A method for efficiently preparing silicon carbide aerogel

Abstract

A method for efficiently preparing silicon carbide aerogel, an inorganic carbon source, an interface dispersing agent and ethanol are added into an aqueous solution of a silicon source, and stirred and uniformly dispersed to obtain a carbon-doped silicon mixed solution A; an acidic compound catalyst is added into the mixed solution A to obtain a carbon-doped silicon solution B; an alkaline compound catalyst is added into the carbon-doped silicon solution B to obtain a carbon-doped silicon sol C; and ethanol is added to obtain a carbon-doped silicon gel D; the carbon-doped silicon gel D is transported through a pipeline to a distributor, and continuously transported to a heat treatment reaction device I provided with an electromagnetic induction coil outside to obtain a composite aerogel D; the composite aerogel D is sequentially transferred to a heat treatment device II and a heat treatment device III provided with electromagnetic induction coils outside to obtain the silicon carbide aerogel, and the method for preparing the silicon carbide aerogel by using the Joule heat synthesis technology is realized to achieve the rapid preparation of the silicon carbide aerogel in seconds, the preparation process is simple, and the heat treatment energy consumption is low.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide aerogels, specifically a method for efficiently preparing silicon carbide aerogels. Background Technology

[0002] Aerogel is a solid material with extremely low density, high porosity and excellent insulation properties. SiC material, as a high-temperature microwave absorbing material, has excellent mechanical properties, high-temperature stability and chemical stability, and can withstand high temperatures of over 800℃, which is superior to metal and carbon-based microwave absorbing materials.

[0003] Chinese patent (patent number: CN114315365B) discloses a method for preparing silicon carbide aerogel. The method involves uniformly mixing terephthalaldehyde, aminosilane, organosiloxane, acetic acid, ethanol, and deionized water, followed by a hydrolysis-co-condensation reaction of the organosilane to obtain a polysiloxane wet gel. The polysiloxane wet gel is then aged and vacuum dried to obtain a polysiloxane aerogel. Finally, the aerogel is heat-treated at 1400-1600℃ for 2-5 hours under an argon atmosphere at a heating rate of 1-5℃ / min to obtain a blocky silicon carbide aerogel.

[0004] Chinese patent (patent number: CN105600785B) discloses a method for preparing silicon carbide aerogel. The method involves dissolving polycarbosilane and a vinyl compound in an organic solvent, reacting them under anaerobic conditions (70℃-90℃) with a Karstedt catalyst for 4-8 hours to obtain a polycarbosilane gel. This gel is then subjected to supercritical drying or freeze-drying to obtain a polycarbosilane aerogel. The polycarbosilane aerogel is then heat-treated to obtain a silicon carbide / carbon composite aerogel. Finally, the silicon carbide / carbon composite aerogel is calcined under aerobic conditions (500℃-700℃) for 1-5 hours to obtain a silicon carbide aerogel.

[0005] Chinese patent (patent number: CN115611632B) discloses a method for preparing silicon carbide aerogel. The method involves mixing and drying a silicon source, solvent, and organic polymer fibers to obtain a silicon-carbon composite material. This composite material is then sintered to obtain silicon carbide rice noodle raw material, which is dispersed in a solvent and mixed with inorganic fibers and a crosslinking agent to obtain a silicon carbide nanowire inorganic fiber suspension. This suspension is then freeze-treated to obtain a composite gel. The composite gel is dried to obtain a pre-prepared high-temperature resistant silicon carbide aerogel composite thermal insulation material. Finally, the pre-prepared high-temperature resistant silicon carbide aerogel composite thermal insulation material is heat-treated at 800-1000℃ for 1-2 hours to obtain a flexible high-temperature resistant silicon carbide aerogel composite thermal insulation material.

[0006] As can be seen from the above preparation methods, the current preparation of silicon carbide aerogel requires a large amount of organic solvents, and the preparation process is cumbersome, resulting in serious pollution and high cost. At the same time, the preparation of silicon carbide aerogel requires heat treatment at about 1000℃ for about 1 hour, which results in a long preparation cycle and relatively complex process, high energy consumption and low production efficiency.

