A method and system for preparing silicon carbide nanowires

Abstract

The application relates to the chemical production field, in particular to a preparation method of silicon carbide nanowires, which comprises the following steps: roasting micro-silicon powder to obtain primary raw materials; adding a binder to the primary raw materials, and then grinding and mixing to obtain precursor powder; assembling a cathode unit: pressing the precursor powder into precursor tablets; wrapping the precursor tablets with a foamed nickel net to form a cathode element, winding and fixing one end of a cathode wire to form a cathode unit; placing the cathode element of the cathode unit in an electrolytic cell, and connecting the other end of the cathode wire to a power supply located outside the electrolytic cell; assembling an anode unit: placing an anode in the electrolytic cell, connecting one end of an anode wire to the anode as an anode unit; leading the other end of the anode wire out of the electrolytic cell and connecting the other end to a power supply; preparing a composite molten salt as an electrolyte, and building an electrolytic cell to electrolytically produce silicon carbide nanowires. The application has lower cost.

Description

Technical Field

[0001] This invention belongs to the field of silicon carbide nanomaterial preparation technology, specifically relating to a method and system for preparing silicon carbide nanowires. Background Technology

[0002] Silicon carbide (SiC) nanowires possess excellent mechanical properties, high-temperature resistance, chemical stability, and good semiconductor characteristics, showing broad application prospects in high-temperature structural materials, electronic devices, composite material reinforcement phases, and catalyst supports. Currently, the main methods for preparing silicon carbide nanowires include gas-phase methods, solid-phase methods, and liquid-phase methods. Gas-phase methods (such as chemical vapor deposition) produce high-purity and uniform morphology products, but suffer from complex equipment, high energy consumption, and expensive raw materials (often using high-purity silanes and methane). Solid-phase methods (such as carbothermal reduction) are simple, but require high reaction temperatures (typically exceeding 1600℃), long reaction times, and the products are prone to agglomeration and have lower purity. Liquid-phase methods face challenges such as poor product dispersibility and complex post-processing. In summary, all of the above preparation methods generally involve high costs. Summary of the Invention

[0003] To address the high raw material costs in existing silicon carbide nanowire preparation methods, this invention provides a method for preparing silicon carbide nanowires, comprising the following steps:

[0004] Step S1. Raw material pretreatment: Calcination of microsilica powder at 500-600℃ for 2-3 hours to obtain primary raw material; Step S2. Precursor preparation: Add a binder to the primary raw material, and then grind and mix for 12-24 hours to obtain precursor powder; Step S3. Cathode Unit Assembly: The precursor powder is pressed into precursor sheets under a pressure of 25~40MPa for 5~20min; each precursor sheet is wrapped with a nickel foam mesh to form a cathode element, and the cathode element is fixed by winding one end of a cathode wire to form a cathode unit; then, the cathode element of the cathode unit is placed in the electrolytic cell, and the other end of the cathode wire is connected to a power source located outside the electrolytic cell; Step S4. Anode Unit Assembly: Place the anode in the electrolytic cell, and connect one end of the anode wire to the anode to form an anode unit; the other end of the anode wire is led out from the electrolytic cell and connected to the power supply; Step S5. Preparation of composite salt: First, remove moisture from CaCl2, Na2CO3 and Li2CO3 by drying. Then, mix CaCl2, Na2CO3 and Li2CO3 to obtain composite salt. The composite salt includes 60-70 parts of CaCl2, 20-30 parts of Na2CO3 and 5-15 parts of Li2CO3 by mass. Step S6. Electrolytic cell construction: Add the composite salt prepared in step S5 to the electrolytic cell, and place the electrolytic cell containing the composite salt in a protective atmosphere. Heat the cell to completely melt the composite salt to form a composite molten salt system as the electrolyte. Step S7. Electrolysis: Maintain the temperature to keep the composite molten salt in a molten state, continuously introduce carbon dioxide gas into the molten composite molten salt system, and simultaneously connect a DC power supply to control the electrolysis voltage at 2.5-3.2V and the electrolysis time at 10-20h; Step S8. Product processing: After electrolysis, turn off the power and stop the carbon dioxide gas supply. After the electrolytic cell cools naturally to room temperature, take out the cathode product. Soak the cathode product in dilute hydrochloric acid to remove residual metal impurities, then wash it with deionized water, and finally vacuum dry it to obtain silicon carbide nanowires.

