Preparation method of mullite-based closed-cell fibrous thermal insulation material with electromagnetic wave absorption performance

Abstract

A method for preparing a mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties is disclosed. The method uses aluminum sec-butoxide and polymethylhydrosiloxane as precursors, isopropanol, N,N-dimethylformamide, and ethyl acetoacetate as solvents, polyvinylpyrrolidone as a spinning aid, and SiC hollow spheres as a pore-forming agent, infrared shielding agent, and wave-absorbing agent, respectively. The material is prepared by electrospinning, curing crosslinking, and high-temperature pyrolysis. This invention effectively solves the problems of insufficient thermal conductivity and limited functionality of existing mullite fiber thermal insulation materials, making it suitable for high-temperature thermal protection and stealth protection of ultra-high-speed aircraft in aerospace and military fields.

Description

Technical Field

[0001] This invention relates to the field of ceramic fiber materials technology, specifically to a method for preparing a mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties. Background Technology

[0002] As hypersonic aircraft, represented by supersonic fighter jets and missiles, continue to develop towards higher Mach numbers and longer endurance, they not only have to endure increasingly severe aerodynamic heating phenomena, but also face the danger of enemy radar detection. This places higher demands on the performance of high-temperature thermal protection materials and radar-absorbing stealth protection materials for hypersonic aircraft.

[0003] Mullite ceramic fiber is lightweight, exhibits excellent high-temperature thermal stability, and low thermal conductivity, making it a crucial raw material for preparing high-temperature thermal protection materials for hypersonic vehicles, such as ceramic fiber insulation felts and tiles. However, mullite fiber is transparent in the ~2.5-7μm infrared range, resulting in high infrared thermal radiation at high temperatures and a significant increase in thermal conductivity, severely impacting its thermal insulation performance. Furthermore, mullite fiber currently has a limited function, primarily used as a thermal insulation material. As hypersonic vehicles face increasingly complex application environments, single-function thermal protection materials are becoming increasingly inadequate to meet the demands.

[0004] The traditional approach to high-temperature thermal protection and stealth protection for hypersonic vehicles involves developing separate high-temperature thermal protection materials and radar-absorbing stealth materials. This typically involves using these materials separately, which not only adds to the vehicle's weight but also contradicts the increasingly lightweight development trend of hypersonic vehicles. Therefore, addressing the challenge of the drastic increase in thermal conductivity of mullite fiber materials at high temperatures while simultaneously endowing them with electromagnetic wave absorption properties—achieving integrated high-temperature thermal protection and radar-absorbing stealth protection—is of great significance for the development of hypersonic vehicles. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of the rapid increase in thermal conductivity and limited functionality of mullite fiber insulation materials at high temperatures, and to provide a method for preparing mullite-based closed-cell fiber materials with electromagnetic wave absorption properties and low thermal conductivity at high temperatures, so as to meet the performance requirements of high-temperature thermal protection and wave-absorbing stealth protection materials for hypersonic aircraft, and to realize the integration of high-temperature thermal protection and stealth protection for hypersonic aircraft.

[0006] This invention proposes to prepare a defined mullite-based closed-cell fiber thermal insulation material by using aluminum sec-butoxide and polymethylhydrosiloxane as precursors, isopropanol, N,N-dimethylformamide and ethyl acetoacetate as solvents, polyvinylpyrrolidone as a spinning aid, and SiC hollow spheres as pore-forming agent, infrared shielding agent and microwave absorbing agent, respectively, through electrospinning, curing crosslinking and high-temperature pyrolysis.

[0007] The present invention adopts the following technical solution:

[0008] A mullite closed-cell fiber thermal insulation material with electromagnetic wave absorption effect; characterized in that SiC hollow spheres are uniformly dispersed in mullite sol, and a mullite-based closed-cell fiber thermal insulation material with a closed-cell structure is formed inside the fiber through electrospinning process.

