A method for preparing silicon carbide nanowires using renewable resources

Abstract

This invention relates to a method for preparing silicon carbide nanowires using renewable resources, belonging to the field of silicon carbide material preparation technology. The carbon source in this invention is natural biomass, which is directly carbonized after pulverization to obtain loose and porous biochar. The silicon source is obtained by wet oxygen oxidation of industrial silicon powder at low temperature, forming a mixed silicon source composed of Si and SiO2. The carbon and silicon sources are placed in an alumina crucible, separated by an alumina ring, and then reacted in a muffle furnace purged with argon to obtain silicon carbide nanowires. Subsequent secondary annealing removes residual biochar, yielding the final silicon carbide nanowires. This invention utilizes a simple chemical vapor deposition method to prepare silicon carbide nanowires, using low-cost waste biomass as the carbon source and highly chemically active Si and SiO2 as the mixed silicon source, which helps reduce carbon emissions, conserves resources, and has significant practical application value.

Description

Technical Field

[0001] This invention belongs to the field of silicon carbide material preparation technology, specifically relating to a method for preparing silicon carbide nanowires using renewable resources. Background Technology

[0002] Silicon carbide is an excellent semiconductor material that is resistant to high temperatures and high pressures, has low density, and strong oxidation resistance. Silicon carbide nanowires, as a one-dimensional structure, possess unique nanoscale fiber structures, resulting in wide bandgap, high dielectric loss, high specific surface area, and corrosion resistance. They are often used as reinforcing materials to compensate for defects in composite materials, thereby producing higher-performance composites. This material has been widely applied in industries such as aerospace, electronics and communications, and ceramics.

[0003] Traditionally, silicon carbide nanomaterials are manufactured using silicon carbide powder as raw material through gel casting, direct foaming, directional freezing, and sacrificial templates. These methods require complex procedures and additional additives, making them both expensive and complicated. Therefore, the construction of porous silicon carbide materials through simple, inexpensive, and environmentally friendly methods has attracted great interest. Patent 1, "CN116120097B," utilizes CVD technology to prepare SiC nanowires on the surface of a C / C composite material, and then uses low-pressure chemical vapor deposition (LPCVD) with methane as the carbon source to obtain SiC nanowire structures and SiC nanowire@carbon nanophase core-shell heterostructures. Patent 2, "CN118084543B," utilizes a C / C-UHT Cs composite material with a rare-earth zirconate / SiC nanowire composite coating and its preparation method. A double-layer crucible is used; the C / C-UHT Cs composite material is placed in the inner crucible, and Si powder is placed in the outer crucible. The SiC nanowire C / C-UHT Cs composite material is then prepared using LPCVD. Patent CN115246646A discloses a method for preparing silicon carbide nanowires using renewable resources or waste as a carbon source, which includes the following steps:

[0004] (1) Fluffing: The process of fluffing renewable resources or waste to obtain fluffy and uniformly distributed pre-treated materials;

[0005] (2) Carbonization: The fluffy and uniformly distributed pretreated material obtained in step (1) is placed in a pyrolysis furnace, and after the oxygen is removed by vacuuming, nitrogen is introduced to atmospheric pressure, and then pyrolyzed at high temperature to obtain fluffy and uniform carbon material.

[0006] (3) Reaction material preparation: Place carbon silica dry gel powder at the bottom of the crucible, then place the fluffy and uniform carbon material obtained in step (2) on top of the carbon silica dry gel powder, and cover the crucible with the lid.

[0007] (4) High-temperature carbothermic reduction: The crucible is placed in a high-temperature sintering furnace, and then a vacuum is drawn and nitrogen gas is introduced to a certain pressure. The reaction is carried out at a high temperature. After the reaction is completed, the product of gray-green silicon carbide nanowires is obtained by cooling.

[0008] (5) Removal of residual carbon: The product obtained in step (4) is placed in a muffle furnace and heated and kept at a constant temperature to remove residual carbon and obtain silicon carbide nanowires. The high-temperature carbothermal reduction temperature of this patent is 1500-1800℃, and carbon-containing silica dry gel powder is used, resulting in extremely high cost.

