to room temperature in the furnace. The method of weaving BN fibers into a preform is as follows: continuous BN fibers are used to make a 2.5D fiber braid.

[0037] The impregnation-pyrolysis process specifically includes the following steps:

[0038] ① Impregnation process: Place the debonded BN preform into an impregnation tank, evacuate the tank to a vacuum level of -0.05 to -0.50 MPa, preferably -0.10 to -0.20 MPa, such as -0.10 MPa or -0.20 MPa. Add the precursor into the impregnation tank. After complete impregnation, the resulting BN... f The SiBN preform is taken out and weighed; during the impregnation process, it is sufficient to ensure complete immersion. The present invention further limits the mass ratio of the reinforcement to the precursor to 1:(1-10), preferably 1:5.

[0039] ② Curing process: The BN obtained in step ① f The SiBN preform is transferred to an autoclave. The autoclave inlet valve is opened, and high-purity nitrogen is introduced until the pressure reaches 2-15 MPa, preferably 5-10 MPa. Then, the inlet valve is closed, and the preform is heated according to the curing temperature regime. The heating rate range is: room temperature to 150-200℃ (preferably 170℃), heating time is 0.5-2 hours (preferably 1.5 hours), holding at this temperature for 2-20 hours (preferably 10 hours), and then allowed to cool naturally in the furnace. f / SiBN preform removed;

[0040] ③ Pyrolysis process: The BN obtained in step ② fThe SiBN preform is placed in a pyrolysis furnace and kept under a vacuum of -0.01 to -0.20 MPa (preferably -0.10 to -0.20 MPa, such as -0.10 MPa or -0.20 MPa) for 20-30 minutes (preferably 30 minutes). The gas filling valve is opened, and high-purity nitrogen is introduced at a flow rate of 200-5000 mL / min, preferably 700 mL / min. When the absolute pressure inside the furnace reaches 100 kPa, the gas valve is opened to carry out the heating pyrolysis. The furnace temperature is raised from room temperature to 600-1000℃ (preferably 800℃) in 1-3 hours, preferably 2 hours. The temperature is then held at 600-1000℃ (preferably 800℃) for 1-6 hours, preferably 5 hours, and then allowed to cool down naturally with the furnace.

[0041] In step 2) of some preferred embodiments of the present invention, the impregnation-pyrolysis process is repeated 2-10 times in BN f After the SiBN preform undergoes a second impregnation-pyrolysis process, the BN... f The SiBN preform is placed in a pyrolysis furnace, evacuated, and heated to 400-1000℃, preferably 800℃, and held at this temperature for 5 hours for pyrolysis to obtain high-temperature resistant and oxidation-resistant BN. f / SiBN wave-transparent composite material.

[0042] The BN fibers used in this invention possess unique properties: high temperature resistance, excellent high-temperature mechanical properties, and superior dielectric properties. The composite material system composed of BN fibers and a SiBN matrix combines the excellent mechanical properties and thermal shock resistance of Si3N4 with the good thermal stability of BN fibers. This makes the BN fiber-reinforced SiBN composite material superior to traditional BN fiber composite materials in terms of oxidation resistance and dielectric constant.

[0043] The above preparation method can be used to prepare high-temperature resistant and antioxidant BN. f / SiBN wave-transparent composite material.

[0044] The technical solution of the present invention will be further illustrated by the following embodiments.

[0045] Example 1

[0046] A high-temperature resistant and antioxidant BN f The preparation method of / SiBN microwave-transparent composite material includes the following steps:

[0047] 1) BN fibers are woven into a preform using a three-dimensional braiding method (specifically, the braiding involves weaving continuous BN fibers into a 2.5D structure using a three-dimensional braiding method, with braided structures in the X, Y, and Z axes to form a complete 2.5D body). Then, the preform is degummed at 600°C in air (because the fiber surface contains sizing agent, residual carbon generated during pyrolysis will affect the dielectric properties of the material, therefore degumming is necessary) for 1 hour, followed by natural cooling to room temperature in the furnace. Then, using polysiloxane as a precursor, the BN preform undergoes a precursor impregnation-pyrolysis (PIP) process, specifically:

[0048] ① Impregnation process: The debonded BN preform is placed in an impregnation tank, and the tank is evacuated to a vacuum degree of -0.10 MPa. The precursor polysiloxane is added to the impregnation tank (the mass ratio of BN braid to precursor is 1:5). After impregnation for 6 hours, the resulting BN... f / The SiBN preform was removed and weighed;

