High-entropy alloy silicon carbide nanofiber composite material as well as preparation method and application thereof

Abstract

The invention discloses a high-entropy alloy silicon carbide nanofiber composite material and a preparation method and application thereof, a high-entropy alloy is loaded on silicon carbide nanofibers, compared with a carbon fiber material carrier, SiC fibers can form a compact SiO2 protective layer in a high-temperature aerobic environment, further oxidation failure of the internal structure can be prevented, and the high-entropy alloy silicon carbide nanofiber composite material is prepared. And meanwhile, SiC also has relatively high high-temperature stability and weather resistance, so that the high-entropy alloy silicon carbide nanofiber composite material can stably work in an extreme high-temperature oxidation environment (such as a spacecraft thermal protection system and an engine tail gas pipeline) of over 1000 DEG C, and perfectly adapts to a high-temperature wave-absorbing scene.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electromagnetic wave absorbing materials, and particularly relates to a high-entropy alloy silicon carbide nanofiber composite material and a preparation method and application thereof. BACKGROUND

[0002] The research and development of electromagnetic wave absorbing materials are crucial to meet the growing application needs in the field of electromagnetism, covering electromagnetic signal interference suppression, stealth technology, and electromagnetic energy capture, etc. These applications often need to operate stably in extremely harsh environments (such as high temperature, high humidity, desert, ocean, or chemically corrosive atmosphere). Therefore, an ideal absorbing material not only needs to have wide-band, strong absorption radar wave attenuation capability, but also must have excellent high-temperature stability, wear resistance, and environmental corrosion resistance.

[0003] Metal oxides are concerned in the field of absorbing materials due to their excellent structural stability and significant electromagnetic energy loss characteristics. In recent years, high-entropy alloy (HEA) materials have shown excellent electromagnetic wave absorption performance due to their unique properties, especially in terms of impedance matching control and enhancement of multiple loss mechanisms (such as dielectric loss and magnetic loss). In order to fully utilize the advantages of HEA in absorbing waves, loading it on a fiber carrier material is a feasible method. For example, there are currently reports of high-entropy alloy loaded on carbon fibers. However, carbon fibers will be severely oxidized and degraded at temperatures above 400°C in air, leading to structural damage and performance failure, which greatly limits their application in high-temperature aerobic environments (such as engine compartments and high-temperature pipelines). SUMMARY

[0004] The purpose of the present application is to provide a high-entropy alloy silicon carbide nanofiber composite material and a preparation method and application thereof. The silicon carbide nanofiber composite material loaded with high-entropy alloy is prepared by electrospinning, pre-oxidation, and high-temperature pyrolysis, and has good high-temperature oxidation resistance and high electromagnetic wave absorption efficiency.

[0005] The technical solution of the present application is as follows:

[0006] A preparation method of a high-entropy alloy silicon carbide nanofiber composite material, comprising the following steps:

[0007] (1) Dissolve polycarbosilane and polyvinylpyrrolidone in tetrahydrofuran and N,N-dimethylformamide to obtain a mixed solution; then mix the mixed solution with metal salt particles to obtain a spinning solution;

[0008] The concentration of polycarbosilane in the mixed solution is 5wt%, the mass ratio of polycarbosilane to polyvinylpyrrolidone is 1:0.2-1.5, and the mass ratio of metal salt particles to polycarbosilane is 4:5.

[0009] (2) Electrospinning technology is used to prepare polymer fiber membranes from spinning solution;

[0010] (3) The polymer fiber membrane is pre-oxidized to obtain oxidized polymer fiber. The pre-oxidation temperature is 180-250℃ and the pre-oxidation holding time is 1-4h.

[0011] (4) The oxidized polymer fibers are subjected to high-temperature pyrolysis under an inert atmosphere to obtain high-entropy alloy silicon carbide nanofiber composite material. The high-temperature pyrolysis temperature is 800-1000℃ and the high-temperature pyrolysis holding time is 2-4h.