[0009] In this invention, waste agricultural and forestry biomass is used as the carbon source for preparing silicon carbide, and industrial silicon powder after wet oxygen oxidation is used as the silicon source. Silicon carbide nanowires are generated in situ on the carbon source through chemical vapor phase reaction. Summary of the Invention

[0010] This invention proposes a method for preparing silicon carbide nanowires using renewable resources. The carbon source in this invention is waste biomass from nature, such as coffee shells, macadamia nut shells, peanut shells, rice husks, rice straw, and tobacco straw. These biomass materials are mostly byproducts of agricultural and forestry products and are often discarded as waste. These waste biomass raw materials not only have high reactivity but also possess a highly porous structure. Direct carbonization yields fluffy and porous biochar, which is very suitable as a carbon source for generating silicon carbide nanowires. The silicon source is a Si / SiO2 mixture formed by oxidizing industrial silicon powder with moist oxygen for a certain period. High-quality SiC nanowires are then obtained through chemical deposition at a relatively low temperature.

[0011] A method for preparing silicon carbide nanowires using renewable resources, comprising the following steps:

[0012] (1) Carbon source pretreatment: Biomass is washed, dried to remove dirt, and then ground into powder to obtain pretreated material;

[0013] (2) Carbonization: The pretreated material obtained in step (1) is placed in a furnace with protective gas for carbonization to obtain fluffy and porous biochar.

[0014] (3) Silicon source pretreatment: A certain amount of silicon powder is placed in an aqueous solution and reacted to obtain a mixture containing Si and silicon oxide. The mixture is then dried and used as a silicon source. The silicon oxide contains silicon dioxide.

[0015] (4) High-temperature carbothermic reduction: Place the silicon source obtained in step (3) at the bottom of the crucible, set a breathable isolation layer on the silicon source, and set the fluffy and porous biochar obtained in step (2) on the isolation layer; after covering the crucible, put in a protective gas and heat it to carry out the reaction. After the reaction is cooled, a product with SiC nanowires is obtained. The reaction temperature is less than or equal to 1500℃.

[0016] (5) Annealing treatment: The product obtained in step (4) is heated to remove the residual carbon, and the remaining product is SiC nanowires.

[0017] Preferably, in step (1), the biomass is selected from at least one of coffee shells, macadamia nut shells, peanut shells, rice husks, rice straw, and tobacco straw. After crushing, the particles are passed through a 100-mesh sieve, and the material passing through the sieve is collected.

[0018] As a further preferred option, the particle size of the pretreated material in step (1) is 50-100 mesh. In industrial applications, powder with a particle size of 50-100 mesh can be obtained by vibratory milling.

[0019] Preferably, the protective gas in step (2) includes at least one of nitrogen and argon.

[0020] Preferably, in step (2), the flow rate of the protective gas is 15-25 ml / min, the carbonization temperature is 500-800℃, the heating rate is 8-12℃ / min, and the holding time is greater than or equal to 1 h, more preferably greater than or equal to 2 h. Carbonization under a protective atmosphere can produce loose, porous carbon as much as possible.

[0021] Preferably, the silicon powder used in step (3) is industrial silicon powder with a purity >99% and a particle size of -100 mesh. In industrial applications, a certain amount of industrial silicon powder is placed in an aqueous solution at a ratio of 4-6g of industrial silicon powder to 15-25ml of water, and reacted at 95-100℃ for at least 4 hours to obtain a mixture containing Si and silicon oxide. This mixture is then dried and used as a silicon source, wherein the silicon oxide contains silicon dioxide. In industrial applications, the reaction time can be 4-20 hours. The control of the reaction time in step (3) in this invention is mainly to control the relative content of zero-valent silicon and tetravalent silicon in the silicon source.

[0022] Preferably, in step (4), a hollow cylinder is used to separate the carbon source and the silicon source, with a spacing of 5-30 mm between the carbon source and the silicon source, and the hollow cylinder is made of aluminum oxide.

[0023] Preferably, in step (4), the carbon source and silicon source are prepared in a ratio of 3-7g carbon source to 5g silicon source. In industrial applications, the ratio of carbon source to silicon source is controlled in step (4) because too much silicon source will result in low permeability of the molten silicon mixture at high temperature, and the generated silicon monoxide gas cannot be properly absorbed by the carbon source. If there is too much carbon source, it will cause a waste of carbon source in the later annealing and decarburization stage.

