Method for preparing silicon carbide nanowire by recycling renewable resources

Abstract

The invention relates to a method for preparing silicon carbide nanowires by recycling renewable resources, and belongs to the technical field of silicon carbide material preparation. Biomass in nature is adopted as a carbon source, and fluffy and porous biochar is obtained through direct carbonization after pulverization. The silicon source is a mixed silicon source composed of Si and SiO2 formed by carrying out wet oxygen oxidation on industrial silicon powder at low temperature. The preparation method comprises the following steps: putting a carbon source and a silicon source into a corundum crucible, separating by using a corundum ring, and reacting in a muffle furnace filled with argon to obtain a silicon carbide nanowire product; and then removing the residual biochar through secondary annealing to obtain the final silicon carbide nanowire. The simple chemical vapor deposition method is used for preparing the silicon carbide nanowire, low-cost waste biomass is used as a carbon source, Si and SiO2 with high chemical activity are used as a mixed silicon source, carbon emission is reduced, resources are saved, and the method has important practical application significance.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicon carbide material preparation, and in particular relates to a method for preparing silicon carbide nanowires by recycling renewable resources. Background Art

[0002] Silicon carbide is an excellent semiconductor material that is resistant to high temperature, high pressure, low density and strong oxidation. Silicon carbide nanowires, as a one-dimensional structure, have a unique nanoscale fiber structure, a wide band gap, high dielectric loss, high specific surface area and corrosion resistance. They are often used as a reinforcing material to make up for the defects in composite materials to prepare higher performance composite materials. This material has been widely used in aviation, electronic communications, ceramics and other industries.

[0003] Traditionally, silicon carbide nanomaterials are made from silicon carbide powder by gel casting, direct foaming, directional freezing and sacrificial templates. These methods require complex procedures and additional additives, which are expensive and complicated. Therefore, the construction of porous silicon carbide materials by simple, cheap and environmentally friendly methods has aroused great interest. Patent 1 "CN116120097B" uses CVD technology to prepare SiC nanowires on the surface of C / C composite materials, and then uses low-pressure chemical vapor deposition method with methane as carbon source to obtain SiC nanowire structure and SiC nanowire@carbon nanophase core-shell heterostructure. Patent 2 "CN118084543B" uses a C / C-UHT Cs composite material containing a rare earth zirconate / SiC nanowire composite coating and its preparation method, using a double-layer crucible, placing the C / C-UHTCs composite material in the inner crucible, placing Si powder in the outer crucible, and using chemical vapor deposition to prepare a C / C-UHT Cs composite material of SiC nanowires. Patent CN115246646A relates to a method for preparing silicon carbide nanowires using renewable resources or waste as a carbon source, which includes the following steps:

[0004] (1) Fluffing: Renewable resources or waste are subjected to a fluffing treatment to obtain a fluffy and evenly distributed pre-treated material;

[0005] (2) Carbonization: placing the fluffy and uniformly distributed pretreated material obtained in step (1) in a cracking furnace, evacuating the furnace to remove oxygen, introducing nitrogen to normal pressure, and then cracking the material at high temperature to obtain a fluffy and uniform carbon material;

[0006] (3) paving the reaction materials: placing the carbon-containing silica dry gel powder at the bottom of the crucible, and then placing the fluffy and uniform carbon material obtained in step (2) on the top of the carbon-containing silica dry gel powder, and covering the crucible with a lid;

[0007] (4) High-temperature carbon thermal reduction: The crucible is placed in a high-temperature sintering furnace, and then evacuated and nitrogen is injected to a certain pressure to react at high temperature. After the reaction is completed, the product of gray-green silicon carbide nanowires is obtained by cooling;

[0008] (5) Removing residual carbon: The product obtained in step (4) is placed in a muffle furnace for heating and heat preservation to remove residual carbon and obtain silicon carbide nanowires. The high-temperature carbon thermal reduction temperature of this patent is 1500-1800°C, and carbon-containing silicon dioxide dry gel powder is used, resulting in extremely high cost.

