A combined silicon nitride ceramic radome and a preparation method thereof

Abstract

The application provides a combined silicon nitride ceramic antenna dome and a preparation method thereof, and belongs to the technical field of silicon nitride ceramic antenna dome; the preparation method of the antenna dome main dome body comprises preparation of a primary dome body and surface sealing; the preparation of the primary dome body comprises preparation of titanium sol, preparation of a blank and sintering; in the preparation of the blank, silicon powder, aluminum nitride powder, a sintering aid and sodium dodecylbenzenesulfonate are mixed, and after uniform stirring, polymethyl methacrylate and polyethylene glycol 2000 are added to obtain a mixture; the mixture is added to the titanium sol, stirred at 900-1200 rpm for 30-40 min under a nitrogen atmosphere, then ball milled for 1.8-2.2 h, methyltrimethoxysilane solution is added, and the ball milling is continued for 26-35 min, then the mixture is placed in a mold and left to stand, and the blank is obtained after drying; the antenna dome prepared by the application has low density, high strength and hardness, high toughness, low thermal conductivity and dielectric constant, and excellent rain erosion resistance.

Description

Technical Field

[0001] This invention belongs to the field of silicon nitride ceramic radome technology, specifically relating to a combined silicon nitride ceramic radome and its preparation method. Background Technology

[0002] Silicon nitride ceramics, as a high-performance ceramic material, possess excellent comprehensive properties. Its core performance characteristics are high strength, high fracture toughness, excellent high-temperature resistance, and dielectric properties. It also exhibits good chemical stability, enabling it to resist corrosion from acidic and alkaline media. Therefore, silicon nitride ceramics demonstrate significant value in aerospace applications.

[0003] In the field of radomes, silicon nitride ceramics have shown extremely high application value. As a key component that protects antenna systems from the influence of harsh external environments, its performance directly determines the working stability and service life of the antenna system. For antennas carried by aerospace vehicles, radomes need to meet multiple stringent requirements such as lightweight, high temperature resistance, and resistance to high-speed airflow erosion.

[0004] However, silicon nitride ceramics present a series of inherent contradictions and technical challenges in radome applications. On the one hand, silicon nitride ceramics have a high thermal conductivity, which causes heat to accumulate in the radome under high temperature conditions. This not only affects the working stability of the internal electronic components of the antenna and increases the temperature control burden, but also fails to meet the heat insulation requirements under some extreme conditions. On the other hand, in order to reduce the dielectric constant of silicon nitride ceramics, high porosity and low density are usually achieved. However, the low density leads to a decrease in the material's hardness and strength. The degradation of mechanical properties severely restricts the radome's ability to resist hail and dust particle erosion during high-speed flight.

[0005] To address the aforementioned issues, a series of studies have been conducted in the existing technology field. For the problem of high thermal conductivity, the common approach is to dope a low thermal conductivity phase (zirconia, alumina, etc.) into a silicon nitride matrix to form a multiphase ceramic, thereby reducing the thermal conductivity by hindering the conduction path. To address the contradiction between density, hardness, and strength, the existing technology typically improves the ceramic density by optimizing the sintering process (such as increasing the sintering temperature), adding composite sintering aids, and introducing specific pore-forming agents, thereby increasing the hardness and strength of the material.

[0006] However, existing technical solutions still have obvious defects. Composite silicon nitride ceramics doped with low thermal conductivity phases have low interfacial bonding strength. Under high-speed rain erosion, the interface is prone to cracking, leading to material peeling. While optimizing the sintering process, the brittleness of the product is increased. The stress generated by rain impact is prone to concentrate inside the material, causing cracking. It cannot adapt to the high-frequency and high-intensity rain erosion environment in aerospace and other fields.

[0007] Therefore, providing a combined silicon nitride ceramic radome and its preparation method, reducing the thermal conductivity of the product, and enhancing hardness and strength while reducing density, and improving rain erosion resistance are technical problems that urgently need to be solved in the existing technology. Summary of the Invention

[0008] To address the technical problems existing in the prior art, this invention provides a combined silicon nitride ceramic radome and its preparation method, which reduces density while increasing hardness and strength, reducing thermal conductivity, and improving rain erosion resistance.

[0009] To address the aforementioned technical problems, the present invention adopts the following technical solution:

[0010] A method for fabricating a combined silicon nitride ceramic radome includes fabricating the main radome body, fabricating the heat-insulating inner cover, fabricating the outer heat-insulating ring, and connecting the components. The specific operations are as follows:

[0011] 1. Fabrication of the main radome body

[0012] (1) Preparation of primary cover

[0013] A. Preparation of titanium sol

[0014] Add tetrabutyl titanate to anhydrous ethanol and stir at 34-36℃ for 28-32 min. Add mixed nitric acid solution, controlling the addition time to 18-23 min. After the addition is complete, stir at 34-36℃ for 1.5-2.0 h to obtain titanium sol.

[0015] The mass ratio of anhydrous ethanol, tetrabutyl titanate, and mixed nitric acid solution is 100:22-27:11.3-11.9;

[0016] The mixed nitric acid solution is a mixture of deionized water, 65wt% nitric acid solution, and Ni(NO3)2·6H2O, wherein the mass ratio of the deionized water, 65wt% nitric acid solution, and Ni(NO3)2·6H2O is 10:0.5-0.7:0.8-1.2.

[0017] B. Preparation of the green body

[0018] Silicon powder, aluminum nitride powder, sintering aid, and sodium dodecylbenzenesulfonate are mixed and stirred evenly. Then, polymethyl methacrylate and polyethylene glycol 2000 are added to obtain a mixture. The mixture is added to titanium sol and stirred at 900-1200 rpm for 30-40 min under a nitrogen atmosphere. Then, ball milling is performed for 1.8-2.2 h at a ball-to-material ratio of 3-5:1 and a ball milling speed of 260-280 rpm. Methyltrimethoxysilane solution is added, and ball milling is continued for 26-35 min. The mixture is then placed in a mold and allowed to stand at 26-30℃ for 12-16 h. After drying, a green body is obtained.

[0019] The mass ratio of silicon powder, aluminum nitride powder, sintering aid, sodium dodecylbenzenesulfonate, polymethyl methacrylate, and polyethylene glycol 2000 is 100:4.8-5.2:4.5-5.2:1.7-2.4:5-20:1.8-2.2.

[0020] The sintering aid is a mixture of yttrium oxide and samarium oxide, with a mass ratio of yttrium oxide to samarium oxide of 1:0.8-1.3;

[0021] The mass ratio of the silicon powder, titanium sol, and methyltrimethoxysilane solution is 100:133.3-138.9:9.5-10.5;

[0022] The methyltrimethoxysilane solution is a mixture of methyltrimethoxysilane and anhydrous ethanol, wherein the mass ratio of methyltrimethoxysilane to anhydrous ethanol is 4.5-5.5:5;

[0023] C. Sintering

[0024] The billet is placed in a muffle furnace and heated to 290-310℃ at a rate of 1.2-1.8℃ / min under a nitrogen atmosphere, and held for 0.8-1.2 hours. Then, the temperature is increased to 595-605℃ at a rate of 2.0-3.0℃ / min and held for 1.4-1.6 hours. Next, under an ammonia atmosphere, the ammonia flow rate is controlled at 0.8-1.2 L / min, and the temperature is increased to 1430-1460℃ at a rate of 2.8-3.3℃ / min. Then, the temperature is increased to 1530-1570℃ at a rate of 0.8-1.2℃ / min and held for 3.3-3.6 hours. Finally, the temperature is decreased to 1185-1210℃ at a rate of 4.7-5.2℃ / min, and the atmosphere is switched to nitrogen. The temperature is then decreased to 795-805℃ at a rate of 4.7-5.2℃ / min and allowed to cool naturally to room temperature to obtain the primary cover.

