Preparation method and equipment of nano silicon

Abstract

The invention relates to a preparation method and equipment of nano silicon. The preparation method comprises the following steps that a silicon source and a carbon source are provided, the silicon source contains silicon dioxide, the silicon dioxide and the carbon are mixed according to the preset molar ratio, raw material pretreatment is conducted, and a to-be-reacted raw material is obtained; providing an electric arc furnace with a built-in arc reaction cavity and a condensation nucleation cavity, introducing a high-voltage power supply into a first graphite electrode and a second graphite electrode in the arc reaction cavity to generate arc discharge, and respectively forming a first high-temperature area and a second high-temperature area; the inert gas feeds the raw materials to be reacted into the arc reaction cavity, reduction reaction is carried out in the first high-temperature area to generate silicon and carbon dioxide, the residual raw materials to be reacted in the first high-temperature area enter the second high-temperature area for further reaction, and the generated silicon is gasified in the first high-temperature area and the second high-temperature area to generate silicon steam; and the inert gas sends the silicon steam and the carbon dioxide gas to the condensation nucleation cavity for condensation treatment, so that the silicon steam is condensed to generate nanoscale silicon particles.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanometer silicon, and particularly relates to a preparation method and equipment of nanometer silicon. BACKGROUND

[0002] In recent years, with the rapid development of nanotechnology, nanometer silicon has shown revolutionary application potential in key technical fields such as energy, electronics and catalysis due to its unique physical and chemical properties, and has become a key research direction in the global new material field. However, the traditional nanometer silicon preparation method often has problems such as high energy consumption, low yield and uneven particle size distribution, which to some extent limits the wide application of nanometer silicon. Although nanometer silicon materials have significant performance advantages, their large-scale application is still limited by the high energy consumption, low yield and structure control problems of the preparation process. SUMMARY

[0003] To solve the technical problems of high energy consumption, low yield and uneven particle size distribution of the traditional nanometer silicon preparation method, the present application provides a preparation method and equipment of nanometer silicon.

[0004] The technical problem of the present application is solved by providing a preparation method of nanometer silicon, which is carried out in a vacuum sealed environment with inert gas being introduced. The preparation method comprises the following steps: providing solid silicon source and carbon source, the silicon source containing silicon dioxide, mixing the silicon dioxide and carbon according to a preset molar ratio to obtain initial raw materials, and pretreating the initial raw materials to obtain reaction-ready raw materials; providing an electric arc furnace with an internal arc reaction chamber and a condensation nucleation chamber, the arc reaction chamber being provided with a first graphite electrode and a second graphite electrode arranged in sequence, and a high-voltage power source being connected to the first graphite electrode and the second graphite electrode to generate electric arc discharge and form a first high-temperature region of 5000-10000 DEG C and a second high-temperature region of 10000-15000 DEG C; sending the reaction-ready raw materials into the arc reaction chamber through flowing inert gas, fully gasifying the reaction-ready raw materials in the first high-temperature region and simultaneously generating silicon vapor and carbon dioxide gas through reduction reaction, the chemical equation being SiO2+C→Si+CO2↑, and the residual reaction-ready raw materials in the first high-temperature region entering the second high-temperature region for further reaction; and sending the silicon vapor and the carbon dioxide gas to the condensation nucleation chamber through the inert gas for condensation treatment, so that the silicon vapor is condensed to form nanoscale silicon particles.

[0005] Preferably, the raw material pretreatment comprises the following steps: airflow mill treatment: crushing the initial raw materials to micron level, the particle size range being 1-10 microns; and mixing treatment: providing a three-dimensional mixing equipment, sending the initial raw materials after the airflow mill treatment into the three-dimensional mixing equipment for mixing for 2-4 hours until uniformity, to obtain the reaction-ready raw materials.

[0006] Preferably, the inert gas carries the silicon vapor and the carbon dioxide gas to the condensation nucleation chamber for condensation treatment, so that the silicon vapor is condensed to form nano-sized silicon particles with a size of 10-150 nm; after the silicon vapor is condensed to form nano-sized silicon particles, the following steps are further included: a cyclone separation device with a first separation chamber and a second separation chamber is provided, the condensation nucleation chamber, the first separation chamber and the second separation chamber are sequentially communicated, the inert gas carries the nano-sized silicon particles from the condensation nucleation chamber to the cyclone separation device, in the first separation chamber and the second separation chamber, one stores the nano-sized silicon particles with a particle size of 100 nm or more, and the other stores the nano-sized silicon particles with a particle size of 100 nm or less; a bag filter system with a first collection chamber and a second collection chamber is provided, the first collection chamber and the second collection chamber filter out nano silicon powder with different particle size ranges respectively, and collect the nano silicon powder.

[0007] Preferably, the silicon source includes one, two or more of silicon dioxide, micron-sized silicon ore and photovoltaic waste silicon; and the carbon source includes one, two or more of charcoal, petroleum coke and coal.

[0008] Preferably, the temperature of the first high-temperature region and the second high-temperature region is adjusted by the voltage and current of the high-voltage power supply; the voltage of the high-voltage power supply ranges from 10 kV to 50 kV, and the current ranges from 100 A to 1 kA.

[0009] Preferably, the preset molar ratio of the silicon dioxide to the carbon ranges from 1:1 to 1:1.5; when the preset molar ratio is 1:1.2, the temperature of the first high-temperature region and the second high-temperature region is set to 8000℃ and 12000℃ respectively; when the preset molar ratio is 1:1.5, the temperature of the first high-temperature region and the second high-temperature region is kept at 8000℃ and 12000℃ respectively, a third graphite electrode is arranged on the side of the second graphite electrode away from the first graphite electrode, and the third graphite electrode is connected to the high-voltage power supply to generate arc discharge and form a third high-temperature region with the same temperature as the second high-temperature region.

[0010] Preferably, the three-dimensional mixing device is one of a V-shaped mixer, a double-cone mixer, a drum-type mixer, a double-planetary mixer and a turbo mixer.

[0011] The application further provides a preparation device for nano silicon, which is used to realize the above preparation method. The preparation device includes a feeding device, an electric arc furnace with an electric arc reaction chamber and a condensation nucleation chamber, a cyclone separation device and an air extraction device. The feeding device, the electric arc reaction chamber, the condensation nucleation chamber, the cyclone separation device and the air extraction device are sequentially communicated to form a vacuum sealed environment. The feeding device is used to provide a silicon source and a carbon source. The silicon source contains silicon dioxide. The silicon dioxide and the carbon are mixed according to a preset molar ratio to obtain initial raw materials. The initial raw materials are pretreated to obtain raw materials for reaction. The air extraction device is used to separate the nano-sized silicon particles from the carbon dioxide gas.

[0012] Preferably, the vacuum degree in the vacuum sealed environment is 10 -3 Pa to 1 Pa, the inert gas introduced into the vacuum sealed environment is one of argon and helium; the air exhaust device is further used for controlling the gas flow rate in the vacuum sealed environment to be 10 m / s to 50 m / s, and the reaction time of the reaction raw material in the electric arc reaction cavity is 1 s to 4 s.

[0013] Preferably, the air exhaust device controls the gas flow rate in the condensation nucleation cavity to be 10 m / s to 30 m / s; when the inert gas sends the silicon vapor and the carbon dioxide gas to the condensation nucleation cavity for condensation treatment, a gradient cooling of 2000 ℃, 500 ℃ and 100 ℃ is realized to make the silicon vapor condense and nucleate.