[0009] This invention uses SiC hollow spheres as a pore-forming agent to construct a closed-cell structure that hinders solid-phase heat transfer in the fiber and reduces the fiber's thermal conductivity; it also uses SiC hollow spheres as an infrared shielding agent to shield against high-temperature infrared thermal radiation, thereby improving its heat insulation effect at high temperatures; and it further uses SiC hollow spheres as a microwave absorbing agent to impart microwave absorption properties to the mullite fiber.

[0010] A method for preparing a mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties includes the following steps:

[0011] Step 1: Tetraethyl orthosilicate, deionized water, anhydrous ethanol, and ammonia are mixed and magnetically stirred for 10–48 h. The reaction product is centrifuged, washed, and dried in an oven to obtain SiO2 spheres of different diameters. The prepared SiO2 spheres and polycarbosilane are added to an organic solvent and stirred for 1–4 h. After removing the organic solvent, the sample is pyrolyzed at high temperature under inert gas protection to obtain SiC / SiO2 spheres. Finally, the SiC / SiO2 spheres are placed in an etching solution to remove SiO2 and obtain SiC hollow spheres.

[0012] Step 2: SiC hollow spheres, polyvinylpyrrolidone, aluminum sec-butoxide and polymethylhydrosiloxane are added to a mixed solvent of isopropanol, N,N-dimethylformamide and ethyl acetoacetate, and magnetically stirred for 1 to 3 hours to obtain the spinning solution.

[0013] Step 3: Spin the spinning solution obtained above using electrospinning to obtain a precursor fiber membrane;

[0014] Step 4: The obtained raw fiber membrane is subjected to oxidative crosslinking and high-temperature pyrolysis to obtain mullite-based closed-cell fiber thermal insulation material.

[0015] Furthermore, in step 1, the mass ratio of tetraethyl orthosilicate, deionized water, anhydrous ethanol, and ammonia is 1:(2.8-3.5):(16.2-25.6):(0.8-1.6); the centrifugal washing solvent is deionized water and anhydrous ethanol, respectively, for three washes; the oven drying temperature is 60-80℃, and the holding time is 2-24h.

[0016] Furthermore, in step 1, the organic solvent is one of tetrahydrofuran, xylene, or n-hexane; the mass ratio of SiO2 spheres, polycarbosilane, and organic solvent is 1:(0.4-1.0):(20-30); the high-temperature reaction temperature for preparing SiC / SiO2 spheres is 1000-1350℃, the holding time is 2-10h, and the inert protective atmosphere is one of argon, nitrogen, or helium.

[0017] Furthermore, in step 1, the etching solution is a 10-30 wt% hydrofluoric acid or sodium hydroxide solution, and the etching time is 10-24 h.

[0018] Furthermore, in step 1, the outer diameter of the prepared SiC hollow spheres is 50–2000 nm, and the shell thickness is 5–200 nm.

[0019] Furthermore, in step 2, the mass ratio of the mixed solvent isopropanol, N,N-dimethylformamide, and ethyl acetoacetate is 1:(0.08-0.12):(0.10-0.17); the mass ratio of aluminum sec-butoxide and polymethylhydrosiloxane is 1:(0.05-0.15); and aluminum sec-butoxide accounts for 10-22% of the mass fraction of the mixed solvent.

[0020] Furthermore, in step 2, the amount of SiC hollow spheres added is 3 to 16 wt% of the mass of the mixed solvent.

[0021] Furthermore, in step 2, the amount of polyvinylpyrrolidone added is 5 to 20 wt% of the mass of the mixed solvent, and the average molecular weight of polyvinylpyrrolidone is 800,000 to 1,300,000.

[0022] Furthermore, in step 3, the spinning conditions are: accelerating voltage 8-25kV, receiving distance 10-22cm, extrusion rate 0.1-1.5ml / h, and spinning temperature 20-30℃.