[0005] In one embodiment, the cathode unit includes one or more cathode elements; when there are multiple cathode elements, the multiple cathode elements are fixed together using cathode wires.

[0006] In one embodiment, the protective atmosphere comprises argon gas at a volume percentage of 99.999%.

[0007] In one embodiment, when carbon dioxide gas is introduced into the composite molten salt system, the purity of the introduced carbon dioxide gas is ≥99.9%, and the gas flow rate is 50-150 mL / min.

[0008] In one embodiment, in step S5, CaCl2, Na2CO3, and Li2CO3 are dried at 120-150°C for 4-6 hours to remove moisture.

[0009] In one embodiment, in step S6, the electrolytic cell containing the composite salt is heated to 750-850°C and held at that temperature for more than 25 minutes to completely melt the composite salt.

[0010] In one embodiment, in step S2, the grinding and mixing method is ball milling, and the binder is polyvinyl butyral and / or liquid paraffin; the amount of binder added is 15%-25% of the weight of the primary raw material.

[0011] In one embodiment, in step S8, the mass fraction of HCl in the dilute hydrochloric acid is 5%-10%; the cathode product is soaked in dilute hydrochloric acid for 2-4 hours, then washed with deionized water until the washing solution is neutral, and finally vacuum dried at 60-80°C for 6-12 hours.

[0012] In addition, the present invention also provides a silicon carbide nanowire preparation system, the system comprising an electrolytic cell device, an acid washing device, a water washing device and a vacuum drying device arranged in sequence; The electrolytic cell device includes a power supply, an electrolytic cell, an electrolyte, a cathode unit, an anode unit, a protective atmosphere, and a gaseous carbon source; the electrolyte is placed in the electrolytic cell, and the electrolyte includes 60-70 parts CaCl2, 20-30 parts Na2CO3, and 5-15 parts Li2CO3 mixed and molten by mass, and the temperature is maintained at 750-800℃ during electrolysis; The cathode unit includes a cathode wire and a cathode element. One end of the cathode wire is connected to the cathode element, and the other end is connected to the power source. The cathode element is immersed in the electrolyte. The cathode element is prepared by: calcining the original microsilica powder to obtain an initial raw material; adding a binder at a mass percentage of 15%-25% of the initial raw material to the initial raw material; grinding and mixing to form a precursor powder; pressing the precursor powder into a precursor sheet; and wrapping each precursor sheet with a nickel foam mesh to form a cathode element. The anode unit includes an anode and an anode wire, one end of which is connected to the anode and the other end of which is connected to the power source; the anode is immersed in the electrolyte. The protective atmosphere includes argon; the electrolytic cell containing the electrolyte is situated within the protective atmosphere. The gaseous carbon source is carbon dioxide gas, which is continuously introduced into the electrolyte during electrolysis.

[0013] In one embodiment, the protective atmosphere comprises argon gas with a volume percentage of 99.999%; the gaseous carbon source is carbon dioxide gas with a purity of ≥99.9%. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the electrolytic cell structure used in the synthesis of silicon carbide nanowire materials according to the method of the present invention.

[0015] Figure 2 The image shows the XRD pattern of the electrolysis product obtained in Example 1 of this invention.

[0016] Figure 3 This is a SEM image of the electrolytic product obtained in Embodiment 1 of the present invention.

[0017] Figure 4 This is a TEM image of the electrolysis product obtained in Embodiment 1 of the present invention.

