A si c aerogel material, preparation and use thereof

Abstract

The application provides a SiC aerogel material, a preparation method and application thereof. The preparation method comprises the following steps: (1) taking silicon powder as a silicon source and a carbon-containing halide as a carbon source, mixing the silicon powder and the carbon-containing halide according to a proportion to obtain raw material powder, and obtaining mixed powder after pretreatment; (2) placing the obtained mixed powder into a combustion synthesis reaction kettle, then introducing high-purity argon with a certain pressure, igniting the mixed powder to occur combustion synthesis reaction through a tungsten wire coil, and obtaining a carbon-rich SiC aerogel block; and (3) oxidizing and removing carbon from the obtained carbon-rich SiC aerogel block at a certain temperature to obtain a layered nanowire-stacked SiC aerogel. The preparation method has the advantages of simple production process, short cycle, easiness in large-scale production, cheap and easily-obtained raw materials, and the obtained SiC aerogel has the characteristics of low density, high porosity, large specific surface area, good thermal stability and chemical stability, and has a wide application prospect in the fields of heat insulation, energy storage, catalysis, environment, electromagnetic wave absorption and electromagnetic interference shielding.

Description

Technical Field

[0001] This invention belongs to the field of aerogel preparation technology, specifically including a SiC aerogel material, its preparation and application. Background Technology

[0002] Aerogels are unique solid materials composed of an interconnected three-dimensional solid network and numerous air-filled pores, with pore sizes less than 100 nm and porosities exceeding 90%. Due to their unique structure, aerogels exhibit excellent properties in multiple fields, including thermal, acoustic, optical, electrical, and mechanical engineering. Traditional ceramic aerogels are primarily composed of oxide nanoparticles, exhibiting low thermal stability. For example, the size stability temperature of SiO2 aerogels is below 600℃, while carbon-based aerogels are prone to oxidation above 400℃ in air, limiting their applications. Novel silicon carbide (SiC) aerogels demonstrate better thermal and chemical stability than oxide ceramic aerogels.

[0003] SiC, due to its excellent properties such as low density, high thermal conductivity, good high-temperature performance, and excellent corrosion resistance, wear resistance, and thermal shock resistance, is a potential aerogel substrate for high-temperature applications. Chinese invention patent CN109320282A, "Preparation of SiC Aerogel by Ultrasonic Mixing of Silicon and Carbon Sources," provides a method combining ultrasound and carbothermal reduction to prepare SiC aerogel composite materials from inorganic silicon source water glass. The prepared SiC aerogel has a complete and uniform pore structure and can be shaped into the desired form. Chinese invention patent CN110668446B, "Preparation Method of High-Temperature Resistant SiC Aerogel," discloses a method using magnesium thermothermal reduction under an inert atmosphere to reduce the aerogel precursor to SiC aerogel. Supercritical drying yields an organosilicon aerogel with uniform pores and a complete shape. Chinese invention patent CN114715896A, "Preparation Method of Silicon Carbide Nanotube Aerogel," proposes a method to obtain silicon carbide nanotube aerogel by sintering carbon felt immersed in a silicon source solution and removing the carbon core. The resulting silicon carbide nanotube aerogel has low thermal conductivity and good elasticity. However, the existing SiC aerogel preparation processes suffer from high cost, complex processes, harsh conditions, and difficulty in preparing large-size materials, which seriously hinders the industrial application of SiC aerogel materials. Summary of the Invention

[0004] To address the aforementioned problems in existing technologies, the first objective of this invention is to provide a method for preparing SiC aerogels. This invention provides a simple and efficient method for preparing SiC aerogels, overcoming the problems of high cost, complex processes, stringent conditions, and difficulty in preparing large-size materials associated with traditional aerogel preparation methods.

[0005] The second objective of this invention is to provide a SiC aerogel material prepared by the above preparation method.

[0006] The third objective of this invention is to provide an application of SiC aerogel material in the preparation of fireproof and heat-insulating materials.