[0014] Compared with the prior art, the preparation method and the device for nanometer silicon provided by the application have the following advantages: 1. The preparation method for nanometer silicon provided by the embodiment of the application is carried out in a vacuum sealed environment with inert gas introduced, so that the prepared nanometer silicon can be prevented from being oxidized, and the purity of the product can be improved; the graphite electrode is connected to a high-voltage power supply to generate electric arc discharge in the electric arc reaction cavity, so that a high-temperature environment is formed for the reduction reaction of silicon dioxide and carbon; compared with the preparation of nanometer silicon by using a traditional heating method, a large amount of energy consumption can be saved, and the preparation cost can be reduced; the first high-temperature region and the second high-temperature region with different temperature ranges are arranged in the electric arc reaction cavity, the reduction reaction of the reaction raw material is first carried out in the first high-temperature region to generate silicon and carbon dioxide, and the residual reaction raw material is further reacted in the second high-temperature region, so that the conversion rate of the reaction raw material can be improved, the residual raw material that has not reacted can be reduced, and the yield can be improved; at the same time, the generated silicon can be gasified to form silicon vapor at high temperature, which is convenient for subsequent condensation nucleation; the flowing inert gas can transport the reaction raw material, the silicon vapor and the carbon dioxide gas after the reduction reaction, the inert gas can be used as a protective gas in the condensation process, which is helpful to the uniform condensation of the silicon vapor in the condensation nucleation cavity, and the nanometer silicon particles with uniform particle size can be formed.

[0015] 2. In the preparation method provided by the embodiment of the application, the initial raw material is crushed to the micron level by the airflow mill, so that the specific surface area of the initial raw material can be increased, the subsequent reduction reaction can be more sufficient, and the utilization rate of the reaction raw material can be improved; the initial raw material is mixed more uniformly by using the three-dimensional mixing device, so that the molar ratio of silicon dioxide and carbon in the initial raw material can be accurate, the excess or deficiency of a certain raw material in a local area can be avoided, the chemical reaction can be more sufficient, the occurrence of side reactions can be reduced, and the purity and yield of the product can be improved.

[0016] 3. In the preparation method provided in the embodiment of the present invention, silicon vapor and carbon dioxide gas are sent to the condensation nucleation chamber for condensation treatment by flowing inert gas, so that the silicon vapor is condensed to generate nano-scale silicon particles with a size of 10nm to 150nm, which can achieve precise control of the particle size range of the nano-scale silicon particles and meet the requirements of specific applications for different particle size ranges; the first separation chamber and the second separation chamber are responsible for storing nano-scale silicon particles with a particle size of more than 100nm and less than 100nm, respectively, and the first collection chamber and the second collection chamber are responsible for filtering and collecting the nano-scale silicon particles stored in the first separation chamber and the second separation chamber, respectively.

[0017] It can be understood that the role of the cyclone separation device is to preliminarily separate the nano-scale silicon particles according to different particle size ranges. The bag filter system can filter the nano-scale silicon particles with larger particle sizes to obtain nano-silicon powder with uniform particle size. In the arc reaction chamber of the electric arc furnace, the high temperature formed by arc discharge can make the reaction of silicon dioxide and carbon more complete, and the nano-silicon powder finally obtained by the bag filter system has a higher purity.

[0018] 4. In the preparation methods provided in the embodiments of the present invention, low-cost, high-purity silicon and carbon sources are primarily selected to reduce raw material costs. Silicon sources can include silicon dioxide, micron-sized silicon ore, and photovoltaic waste silicon. Silicon dioxide, as a common silicon source, is widely available and low-cost. Micron-sized silicon ore is more reactive, improving raw material utilization. The use of photovoltaic waste silicon recycles industrial waste, reducing raw material costs and being more environmentally friendly. Carbon sources can include common carbon-containing materials such as charcoal, petroleum coke, and coal, which are abundant and low-cost.

[0019] 5. In the preparation method provided in the embodiment of the present invention, the temperature of the first high-temperature zone and the second high-temperature zone is adjusted by the voltage and current of the high-voltage power supply, so that the reaction temperature can be precisely controlled, with good flexibility and adaptability, ensuring that the reduction reaction and the reaction of the residual raw materials to be reacted are fully carried out, thereby improving the conversion rate and yield of the raw materials; the temperature of the first high-temperature zone and the second high-temperature zone can also be adjusted according to the preparation requirements of nano-silicon to ensure the stability and efficiency of the preparation of nano-silicon.

[0020] It should be noted that when the current and voltage of the high-voltage power supply are increased, the temperatures of the first high-temperature region and the second high-temperature region may continue to increase, thereby increasing the content of silicon vapor in the reaction product.

[0021] 6. In the preparation method provided by the embodiment of the present invention, when the molar ratio of carbon dioxide to carbon is in the range of 1:1 to 1:1.5, the reduction reaction can be fully carried out, thereby avoiding waste of raw materials or incomplete reaction due to excessive raw materials, and improving the utilization rate of raw materials and the purity of the product. It can be understood that when a third graphite electrode is added to form a third high-temperature region with the same temperature as the second high-temperature region, the temperatures of the first and second high-temperature regions are maintained unchanged. By adjusting the high-temperature reaction region by adding or removing graphite electrodes, the requirements of raw material ratios with different molar ratios can be met, thereby improving the flexibility and stability of the preparation of nano-silicon.

[0022] 7. In the preparation method provided by the embodiment of the present invention, the use of a three-dimensional mixing device can promote the sufficiency of the reaction and reduce the waste of raw materials. It can be understood that through the three-dimensional motion trajectory of the three-dimensional mixing device, the silicon source and carbon source in the initial raw materials are fully dispersed in three-dimensional space, avoiding local agglomeration or uneven mixing, thereby allowing the silicon source and carbon source to contact more fully during the reaction, reducing the problem of incomplete reaction caused by uneven mixing, and improving the conversion rate of the raw materials; uniform mixing can avoid the presence of residues to be reacted due to excess or insufficient amount of a certain raw material in a local area, reducing raw material waste, allowing more raw materials to participate in the reaction to generate the target product, and thus improving the yield.

[0023] 8. An embodiment of the present invention also provides a nano-silicon preparation device, wherein the feeding device, arc reaction chamber, condensation nucleation chamber, cyclone separation device and exhaust device of the preparation device are connected in sequence to form a vacuum sealed environment, forming a complete preparation process of "feeding, reaction, condensation, and separation", reducing the loss in the intermediate links, improving process continuity and production efficiency, and the sealing design can reduce energy consumption and the risks brought by environmental pollution.

[0024] It can be understood that the vacuum sealed environment can ensure that the reaction is carried out under oxygen-free conditions, avoid contact between the silicon source, carbon source and reaction products and oxygen in the air, and ensure the purity of the nano-silicon finally prepared and the safety of the reaction process; the partition design of the arc reaction chamber and the condensation nucleation chamber can make the high-temperature reaction process and the condensation nucleation process proceed in an orderly manner, improve the preparation efficiency of nano-silicon, and also improve the nucleation uniformity of nano-silicon particles; the cyclone separation device can separate carbon dioxide gas from nano-scale silicon particles, and store the nano-silicon particles in the cyclone separation device. The exhaust device can ensure the circulation of the airflow in the vacuum sealed environment and blow the carbon dioxide gas away from the cyclone separation device, ensuring the separation efficiency of the nano-silicon particles and ensuring the stability of the system pressure of the entire preparation equipment.