[0018] Figure reference numerals: 1-Electrolytic cell, 2-Nickel foam mesh, 3-Composite molten salt system, 4-Anode, 51-Cathode wire, 52-Anode wire, 6-Cathode unit. Detailed Implementation

[0019] To address the high cost and energy consumption issues of existing technologies, this invention analyzes existing techniques and finds that current silicon carbide preparation methods often use high-purity silicon dioxide and solid carbon (such as graphite and activated carbon) as raw materials, resulting in high raw material costs. Furthermore, the poor uniformity of mixing the solid carbon source and silicon source easily leads to uneven product composition. Therefore, this invention proposes using microsilica powder as the silicon source and carbon dioxide as the carbon source to prepare silicon carbide nanowires. Microsilica powder is a byproduct of industrial production processes such as ferroalloy plants and silicon plants. Its main component is amorphous silicon dioxide. It is produced in large quantities and is inexpensive, but its recycling rate is low. Large-scale accumulation not only wastes resources but also causes environmental pollution. Carbon dioxide, as an industrial waste gas, has significantly lower acquisition and usage costs than solid carbon sources. Moreover, as a major greenhouse gas, the reduction and resource utilization of carbon dioxide has become a global focus. Combining microsilica powder with carbon dioxide to prepare high-value silicon carbide nanowires reduces the use of high-purity silica raw materials and solid carbon, thereby lowering costs to some extent. At the same time, it can also realize the resource utilization of industrial solid waste, improve the mixing effect of silicon and carbon sources to some extent, and complete the fixation and conversion of greenhouse gases, which has significant economic and environmental benefits.

[0020] Furthermore, to ensure the successful preparation of the target product from the aforementioned raw materials, this invention proposes the use of the FFC molten salt electrolysis method. The FFC molten salt electrolysis method is a highly efficient technology for preparing metal and ceramic materials, possessing advantages such as moderate electrolysis temperature, strong reaction controllability, and high product purity. It has been successfully applied to the preparation of refractory metals and oxide ceramics such as titanium and zirconium. In the prior art, there are no reports on the use of the FFC molten salt electrolysis method to prepare silicon carbide nanowires by using microsilica powder as the silicon source and capturing carbon dioxide through molten salt and converting it into a carbon source.

[0021] The following is the overall scheme of the preparation method provided in this application.

[0022] A method for preparing silicon carbide nanowires includes the following steps: Step S1. Raw material pretreatment: Place the silica powder (raw material) in a muffle furnace and calcine it at 500-600℃ for 2-3 hours to remove carbon impurities and organic pollutants from the silica powder and obtain the primary raw material.

[0023] Step S2. Precursor preparation: A binder is added to the primary raw material, the amount of binder being 15%-25% of the weight of the primary raw material, and then the mixture is ground and mixed for 12-24 hours to obtain precursor powder. Specifically, the grinding and mixing method is ball milling, and the binder is polyvinyl butyral and / or liquid paraffin.

[0024] Step S3. Cathode Unit Assembly: The precursor powder is pressed into a circular sheet under a pressure of 25-40 MPa for 5-20 minutes, referred to as a precursor sheet. Tests have shown that the precursor sheet has sufficient strength without sintering, therefore sintering is unnecessary. Each precursor sheet is wrapped with a nickel foam mesh to form a cathode element. At least one cathode element is fixed by winding one end of an iron-chromium-aluminum wire electrode conductor, forming a wrapped cathode unit. Specifically, the cathode unit may contain one or more cathode elements. When there are multiple cathode elements, one end of the iron-chromium-aluminum wire conductor is used to wind the multiple cathode elements together to form an electrolytic cathode unit. Subsequently, the cathode element of the cathode unit is placed in the electrolytic cell. The other end of the iron-chromium-aluminum wire is connected to a power source located outside the electrolytic cell; that is, the iron-chromium-aluminum wire conductor also serves as a cathode conductor.