[0007] Therefore, Chinese Patent (Patent No.: CN10932022A) discloses a method for preparing SiC aerogel by ultrasonically mixing a silicon source and a carbon source, including the preparation of a SiC precursor and the preparation of SiC aerogel. The preparation of the SiC precursor involves mixing water glass with an acid solution and stirring at 0-50℃ for 10-60 min to prepare silicic acid. Sodium salt is removed by alcohol precipitation at 0-50℃ for 10-60 min. A carbon source is then added, and the mixture is ultrasonically mixed at 30-50℃ for 0.5-1.5 h. The water glass... The molar ratio of glass to carbon source is 1-5:1. Preparation of SiC aerogel: Ammonia water is added to the liquid obtained in the above steps and stirred to obtain a sol. A fiber felt is immersed in the sol using a micro-pressure device, and the gel is allowed to stand. Aging and displacement are carried out at a temperature of 30-50℃ and an ultrasonic frequency of 25kHz-130kHz for 0.5-2 hours. The gel is then dried and kept at an inert atmosphere and 1300-1500℃ for 2-6 hours. Finally, the temperature is lowered to 100-600℃, and air is introduced for 2-5 hours to obtain SiC aerogel. This method does not require a large amount of organic solvent, reducing pollution and lowering costs; however, this method still requires long-term heat treatment at high temperatures, resulting in high energy consumption and low production efficiency. Summary of the Invention

[0008] To address the issues of high energy consumption and low production efficiency in the preparation of silicon carbide aerogels in existing technologies, this invention provides a method for the efficient preparation of silicon carbide aerogels in seconds using Joule thermal synthesis technology. The preparation process is simple, with low energy consumption for heat treatment and high production efficiency.

[0009] To achieve the above objectives, the specific solution adopted by the present invention is as follows: a method for efficiently preparing silicon carbide aerogel, comprising the following steps:

[0010] S1, add inorganic carbon source, interfacial dispersant and ethanol to the aqueous solution of silicon source, stir and disperse evenly to obtain carbon-doped silicon mixed solution A;

[0011] S2, add an acidic composite catalyst to the mixed solution A in S1, control the pH of the solution to be 2 to 6.5, and react at 20 to 55℃ for 0.2 to 6 hours to obtain carbon-doped silicon solution B;

[0012] S3, add an alkaline composite catalyst to the carbon-doped silicon solution B in S2, control the pH of the solution to 7.5-10.5, and react for 0.1-5 h at 20-55 °C to obtain carbon-doped silicon sol C; add ethanol to carbon-doped silicon sol C and age at room temperature for 1-3 days to obtain carbon-doped silicon gel D.

[0013] S4, control the pressure in the conveying pipeline to be 0.5-2.5MPa, the temperature of carbon-doped silicon gel D in the conveying pipeline to be 90-220℃, and convey the carbon-doped silicon gel D in S3 to the distributor through the pipeline. It is continuously conveyed to the heat treatment reaction device I equipped with an electromagnetic induction coil. The residence time of carbon-doped silicon gel D in the reaction chamber of heat treatment device I is 0.5-60s. The reaction chamber is in an inert gas atmosphere to obtain composite aerogel D.

[0014] S5, the composite aerogel D in S4 is transferred to the heat treatment device II equipped with an electromagnetic induction coil. The composite aerogel D stays in the reaction chamber of the heat treatment device II for 0.5 to 30 seconds to obtain carbon-rich aerogel E.

[0015] S6, the carbon-rich aerogel E in S5 is transferred to the heat treatment device III equipped with an electromagnetic induction coil. The carbon-rich aerogel E stays in the reaction chamber of the heat treatment device III for 2 to 1200 seconds to obtain silicon carbide aerogel.

[0016] As an optimized scheme of the above-mentioned efficient method for preparing silicon carbide aerogel: the inorganic carbon powder in step S1 is one or more of carbon black, carbon nanotubes, C60, fullerene, graphite, and graphene; the average particle size of the carbon powder is 0.1-200 nm.

[0017] As another optimized method for the above-mentioned efficient preparation of silicon carbide aerogel: the interfacial dispersant in step S1 is one or more of polyacrylamide, sodium dodecyl sulfate, sodium polyacrylate, KH550, polyvinyl alcohol, sodium polyacrylate, and BYK163; the mass ratio of inorganic carbon powder, interfacial dispersant, and silicon source in step S1 is 0.5-4.5:0.003-0.01:1.