[0024] Preferably, the reaction temperature in step (4) is 1200-1500℃, more preferably 1200-1400℃, and the holding time is 2-6h. In industrial applications, considering the diameter and yield of the product, a longer reaction time of 1200-1400℃ can be used.

[0025] Preferably, the product obtained in step (4) is placed directly in a muffle furnace and heated to 600-850°C at a heating rate of 8-12°C / min, held for 1-3 hours, and then cooled to obtain the final SiC nanowire product.

[0026] Reaction principle:

[0027] The silicon source of this invention is a mixture of Si and SiO2. At high temperatures, these two components undergo a disproportionation reaction, generating a large amount of SiO gas. Under these conditions, the carbon source reacts with SiO to produce CO gas and a SiC substrate. Subsequently, during the cooling phase, the excess SiO and CO gas grows SiC nanowires on the SiC substrate through chemical vapor deposition. The specific reaction mechanism is as follows:

[0028] SiO2(s) + Si(s) = 2SiO(g) #(1)

[0029] SiO(g)+2C(s)=SiC(s)+CO(g)#(2)

[0030] SiO(g)+3CO(g)=SiC(s)+2CO2(g)#(3)

[0031] The beneficial effects of this invention are:

[0032] (1) This invention uses waste biomass as raw material, which has low raw material cost and a simple and quick process. Through pulverization and carbonization, fluffy and porous biochar is obtained, providing a high-value recycling method for waste biomass.

[0033] (2) In this invention, industrial silicon powder is subjected to wet oxygen oxidation at low temperature to form amorphous SiO2 with high chemical activity, which enables the mixed silicon source composed of Si and SiO2 to react better at high temperature.

[0034] (3) In this invention, silicon carbide nanowires are prepared by a simple chemical deposition method, which is beneficial to reducing carbon emissions and saving resources, and has important practical application significance. Attached Figure Description

[0035] Appendix Figure 1 This is a flowchart of the silicon carbide nanowire preparation process in Example 1;

[0036] Appendix Figure 2 This is a schematic diagram of the specific reaction apparatus in Example 1;

[0037] Appendix Figure 3 The macroscopic morphology of silicon carbide obtained in Example 1;

[0038] Appendix Figure 4 The microstructure of silicon carbide prepared in Example 1;

[0039] Appendix Figure 5 The microstructure of silicon carbide prepared in Example 3 is shown below.

[0040] Appendix Figure 6 The microstructure of silicon carbide prepared in Example 8; Detailed Implementation

[0041] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0042] Example 1: A method for preparing silicon carbide nanowires using renewable resources, the specific steps of which are as follows:

[0043] (1) Wash and dry the peanut shells to remove dirt, and then crush them into 100-mesh powder using a vibratory mill.

[0044] (2) Weigh 10g of the powder obtained in step (1) and place it in a Φ60×40mm crucible. Spread it evenly and then place it in a horizontal tube furnace with argon gas. The argon gas flow rate is 20ml / min, the carbonization temperature is 600℃, the heating rate is 10℃ / min, and the holding time is 2h to obtain 3.45g of peanut shell biochar.

[0045] (3) The industrial silicon powder was placed in 20 ml of deionized water and oxidized with wet oxygen at 100 °C for 12 h to obtain a mixed silicon source with Si and SiO2 composition.

[0046] (4) Place the silicon source (5g) obtained in step (3) at the bottom of the crucible, set a breathable isolation layer (a hollow corundum cylinder with a height of 15mm) on the silicon source, and set the loose and porous biochar (3.15g) obtained in step (2) on the isolation layer; after covering the crucible, put it into the furnace, introduce argon into the furnace and carry out the reaction. The argon flow rate is 20ml / min, the maximum reaction temperature is 1500℃, the heating rate is 10℃ / min, the holding time is 4h, the cooling rate is 5℃ / min, and after cooling to room temperature, 5.13g of product is obtained.