[0025] Step S4. Anode Unit Assembly: In this invention, a graphite carbon rod is used as the anode. The graphite carbon rod is placed in the electrolytic cell. One end of the iron-chromium-aluminum wire is connected to the graphite carbon rod with a diameter of 15 mm and a length of 150 mm to serve as the anode unit. The other end of the wire is led out from the electrolytic cell and connected to the power supply. That is, the iron-chromium-aluminum wire serves as the anode wire.

[0026] Step S5. Preparation of Composite Salt: This invention uses a CaCl2-Na2CO3-Li2CO3 composite molten salt system as the electrolyte. First, the components are prepared into a composite salt, which is then melted to form a composite molten salt system as the electrolyte during the subsequent construction of the electrolytic cell. Specifically, in step S5, CaCl2, Na2CO3, and Li2CO3 are first dried at 120-150℃ for 4-6 hours to remove moisture. Then, CaCl2, Na2CO3, and Li2CO3 are mixed in a certain proportion to obtain the composite salt. The composite salt, based on anhydrous crystallization, has the following mass fractions: CaCl2 60%-70%, Na2CO3 20%-30%, and Li2CO3 5%-15%.

[0027] Step S6. Electrolytic Cell Setup: Using a corundum crucible as the electrolytic cell, the composite salt prepared in step S5 is added to the electrolytic cell. High-purity argon gas (99.999% purity by volume) is used as the protective atmosphere to keep the electrolytic cell containing the composite salt within this protective atmosphere. The electrolytic cell is then placed in a high-temperature furnace and heated to 750-850°C, held for at least 25 minutes to completely melt the composite salt, forming a composite molten salt system as the electrolyte. At this point, both the anode and cathode units are placed in the electrolyte and connected to the power supply via wires, thus forming the electrolytic cell.

[0028] Step S7. Electrolysis: Maintain the temperature of the composite molten salt at 750-850℃, continuously introduce carbon dioxide gas with a purity ≥99.9% into the molten composite molten salt at a rate of 50-150mL / min; at the same time, connect the DC power supply, control the electrolysis voltage at 2.5-3.2V, and the electrolysis time at 10-20h.

[0029] Step S8. Product processing: After electrolysis, turn off the power and stop the carbon dioxide gas supply. After the electrolytic cell cools naturally to room temperature, take out the cathode product obtained by electrolysis in the above steps, peel off the nickel foam, and soak the cathode product in dilute hydrochloric acid (mass fraction 5%-10%) for 2-4 hours to remove residual molten salt and metal impurities such as calcium and sodium. Then wash with deionized water until neutral, and finally vacuum dry at 60-80℃ for 6-12 hours to obtain silicon carbide nanowires (purity ≥99.5%).

[0030] The principle of the method of this invention is: This invention utilizes inexpensive industrial byproduct microsilica powder as the cathode and silicon source, graphite carbon rods as the anode, and carbon dioxide (a greenhouse gas) as the carbon source. Through an optimized composite solution system and an FFC molten salt electrolysis method, it achieves efficient capture and in-situ conversion of carbon dioxide, producing high-purity, uniformly morphological silicon carbide nanowires. At the cathode, SiO3²⁻ in the composite molten salt… - It is gradually reduced to elemental silicon. Simultaneously, CO3²⁺, converted from CO2, is present in the composite molten salt. - It is also reduced near the cathode, generating active carbon atoms or carbon ions (CO3²⁻). - + 4e - → C + 3O² - The newly formed active silicon and active carbon undergo an in-situ reaction on the cathode surface (at the interface of micro silicon powder particles), following a gas-liquid-solid or solid-liquid-solid growth mechanism to generate silicon carbide crystal nuclei and grow along a one-dimensional direction, eventually forming nanowires.

[0031] Furthermore, based on the same concept described above, the present invention also provides a system for preparing silicon carbide nanowires. The system includes an electrolytic cell, an acid washing device, a water washing device, and a vacuum drying device arranged sequentially.