[0018] As another optimized method for the efficient preparation of silicon carbide aerogels described above: the molar concentration of the silicon source in step S1 is 0.1–10 mol / L, and the silicon source is one or more of organosilicon and inorganic silicon sources. The inorganic silicon source includes sodium silicate, sodium methylsilicate, potassium silicate, or silica sol. The organosilicon source is a substance that satisfies three general structural formulas, where R1, R2, R3, and R4 are H, alkyl groups, or alkyl groups containing heteroatoms. The three general structural formulas are as follows:

[0019]

[0020] As another optimized scheme of the above-mentioned efficient method for preparing silicon carbide aerogel: the acidic composite catalyst in step S2 is a mixture of acidic substance and acetic acid, and the molar ratio of acidic substance to acetic acid is 0.02 to 0.10:1; the acidic substance includes one or more of organic acid, inorganic acid, and acidic gas, the organic acid is formic acid, acetic acid, oxalic acid or lactic acid, the inorganic acid is sulfuric acid, nitric acid or hydrochloric acid, and the acidic gas is sulfur oxide, nitrogen oxide or carbon dioxide.

[0021] As another optimized scheme of the above-mentioned efficient method for preparing silicon carbide aerogel: the alkaline composite catalyst in step S3 is a mixture of alkaline substance and ethanol, and the molar ratio of alkaline substance to ethanol is 0.01 to 0.12:1; the alkaline substance is an inorganic alkaline solution or an aqueous solution of an inorganic alkaline substance, and the organic alkaline solution is an organic amine; the aqueous solution of the organic alkaline substance is ethylenediamine, triethanolamine or triethylenetetramine, and the inorganic alkaline solution is sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution or ammonia water.

[0022] As another optimized method for the above-mentioned efficient preparation of silicon carbide aerogel: in S3, ethanol is added to carbon-doped silica sol C, and the mass ratio of ethanol to carbon-doped silica sol C is 0.01 to 0.20:1.

[0023] As another optimized scheme of the above-mentioned efficient method for preparing silicon carbide aerogel: heat treatment device I, heat treatment device II, and heat treatment device III all include a vertical cylinder. The top of the cylinder is provided with a distributor for the entry of carbon-doped silicon sol C or carbon-doped silicon gel D and an air inlet for the entry of inert gas, air, or oxygen. The cylinder includes a feeding section, a heat treatment section, and a cooling section arranged from top to bottom. Electromagnetic induction coils are wound on the outer walls of the heat treatment section and the cooling section. An oxygen content analyzer, pressure, and temperature sensors are installed inside the reaction chamber.

[0024] As another optimized scheme of the above-mentioned efficient method for preparing silicon carbide aerogel: the reaction chamber of the heat treatment device I in step S4 is filled with a flowing inert gas atmosphere, with a temperature of 150-300℃ and a pressure of 3-10MPa.

[0025] As another optimized method for the above-mentioned efficient preparation of silicon carbide aerogel: the reaction chamber of the heat treatment device II in step S5 is in an inert gas atmosphere, with a temperature of 1000-1500℃ and a pressure of 0.02-0.5MPa.

[0026] As another optimized method for the efficient preparation of silicon carbide aerogels described above: the reaction chamber of the heat treatment apparatus III in step S6 is filled with oxygen or air, the temperature is 400-800℃, and the pressure is 0.02-0.5MPa.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. This invention provides a highly efficient method for preparing silicon carbide aerogel. Using inorganic carbon powder and silicon source as raw materials, the inorganic carbon powder, dispersant, and silicon source are thoroughly and uniformly dispersed to obtain a carbon-doped silicon mixed solution A. An acidic composite catalyst and an alkaline composite catalyst are sequentially added to the carbon-doped silicon mixed solution A to obtain a carbon-doped silicon sol C. The carbon-doped silicon sol C is preheated, and then the preheated carbon-doped silicon sol C enters a heat treatment device I equipped with an external electromagnetic induction coil. The carbon-doped silicon sol C is calcined under inert gas conditions to form a composite aerogel D. The composite aerogel D is transferred to a heat treatment device II equipped with an external electromagnetic induction coil to obtain a carbon-rich aerogel E. The carbon-rich aerogel E remains in the reaction chamber of the heat treatment device III for 2–1200 s to obtain silicon carbide aerogel. The heat treatment temperature is low and the material residence time in the heat treatment device is short, meaning this preparation method has low energy consumption and high production efficiency; simultaneously, it increases the concentration of silicon carbide aerogel.