[0023] Furthermore, in step 4, the oxidative crosslinking conditions are: in an air atmosphere, the temperature is increased to 160-220°C at a rate of 1-5°C / min and held for 1-4 hours; the pyrolysis conditions are: in an air atmosphere, the temperature is increased to 800-1300°C at a rate of 2-10°C / min and held for 1-4 hours.

[0024] As can be seen from the above description of the present invention, compared with the prior art, the beneficial effects of the present invention are:

[0025] First, the present invention uses hollow spheres as pore-forming materials to construct porous fibers, which can not only overcome the defect that the pore size of porous fibers is not easy to control in the traditional sacrificial template method, but also theoretically make the fibers exhibit better mechanical properties due to fewer microcracks in the resulting annular closed-cell structure.

[0026] Secondly, the porous mullite fiber constructed with SiC hollow spheres not only hinders solid-phase heat transfer and reduces the room temperature thermal conductivity of the fiber, but SiC material is also an infrared shielding agent, which can reduce the infrared radiation heat transfer of mullite-based closed-cell fibers at high temperatures, thereby reducing their high-temperature thermal conductivity.

[0027] Third, the preparation method of SiC hollow spheres is specifically defined. The prepared SiO2 spheres are first mixed and stirred with polycarbosilane and organic solvent to form a coating on the SiO2 spheres. During high-temperature pyrolysis, the coated polycarbosilane is pyrolyzed to directly produce silicon carbide. The overall reaction process is relatively easy to control. The SiO2 spheres only act as templates and do not participate in the reaction. Moreover, the prepared SiC hollow spheres are not easy to break and the yield is high.

[0028] Fourth, SiC hollow spheres are also a type of microwave absorbing material. When combined with mullite fibers, they can impart electromagnetic wave absorption properties to the mullite fibers. Attached Figure Description

[0029] Figure 1 SEM image of the mullite and closed-cell fiber thermal insulation material with electromagnetic wave absorption properties prepared in Example 1.

[0030] Figure 2 TEM image of the SiC hollow spheres prepared in Example 2;

[0031] Figure 3 TEM image of the mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties prepared in Example 2;

[0032] Figure 4 Infrared transmittance of the mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties prepared in Example 3 in the wavelength range of 2.5–7.0 μm.

[0033] Figure 5 The electromagnetic wave reflection loss diagram is shown for the mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties prepared in Example 4. Detailed Implementation

[0034] The present invention will be further described below through specific embodiments.

[0035] A method for preparing a mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties includes the following steps:

[0036] Step 1: Tetraethyl orthosilicate, deionized water, anhydrous ethanol, and ammonia are mixed and magnetically stirred for 10–48 h. The reaction product is centrifuged, washed, and dried in an oven to obtain SiO2 spheres of different diameters. The prepared SiO2 spheres and polycarbosilane are added to an organic solvent and stirred for 1–4 h. After removing the organic solvent, the sample is pyrolyzed at high temperature under inert gas protection to obtain SiC / SiO2 spheres. Finally, the SiC / SiO2 spheres are placed in an etching solution to remove SiO2 and obtain SiC hollow spheres.

[0037] Step 2: SiC hollow spheres, polyvinylpyrrolidone, aluminum sec-butoxide and polymethylhydrosiloxane are added to a mixed solvent of isopropanol, N,N-dimethylformamide and ethyl acetoacetate, and magnetically stirred for 1 to 3 hours to obtain the spinning solution.

[0038] Step 3: Spin the spinning solution obtained above using electrospinning to obtain a precursor fiber membrane;

[0039] Step 4: The obtained raw fiber membrane is subjected to oxidative crosslinking and high-temperature pyrolysis to obtain mullite-based closed-cell fiber thermal insulation material.