[0007] To achieve the first objective mentioned above, the present invention adopts the following technical solution:

[0008] This invention discloses a method for preparing SiC aerogel, comprising the following steps:

[0009] (1) Using silicon powder as the silicon source and carbon-containing halide as the carbon source, the silicon powder and carbon-containing halide are mixed in proportion to obtain raw material powder, and after pretreatment, mixed powder is obtained.

[0010] (2) The obtained mixed powder is placed in a closed combustion synthesis reactor, and then high-purity argon gas at a certain pressure is introduced. The mixed powder is then ignited by a tungsten wire coil to produce a combustion synthesis reaction, and carbon-rich SiC aerogel blocks are obtained.

[0011] (3) The carbon-rich SiC aerogel block was oxidized at a certain temperature to remove carbon, resulting in SiC aerogel with stacked layered nanowires.

[0012] This invention uses inexpensive silicon powder and carbon-containing halides as raw materials. It utilizes the cracking reaction between silicon and carbon-containing halides to generate gaseous halides and solid carbon, releasing a large amount of heat to activate a chemical reaction in the silicon-carbon system. The carbon source provided by the cracking of carbon-containing halides is continuously consumed, while SiC nanowires are generated in large quantities and intertwine and stack to self-assemble into SiC aerogel. This preparation condition is simple and the reaction time is short, which is conducive to industrial production. It solves the problems of high production cost, long processing time, complex production process, and the need for specific equipment in traditional aerogel production. The obtained SiC aerogel has a layered structure formed by intertwined and stacked SiC nanowires, unlike traditional aerogels which use nanocolloidal particles to form a nanoskeleton and nanoporous network structure. It has certain compression resilience and ultra-flexibility, can withstand thermal shock at 1200℃, and has good thermal and chemical stability. It has broad application prospects in energy storage, catalysis, thermal insulation, environmental protection, electromagnetic wave absorption, and electromagnetic interference shielding.

[0013] The inventors also discovered that the particle size of the raw materials, the proportion of each raw material, the type of inert gas introduced, the argon pressure, and the ratio of the mass of the raw material powder to the volume of the combustion synthesis reactor all have a certain impact on the morphology of the generated material. Only under the preparation parameters provided by this invention can SiC aerogel with stacked layered nanowires be prepared; otherwise, impurities such as Si3N4 will be generated, ultimately affecting the overall performance of the material.

[0014] Furthermore, the carbon-containing halides include, but are not limited to, one or more of polytetrafluoroethylene, polyvinylidene fluoride, and polyvinyl chloride.

[0015] Furthermore, the smaller the particle size of the raw materials, the more uniform the mixing of the raw materials, the higher the reactivity, and the more conducive the reaction. In one specific embodiment, the average particle size of the silicon powder and the carbon-containing halide is 0.1-100 μm; exemplaryly, the average particle size of the silicon powder and the carbon-containing halide can also be 0.1-1 μm, 0.1-2 μm, 0.1-3 μm, 0.1-5 μm, 0.1-10 μm, 0.1-20 μm, 0.1-50 μm, 1-2 μm, 1-3 μm, 1-5 μm, 1-10 μm, 1-20 μm, 1-50 μm, 1-100 μm, 2-3 μm, 2-5 μm, 2-10 μm, 2 -20μm, 2-50μm, 2-100μm, 3-5μm, 3-10μm, 3-20μm, 3-50μm, 3-100μm, 5-10μm, 5-20μm, 5-50μm, 5-100μm, 10-20μm, 10-50μm, 10-100μm, 20-50μm, 20-100μm, 50-100μm, etc.; preferably, when the average particle size of the silicon powder and the carbon halide is 0.1-3μm, it is more conducive to generating the SiC aerogel required by the present invention.

