A ceramic radome material and a method for manufacturing the same
By preparing a Si3N4-Si composite preform with a shell-like nacreous layered structure and forming a Si3N4 fiber network filling layer, the problems of lightweighting and strengthening of silicon nitride radome materials were solved, and the material performance of hypersonic vehicles was improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- UNIV OF SCI & TECH BEIJING
- Filing Date
- 2024-04-30
- Publication Date
- 2026-07-24
AI Technical Summary
Existing silicon nitride radome materials are insufficient in terms of lightweighting and toughness, making it difficult to meet the high-performance requirements of hypersonic vehicles.
A ceramic radome material with high open porosity and high fracture toughness was prepared by using a nitrided Si3N4-Si composite preform with a shell-like nacreous layered structure, forming a Si3N4 fiber network filling layer through high-temperature in-situ nitriding, and interleaving dense layers and filling layers. Combined with mechanical stirring, directional freezing, vacuum drying and nitriding heat treatment processes.
The material achieves lightweighting and improved mechanical properties, with an apparent porosity of 36.0–76.0%, a bulk density of 1.5–2.6 g/cm³, a compressive strength of 50–150 MPa, and a fracture toughness of 4.6–6.9 MPa·m¹/², making it suitable for hypersonic vehicles.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of radome technology, and particularly relates to a ceramic radome material and its preparation method. Background Technology
[0002] Silicon nitride radomes are important thermal structural materials widely used in missile warhead radomes. Due to their outstanding wave transmission, dielectric properties, and mechanical properties, they have become the preferred material for high-performance missile radomes. In recent years, with the rapid development of hypersonic missiles, the service environment of radome components has significantly deteriorated. Under these conditions, radome materials must possess characteristics such as lightweight, high strength, and high toughness to meet the requirements of hypersonic missile flight.
[0003] Traditional research on silicon nitride radome materials mainly focuses on sintering and molding processes, and the toughening methods are mainly through external or in-situ fiber formation. As a result, the various phases and structures in the prepared radome materials have not achieved the maximum toughening effect.
[0004] Patents with application numbers CN200910150098.8 and CN200610070747.X disclose two methods for preparing low dielectric constant, high strength porous silicon nitride wave-transparent ceramics. The core process uses silicon nitride powder and other oxide powders as the main raw materials and a pore-forming agent to increase its porosity. However, the pore structure formed by the pore-forming agent does not benefit the toughness of the material. While achieving the lightweighting of the radome, it also reduces the mechanical properties of the material.
[0005] Patents with application numbers CN201310309109.9 and CN202010089310.0 disclose two methods for preparing fiber-reinforced silicon nitride transparent ceramics. The core technology involves dispersing fibers within a silicon nitride matrix through in-situ deposition or external impregnation, thereby enhancing mechanical properties. These radome materials optimize the mechanical properties and fracture toughness of the radome solely from the perspective of fiber reinforcement, achieving a relatively good improvement, but they do not contribute to the lightweighting of the radome material.
[0006] Therefore, to achieve lightweighting while maximizing its toughness, further development of new technologies is needed to meet the higher requirements of practical applications. Summary of the Invention
[0007] To address the shortcomings of existing technologies, this invention provides a ceramic radome material and its preparation method. The silicon nitride ceramic radome material prepared by this invention features high open porosity, lightweight, and high fracture toughness. The preparation process is simple, and it can improve the mechanical properties and fracture toughness of the radome material while reducing its weight, showing promising application prospects in fields such as hypersonic vehicles.
[0008] To achieve the above objectives, the present invention adopts the following technical solution.
[0009] A ceramic radome material has a structure that mimics the layered structure of a pearl shell. After high-temperature in-situ nitriding of a Si3N4-Si composite preform, a Si3N4 fiber network filling layer is formed in-situ between the dense Si3N4 sintering layers. The dense layers and the filling layers are arranged alternately. The thickness of the dense layer is 50-200 μm, the thickness of the filling layer is 10-100 μm, and the thickness of the radome material is 5-15 cm.
[0010] The obtained ceramic radome material has an apparent porosity of 36.0–76.0% and a bulk density of 1.5–2.6 g / cm³. 3 The compressive strength is 50–150 MPa, and the fracture toughness is 4.6–6.9 MPa·m. 1 / 2 .
[0011] The above-mentioned method for preparing ceramic radome material involves first dispersing 20-80 parts of silicon nitride powder, 40-90 parts of elemental silicon powder, 0.2-0.5 parts of sintering aid, 1-3 parts of binder, and 0.01-0.05 parts of surfactant in a solvent to form a suspension with a solid content of 30-60 wt%. Subsequently, the ceramic radome material is obtained by mechanical stirring, vacuum degassing, directional freezing, demolding, vacuum drying, and nitriding heat treatment.