[0025] 9. In the preparation equipment provided in the embodiment of the present invention, the vacuum degree is controlled at 10 -3Pa to 1 Pa and inert gas can be excluded from the interference of air, forming an oxygen-free, stable inert environment, preventing the silicon source, carbon source and including nano-silicon, carbon dioxide in the reaction product is oxidized, to ensure the purity of the product and the safety of the reaction; vacuum sealed into the inert gas is one of argon and helium, to avoid chemical reactions in the vacuum sealed environment, to ensure that the purity of the final product is not disturbed by the reduction reaction.

[0026] It can be understood that the air extraction device can control the reaction time of the raw materials to be reacted in the electric arc reaction chamber by adjusting the gas flow rate in the vacuum sealed environment, ensuring the rapid reduction reaction of the silicon source and the carbon source under high temperature conditions, reducing energy consumption and also reducing the occurrence of side reactions, improving the preparation efficiency and the utilization rate of raw materials.

[0027] 10、The preparation equipment provided by the embodiment of the present application, the air extraction device controls the gas flow rate in the condensation nucleation chamber at 10 m / s to 30 m / s, which can make the silicon vapor have a suitable residence time in the condensation nucleation chamber, avoid incomplete condensation of the silicon vapor due to too fast flow rate, or particle agglomeration due to too slow flow rate, thereby ensuring the uniformity and dispersity of the nucleation of the nano-silicon particles; through the gradient cooling design of 2000℃→500℃→100℃, the silicon vapor can experience orderly cooling in different temperature zones during the condensation process, gradually form nano-level crystal nuclei and control the growth rate of the particles, avoid uneven particle size caused by sudden temperature drop, or excessive particle growth caused by slow cooling, thereby obtaining nano-silicon particles with uniform particle size and good dispersity, and ensuring the performance of the product. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0029] Figure 1 is a flowchart of steps S1 to S4 in a nano-silicon preparation method provided by the embodiment of the present application.

[0030] Figure 2 is a flowchart of steps S11 to S12 in a nano-silicon preparation method provided by the embodiment of the present application.

[0031] Figure 3 is a flowchart of steps S5 to S6 in a nano-silicon preparation method provided by the embodiment of the present application.

[0032] Figure 4It is a kind of whole frame schematic diagram of the preparation equipment of nano silicon provided by the embodiment of the application.

[0033] The drawing identification is explained as follows: 10, preparation equipment; 1, feeding device; 2, electric arc furnace; 21, electric arc reaction cavity; 211, first graphite electrode; 212, second graphite electrode; 213, first high-temperature area; 22, condensation nucleation cavity; 214, second high-temperature area; 3, cyclone separation device; 31, first separation cavity; 32, second separation cavity; 4, air draft device; 5, bag filter system; 51, first collection cavity; 52, second collection cavity. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the present application clearer and more comprehensible, the present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0035] In the embodiments provided in the present application, it should be understood that "B corresponding to A" means that B is associated with A, and B can be determined according to A. However, it should also be understood that the determination of B according to A does not mean that B is determined only according to A, but B can also be determined according to A and / or other information.

[0036] It should be understood that "one embodiment" or "an embodiment" mentioned throughout the specification means that the specific features, structures or characteristics related to the embodiment are included in at least one embodiment of the present application. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. In addition, these specific features, structures or characteristics can be combined in one or more embodiments in any suitable manner. Those skilled in the art should also know that the embodiments described in the specification are all optional embodiments, and the actions and modules involved are not necessarily required by the present application.

[0037] In various embodiments of the present application, it should be understood that the size of the serial number of the above-mentioned processes does not mean the inevitable sequence of execution, and the execution sequence of the processes should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0038] The flow diagrams and the block diagrams in the drawings of the present application illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products of various embodiments of the present application. In this regard, each block in the flow diagrams or block diagrams can represent a module, a segment, or a portion of code, which comprises one or more executable instructions for implementing the specified logical functions. It should also be noted that in some alternative implementations, the functions noted in the blocks can occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It is therefore imperative that the blocks be interpreted as merely representative of the functionality of the underlying system, method, or computer program product.

[0039] The existing nano-silicon preparation technology mainly includes chemical vapor deposition method and mechanical ball milling method. The chemical vapor deposition method is to obtain silicon atoms by thermal decomposition reaction, and make the silicon atoms adsorb, migrate and agglomerate on the substrate surface to form nano-silicon, and the chemical equation is SiH4→Si+2H2↑. The mechanical ball milling method is to add micron-sized silicon, solvent and dispersant into a sand mill, and perform sand milling at a certain speed, so as to reduce the size of particles through collision and extrusion of particles.

[0040] Specifically, the chemical vapor deposition method is a technology of depositing solid thin film on the substrate surface by high-temperature decomposition of gaseous precursor, and flammable, explosive or toxic gases such as silane (SiH4) and silicon tetrachloride (SiCl4) are often used, so that the operation risk is high and there is a safety hazard. The mechanical ball milling method is a method of crushing materials into nanoscale by mechanical force, which has the characteristics of simple operation and low cost, but has the limitations of low product purity and uneven particle distribution.

[0041] Therefore, the embodiment of the present application provides a method and equipment for preparing nano-silicon particles based on multi-stage arc reduction, and the technical solutions of the present application will be described below.

[0042] Please refer to Figure 1 The embodiment of the present application provides a preparation method of nano-silicon, which is carried out in a vacuum sealed environment with inert gas, and the preparation method comprises the following steps: S1: providing a solid silicon source and a carbon source, the silicon source containing silicon dioxide, mixing the silicon dioxide and the carbon according to a preset molar ratio to obtain initial raw materials, and performing raw material pretreatment on the initial raw materials to obtain reaction raw materials; S2: provide an arc furnace with a built-in arc reaction chamber and a condensation nucleation chamber, the arc reaction chamber is provided with a first graphite electrode and a second graphite electrode arranged in sequence, high-voltage power is supplied to the first graphite electrode and the second graphite electrode to generate arc discharge, and a first high-temperature region of 5000 DEG C to 10000 DEG C and a second high-temperature region of 10000 DEG C to 15000 DEG C are formed respectively; S3: the raw materials to be reacted are sent into the arc reaction chamber by flowing inert gas, the raw materials are fully gasified and reduced in the first high-temperature region to generate silicon vapor and carbon dioxide gas, and the chemical equation is: SiO2+C→Si+CO2↑, the residual raw materials to be reacted in the first high-temperature region enter the second high-temperature region for further reaction; S4: the inert gas carries the silicon vapor and the carbon dioxide gas to the condensation nucleation chamber for condensation treatment, so that the silicon vapor is condensed to generate nano-sized silicon particles.

[0043] In the nano-silicon preparation method provided by the embodiment of the application, the preparation is carried out in a vacuum sealed environment with inert gas, and the vacuum extraction before the start of the preparation method can avoid the oxidation of the finally prepared nano-silicon, which is beneficial to improve the purity of the product; the high-voltage power is supplied to the graphite electrodes in the arc reaction chamber to generate arc discharge and form a high-temperature environment for the gasification of silicon dioxide and carbon to form vapor and the reduction reaction, when the high-voltage power acts on the graphite electrodes, the inert gas between the two electrodes is ionized to form arc plasma, the energy conversion rate is high and there is almost no intermediate energy loss, while the traditional heating mode is realized by an electric resistance furnace or an induction furnace, which needs to indirectly heat the reactants through heat conduction, convection or radiation, and the energy needs to be transmitted through intermediate medium, which leads to a low energy conversion rate; compared with the preparation of nano-silicon by using the traditional heating mode, the present scheme saves a large amount of energy consumption and greatly reduces the preparation cost of nano-silicon.