[0025] (2) Surface sealing

[0026] A. Preparation of sealing slurry

[0027] The lithium aluminum silicon microcrystalline glass precursor powder was added to deionized water and stirred evenly. Then, an additive was added, and the mixture was ultrasonically dispersed for 2.5-3.0 hours. The ultrasonic power was 95-105W and the ultrasonic frequency was 30-35kHz. After ultrasonic dispersion, the mixture was allowed to stand at room temperature for 5.8-6.5 hours to obtain the first sealing slurry.

[0028] In the first sealing slurry, the mass ratio of lithium aluminum silicon microcrystalline glass precursor powder, deionized water and additives is 37-43:80:4-8;

[0029] The lithium aluminum silicon microcrystalline glass precursor powder was added to deionized water and stirred evenly. Then, an additive was added, and the mixture was ultrasonically dispersed for 2.5-3.0 hours. The ultrasonic power was 95-105W and the ultrasonic frequency was 30-35kHz. After ultrasonic dispersion, the mixture was allowed to stand at room temperature for 5.8-6.5 hours to obtain the second sealing slurry.

[0030] In the second sealing slurry, the mass ratio of lithium aluminum silicon microcrystalline glass precursor powder, deionized water and additives is 22-28:80:4-8;

[0031] The additive is a mixture of titanium dioxide and calcium oxide, wherein the mass ratio of titanium dioxide to calcium oxide is 1:0.8-1.3;

[0032] The preparation method of the lithium aluminum silicon microcrystalline glass precursor powder is as follows: Tetraethyl orthosilicate and anhydrous ethanol are mixed and stirred until homogeneous to obtain solution one; 64-66 wt% nitric acid solution, deionized water, and anhydrous ethanol are mixed and stirred until homogeneous, then added to solution one; after addition, the temperature is raised to 68-72℃ and stirred for 2.3-2.6 h to obtain silica sol; the temperature of deionized water is raised to 38-43℃, and Al(NO3)3· After mixing 9H2O and LiNO3 evenly, add them to the silica sol and stir in a water bath at 48-53℃ for 14-16 hours. Then let it stand at 37-43℃ for 23-26 hours. After drying, raise the temperature to 348-354℃ and hold for 1.8-2.2 hours. Then raise the temperature to 640-660℃ at a rate of 2.0-3.0℃ / min and hold for 2.8-3.2 hours. After cooling, the lithium aluminum silicon microcrystalline glass precursor powder is obtained.

[0033] The mass ratio of the tetraethyl orthosilicate to anhydrous ethanol is 28-29:68-73;

[0034] The volume-to-mass ratio of the 64-66 wt% nitric acid solution, deionized water, anhydrous ethanol, and solution one is 2 mL: 16-20 g: 8-10 mL: 96-102 g;

[0035] The mass ratio of deionized water, Al(NO3)3·9H2O, LiNO3, and silica sol is 78-82:30-32:10-12:116-124.

[0036] B. Scraping

[0037] A sealing slurry is applied to the surface of the primary radome. The first sealing slurry is applied in two coats. After each coat, the radome is heat-treated at 375-385℃ for 0.7-1.0 h, controlling the thickness of the first sealing slurry layer penetrating the primary radome to be 10-25 μm. Then, a second sealing slurry is applied. After each coat, the radome is heat-treated at 375-385℃ for 0.7-1.0 h, controlling the thickness of the second sealing slurry layer penetrating the primary radome to be 10-35 μm. After the coating is completed, the radome is kept at 645-655℃ for 2.8-3.2 h and then allowed to cool naturally to room temperature to obtain the main radome body.

[0038] 2. Preparation of the heat-insulating inner cover

[0039] Tetraethyl orthosilicate, anhydrous ethanol, and 34-36 wt% hydrochloric acid solution are mixed and stirred evenly to obtain the first sol impregnation solution. The quartz fiber preform and 10-14 times the mass of the first sol impregnation solution are placed in a vacuum impregnation tank for vacuum impregnation. The impregnation pressure is controlled at -0.075 to -0.085 MPa, the impregnation time is 70-90 min, the mixture is allowed to stand at 43-47℃ for 3.8-4.2 h, aged at 52-58℃ for 23-26 h, and then supercritically dried. The drying medium is carbon dioxide, the drying temperature is 280-320℃, and the drying pressure is 8-12 MPa to obtain the heat-insulating inner cover.

[0040] The quartz fiber preform has a density of 0.20-0.25 g / cm³. 3 ;

[0041] In the first sol-impregnation solution, the molar ratio of tetraethyl orthosilicate, anhydrous ethanol, and hydrochloric acid solution is 3-5:6-10:0.8-1.2.

[0042] 3. Fabrication of the outer heat insulation ring

[0043] Tetraethyl orthosilicate, anhydrous ethanol, and 34-36 wt% hydrochloric acid solution are mixed and stirred evenly to obtain a second sol-impregnation solution. The alumina fiber preform and 10-14 times its mass of the second sol-impregnation solution are placed in a vacuum impregnation tank for vacuum impregnation. The impregnation pressure is controlled at -0.075 to -0.085 MPa, the impregnation time is 70-90 min, and the mixture is allowed to stand at 43-47℃ for 3.8-4.2 h, aged at 52-58℃ for 23-26 h, and then subjected to supercritical drying. The drying medium is carbon dioxide, the drying temperature is 280-320℃, and the drying pressure is 8-12 MPa to obtain the outer heat insulation ring.

[0044] The alumina fiber preform has a density of 0.28-0.33 g / cm³. 3 ;

[0045] In the second sol-impregnation solution, the molar ratio of tetraethyl orthosilicate, anhydrous ethanol, and hydrochloric acid solution is 3-5:6-10:0.8-1.2.

[0046] 4. Connection

[0047] The main radome body and the end cap are connected by threads, and adhesive is applied in the middle. The bonding area is sandblasted to a surface roughness of 7.0-7.5. Adhesive is applied to both sides. The end cap is screwed into the middle of the small end face of the main radome body, with the outer surfaces aligned and the end face gap less than 0.2mm. It is then cured at 168-172℃ for 1.8-2.2h. The main radome body is bonded to the inner heat insulation cover and the outer heat insulation ring using aluminum dihydrogen phosphate solution adhesive, with a bonding thickness of 0.20-0.25mm, to obtain a combined silicon nitride ceramic radome.

[0048] The end cap is made of silicon nitride ceramic, and the density of the silicon nitride ceramic is 2.8-3.3 g / cm³. 3 The bending strength is 760-780 MPa, and the dielectric constant is 5.8-6.2.

[0049] The adhesive is prepared by mixing deionized water, hydrochloric acid solution and 13-16g of anhydrous ethanol to obtain an aqueous hydrochloric acid solution; mixing tetraethyl orthosilicate, α,ω-dihydroxypolydimethylsiloxane, kH560 silane coupling agent and anhydrous ethanol to obtain an aqueous hydrochloric acid solution at 0-2℃, stirring at 38-43℃ for 1.7-2.3h, adding stannous octoate, and stirring at room temperature for 30-37min to obtain the adhesive.