[0040] Specifically, in step 1, the outer diameter of the prepared SiC hollow spheres is 50–2000 nm, and the shell thickness is 5–200 nm; the mass ratio of tetraethyl orthosilicate, deionized water, anhydrous ethanol, and ammonia is 1:(2.8–3.5):(16.2–25.6):(0.8–1.6); the centrifugal washing solvent is deionized water and anhydrous ethanol, respectively, for three washes; the oven drying temperature is 60–80℃, and the holding time is 2–24 h; the organic solvent is tetraethyl orthosilicate. One of hydrogenated furan, xylene, and n-hexane; the mass ratio of SiO2 spheres, polycarbosilane, and organic solvent is 1:(0.4~1.0):(20~30); the high-temperature reaction temperature for preparing SiC / SiO2 spheres is 1000~1350℃, the holding time is 2~10h, and the inert protective atmosphere is one of argon, nitrogen, or helium; the etching solution is 10~30wt% hydrofluoric acid or sodium hydroxide solution, and the etching time is 10~24h.

[0041] In step 2, the mass ratio of the mixed solvent isopropanol, N,N-dimethylformamide, and ethyl acetoacetate is 1:(0.08–0.12):(0.10–0.17); the mass ratio of aluminum sec-butoxide and polymethylhydrosiloxane is 1:(0.05–0.15); aluminum sec-butoxide accounts for 10–22% of the mass fraction of the mixed solvent; the amount of SiC hollow spheres added is 3–16 wt% of the mass of the mixed solvent; the amount of polyvinylpyrrolidone added is 5–20 wt% of the mass of the mixed solvent, and the average molecular weight of polyvinylpyrrolidone is 800,000–1,300,000.

[0042] In step 3, the spinning conditions are: accelerating voltage 8-25kV, receiving distance 10-22cm, extrusion rate 0.1-1.5ml / h, and spinning temperature 20-30℃.

[0043] In step 4, the oxidative crosslinking conditions are: in an air atmosphere, the temperature is increased to 160-220°C at a rate of 1-5°C / min and held for 1-4 hours; the pyrolysis conditions are: in an air atmosphere, the temperature is increased to 800-1300°C at a rate of 2-10°C / min and held for 1-4 hours.

[0044] Example 1

[0045] A method for preparing a mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties includes the following steps:

[0046] Step 1: Mix 9g tetraethyl orthosilicate, 28g deionized water, 160g anhydrous ethanol and 10g ammonia water in a mass ratio of 1:3.1:17.8:1.1 and stir magnetically for 25h. After the reaction, centrifuge and wash the product and dry it in an oven at 60℃ for 5h. Then, mix 1g SiO2 spheres, 0.5g polycarbosilane and 22g n-hexane in a mass ratio of 1:0.5:22 and stir magnetically for 2h. After removing the organic solvent n-hexane, place the sample in a tube furnace and react at 1000℃ for 3h under argon protection to obtain SiC / SiO2 spheres. Place the SiC / SiO2 spheres in a 20wt% hydrofluoric acid solution and stir for 20h to remove SiO2, obtaining hollow SiC spheres with an outer diameter of 120nm and a shell thickness of 16nm.

[0047] Step 2: 0.44g SiC hollow spheres, 1.17g polyvinylpyrrolidone, 2g aluminum sec-butoxide, and 0.17g polymethylhydrosiloxane were added to a mixed solvent of 10g isopropanol, 1g N,N-dimethylformamide, and 1.5g ethyl acetoacetate, and the mixture was magnetically stirred for 1 hour to obtain a spinning solution. The mass ratio of aluminum sec-butoxide to polymethylhydrosiloxane was 1:0.085, the mass ratio of the mixed solvent of isopropanol, N,N-dimethylformamide, and ethyl acetoacetate was 1:0.1:0.15, and aluminum sec-butoxide accounted for 16% of the mass fraction of the mixed solvent. The amount of SiC hollow spheres added was 3.5wt% of the mass of the mixed solvent, and the amount of PVP with an average molecular weight of 1,300,000 added was 9.36wt% of the mass of the mixed solvent.

[0048] Step 3: Spin the above-obtained spinning solution using electrospinning, wherein the accelerating voltage is 12kV, the receiving distance is 15cm, the extrusion rate is 0.5ml / h, and the spinning temperature is 25℃, to obtain a precursor fiber membrane.