[0029] 2. In this invention, electromagnetic induction coils are provided on the outer walls of heat treatment device I, heat treatment device II and heat treatment device III. That is, carbon-doped silicon sol C, carbon-doped silicon gel D and carbon-rich aerogel E are heat-treated by electromagnetic induction heating. This can heat them in a short time, shorten the heat treatment time and improve the production efficiency of silicon carbide aerogel. Attached Figure Description

[0030] Figure 1 These are schematic diagrams of the structures of heat treatment apparatus I and heat treatment apparatus II;

[0031] Figure 2 This is a schematic diagram of the structure of heat treatment device III;

[0032] Figure 3 This is a SEM image of the silicon carbide aerogel in Example 1;

[0033] Figure 4 This is a SEM image of the silicon carbide aerogel in Example 2;

[0034] Figure 5 These are HR-TEM and electron diffraction images of silicon carbide aerogel. Detailed Implementation

[0035] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. Parts not described or disclosed in detail in the following embodiments of the present invention should be understood as prior art known or should be known by those skilled in the art.

[0036] A method for efficiently preparing silicon carbide aerogel includes the following steps:

[0037] S1, an inorganic carbon source, an interfacial dispersant, and ethanol are added to an aqueous solution of a silicon source and stirred until uniformly dispersed to obtain a carbon-doped silicon mixed solution A. The mass ratio of inorganic carbon powder, interfacial dispersant, and silicon source is 0.5–2.5:0.003–0.01:1. The particle size of the inorganic carbon powder is 0.1–200 nm, preferably 0.1–50 nm, which is beneficial for the high dispersion of inorganic carbon powder within the silicon source. Inorganic carbon powder refers to one or more carbon materials and carbon-containing powder materials. Specifically, inorganic carbon powder is one or more of carbon black, carbon nanotubes, C60, fullerene, graphite, and graphene. The interfacial dispersant is one or more of polyacrylamide, sodium dodecyl sulfate, sodium polyacrylate, KH550, polyvinyl alcohol, sodium polyacrylate, and BYK163; the molar concentration of the silicon source is 0.1-10 mol / L, and the silicon source is one or more of organosilicon and inorganic silicon sources, wherein the inorganic silicon source includes sodium silicate, potassium silicate, or silica sol; the organosilicon source is a substance that satisfies three general structural formulas, where R1, R2, R3, and R4 can be H, alkyl, or alkyl containing heteroatoms, and the three general structural formulas are as follows:

[0038]

[0039] S2, add an acidic composite catalyst to the mixed solution A in S1, control the pH of the solution to be 2-6.5, and react at 20-55℃ for 0.2-6 h to obtain carbon-doped silicon solution B; the carbon-doped silicon mixed solution A is mixed with the acidic substance using an atmospheric pressure or pressure vessel. The acidic composite catalyst is a mixture of acidic substance and acetic acid, with a molar ratio of acidic substance to acetic acid of 0.02-0.10:1; the acidic substance includes one or more of organic acids, inorganic acids, and acidic gases, the organic acid being formic acid, acetic acid, oxalic acid, or lactic acid, the inorganic acid being sulfuric acid, nitric acid, or hydrochloric acid, and the acidic gas being sulfur oxides, nitrogen oxides, or carbon dioxide.

[0040] In step S3, an alkaline composite catalyst is added to the carbon-doped silicon solution B in step S2. The pH of the solution is controlled at 7.5–10.5, and the reaction is carried out at 20–55°C for 0.1–5 hours to obtain carbon-doped silicon sol C. The alkaline composite catalyst is a mixture of an alkaline substance and ethanol, with a molar ratio of alkaline substance to ethanol of 0.01–0.12:1. The alkaline substance is an inorganic alkali solution or an aqueous solution of an inorganic alkali, and the organic alkali solution is an organic amine. The aqueous solution of the organic alkali is ethylenediamine, triethanolamine, or triethylenetetramine, and the inorganic alkali solution is sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, or ammonia. Ethanol is added to carbon-doped silicon sol C, and the mixture is aged at room temperature for 1–3 days to obtain carbon-doped silicon gel D.

[0041] In step S4, the pressure inside the conveying pipeline is controlled at 0.5-2.5 MPa, and the temperature of the carbon-doped silicon gel D inside the pipeline is 90-220℃. The carbon-doped silicon gel D from step S3 is conveyed through the pipeline to the distributor and continuously conveyed to the heat treatment reaction device I equipped with an external electromagnetic induction coil. The residence time of the carbon-doped silicon gel D in the reaction chamber of the heat treatment device I is 0.5-60 s, resulting in composite aerogel D. The reaction chamber of the heat treatment device I is filled with a flowing inert gas atmosphere, with a temperature of 150-300℃ and a pressure of 3-10 MPa. In other words, the preheated carbon-doped silicon gel D flows through the heat treatment device I for supercritical drying to form powdered composite aerogel D. The inorganic carbon powder is highly dispersed in the silicon source, and under the heating of the electromagnetic induction coil, the carbon can rapidly heat up within a short period of time to obtain composite aerogel D.