[0049] ② Curing process: The BN obtained in step ① f The SiBN preform was transferred to an autoclave. The autoclave inlet valve was opened, and high-purity nitrogen was introduced until the pressure reached 5 MPa. The inlet valve was then closed, and the preform was heated according to the curing temperature regime. The heating rate range was: room temperature to 170°C, heating time 1.5 hours, holding at that temperature for 10 hours, followed by natural cooling with the furnace. f / SiBN preform removed;

[0050] ③ Pyrolysis process: The BN obtained in step ② f The SiBN preform was placed in a pyrolysis furnace and maintained under a vacuum of -0.10 MPa for 30 minutes. Then, the gas filling valve was opened, and high-purity nitrogen was introduced at a flow rate of 700 mL / min. When the absolute pressure inside the furnace reached 100 kPa, the gas filling valve was opened to initiate pyrolysis. The furnace temperature was raised from room temperature to 800°C in 2 hours, and then held at 800°C for 5 hours. The furnace was then allowed to cool naturally to obtain BN. f / SiBN preform;

[0051] 2) Take the BN obtained in step 1). f The SiBN preform underwent an impregnation-pyrolysis process five times, followed by the addition of BN. f The SiBN preform was placed in a pyrolysis furnace, evacuated, and heated to 800℃, held for 5 hours to obtain high-temperature resistant and oxidation-resistant BN. f / SiBN wave-transparent composite material.

[0052] Figure 1 The high-temperature resistant and antioxidant BN prepared in Example 1 fThe image shows the appearance of the SiBN microwave-transparent composite material; as shown in the image, the structure of the sample after curing and pyrolysis is intact, and the fiber matrix has a good bonding effect.

[0053] Figure 2 The high-temperature resistant and antioxidant BN prepared in Example 1 f The microstructure of the SiBN microwave-transparent composite material observed under SEM is shown in (a) as a cross-sectional scanning image after curing and pyrolysis, and (b) as a magnified structure. The images show that the BN fibers are tightly bonded to the SiBN matrix, indicating that the prepared BN... f The SiBN composite material scheme is already very well-developed. Figures (c) and (d) show the microstructure of the composite material after high-temperature oxidation in air. It can be seen that the SiBN matrix exhibits a molten flow state after high-temperature oxidation. The molten material is BN oxide B2O3. In Figure (d), it can be clearly seen that the molten B2O3 coats the surface of BN fibers, protecting the structural integrity of the internal fibers.

[0054] Example 2

[0055] Same as Example 1, except that the glue discharge temperature in step 1) is 1000℃.

[0056] Example 3

[0057] Same as Example 1, except that in step 2), BN f The SiBN preform underwent an impregnation-pyrolysis process repeated eight times.

[0058] Example 4

[0059] Same as Example 1, except that the pyrolysis temperature in step 1) is 1000℃.

[0060] Example 5

[0061] Same as Example 1, except that in step 1) ② the curing process, high-purity nitrogen is introduced into the reactor until the pressure is 15MPa.

[0062] Comparative Example 1

[0063] Similar to Example 1, except that in step 1), a three-dimensional weaving method is used to use the SiO2 fiber braid as a preform.

[0064] Comparative Example 2

[0065] Same as Example 1, except that the pyrolysis process in step 1) ③ is carried out in an air atmosphere.

[0066] Comparative Example 3

[0067] Same as Example 1, except that the impregnation process in step 1) is not vacuumed.

[0068] Comparative Example 4

[0069] Same as Example 1, except that the impregnation-pyrolysis process in step 1) is repeated only once.

[0070] Performance testing:

[0071] The products prepared in Examples 1-5 and Comparative Examples 1-4 were subjected to high-temperature treatment at 1400°C. Their mechanical properties (referencing standard: according to GB / T 4741-1999, the bending strength of this material was determined using the three-point load method) were measured. The material was prepared into cuboid specimens with a length of 120 mm and a width-to-thickness ratio of 1:1. The specimens were prepared using the same process conditions as in actual production of this material. The specimens were placed in an oven at 110°C ± 5°C, and the bending strength was measured.