[0044] Specifically, the silicon source refers to a substance capable of providing silicon elements, and the carbon source refers to a substance capable of providing carbon elements; the silicon source provided in step S1 contains silicon dioxide (SiO2), and the carbon source contains carbon (C); the present application can select silicon sources and carbon sources with low prices and high purity to reduce raw material costs; in some embodiments, the silicon source includes one, two or more of silicon dioxide, micron-sized silicon ore and photovoltaic waste silicon, and the carbon source includes one, two or more of charcoal, petroleum coke and coal. In the preparation method provided in the embodiments of the present application, silicon sources and carbon sources with low prices and high purity are mainly selected to reduce raw material costs. Specifically, the selection of the silicon source can include silicon dioxide, micron-sized silicon ore and photovoltaic waste silicon; silicon dioxide is a common silicon source, widely available and low in cost; micron-sized silicon ore is easier to react, which can improve the utilization rate of raw materials; the use of photovoltaic waste silicon is the recycling of industrial waste, which reduces the cost of raw materials and is more environmentally friendly. The selection of the carbon source can include common carbon-containing materials such as charcoal, petroleum coke and coal, which are abundant in source and low in cost.

[0045] The nano-silicon preparation method provided in the embodiments of the present application selects silicon sources and carbon sources with low prices and high purity to reduce raw material costs, and the continuous input of the silicon source and the carbon source can reduce the energy consumption of high-voltage arc discharge heating. It can be understood that the chemical substances participating in the reaction in the silicon source and the carbon source are silicon dioxide and carbon, respectively, so a single silicon source or a composite silicon source, a single carbon source or a composite carbon source can all undergo a reduction reaction under high-temperature conditions. Through this design, it is not necessary to specially purchase or collect a single specific silicon source or carbon source, which can improve the utilization rate of raw materials and further achieve cost reduction and efficiency improvement in the preparation of nano-silicon. Compared with the preparation of nano-silicon using silane gas, the present application uses silicon dioxide, micron-sized silicon ore and / or photovoltaic waste silicon, which has lower raw material costs when preparing the same output of nano-silicon material. Through the step of raw material pretreatment of the initial raw material, the subsequent reduction reaction of silicon dioxide and carbon at high temperature can be more complete, thereby improving the utilization rate of the raw materials to be reacted from the stage of raw material preparation.

[0046] Further, in step S2, the first graphite electrode and the second graphite electrode are arranged in the electric arc reaction chamber of the electric arc furnace, and the first high-temperature region and the second high-temperature region with different temperature ranges are formed by respectively inputting high-voltage power to the first graphite electrode and the second graphite electrode to generate electric arc discharge. Through this design, only the silicon source and the carbon source mixed according to the preset molar ratio of silicon dioxide and carbon need to be sent into the electric arc reaction chamber to generate silicon and carbon dioxide gas in a high-temperature environment.

[0047] In some embodiments, the silicon source and the carbon source are mixed and then fed into the electric arc reaction chamber, which can be achieved by a spiral gas flow feeding mode. The spiral can ensure that the to-be-reacted raw materials do not cluster, and the gas flow feeding forms a jet. In the embodiments of the present application, the to-be-reacted raw materials are fed into the electric arc reaction chamber at a jet speed of 30 m / s to 50 m / s. If the jet speed is too high, the reaction of the to-be-reacted raw materials in the electric arc reaction chamber may not be sufficient. If the jet speed is too low, it is difficult to accurately reach the high-temperature region between the two poles of the graphite electrode. In the embodiments of the present application, the distance between the jet position of the to-be-reacted raw materials and the first high-temperature region is 1 meter. It can be understood that this distance can be adjusted according to actual needs, that is, when the jet speed is high, the distance can be appropriately reduced, and when the jet speed is low, the distance can be appropriately increased.

[0048] It should be noted that solid silicon can be gasified at a temperature above 3000℃, while the temperature for preparing nano-silicon by using a traditional electric arc method can only reach 1000℃ to 3000℃. The traditional electric arc method can only be used for material smelting and cannot gasify silicon. By contrast, in order to quickly gasify silicon, the technical solution provided by the present application controls the reaction temperature to be above 5000℃, shortens the time for the reduction reaction of silicon dioxide and carbon, and thus improves the production capacity. In steps S2 and S3, the first high-temperature region of 5000℃ to 10000℃ and the second high-temperature region of 10000℃ to 15000℃ are arranged in the electric arc reaction chamber, which can ensure that the silicon dioxide and the carbon are preferentially fully gasified in the first high-temperature region. The gasification also causes the reduction reaction of the silicon dioxide gas and the carbon vapor to generate silicon vapor and carbon dioxide gas. The residual and fully gasified to-be-reacted raw materials are further fully reacted in the second high-temperature region. Since the reduction reaction of silicon dioxide and carbon at high temperature is relatively complete, the embodiments of the present application can use silicon sources and carbon sources that are low in price and high in purity. Through this design, the conversion rate of the to-be-reacted raw materials can be improved, the residual raw materials that have not yet reacted can be reduced, the raw material cost can be reduced, and the yield can be improved. At the same time, the generated silicon can be fully gasified at high temperature to ensure that silicon vapor can be formed, so as to be transported by an inert gas and subsequently condensed and nucleated.

[0049] In step S3, the reduction reaction of silicon dioxide and carbon at high temperature is used to generate silicon vapor and carbon dioxide gas by using an electric arc furnace, so as to facilitate the next process. The entire reaction process is carried out in a vacuum closed electric arc furnace. Through this design, harmful emissions can be effectively reduced, and the green production requirement can be met. The silicon source and the carbon source of the embodiments of the present application can be continuously input, and a high-temperature environment for the reduction reaction of silicon dioxide and carbon is formed in the electric arc reaction chamber by using a high-voltage electric arc discharge technology. After the reduction reaction of the previous batch of to-be-processed raw materials is completed, a new batch of to-be-processed raw materials can be continuously input into the electric arc reaction chamber for reaction, which saves at least 40% of energy consumption, reduces the preparation cost, and makes the reaction of silicon dioxide and carbon at high temperature more complete by using an electric arc furnace.

[0050] As an embodiment of the present application, the discharge end of the arc reaction chamber is directly connected to the feed end of the condensation nucleation chamber. Through this design, the inert gas flowing after the reduction reaction of the raw material in the arc reaction chamber is directly used to send the silicon vapor and carbon dioxide gas generated by the reaction to the condensation nucleation chamber for condensation treatment, so as to avoid the silicon vapor from being condensed into silicon particles before reaching the cooling area, thereby improving the yield of nanosilicon.

[0051] It can be understood that the flowing inert gas can not only ensure that the reduction reaction is in a vacuum sealed environment, but also can transport the raw material to be reacted and the silicon vapor and carbon dioxide gas after the reduction reaction. In step S4, the inert gas can be used as a protective gas during the condensation treatment, which helps the silicon vapor to uniformly condense in the condensation nucleation chamber and form nanoscale silicon particles with uniform particle size.