[0032] Specifically, such as Figure 1 As shown, the electrolytic cell device is used to electrolyze and generate silicon carbide nanowires, and includes: a power supply, an electrolytic cell 1, an electrolyte, a cathode unit 6, an anode unit, a protective atmosphere, and a gaseous carbon source. The specific structure is as follows.

[0033] The power supply is specifically a DC power supply with a voltage of 2.5-3.2V.

[0034] The electrolytic cell 1 is specifically a corundum crucible.

[0035] The electrolyte, placed in the electrolytic cell 1, is specifically a composite molten salt system 3, comprising 60%-70% CaCl2, 20%-30% Na2CO3, and 5%-15% Li2CO3 by mass, mixed and molten. The temperature is maintained at 750-800℃ during electrolysis. The electrolyte is prepared according to steps S5-S6 described above.

[0036] The cathode unit 6 includes a cathode wire 51 and a cathode element. The cathode wire 51 is an iron-aluminum wire, one end of which is wound around the cathode element, and the other end is connected to the power source. The cathode element is immersed in the electrolyte. The cathode unit 6 is prepared according to the methods described in steps S1-S3 above.

[0037] The anode unit includes a graphite carbon rod and an anode wire 52. The anode wire 52 is an iron-aluminum wire, one end of which is connected to the graphite carbon rod and the other end is connected to the power source. The graphite carbon rod is immersed in the electrolyte.

[0038] The protective atmosphere is specifically argon gas with a volume percentage of 99.999%. The electrolytic cell 1 containing the electrolyte is situated within this protective atmosphere.

[0039] The gaseous carbon source is specifically carbon dioxide gas with a purity of ≥99.9%, which is continuously introduced into the electrolyte during electrolysis at a rate of 100 mL / min.

[0040] The pickling device includes dilute hydrochloric acid for soaking the electrolytic cathode product. The dilute hydrochloric acid has an HCl mass fraction of 5%-10% and is used to soak and remove residual metal impurities in the electrolytic cathode product, i.e., silicon carbide nanowires.

[0041] The washing device includes deionized water for washing away residual dilute hydrochloric acid on the electrolytic cathode product after acid washing. In one embodiment, the washing device includes several tanks filled with deionized water.

[0042] The vacuum drying device has a drying temperature of 60-80℃ and is used to dry the electrolytic products after water washing.

[0043] The cathode product generated by electrolysis using the electrolytic cell device in this system for 10-20 hours is silicon carbide nanowires. The obtained silicon carbide nanowires are immersed in the acid washing device for 6-12 hours, then washed with water until neutral, and finally dried using a vacuum drying device to obtain the final silicon carbide nanowires.

[0044] Compared with the prior art, the method and system provided by the present invention have the following obvious and prominent substantive features and significant advantages: 1. Low-cost and environmentally friendly raw materials: Using industrial by-product microsilica powder as the silicon source and carbon dioxide captured by composite molten salt as the carbon source, this method replaces the high-purity silicon and solid carbon source used in traditional processes. No additional processes are required; high-purity silicon carbide nanowires are directly synthesized at a lower temperature through a one-step electrolysis method. This is a simple, low-cost, and environmentally friendly method for preparing silicon carbide nanowires. Simultaneously, it achieves the dual goals of "waste-to-waste" treatment and CO2 resource utilization, realizing the dual objectives of industrial solid waste resource utilization and greenhouse gas emission reduction. The raw material cost is significantly reduced, resulting in significant economic and environmental benefits.

[0045] 2. Multifunctional composite molten salt system: The innovative CaCl2-Na2CO3-Li2CO3 composite molten salt system 3 not only has good conductivity and fluxing effect, but also can efficiently capture carbon dioxide and convert it into a carbon source in situ. It solves the problems of single function and uneven carbon source distribution of traditional molten salt systems, and provides an ideal reaction environment for the preparation of silicon carbide.