[0049] Step 4: The obtained raw fiber membrane is first subjected to oxidative crosslinking. The oxidative crosslinking conditions are: in an air atmosphere, the temperature is increased to 200℃ at 2℃ / min and held for 2h.

[0050] Step 5: The above-mentioned oxidized and cross-linked fibers are subjected to high-temperature pyrolysis. The pyrolysis conditions are: heating to 800°C at 2°C / min in air atmosphere and holding for 2 hours to obtain mullite-based closed-cell fiber thermal insulation material.

[0051] SEM images of the mullite-based closed-cell fiber thermal insulation material prepared above are attached. Figure 1 As shown; the fiber has a thermal conductivity of 0.021 W·m at room temperature (25℃). -1 ·K -1 The high-temperature thermal conductivity at 1000℃ is 0.072 W·m. -1 ·K -1 The infrared transmittance is less than 6% in the band between 2.5 and 7.0 μm; and the minimum reflection loss at 4.0 GHz reaches -46.8 dB when the thickness is 4.9 mm.

[0052] Example 2

[0053] A method for preparing a mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties includes the following steps:

[0054] Step 1: Mix 9g of tetraethyl orthosilicate, 26.1g of deionized water, 166.5g of anhydrous ethanol, and 10.8g of ammonia water in a mass ratio of 1:2.9:18.5:1.2 and stir magnetically for 20h. After the reaction, centrifuge, wash, and dry in an oven at 60℃ for 8h. Then, mix 1g of SiO2 spheres, 0.8g of polycarbosilane, and 25g of tetrahydrofuran in a mass ratio of 1:0.8:25 and stir magnetically for 3h. After removing the organic solvent tetrahydrofuran, place the sample in a tube furnace and react at 1100℃ for 3h under argon protection to obtain SiC / SiO2 spheres. Place the SiC / SiO2 spheres in a 15wt% sodium hydroxide solution and stir for 24h to remove SiO2, obtaining hollow SiC spheres with an outer diameter of 260nm and a shell thickness of 21nm.

[0055] Step 2: 0.84g SiC hollow spheres, 1.25g polyvinylpyrrolidone, 1.8g aluminum sec-butoxide, and 0.14g polymethylhydrosiloxane were added to a mixed solvent of 10g isopropanol, 0.8g N,N-dimethylformamide, and 1.2g ethyl acetoacetate. The mixture was magnetically stirred for 2 hours until homogeneous to obtain the spinning solution. The mass ratio of aluminum sec-butoxide to polymethylhydrosiloxane was 1:0.08, the mass ratio of the mixed solvent of isopropanol, N,N-dimethylformamide, and ethyl acetoacetate was 1:0.08:0.12, and aluminum sec-butoxide accounted for 15% of the mass fraction of the mixed solvent. The amount of SiC hollow spheres added was 7wt% of the mass of the mixed solvent, and the amount of PVP with an average molecular weight of 1,300,000 added was 10.42wt% of the mass of the mixed solvent.

[0056] Step 3: Spin the above-obtained spinning solution using electrospinning, wherein the accelerating voltage is 15kV, the receiving distance is 15cm, the extrusion rate is 0.8ml / h, and the spinning temperature is 25℃, to obtain a precursor fiber membrane.

[0057] Step 4: The obtained raw fiber membrane is first subjected to oxidative crosslinking. The oxidative crosslinking conditions are: heating to 210°C at 2°C / min and holding for 1 hour in an air atmosphere.

[0058] Step 5: The above-mentioned oxidized and cross-linked fibers are subjected to high-temperature pyrolysis. The pyrolysis conditions are: heating to 900°C at 1°C / min in air atmosphere and holding for 2 hours to obtain mullite-based closed-cell fiber thermal insulation material.