[0052] Before performing the preparation steps of the embodiment of the present application, inert gas is introduced into the arc furnace. The inert gas does not react with the silicon vapor and carbon dioxide gas, can exclude the interference of air, and thus forms an oxygen-free and stable inert environment, prevents the silicon source, carbon source and reaction products including nanosilicon and carbon dioxide from being oxidized, and ensures the purity of the product and the safety of the reaction. If the arc furnace contains an explosive gas such as hydrogen, it is not safe, and if it contains nitrogen, it will react with silicon and affect the purity. The inert gas is also used for the transportation of the silicon source, carbon source and reaction products in the vacuum sealed environment. The inert gas flowing in the vacuum sealed environment can send the raw material to be reacted into the arc reaction chamber, and can also send the silicon vapor and carbon dioxide gas to the condensation nucleation chamber for condensation treatment to generate nanoscale silicon particles. In particular, when the inert gas sends the silicon vapor and carbon dioxide gas to the condensation nucleation chamber for condensation treatment, it can also send the raw material to be reacted for the next reduction reaction into the arc reaction chamber, thereby shortening the idle time between high-temperature reaction and condensation treatment, and ensuring continuous production of up to 200 kg / h, thereby improving the efficiency of preparing nanosilicon.

[0053] Further, please refer to Figure 2 The raw material pretreatment includes the following steps: S11: airflow mill treatment: the initial raw material is pulverized to a micron level, and the particle size range is 1 μm to 10 μm; S12: mixing treatment: a three-dimensional mixing device is provided, and the initial raw material after the airflow mill treatment is sent into the three-dimensional mixing device for mixing for 2 h to 4 h until uniform, to obtain the raw material to be reacted.

[0054] In the preparation method provided by the embodiment of the application, the initial raw material is pulverized to micron level by airflow milling treatment, the particle size range is 1 μm to 10 μm, the specific surface area of the initial raw material can be increased, the diffusion distance between molecules can be shortened, the contact between the silicon source and the carbon source in the subsequent arc reaction can be more sufficient, the reduction reaction rate can be accelerated, the reaction can be more sufficient, and the utilization rate of the raw material to be reacted can be improved; wherein the unit of the specific surface area is m 2 / g, which refers to the total area possessed by unit mass of material, usually refers to the specific surface area of materials such as powder, fiber and particle, and is generally obtained by a BET specific surface area tester. The initial raw material is mixed more uniformly by using a three-dimensional mixing device, on the one hand, the raw material to be reacted can be fully dispersed in the three-dimensional space to provide the raw material to be reacted with uniform composition for the subsequent arc reaction, reduce the uneven particle size or side reaction caused by uneven mixing, for example, SiO2+C→SiO+CO↑, thereby ensuring the purity and nucleation uniformity of the nano-silicon particles, on the other hand, the molar ratio of silicon dioxide and carbon in the initial raw material can be ensured to be accurate, and local excess or deficiency of a raw material can be avoided, which can promote more sufficient chemical reaction and reduce the occurrence of side reactions, thereby further improving the purity and yield of the product.

[0055] Understandably, in step S11, the airflow milling treatment refers to accelerating the initial raw material to supersonic speed by using high-pressure airflow, so that the initial raw material can be broken in the pulverizing cavity by mutual collision or impact on the target plate, and the particle size is controlled by a classifier; the classifier is mainly used for separating and screening the pulverized material particles according to the particle size, and its core function is particle size control and circulating pulverization. By setting specific classification conditions such as centrifugal force, airflow speed and classification impeller speed, the broken initial raw material particles in the pulverizing cavity are separated into fine particles meeting the particle size requirement of 1 μm to 10 μm and coarse particles exceeding the particle size range, the coarse particles are returned to the pulverizing cavity of the airflow mill for further breaking, forming a closed loop of “pulverization, classification and re-pulverization”, so as to ensure that the particle size of the final raw material to be reacted meets the requirement, and provides the raw material to be reacted with uniform particle size for the subsequent arc reaction.

[0056] The airflow milling treatment can pulverize the initial raw material with larger particle size to smaller particle size, thereby increasing the surface area of the reactant. In chemical reaction, the reaction rate is faster when the contact area is larger, and the reaction between smaller particles means that the reaction is more sufficient, reducing the unreacted residual raw material, thereby improving the reaction rate and the utilization rate of the raw material to be reacted.

[0057] In step S12, the three-dimensional mixing device, also referred to as a multi-directional motion mixer, can uniformly mix powdery or granular materials with good fluidity; when the three-dimensional mixing device is in operation, the mixing barrel therein has multi-directional running actions, which can accelerate the flow and diffusion of various materials in the mixing process, and meanwhile, the segregation and accumulation of materials due to centrifugal force in traditional mixers are avoided, and the mixing effect is good. In the embodiment of the present application, the mixing time is set to 2h to 4h, which can ensure the uniformity of the raw materials to be reacted, and also will not waste energy and operation time excessively, thereby ensuring the balance of the mixing effect and the mixing efficiency.

[0058] In some embodiments, the three-dimensional mixing device is one of a V-shaped mixer, a double-cone mixer, a drum-type mixer, a double-planetary mixer, and a turbo-type mixer.

[0059] In the preparation method provided in the embodiment of the present application, the use of the three-dimensional mixing device can promote the completeness of the reaction and reduce the waste of raw materials. It can be understood that, through the three-dimensional motion trajectory of the three-dimensional mixing device, the silicon source and the carbon source in the initial raw materials are fully dispersed in the three-dimensional space, local agglomeration or uneven mixing is avoided, the contact between the silicon source and the carbon source in the reaction is more sufficient, the problem of incomplete reaction caused by uneven mixing is reduced, and the conversion rate of the raw materials is improved; uniform mixing can avoid the existence of residual materials to be reacted due to the excess or deficiency of a local raw material, reduce the waste of raw materials, make more raw materials participate in the reduction reaction to generate the target product, and thereby improve the yield.

[0060] Further, the inert gas sends the silicon vapor and the carbon dioxide gas to the condensation nucleation cavity for condensation treatment, so that the silicon vapor is condensed to generate nanoscale silicon particles with a particle size range of 10nm to 150nm; the particle size range of the nanoscale silicon particles can be accurately controlled, and the demand for different particle size ranges in specific applications can be met.

[0061] Please refer to Figure 3 After the silicon vapor is condensed to generate nanoscale silicon particles, the following steps are further included: S5: A cyclone separation device with a first separation cavity and a second separation cavity is provided, the condensation nucleation cavity, the first separation cavity, and the second separation cavity are sequentially communicated, the inert gas sends the nanoscale silicon particles from the condensation nucleation cavity into the cyclone separation device, in the first separation cavity and the second separation cavity, one stores nanoscale silicon particles with a particle size of 100nm or more, and the other stores nanoscale silicon particles with a particle size of 100nm or less; S6: A bag filter system with a first collection cavity and a second collection cavity is provided, the first collection cavity and the second collection cavity respectively filter out nanoscale silicon powder with different particle size ranges, and collect the nanoscale silicon powder.

[0062] It can be understood that the cyclone separation device is used to preliminarily separate the nano-sized silicon particles according to different particle size ranges, the bag filter system can filter the nano-sized silicon particles with larger particle sizes, and then the nano silicon powder with uniform particle sizes is obtained, and the nano silicon powder with high purity can be obtained in the process of filtering and collecting; in the electric arc reaction chamber of the electric arc furnace, the high temperature formed by the electric arc discharge can make the reduction reaction of silicon dioxide and carbon more complete, and further make the purity of the finally collected nano silicon powder higher.