[0012] In the above steps, electrospinning technology stretches the spinning solution into nanoscale fibers under a high-voltage electric field, forming a polymer fiber membrane. During this process, the metal salt is uniformly dispersed in the matrix. In the pre-oxidation process, the polymer fiber surface cross-links and solidifies to form a stable fiber structure, and the metal salt decomposes to generate metal oxides. During high-temperature pyrolysis, polycarbosilane decomposes to generate silicon carbide fibers rich in free carbon. Polyvinylpyrrolidone also partially forms free carbon during pyrolysis. The free carbon inside the fiber reduces the metal oxides to elemental metals. These elemental metals mix at high temperatures, forming high-entropy alloy particles loaded on the surface or inside the silicon carbide fibers.

[0013] In some preferred embodiments, the voltage of the electrospinning technology is 10-20 kV, the injection speed is 0.5-5 mL / h, and the distance between the needle and the collecting roller is 12-20 cm.

[0014] In some preferred embodiments, the mass ratio of tetrahydrofuran to N,N-dimethylformamide is 7:3.

[0015] In some preferred embodiments, the metal element in the metal salt particles is selected from at least five of the following: iron, cobalt, nickel, manganese, magnesium, zinc, copper, vanadium, silicon, tin, lead, and chromium. The metal salt is at least one of the following: acetylacetone salts and their hydrates, chloride salts and their hydrates, acetate salts and their hydrates, and nitrate salts and their hydrates.

[0016] In some preferred embodiments, the metal salt particles comprise cobalt, nickel, manganese, iron, and chromium in a stoichiometric ratio of 1:1:1:1:1.

[0017] In some preferred embodiments, the pre-oxidation heating rate is 1°C / min.

[0018] In some preferred embodiments, the heating rate of high-temperature pyrolysis is 2 to 5 °C / min.

[0019] A high-entropy alloy silicon carbide nanofiber composite material is prepared by the above-described method.

[0020] An electromagnetic wave absorbing material comprising 10wt% to 30wt% of the above-mentioned high-entropy alloy silicon carbide nanofiber composite material.

[0021] The application of the above-mentioned high-entropy alloy silicon carbide nanofiber composite material in electromagnetic wave absorption.

[0022] The present invention has at least the following beneficial effects:

[0023] 1. This invention loads a high-entropy alloy onto silicon carbide nanofibers to obtain a high-entropy alloy silicon carbide nanofiber composite material. Compared with the carbon fiber material carriers reported so far, silicon carbide (SiC) nanofibers can form a dense silicon dioxide (SiO2) protective layer in a high-temperature oxygen environment, protecting the internal structure of SiC fibers from further oxidation and failure. At the same time, SiC also has strong high-temperature stability and weather resistance, enabling the high-entropy alloy silicon carbide nanofiber composite material to work stably in extreme high-temperature oxidation environments above 1000℃ (such as spacecraft thermal protection systems and engine exhaust pipes), perfectly suited for high-temperature microwave absorption scenarios.

[0024] 2. The semiconductor properties of silicon carbide contribute to dielectric losses based on electronic transitions and defect polarization; by introducing magnetic elements (such as Fe and Ni) for doping, a magnetic loss mechanism can be effectively introduced to achieve synergistic dielectric-magnetic losses, significantly broadening the effective absorption bandwidth and enhancing the absorption intensity.

[0025] 3. The high-entropy alloy silicon carbide nanofiber composite material prepared by this invention contains free carbon encapsulated in silicon carbide fibers. In subsequent applications, these free carbons can provide a conductive network and enhance dielectric loss (electron migration, interface polarization), thereby improving the microwave absorption performance.

[0026] 4. When the above-mentioned high-entropy alloy silicon carbide nanofiber composite material is used as an electromagnetic wave absorbing material, its minimum reflection loss in the range of 2 to 18 GHz is less than -40 dB, which shows high electromagnetic wave absorption efficiency; when tested in air at 1000 °C with high temperature and oxygen, its mass loss rate is less than 2 wt%, which shows excellent high temperature oxidation resistance. Attached Figure Description

[0027] Figure 1 This is a scanning electron microscope image of the high-entropy alloy silicon carbide nanofiber composite material prepared in Example 1;

[0028] Figure 2 Thermogravimetric analysis (TGA) of the high-entropy alloy silicon carbide nanofiber composite material prepared in Example 2 in air at 1000°C.