[0012] Furthermore, the silicon nitride powder has a particle size of 0.5–10 μm and a purity of Si3N4 ≥ 99 wt%; the elemental silicon powder has a diameter of 1–5 μm and a purity of Si ≥ 98 wt%.
[0013] Furthermore, the sintering aid is one or more of alumina micro powder, magnesium oxide micro powder, and yttrium oxide micro powder; the alumina micro powder has a particle size ≤1μm, the magnesium oxide micro powder has a particle size ≤1μm, and the yttrium oxide micro powder has a particle size ≤1μm.
[0014] Furthermore, the adhesive is one or more of polyvinyl alcohol, polyethylene glycol, and carrageenan.
[0015] Furthermore, the solvent is one or more of deionized water, camphene, tert-butanol, and glycerol.
[0016] Furthermore, the surfactant is one or more of ammonium polyacrylate, polyacrylamide, polyacrylate, tetramethylammonium hydroxide, and hexadecyltrimethylammonium bromide.
[0017] Furthermore, the pressure of high-purity nitrogen gas during the nitriding heat treatment process is 0.5–2 MPa, and the heat treatment temperature is 1700–1900 °C.
[0018] The method for preparing the ceramic radome material as described above includes the following steps:
[0019] ① The raw materials and their contents of the ceramic radome material are prepared by mixing the silicon nitride powder, elemental silicon powder, binder, adhesive, surfactant and solvent by ball milling for 1 to 6 hours to prepare a suspension; the pH of the suspension is adjusted to between 6 and 8, and then the suspension is vacuum defoamed at a speed of 100 to 1000 rpm for 3 to 20 minutes to obtain a uniform suspension;
[0020] ② The uniform suspension is poured into a directional freezing mold and frozen for 0.5 to 2 hours to obtain a frozen suspension; then it is dried at 25°C and -0.1MPa vacuum for 2 to 4 days to obtain a porous ceramic blank;
[0021] ③ The porous ceramic blank is placed in an atmosphere furnace, nitrogen is passed through it at a set flow rate, and the temperature is raised to 1700-1900℃ and held for 2-5 hours to obtain the ceramic radome material.
[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0023] 1. First, this invention uses silicon nitride powder and elemental silicon powder as the main raw materials. Silicon nitride radome materials are prepared by preparing a suspension, defoaming, freeze-drying, and nitriding sintering. The freezing mold can be adjusted according to the radome size, making it suitable for large-scale production. The suspension of fiber-containing silicon nitride and elemental silicon is dispersed in different solvents. The spacing between dry blank layers and the thickness within each layer can be adjusted by controlling the type of solvent and the solid content of the suspension. The number of fibers in the fiber-filled layer during the nitriding sintering process can be adjusted by the ratio of silicon nitride to elemental silicon.
[0024] 2. Current methods for constructing pores in ceramic radome materials involve adding pore-forming agents. While introducing pores can improve lightweight properties, the irregularity of the pores and their inability to achieve a toughening effect prevent the radome material from reaching its maximum strength and toughness. This invention addresses this by reacting elemental silicon with nitrogen during nitriding, depositing a fibrous silicon nitride network filling layer between the layers, forming a biomimetic pearl layer resembling a seashell. In situ, a Si3N4 fiber filling layer is formed between the layers of the in-situ nitrided Si3N4-Si composite preform, achieving alternating construction of soft and hard phases. This ensures both the lightweight nature of the radome material and the construction of a toughening layer. Unvaporized elemental silicon, after reaching its melting point at 1410℃, forms a liquid phase dispersed among the silicon nitride particles, further promoting the sintering of the silicon nitride matrix through liquid-phase mass transfer.
[0025] 3. The biomimetic lightweight silicon nitride ceramic radome material prepared by this invention has low cost and simple processing, making it suitable for large-scale mass production. The product, after testing, has an apparent porosity of 36.0–76.0% and a bulk density of 1.5–2.6 g / cm³. 3 The compressive strength is 50–150 MPa, and the fracture toughness is 4.6–6.9 MPa·m. 1 / 2 The silicon nitride ceramic radome material prepared by this invention has the characteristics of high open porosity, light weight, and high fracture toughness. The preparation process is simple, and it can improve the mechanical properties and fracture toughness of the radome material while reducing its weight. It has great application prospects in hypersonic vehicles and other fields. Attached Figure Description
[0026] Figure 1 The image shows the microstructure of the ceramic radome material prepared in Example 1 of this invention, where a is the microstructure of the radome material after nitriding and sintering, and b and c are the microstructures of the filling layer after further magnification. Detailed Implementation
[0027] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.