[0016] Furthermore, the ratio of silicon powder to carbon halide powder directly affects the temperature range achievable by the reaction; only by reaching the target temperature range can SiC aerogel material be ultimately generated. In one specific embodiment, the molar ratio of silicon powder to carbon halide is 1-7:1; exemplaryly, the molar ratio of silicon powder to carbon halide can also be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, etc., or any range formed by any two values; preferably, when the molar ratio of silicon powder to carbon halide is 3:1, it is more conducive to generating the SiC aerogel required by the present invention.

[0017] Furthermore, the ratio between the mass of the raw material powder and the volume of the combustion synthesis reactor is a crucial factor affecting material formation. When the ratio is too small, insufficient heat is generated during the reaction, and the heat disperses rapidly, resulting in a short sintering time after reaching the reaction temperature. This makes the synthesis of SiC aerogel increasingly difficult, and it also fails to effectively constrain the aerogel, thus hindering the formation of aerogel blocks. Conversely, when the ratio is too large, the transient pressure during the reaction increases dramatically, potentially exceeding the working pressure of the reactor's safety valve. This could cause the release of reaction gases, which is also detrimental to SiC aerogel formation. In one specific embodiment, the ratio between the mass of the raw material powder and the volume of the combustion synthesis reactor is (6-40) g:1 L; exemplarily, the ratio between the mass of the raw material powder and the volume of the combustion synthesis reactor can also be (6-10) g:1 L, (6-15) g:1 L, (6-20) g:1 L, (6-25) g:1 L, (6-30) g:1 L, (6-35) g:1 L, (10-15) g:1 L, (10-20) g:1 L, (10-25) g:1 L, (10-30) g:1 L, ( (10-35)g:1L, (10-40)g:1L, (15-20)g:1L, (15-25)g:1L, (15-30)g:1L, (15-35)g:1L, (15-40)g:1L, (20-25)g:1L, (20-30)g:1L, (20-35)g:1L, (20-40)g:1L, etc.; preferably, when the ratio between the mass of the raw material powder and the volume of the combustion synthesis reactor is (10-15)g:1L, it is more conducive to generating the SiC aerogel required by the present invention.

[0018] Furthermore, the inventors' experiments revealed that when a nitrogen atmosphere was used, SiC aerogels with the same morphology as those of this invention could not be formed; in fact, some Si3N4 impurities were generated. Conversely, if the argon gas pressure was too low, the silicon powder reaction would be incomplete, which was also detrimental to the reaction. Therefore, in this invention, an argon atmosphere was selected as the inert atmosphere, with an argon gas pressure of 0.1-10 MPa. Exemplarily, the argon gas pressure could also be 0.1-0.5 MPa, 0.1-1 MPa, 0.1-2 MPa, 0.1-3 MPa, 0.1-5 MPa, 0.1-8 MPa, 0.5-1 MPa, 0.5-2 MPa, 0.5-3 MPa, or 0.5-5 MPa. a. 0.5-8MPa, 0.5-10MPa, 1-2MPa, 1-3MPa, 1-5MPa, 1-8MPa, 1-10MPa, 2-3MPa, 2-5MPa, 2-8MPa, 2-10MPa, 3-5MPa, 3-8MPa, 3-10MPa, 5-8MPa, 5-10MPa, 8-10MPa, etc.; preferably, when the pressure of the introduced argon gas is 0.5-1MPa, it is more conducive to the generation of the SiC aerogel required by the present invention.

[0019] Furthermore, the specific steps of the preprocessing are as follows:

[0020] Add anhydrous ethanol to the mixture of silicon powder and carbon halide, and ball mill the mixture at 200-500 rpm for 2-8 hours. Then, put the ball-milled mixture into an oven to dry and sieve it.

[0021] Furthermore, the mass ratio of the mixture to anhydrous ethanol is 1:0.5-2.

[0022] Furthermore, the grinding balls used in the ball mill are made of zirconium oxide.

[0023] Furthermore, the mass ratio of the grinding balls to the mixture is 3-10:1.

[0024] Furthermore, the reaction temperature of the combustion synthesis reaction is 1300-2200℃, and the reaction time of the combustion synthesis reaction is 0.1-10 min.