[0042] The heat treatment device I includes a vertical cylindrical body, comprising a feeding section, a heat treatment section, and a cooling section arranged from top to bottom. Electromagnetic induction coils are wound around the outer walls of the heat treatment and cooling sections, and a heat insulation pad is fitted onto the outer wall at the connection point between the heat treatment and cooling sections. The top of the cylindrical body is equipped with a distributor for the entry of carbon-doped silicon gel D and an inlet for introducing inert gas. An oxygen meter for detecting the internal oxygen content is also installed at the top of the cylindrical body. The bottom of the cooling section is equipped with a pressure relief valve and a burst relief plate. The bottom of the cooling section tapers inwards to form an inward section, with an outlet at the bottom for the composite aerogel D to flow out. A one-way valve is installed at the outlet. The carbon-doped silicon gel D continuously enters the feeding section of the cylindrical body through the distributor and, under its own gravity, flows sequentially through the heat treatment and cooling sections to form composite aerogel D. The temperature is reduced to 90-100℃ in the cooling section. Finally, the composite aerogel D flows out through the outlet.

[0043] S5, the composite aerogel D in S4 is transferred to the heat treatment device II equipped with an electromagnetic induction coil. The composite aerogel D stays in the reaction chamber of the heat treatment device II for 0.5 to 30 seconds to obtain carbon-rich aerogel E. The reaction chamber of the heat treatment device II is in an inert gas atmosphere, with a temperature of 1000 to 1500°C and a pressure of 0.02 to 0.5 MPa.

[0044] The heat treatment device II includes a vertical cylindrical body, comprising a feeding section, a heat treatment section, and a cooling section arranged from top to bottom. Electromagnetic induction coils are wound around the outer walls of the heat treatment and cooling sections, and a heat insulation pad is fitted onto the outer wall at the connection point between the heat treatment and cooling sections. The top of the cylindrical body is equipped with a distributor for the entry of composite aerogel D and an inlet for introducing inert gas. An oxygen meter for detecting the internal oxygen content is also located at the top of the cylindrical body. The bottom of the cooling section is equipped with a pressure relief valve and a burst relief plate. The bottom of the cooling section tapers inwards to form an inward section, with an outlet at the bottom for the outflow of carbon-rich aerogel E. A one-way valve is installed at the outlet. Composite aerogel D continuously enters the feeding section of the cylindrical body through the distributor and, under its own gravity, flows sequentially through the heat treatment and cooling sections to generate carbon-rich aerogel E. The temperature of carbon-rich aerogel E is reduced to 90-100℃ in the cooling section. Finally, carbon-rich aerogel E flows out through the outlet.

[0045] S6, the carbon-rich aerogel E in S5 is transferred to a heat treatment device III equipped with an electromagnetic induction coil. The carbon-rich aerogel E stays in the reaction chamber of the heat treatment device III for 2 to 1200 seconds to obtain silicon carbide aerogel. The residual carbon in the carbon-rich aerogel E is calcined to increase the concentration of silicon carbide aerogel.

[0046] The heat treatment device III includes a vertical cylindrical body, comprising a feeding section, a heat treatment section, and a cooling section arranged from top to bottom. Electromagnetic induction coils are wound around the outer walls of the heat treatment and cooling sections, and heat insulation pads are fitted onto the outer walls at the connection points of the heat treatment and cooling sections. The top of the cylindrical body is equipped with a distributor for the entry of carbon-rich aerogel E and an air inlet for the introduction of air or oxygen. An oxygen meter for detecting the internal oxygen content is also installed at the top of the cylindrical body. The bottom of the cooling section is equipped with a pressure relief valve and a burst relief plate. The bottom of the cooling section tapers inwards to form an inward section, with an outlet at the bottom for the silicon carbide aerogel to flow out. A one-way valve is installed at the outlet. The carbon-rich aerogel E continuously enters the feeding section of the cylindrical body through the distributor and, under its own gravity, flows sequentially through the heat treatment and cooling sections to form silicon carbide aerogel, which finally flows out through the outlet.