[0029] Figure 3 The image shows the reflection loss of the high-entropy alloy silicon carbide nanofiber composite material prepared in Example 3 at 2.4 mm and 7.5 GHz. Detailed Implementation

[0030] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0031] In the following embodiments, unless otherwise specified, the water used may be one or more of distilled water, purified water, and drinking water; the detection methods in the following embodiments are conventional detection methods unless otherwise specified; the reagents in the following embodiments are commercially available unless otherwise specified.

[0032] Example 1

[0033] A method for preparing a high-entropy alloy silicon carbide nanofiber composite material includes the following steps:

[0034] (1) Preparation of spinning solution: Mix 0.5g polycarbosilane (PCS), 0.2g polyvinylpyrrolidone (PVP), 7ml tetrahydrofuran (THF) and 3ml N,N-dimethylformamide (DMF), and stir thoroughly for 30min to completely dissolve PCS and PVP to obtain a mixed solution;

[0035] Then, the metal salt particles and the mixed solution were mixed and stirred for another 15 hours to obtain a uniformly mixed spinning solution.

[0036] The metal salt particles include 0.07g Co(NO3)2·6H2O, 0.07g Ni(NO3)2·6H2O, 0.069g Mn(NO3)2·6H2O, 0.1g Cr(NO3)3·9H2O, and 0.1g Fe(NO3)3·9H2O.

[0037] (2) Preparation of polymer fiber membrane: The spinning solution was transferred to a syringe for electrospinning. Electrospinning was performed using a No. 21 stainless steel needle connected to a 20kV high voltage. The spinning solution flow rate was 1mL / h, and the distance between the needle and the collecting roller was set to 15cm. Electrospinning was carried out at a temperature of 25±2℃. Then, the electrospinned product was removed and dried at 60℃ for 5h. After cooling, the polymer fiber membrane was obtained.

[0038] (3) The polymer fiber membrane was placed in a muffle furnace for pre-oxidation. The temperature was slowly increased to 250°C at a rate of 1°C / min and held for 1 hour to obtain the oxidized polymer fiber.

[0039] (4) The oxidized polymer fibers are placed in a tube furnace and pyrolyzed at high temperature in an inert argon atmosphere. The temperature is increased to 800℃ at a rate of 2℃ / min and held for 2 hours. After cooling, a high-entropy alloy silicon carbide nanofiber composite material is obtained.

[0040] The high-entropy alloy silicon carbide nanofiber composite material prepared in Example 1 was placed under a scanning electron microscope, and the results are as follows: Figure 1 This demonstrates that Example 1 successfully loaded a high-entropy alloy onto silicon carbide nanofibers.

[0041] Paraffin wax was placed in a container and kept in a forced-air oven at 60°C for 10 minutes until it was completely melted. The paraffin wax was then removed and mixed with a high-entropy alloy silicon carbide nanofiber composite material. The mixture was stirred until homogeneous, and after solidification, an electromagnetic wave absorbing material was obtained. This electromagnetic wave absorbing material included 10 wt% of the aforementioned high-entropy alloy silicon carbide nanofiber composite material. The electromagnetic wave absorbing material was placed in a stainless steel mold to prepare a concentric ring sample. Electromagnetic parameters were tested in the frequency range of 2–18 GHz. The test results showed that, with a thickness of 2.9 mm, the minimum reflection loss at 7.6 GHz reached -45.3 dB.

[0042] The prepared high-entropy alloy silicon carbide nanofiber composite material was subjected to thermogravimetric analysis in air at 1000℃, and its mass loss rate was 1.36wt%, showing excellent high-temperature oxidation resistance.

[0043] Example 2

[0044] A method for preparing a high-entropy alloy silicon carbide nanofiber composite material includes the following steps:

[0045] (1) Preparation of spinning solution: Mix 0.5g polycarbosilane (PCS), 0.5g polyvinylpyrrolidone (PVP), 7ml tetrahydrofuran (THF) and 3ml N,N-dimethylformamide (DMF), and stir thoroughly for 30min to completely dissolve PCS and PVP to obtain a mixed solution;

[0046] Then, the metal salt particles and the mixed solution were mixed and stirred for another 15 hours to obtain a uniformly mixed spinning solution.