[0009] In the present invention, it is proposed to use waste agricultural and forestry biomass as a carbon source for preparing silicon carbide, use industrial silicon powder after wet oxygen oxidation as a silicon source, and generate silicon carbide nanowires in situ on the carbon source through a chemical vapor reaction. Summary of the invention

[0010] The present invention proposes a method for preparing silicon carbide nanowires by recycling renewable resources. The carbon source in the present invention is waste biomass in nature, such as coffee shells, macadamia shells, peanut shells, rice husks, rice straw, tobacco straw, etc. Most of these biomass are by-products of agricultural and forestry products. Most of these materials are discarded as waste. These waste biomass raw materials not only have high reactivity, but also have a highly porous structure. Fluffy and porous biochar is obtained by direct carbonization, which is very suitable as a carbon source for generating silicon carbide nanowires. The silicon source is a Si / SiO2 mixture formed by wet oxygen oxidation of industrial silicon powder for a certain period of time. Then, high-quality SiC nanowires are obtained by chemical deposition at a lower temperature.

[0011] A method for preparing silicon carbide nanowires by recycling renewable resources, the specific steps are as follows:

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

[0013] (2) Carbonization: placing the pretreated material obtained in step (1) in a furnace with a protective gas for carbonization to obtain fluffy and porous biochar;

[0014] (3) Silicon source pretreatment: placing a certain amount of silicon powder in an aqueous solution, reacting to obtain a mixture of Si and silicon oxide, taking it out and drying it as a silicon source, wherein the silicon oxide contains silicon dioxide;

[0015] (4) high-temperature carbon thermal reduction: placing the silicon source obtained in step (3) at the bottom of a crucible, providing an air-permeable isolation layer on the silicon source, and providing the fluffy porous biochar obtained in step (2) on the isolation layer; after covering the crucible with a lid, a protective gas is introduced and heated to react, and after the reaction is cooled, a product having SiC nanowires is obtained, and the reaction temperature is less than or equal to 1500° C.;

[0016] (5) Annealing treatment: The product obtained in step (4) is heated to remove 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 shells, peanut shells, rice husks, rice straws, and tobacco straws. After crushing, the particles are passed through a 100-mesh sieve and the sieve residue is taken.

[0018] As a further preference, the particle size of the pre-treated material in step (1) is 50-100 mesh. In industrial applications, a powder with a particle size of 50-100 mesh can be obtained by vibration 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° C., the heating rate is 8-12° C. / min, and the holding time is greater than or equal to 1 hour, more preferably greater than or equal to 2 hours. Ventilation carbonization under a protective atmosphere can prepare fluffy porous carbon as much as possible.

[0021] Preferably, the silicon powder used in step (3) is industrial silicon powder, the purity of which is greater than 99% and the particle size is -100 mesh. In industrial applications, a certain amount of industrial silicon powder is placed in an aqueous solution at a ratio of 4-6g industrial silicon powder to 15-25ml water, and reacted at 95-100°C for at least 4 hours to obtain a mixture of Si and silicon oxide, which is then taken out and dried as a silicon source, wherein the silicon oxide contains silicon dioxide. In industrial applications, the reaction time can be 4-20h. The present invention controls the reaction time of step (3) 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 from the silicon source, the distance between the carbon source and the silicon source is 5-30 mm, and the material of the hollow cylinder is aluminum oxide.

[0023] Preferably, in step (4), the carbon source and the silicon source are prepared in a ratio of 3-7 g of carbon source to 5 g of silicon source. In industrial applications, the ratio of the carbon source to the 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 smoothly absorbed by the carbon source. If the carbon source is excessive at this time, it will cause a problem of wasting carbon source in the later annealing and carbon removal stage.

[0024] Preferably, the reaction temperature of step (4) is 1200-1500° C., preferably 1200-1400° C., and the holding time is 2-6 hours. In industrial applications, considering the diameter and yield of the product, a long reaction time at 1200-1400° C. may be used.