[0028] To avoid repetition, the materials involved in this specific implementation method are described uniformly as follows, and will not be repeated in the embodiments:
[0029] In the examples, the selected silicon nitride powder has a particle size of 0.5–10 μm and a purity of Si3N4 ≥ 99 wt%; the elemental silicon powder has a diameter of 1–5 μm and a purity of Si ≥ 98 wt%; the sintering aid is one or more of alumina micro powder, magnesium oxide micro powder, and yttrium oxide micro powder, with a particle size ≤ 1 μm for each of the micro powders; the binder is one or more of polyvinyl alcohol, polyethylene glycol, and carrageenan; the solvent is one or more of deionized water, camphene, tert-butanol, and glycerol; and the surfactant is one or more of ammonium polyacrylate, polyacrylamide, polyacrylate, tetramethylammonium hydroxide, and hexadecyltrimethylammonium bromide.
[0030] Example 1
[0031] A ceramic radome material and its preparation method:
[0032] ① The raw materials and their contents of the ceramic radome material are prepared according to the following steps: First, 35 parts of silicon nitride powder, 50 parts of elemental silicon powder, 0.15 parts of sintering aid alumina micro powder, 1 part of binder polyvinyl alcohol, and 0.01 parts of tetramethylammonium hydroxide are dispersed in a mixed solution of water and glycerol to form a suspension with a solid content of 30 wt%. The suspension is then blended by ball milling at a water-to-glycerol ratio of 8:2 for 1 hour to prepare the suspension. The pH of the suspension is adjusted to 7.0, and then the suspension is vacuum defoamed at 500 rpm for 6 minutes to obtain a uniform suspension.
[0033] ② The uniform suspension is poured into a directional freezing mold and frozen for 0.5 hours to obtain a frozen suspension; then it is dried at 25°C and -0.1MPa vacuum for 3 days to obtain a porous ceramic blank;
[0034] ③ The porous ceramic blank is placed in an atmosphere furnace, nitrogen is passed through it at a set flow rate, and the temperature is raised to 1700°C and held for 2 hours to obtain the ceramic radome material.
[0035] The silicon nitride ceramic radome material prepared in this embodiment was tested and found to have an apparent porosity of 76.0% and a bulk density of 1.5 g / cm³. 3 The compressive strength is 50 MPa, and the fracture toughness is 4.6 MPa·m. 1 / 2 .
[0036] Figure 1 This indicates that after freeze-drying and nitriding sintering, the radome material forms a layered structure similar to the nacreous layers of a seashell, with dense silicon nitride sintered layers and in-situ formed silicon nitride fiber filling layers arranged alternately.
[0037] Example 2
[0038] A ceramic radome material and its preparation method:
[0039] ① The raw materials and their contents of the ceramic radome material are prepared according to the following steps: First, 70 parts of silicon nitride powder, 85 parts of elemental silicon powder, 0.3 parts of magnesium oxide micro powder (sintering aid), 2 parts of polyethylene glycol (binder), and 0.03 parts of ammonium polyacrylate are dispersed in a mixed solution of camphene and tert-butanol to form a suspension with a solid content of 50 wt%. The suspension is then blended by ball milling with water and camphene at a ratio of 5:5 for 3 hours to prepare the suspension. The pH of the suspension is adjusted to 8.0, and then the suspension is vacuum defoamed at a speed of 1000 rpm for 15 minutes to obtain a uniform suspension.
[0040] ② The uniform suspension is poured into a directional freezing mold and frozen for 1 hour to obtain a frozen suspension; then it is dried at 25°C and -0.1MPa vacuum for 3 days to obtain a porous ceramic blank;
[0041] ③ The porous ceramic blank is placed in an atmosphere furnace, nitrogen is passed through it at a set flow rate, and the temperature is raised to 1900°C and held for 4 hours to obtain the ceramic radome material.
[0042] The silicon nitride ceramic radome material prepared in this embodiment was tested and found to have an apparent porosity of 46.0% and a bulk density of 2.6 g / cm³. 3 The compressive strength is 140 MPa, and the fracture toughness is 6.8 MPa·m. 1 / 2 .