[0063] It should be noted that the cyclone separation device is a device for separating gas and solid or liquid and solid, and its working principle is to make the solid particles or liquid drops with larger inertia centrifugal force separate from the outer wall surface by the rotational motion caused by the tangential introduction of gas flow. The cyclone separation device of the embodiment of the present application can separate the carbon dioxide gas and the nano-sized silicon particles, and the rotational motion of the nano-sized silicon particles is realized by setting the size of the internal gas flow of the cyclone separation device; wherein the cavity of the first separation cavity is larger than the cavity of the second separation cavity, when the nano-sized silicon particles enter the first separation cavity, the decrease of the gas flow force will cause the nano-sized silicon particles with a particle size range of more than 100 nm to fall in the first separation cavity due to gravity, and finally be filtered and collected by the first collection cavity; similarly, when the remaining nano-sized silicon particles enter the second separation cavity, the nano-sized silicon particles with a particle size range of less than 100 nm fall in the second separation cavity due to gravity, and finally are filtered and collected by the second collection cavity.

[0064] In step S5 of the embodiment of the present application, the first separation cavity and the second separation cavity of the cyclone separation device store the nano-sized silicon particles with a particle size of more than 100 nm and a particle size of less than 100 nm respectively; in step S6, the bag filter system is arranged at the bottom of the cyclone separation device, the first collection cavity is in communication with the first separation cavity, the second collection cavity is in communication with the second separation cavity, and the first collection cavity and the second collection cavity filter the nano-sized silicon particles stored in the first separation cavity and the second separation cavity respectively, and collect the nano silicon powder with uniform particle sizes.

[0065] In some embodiments, the temperature of the first high-temperature region and the second high-temperature region is adjusted by the voltage and current of the high-voltage power supply; the voltage range of the high-voltage power supply is 10kV to 50kV, and the current range is 100A to 1kA.

[0066] In the preparation method provided by the embodiment of the present application, the temperature of the first high-temperature region and the second high-temperature region can be adjusted by the voltage and current of the high-voltage power supply, so that the reaction temperature can be accurately controlled, and good flexibility and adaptability are achieved, so that the reduction reaction and the reaction of the residual raw materials to be reacted can be fully carried out, and the conversion rate and yield of the raw materials are improved; the temperature of the first high-temperature region and the second high-temperature region can also be adjusted according to the preparation requirements of the nanometer silicon, so that the stability and efficiency of the preparation of the nanometer silicon are ensured. The voltage and current of the high-voltage power supply can be adjusted in a relatively large range, and when the current and voltage of the high-voltage power supply are increased, the temperature of the first high-temperature region and the second high-temperature region can continue to be increased, so that the reduction reaction of the silicon dioxide and the carbon is more complete, and the content of the silicon vapor in the reaction product is increased.

[0067] In some embodiments, the preset molar ratio of the silicon dioxide and the carbon is in the range of 1:1 to 1:1.5; within this range, it can be ensured that the reduction reaction is fully carried out, the waste caused by excessive raw materials or incomplete reaction is avoided, the utilization rate of the raw materials is improved, and the product prepared finally has a purity of >99.5% and a particle size distribution of the silicon particles of 10 nm to 150 nm.

[0068] As an implementation, when the preset molar ratio is 1:1.2, the temperature of the first high-temperature region and the second high-temperature region is respectively set to 8000°C and 12000°C; under this condition, the reaction temperature and the raw material ratio are optimized to improve the reaction effect, and the reaction efficiency and product purity are ensured.

[0069] As another implementation, when the preset molar ratio is 1:1.5, the temperature of the first high-temperature region and the second high-temperature region is respectively maintained at 8000°C and 12000°C, a third graphite electrode is arranged on the side of the second graphite electrode away from the first graphite electrode, and the third graphite electrode is connected to the high-voltage power supply to generate arc discharge and form a third high-temperature region with the same temperature as the second high-temperature region.

[0070] It can be understood that whether the third graphite electrode is added depends on the reaction sufficiency of the first two stages of graphite electrodes, because the reaction speed of the first two stages is relatively fast, and if the reaction is not sufficient, the third graphite electrode needs to be added; when the third graphite electrode is added to form a third high-temperature region with the same temperature as the second high-temperature region, the temperature of the first high-temperature region and the second high-temperature region is maintained unchanged, so that the process control can be simplified, and the voltage and current do not need to be re-adjusted. By adjusting the high-temperature reaction region through the increase or decrease of the graphite electrode, the raw material ratio requirements of different molar ratios can be met, and the flexibility and stability of the preparation of the nanometer silicon are improved.

[0071] In the preparation method provided by the embodiment of the present invention, an exhaust device is further provided in a vacuum-sealed environment into which an inert gas is introduced, one end of the exhaust device being connected to the second separation chamber of the cyclone separation device, and the other end being connected to the feed end for providing the silicon source and the carbon source; the exhaust device can control the gas flow rate in the vacuum-sealed environment to be 10m / s to 50m / s, and the reaction time of the raw materials to be reacted in the arc reaction chamber to be 1s to 4s. It can be understood that the exhaust device can control the reaction time of the raw materials to be reacted in the first high-temperature region and the second high-temperature region by adjusting the gas flow rate in the vacuum-sealed environment to ensure that the reaction is fully carried out; ensure that the silicon source and the carbon source quickly complete the reduction reaction under high-temperature conditions, reduce energy consumption while also reducing the occurrence of side reactions, thereby improving preparation efficiency and raw material utilization.

[0072] Furthermore, the exhaust device can control the gas flow rate within the condensation nucleation chamber to be between 10 m / s and 30 m / s. By controlling the gas flow rate within the condensation nucleation chamber through the exhaust device, the silicon vapor can be kept in the condensation nucleation chamber for an appropriate residence time, thereby preventing insufficient condensation of the silicon vapor due to excessively fast flow rates, or particle agglomeration due to excessively slow flow rates, thereby affecting the nucleation uniformity and dispersion of the nano-silicon particles.

[0073] See also Figure 4 The embodiment of the present invention further provides a nano-silicon preparation device 10 for implementing the above-mentioned preparation method; the preparation device 10 includes a feeding device 1, an arc furnace 2 with a built-in arc reaction chamber 21 and a condensation nucleation chamber 22, a cyclone separation device 3 and an exhaust device 4, and the feeding device 1, the arc reaction chamber 21, the condensation nucleation chamber 22, the cyclone separation device 3 and the exhaust device 4 are sequentially connected to form a vacuum sealed environment.

[0074] In the preparation equipment 10 provided in an embodiment of the present invention, the feeding device 1, the arc reaction chamber 21, the condensation nucleation chamber 22, the cyclone separation device 3 and the exhaust device 4 are connected in sequence to form a vacuum sealed environment, forming a complete preparation process of "feeding, reaction, condensation, and separation", reducing the loss in the intermediate links, improving process continuity and production efficiency, and the sealing design can reduce energy consumption and the risks brought by environmental pollution.

[0075] It can be understood that the vacuum sealed environment can ensure that the reduction reaction is carried out under oxygen-free conditions, avoiding contact between the silicon source, carbon source and reaction products and oxygen in the air, ensuring the purity of the nano-silicon finally prepared and the safety of the reaction process; the arc reaction chamber 21 and the condensation nucleation chamber 22 are partitioned and designed to make the high-temperature reaction process and the condensation nucleation process proceed in an orderly manner, thereby improving the preparation efficiency of nano-silicon and also improving the nucleation uniformity of nano-silicon particles; the cyclone separation device 3 can separate and store carbon dioxide gas from nano-scale silicon particles.

