Method for synthesizing SiC powder in one step by microwave heating of agricultural waste biomass

Abstract

The invention relates to the technical field of inorganic non-metallic materials, in particular to a method for synthesizing SiC powder in one step by microwave heating of agricultural waste biomass. The method comprises the following steps: combining agricultural waste biomass serving as a carbon source with a silicon source, and carrying out sol-gel reaction to obtain raw material powder; and carrying out compression molding on the raw material powder, and then carrying out microwave heating one-step synthesis at 800-1500 DEG C in an air atmosphere to obtain the SiC powder. According to the method, a protective atmosphere is not needed, a carbonization step is omitted, the process is simple, the cost is low, the method is environment-friendly, the product morphology comprises nanofibers, particles, rod-like structures and the like, resource utilization of agricultural wastes is realized, and the method has a good application prospect in the field of advanced ceramics.

Description

Technical Field

[0001] This invention relates to the field of inorganic non-metallic materials technology, specifically to a method for one-step synthesis of SiC powder from agricultural waste biomass using microwave heating. Background Technology

[0002] With the continuous expansion of agricultural scale, the output of agricultural waste is increasing year by year. Annual climate instability also leads to widespread mold and sprouting problems in crops, causing varying degrees of damage to the agricultural economy. Agricultural waste is a valuable biomass resource, exhibiting enormous application potential due to its wide availability, low cost, and diverse structure. Therefore, realizing the resource utilization of agricultural waste biomass is urgently needed.

[0003] Among biomass derivatives, SiC, as a high-performance advanced ceramic, is widely used due to its excellent physicochemical properties, becoming an indispensable strategic material in the development of high-tech fields. SiC possesses high tensile strength, high elastic modulus, excellent high-temperature resistance, wear resistance, corrosion resistance, and thermal stability, while also exhibiting outstanding semiconductor properties, making it suitable for a wide range of applications. Conventional methods for preparing biomass-derived SiC involve multiple steps, inert atmosphere protection, and high-temperature slow reactions. The multi-step process requires carbonizing the biomass raw materials before combining them with a silicon source to prepare SiC materials. This carbonization process must be carried out in an inert gas atmosphere at a temperature range of 600℃ to 1000℃. The preparation of biomass-derived SiC also requires heating and synthesis at temperatures above 1300℃ under inert atmosphere protection. While these methods utilize agricultural waste resources, the preparation process is complex and production costs are high. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a one-step microwave heating method for synthesizing SiC powder from agricultural waste biomass. This invention employs a one-step microwave heating process to prepare SiC powder, using inexpensive agricultural waste biomass as the carbon source and biomass carbon and silicon sources as raw materials to prepare the raw material powder via a sol-gel method. This optimizes the preparation process, saves preparation time, and solves the problems of complex processes and high production costs in existing biomass-derived SiC preparation methods, as well as the environmental pollution problems caused by traditional agricultural waste treatment methods, thereby achieving one-step synthesis of biomass-derived SiC powder.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: The purpose of this invention is to provide a method for one-step synthesis of SiC powder from agricultural waste biomass using microwave heating, comprising the following steps: S1. Using agricultural waste biomass as a carbon source, it is combined with a silicon source to carry out a sol-gel reaction to obtain a gel product.

[0006] S2. Under air atmosphere, the gel product is microwave-heated at 800℃~1500℃ to synthesize SiC powder in one step.

[0007] In a preferred embodiment of the present invention, the molar ratio of carbon source to silicon source is 3:0.8~1.5; the silicon source is tetraethyl orthosilicate, silica sol, quartz sand or silicon powder.

[0008] In a preferred embodiment of the present invention, before microwave heating for one-step synthesis, the gel product is pressed into shape at a pressure of 1 MPa to 50 MPa.

[0009] In a preferred embodiment of the present invention, during the microwave heating process, the temperature is raised from room temperature to 800℃~1500℃ and then kept at that temperature for 0min~120min.

[0010] In a preferred embodiment of the present invention, the microwave heating time is 30 min to 200 min; the frequency is 2450 MHz; the wavelength is 1 mm to 1 m; and the microwave input power rate is 0.05 kW / min to 1.00 kW / min.

[0011] In a preferred embodiment of the present invention, the temperature of the sol-gel reaction is 40°C to 60°C.

[0012] In a preferred embodiment of the present invention, the specific preparation process of the sol-gel reaction includes the following steps: adding a carbon source and a dispersant to an acidic solution to obtain a mixed solution, then adding a silicon source and adjusting the pH to hydrolyze the mixed solution into a gel state to obtain a gel-state raw material.