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

[0026] Reaction principle:

[0027] The silicon source of the present invention is a mixture of Si and SiO2, which will undergo a disproportionation reaction at high temperature to generate a large amount of SiO gas. The carbon source will react with SiO in this environment to produce CO gas and SiC substrate. Then, in the cooling stage, the excess SiO gas and CO gas will grow SiC nanowires on the SiC substrate through chemical vapor multiplication. 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 the present invention are:

[0032] (1) The present invention uses waste biomass as raw material, which has low raw material cost and simple and fast process flow. Fluffy and porous biochar is obtained through pulverization and carbonization, which provides a high-value recycling method for waste biomass.

[0033] (2) In the present invention, industrial silicon powder is oxidized by wet oxygen 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 the present invention, a simple chemical deposition method is used to prepare silicon carbide nanowires, which is beneficial to reducing carbon emissions, saving resources, and has important practical application significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Attached Figure 1 This is a process flow chart of preparing silicon carbide nanowires in Example 1;

[0036] Attached Figure 2 This is a schematic diagram of a specific reaction device in Example 1;

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

[0038] Attached Figure 4 The microscopic morphology of silicon carbide obtained in Example 1;

[0039] Attached Figure 5 The microscopic morphology of silicon carbide obtained in Example 3;

[0040] Attached Figure 6 The microscopic morphology of silicon carbide obtained in Example 8; DETAILED DESCRIPTION

[0041] The present invention is further described in detail below in conjunction with specific implementation modes, but the protection scope of the present invention is not limited to the described contents.

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

[0043] (1) Washing and drying the peanut shells to remove dirt, and then crushing them into 100 mesh powder using a vibration mill;

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

[0045] (3) placing industrial silicon powder in 20 ml of deionized water and subjecting it to wet oxygen oxidation at 100° C. for 12 h to obtain a mixed silicon source having a composition of Si and SiO2;

[0046] (4) placing the silicon source (5 g) obtained in step (3) at the bottom of a crucible, setting a breathable isolation layer (corundum hollow cylinder, height 15 mm) on the silicon source, and setting the fluffy porous biochar (3.15 g) obtained in step (2) on the isolation layer; after covering the crucible, placing it into a furnace, introducing argon into the furnace for reaction, the argon flow rate is 20 ml / min, the maximum reaction temperature is 1500°C, the heating rate is 10°C / min, the insulation time is 4 h, the cooling rate is 5°C / min, and after cooling to room temperature, 5.13 g of product is obtained;

[0047] (5) The product obtained in step (4) was directly placed in a muffle furnace, heated to 800°C at a heating rate of 10°C / min, and kept warm 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 by recycling renewable resources, the specific steps are as follows:

[0049] (1) Washing and drying the peanut shells to remove dirt, and then crushing them into 100 mesh powder using a vibration mill;

[0050] (2) Weigh 10 g of the powder obtained in step (1) and place it in a Φ60×40 mm crucible, evenly flatten it and place it in a horizontal tube furnace filled with argon gas, with an argon gas flow rate of 20 ml / min, a carbonization temperature of 500°C, a heating rate of 10°C / min, and a holding time of 2 h to obtain 5.88 g of peanut shell biochar;

[0051] (3) placing industrial silicon powder in 20 ml of deionized water and subjecting it to wet oxygen oxidation at 100° C. for 4 h to obtain a mixed silicon source having a composition of Si and SiO2;

[0052] (4) placing the silicon source (5 g) obtained in step (3) at the bottom of a crucible, setting a breathable isolation layer (corundum hollow cylinder, height 15 mm) on the silicon source, and setting the fluffy porous biochar (5.88 g) obtained in step (2) on the isolation layer; after covering the crucible, placing it into a furnace, introducing argon into the furnace for reaction, the argon flow rate is 20 ml / min, the maximum reaction temperature is 1200°C, the heating rate is 10°C / min, the insulation time is 2h, the cooling rate is 5°C / min, and after cooling to room temperature, 6.12 g of product is obtained;

[0053] (5) The product obtained in step (4) was directly placed in a muffle furnace, heated to 800°C at a heating rate of 10°C / min, and kept warm 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 by recycling renewable resources, the specific steps are as follows:

[0055] (1) Washing and drying the peanut shells to remove dirt, and then crushing them into 100 mesh powder using a vibration mill;

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

[0057] (3) placing industrial silicon powder in 20 ml of deionized water and subjecting it to wet oxygen oxidation at 100° C. for 8 h to obtain a mixed silicon source having a composition of Si and SiO2;

[0058] (4) placing the silicon source (5 g) obtained in step (3) at the bottom of a crucible, setting a breathable isolation layer (corundum hollow cylinder, height 15 mm) on the silicon source, and setting the fluffy porous biochar (3.42 g) obtained in step (2) on the isolation layer; after covering the crucible, placing it into a furnace, introducing argon into the furnace for reaction, the argon flow rate is 20 ml / min, the maximum reaction temperature is 1400°C, the heating rate is 10°C / min, the insulation time is 3h, the cooling rate is 5°C / min, and after cooling to room temperature, 4.52 g of product is obtained;

[0059] (5) The product obtained in step (4) was directly placed in a muffle furnace, heated to 800°C at a heating rate of 10°C / min, and kept warm 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 by recycling renewable resources, the specific steps are as follows:

[0061] (1) Washing and drying the peanut shells to remove dirt, and then crushing them into 100 mesh powder using a vibration mill;

[0062] (2) Weigh 10 g of the powder obtained in step (1) and place it in a Φ60×40 mm crucible, evenly flatten it and place it in a horizontal tube furnace filled with argon gas, with an argon gas flow rate of 20 ml / min, a carbonization temperature of 800°C, a heating rate of 10°C / min, and a holding time of 2 h to obtain 3.06 g of peanut shell biochar;

[0063] (3) placing industrial silicon powder in 20 ml of deionized water and subjecting it to wet oxygen oxidation at 100° C. for 16 h to obtain a mixed silicon source having a composition of Si and SiO2;

[0064] (4) placing the silicon source (5 g) obtained in step (3) at the bottom of a crucible, setting a breathable isolation layer (corundum hollow cylinder, height 15 mm) on the silicon source, and setting the fluffy porous biochar (3.06 g) obtained in step (2) on the isolation layer; after covering the crucible, placing it into a furnace, introducing argon into the furnace for reaction, the argon flow rate is 20 ml / min, the maximum reaction temperature is 1300°C, the heating rate is 10°C / min, the insulation time is 6 h, the cooling rate is 5°C / min, and after cooling to room temperature, 4.12 g of product is obtained;

[0065] (5) The product obtained in step (4) was directly placed in a muffle furnace, heated to 800°C at a heating rate of 10°C / min, and kept warm 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 by recycling renewable resources, the specific steps are as follows:

[0067] (1) The coffee husks are washed and dried to remove dirt, and then crushed into 100 mesh powder using a vibration mill;

[0068] (2) Weigh 10 g of the powder obtained in step (1) and place it in a Φ60×40 mm crucible, evenly flatten it and place it in a horizontal tube furnace filled with argon gas, with an argon gas flow rate of 20 ml / min, a carbonization temperature of 600°C, a heating rate of 10°C / min, and a holding time of 2 h to obtain 3.82 g of coffee shell biochar;

[0069] (3) placing industrial silicon powder in 20 ml of deionized water and subjecting it to wet oxygen oxidation at 100° C. for 12 h to obtain a mixed silicon source having a composition of Si and SiO2;

[0070] (4) placing the silicon source (5 g) obtained in step (3) at the bottom of a crucible, setting a breathable isolation layer (corundum hollow cylinder, height 15 mm) on the silicon source, and setting the fluffy porous biochar (3.82 g) obtained in step (2) on the isolation layer; after covering the crucible, placing it into a furnace, introducing argon into the furnace for reaction, the argon flow rate is 20 ml / min, the maximum reaction temperature is 1400°C, the heating rate is 10°C / min, the insulation time is 4h, the cooling rate is 5°C / min, and after cooling to room temperature, 4.91 g of product is obtained;

[0071] (5) The product obtained in step (4) was directly placed in a muffle furnace, heated to 800°C at a heating rate of 10°C / min, and kept warm 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 by recycling renewable resources, the specific steps are as follows:

[0073] (1) The coffee husks are washed and dried to remove dirt, and then crushed into 100 mesh powder using a vibration mill;

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

[0075] (3) placing industrial silicon powder in 20 ml of deionized water and subjecting it to wet oxygen oxidation at 100° C. for 16 h to obtain a mixed silicon source having a composition of Si and SiO2;

[0076] (4) placing the silicon source (5 g) obtained in step (3) at the bottom of a crucible, setting a breathable isolation layer (corundum hollow cylinder, height 15 mm) on the silicon source, and setting the fluffy porous biochar (3.15 g) obtained in step (2) on the isolation layer; after covering the crucible, placing it into a furnace, introducing argon into the furnace for reaction, the argon flow rate is 20 ml / min, the maximum reaction temperature is 1300°C, the heating rate is 10°C / min, the insulation time is 6 h, the cooling rate is 5°C / min, and after cooling to room temperature, 5.26 g of product is obtained;

[0077] (5) The product obtained in step (4) was directly placed in a muffle furnace, heated to 800°C at a heating rate of 10°C / min, and kept warm 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 by recycling renewable resources, the specific steps are as follows:

[0079] (1) The coffee husks are washed and dried to remove dirt, and then crushed into 100 mesh powder using a vibration mill;

[0080] (2) Weigh 10 g of the powder obtained in step (1) and place it in a Φ60×40 mm crucible, evenly flatten it and place it in a horizontal tube furnace filled with argon gas, with an argon gas flow rate of 20 ml / min, a carbonization temperature of 700°C, a heating rate of 10°C / min, and a holding time of 2 h to obtain 3.47 g of coffee shell biochar;

[0081] (3) placing industrial silicon powder in 20 ml of deionized water and subjecting it to wet oxygen oxidation at 100° C. for 8 h to obtain a mixed silicon source having a composition of Si and SiO2;

[0082] (4) placing the silicon source (5 g) obtained in step (3) at the bottom of a crucible, setting a breathable isolation layer (corundum hollow cylinder, height 15 mm) on the silicon source, and setting the fluffy porous biochar (3.47 g) obtained in step (2) on the isolation layer; after covering the crucible, placing it into a furnace, introducing argon into the furnace for reaction, the argon flow rate is 20 ml / min, the maximum reaction temperature is 1200°C, the heating rate is 10°C / min, the insulation time is 5 h, the cooling rate is 5°C / min, and after cooling to room temperature, 4.26 g of product is obtained;

[0083] (5) The product obtained in step (4) was directly placed in a muffle furnace, heated to 800°C at a heating rate of 10°C / min, and kept warm 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 by recycling renewable resources, the specific steps are as follows:

[0085] (1) The coffee husks are washed and dried to remove dirt, and then crushed into 100 mesh powder using a vibration mill;

[0086] (2) Weigh 10 g of the powder obtained in step (1) and place it in a Φ60×40 mm crucible, evenly flatten it and place it in a horizontal tube furnace filled with argon gas, with an argon gas flow rate of 20 ml / min, a carbonization temperature of 500°C, a heating rate of 10°C / min, and a holding time of 2 h to obtain 6.23 g of coffee shell biochar;

[0087] (3) placing industrial silicon powder in 20 ml of deionized water and subjecting it to wet oxygen oxidation at 100° C. for 4 h to obtain a mixed silicon source having a composition of Si and SiO2;

[0088] (4) placing the silicon source (5 g) obtained in step (3) at the bottom of a crucible, setting a breathable isolation layer (corundum hollow cylinder, height 15 mm) on the silicon source, and setting the fluffy porous biochar (6.23 g) obtained in step (2) on the isolation layer; after covering the crucible, placing it into a furnace, introducing argon into the furnace for reaction, the argon flow rate is 20 ml / min, the maximum reaction temperature is 1200°C, the heating rate is 10°C / min, the insulation time is 5 h, the cooling rate is 5°C / min, and after cooling to room temperature, 6.76 g of product is obtained;

[0089] (5) The product obtained in step (4) was directly placed in a muffle furnace, heated to 800°C at a heating rate of 10°C / min, and kept warm 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] Other conditions are the same as those in Example 8, except that:

[0092] Industrial silicon was directly used as the silicon source for the reaction, and it was found that no silicon carbide was generated.