[0046] 3. Simple process and low energy consumption: The electrolysis temperature is controlled at 750-850℃, which is much lower than the reaction temperature of the traditional carbothermal reduction method, resulting in a significant reduction in energy consumption; at the same time, the process steps are simple, requiring no complex equipment and subsequent processing procedures, making it easy to achieve industrial-scale production.

[0047] The present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0048] Example 1 This embodiment follows the following... Figure 1 The simplified process shown is used to prepare silicon carbide nanowire materials as an example. Low-quality microsilicon powder (SiO2 content 92.5%) from a silicon smelting enterprise in Yunnan Province is placed in a muffle furnace and calcined at 550℃ for 2.5 hours. Using the treated silicon micropowder as the primary raw material, 20% by weight of polyvinyl butyral binder is added, followed by ball milling for 15 hours to obtain a uniformly mixed precursor powder. ~1.0 g of the precursor powder is weighed and pressed into a circular sheet under 30 MPa to obtain a precursor sheet. A precursor sheet is wrapped with a nickel foam mesh 2 to form a cathode element, and an iron-chromium-aluminum wire is used as the cathode wire 51, with one end wrapped around the cathode element to form a cathode unit 6. The cathode element of the prepared cathode unit 6 is then... Figure 1The cathode wire 51 is placed in the corundum crucible electrolytic cell 1 as shown. The other end of the cathode wire 51 extends out of the electrolytic cell 1 and is connected to an external power source. A graphite carbon rod (15 mm in diameter and 150 mm in length) is used as the anode 4 and placed in the electrolytic cell 1. Another iron-aluminum wire is used as the anode wire 52, with one end connected to the anode 4 and the other end extending out of the electrolytic cell 1 and connected to the power source. CaCl2, Na2CO3, and Li2CO3 were dried at 130℃ for 5 hours. A composite salt was prepared by uniformly mixing CaCl2, Na2CO3, and Li2CO3 in a mass fraction of 65%. The mixture was placed in an alumina crucible as the reaction vessel, and high-purity argon was used as the protective atmosphere. The temperature was raised to 800℃ at a rate of 10℃ / min in a sealed resistance furnace and held for 30 minutes to completely melt the composite salt and form a composite molten salt system. The temperature was maintained at 800℃, and carbon dioxide gas with a purity ≥99.9% was continuously introduced into the molten salt at a rate of 100 mL / min. A DC power supply was connected, and the electrolysis voltage was set to 3.2V for 15 hours. After electrolysis, the power supply and carbon dioxide cylinder were turned off, and the mixture was allowed to cool naturally to room temperature. The cathode product was then removed. The cathode product was soaked in 8% dilute hydrochloric acid for 3 hours, with stirring every 30 minutes during this period. The silicon carbide nanowires were then repeatedly washed with deionized water until the pH of the washing solution was 7, and finally dried under vacuum at 70°C for 8 hours.

[0049] The product was determined by XRD to be pure-phase SiC (e.g., ...). Figure 2 As shown), no obvious impurity peaks were observed. SEM and TEM characterization revealed nanowires with diameters of 10-30 nm and lengths of 10-20 μm (e.g., ...). Figure 3 , 4 As shown), the purity is 99.6%.