[0013] In a preferred embodiment of the present invention, the acidic solution is an aqueous solution of citric acid or oxalic acid, and the pH of the acidic solution is 2-4; the molar ratio of carbon source to acid is 100:8-15; the volume ratio of silicon source to dispersant is 1-3:3-20, and the dispersant is anhydrous ethanol or water; the pH is adjusted by ammonia or sodium hydroxide solution, and the adjusted pH is 8-10.

[0014] In a preferred embodiment of the present invention, the agricultural waste biomass is moldy crops, agricultural waste straw, crop roots and stems, crop leaves or crop husks; the particle size of the agricultural waste biomass is 40 mesh to 80 mesh; the agricultural waste biomass needs to be pretreated, and the pretreatment steps are drying and grinding.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention provides a method for one-step synthesis of SiC powder from agricultural waste biomass using microwave heating. Agricultural waste biomass is used as a carbon source, combined with a silicon source, and undergoes a sol-gel reaction to obtain a gel product. The gel product is then microwave-heated at 800℃~1500℃ in an air atmosphere to synthesize SiC powder in one step. This invention uses inexpensive agricultural waste biomass as a carbon source, significantly reducing the cost. Using biomass carbon and silicon sources as basic raw materials, a raw material powder with silicon source uniformly coated with carbon source is prepared using the sol-gel method. The raw material powder is shaped, buried in quartz sand, and placed in an insulated structure. The environmentally friendly microwave heating technology is used to achieve rapid and efficient one-step synthesis of biomass-derived SiC powder. This invention transforms the traditional multi-step, inert atmosphere-protected, high-temperature slow reaction synthesis route for biomass-derived SiC into a one-step, air-atmosphere, medium-high temperature rapid direct synthesis, thereby solving the problems of complex processes and high production costs in existing biomass-derived SiC preparation methods.

[0016] 2. This invention employs the sol-gel method to prepare raw material powder with silica uniformly coated on the surface of carbon particles. The sol-gel method can increase the contact area between the carbon source and the silicon source, promoting rapid reaction of the raw materials and accelerating the melting of silica during the reaction process. The preparation steps of this invention are simple, the operation method is clear, the preparation time is short, there is no pollution, and it is energy-saving and environmentally friendly. This invention innovatively uses a one-step synthesis method with microwave heating to prepare SiC powder, optimizing the preparation process and saving preparation time. It provides a new technical path and solution for solving the environmental pollution problems caused by traditional agricultural waste treatment methods and realizing the one-step synthesis of biomass-derived SiC powder. Attached Figure Description

[0017] Figure 1 This is a heating curve diagram of the microwave heating one-step synthesis process of SiC powder in Example 1 of the present invention.

[0018] Figure 2 This is the XRD pattern of SiC powder in Example 1 of the present invention.

[0019] Figure 3 This is the XRD pattern of SiC powder in Example 2 of the present invention.

[0020] Figure 4 This is the XRD pattern of SiC powder in Example 3 of the present invention.

[0021] Figure 5 This is a microscopic morphology diagram of the SiC powder in Example 2 of the present invention.

[0022] Figure 6 This is a microscopic morphology diagram of the SiC powder in Example 4 of the present invention.

[0023] Figure 7This is the XRD pattern of the SiC powder in Example 6 of the present invention.

[0024] Figure 8 This is the XRD pattern of SiC powder in Comparative Example 1 of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0027] While existing methods for synthesizing SiC have enabled the utilization of agricultural waste resources, the preparation processes are complex and production costs are high. Therefore, developing a one-step synthesis process for biomass-derived SiC is crucial.

[0028] Based on this, the present invention provides a method for preparing SiC powder by microwave one-step synthesis from agricultural waste biomass, comprising the following steps: (1) Agricultural waste biomass is crushed and ground to obtain the original biomass carbon source, which is combined with silicon source to prepare gel raw material by sol-gel method.

[0029] (2) The gel-state raw material described in (1) is dried and ground to obtain biomass raw material powder, and the raw material powder is shaped into a blank.

[0030] (3) The raw material blank obtained in (2) is buried and placed in the heat preservation structure. The heat preservation structure is placed in the microwave oven for heating and preparation. The SiC powder is obtained by heat preservation for 0 min to 120 min under microwave heating conditions of 800℃~1500℃.