[0093] Comparative Example 2

[0094] Other conditions are the same as those in Example 3, except that:

[0095] (4) placing the carbon source (4.26 g) and silicon source (5 g) obtained in step (2) and step (3) in a corundum crucible, wherein the carbon source and the silicon source are not separated by a corundum ring, and then placing the crucible in a muffle furnace filled with argon gas for reaction. The argon gas flow rate is 20 ml / min, the maximum reaction temperature is 1400°C, the heating rate is 10°C / min, the holding time is 4h, the cooling rate is 5°C / min, and after cooling to room temperature, 4.89 g of product is obtained. It is observed that the carbon source and the silicon source are closely attached to each other.

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

[0097] The specific implementation modes of the present invention are described in detail above, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A method for preparing silicon carbide nanowires by recycling renewable resources, characterized in that The steps include: (1) Carbon source pretreatment: The biomass is washed, dried to remove dirt, and then ground into powder to obtain a pretreated material; (2) Carbonization: placing the pretreated material obtained in step (1) in a furnace with a 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 to react to obtain a mixture of Si and silicon oxide, which is then taken out and dried to serve as a silicon source, wherein the silicon oxide contains silicon dioxide; (4) high-temperature carbon thermal reduction: placing the silicon source obtained in step (3) at the bottom of a crucible, providing an air-permeable isolation layer on the silicon source, and providing the fluffy porous biochar obtained in step (2) on the isolation layer; after covering the crucible with a lid, a protective gas is introduced and heated to react, and after the reaction is cooled, a product having SiC nanowires is obtained, and the reaction temperature is less than or equal to 1500° C.; (5) Annealing treatment: The product obtained in step (4) is heated to remove residual carbon, and the remaining product is SiC nanowires.

2. The method for preparing silicon carbide nanowires by recycling renewable resources according to claim 1, characterized in that: In step (1), the biomass is selected from at least one of coffee shells, macadamia shells, peanut shells, rice husks, rice straws, and tobacco straws. After crushing, the particles are passed through a 100-mesh sieve, and the sieve residue is taken.

3. The method for preparing silicon carbide nanowires by recycling 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 by recycling 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° C., the heating rate is 8-12° C. / min, and the holding time is greater than or equal to 1 hour, and more preferably greater than or equal to 2 hours. Carbonization under a protective atmosphere can prepare fluffy porous carbon as much as possible.

5. The method for preparing silicon carbide nanowires by recycling renewable resources according to claim 1, characterized in that: The silicon powder used in step (3) is industrial silicon powder, the purity of which is greater than 99% and the particle size is -100 mesh.

6. The method for preparing silicon carbide nanowires by recycling renewable resources according to claim 5, characterized in that: A certain amount of industrial silicon powder is placed in an aqueous solution at a ratio of 4-6g industrial silicon powder to 15-25ml water, and reacted at 95-100°C for at least 4 hours to obtain a mixture of Si and silicon oxide, which is taken out and dried as a silicon source. The silicon oxide contains silicon dioxide. In industrial applications, the reaction time can be 4-20 hours.

7. The method for preparing silicon carbide nanowires by recycling renewable resources according to claim 1, characterized in that: Preferably, 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 5-30 mm, and the material of the hollow cylinder is aluminum oxide.

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

9. The method for preparing silicon carbide nanowires by recycling renewable resources according to claim 1, characterized in that: The reaction temperature of step (4) is 1200-1500° C., preferably 1200-1400° C., and the insulation time is 2-6 h.

10. The method for preparing silicon carbide nanowires by recycling renewable resources according to claim 1, characterized in that: The product obtained in step (4) is directly placed in a muffle furnace and heated to 600-850°C at a heating rate of 8-12°C / min, then kept warm for 1-3 hours, and cooled to obtain the final SiC nanowire product.

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