[0025] Furthermore, before introducing high-purity argon, the process includes evacuating the reactor or purging it multiple times with high-purity argon to reduce the impact of air inside the reactor on the preparation of SiC aerogel.

[0026] Furthermore, in the combustion synthesis reactor, the combustion synthesis reaction of the mixed powder is ignited by energizing a tungsten wire coil at one end of the mixed powder.

[0027] Furthermore, the oxidation and decarbonization temperature is 500-800℃, and the oxidation and decarbonization time is 2-4 hours.

[0028] To achieve the second objective mentioned above, the present invention adopts the following technical solution:

[0029] This invention discloses a SiC aerogel prepared by the above method. The SiC aerogel has a layered SiC nanowire stacked structure with an interlayer spacing of 100-600 μm and a density of 3-20 mg / cm³. 3 Porosity is 99.3-99.9%; thermal conductivity is 21-35 mW / (m·K);

[0030] The SiC nanowires have a diameter of 10-300 nm and an aspect ratio of 500-4000.

[0031] Each SiC nanowire is coated with an amorphous SiO2 layer with a thickness of 1-8 nm.

[0032] Furthermore, the diameter of the SiC nanowires is 20-260 nm, and their aspect ratio is 1000-3000.

[0033] To achieve the third objective mentioned above, the present invention adopts the following technical solution:

[0034] This invention discloses the application of SiC aerogel in the preparation of fireproof and heat-insulating materials.

[0035] Beneficial effects of this invention:

[0036] This invention uses inexpensive silicon powder and carbon-containing halides as raw materials. It utilizes the cracking reaction between silicon and carbon-containing halides to generate gaseous halides and solid carbon, releasing a large amount of heat to activate a chemical reaction in the silicon-carbon system. The carbon source provided by the cracking of carbon-containing halides is continuously consumed, while SiC nanowires are generated in large quantities and intertwine and stack to self-assemble into SiC aerogel. This preparation condition is simple and the reaction time is short, which is conducive to industrial production. It solves the problems of high production cost, long processing time, complex production process, and the need for specific equipment in traditional aerogel production. The obtained SiC aerogel has a layered structure formed by intertwined and stacked SiC nanowires, unlike traditional aerogels which use nanocolloidal particles to form a nanoskeleton and nanoporous network structure. It has certain compression resilience and ultra-flexibility, can withstand thermal shock at 1200℃, and has good thermal and chemical stability. It has broad application prospects in energy storage, catalysis, thermal insulation, environmental protection, electromagnetic wave absorption, and electromagnetic interference shielding. Attached Figure Description

[0037] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0038] Figure 1This is a SEM image of the SiC aerogel prepared in Example 1 of the present invention. Figure 1 In the middle, a is a SEM image of the SiC aerogel layered structure; Figure 1 b is a SEM image of SiC nanowires.

[0039] Figure 2 This is a TEM image of the SiC nanowires prepared in Example 1 of the present invention.

[0040] Figure 3 The X-ray diffraction pattern is shown for the SiC aerogel prepared in Example 1 of this invention.

[0041] Figure 4 The thermal conductivity of the SiC aerogel prepared in Example 1 of this invention is shown at different temperatures.

[0042] Figure 5 This is a test of the SiC aerogel prepared in Example 1 of the present invention in terms of thermal shock resistance and fire resistance. Figure 5 Image a shows the experiment conducted using a butane spray gun (1100℃). Figure 5 Image b shows an experiment conducted using an alcohol lamp (700℃).