[0031] It should be noted that although conventional methods have made significant progress in morphology control, their preparation processes generally rely on the multi-step, time-consuming traditional technical route of "pre-carbonization-high-temperature reaction." This common step increases the complexity and energy consumption of the process, limiting the efficiency improvement and large-scale application potential of biomass SiC preparation technology. Microwave heating technology, with its advantages of rapid heating, volumetric heating, and green preparation, has become a hot topic in the synthesis of advanced ceramic materials. The microwave preparation process of this invention successfully transforms the synthesis route of biomass-derived SiC from the traditional multi-step, inert atmosphere-protected, high-temperature slow reaction to a one-step, air-atmosphere, medium-high temperature rapid direct synthesis. This invention directly uses the original carbon source of agricultural waste biomass, reducing carbonization and purification steps. Using microwave heating technology, silicon carbide can be synthesized in one step in an air atmosphere (without any protective atmosphere, such as argon or nitrogen), and silicon carbide powder can be synthesized in a short time. The preparation process is simple and pollution-free, and the synthesized morphology exhibits various forms such as fibers, whiskers, rods, and particles based on the intrinsic characteristics of the material, effectively promoting the resource utilization research of agricultural waste biomass.

[0032] It is worth noting that most studies have demonstrated that microwave heating technology can prepare SiC materials under both protective and oxygen-containing atmospheres. In the context of this invention's synthesis of SiC materials from agricultural waste biomass, most conventional methods involve carbonization and SiC preparation under a protective atmosphere. Microwave heating technology can also synthesize biomass-derived SiC in a protective atmosphere step. However, using a protective atmosphere requires cumbersome and costly processes such as vacuum extraction and the introduction of high-purity inert gases, hindering rapid and efficient SiC synthesis. Therefore, this invention synthesizes SiC under both protective and oxygen-containing atmospheres, preferentially choosing an oxygen-containing environment for microwave preparation of biomass-derived SiC.

[0033] This invention utilizes microwave heating technology, which exhibits unique advantages in the field of advanced ceramic preparation due to its green and efficient characteristics. Compared to conventional methods, microwaves, with their thermal and non-thermal effects, can significantly shorten reaction time and allow for precise control of product morphology through the adjustment of process parameters. Therefore, the microwave heating method for one-step synthesis of SiC powder provided by this invention can effectively expand the resource recovery and reuse of agricultural waste on a low-carbon and environmentally friendly basis.

[0034] The carbon source is mainly agricultural waste biomass, including moldy crops such as corn, peanuts, wheat, soybeans, and rice, as well as agricultural waste such as straw, roots, leaves, and husks. Most agricultural waste biomass is rich in cellulose, hemicellulose, and lignin, making it an ideal carbon source. Its resource utilization is of dual significance in addressing both the energy crisis and environmental pollution. Different carbon sources also possess different microstructures, which can induce different microwave heating effects and behaviors during the microwave heating preparation of biomass-derived SiC, further influencing the final synthesized product.

[0035] The silicon source is tetraethyl orthosilicate, silica sol, quartz sand, silicon powder, etc.

[0036] The specific steps of the sol-gel method in step (1) are as follows: deionized water and acid are mixed to obtain an acidic solution, biomass carbon source is added to the acidic solution to obtain a carbon source dispersion, a dispersant is added and stirred in a water bath, a silicon source is added after stirring for 1-2 hours, an alkaline solution is added after stirring for 1-5 hours to regulate the mixed solution, and then the mixed solution is gradually hydrolyzed into a gel state of raw material.

[0037] The water bath temperature range is 40℃~70℃, and the stirring rate is 200rad / min~400rad / min.

[0038] In step (1), the particle size of the biomass carbon source after crushing and grinding is 40 mesh to 80 mesh.

[0039] The molar mass of the biomass carbon source is 2 to 3 times the molar mass of the carbon material, and the molar ratio of biomass carbon source to silicon source is 3:0.8 to 1.5. The molar ratio affects the reaction process. Generally, the more carbon source, the more vigorous the reaction. Typically, in microwave synthesis of SiC materials under oxygen-containing conditions, the carbon-silicon molar ratio is generally 3:1, with the majority of carbon used to react with the silicon source to synthesize SiO gas. In this invention, a floating range for the molar ratio is set.

[0040] The acid used to adjust the pH is citric acid or oxalic acid, and the base used to adjust the pH is ammonia or a diluted sodium hydroxide solution. The molar ratio of the carbon source to the acid is 100:8~15.