[0050] The mass ratio of the deionized water, 4.8-5.2 wt% hydrochloric acid solution, and anhydrous ethanol is 1.8-2.3:0.4-0.6:13-16;

[0051] The mass ratio of tetraethyl orthosilicate, α,ω-dihydroxypolydimethylsiloxane, kH560 silane coupling agent, anhydrous ethanol, hydrochloric acid aqueous solution, and stannous octoate is 18-23:8-12:2.7-3.2:8-12:15.2-18.9:0.18-0.22.

[0052] The mass concentration of the aluminum dihydrogen phosphate solution is 54-56%.

[0053] A composite silicon nitride ceramic radome is prepared using the aforementioned method.

[0054] This invention employs a specific method to prepare the radome. First, the radome body is prepared, specifically using silicon powder as a matrix, with aluminum nitride, rare earth oxides, and pore-forming agents mixed with titanium sol. The titanium sol introduces nickel ions, which promotes sintering performance. During sintering, under an ammonia atmosphere, ammonia decomposes to generate nitrogen atoms, which react with the silicon powder to form silicon nitride. Furthermore, the sintering aids and aluminum nitride significantly accelerate the sintering process at high temperatures, resulting in a porous structure while enhancing the strength and hardness of the primary radome body. Then, lithium aluminum silicon microcrystalline glass is used as the sealing material to control the penetration of the slurry into the pores. The sealing slurry exhibits excellent thermal compatibility with the primary radome body, resulting in a strong bond and further enhancing the hardness and strength of the main radome body. During the coating process, a high-solids-content slurry is first applied... The process involves coating with a low-solids slurry, followed by a gradient sealing process that deeply fills the fine pores, ensuring excellent resistance to rain erosion. In the fabrication of the inner and outer heat insulation rings, silica sol is used as an impregnating solution to impregnate and fill the fibers. The silica sol penetrates into the fiber skeleton, improving the product's mechanical properties. During subsequent aging, the sol gels at the fiber nodes, forming a network of interconnected nanoparticles. Combined with supercritical drying, the liquid inside the pores is removed while maintaining the nanostructure. The resulting inner and outer heat insulation rings possess extremely low thermal conductivity, and the fibers are reinforcing. This allows the radome to have a certain porosity to reduce density while improving mechanical properties, exhibiting low thermal conductivity and excellent heat insulation performance, effectively extending the product's service life.

[0055] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0056] 1. The primary cover obtained by this invention has a density of 1.12-1.87 g / cm³. 3 ;

[0057] 2. The combined silicon nitride ceramic radome prepared by this invention has a bending strength of 103.2-287.3 MPa, a Mohs hardness of 7-9, a thermal conductivity of 0.025-0.030 W / (m·K) at 25℃ and 0.038-0.046 W / (m·K) at 1000℃, a dielectric constant of 2.33-3.82 at 25℃ and 2.54-4.13 at 1000℃, and a fracture toughness of 5.74-7.36 MPa·m. 1 / 2 ;

[0058] 3. The combined silicon nitride ceramic radome prepared by this invention was sprayed with deionized water, with the water droplet size controlled at 4.0 mm, the spraying distance at 100 mm, the temperature at 10 °C, the spraying speed at 400 m / s, the spraying angle at 90 °C, the spraying intensity at 70 mm / h, and the spraying time at 12 h. The bending strength of the combined silicon nitride ceramic radome was tested to be 98.1-279.8 MPa, and the fracture toughness was 5.41-7.12 MPa·m. 1 / 2 . Detailed Implementation

[0059] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described.

[0060] Example 1

[0061] 1. Fabrication of the main radome body

[0062] (1) Preparation of primary cover

[0063] A. Preparation of titanium sol

[0064] Add 22g of tetrabutyl titanate to 100g of anhydrous ethanol, stir at 34℃ for 28min, add 11.3g of mixed nitric acid solution, control the addition time to be 18min, and after the addition is completed, stir at 34℃ for 1.5h to obtain titanium sol.

[0065] The mixed nitric acid solution is a mixture of deionized water, 65wt% nitric acid solution, and Ni(NO3)2·6H2O, wherein the mass ratio of the deionized water, 65wt% nitric acid solution, and Ni(NO3)2·6H2O is 10:0.5:0.8.

[0066] B. Preparation of the green body

[0067] Mix 100g of silicon powder, 4.8g of aluminum nitride powder, 4.5g of sintering aid, and 1.7g of sodium dodecylbenzenesulfonate. After stirring evenly, add 20g of polymethyl methacrylate and 1.8g of polyethylene glycol 2000 to obtain a mixture. Add all of the mixture to 133.3g of titanium sol and stir at 900rpm for 30min under a nitrogen atmosphere. Then, ball mill the mixture for 1.8h at a ball-to-material ratio of 3:1 at 260rpm. Add 9.50g of methyltrimethoxysilane solution and continue ball milling for 26min. Place the mixture in a mold and let it stand at 26℃ for 16h. After drying, obtain the green body.

[0068] The sintering aid is a mixture of yttrium oxide and samarium oxide, with a mass ratio of yttrium oxide to samarium oxide of 1:0.8;

[0069] The methyltrimethoxysilane solution is a mixture of methyltrimethoxysilane and anhydrous ethanol, wherein the mass ratio of methyltrimethoxysilane to anhydrous ethanol is 4.5:5.

[0070] C. Sintering

[0071] The billet was placed in a muffle furnace and heated to 290°C at a rate of 1.2°C / min under a nitrogen atmosphere, and held for 0.8 h. Then, the temperature was increased to 595°C at a rate of 2.0°C / min and held for 1.4 h. Next, under an ammonia atmosphere, the ammonia flow rate was controlled at 0.8 L / min, and the temperature was increased to 1430°C at a rate of 2.8°C / min. Then, the temperature was increased to 1530°C at a rate of 0.8°C / min and held for 3.3 h. The temperature was then decreased to 1185°C at a rate of 4.7°C / min. The atmosphere was then switched to nitrogen and the temperature was decreased to 795°C at a rate of 4.7°C / min. The billet was then allowed to cool naturally to room temperature to obtain the primary cover.

[0072] (2) Surface sealing

[0073] A. Preparation of sealing slurry

[0074] 37g of lithium aluminum silicon microcrystalline glass precursor powder was added to 80g of deionized water and stirred evenly. Then, 4g of additive was added and ultrasonically dispersed for 2.5h. The ultrasonic power was 95W and the ultrasonic frequency was 30kHz. After ultrasonic dispersion, the mixture was allowed to stand at room temperature for 5.8h to obtain the first sealing slurry.

[0075] 22g of lithium aluminum silicon microcrystalline glass precursor powder was added to 80g of deionized water and stirred evenly. Then, 4g of additive was added and ultrasonically dispersed for 2.5h. The ultrasonic power was 95W and the ultrasonic frequency was 30kHz. After ultrasonic dispersion, the mixture was allowed to stand at room temperature for 5.8h to obtain the second sealing slurry.