[0047] (5) The product obtained in step (4) was placed directly in a muffle furnace and heated to 800°C at a heating rate of 10°C / min. The temperature was held for 2 hours to remove excess biochar. After cooling, 3.78 g of SiC nanowires (with an average diameter of 161 nm) were obtained.

[0048] Example 2: A method for preparing silicon carbide nanowires using renewable resources, the specific steps of which are as follows:

[0049] (1) Wash and dry the peanut shells to remove dirt, and then crush them into 100-mesh powder using a vibratory mill.

[0050] (2) Weigh 10g of the powder obtained in step (1) and place it in a Φ60×40mm crucible. Spread it evenly and then place it in a horizontal tube furnace with argon gas. The argon gas flow rate is 20ml / min, the carbonization temperature is 500℃, the heating rate is 10℃ / min, and the holding time is 2h. 5.88g of peanut shell biochar is obtained.

[0051] (3) Place industrial silicon powder in 20 ml of deionized water and oxidize it with wet oxygen at 100°C for 4 h to obtain a mixed silicon source composed of Si and SiO2.

[0052] (4) Place the silicon source (5g) obtained in step (3) at the bottom of the crucible, and set a breathable isolation layer (a hollow corundum cylinder with a height of 15mm) on the silicon source. Place the loose and porous biochar (5.88g) obtained in step (2) on the isolation layer. After covering the crucible, put it into the furnace, introduce argon gas into the furnace and carry out the reaction. The argon gas flow rate is 20ml / min, the maximum reaction temperature is 1200℃, the heating rate is 10℃ / min, the holding time is 2h, the cooling rate is 5℃ / min, and after cooling to room temperature, 6.12g of product is obtained.

[0053] (5) The product obtained in step (4) was placed directly in a muffle furnace and heated to 800°C at a heating rate of 10°C / min. The temperature was held for 2 hours to remove excess biochar. After cooling, 1.98 g of SiC nanowires (with an average diameter of 87 nm) were obtained.

[0054] Example 3: A method for preparing silicon carbide nanowires using renewable resources, the specific steps of which are as follows:

[0055] (1) Wash and dry the peanut shells to remove dirt, and then crush them into 100-mesh powder using a vibratory mill.

[0056] (2) Weigh 10g of the powder obtained in step (1) and place it in a Φ60×40mm crucible. Spread it evenly and then place it in a horizontal tube furnace with argon gas. The argon gas flow rate is 20ml / min, the carbonization temperature is 700℃, the heating rate is 10℃ / min, and the holding time is 2h to obtain 3.12g of peanut shell biochar.

[0057] (3) The industrial silicon powder was placed in 20 ml of deionized water and oxidized at 100°C for 8 h to obtain a mixed silicon source with Si and SiO2 composition.

[0058] (4) Place the silicon source (5g) obtained in step (3) at the bottom of the crucible, and set a breathable isolation layer (a hollow corundum cylinder with a height of 15mm) on the silicon source. Place the loose and porous biochar (3.42g) obtained in step (2) on the isolation layer. After covering the crucible, put it into the furnace, introduce argon gas into the furnace and carry out the reaction. The argon gas flow rate is 20ml / min, the maximum reaction temperature is 1400℃, the heating rate is 10℃ / min, the holding time is 3h, the cooling rate is 5℃ / min, and after cooling to room temperature, 4.52g of product is obtained.

[0059] (5) The product obtained in step (4) was placed directly in a muffle furnace and heated to 800°C at a heating rate of 10°C / min. The temperature was held for 2 hours to remove excess biochar. After cooling, 3.26 g of SiC nanowires (with an average diameter of 121 nm) were obtained.

[0060] Example 4: A method for preparing silicon carbide nanowires using renewable resources, the specific steps of which are as follows:

[0061] (1) Wash and dry the peanut shells to remove dirt, and then crush them into 100-mesh powder using a vibratory mill.

[0062] (2) Weigh 10g of the powder obtained in step (1) and place it in a Φ60×40mm crucible. Spread it evenly and then place it in a horizontal tube furnace with argon gas. The argon gas flow rate is 20ml / min, the carbonization temperature is 800℃, the heating rate is 10℃ / min, and the holding time is 2h. 3.06g of peanut shell biochar is obtained.