[0041] The dispersant includes anhydrous ethanol, deionized water, etc.; the volume ratio of the silicon source, dispersant and water is 1~3:3~20:3~20.

[0042] The pH of the acidic solution is adjusted to 2-4, which accelerates the dispersion of particles; the pH of the sol-gel reaction is adjusted to 8-10; and the temperature of the sol-gel reaction is 40℃-60℃.

[0043] The drying temperature is 60℃~110℃, and the time is 8h~20h.

[0044] The blanking process in step (2) involves weighing raw material powder of different masses and using molds of different diameters for molding, including but not limited to molds of 10mm, 30mm, 60mm, and 120mm, with a molding pressure of 1MPa to 50MPa.

[0045] The microwave heating conditions in step (3) include: a temperature of 800℃~1500℃, a holding time of 0min~120min, a microwave frequency of 2450MHz, a wavelength of 1mm~1m, and an input power rate of 0.05kW / min~1.00kW / min; the time for a single microwave preparation is 30min~200min. The microwave heating temperature, holding time, and microwave input power rate can affect the crystallinity, phase structure, and microstructure morphology of the SiC product.

[0046] The morphology of the SiC powder obtained in step (3) includes nanofibers, nanoparticles, rods, etc. Because the raw materials are different, the morphology varies. Nanofibers, nanoparticles or nanorods can basically encompass the microstructure of most SiC materials.

[0047] The following specific examples will provide further explanation.

[0048] Example 1 A method for one-step synthesis of SiC using agricultural waste biomass via microwave heating includes the following steps: (1) Preparation of raw material powder using the sol-gel method: Waste peanut leaves were placed in a forced-air drying oven and dried at 80℃ for 10 hours. The dried leaves were then crushed and ground to obtain a peanut leaf biomass carbon source with a particle size of approximately 40 mesh. A pH 3 acidic solution was prepared by mixing 480 mL of deionized water and 6 g of citric acid. 40 g of the peanut leaf biomass carbon source was added to this solution and stirred for 30 min. Then, 300 mL of anhydrous ethanol was added, and the solution was stirred for 50 min in a constant-temperature water bath at 50℃. Next, 60 mL of tetraethyl orthosilicate was added, and the solution was stirred for another 180 min at 350 rpm in a constant-temperature water bath at 50℃. The solution was then titrated with 28% ammonia solution until the pH reached 9, at which point the solution became a mesogel-like precursor powder. Finally, the precursor powder was placed in a forced-air drying oven and dried at 80℃ for 15 hours. After grinding, the biomass raw material powder was obtained. The molar ratio of carbon source to citric acid is 100:17; the molar ratio of carbon in the original biomass raw material to silicon in tetraethyl orthosilicate is 3:1; and the volume ratio of tetraethyl orthosilicate, anhydrous ethanol, and deionized water is 1:5:8.

[0049] (2) Preparation of SiC powder by microwave heating: Biomass precursor powder was placed in a 60mm mold and pre-pressed into a compact at a pressure of 5MPa. The compact was then pressed into a cake using an electric tablet press and placed in an insulated structure, buried in quartz sand. Microwave heating was then employed, with the microwave input power rate controlled at 0.14kW / min, a wavelength of 1m, a frequency of 2450MHz, and a heating temperature of 1200℃. The temperature was maintained for 10 minutes to obtain SiC powder. The total microwave preparation time was 97 minutes, including 72 minutes from room temperature to 600℃ (heat accumulation stage), 16 minutes from 600℃ to 1200℃, and a 10-minute holding at 1200℃.

[0050] Example 2 The difference from Example 1 is that the biomass carbon source is moldy corn kernels; the gel-state raw material is dried at 70°C in a blower dryer for 8 hours.

[0051] This embodiment illustrates that other agricultural wastes can also be used to prepare biomass-derived SiC, and that different biomass raw materials affect the morphology of the synthesized SiC; therefore, other biomass carbon sources were selected. Furthermore, due to the intrinsic differences between different carbon sources, a temperature and time more conducive to the drying of the gel-like raw material were chosen.

[0052] Example 3 The difference from Example 1 is that the microwave heating temperature is 1000℃.

[0053] In this embodiment, to illustrate that other microwave heating temperatures can also be used to prepare biomass-derived SiC, the heating temperature was changed.