[0043] Figure 6 This is a SEM image of the SiC aerogel prepared in Example 2 of the present invention. Detailed Implementation

[0044] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further clarifies the invention. It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0045] Example 1

[0046] 160.0g of silicon powder (average particle size 2.8μm) and 190.0g of polytetrafluoroethylene powder (average particle size 3μm) were selected, with a molar ratio of silicon powder to polytetrafluoroethylene of 3:1. The silicon powder and polytetrafluoroethylene were mixed to obtain 350g of raw material powder. Anhydrous ethanol at a weight ratio of 1:1 to the raw material powder was added, and the mixture was transferred to a ball mill jar. The mixture was wet-milled at 360rpm for 2 hours using a planetary ball mill. Zirconia balls were selected as the grinding balls, with a ball-to-powder weight ratio of 5:1. The milled mixture was then dried in a 60℃ oven for 24 hours. The dried powder was then sieved through a 100-mesh sieve.

[0047] The sieved mixed powder was placed in a stainless steel reaction boat lined with carbon felt, and a tungsten wire coil for ignition was placed at one end of the mixed powder. Then, the mixture was placed in a sealed 30L combustion synthesis reactor. At this point, the mass ratio of the raw powder to the reactor volume was 11.7 g:1 L. The reactor was evacuated to -0.09 MPa or purged twice with high-purity argon, then filled with 1 MPa of high-purity argon. Alternating current was then applied to the tungsten wire coil to initiate the combustion synthesis reaction of the mixed powder. The highest temperature during the reaction was 1700℃, and the temperature remained above 1300℃ for 2 minutes, yielding carbon-rich SiC aerogel blocks. Finally, the obtained carbon-rich SiC aerogel blocks were oxidized in a muffle furnace at 600℃ for 4 hours to obtain layered nanowire stacked SiC aerogel with a density of 12 mg / cm³. 3 The porosity is 99.6%.

[0048] refer to Figure 1 SEM characterization revealed a distinct layered structure on the side of the product. At a smaller scale, the nanowires had an average diameter of 150 nm. The internal structure consisted of interwoven nanowires and interconnected aggregated Si and SiC particles with an average particle diameter of 1 μm. (Reference) Figure 2 TEM characterization revealed that each SiC nanowire was tightly coated with a SiO2 layer approximately 5 nm thick. (Reference) Figure 3 XRD characterization revealed that the product was pure β-SiC, containing no free silicon, and the SF (silicon superoxide dismutase) was due to stacking faults in silicon carbide. (Reference) Figure 4 It can be seen that the thermal conductivity of SiC aerogel at room temperature is 27 mW / (m·K), and the thermal conductivity at a high temperature of 600℃ is 125 mW / (m·K).

[0049] To further evaluate the high-temperature elasticity and fire resistance of SiC aerogel (see...), Figure 5 In-situ compression tests were conducted on SiC aerogels under the flames of an alcohol lamp (700℃) and a butane torch (1100℃). No ignition or structural collapse was observed when the SiC aerogels were exposed to the high-temperature flames during the compression tests. The aerogels were well compressed when further compressed with tweezers. Upon release of the tweezers, they returned to their original shape. This indicates that the SiC aerogels exhibit good elastic resilience and super-flexibility under extreme temperature conditions.

[0050] Example 2

[0051] 91.5g of silicon powder (average particle size 2.5μm) and 108.5g of polytetrafluoroethylene powder (average particle size 3μm) were selected, with a silicon to PTFE molar ratio of 3:1. The silicon powder and PTFE were mixed to obtain 200g of raw material powder. Anhydrous ethanol at a weight ratio of 1:1 to the raw material powder was added, and the mixture was transferred to a ball mill jar. The mixture was wet-milled at 360 rpm for 2 hours using a planetary ball mill. Zirconia balls were selected as the grinding balls, with a ball-to-powder weight ratio of 5:1. The milled mixture was then dried in a 60℃ oven for 24 hours. The dried powder was then sieved through a 100-mesh sieve.