[0063] (3) The industrial silicon powder was placed in 20 ml of deionized water and oxidized with wet oxygen at 100 °C for 16 h to obtain a mixed silicon source with Si and SiO2 composition.

[0064] (4) Place the silicon source (5g) obtained in step (3) at the bottom of the crucible, and set a breathable isolation layer (a hollow corundum cylinder with a height of 15mm) on the silicon source. Place the loose and porous biochar (3.06g) obtained in step (2) on the isolation layer. After covering the crucible, put it into the furnace, introduce argon gas into the furnace and carry out the reaction. The argon gas flow rate is 20ml / min, the maximum reaction temperature is 1300℃, the heating rate is 10℃ / min, the holding time is 6h, the cooling rate is 5℃ / min, and 4.12g of product is obtained after cooling to room temperature.

[0065] (5) The product obtained in step (4) was placed directly in a muffle furnace and heated to 800°C at a heating rate of 10°C / min. The temperature was held for 2 hours to remove excess biochar. After cooling, 2.76 g of SiC nanowires (with an average diameter of 94 nm) were obtained.

[0066] Example 5: A method for preparing silicon carbide nanowires using renewable resources, the specific steps of which are as follows:

[0067] (1) The coffee shells are washed, dried to remove dirt, and then crushed into 100-mesh powder using a vibratory mill.

[0068] (2) Weigh 10g of the powder obtained in step (1) and place it in a Φ60×40mm crucible. Spread it evenly and then place it in a horizontal tube furnace with argon gas. The argon gas flow rate is 20ml / min, the carbonization temperature is 600℃, the heating rate is 10℃ / min, and the holding time is 2h. 3.82g of coffee shell biochar is obtained.

[0069] (3) The industrial silicon powder was placed in 20 ml of deionized water and oxidized with wet oxygen at 100 °C for 12 h to obtain a mixed silicon source with Si and SiO2 composition.

[0070] (4) Place the silicon source (5g) obtained in step (3) at the bottom of the crucible, and set a breathable isolation layer (a hollow corundum cylinder with a height of 15mm) on the silicon source. Place the loose and porous biochar (3.82g) obtained in step (2) on the isolation layer. After covering the crucible, put it into the furnace, introduce argon gas into the furnace and carry out the reaction. The argon gas flow rate is 20ml / min, the maximum reaction temperature is 1400℃, the heating rate is 10℃ / min, the holding time is 4h, the cooling rate is 5℃ / min, and 4.91g of product is obtained after cooling to room temperature.

[0071] (5) The product obtained in step (4) was placed directly in a muffle furnace and heated to 800°C at a heating rate of 10°C / min. The temperature was held for 2 hours to remove excess biochar. After cooling, 3.58 g of SiC nanowires (with an average diameter of 117 nm) were obtained.

[0072] Example 6: A method for preparing silicon carbide nanowires using renewable resources, the specific steps of which are as follows:

[0073] (1) The coffee shells are washed, dried to remove dirt, and then crushed into 100-mesh powder using a vibratory mill.

[0074] (2) Weigh 10g of the powder obtained in step (1) and place it in a Φ60×40mm crucible. Spread it evenly and then place it in a horizontal tube furnace with argon gas. The argon gas flow rate is 20ml / min, the carbonization temperature is 800℃, the heating rate is 10℃ / min, and the holding time is 2h to obtain 3.15g of coffee shell biochar.

[0075] (3) The industrial silicon powder was placed in 20 ml of deionized water and oxidized with wet oxygen at 100 °C for 16 h to obtain a mixed silicon source with Si and SiO2 composition.

[0076] (4) Place the silicon source (5g) obtained in step (3) at the bottom of the crucible, and set a breathable isolation layer (a hollow corundum cylinder with a height of 15mm) on the silicon source. Place the loose and porous biochar (3.15g) obtained in step (2) on the isolation layer. After covering the crucible, put it into the furnace, introduce argon gas into the furnace and carry out the reaction. The argon gas flow rate is 20ml / min, the maximum reaction temperature is 1300℃, the heating rate is 10℃ / min, the holding time is 6h, the cooling rate is 5℃ / min, and after cooling to room temperature, 5.26g of product is obtained.