[0050] Example 2 This embodiment follows the following... Figure 1The simplified process shown is used to prepare silicon carbide nanowire materials. Low-quality microsilica powder (SiO2 content 91.3%) is placed in a muffle furnace and calcined at 600℃ for 2 hours. Using the treated microsilica powder as the primary raw material, 25% by weight of polyvinyl butyral binder is added, followed by ball milling for 20 hours to obtain a uniformly mixed precursor powder. ~1.5 g of the precursor powder is weighed and pressed into a circular sheet under 40 MPa to obtain a precursor sheet. A precursor sheet is wrapped with a nickel foam mesh 2 to form a cathode element, and an iron-chromium-aluminum wire is used as the cathode conductor 51, with one end wrapped to form a cathode unit 6. The cathode element of the cathode unit 6 is placed in an alumina crucible electrolytic cell 1. The other end of the cathode conductor 51 is led out of the electrolytic cell 1 and connected to an external power source. A graphite carbon rod (15 mm in diameter and 150 mm in length) is placed as the anode 4 in the electrolytic cell 1. Another iron-aluminum wire is used as the anode wire 52, with one end connected to the graphite carbon rod and the other end connected to the power supply. CaCl2, Na2CO3, and Li2CO3 are dried at 140℃ for 4 h respectively. They are then mixed evenly in a mass fraction of 65% CaCl2, 20% Na2CO3, and 15% Li2CO3 to obtain a composite salt. The composite salt is placed in an alumina crucible electrolytic cell 1, and high-purity argon is used as the protective atmosphere. The temperature is raised to 850℃ at a rate of 10℃ / min in a sealed resistance furnace and held for 30 min to completely melt the composite salt and form a composite molten salt system 3. The temperature is maintained at 850℃, and carbon dioxide gas with a purity ≥99.9% is continuously introduced into the molten salt at a rate of 120 mL / min. A DC power supply is connected, and the electrolysis voltage is set to 3.2V for 18 h. After electrolysis, turn off the power and the carbon dioxide cylinder, allow it to cool naturally to room temperature, and then remove the cathode product. Post-processing of the product is the same as in Example 1.

[0051] The product is pure-phase SiC nanowires with a diameter of 20-40 nm, a length of 8-15 μm, and a purity of 99.7%.

[0052] This invention, through multi-dimensional technological innovation, creatively utilizes a molten salt electrolysis cell as both a "CO2 trap" and a "nanomaterial synthesizer." Its novel principle provides a new approach for the high-value-added conversion of CO2 and the green preparation of nanomaterials, and has broad prospects for industrial application. Any modifications, equivalent substitutions, or improvements made based on the spirit and principles of this invention should be included within the scope of protection of this invention.

[0053] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application. The singular forms “a,” “the,” and “the” used in the embodiments and claims of this application are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that, unless otherwise stated, “a plurality” means two or more; the terms “first,” “second,” “third,” etc., are used only to distinguish and not to describe a particular order or sequence, nor should they be construed as indicating or implying relative importance. The term “and / or” as used herein refers to and includes any or all possible combinations of one or more associated listed items. When the above description relates to drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. In the description of this application, those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0054] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing silicon carbide nanowires, characterized in that, Includes the following steps: Step S1. Raw material pretreatment: Calcination of microsilica powder at 500-600℃ for 2-3 hours to obtain primary raw material; Step S2. Precursor preparation: Add a binder to the primary raw material, and then grind and mix for 12-24 hours to obtain precursor powder; Step S3. Cathode Unit Assembly: The precursor powder is pressed into precursor sheets under a pressure of 25~40MPa for 5~20min; each precursor sheet is wrapped with a nickel foam mesh to form a cathode element; and the cathode element is fixed with one end of a cathode wire to form a cathode unit; subsequently, the cathode element of the cathode unit is placed in the electrolytic cell, and the other end of the cathode wire is connected to a power source located outside the electrolytic cell; Step S4. Anode unit assembly: Place the anode in the electrolytic cell and connect one end of the anode wire to the anode to form an anode unit; The other end of the anode wire is led out from the electrolytic cell and connected to the power source; Step S5. Preparation of composite salt: First, remove moisture from CaCl2, Na2CO3 and Li2CO3 by drying. Then, mix CaCl2, Na2CO3 and Li2CO3 to obtain composite salt. The composite salt includes 60-70 parts of CaCl2, 20-30 parts of Na2CO3 and 5-15 parts of Li2CO3 by mass. Step S6. Electrolytic cell construction: Add the composite salt prepared in step S5 to the electrolytic cell, and place the electrolytic cell containing the composite salt in a protective atmosphere. Heat the cell to completely melt the composite salt to form a composite molten salt system as the electrolyte. Step S7. Electrolysis: Maintain the temperature to keep the composite molten salt in a molten state, continuously introduce carbon dioxide gas into the molten composite molten salt system, and simultaneously connect a DC power supply to control the electrolysis voltage at 2.5-3.2V and the electrolysis time at 10-20h; Step S8. Product processing: After electrolysis, turn off the power and stop the carbon dioxide gas supply. After the electrolytic cell cools naturally to room temperature, take out the cathode product. Soak the cathode product in dilute hydrochloric acid to remove residual metal impurities, then wash it with deionized water, and finally vacuum dry it to obtain silicon carbide nanowires.