[0076] The preparation method of the lithium aluminum silicon microcrystalline glass precursor powder is as follows: 28g of tetraethyl orthosilicate and 68g of anhydrous ethanol are mixed and stirred evenly to obtain solution one; 2.0mL of 64wt% nitric acid solution, 16g of deionized water and 8mL of anhydrous ethanol are mixed and stirred evenly, and then added to 96g of solution one. After the addition is completed, the temperature is raised to 68℃ and stirred for 2.3h to obtain silica sol; 78g of deionized water is raised to 38℃, 30g of Al(NO3)3·9H2O and 10g of LiNO3 are added, stirred evenly, and then added to 116g of silica sol. The mixture is stirred in a water bath at 48℃ for 14h, then allowed to stand at 37℃ for 26h, dried, and then the temperature is raised to 348℃ and held for 2.2h. The temperature is then raised to 640℃ at a rate of 2.0℃ / min and held for 2.8h. After cooling, the lithium aluminum silicon microcrystalline glass precursor powder is obtained.

[0077] The additive is a mixture of titanium dioxide and calcium oxide, wherein the mass ratio of titanium dioxide to calcium oxide is 1:0.8;

[0078] B. Scraping

[0079] A sealing slurry is applied to the surface of the primary radome. The first sealing slurry is applied twice. After each application, the radome is heat-treated at 375°C for 1.0 h to ensure that the thickness of the first sealing slurry layer penetrating the primary radome is 10 μm. Then, a second sealing slurry is applied. After each application, the radome is heat-treated at 375°C for 1.0 h to ensure that the thickness of the second sealing slurry layer penetrating the primary radome is 10 μm. After the coating is completed, the radome is kept at 645°C for 2.8 h and then allowed to cool naturally to room temperature to obtain the main radome body.

[0080] 2. Preparation of the heat-insulating inner cover

[0081] Tetraethyl orthosilicate, anhydrous ethanol, and 34 wt% hydrochloric acid solution were mixed and stirred evenly to obtain the first sol impregnation solution. The quartz fiber preform and 10 times the mass of the first sol impregnation solution were placed in a vacuum impregnation tank for vacuum impregnation. The impregnation pressure was controlled at -0.085 MPa, the impregnation time was 70 min, the mixture was allowed to stand at 43℃ for 3.8 h, aged at 52℃ for 26 h, and then supercritically dried. The drying medium was carbon dioxide, the drying temperature was 280℃, and the drying pressure was 8 MPa to obtain the heat-insulating inner cover.

[0082] The quartz fiber preform has a density of 0.20 g / cm³. 3 ;

[0083] In the first sol-impregnation solution, the molar ratio of tetraethyl orthosilicate, anhydrous ethanol, and hydrochloric acid solution is 3:6:0.8.

[0084] 3. Fabrication of the outer heat insulation ring

[0085] Tetraethyl orthosilicate, anhydrous ethanol, and 34 wt% hydrochloric acid solution were mixed and stirred evenly to obtain a second sol-impregnation solution. The alumina fiber preform and 10 times the mass of the second sol-impregnation solution were placed in a vacuum impregnation tank for vacuum impregnation. The impregnation pressure was controlled at -0.085 MPa, the impregnation time was 70 min, the mixture was allowed to stand at 43℃ for 3.8 h, aged at 52℃ for 26 h, and then supercritically dried. The drying medium was carbon dioxide, the drying temperature was 280℃, and the drying pressure was 8 MPa to obtain the outer heat insulation ring.

[0086] The alumina fiber preform has a density of 0.28 g / cm³. 3 ;

[0087] In the second sol-impregnation solution, the molar ratio of tetraethyl orthosilicate, anhydrous ethanol, and hydrochloric acid solution is 3:6:0.8.

[0088] 4. Connection

[0089] The main radome body and the end cap are connected by threads, and adhesive is applied in the middle. The bonding area is sandblasted to a surface roughness of 7.0. Adhesive is applied to both sides. The end cap is screwed into the middle of the small end face of the main radome body, with the outer surfaces aligned and the end face gap less than 0.2mm. It is then cured at 168℃ for 1.8h. The main radome body is bonded to the inner heat insulation cover and the outer heat insulation ring using aluminum dihydrogen phosphate solution adhesive with a bonding thickness of 0.20mm, resulting in a combined silicon nitride ceramic radome.

[0090] The end cap is made of silicon nitride ceramic, and the density of the silicon nitride ceramic is 2.8 g / cm³. 3 Its bending strength is 760 MPa and its dielectric constant is 6.2;

[0091] The adhesive is prepared by mixing 1.8g of deionized water, 0.4g of 4.8wt% hydrochloric acid solution and 13g of anhydrous ethanol to obtain an aqueous hydrochloric acid solution; mixing 18g of tetraethyl orthosilicate, 8g of α,ω-dihydroxypolydimethylsiloxane, 2.7g of KH560 silane coupling agent and 8g of anhydrous ethanol to obtain an aqueous hydrochloric acid solution; adding 15.2g of the aqueous hydrochloric acid solution at 2°C; stirring at 38°C for 2.3h; adding 0.18g of stannous octoate; and stirring at room temperature for 30min to obtain the adhesive.

[0092] The mass concentration of the aluminum dihydrogen phosphate solution is 54%.

[0093] Example 2

[0094] 1. Fabrication of the main radome body

[0095] (1) Preparation of primary cover

[0096] A. Preparation of titanium sol

[0097] Add 25g of tetrabutyl titanate to 100g of anhydrous ethanol, stir at 35℃ for 30min, add 11.6g of mixed nitric acid solution, control the addition time to be 20min, and after the addition is completed, stir at 35℃ for 1.8h to obtain titanium sol.

[0098] The mixed nitric acid solution is a mixture of deionized water, 65wt% nitric acid solution, and Ni(NO3)2·6H2O, wherein the mass ratio of the deionized water, 65wt% nitric acid solution, and Ni(NO3)2·6H2O is 10:0.6:1.0.

[0099] B. Preparation of the green body

[0100] Mix 100g silicon powder, 5.0g aluminum nitride powder, 5.0g sintering aid and 2.0g sodium dodecylbenzenesulfonate, stir evenly, then add 12g polymethyl methacrylate and 2.0g polyethylene glycol 2000 to obtain a mixture. Add all the mixture to 136.6g titanium sol, stir at 1000rpm for 35min under nitrogen atmosphere, then ball mill for 2.0h, ball-to-material ratio of 4:1, ball milling speed of 270rpm, add 10g methyltrimethoxysilane solution, continue ball milling for 30min, then place in a mold, stand at 28℃ for 14h, and dry to obtain a green body.

[0101] The sintering aid is a mixture of yttrium oxide and samarium oxide, with a mass ratio of yttrium oxide to samarium oxide of 1:1;

[0102] The methyltrimethoxysilane solution is a mixture of methyltrimethoxysilane and anhydrous ethanol, wherein the mass ratio of methyltrimethoxysilane to anhydrous ethanol is 5:5.

[0103] C. Sintering

[0104] The billet is placed in a muffle furnace and heated to 300°C at a rate of 1.5°C / min under a nitrogen atmosphere, and held for 1.0 h. Then, the temperature is increased to 600°C at a rate of 2.5°C / min and held for 1.5 h. Next, under an ammonia atmosphere, the ammonia flow rate is controlled at 1.0 L / min, and the temperature is increased to 1450°C at a rate of 3.0°C / min. Then, the temperature is increased to 1550°C at a rate of 1.0°C / min and held for 3.5 h. The temperature is then decreased to 1200°C at a rate of 5.0°C / min. The atmosphere is then switched to nitrogen and the temperature is decreased to 800°C at a rate of 5.0°C / min. The billet is then allowed to cool naturally to room temperature to obtain the primary cover.