[0076] Further, the feeding device 1 is used to provide a silicon source and a carbon source, the silicon source contains silicon dioxide, and the initial raw material is obtained by mixing the silicon dioxide and the carbon according to a preset molar ratio, and the initial raw material is pretreated to obtain the raw material to be reacted.

[0077] In some embodiments, the first graphite electrode 211 and the second graphite electrode 212 are arranged in the arc reaction cavity 21 in sequence, and after the high-voltage power supply is connected to the first graphite electrode 211 and the second graphite electrode 212 to generate arc discharge, a first high-temperature region 213 with a temperature of 5000-10000℃ and a second high-temperature region 214 with a temperature of 10000-15000℃ can be formed, respectively. The inert gas can send the raw material to be reacted in the feeding device 1 into the first high-temperature region 213 to generate silicon and carbon dioxide through reduction reaction, and the residual raw material to be reacted is further reacted in the second high-temperature region 214, and the generated silicon is vaporized in the first high-temperature region 213 and the second high-temperature region 214 to generate silicon vapor, so as to facilitate subsequent condensation and nucleation in the condensation and nucleation cavity 22.

[0078] In some embodiments, the cyclone separation device 3 is provided with a first separation cavity 31 and a second separation cavity 32, and the condensation and nucleation cavity 22, the first separation cavity 31 and the second separation cavity 32 are sequentially communicated, the inert gas sends the nanoscale silicon particles into the cyclone separation device 3, and the first separation cavity 31 and the second separation cavity 32 store nanoscale silicon particles with different particle size ranges, respectively.

[0079] In some embodiments, the preparation device 10 further comprises a cloth bag filtering system 5, which is arranged at the bottom of the cyclone separation device 3 and communicates with the cyclone separation device 3; the cloth bag filtering system 5 is provided with a first collection cavity 51 and a second collection cavity 52, the first collection cavity 51 communicates with the first separation cavity 31, can filter the nanoscale silicon particles stored in the first separation cavity 31, and collect nanosilicon powder with uniform particle size, and the second collection cavity 52 communicates with the second separation cavity 32, can filter the nanoscale silicon particles stored in the second separation cavity 32, and collect nanosilicon powder with uniform particle size.

[0080] In some embodiments, the silicon source includes one, two or more of silicon dioxide, micron-sized silicon ore and photovoltaic waste silicon, and the carbon source includes one, two or more of charcoal, petroleum coke and coal. It can be understood that the silicon source contains silicon dioxide (SiO2) and the carbon source contains carbon (C), the silicon source and the carbon source with low price and high purity are selected to reduce the cost of raw materials; the silicon dioxide is a common silicon source, which is widely available and has low cost; the micron-sized silicon ore is easier to react, which can improve the utilization rate of raw materials; the use of photovoltaic waste silicon is the recycling of industrial waste, which reduces the cost of raw materials and is more environmentally friendly. The selection of the carbon source can include common carbon-containing materials such as charcoal, petroleum coke and coal, which are abundant in source and low in cost.

[0081] In some embodiments, the preset molar ratio of silicon dioxide to carbon ranges from 1:1 to 1:1.5; within this range, it can be ensured that the reduction reaction is fully carried out, the excessive raw materials are avoided to cause waste or incomplete reaction, the utilization rate of raw materials is improved, the purity of the product prepared finally is > 99.5%, and the particle size distribution of silicon particles is 10 nm to 150 nm.

[0082] In some embodiments, the raw material pretreatment includes airflow mill treatment and mixing treatment; the airflow mill treatment is to crush the initial raw material to micron level, and the particle size range is 1 μm to 10 μm; the mixing treatment is to send the initial raw material after the airflow mill treatment into a three-dimensional mixing device to mix to be uniform, to obtain the raw material to be reacted. Specifically, the specific surface area of the initial raw material can be increased by the airflow mill treatment, the diffusion distance between molecules is shortened, the contact between the silicon source and the carbon source in the subsequent arc reaction is more sufficient, the reduction reaction rate is accelerated, the reaction is more sufficient, and the utilization rate of the raw material to be reacted is improved; the three-dimensional mixing device is used to mix the initial raw material uniformly, the purity and nucleation uniformity of the nanosilicon particles are better guaranteed, the chemical reaction is more fully promoted, and the occurrence of side reactions is reduced.

[0083] It should be noted that the air extraction device 4 is at least used to separate the nanoscale silicon particles from the carbon dioxide gas; the air extraction device 4 can ensure the circulation of airflow in the vacuum sealed environment, and blow the carbon dioxide gas away from the cyclone separation device 3, to ensure the separation efficiency of the nanosilicon particles, and to guarantee the stability of the system pressure of the entire preparation device 10.

[0084] In some embodiments, the vacuum degree in the vacuum sealed environment is 10 -3 Pa to 1 Pa, and the inert gas introduced in the vacuum sealing is one of argon and helium.

[0085] In the preparation device 10 provided in the embodiments of the present application, the vacuum degree is controlled to be 10 -3 Pa to 1 Pa and the inert gas is introduced, the interference of air can be excluded, an oxygen-free and stable inert environment is formed, the silicon source, the carbon source and the reaction products including nanosilicon and carbon dioxide are prevented from being oxidized, the purity of the product and the reaction safety are ensured; the inert gas introduced in the vacuum sealing is one of argon and helium, to avoid the occurrence of chemical reaction in the vacuum sealed environment, to ensure that the reduction reaction and the purity of the final product are not disturbed, and the preferred inert gas in the embodiments of the present application is argon, which has relatively lower cost and is relatively less difficult to obtain in industrial application.

[0086] Further, the air extraction device 4 is also used to control the gas flow rate in the vacuum sealed environment to be 10-50 m / s, and the reaction time of the raw materials to be reacted in the electric arc reaction chamber 21 to be 1-4 s. Understandably, the air extraction device 4 can control the reaction time of the raw materials to be reacted in the electric arc reaction chamber 21 by adjusting the gas flow rate in the vacuum sealed environment, so as to ensure the rapid reduction reaction of the silicon source and the carbon source under high temperature conditions, reduce the energy consumption, and also reduce the occurrence of side reactions, and improve the preparation efficiency and the utilization rate of raw materials.

[0087] In some embodiments, the air extraction device 4 controls the gas flow rate in the condensation nucleation chamber 22 to be 10-30 m / s. In the preparation device 10 provided by the embodiments of the present application, the air extraction device 4 controls the gas flow rate in the condensation nucleation chamber 22, so that the silicon vapor has a suitable residence time in the condensation nucleation chamber 22, avoids the silicon vapor from not being fully condensed due to too fast flow rate, or causes particle agglomeration due to too slow flow rate, and thus guarantees the nucleation uniformity and dispersity of the nanosilicon particles.

[0088] In some embodiments, when the inert gas sends the silicon vapor and the carbon dioxide gas to the condensation nucleation chamber 22 for condensation treatment, a gradient cooling of 2000℃, 500℃ and 100℃ is realized to make the silicon vapor condense and nucleate. Through the gradient cooling of 2000℃→500℃→100℃, the silicon vapor can experience orderly cooling in different temperature zones in the condensation process, gradually form nanoscale crystal nuclei and control the growth rate of particles, avoid the phenomenon of uneven particle size caused by sudden temperature drop, or the phenomenon of excessive particle growth caused by slow cooling, so that the nanosilicon particles with uniform particle size and good dispersity can be obtained, and the performance of the product is guaranteed.