[0047] The above preparation method takes less time and has a lower heat treatment temperature, which reduces energy consumption and improves production efficiency, enabling it to be mass-produced.

[0048] Example 1

[0049] A method for efficiently preparing silicon carbide aerogel includes the following steps:

[0050] S1, graphite with a particle size of 0.1 nm and polyacrylamide are added to sodium silicate to obtain carbon-doped silicon mixed solution A, and the mass ratio of graphite, polyacrylamide and sodium silicate is 0.005:0.003:1;

[0051] S2, add a mixture of hydrochloric acid and acetic acid to the carbon-doped silicon mixed solution A in S1 to obtain carbon-doped silicon solution B, control the pH to 3.6, and react at 20℃ for 0.2 h to obtain carbon-doped silicon solution B;

[0052] S3, add an alkaline composite catalyst to the carbon-doped silicon solution B in S2, control the solution pH to 7.5, and react at 20℃ for 0.1h to obtain carbon-doped silicon sol C; add ethanol to carbon-doped silicon sol C and age at room temperature for 1 day to obtain carbon-doped silicon gel D.

[0053] S4, the pressure inside the conveying pipeline is controlled at 0.5MPa, and the temperature of the carbon-doped silicon gel D inside the conveying pipeline is 90℃. The carbon-doped silicon gel D in S3 is conveyed to the distributor through the pipeline and continuously conveyed to the heat treatment reaction device I equipped with an external electromagnetic induction coil. The residence time of the carbon-doped silicon gel D in the reaction chamber of the heat treatment device I is 60s, and composite aerogel D is obtained. The reaction chamber of the heat treatment device I is filled with a flowing inert gas atmosphere, with a temperature of 150℃ and a pressure of 10MPa.

[0054] S5, the composite aerogel D in S4 is transferred to the heat treatment device II equipped with an electromagnetic induction coil. The composite aerogel D stays in the reaction chamber of the heat treatment device II for 30s to obtain carbon-rich aerogel E. The reaction chamber of the heat treatment device II is in an inert gas atmosphere, at a temperature of 1000℃ and a pressure of 0.5MPa.

[0055] In step S6, the carbon-rich aerogel E from step S5 is transferred to a heat treatment apparatus III equipped with an external electromagnetic induction coil. The carbon-rich aerogel E remains in the reaction chamber of heat treatment apparatus III for 1200 seconds to obtain silicon carbide aerogel. The reaction chamber of heat treatment apparatus III is filled with an oxygen atmosphere at a temperature of 400℃ and a pressure of 0.5 MPa. The SEM image of the silicon carbide aerogel is shown below. Figure 3 As shown, the HR-TEM image of the silicon carbide aerogel is as follows: Figure 5 Electron diffraction images of silicon carbide aerogels are shown in (a) and (b). Figure 5 (c) in the middle.

[0056] Example 2

[0057] A method for efficiently preparing silicon carbide aerogel includes the following steps:

[0058] S1, graphite with a particle size of 200 nm and polyacrylamide are added to sodium silicate to obtain carbon-doped silicon mixed solution A, with the mass ratio of graphite, polyacrylamide and sodium silicate being 0.02:0.01:1;

[0059] S2, add a mixture of hydrochloric acid and acetic acid to the carbon-doped silicon mixed solution A in S1 to obtain carbon-doped silicon solution B. Control the pH to 6.5 and react at 55℃ for 6 hours to obtain carbon-doped silicon solution B.

[0060] S3, add an alkaline composite catalyst to the carbon-doped silicon solution B in S2, control the pH of the solution to 10.5, and react at 55℃ for 5h to obtain carbon-doped silicon sol C; add ethanol to carbon-doped silicon sol C and age at room temperature for 3 days to obtain carbon-doped silicon gel D.

[0061] S4, the pressure inside the conveying pipeline is controlled at 2.5 MPa, and the temperature of the carbon-doped silicon gel D inside the conveying pipeline is 220℃. The carbon-doped silicon gel D in S3 is conveyed to the distributor through the pipeline and continuously conveyed to the heat treatment reaction device I equipped with an electromagnetic induction coil. The residence time of the carbon-doped silicon gel D in the reaction chamber of the heat treatment device I is 0.5 s, and composite aerogel D is obtained. The reaction chamber of the heat treatment device I is filled with a flowing inert gas atmosphere, with a temperature of 300℃ and a pressure of 3 MPa.