[0105] (2) Surface sealing

[0106] A. Preparation of sealing slurry

[0107] 40g of lithium aluminum silicon microcrystalline glass precursor powder was added to 80g of deionized water and stirred evenly. Then, 6g of additive was added and ultrasonically dispersed for 2.8h. The ultrasonic power was 100W and the ultrasonic frequency was 32kHz. After ultrasonic dispersion, the mixture was allowed to stand at room temperature for 6.0h to obtain the first sealing slurry.

[0108] 25g of lithium aluminum silicon microcrystalline glass precursor powder was added to 80g of deionized water and stirred evenly. Then, 6g of additive was added and ultrasonically dispersed for 2.8h. The ultrasonic power was 100W and the ultrasonic frequency was 32kHz. After ultrasonic dispersion, the mixture was allowed to stand at room temperature for 6.0h to obtain the second sealing slurry.

[0109] The preparation method of the lithium aluminum silicon microcrystalline glass precursor powder is as follows: 28.5g of tetraethyl orthosilicate and 70g of anhydrous ethanol are mixed and stirred evenly to obtain solution one; 2.0mL of 65wt% nitric acid solution, 18g of deionized water and 10mL of anhydrous ethanol are mixed and stirred evenly, and then added to 98.5g of solution one. After the addition is completed, the temperature is raised to 70℃ and stirred for 2.5h to obtain silica sol; 80g of deionized water is raised to 40℃, 31g of Al(NO3)3·9H2O and 11g of LiNO3 are added, stirred evenly, and then added to 120g of silica sol. The mixture is stirred in a 50℃ water bath for 15h, then allowed to stand at 40℃ for 24h, dried, and then the temperature is raised to 350℃ and held for 2.0h. The temperature is then raised to 650℃ at a rate of 2.5℃ / min and held for 3.0h. After cooling, the lithium aluminum silicon microcrystalline glass precursor powder is obtained.

[0110] The additive is a mixture of titanium dioxide and calcium oxide, wherein the mass ratio of titanium dioxide to calcium oxide is 1:1;

[0111] B. Scraping

[0112] A sealing slurry is applied to the surface of the primary radome. The first sealing slurry is applied twice. After each application, the radome is heat-treated at 380°C for 0.8 hours to ensure that the thickness of the first sealing slurry layer penetrating the primary radome is 15 μm. Then, a second sealing slurry is applied. After each application, the radome is heat-treated at 380°C for 0.8 hours to ensure that the thickness of the second sealing slurry layer penetrating the primary radome is 20 μm. After the coating is completed, the radome is kept at 650°C for 3.0 hours and then allowed to cool naturally to room temperature to obtain the main radome body.

[0113] 2. Preparation of the heat-insulating inner cover

[0114] Tetraethyl orthosilicate, anhydrous ethanol, and 35 wt% hydrochloric acid solution were mixed and stirred evenly to obtain the first sol impregnation solution. The quartz fiber preform and 12 times the mass of the first sol impregnation solution were placed in a vacuum impregnation tank for vacuum impregnation. The impregnation pressure was controlled at -0.08 MPa, the impregnation time was 80 min, the mixture was allowed to stand at 45℃ for 4.0 h, aged at 55℃ for 24 h, and then supercritically dried. The drying medium was carbon dioxide, the drying temperature was 300℃, and the drying pressure was 10 MPa to obtain the heat-insulating inner cover.

[0115] The quartz fiber preform has a density of 0.22 g / cm³. 3 ;

[0116] In the first sol-impregnation solution, the molar ratio of tetraethyl orthosilicate, anhydrous ethanol, and hydrochloric acid solution is 4:8:1.0.

[0117] 3. Fabrication of the outer heat insulation ring

[0118] Tetraethyl orthosilicate, anhydrous ethanol, and 35 wt% hydrochloric acid solution were mixed and stirred evenly to obtain a second sol-impregnation solution. The alumina fiber preform and 12 times the mass of the second sol-impregnation solution were placed in a vacuum impregnation tank for vacuum impregnation. The impregnation pressure was controlled at -0.08 MPa, the impregnation time was 80 min, the mixture was allowed to stand at 45℃ for 4.0 h, aged at 55℃ for 24 h, and then supercritically dried. The drying medium was carbon dioxide, the drying temperature was 300℃, and the drying pressure was 10 MPa to obtain the outer heat insulation ring.

[0119] The alumina fiber preform has a density of 0.30 g / cm³. 3 ;

[0120] In the second sol-impregnation solution, the molar ratio of tetraethyl orthosilicate, anhydrous ethanol, and hydrochloric acid solution is 4:8:1.0.

[0121] 4. Connection

[0122] The main radome body and the end cap are connected by threads, and adhesive is applied in the middle. The bonding area is sandblasted to a surface roughness of 7.0. Adhesive is applied to both sides. The end cap is screwed into the middle of the small end face of the main radome body, with the outer surfaces aligned and the end face gap less than 0.2mm. It is then cured at 170℃ for 2.0h. The main radome body is bonded to the inner heat insulation cover and the outer heat insulation ring using aluminum dihydrogen phosphate solution adhesive, with a bonding thickness of 0.22mm, to obtain a combined silicon nitride ceramic radome.

[0123] The end cap is made of silicon nitride ceramic, and the density of the silicon nitride ceramic is 3.0 g / cm³. 3 Its bending strength is 770 MPa and its dielectric constant is 6.0;

[0124] The adhesive is prepared by mixing 2.0g of deionized water, 0.5g of 5.0wt% hydrochloric acid solution and 15g of anhydrous ethanol to obtain an aqueous hydrochloric acid solution; mixing 20g of tetraethyl orthosilicate, 10g of α,ω-dihydroxypolydimethylsiloxane, 3.0g of KH560 silane coupling agent and 10g of anhydrous ethanol to obtain an aqueous hydrochloric acid solution; adding 17.5g of the aqueous hydrochloric acid solution at 0℃; stirring at 40℃ for 2.0h; adding 0.2g of stannous octoate; and stirring at room temperature for 35min to obtain the adhesive.

[0125] The mass concentration of the aluminum dihydrogen phosphate solution is 55%.

[0126] Example 3

[0127] 1. Fabrication of the main radome body

[0128] (1) Preparation of primary cover

[0129] A. Preparation of titanium sol

[0130] Add 27g of tetrabutyl titanate to 100g of anhydrous ethanol, stir at 36℃ for 32min, add 11.9g of mixed nitric acid solution, control the addition time to 23min, and after the addition is completed, stir at 36℃ for 2.0h to obtain titanium sol.

[0131] The mixed nitric acid solution is a mixture of deionized water, 65wt% nitric acid solution, and Ni(NO3)2·6H2O, wherein the mass ratio of the deionized water, 65wt% nitric acid solution, and Ni(NO3)2·6H2O is 10:0.7:1.2.

[0132] B. Preparation of the green body

[0133] Mix 100g of silicon powder, 5.2g of aluminum nitride powder, 5.2g of sintering aid, and 2.4g of sodium dodecylbenzenesulfonate. After stirring evenly, add 5g of polymethyl methacrylate and 2.2g of polyethylene glycol 2000 to obtain a mixture. Add all of the mixture to 138.9g of titanium sol and stir at 1200rpm for 40min under a nitrogen atmosphere. Then, ball mill for 2.2h at a ball-to-material ratio of 5:1 and a ball milling speed of 280rpm. Add 10.5g of methyltrimethoxysilane solution and continue ball milling for 35min. Place the mixture in a mold and let it stand at 30℃ for 12h. After drying, obtain the green body.