[0054] Example 4 The difference from Example 1 is that the biomass carbon source is waste straw; and the stirring speed for the sol-gel reaction in a constant temperature water bath at 40°C is 300 r / min.

[0055] This embodiment illustrates that other agricultural wastes can also be used to prepare biomass-derived SiC, and that different biomass raw materials will affect the morphology of the synthesized SiC; therefore, other biomass carbon sources were selected. Furthermore, due to the density differences of different carbon sources, a stirring speed that is more conducive to uniform mixing was chosen.

[0056] Example 5 The difference from Example 1 is that the rate at which the microwave input power is adjusted is 0.5 kW / min.

[0057] This embodiment aims to illustrate the effect of microwave input power rate on the preparation of biomass-derived SiC, therefore the microwave input power rate was changed.

[0058] Example 6 The difference from Example 1 is that the microwave heating holding time is 0 min.

[0059] In this embodiment, to illustrate that other microwave heating and holding times can also be used to prepare biomass-derived SiC, the microwave heating and holding time was changed.

[0060] Comparative Example 1 (1) Preparation of raw material powder by dry ball milling: Waste peanut leaves and analytical grade quartz sand powder were mixed and placed in a ball mill jar made of polytetrafluoroethylene. Zirconia balls with a mass approximately three times the total mass of the peanut leaves and quartz sand were added to the jar, and the mixture was subjected to high-energy ball milling at a speed of 350 r / min for 180 min to obtain biomass raw material powder.

[0061] (2) Preparation of SiC powder by microwave heating: The biomass precursor powder was placed in a 60mm mold and processed using a pre-pressing process at a pressure of 5MPa. It was then pressed into a cake using an electric tablet press and placed in an insulated structure, which was then buried with quartz sand. Microwave heating technology was used, with the microwave input power rate adjusted to 0.14kW / min, the microwave wavelength selected to be 1m, the frequency 2450MHz, and the heating temperature set at 1200℃. After holding at this temperature for 10min, SiC powder was obtained.

[0062] Compared to Example 1, which used the sol-gel method to prepare raw materials and synthesize SiC, this microwave preparation process took 113 min, an increase of 16 min compared to Example 1. This process also took longer, increasing the temperature from room temperature to 600°C (81 min) and from 600°C to 1200°C (23 min). Under the same microwave heating temperature and holding time conditions, residual SiO2 phase was detected in the XRD pattern of the synthesized sample, and a relatively pure SiC phase was not obtained.

[0063] Next, the structure and properties of the SiC powders from Examples 1 to 6 and Comparative Example 1 were characterized.

[0064] Figure 1 This is a heating curve diagram of the one-step microwave heating synthesis of SiC powder in Example 1 of the present invention. Figure 1As shown, using microwave heating, by adjusting the rate of microwave input power, the sample reached 600℃ in 72 minutes and 1200℃ in 88 minutes, followed by a 10-minute holding period, with the entire process completed within 100 minutes. During the microwave preparation of biomass-derived SiC, a significant thermal change phenomenon occurred, which is related to the plasma thermal effect of microwave heating. This indicates that the unique thermal effect of microwave heating technology can facilitate the one-step synthesis of biomass-derived SiC.

[0065] In this invention, X-ray diffraction testing was performed using a SmartLab X-ray diffractometer (XRD) from Rigaku Electric Co., Ltd., Japan. Scanning electron microscopy testing was performed using a JSM7001F scanning electron microscope (SEM) from NEC Corporation.

[0066] Figure 2 This is the XRD pattern of SiC powder from Example 1 of the present invention. Figure 2 It can be seen that the diffraction peak of 3C-SiC was detected within the detection range, and no other impurity peaks were detected, proving that SiC can be synthesized in one step using peanut leaves as a biomass carbon source and microwave heating technology.

[0067] Figure 3 This is the XRD pattern of SiC powder from Example 2 of the present invention. Figure 3 It can be seen that the diffraction peak of 3C-SiC was detected within the detection range, and no other impurity peaks were detected, proving that SiC can be synthesized in one step using moldy corn kernels as biomass carbon source and microwave heating technology.

[0068] Figure 4 This is the XRD pattern of the SiC powder from Example 3 of the present invention. Figure 4 It can be seen that after changing the microwave heating temperature, the XRD detected by the sample still matches the main diffraction peaks of 3C-SiC, indicating that SiC can still be synthesized in one step by changing the microwave heating temperature.