[0077] (5) The product obtained in step (4) was placed directly in a muffle furnace and heated to 800°C at a heating rate of 10°C / min. The temperature was held for 2 hours to remove excess biochar. After cooling, 2.81 g of SiC nanowires (with an average diameter of 95 nm) were obtained.

[0078] Example 7: A method for preparing silicon carbide nanowires using renewable resources, the specific steps of which are as follows:

[0079] (1) The coffee shells are washed, dried to remove dirt, and then crushed into 100-mesh powder using a vibratory mill.

[0080] (2) Weigh 10g of the powder obtained in step (1) and place it in a Φ60×40mm crucible. Spread it evenly and then place it in a horizontal tube furnace with argon gas. The argon gas flow rate is 20ml / min, the carbonization temperature is 700℃, the heating rate is 10℃ / min, and the holding time is 2h. 3.47g of coffee shell biochar is obtained.

[0081] (3) The industrial silicon powder was placed in 20 ml of deionized water and oxidized at 100°C for 8 h to obtain a mixed silicon source with Si and SiO2 composition.

[0082] (4) Place the silicon source (5g) obtained in step (3) at the bottom of the crucible, and set a breathable isolation layer (a hollow corundum cylinder with a height of 15mm) on the silicon source. Place the loose and porous biochar (3.47g) obtained in step (2) on the isolation layer. After covering the crucible, put it into the furnace, introduce argon gas into the furnace and carry out the reaction. The argon gas flow rate is 20ml / min, the maximum reaction temperature is 1200℃, the heating rate is 10℃ / min, the holding time is 5h, the cooling rate is 5℃ / min, and after cooling to room temperature, 4.26g of product is obtained.

[0083] (5) The product obtained in step (4) was placed directly in a muffle furnace and heated to 800°C at a heating rate of 10°C / min. The temperature was held for 2 hours to remove excess biochar. After cooling, 1.93 g of SiC nanowires (with an average diameter of 84 nm) were obtained.

[0084] Example 8: A method for preparing silicon carbide nanowires using renewable resources, the specific steps of which are as follows:

[0085] (1) The coffee shells are washed, dried to remove dirt, and then crushed into 100-mesh powder using a vibratory mill.

[0086] (2) Weigh 10g of the powder obtained in step (1) and place it in a Φ60×40mm crucible. Spread it evenly and then place it in a horizontal tube furnace with argon gas. The argon gas flow rate is 20ml / min, the carbonization temperature is 500℃, the heating rate is 10℃ / min, and the holding time is 2h. 6.23g of coffee shell biochar is obtained.

[0087] (3) Place industrial silicon powder in 20 ml of deionized water and oxidize it with wet oxygen at 100°C for 4 h to obtain a mixed silicon source composed of Si and SiO2.

[0088] (4) Place the silicon source (5g) obtained in step (3) at the bottom of the crucible, and set a breathable isolation layer (a hollow corundum cylinder with a height of 15mm) on the silicon source. Place the loose and porous biochar (6.23g) obtained in step (2) on the isolation layer. After covering the crucible, put it into the furnace, introduce argon gas into the furnace and carry out the reaction. The argon gas flow rate is 20ml / min, the maximum reaction temperature is 1200℃, the heating rate is 10℃ / min, the holding time is 5h, the cooling rate is 5℃ / min, and 6.76g of product is obtained after cooling to room temperature.

[0089] (5) The product obtained in step (4) was placed directly in a muffle furnace and heated to 800°C at a heating rate of 10°C / min. The temperature was held for 2 hours to remove excess biochar. After cooling, 1.53 g of SiC nanowires (with an average diameter of 76 nm) were obtained.

[0090] Comparative Example 1

[0091] All other conditions are the same as in Example 8, except that:

[0092] When industrial silicon was used directly as the silicon source for the reaction, no silicon carbide was found to be formed.