[0134] The sintering aid is a mixture of yttrium oxide and samarium oxide, with a mass ratio of yttrium oxide to samarium oxide of 1:1.3;

[0135] The methyltrimethoxysilane solution is a mixture of methyltrimethoxysilane and anhydrous ethanol, wherein the mass ratio of methyltrimethoxysilane to anhydrous ethanol is 5.5:5.

[0136] C. Sintering

[0137] The billet was placed in a muffle furnace and heated to 310°C at a rate of 1.8°C / min under a nitrogen atmosphere, and held for 1.2 hours. Then, the temperature was increased to 605°C at a rate of 2.0°C / min and held for 1.6 hours. Next, under an ammonia atmosphere, the ammonia flow rate was controlled at 1.2 L / min, and the temperature was increased to 1460°C at a rate of 3.3°C / min. Then, the temperature was increased to 1570°C at a rate of 1.2°C / min and held for 3.6 hours. Finally, the temperature was decreased to 1210°C at a rate of 5.2°C / min. The furnace was then switched to a nitrogen atmosphere and decreased to 805°C at a rate of 5.2°C / min. The billet was then allowed to cool naturally to room temperature to obtain the primary cover.

[0138] (2) Surface sealing

[0139] A. Preparation of sealing slurry

[0140] 43g of lithium aluminum silicon microcrystalline glass precursor powder was added to 80g of deionized water and stirred evenly. Then, 8g of additive was added and ultrasonically dispersed for 3.0h. The ultrasonic power was 105W and the ultrasonic frequency was 35kHz. After ultrasonic dispersion, the mixture was allowed to stand at room temperature for 6.5h to obtain the first sealing slurry.

[0141] 28g of lithium aluminum silicon microcrystalline glass precursor powder was added to 80g of deionized water and stirred evenly. Then, 8g of additive was added and ultrasonically dispersed for 3.0h. The ultrasonic power was 105W and the ultrasonic frequency was 35kHz. After ultrasonic dispersion, the mixture was allowed to stand at room temperature for 6.5h to obtain the second sealing slurry.

[0142] The preparation method of the lithium aluminum silicon microcrystalline glass precursor powder is as follows: 29g of tetraethyl orthosilicate and 73g of anhydrous ethanol are mixed and stirred evenly to obtain solution one; 2.0mL of 66wt% nitric acid solution, 20g of deionized water and 10mL of anhydrous ethanol are mixed and stirred evenly, and then added to 102g of solution one. After the addition is completed, the temperature is raised to 72℃ and stirred for 2.6h to obtain silica sol; 82g of deionized water is raised to 43℃, 32g of Al(NO3)3·9H2O and 12g of LiNO3 are added, stirred evenly, and then added to 124g of silica sol. The mixture is stirred in a water bath at 53℃ for 16h, then allowed to stand at 43℃ for 23h, dried, and then the temperature is raised to 354℃ and held for 1.8h. The temperature is then raised to 660℃ at a rate of 3.0℃ / min and held for 3.2h. After cooling, the lithium aluminum silicon microcrystalline glass precursor powder is obtained.

[0143] The additive is a mixture of titanium dioxide and calcium oxide, wherein the mass ratio of titanium dioxide to calcium oxide is 1:1.3;

[0144] B. Scraping

[0145] A sealing slurry is applied to the surface of the primary radome. The first sealing slurry is applied twice. After each application, the radome is heat-treated at 385°C for 0.7 hours to control the thickness of the first sealing slurry layer penetrating the primary radome to 25 μm. Then, the second sealing slurry is applied, and after each application, the radome is heat-treated at 385°C for 0.7 hours to control the thickness of the second sealing slurry layer penetrating the primary radome to 35 μm. After the coating is completed, the radome is kept at 655°C for 3.2 hours and then allowed to cool naturally to room temperature to obtain the main radome body.

[0146] 2. Preparation of the heat-insulating inner cover

[0147] Tetraethyl orthosilicate, anhydrous ethanol, and 36 wt% hydrochloric acid solution were mixed and stirred evenly to obtain the first sol impregnation solution. The quartz fiber preform and 14 times the mass of the first sol impregnation solution were placed in a vacuum impregnation tank for vacuum impregnation. The impregnation pressure was controlled at -0.075 MPa, the impregnation time was 90 min, the mixture was allowed to stand at 47℃ for 4.2 h, aged at 58℃ for 23 h, and then supercritically dried. The drying medium was carbon dioxide, the drying temperature was 320℃, and the drying pressure was 12 MPa to obtain the heat-insulating inner cover.

[0148] The quartz fiber preform has a density of 0.25 g / cm³. 3 ;

[0149] In the first sol-impregnation solution, the molar ratio of tetraethyl orthosilicate, anhydrous ethanol, and hydrochloric acid solution is 5:10:1.2.

[0150] 3. Fabrication of the outer heat insulation ring

[0151] Tetraethyl orthosilicate, anhydrous ethanol, and 36 wt% hydrochloric acid solution were mixed and stirred until homogeneous to obtain a second sol-impregnation solution. The alumina fiber preform and 14 times the mass of the second sol-impregnation solution were placed in a vacuum impregnation tank for vacuum impregnation. The impregnation pressure was controlled at -0.075 MPa, the impregnation time was 90 min, the mixture was allowed to stand at 47℃ for 4.2 h, aged at 58℃ for 23 h, and then supercritically dried using carbon dioxide as the drying medium at 320℃ and 12 MPa to obtain the outer heat insulation ring.

[0152] The alumina fiber preform has a density of 0.33 g / cm³. 3 ;

[0153] In the second sol-impregnation solution, the molar ratio of tetraethyl orthosilicate, anhydrous ethanol, and hydrochloric acid solution is 5:10:1.2.

[0154] 4. Connection

[0155] The main radome body and the end cap are connected by threads, and adhesive is applied in the middle. The bonding area is sandblasted to a surface roughness of 7.5. Adhesive is applied to both sides. The end cap is screwed into the middle of the small end face of the main radome body, with the outer surfaces aligned and the end face gap less than 0.2mm. It is then cured at 172℃ for 2.2h. The main radome body is bonded to the inner heat insulation cover and the outer heat insulation ring using aluminum dihydrogen phosphate solution adhesive with a bonding thickness of 0.25mm, resulting in a combined silicon nitride ceramic radome.

[0156] The end cap is made of silicon nitride ceramic, and the density of the silicon nitride ceramic is 3.3 g / cm³. 3 Its bending strength is 780 MPa and its dielectric constant is 5.8;

[0157] The adhesive is prepared by mixing 2.3g of deionized water, 0.6g of 5.2wt% hydrochloric acid solution and 16g of anhydrous ethanol to obtain an aqueous hydrochloric acid solution; mixing 23g of tetraethyl orthosilicate, 12g of α,ω-dihydroxypolydimethylsiloxane, 3.2g of KH560 silane coupling agent and 12g of anhydrous ethanol to obtain an aqueous hydrochloric acid solution; adding 18.9g of the aqueous hydrochloric acid solution at 0℃; stirring at 43℃ for 1.7h; adding 0.22g of stannous octoate; and stirring at room temperature for 37min to obtain the adhesive.

[0158] The mass concentration of the aluminum dihydrogen phosphate solution is 56%.