[0052] The sieved mixed powder was placed in a stainless steel reaction boat lined with carbon felt, and a tungsten wire coil for ignition was placed at one end of the powder. The boat was then placed in a sealed 20L combustion synthesis reactor. The mass ratio of the raw powder to the reactor volume was 10g:1L. The reactor was evacuated to -0.06MPa or purged twice with high-purity argon, then filled with 1MPa of high-purity argon. Alternating current was then applied to the tungsten wire coil to initiate the combustion synthesis reaction of the mixed powder. The highest temperature during the reaction was 1802℃, and the temperature remained above 1300℃ for 1.5 minutes, yielding carbon-rich SiC aerogel blocks. Finally, the product was oxidized in a muffle furnace at 600℃ for 4 hours to obtain layered nanowire stacked SiC aerogel with a density of 8.9 mg / cm³. 3 The porosity is 99.7%. (Reference) Figure 6 SEM characterization revealed that a large number of SiC nanowires still exist inside the SiC aerogel, with a thermal conductivity of 26 mW / (m·K) at room temperature.

[0053] Examples 3-7

[0054] By adjusting only the average particle size of the silicon powder, while keeping other conditions the same as in Example 1, the influence of the average particle size of the silicon powder on the properties of the SiC aerogel material was investigated. The results are shown in the table below.

[0055] Table 1. Effect of different average particle sizes of silicon powder on material properties

[0056] Example number Average particle size of silicon powder (μm) <![CDATA[SiC aerogel density mg / cm 3 > Porosity % Thermal conductivity (mW / (m·K)) 3 1 16 99.4 32 4 2.9 12 99.6 27 5 10 7.9 99.7 26 6 26 6.6 99.8 26 7 45 4.8 99.8 27

[0057] Conclusion: As the average particle size of silicon powder increases from 1 μm to 45 μm, the density of the synthesized SiC aerogel material increases from 16 mg / cm³. 3 Reduced to 4.8 mg / cm 3 The porosity increased from 99.4% to 99.8%, while the thermal conductivity decreased from 32 mW / (m·K) to 27 mW / (m·K).

[0058] Examples 8-12

[0059] By adjusting only the average particle size of the carbon-containing halides, while keeping other conditions the same as in Example 1, the influence of the average particle size of the carbon-containing halides on the properties of the SiC aerogel material was investigated. The results are shown in the table below.

[0060] Table 2. Effect of average particle size of different carbon halide on material properties

[0061]

[0062] Conclusion: The average particle size of carbon halide has a certain influence on the density of SiC aerogel. Adjusting the average particle size of the raw materials is necessary to obtain SiC aerogels with the desired density. The lower the density of the SiC aerogel, the lower its thermal conductivity and the better its thermal insulation effect.

[0063] Examples 13-17

[0064] Only the argon gas pressure was adjusted, while other conditions remained the same as in Example 1. The effect of argon gas pressure on the properties of the SiC aerogel material was examined, and the results are shown in the table below.

[0065] Table 3. Effects of different argon gas pressures on material properties

[0066] Example number air pressure value MPa <![CDATA[SiC aerogel density mg / cm 3 > Porosity % Thermal conductivity (mW / (m·K)) 13 0.5 8.5 99.7 26 14 2 12.7 99.6 29 15 3 11 99.6 28 16 4 12.1 99.6 30 17 5 9.8 99.6 25

[0067] Conclusion: The synthesized SiC aerogel material exhibits excellent properties under argon pressures of 0.5-5 MPa, with a density ≥6 mg / cm³. 3 Porosity ≥ 99.6%, thermal conductivity ≤ 30 mW / (m·K).

[0068] Examples 18-21

[0069] With the reactor volume (5L) kept constant, only the mass of the raw material powder was adjusted, and other conditions and parameters were the same as in Example 1. The effect of the ratio of the mass of the raw material powder to the reactor volume on the properties of the SiC aerogel material was tested, and the results are shown in the table below.

[0070] Table 4. Effects of different raw material powder quality on material properties

[0071] Example number Mass of raw material powder (g) <![CDATA[SiC aerogel density mg / cm 3 > Porosity % Thermal conductivity (mW / (m·K)) 18 30 8.4 99.6 29 19 60 8.9 99.6 28 20 90 7.9 99.7 27 21 120 4.6 99.8 25

[0072] Conclusion: When the mass of the raw material powder is 30-120g, i.e., the mass ratio of the raw material powder to the reactor volume is (6-24)g:1L, the synthesized SiC aerogel material exhibits excellent properties with a density ≥4.6mg / cm³. 3 Porosity ≥ 99.6%, thermal conductivity ≤ 29 mW / (m·K).