[0059] TEM images of the SiC hollow spheres and mullite-based closed-cell fiber thermal insulation materials prepared in this embodiment are attached. Figure 2 and 3 As shown; the thermal conductivity at room temperature (25℃) is 0.025 W·m. -1 ·K -1 The high-temperature thermal conductivity at 1000℃ is 0.066 W·m. -1 ·K -1 The infrared transmittance is less than 8% in the band between 2.5 and 7.0 μm; and at a thickness of 5.2 mm, the minimum reflection loss at 3.9 GHz reaches -50.6 dB.

[0060] Example 3

[0061] A method for preparing a mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties includes the following steps:

[0062] Step 1: Mix 9g of tetraethyl orthosilicate, 28.8g of deionized water, 198g of anhydrous ethanol, and 13.5g of ammonia water in a mass ratio of 1:3.2:22:1.5 and stir magnetically for 25 hours. After the reaction, centrifuge, wash, and dry in a 70°C oven for 10 hours. Then, mix 1g of SiO2 spheres, 0.6g of polycarbosilane, and 26g of xylene in a mass ratio of 1:0.6:26 and stir magnetically for 3 hours. After removing the xylene solvent, place the sample in a tube furnace and react at 1300°C for 2 hours under nitrogen protection to obtain SiC / SiO2 spheres. Place the SiC / SiO2 spheres in a 20wt% hydrofluoric acid solution and stir for 24 hours to remove SiO2, obtaining hollow SiC spheres with an outer diameter of 600nm and a shell thickness of 55nm.

[0063] Step 2: 1.44g SiC hollow spheres, 1.78g polyvinylpyrrolidone (PVP), 2.3g aluminum sec-butoxide, and 0.23g polymethylhydrosiloxane were added to a mixed solvent of 10g isopropanol, 0.9g N,N-dimethylformamide, and 1.4g ethyl acetoacetate. The mixture was magnetically stirred for 1.5h until homogeneous to obtain the spinning solution. The mass ratio of aluminum sec-butoxide to polymethylhydrosiloxane was 1:0.1, and the mass ratio of the mixed solvent of isopropanol, N,N-dimethylformamide, and ethyl acetoacetate was 1:0.09:0.14. Aluminum sec-butoxide accounted for 18.7% of the mass fraction of the mixed solvent. The amount of SiC hollow spheres added was 11.7wt% of the mass of the mixed solvent, and the amount of PVP with an average molecular weight of 800,000 added was 14.47wt% of the mass of the mixed solvent.

[0064] Step 3: Spin the above-obtained spinning solution using electrospinning, wherein the accelerating voltage is 18kV, the receiving distance is 12cm, the extrusion rate is 0.7ml / h, and the spinning temperature is 28℃, to obtain a precursor fiber membrane.

[0065] Step 4: The obtained raw fiber membrane is first subjected to oxidative crosslinking. The oxidative crosslinking conditions are: heating to 180°C at 1°C / min and holding for 2 hours in an air atmosphere.

[0066] Step 5: The above-mentioned oxidized and cross-linked fibers are subjected to high-temperature pyrolysis. The pyrolysis conditions are: heating to 1100℃ at 5℃ / min in air atmosphere and holding for 2 hours to obtain mullite-based closed-cell fiber thermal insulation material.

[0067] The mullite-based closed-cell fiber thermal insulation material prepared in this embodiment has a thermal conductivity of 0.022 W·m at room temperature (25°C). -1 ·K -1 The high-temperature thermal conductivity at 1000℃ is 0.057 W·m. -1 ·K -1 The infrared transmittance is less than 5% in the wavelength range of 2.5–7.0 μm; as shown in the attached image. Figure 4 As shown, with a thickness of 3.8 mm, its minimum reflection loss at 5.1 GHz reaches -42.1 dB.