[0043] Example 3
[0044] A ceramic radome material and its preparation method:
[0045] ① The raw materials and their contents of the ceramic radome material are prepared according to the following steps: First, 70 parts of silicon nitride powder, 80 parts of elemental silicon powder, 0.5 parts of sintering aid alumina micro powder, 2.5 parts of binder carrageenan, and 0.04 parts of polyacrylamide are dispersed in a mixed solution of water and tert-butanol to form a suspension with a solid content of 55 wt%. The suspension is then blended by ball milling at a water-to-tert-butanol ratio of 6:4 for 6 hours to prepare the suspension. The pH of the suspension is adjusted to 7.5, and then the suspension is vacuum defoamed at 800 rpm for 14 minutes to obtain a uniform suspension.
[0046] ② The uniform suspension is poured into a directional freezing mold and frozen for 2 hours to obtain a frozen suspension; then it is dried at 25°C and -0.1MPa vacuum for 4 days to obtain a porous ceramic blank;
[0047] ③ The porous ceramic blank is placed in an atmosphere furnace, nitrogen is passed through it at a set flow rate, and the temperature is raised to 1850°C and held for 5 hours to obtain the ceramic radome material.
[0048] The silicon nitride ceramic radome material prepared in this embodiment was tested and found to have an apparent porosity of 46.0% and a bulk density of 2.3 g / cm³. 3 The compressive strength is 120 MPa, and the fracture toughness is 6.0 MPa·m. 1 / 2 .
Claims
1. A method for preparing a ceramic radome material, characterized in that, First, 20-80 parts of silicon nitride powder, 40-90 parts of elemental silicon powder, 0.2-0.5 parts of sintering aid, 1-3 parts of binder, and 0.01-0.05 parts of surfactant are dispersed in a solvent to form a suspension with a solid content of 30-60 wt%. Then, through mechanical stirring, vacuum degassing, directional freezing, demolding, vacuum drying, and nitriding heat treatment, the ceramic radome material is obtained. The directional freezing process involves pouring a well-stirred suspension into a directional freezing mold and freezing it for 0.5 to 2 hours to obtain a frozen suspension. This suspension is then dried at 25°C and a vacuum of -0.1 MPa for 2 to 4 days to obtain a porous ceramic blank. The nitriding heat treatment involves placing the porous ceramic blank in an atmosphere furnace, passing nitrogen gas at a set flow rate (0.5 to 2 MPa), and simultaneously raising the temperature to 1700 to 1900°C and holding it there for 2 to 5 hours. The ceramic radome material has a shell-like nacreous layered structure. After high-temperature in-situ nitriding of the Si3N4-Si composite preform, a Si3N4 fiber network filling layer is formed in-situ between the dense Si3N4 sintering layers. The dense layer and the filling layer are arranged alternately. The thickness of the dense layer is 50~200μm, the thickness of the filling layer is 10~100μm, and the thickness of the radome material is 5~15 cm.
2. The method for preparing the ceramic radome material according to claim 1, characterized in that, The material has an apparent porosity of 36.0–76.0% and a bulk density of 1.5–2.6 g / cm³. 3 The compressive strength is 50~150 MPa, and the fracture toughness is 4.6~6.9 MPa·m. 1 / 2 .
3. The method for preparing the ceramic radome material according to claim 1, characterized in that, The silicon nitride powder has a particle size of 0.5~10 μm and a purity of Si3N4≥99wt%; the elemental silicon powder has a diameter of 1~5 μm and a purity of Si≥98wt%.
4. The method for preparing the ceramic radome material according to claim 1, characterized in that, The sintering aid is one or more of alumina micro powder, magnesium oxide micro powder, and yttrium oxide micro powder; the alumina micro powder has a particle size ≤1μm, the magnesium oxide micro powder has a particle size ≤1μm, and the yttrium oxide micro powder has a particle size ≤1μm.
5. The method for preparing the ceramic radome material according to claim 1, characterized in that, The adhesive is one or more of polyvinyl alcohol, polyethylene glycol, and carrageenan.
6. The method for preparing the ceramic radome material according to claim 1, characterized in that, The solvent is one or more of deionized water, camphene, tert-butanol, and glycerol.
7. The method for preparing the ceramic radome material according to claim 1, characterized in that, The surfactant is one or more of the following: ammonium polyacrylate, polyacrylamide, polyacrylate, tetramethylammonium hydroxide, and hexadecyltrimethylammonium bromide.
8. The method for preparing the ceramic radome material according to claim 1, characterized in that, The mechanical stirring involves mixing the silicon nitride powder, elemental silicon powder, binder, surfactant, and solvent by ball milling for 1 to 6 hours to prepare a suspension.
9. The method for preparing the ceramic radome material according to claim 1, characterized in that, The vacuum defoaming process involves adjusting the pH of the suspension to between 6 and 8, then subjecting the suspension to vacuum defoaming at a speed of 100 to 1000 rpm for 3 to 20 minutes to obtain a uniform suspension.