[0073] Comparative Example 1

[0074] 91.5g of silicon powder (average particle size 2.5μm) and 108.5g of polytetrafluoroethylene powder (average particle size 3μm) were selected, with a silicon to PTFE molar ratio of 3:1. The silicon powder and PTFE were mixed to obtain 200g of raw material powder. Anhydrous ethanol at a weight ratio of 1:1 to the raw material powder was added, and the mixture was transferred to a ball mill jar. The mixture was wet-milled at 360 rpm for 2 hours using a planetary ball mill. Zirconia balls were selected as the grinding balls, with a ball-to-powder weight ratio of 5:1. The milled mixture was then dried in a 60℃ oven for 24 hours. The dried powder was then sieved through a 100-mesh sieve.

[0075] The sieved mixed powder was placed in a stainless steel reaction boat lined with carbon felt, and a tungsten wire coil for ignition was placed at one end of the powder. The mixture was then placed in a sealed 20L combustion synthesis reactor. The mass ratio of the raw powder to the reactor volume was 10g:1L. The reactor was evacuated to -0.04MPa or purged twice with high-purity argon, then filled with high-purity argon to 0.01MPa. Alternating current was then applied to the tungsten wire coil to initiate the combustion synthesis reaction of the mixed powder. The highest temperature during the reaction was 1792℃, and the temperature remained above 1300℃ for 1 minute. Carbon- and silicon-rich SiC powder was obtained, but SiC aerogel was not obtained.

[0076] Comparative Example 2

[0077] 11.4g of silicon powder (average particle size 2.5μm) and 13.5g of polytetrafluoroethylene powder (average particle size 3μm) were selected, with a silicon to PTFE molar ratio of 3:1. The silicon powder and PTFE were mixed to obtain 25g of raw material powder. Anhydrous ethanol at a weight ratio of 1:1 to the raw material powder was added, and the mixture was transferred to a ball mill jar. The mixture was wet-milled at 360 rpm for 2 hours using a planetary ball mill. Zirconia balls were selected as the grinding balls, with a ball-to-powder weight ratio of 5:1. The milled mixture was then dried in a 60℃ oven for 24 hours. The dried powder was then sieved through a 100-mesh sieve.

[0078] The sieved mixed powder was placed in a stainless steel reaction boat lined with carbon felt, and a tungsten wire coil for ignition was placed at one end of the powder. Then, the mixture was placed in a sealed 5L combustion synthesis reactor. At this point, the mass ratio of the raw powder to the reactor volume was 5g:1L. The reactor was evacuated to -0.06MPa or purged twice with high-purity argon, then filled with 1MPa of high-purity argon. Alternating current was then passed through the tungsten wire coil to initiate the combustion synthesis reaction of the mixed powder. The highest temperature during the reaction was 1850℃, and the temperature remained above 1300℃ for 1 minute. Carbon-rich SiC powder and a small amount of SiC nanowires were obtained; SiC aerogel blocks were not obtained.

[0079] Comparative Example 3

[0080] 91.5g of silicon powder (average particle size 2.5μm) and 108.5g of polytetrafluoroethylene powder (average particle size 3μm) were selected, with a silicon to PTFE molar ratio of 3:1. The silicon powder and PTFE were mixed to obtain 200g of raw material powder. Anhydrous ethanol at a weight ratio of 1:1 to the raw material powder was added, and the mixture was transferred to a ball mill jar. The mixture was wet-milled at 360 rpm for 2 hours using a planetary ball mill. Zirconia balls were selected as the grinding balls, with a ball-to-powder weight ratio of 5:1. The milled mixture was then dried in a 60℃ oven for 24 hours. The dried powder was then sieved through a 100-mesh sieve.