[0093] Comparative Example 2

[0094] All other conditions are the same as in Example 3, except that:

[0095] (4) The carbon source (4.26g) and silicon source (5g) obtained in steps (2) and (3) were placed in a corundum crucible. The carbon source and silicon source were not separated by a corundum ring. After covering the crucible, it was placed in a muffle furnace with argon gas to carry out the reaction. The argon gas flow rate was 20ml / min, the maximum reaction temperature was 1400℃, the heating rate was 10℃ / min, the holding time was 4h, the cooling rate was 5℃ / min, and after cooling to room temperature, 4.89g of product was obtained. It was observed that the carbon source and silicon source were largely adhered together.

[0096] (5) The product obtained in step (4) is placed directly in a muffle furnace and heated to 800°C at a heating rate of 10°C / min. The temperature is held for 2 hours to remove excess biochar. After cooling, 1.45 g of SiC large particles are obtained.

[0097] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for preparing silicon carbide nanowires using renewable resources, characterized in that... Includes the following steps: (1) Carbon source pretreatment: Biomass is washed, dried to remove dirt, and then ground into powder to obtain pretreated material; (2) Carbonization: The pretreated material obtained in step (1) is placed in a furnace with protective gas for carbonization to obtain fluffy and porous biochar. (3) Silicon source pretreatment: A certain amount of silicon powder is placed in an aqueous solution and reacted to obtain a mixture containing Si and silicon oxide. The mixture is then dried and used as a silicon source. The silicon oxide contains silicon dioxide. (4) High-temperature carbothermic reduction: The silicon source obtained in step (3) is placed at the bottom of the crucible, and a breathable isolation layer is set on the silicon source. The loose and porous biochar obtained in step (2) is set on the isolation layer. After the crucible is covered, a protective gas is placed in and heated to carry out the reaction. After the reaction is cooled, a product with SiC nanowires is obtained. The reaction temperature is less than or equal to 1500℃. In step (4), a hollow cylinder is used to separate the carbon source from the silicon source. The distance between the carbon source and the silicon source is 5-30mm. The hollow cylinder is made of aluminum oxide. (5) Annealing treatment: The product obtained in step (4) is heated to remove the residual carbon, and the remaining product is SiC nanowires.

2. The method for preparing silicon carbide nanowires using renewable resources according to claim 1, characterized in that: In step (1), the biomass is selected from at least one of coffee shells, macadamia nut shells, peanut shells, rice shells, rice straw, and tobacco straw; after crushing, the particles are passed through a 100-mesh sieve and the sieve-passing material is collected.

3. The method for preparing silicon carbide nanowires using renewable resources according to claim 1, characterized in that: The protective gas in step (2) includes at least one of nitrogen and argon.

4. The method for preparing silicon carbide nanowires using renewable resources according to claim 1, characterized in that: In step (2), the flow rate of the protective gas is 15~25 ml / min, the carbonization temperature is 500-800℃, the heating rate is 8~12℃ / min, and the holding time is greater than or equal to 1h. Fluffy porous carbon is prepared by carbonization under a protective atmosphere.

5. The method for preparing silicon carbide nanowires using renewable resources according to claim 1, characterized in that: The silicon powder used in step (3) is industrial silicon powder with a purity of >99% and a particle size of -100 mesh.

6. The method for preparing silicon carbide nanowires using renewable resources according to claim 5, characterized in that: The specific process of step (3) is as follows: 4-6g of industrial silicon powder is mixed with 15-25ml of water. A certain amount of industrial silicon powder is placed in an aqueous solution and reacted at 95-100℃ for at least 4 hours to obtain a mixture containing Si and silicon oxide. The mixture is then dried and used as a silicon source.

7. The method for preparing silicon carbide nanowires using renewable resources according to claim 1, characterized in that: In step (4), carbon source and silicon source are prepared in a ratio of 3-7g carbon source to 5g silicon source.

8. The method for preparing silicon carbide nanowires using renewable resources according to claim 1, characterized in that: The reaction temperature in step (4) is 1200-1500℃, and the holding time is 2-6h.

9. The method for preparing silicon carbide nanowires using renewable resources according to claim 1, characterized in that: The product obtained in step (4) is placed directly in a muffle furnace and heated to 600~850℃ at a heating rate of 8-12℃ / min, and then held for 1-3h. After cooling, the final SiC nanowire product is obtained.

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