[0068] Example 4

[0069] A method for preparing a mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties includes the following steps:

[0070] Step 1: Mix 9g of tetraethyl orthosilicate, 27g of deionized water, 162g of anhydrous ethanol, and 10.8g of ammonia water at a mass ratio of 1:3:18:1.2 and stir magnetically for 20h. After the reaction, centrifuge, wash, and dry in an oven at 80℃ for 3h. Then, mix 1g of SiO2 spheres, 1g of polycarbosilane, and 30g of tetrahydrofuran at a mass ratio of 1:1:30 and stir magnetically for 3h. After removing the organic solvent tetrahydrofuran, place the sample in a tube furnace and react at 1350℃ for 6h under argon protection to obtain SiC / SiO2 spheres. Place the SiC / SiO2 spheres in a 30wt% sodium hydroxide solution and stir for 24h to remove SiO2, obtaining hollow SiC spheres with an outer diameter of 820nm and a shell thickness of 60nm.

[0071] Step 2: 1.88g of SiC hollow spheres, 2.5g of polyvinylpyrrolidone (PVP), 2.56g of aluminum sec-butoxide, and 0.31g of polymethylhydrosiloxane were added to a mixed solvent of 10g of isopropanol, 1.1g of N,N-dimethylformamide, and 1.7g of ethyl acetoacetate. The mixture was magnetically stirred for 4 hours until homogeneous to obtain the spinning solution. The mass ratio of aluminum sec-butoxide to polymethylhydrosiloxane was 1:0.12, the mass ratio of the mixed solvent of isopropanol, N,N-dimethylformamide, and ethyl acetoacetate was 1:0.11:0.17, and aluminum sec-butoxide accounted for 20% of the mass fraction of the mixed solvent. The amount of SiC hollow spheres added was 14.69 wt% of the mass of the mixed solvent, and the amount of PVP with an average molecular weight of 800,000 added was 19.53 wt% of the mass of the mixed solvent.

[0072] Step 3: Spin the above-obtained spinning solution using electrospinning, wherein the accelerating voltage is 20kV, the receiving distance is 15cm, the extrusion rate is 1.2ml / h, and the spinning temperature is 30℃, to obtain a precursor fiber membrane.

[0073] Step 4: The obtained raw fiber membrane is first subjected to oxidative crosslinking. The oxidative crosslinking conditions are: heating to 210°C at 3°C / min and holding for 2 hours in an air atmosphere.

[0074] Step 5: The above-mentioned oxidized and cross-linked fibers are subjected to high-temperature pyrolysis. The pyrolysis conditions are: heating to 1200℃ at 5℃ / min in air atmosphere and holding for 2 hours to obtain mullite-based closed-cell fiber thermal insulation material.

[0075] The mullite-based closed-cell fiber thermal insulation material prepared in the above embodiments has a thermal conductivity of 0.019 W·m at room temperature (25°C). -1 ·K -1 The high-temperature thermal conductivity at 1000℃ is 0.054 W·m. -1 ·K -1 Infrared transmittance is less than 2% in the 2.5–7.0 μm band; at a thickness of 4.3 mm, its minimum reflection loss reaches -44.7 dB at 6.2 GHz, and its electromagnetic wave reflection loss is as follows: Figure 5 As shown.

[0076] In summary, the design of constructing a closed-cell structure by incorporating SiC hollow spheres inside the fiber can hinder solid-phase heat transfer and high-temperature thermal radiation, thereby reducing the thermal conductivity of mullite fibers. Selecting SiC hollow spheres with excellent microwave absorption properties as a pore-forming agent can simultaneously impart electromagnetic wave absorption effects to mullite fibers. By rationally adjusting the concentration of SiC hollow spheres inside the fiber, the microstructure, thermal insulation performance, and microwave absorption performance of mullite fibers can be adjusted and controlled.

[0077] This invention effectively solves the problems of insufficient thermal conductivity and limited functionality of existing mullite fiber insulation materials, and is suitable for high-temperature thermal protection and stealth protection of ultra-high-speed aircraft in aerospace and military fields.