[0047] The metal salt particles included 0.087g Co(NO3)2·6H2O, 0.057g Ni(CH3COO)2·4H2O, and 0.078g C. 10 H 14 MnO4·2H2O, 0.123gCr(NO3)3·9H2O and 0.056gFe(CH3COO)2·4H2O.

[0048] (2) Preparation of polymer fiber membrane: The spinning solution was transferred to a syringe for electrospinning. Electrospinning was performed using a No. 21 stainless steel needle connected to a 15kV high voltage. The spinning solution flow rate was 0.5mL / h, and the distance between the needle and the collecting roller was set to 20cm. Electrospinning was carried out at a temperature of 25±2℃. Then, the polymer fiber membrane was removed and dried at 60℃ for 5h. After cooling, the polymer fiber membrane was obtained.

[0049] (3) The polymer fiber membrane was placed in a muffle furnace for pre-oxidation. The temperature was slowly increased to 200°C at a rate of 1°C / min and kept at that temperature for 3 hours to obtain the oxidized polymer fiber.

[0050] (4) The oxidized polymer fibers are placed in a tube furnace and pyrolyzed at high temperature in an inert argon atmosphere. The temperature is increased to 900℃ at a rate of 2℃ / min and held for 3 hours. After cooling, a high-entropy alloy silicon carbide nanofiber composite material is obtained.

[0051] Paraffin wax was placed in a container and kept in a forced-air oven at 60°C for 10 minutes until it was completely melted. The paraffin wax was then removed and mixed with a high-entropy alloy silicon carbide nanofiber composite material. The mixture was stirred until homogeneous, and after solidification, an electromagnetic wave absorbing material was obtained. This electromagnetic wave absorbing material included 20 wt% of the aforementioned high-entropy alloy silicon carbide nanofiber composite material. The electromagnetic wave absorbing material was placed in a stainless steel mold to prepare a concentric ring sample. Electromagnetic parameters were tested in the frequency range of 2–18 GHz. The test results showed that, with a thickness of 2.2 mm, the minimum reflection loss at 5.9 GHz reached -42.6 dB.

[0052] The prepared high-entropy alloy silicon carbide nanofiber composite material was subjected to thermogravimetric analysis in air at 1000℃, and its mass loss rate was 1.91 wt%. Figure 2 It exhibits excellent high-temperature antioxidant properties.

[0053] Example 3

[0054] A method for preparing a high-entropy alloy silicon carbide nanofiber composite material includes the following steps:

[0055] (1) Preparation of spinning solution: Mix 0.5g polycarbosilane (PCS), 1.0g polyvinylpyrrolidone (PVP), 7ml tetrahydrofuran (THF) and 3ml N,N-dimethylformamide (DMF), and stir thoroughly for 30min to completely dissolve PCS and PVP to obtain a mixed solution;

[0056] Then, the metal salt particles and the mixed solution were mixed and stirred for another 15 hours to obtain a uniformly mixed spinning solution.

[0057] The metal salt particles include Co(NO3)2·6H2O, Ni(CH3COO)2·4H2O, and C. 10 H 14 1 mmol each of MnO4·2H2O, Fe(CH3COO)2·4H2O, and Cr(NO3)3·9H2O.

[0058] (2) Preparation of polymer fiber membrane: The spinning solution was transferred to a syringe for electrospinning. Electrospinning was performed using a No. 21 stainless steel needle connected to an 18kV high voltage. The spinning solution flow rate was 0.8mL / h, and the distance between the needle and the collecting roller was set to 20cm. Electrospinning was carried out at a temperature of 25±2℃. Then, the polymer fiber membrane was removed and dried at 60℃ for 5h. After cooling, the polymer fiber membrane was obtained.

[0059] (3) The polymer fiber membrane was placed in a muffle furnace for pre-oxidation. The temperature was slowly increased to 190°C at a rate of 1°C / min and held for 4 hours to obtain the oxidized polymer fiber.