[0159] Comparative Example

[0160] The changes made in Example 2 are as follows:

[0161] 1. Fabrication of the main radome body

[0162] (1) In the preparation of the primary cover

[0163] The step of preparing titanium sol is omitted;

[0164] The steps for preparing the green body are as follows: 100g of silicon powder, 5.0g of aluminum nitride powder, 5.0g of sintering aid yttrium oxide and 2.0g of sodium dodecylbenzenesulfonate are mixed and stirred evenly. Then, 12g of polymethyl methacrylate and 2.0g of polyethylene glycol 2000 are added to obtain a mixture. The mixture is placed in a mold and left to stand at 28°C for 14 hours. After drying, the green body is obtained.

[0165] The sintering process is exactly the same as in Example 2;

[0166] (2) Surface sealing

[0167] The sealing slurry is silica sol, and the silica sol has a mass content of 36 wt%.

[0168] A sealing slurry is applied to the surface of the primary radome. After each application, the radome is heat-treated at 380°C for 0.8 hours to control the thickness of the sealing slurry layer penetrating into the primary radome to be 40 μm. After the application is completed, the radome is kept at 650°C for 3.0 hours and then allowed to cool naturally to room temperature to obtain the main radome body.

[0169] 2. Preparation of the heat-insulating inner cover

[0170] The operation is exactly the same as in Example 2;

[0171] 3. Fabrication of the outer heat insulation ring

[0172] The operation is exactly the same as in Example 2;

[0173] 4. Connection

[0174] The operation is exactly the same as in Example 2.

[0175] Performance testing

[0176] The performance of the combined silicon nitride ceramic radomes prepared in Examples 1-3 and Comparative Example 2 was tested, as follows:

[0177] 1. Basic performance

[0178] (1) The densities of the primary covers prepared in Examples 1-3 and the comparative examples were tested, and the results are as follows:

[0179]

[0180] (2) The bending strength, Mohs hardness, thermal conductivity, dielectric constant and fracture toughness of the combined silicon nitride ceramic radomes prepared in Examples 1-3 and the comparative examples were tested. The test results are as follows:

[0181]

[0182] 2. Rain erosion resistance

[0183] The combined silicon nitride ceramic radomes prepared in Examples 1-3 and the comparative examples were sprayed with deionized water. The water droplet size was controlled at 4.0 mm, the spraying distance at 100 mm, the temperature at 10 °C, the spraying speed at 400 m / s, the spraying angle at 90 °C, the spraying intensity at 70 mm / h, and the spraying time at 12 h. The bending strength and fracture toughness of the combined silicon nitride ceramic radomes were tested, and the test results are as follows:

[0184]

[0185] As shown in the table above, the comparative example omitted the titanium sol step in the preparation of the main radome body and omitted methyltrimethoxysilane in the preparation of the green body. The resulting green body has low strength and a loose structure. During sintering, it is prone to severe volume expansion, forming irregular large pores, which reduces the density of the primary radome body. This results in a lower initial dielectric constant and thermal conductivity. However, under high temperature conditions, the dielectric and thermal conductivity of the comparative example deteriorate rapidly, thus reducing the overall performance of the product. Furthermore, in the rain erosion resistance test, the comparative example showed poor stability, with its strength and toughness decreasing sharply, ultimately shortening the product's service life.

[0186] Unless otherwise stated, all percentages used in this invention are mass percentages.

[0187] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of manufacturing a combined silicon nitride ceramic radome, characterized by, The method comprises a preparation of a main cover body of the radome, a preparation of a heat-insulating inner cover, a preparation of an outer heat-insulating ring and a connecting step; The preparation of the main cover body of the radome comprises a preparation of a primary cover body and a surface sealing step; The preparation of the primary cover body comprises a preparation of a titanium sol, a preparation of a blank and a sintering step; The preparation of the blank comprises the following steps: mixing silicon powder, aluminum nitride powder, a sintering aid and sodium dodecyl benzene sulfonate, uniformly stirring, adding polymethyl methacrylate and polyethylene glycol 2000 to obtain a mixture; adding the mixture into the titanium sol, stirring at 900-1200 rpm for 30-40 min under a nitrogen atmosphere, then ball milling for 1.8-2.2 h, adding a methyltrimethoxysilane solution, continuously ball milling for 26-35 min, then placing in a mold for standing, drying to obtain the blank; The surface sealing comprises a preparation of a sealing slurry and a scraping step; The preparation of the sealing slurry comprises the following steps: adding lithium-aluminum-silicon glass-ceramic precursor powder into deionized water, adding an additive, ultrasonic dispersion and standing to obtain a first sealing slurry; adding lithium-aluminum-silicon glass-ceramic precursor powder into deionized water, adding an additive, ultrasonic dispersion and standing to obtain a second sealing slurry; In the first sealing slurry, the mass ratio of lithium-aluminum-silicon glass-ceramic precursor powder, deionized water and the additive is 37-43:80:4-8; In the second sealing slurry, the mass ratio of lithium-aluminum-silicon glass-ceramic precursor powder, deionized water and the additive is 22-28:80:4-8; The preparation method of the lithium-aluminum-silicon glass-ceramic precursor powder comprises the following steps: mixing tetraethyl orthosilicate and anhydrous ethanol, uniformly stirring to obtain a solution one; mixing nitric acid solution, deionized water and anhydrous ethanol, uniformly stirring, then adding into the solution one, stirring at 68-72℃ for 2.3-2.6 h to obtain a silicon sol; increasing the temperature of the deionized water to 38-43℃, adding Al(NO3)3·9H2O and LiNO3, uniformly stirring, then adding into the silicon sol, stirring at 48-53℃ for 14-16 h, standing at 37-43℃ for 23-26 h, drying and calcining to obtain the lithium-aluminum-silicon glass-ceramic precursor powder; The scraping step comprises the following steps: scraping the sealing slurry on the surface of the primary cover body, scraping the first sealing slurry for the first time and the second time, heat treating at 375-385℃ for 0.7-1.0 h after single scraping, controlling the thickness of the first sealing slurry layer penetrating into the primary cover body to be 10-25 μm, then scraping the second sealing slurry, heat treating at 375-385℃ for 0.7-1.0 h after single scraping, controlling the thickness of the second sealing slurry layer penetrating into the primary cover body to be 10-35 μm, after the scraping is completed, heat treating at 645-655℃ for 2.8-3.2 h, naturally cooling to room temperature to obtain the main cover body of the radome; The preparation of the heat-insulating inner cover comprises the following steps: mixing tetraethyl orthosilicate, anhydrous ethanol and 34-36 wt% hydrochloric acid solution, uniformly stirring to obtain a first sol impregnating solution; placing a quartz fiber preform and 10-14 times the mass of the first sol impregnating solution into a vacuum impregnation tank for vacuum impregnation, aging and drying to obtain the heat-insulating inner cover. The preparation of the outer thermal insulation ring is mixing tetraethyl orthosilicate, anhydrous ethanol and 34-36wt% hydrochloric acid solution, stirring uniformly to obtain a second sol impregnating solution; placing the alumina fiber preform and 10-14 times the mass of the second sol impregnating solution into a vacuum impregnation tank for vacuum impregnation, aging and drying to obtain the outer thermal insulation ring.

2. The preparation method of the combined silicon nitride ceramic radome according to claim 1, characterized in that, The preparation of the titanium sol is adding tetrabutyl titanate into anhydrous ethanol, stirring at 34-36℃ for 28-32min, adding mixed nitric acid solution, controlling the adding time to be 18-23min, stirring at 34-36℃ for 1.5-2.0h after the adding is completed, and obtaining the titanium sol; The mass ratio of the anhydrous ethanol, tetrabutyl titanate and mixed nitric acid solution is 100:22-27:11.3-11.9; The mixed nitric acid solution is a mixture of deionized water, 65wt% nitric acid solution and Ni(NO3)2·6H2O, and the mass ratio of the deionized water, 65wt% nitric acid solution and Ni(NO3)2·6H2O is 10:0.5-0.7:0.8-1.