[0062] S5, the composite aerogel D in S4 is transferred to the heat treatment device II equipped with an electromagnetic induction coil. The composite aerogel D stays in the reaction chamber of the heat treatment device II for 0.5s to obtain carbon-rich aerogel E. The reaction chamber of the heat treatment device II is in an inert gas atmosphere, at a temperature of 1500℃ and a pressure of 0.02MPa.

[0063] S6, the carbon-rich aerogel E from S5 is transferred to a heat treatment device III equipped with an electromagnetic induction coil. The carbon-rich aerogel E remains in the reaction chamber of heat treatment device III for 2 seconds to obtain silicon carbide aerogel. The reaction chamber of heat treatment device III is filled with an oxygen atmosphere at a temperature of 800℃ and a pressure of 0.02 MPa. The SEM image of the silicon carbide aerogel is shown below. Figure 4 As shown.

[0064] Example 3

[0065] A method for efficiently preparing silicon carbide aerogel includes the following steps:

[0066] S1, graphite with a particle size of 50 nm and polyacrylamide are added to sodium silicate to obtain carbon-doped silicon mixed solution A, the mass ratio of graphite, polyacrylamide and sodium silicate is 0.01:0.008:1;

[0067] S2, add a mixture of hydrochloric acid and acetic acid to the carbon-doped silicon mixed solution A in S1 to obtain carbon-doped silicon solution B, control the pH to 5.3, and react at 30℃ for 3h to obtain carbon-doped silicon solution B;

[0068] S3, add an alkaline composite catalyst to the carbon-doped silicon solution B in S2, control the solution pH to 9.2, and react at 30℃ for 2.5 h to obtain carbon-doped silicon sol C; add ethanol to carbon-doped silicon sol C and age at room temperature for 2 days to obtain carbon-doped silicon gel D.

[0069] S4, control the pressure inside the conveying pipeline to 2MPa, and the temperature of the carbon-doped silicon gel D inside the conveying pipeline to 100℃. The carbon-doped silicon gel D in S3 is conveyed to the distributor through the pipeline and continuously conveyed to the heat treatment reaction device I equipped with an external electromagnetic induction coil. The residence time of the carbon-doped silicon gel D in the reaction chamber of the heat treatment device I is 30s, and composite aerogel D is obtained. The reaction chamber of the heat treatment device I is filled with a flowing inert gas atmosphere, with a temperature of 220℃ and a pressure of 5MPa.

[0070] S5, the composite aerogel D in S4 is transferred to the heat treatment device II equipped with an electromagnetic induction coil. The composite aerogel D stays in the reaction chamber of the heat treatment device II for 15s to obtain carbon-rich aerogel E. The reaction chamber of the heat treatment device II is in an inert gas atmosphere, at a temperature of 1250℃ and a pressure of 0.25MPa.

[0071] S6, the carbon-rich aerogel E in S5 is transferred to a heat treatment device III equipped with an electromagnetic induction coil. The carbon-rich aerogel E stays in the reaction chamber of the heat treatment device III for 600s to obtain silicon carbide aerogel. The reaction chamber of the heat treatment device III is filled with oxygen, the temperature is 600℃, and the pressure is 0.25MPa.

[0072] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for efficiently preparing silicon carbide aerogel, characterized in that, Includes the following steps: S1, add inorganic carbon source, interfacial dispersant and ethanol to the aqueous solution of silicon source, stir and disperse evenly to obtain carbon-doped silicon mixed solution A; S2, add an acidic composite catalyst to the mixed solution A in S1, control the pH of the solution to 2~6.5, and react at 20~55℃ for 0.2~6h to obtain carbon-doped silicon solution B; S3, add an alkaline composite catalyst to the carbon-doped silicon solution B in S2, control the pH of the solution to 7.5~10.5, and react for 0.1~5h at 20~55℃ to obtain carbon-doped silicon sol C; add ethanol to carbon-doped silicon sol C and age at room temperature for 1~3 days to obtain carbon-doped silicon gel D. S4, the pressure inside the conveying pipeline is controlled at 0.5-2.5 MPa, and the temperature of the carbon-doped silicon gel D inside the conveying pipeline is 90-220℃. The carbon-doped silicon gel D in S3 is continuously conveyed through the pipeline and distributor to the heat treatment reaction device I equipped with an external electromagnetic induction coil. The residence time of the carbon-doped silicon gel D in the reaction chamber of the heat treatment device I is 0.5-60s, to obtain composite aerogel D. The reaction chamber of the heat treatment device I is filled with a flowing inert gas atmosphere, with a temperature of 150-300℃ and a pressure of 3-10 MPa. S5, the composite aerogel D from S4 is transferred to a heat treatment device II equipped with an electromagnetic induction coil. The composite aerogel D stays in the reaction chamber of the heat treatment device II for 0.5~30s to obtain carbon-rich aerogel E. The reaction chamber of the heat treatment device II is in an inert gas atmosphere, with a temperature of 1000~1500℃ and a pressure of 0.02~0.5MPa. S6, the carbon-rich aerogel E from S5 is transferred to a heat treatment device III equipped with an electromagnetic induction coil. The carbon-rich aerogel E stays in the reaction chamber of the heat treatment device III for 2~1200s. The reaction chamber is in an air or oxygen atmosphere to obtain silicon carbide aerogel. The reaction chamber of the heat treatment device III is in an oxygen or air atmosphere, with a temperature of 400~800℃ and a pressure of 0.02~0.5MPa.