[0060] (4) The oxidized polymer fibers are placed in a tube furnace and pyrolyzed at high temperature in an inert argon atmosphere. The temperature is increased to 1000℃ at a rate of 3℃ / min and held for 4 hours. After cooling, a high-entropy alloy silicon carbide nanofiber composite material is obtained.

[0061] Paraffin wax was placed in a container and kept in a forced-air oven at 60°C for 10 minutes until completely melted. The paraffin wax was then removed and mixed with a high-entropy alloy silicon carbide nanofiber composite material. The mixture was stirred until homogeneous, and after solidification, an electromagnetic wave absorbing material was obtained, comprising 30 wt% of the aforementioned high-entropy alloy silicon carbide nanofiber composite material. The electromagnetic wave absorbing material was placed in a stainless steel mold to prepare a concentric ring sample. Electromagnetic parameters were tested in the frequency range of 2–18 GHz. The test results showed that, with a thickness of 2.4 mm, the minimum reflection loss at 7.5 GHz reached -46.82 dB. Figure 3 ).

[0062] The prepared high-entropy alloy silicon carbide nanofiber composite material was subjected to thermogravimetric analysis in air at 1000℃, and its mass loss rate was 1.67wt%, showing excellent high-temperature oxidation resistance.

[0063] The above description is merely a preferred embodiment of the present invention, and therefore 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 patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for preparing a high-entropy alloy silicon carbide nanofiber composite material, characterized in that, Includes the following steps: (1) Polycarbosilane and polyvinylpyrrolidone are dissolved in tetrahydrofuran and N,N-dimethylformamide to obtain a mixed solution; then the mixed solution is mixed with metal salt particles to obtain a spinning solution; The concentration of the polycarbosilane in the mixed solution is 5 wt%, the mass ratio of the polycarbosilane to the polyvinylpyrrolidone is 1:0.2-1.5, and the mass ratio of the metal salt particles to the polycarbosilane is 4:

5. (2) The spinning solution is made into a polymer fiber membrane using electrospinning technology; (3) The polymer fiber membrane is pre-oxidized to obtain oxidized polymer fiber. The pre-oxidation temperature is 180-250°C and the pre-oxidation holding time is 1-4 hours. (4) The oxidized polymer fibers are subjected to high-temperature pyrolysis under an inert atmosphere to obtain the high-entropy alloy silicon carbide nanofiber composite material. The high-temperature pyrolysis temperature is 800-1000℃ and the high-temperature pyrolysis holding time is 2-4h.

2. The preparation method according to claim 1, characterized in that, The electrospinning technology uses a voltage of 10–20 kV, an injection speed of 0.5–5 mL / h, and a distance of 12–20 cm between the needle and the collecting roller.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the tetrahydrofuran to the N,N-dimethylformamide is 7:

3.

4. The preparation method according to claim 1, characterized in that, The metal salt particles contain at least five metal elements selected from iron, cobalt, nickel, manganese, magnesium, zinc, copper, vanadium, silicon, tin, lead, and chromium. The metal salt is at least one of the following: acetylacetone salt and its hydrate, chloride salt and its hydrate, acetate salt and its hydrate, and nitrate salt and its hydrate.

5. The preparation method according to claim 4, characterized in that, The metal salt particles comprise cobalt, nickel, manganese, iron, and chromium in a stoichiometric ratio of 1:1:1:1:

1.

6. The preparation method according to claim 1, characterized in that, The heating rate for the pre-oxidation is 1 °C / min.

7. The preparation method according to claim 1, characterized in that, The heating rate of the high-temperature pyrolysis is 2–5 °C / min.

8. A high-entropy alloy silicon carbide nanofiber composite material, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 7.

9. An electromagnetic wave absorbing material, characterized in that, It includes 10wt% to 30wt% of the high-entropy alloy silicon carbide nanofiber composite material as described in claim 8.

10. The application of the high-entropy alloy silicon carbide nanofiber composite material according to claim 8 in electromagnetic wave absorption.

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