2. The method according to claim 1, characterized in that, The cathode unit includes one or more cathode elements; when there are multiple cathode elements, the multiple cathode elements are fixed together using the cathode wire.

3. The method according to claim 1, characterized in that, The protective atmosphere comprises argon gas at a volume percentage of 99.999%.

4. The method according to claim 1, characterized in that, When carbon dioxide gas is introduced into the composite molten salt system, the purity of the introduced carbon dioxide gas is ≥99.9%, and the gas flow rate is 50-150 mL / min.

5. The method according to claim 1, characterized in that, In step S5, CaCl2, Na2CO3, and Li2CO3 are dried at 120-150℃ for 4-6 hours to remove moisture.

6. The method according to claim 5, characterized in that, In step S6, the electrolytic cell containing the composite salt is heated to 750-850°C and held at that temperature for more than 25 minutes to completely melt the composite salt.

7. The method according to claim 1, characterized in that, In step S2, the grinding and mixing method is ball milling, and the binder is polyvinyl butyral and / or liquid paraffin; the amount of binder added is 15-25% of the weight of the primary raw material.

8. The method according to claim 1, characterized in that, In step S8, the mass fraction of HCl in the dilute hydrochloric acid is 5%-10%; the cathode product is soaked in dilute hydrochloric acid for 2-4 hours, then washed with deionized water until the washing solution is neutral, and finally vacuum dried at 60-80℃ for 6-12 hours.

9. A system for preparing silicon carbide nanowires, characterized in that, The system includes an electrolytic cell device, an acid washing device, a water washing device, and a vacuum drying device arranged in sequence. The electrolytic cell device includes a power supply, an electrolytic cell, an electrolyte, a cathode unit, an anode unit, a protective atmosphere, and a gaseous carbon source; the electrolyte is placed in the electrolytic cell, and the electrolyte includes 60-70 parts CaCl2, 20-30 parts Na2CO3, and 5-15 parts Li2CO3 mixed and molten by mass, and the temperature is maintained at 750-800℃ during electrolysis; The cathode unit includes a cathode wire and a cathode element. One end of the cathode wire is connected to the cathode element, and the other end is connected to the power source. The cathode element is immersed in the electrolyte. The cathode element is prepared by: calcining microsilica powder to obtain initial raw materials, adding a binder at a mass percentage of 15%-25% of the initial raw materials to the initial raw materials, grinding and mixing to form precursor powder, and pressing the precursor powder into precursor sheets; wrapping each precursor sheet with a nickel foam mesh to form a cathode element. The anode unit includes an anode and an anode wire, one end of which is connected to the anode and the other end of which is connected to the power source; the anode is immersed in the electrolyte. The protective atmosphere includes argon; the electrolytic cell containing the electrolyte is situated within the protective atmosphere. The gaseous carbon source is carbon dioxide gas, which is continuously introduced into the electrolyte during electrolysis.

10. The system according to claim 9, characterized in that, The protective atmosphere comprises argon gas with a volume percentage of 99.999%; the gaseous carbon source is carbon dioxide gas with a purity of ≥99.9%.

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