2.

3. The preparation method of the combined silicon nitride ceramic radome according to claim 1, characterized in that, In the preparation of the green body, the mass ratio of the silicon powder, aluminum nitride powder, sintering aid, sodium dodecylbenzenesulfonate, polymethyl methacrylate and polyethylene glycol 2000 is 100:4.8-5.2:4.5-5.2:1.7-2.4:5-20:1.8-2.2; The sintering aid is a mixture of yttrium oxide and samarium oxide, and the mass ratio of the yttrium oxide and samarium oxide is 1:0.8-1.3; The mass ratio of the silicon powder, titanium sol and methyltrimethoxysilane solution is 100:133.3-138.9:9.5-10.5; The methyltrimethoxysilane solution is a mixture of methyltrimethoxysilane and anhydrous ethanol, and the mass ratio of the methyltrimethoxysilane and anhydrous ethanol is 4.5-5.5:

5.

4. The preparation method of the combined silicon nitride ceramic radome according to claim 1, characterized in that, The sintering is placing the green body into a muffle furnace, increasing the temperature to 290-310℃ at a rate of 1.2-1.8℃ / min under a nitrogen atmosphere, keeping the temperature for 0.8-1.2h, then increasing the temperature to 595-605℃ at a rate of 2.0-3.0℃ / min, keeping the temperature for 1.4-1.6h, then increasing the temperature to 1430-1460℃ at a rate of 2.8-3.3℃ / min under an ammonia atmosphere with the ammonia flow being controlled to be 0.8-1.2L / min, increasing the temperature to 1530-1570℃ at a rate of 0.8-1.2℃ / min, keeping the temperature for 3.3-3.6h, decreasing the temperature to 1185-1210℃ at a rate of 4.7-5.2℃ / min, switching to a nitrogen atmosphere, decreasing the temperature to 795-805℃ at a rate of 4.7-5.2℃ / min, and naturally cooling to room temperature to obtain the primary radome body.

5. The preparation method of the combined silicon nitride ceramic radome according to claim 1, wherein, in the surface sealing step, the additive is a mixture of titanium oxide and calcium oxide, and the mass ratio of the titanium oxide to the calcium oxide is 1:0.8-1.3; in the preparation method of the lithium aluminum silicon glass-ceramic precursor powder, the mass ratio of the tetraethyl orthosilicate to the anhydrous ethanol is 28-29:68-73; in the preparation method of the lithium aluminum silicon glass-ceramic precursor powder, the mass ratio of the tetraethyl orthosilicate to the anhydrous ethanol is 28-29:68-73; in the preparation method of the lithium aluminum silicon glass-ceramic precursor powder, the mass ratio of the tetraethyl orthosilicate to the anhydrous ethanol is 28-29:68-73.

6. The preparation method of the combined silicon nitride ceramic radome according to claim 1, wherein, in the preparation of the heat-insulating inner cover, tetraethyl orthosilicate, anhydrous ethanol and 34-36wt% hydrochloric acid solution are mixed, stirred uniformly, and then a first sol impregnating solution is obtained; a quartz fiber preform and 10-14 times the mass of the first sol impregnating solution are placed into a vacuum impregnation tank for vacuum impregnation, the impregnation pressure is controlled to be-0.075~ -0.085MPa, the impregnation time is 70-90min, the temperature is kept at 43-47℃ for 3.8-4.2h, the temperature is kept at 52-58℃ for 23-26h, supercritical drying is performed, the drying medium is carbon dioxide, the drying temperature is 280-320℃, the drying pressure is 8-12MPa, and then the heat-insulating inner cover is obtained; The quartz fiber preform has a density of 0.20-0.25 g / cm 3 ; in the first sol impregnating solution, the molar ratio of the tetraethyl orthosilicate to the anhydrous ethanol to the hydrochloric acid solution is 3-5:6-10:0.8-1.

2.

7. The preparation method of the combined silicon nitride ceramic radome according to claim 1, wherein, in the preparation of the outer heat-insulating ring, tetraethyl orthosilicate, anhydrous ethanol and 34-36wt% hydrochloric acid solution are mixed, stirred uniformly, and then a second sol impregnating solution is obtained; an alumina fiber preform and 10-14 times the mass of the second sol impregnating solution are placed into a vacuum impregnation tank for vacuum impregnation, the impregnation pressure is controlled to be-0.075~ -0.085MPa, the impregnation time is 70-90min, the temperature is kept at 43-47℃ for 3.8-4.2h, the temperature is kept at 52-58℃ for 23-26h, supercritical drying is performed, the drying medium is carbon dioxide, the drying temperature is 280-320℃, the drying pressure is 8-12MPa, and then the outer heat-insulating ring is obtained; The alumina fiber preform has a density of 0.28-0.33 g / cm 3 ; in the second sol impregnating solution, the molar ratio of the tetraethyl orthosilicate to the anhydrous ethanol to the hydrochloric acid solution is 3-5:6-10:0.8-1.

2.

8. The preparation method of the combined silicon nitride ceramic radome according to claim 1, wherein, The connecting step is that the radome main cover body and the end cap are connected by threads, and adhesive is applied in the middle, the bonding area is sandblasted to a surface roughness of 7.0-7.5, the adhesive is applied on both sides, the end thread is screwed into the middle of the small end face of the radome main cover body, the contour surface is aligned, the end face gap is less than 0.2mm, 168-172℃ heat preservation and curing for 1.8-2.2h, the radome main cover body and the heat-insulating inner cover and the outer heat-insulating ring are bonded by using aluminum dihydrogen phosphate solution adhesive, the bonding thickness is 0.20-0.25mm, and a combined silicon nitride ceramic radome is obtained. The end cap is silicon nitride ceramic, the density of the silicon nitride ceramic is 2.8-3.3 g / cm 3 , the bending strength is 760-780 MPa, and the dielectric constant is 5.8-6.2; The preparation method of the adhesive is that deionized water, hydrochloric acid solution and 13-16g of anhydrous ethanol are uniformly mixed to obtain a hydrochloric acid aqueous solution; tetraethyl orthosilicate, alpha, omega-dihydroxy polydimethylsiloxane, kH560 silane coupling agent and anhydrous ethanol are uniformly mixed, the hydrochloric acid aqueous solution is added at 0-2℃, stirring is carried out at 38-43℃ for 1.7-2.3h, stannous octoate is added, stirring is carried out at room temperature for 30-37min, and the adhesive is obtained; The mass ratio of the deionized water, 4.8-5.2wt% hydrochloric acid solution and anhydrous ethanol is 1.8-2.3:0.4-0.6:13-16; The mass ratio of the tetraethyl orthosilicate, alpha, omega-dihydroxy polydimethylsiloxane, kH560 silane coupling agent, anhydrous ethanol, hydrochloric acid aqueous solution and stannous octoate is 18-23:8-12:2.7-3.2:8-12:15.2-18.9:0.18-0.22; The mass concentration of the aluminum dihydrogen phosphate solution is 54-56%.

9. A combined silicon nitride ceramic radome, characterized by, Prepared by the preparation method in any one of claims 1-8.

Images