[0081] The sieved mixed powder was placed in a stainless steel reaction boat lined with carbon felt, and a tungsten wire coil for ignition was placed at one end of the powder. Then, the mixture was placed in a sealed 20L combustion synthesis reactor. At this point, the mass ratio of the raw material powder to the reactor volume was 10g:1L. The reactor was evacuated to -0.06MPa or purged twice with high-purity nitrogen, then filled with 1MPa of high-purity nitrogen. Alternating current was then passed through the tungsten wire coil to initiate the combustion synthesis reaction of the mixed powder. The highest temperature during the reaction was 1973℃, and the duration above 1300℃ was 2 minutes. A mixed powder of SiC and Si3N4 was obtained, but SiC aerogel was not obtained.

[0082] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing SiC aerogel, characterized in that, Includes the following steps: (1) Using silicon powder as the silicon source and carbon-containing halide as the carbon source, the silicon powder and carbon-containing halide are mixed in proportion to obtain raw material powder, and the mixed powder is obtained after pretreatment; (2) The obtained mixed powder is placed in a closed combustion synthesis reactor, and then high-purity argon gas at a certain pressure is introduced. The mixed powder is then ignited by a tungsten wire coil to produce a combustion synthesis reaction, and carbon-rich SiC aerogel blocks are obtained. (3) The carbon-rich SiC aerogel block was oxidized at a certain temperature to remove carbon, and SiC aerogel with stacked layered nanowires was obtained. The pressure of the introduced argon gas is 0.1-10 MPa; The ratio between the mass of the raw material powder and the volume of the combustion synthesis reactor is (6-40) g: 1 L; The carbon-containing halides include one or more of polytetrafluoroethylene, polyvinylidene fluoride, and polyvinyl chloride.

2. The preparation method according to claim 1, characterized in that, The average particle size of the silicon powder and carbon-containing halides is 0.1-100 μm.

3. The preparation method according to claim 1, characterized in that, The molar ratio of silicon powder to carbon-containing halide is 1-7:

1.

4. The preparation method according to claim 1, characterized in that, The specific steps of the preprocessing are as follows: Add anhydrous ethanol to the mixture of silicon powder and carbon halide, and ball mill the mixture at 200-500 rpm for 2-8 hours. Then, put the ball-milled mixture into an oven to dry and sieve it.

5. The preparation method according to claim 4, characterized in that, The mass ratio of the mixture to anhydrous ethanol is 1:0.5-2.

6. The preparation method according to claim 4, characterized in that, The grinding balls used in the ball mill are made of zirconium oxide.

7. The preparation method according to claim 6, characterized in that, The mass ratio of the grinding balls to the mixture is 3-10:

1.

8. The preparation method according to claim 1, characterized in that, The reaction temperature of the combustion synthesis reaction is 1300-2200℃, and the reaction time is 0.1-10 min.

9. The preparation method according to claim 1, characterized in that, The oxidation and decarbonization temperature is 500-800℃, and the oxidation and decarbonization time is 2-4 hours.

10. The SiC aerogel prepared by the preparation method according to any one of claims 1-9, characterized in that, The SiC aerogel has a layered SiC nanowire stacked structure with an interlayer spacing of 100-600 μm and a density of 3-20 mg / cm³. 3 The porosity is 99.3-99.9%; the thermal conductivity is 21-35 mW / (m·K); The SiC nanowires have a diameter of 10-300 nm and an aspect ratio of 500-4000. Each SiC nanowire is coated with an amorphous SiO2 layer with a thickness of 1-8 nm.

11. The SiC aerogel according to claim 10, characterized in that, The SiC nanowires have a diameter of 20-260 nm and an aspect ratio of 1000-3000.

12. The application of the SiC aerogel prepared by the preparation method according to any one of claims 1-9 or the SiC aerogel according to any one of claims 10-11 in the preparation of fireproof and heat-insulating materials.

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