[0072] According to national standard GB / T 8489-2006, the cross-sectional area of ​​a square prism specimen should be 5mm ± 0.1mm on each side and 12.5 ± 0.1mm in height. The top and bottom surfaces should be ground until parallel with an error of 0.01mm, and the perpendicularity error to the axis should not exceed 0.01mm. The edges of the top and bottom surfaces should be chamfered at 45° or rounded to a depth of 0.1mm to 0.2mm. The surface roughness Rz of the specimen should not exceed 3.2μm as specified in GB / T 1031. The diameter of the specimen should be measured, and the specimen should be placed in the center of the pressure plate of the testing machine. A continuous test force should be applied to the specimen, with a beam displacement speed of 0.2mm / min. The critical load at which the specimen fails under compression should be recorded. After each compression test, the contact blocks and pressure plate should be carefully cleaned to prevent debris from affecting the testing of the next specimen. The oxidation rate and antioxidant properties (since the oxidation product B2O3 of BN and SiBN is easy to flow or generate gas to escape, the oxidation rate can be calculated by detecting the ratio of the defect depth of the microstructure to the oxidation time) are shown in Table 1.

[0073] Table 1

[0074]

[0075] Based on the flexural strength and compressive strength in Examples 1-5 of Table 1, it can be seen that BN f / SiBN microwave-transparent composite materials have excellent mechanical properties and oxidation resistance.

[0076] Based on the data from Comparative Examples 1-4 in Table 1, it can be seen that in Comparative Example 1, the SiO2 fiber reinforcement suffers from severe impact on mechanical properties due to crystallization above 900℃, although SiO2 exhibits good oxidation resistance and does not exhibit large-area defects. In Comparative Example 2, pyrolysis is performed in an air atmosphere, resulting in a matrix that is no longer a SiBN matrix but is composed of B2O3 and SiO2. B2O3 generates a large amount of liquid at 1400℃, and the gaseous phase is lost, severely affecting the mechanical properties of the material. In Comparative Example 3, without vacuum impregnation, the precursor solution cannot penetrate into the braid, resulting in the inability to form fiber-reinforced composite materials, and poor mechanical properties after oxidation. In Comparative Example 4, only one impregnation, curing, and pyrolysis cycle is performed, resulting in a large number of unfilled pores in the matrix, providing numerous oxygen permeation channels and poor oxidation resistance.

[0077] The data comparison shows that the mechanical properties of the composite material obtained in the comparative example are not as good as those of the composite material obtained in the example.

[0078] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A high-temperature resistant and antioxidant BN f The method for preparing SiBN microwave-transparent composite materials is characterized by, Includes the following steps: BN fibers are woven into a preform, and the resulting BN preform is then debonded and used as a reinforcement. Using polysiloxane as a precursor, an impregnation-pyrolysis process is employed to obtain BN. f / SiBN preform; the BN f The SiBN preform undergoes a repeated impregnation-pyrolysis process, followed by placement in a pyrolysis furnace, vacuuming, and pyrolysis to obtain high-temperature resistant and oxidation-resistant BN. f / SiBN wave-transparent composite material; The impregnation-pyrolysis process specifically includes the following steps: The BN preform is placed in an impregnation tank, which is then evacuated to a vacuum level of -0.05 to -0.50 MPa. The precursor polysiloxane is then placed inside for impregnation to obtain BN. f / SiBN preform; The obtained BN f The SiBN preform is transferred to an autoclave, and high-purity nitrogen is introduced into the autoclave until the pressure reaches 2-15 MPa. The inlet valve is then closed, and the autoclave is heated according to the curing temperature regime. BN heat treatment f The SiBN preform is placed in a pyrolysis furnace and kept under a vacuum of -0.01 to -0.20 MPa for 20-30 minutes. Then, high-purity nitrogen is introduced at a flow rate of 200-5000 mL / min. When the absolute pressure inside the furnace reaches 100 kPa, the gas valve is opened to allow for heating and pyrolysis. The preform is then allowed to cool down naturally with the furnace. The impregnation-pyrolysis process is repeated 2-10 times; During the pyrolysis process, the furnace temperature is raised from room temperature to 600-1000℃ in 1-3 hours, and then held at 600-1000℃ for 1-6 hours.

2. The high-temperature resistant and antioxidant BN according to claim 1 f The method for preparing SiBN microwave-transparent composite materials is characterized by, The debinding process specifically refers to: holding the product in air or inert gas at 400-1000℃ for 0.5-10 hours, and then allowing it to cool naturally to room temperature with the furnace.

3. The high-temperature resistant and antioxidant BN according to claim 1 f The method for preparing SiBN microwave-transparent composite materials is characterized by, The impregnation time is 3-10 hours; the curing temperature regime is as follows: the room temperature is raised to 150-200℃, the heating time is 0.5-2 hours, the temperature is maintained for 2-20 hours, and then the temperature is lowered to room temperature.

4. A high-temperature resistant and antioxidant BN prepared by the preparation method according to any one of claims 1-3 f / SiBN wave-transparent composite material.

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