[0089] Understandably, by setting the size and height of the condensation nucleation chamber 22, the vacuum sealed environment into which the inert gas is introduced, and the gas flow rate in the vacuum sealed environment controlled by the air extraction device 4, the cooling speed of the silicon vapor and the carbon dioxide gas in the condensation nucleation chamber 22 can be controlled, and the gradient cooling is realized. The condensation and nucleation of the silicon vapor depend on the supercooling degree ΔT, and ΔT=theoretical condensation temperature-actual temperature. The supercooling degree refers to the degree that the actual temperature of the silicon vapor is lower than the theoretical condensation temperature. The higher the supercooling degree is, the smaller the critical nucleus radius required for forming stable crystal nuclei is, and the easier the condensation and nucleation are. In the embodiments of the present application, the silicon forms silicon vapor at high temperature, and has a large enough supercooling degree when entering the condensation nucleation chamber 22. The small critical nucleus radius makes the silicon vapor quickly nucleate, and the nucleation time is short, so that the nanosilicon particles with small particle size are finally formed.

[0090] The above has carried out the detailed introduction to the preparation method and equipment of the nano silicon disclosed in the embodiment of the application, the principle and implementation mode of the application are described by applying specific examples in this paper, the above embodiment is only used for helping understanding the method and core idea of the application. Meanwhile, for the general skilled person in the art, according to the idea of the application, the specific implementation mode and application range will be changed, and the above description should not be understood as the limitation of the application, any modification, equivalent replacement and improvement within the principle of the application should be included in the protection scope of the application.

Claims

1. A method for preparing nano-silicon, carried out in a vacuum sealed environment with an inert gas, characterized in that: The preparation method comprises the following steps: Providing a solid silicon source and a carbon source, wherein the silicon source contains silicon dioxide, mixing the silicon dioxide and carbon according to a preset molar ratio to obtain an initial raw material, and pre-treating the initial raw material to obtain a raw material to be reacted; An arc furnace is provided with a built-in arc reaction chamber and a condensation nucleation chamber. A first graphite electrode and a second graphite electrode are arranged in sequence in the arc reaction chamber. A high-voltage power supply is applied to the first graphite electrode and the second graphite electrode to generate arc discharge, thereby forming a first high-temperature region of 5000°C to 10000°C and a second high-temperature region of 10000°C to 15000°C, respectively. The raw materials to be reacted are fed into the arc reaction chamber by flowing inert gas, where they are fully vaporized in the first high-temperature zone and undergo a reduction reaction to generate silicon vapor and carbon dioxide gas. The chemical equation is: SiO2+C→Si+CO2↑. The remaining raw materials to be reacted in the first high-temperature zone enter the second high-temperature zone for further reaction. The inert gas transports the silicon vapor and carbon dioxide gas to the condensation nucleation chamber for condensation treatment, so that the silicon vapor is condensed to form nano-scale silicon particles.

2. The preparation method according to claim 1, wherein Raw material pretreatment includes the following steps: Jet milling: crush the initial raw materials to micron level, with particle size ranging from 1μm to 10μm; Mixing treatment: Provide a three-dimensional mixing device, send the initial raw materials after the airflow milling treatment into the three-dimensional mixing device and mix them for 2 to 4 hours until they are uniform, to obtain the raw materials to be reacted.

3. The preparation method according to claim 2, wherein The inert gas transports silicon vapor and carbon dioxide gas to the condensation nucleation chamber for condensation, causing the silicon vapor to condense into nano-scale silicon particles ranging from 10nm to 150nm; After the silicon vapor is condensed to form nano-sized silicon particles, the following steps are also included: A cyclone separation device is provided, which has a first separation chamber and a second separation chamber. The condensation nucleation chamber, the first separation chamber, and the second separation chamber are sequentially connected. An inert gas transports nano-sized silicon particles from the condensation nucleation chamber into the cyclone separation device. The first separation chamber stores nano-sized silicon particles with a particle size of 100 nm or more, while the second separation chamber stores nano-sized silicon particles with a particle size of 100 nm or less. A bag filter system is provided, which is provided with a first collecting chamber and a second collecting chamber. The first collecting chamber and the second collecting chamber respectively filter out nano silicon powders in different particle size ranges and collect the nano silicon powders.

4. The preparation method according to claim 3, wherein: The silicon source includes one, two or more of silicon dioxide, micron-sized silicon ore and photovoltaic waste silicon; The carbon source includes one, two or more of charcoal, petroleum coke and coal.

5. The preparation method according to claim 1, wherein: The temperatures of the first high temperature region and the second high temperature region are adjusted by the voltage and current of the high voltage power supply; The high voltage power supply has a voltage range of 10kV to 50kV and a current range of 100A to 1kA.

6. The preparation method according to claim 5, wherein: The preset molar ratio of silica to carbon ranges from 1:1 to 1:1.5; When the preset molar ratio is 1:1.2, the temperatures of the first high temperature zone and the second high temperature zone are set to 8000°C and 12000°C, respectively; When the preset molar ratio is 1:1.5, the temperatures of the first high-temperature zone and the second high-temperature zone are maintained at 8000°C and 12000°C respectively. A third graphite electrode is arranged on the side of the second graphite electrode away from the first graphite electrode. A high-voltage power supply is passed through the third graphite electrode to generate arc discharge, thereby forming a third high-temperature zone with the same temperature as the second high-temperature zone.

7. The preparation method according to claim 2, wherein: The three-dimensional mixing equipment is one of a V-type mixer, a double-cone mixer, a drum mixer, a double planetary mixer and a turbine mixer.

8. A nano-silicon preparation device for implementing the preparation method according to any one of claims 1 to 7, characterized in that: The preparation equipment includes a feeding device, an arc furnace with a built-in arc reaction chamber and a condensation nucleation chamber, a cyclone separation device, and an exhaust device. The feeding device, the arc reaction chamber, the condensation nucleation chamber, the cyclone separation device, and the exhaust device are sequentially connected to form a vacuum sealed environment. The feeding device is used to provide a silicon source and a carbon source. The silicon source contains silicon dioxide, which is mixed according to a preset molar ratio of silicon dioxide and carbon to obtain an initial raw material. The initial raw material is pretreated to obtain a raw material to be reacted; the exhaust device is at least used to separate nano-sized silicon particles from carbon dioxide gas.

9. The preparation device according to claim 8, characterized in that: The vacuum degree in the vacuum sealing environment is 10 -3 Pa to 1Pa, the inert gas introduced into the vacuum seal is one of argon and helium; The exhaust device is also used to control the gas flow rate in the vacuum sealed environment to be 10m / s to 50m / s, and the reaction time of the raw materials to be reacted in the arc reaction chamber to be 1s to 4s.

10. The preparation device according to claim 9, characterized in that: The exhaust device controls the gas flow rate in the condensation core cavity to be 10m / s to 30m / s; When the inert gas delivers silicon vapor and carbon dioxide gas to the condensation nucleation chamber for condensation treatment, a gradient temperature drop of 2000°C, 500°C, and 100°C is achieved to condense the silicon vapor into nuclei.

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