2. The method for efficiently preparing silicon carbide aerogel as described in claim 1, characterized in that: The inorganic carbon source mentioned in step S1 is one or more of carbon black, carbon nanotubes, C60, fullerene, graphite, and graphene; the average particle size of the inorganic carbon source is 0.1~200nm.

3. The method for efficiently preparing silicon carbide aerogel as described in claim 1, characterized in that: The interfacial dispersant in step S1 is one or more of polyacrylamide, sodium dodecyl sulfate, sodium polyacrylate, KH550, polyvinyl alcohol, sodium polyacrylate, and BYK163; the mass ratio of the inorganic carbon source, interfacial dispersant, and silicon source in step S1 is 0.5~4.5:0.003~0.01:

1.

4. The method for efficiently preparing silicon carbide aerogel as described in claim 1, characterized in that: The molar concentration of the silicon source in step S1 is 0.1~10 mol / L. The silicon source is one or more of organosilicon and inorganic silicon sources. Inorganic silicon sources include sodium silicate, sodium methylsilicate, potassium silicate, or silica sol. The organosilicon source is a substance that satisfies three general structural formulas, where R1, R2, R3, and R4 are H, alkyl groups, or alkyl groups containing heteroatoms. The three general structural formulas are as follows: 。 5. The method for efficiently preparing silicon carbide aerogel as described in claim 1, characterized in that: The acidic compound catalyst described in step S2 is a mixture of acidic substances and acetic acid, with a molar ratio of acidic substances to acetic acid of 0.02 to 0.10:

1. The acidic substances include one or more of organic acids, inorganic acids, and acidic gases. The organic acids are formic acid, acetic acid, oxalic acid, or lactic acid, the inorganic acids are sulfuric acid, nitric acid, or hydrochloric acid, and the acidic gases are sulfur oxides, nitrogen oxides, or carbon dioxide.

6. The method for efficiently preparing silicon carbide aerogel as described in claim 1, characterized in that: The alkaline compound catalyst described in step S3 is a mixture of an alkaline substance and ethanol, with a molar ratio of acidic substance to ethanol of 0.01~0.12:1; the alkaline substance is an inorganic alkaline solution or an aqueous solution of an inorganic alkaline substance, and the organic alkaline solution is an organic amine; the aqueous solution of the organic alkaline substance is ethylenediamine, triethanolamine or triethylenetetramine, and the inorganic alkaline solution is sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution or ammonia water.

7. The method for efficiently preparing silicon carbide aerogel as described in claim 1, characterized in that: In S3, ethanol is added to carbon-doped silica sol C, and the mass ratio of ethanol to carbon-doped silica sol C is 0.01~0.20:

1.

8. The method for efficiently preparing silicon carbide aerogel as described in claim 1, characterized in that: Heat treatment apparatus I, heat treatment apparatus II, and heat treatment apparatus III all include a vertical cylindrical body. The top of the cylindrical body is equipped with a distributor for the entry of carbon-doped silicon sol C or carbon-doped silicon gel D, and an air inlet for the entry of inert gas, air, or oxygen. The cylindrical body includes a feeding section, a heat treatment section, and a cooling section arranged from top to bottom. Electromagnetic induction coils are wound around the outer walls of the heat treatment section and the cooling section. An oxygen content analyzer, pressure, and temperature sensors are installed inside the reaction chamber.

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