[0069] Figure 5 This is a microscopic morphology image of the SiC powder from Example 2 of the present invention. Figure 5 It can be seen that the morphology of SiC is mainly large particles, indicating that SiC powder with a microscopic morphology of particles can be synthesized by using moldy corn kernels as biomass carbon source and microwave heating in one step.

[0070] Figure 6 This is a microscopic morphology image of the SiC powder from Example 4 of the present invention. Figure 6 It can be seen that the morphology of SiC is mainly nanofibers with a spherical chain structure, indicating that SiC powder with a fibrous microstructure can be synthesized by using waste crop straw as a biomass carbon source and a one-step synthesis method with microwave heating.

[0071] Figure 7 This is the XRD pattern of the SiC powder from Example 6 of the present invention. Figure 7 It can be seen that changing the holding time of microwave heating does not change the XRD detection of the sample, which still matches the main diffraction peak of 3C-SiC, indicating that SiC can still be synthesized in one step under the condition of holding time of 0 min.

[0072] Figure 8 This is the XRD pattern of the SiC powder used in Comparative Example 1 of this invention. Figure 8 It can be seen that by changing the raw material powder preparation process and using dry ball milling to prepare the raw material powder, under the same microwave preparation conditions as in Example 1, although the XRD detected in the sample could match the main diffraction peaks of 3C-SiC, diffraction peaks related to SiO2 were found within the detection range. This indicates that the present invention uses the sol-gel method to prepare raw materials, and microwave heating technology can synthesize relatively pure SiC powder. Changing the raw material preparation process results in a sample with more impurity peaks.

[0073] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of this invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended scope of protection is intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of this invention.

[0074] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of protection of this invention and its equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for one-step synthesis of SiC powder from agricultural waste biomass using microwave heating, characterized in that, Includes the following steps: Agricultural waste biomass was used as a carbon source and combined with a silicon source to carry out a sol-gel reaction to obtain a gel product. SiC powder was synthesized in one step by microwave heating of the gel-state product at 800℃~1500℃ in an air atmosphere.

2. The method for one-step synthesis of SiC powder from agricultural waste biomass via microwave heating according to claim 1, characterized in that, The molar ratio of carbon source to silicon source is 3:0.8~1.5; the silicon source is tetraethyl orthosilicate, silica sol, quartz sand or silica powder.

3. The method for one-step synthesis of SiC powder from agricultural waste biomass via microwave heating according to claim 1, characterized in that, Before one-step synthesis by microwave heating, the gel product is pressed into shape at a pressure of 1 MPa to 50 MPa.

4. The method for one-step synthesis of SiC powder from agricultural waste biomass via microwave heating according to claim 1, characterized in that, During the microwave heating process, the temperature is raised from room temperature to 800℃~1500℃ and then kept at that temperature for 0min~120min.

5. The method for one-step synthesis of SiC powder from agricultural waste biomass via microwave heating according to claim 1, characterized in that, The microwave heating time is 30min~200min, the frequency is 2450MHz, the wavelength is 1mm~1m, and the microwave input power rate is 0.05kW / min~1.00kW / min.

6. The method for one-step synthesis of SiC powder from agricultural waste biomass via microwave heating according to claim 1, characterized in that, The temperature for the sol-gel reaction is 40℃~60℃.

7. The method for one-step synthesis of SiC powder from agricultural waste biomass via microwave heating according to claim 1, characterized in that, The specific preparation process of the sol-gel reaction includes the following steps: adding a carbon source and a dispersant to an acidic solution to obtain a mixed solution, then adding a silicon source and adjusting the pH to hydrolyze the mixed solution into a gel state to obtain a gel-state raw material.

8. The method for one-step synthesis of SiC powder from agricultural waste biomass via microwave heating according to claim 7, characterized in that, The acidic solution is an aqueous solution of citric acid or oxalic acid, with a pH of 2-4; the molar ratio of carbon source to acid is 100:8-15; the volume ratio of silicon source to dispersant is 1-3:3-20, and the dispersant is anhydrous ethanol or water; the pH is adjusted using ammonia or sodium hydroxide solution, resulting in a pH of 8-10.

9. The method for one-step synthesis of SiC powder from agricultural waste biomass via microwave heating according to claim 1, characterized in that, Agricultural waste biomass includes moldy crops, agricultural waste straw, crop roots and stems, crop leaves, or crop husks; the particle size of agricultural waste biomass is 40-80 mesh; the agricultural waste biomass needs to be pretreated, and the pretreatment steps are drying and grinding.

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