[0078] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the present invention and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for preparing a mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties, characterized in that: Includes the following steps: Step 1: Tetraethyl orthosilicate, deionized water, anhydrous ethanol, and ammonia are mixed and magnetically stirred for 10–48 h. The reaction product is centrifuged, washed, and dried in an oven to obtain SiO2 spheres of different diameters. The prepared SiO2 spheres and polycarbosilane are added to an organic solvent and stirred for 1–4 h. After removing the organic solvent, the sample is pyrolyzed at high temperature under inert gas protection to obtain SiC / SiO2 spheres. Finally, the SiC / SiO2 spheres are placed in an etching solution to remove SiO2 and obtain SiC hollow spheres. Step 2: SiC hollow spheres, polyvinylpyrrolidone, aluminum sec-butoxide and polymethylhydrosiloxane are added to a mixed solvent of isopropanol, N,N-dimethylformamide and ethyl acetoacetate, and magnetically stirred for 1 to 3 hours to obtain the spinning solution. Step 3: Spin the spinning solution obtained above using electrospinning to obtain a precursor fiber membrane; Step 4: The obtained raw fiber membrane is subjected to oxidative crosslinking and high-temperature pyrolysis to obtain mullite-based closed-cell fiber thermal insulation material.

2. The method for preparing a mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties according to claim 1, characterized in that: In step 1, the mass ratio of tetraethyl orthosilicate, deionized water, anhydrous ethanol and ammonia is 1:(2.8-3.5):(16.2-25.6):(0.8-1.6); the centrifugal washing solvent is deionized water and anhydrous ethanol, respectively, for three washes; the oven drying temperature is 60-80℃, and the holding time is 2-24h.

3. The method for preparing a mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties according to claim 1, characterized in that: In step 1, the organic solvent is one of tetrahydrofuran, xylene, or n-hexane; the mass ratio of SiO2 spheres, polycarbosilane, and organic solvent is 1:(0.4-1.0):(20-30); the high-temperature reaction temperature for preparing SiC / SiO2 spheres is 1000-1350℃, the holding time is 2-10h, and the inert protective atmosphere is one of argon, nitrogen, or helium.

4. The method for preparing a mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties according to claim 1, characterized in that: In step 1, the etching solution is a 10-30 wt% hydrofluoric acid or sodium hydroxide solution, and the etching time is 10-24 h.

5. The method for preparing a mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties according to claim 1, characterized in that: In step 1, the outer diameter of the prepared SiC hollow spheres is 50–2000 nm, and the shell thickness is 5–200 nm.

6. The method for preparing a mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties according to claim 1, characterized in that: In step 2, the mass ratio of the mixed solvent isopropanol, N,N-dimethylformamide and ethyl acetoacetate is 1:(0.08-0.12):(0.10-0.17); the mass ratio of aluminum sec-butoxide and polymethylhydrosiloxane is 1:(0.05-0.15); and aluminum sec-butoxide accounts for 10-22% of the mass fraction of the mixed solvent.

7. The method for preparing a mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties according to claim 1, characterized in that: In step 2, the amount of SiC hollow spheres added is 3 to 16 wt% of the mass of the mixed solvent.

8. The method for preparing a mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties according to claim 1, characterized in that: In step 2, the amount of polyvinylpyrrolidone added is 5 to 20 wt% of the mass of the mixed solvent, and the average molecular weight of polyvinylpyrrolidone is 800,000 to 1,300,000.

9. The method for preparing a mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties according to claim 1, characterized in that: In step 3, the spinning conditions are: accelerating voltage 8-25kV, receiving distance 10-22cm, extrusion rate 0.1-1.5ml / h, and spinning temperature 20-30℃.

10. The method for preparing a mullite-based closed-cell fiber thermal insulation material with electromagnetic wave absorption properties according to claim 1, characterized in that: In step 4, the oxidative crosslinking conditions are: in an air atmosphere, the temperature is increased to 160-220°C at a rate of 1-5°C / min and held for 1-4 hours; the pyrolysis conditions are: in an air atmosphere, the temperature is increased to 800-1300°C at a rate of 2-10°C / min and held for 1-4 hours.

Images