Method for producing nanosilicon powder from induction plasma pyrolysis silane

Abstract

The present invention discloses a method for producing nanosilicon powder from induced plasma pyrolysis silane, which includes the steps of: exciting the working gas in an induced plasma reactor to form a stable high-temperature plasma; mixing silane gas with dilution gas and injecting it into a high-temperature plasma thermal field; decomposing the silane gas under the combined action of the hot air flow in the high-temperature plasma thermal field and the high-temperature circulating cooling air flow; and condensing the silicon atoms produced by pyrolysis into nano-scale spherical silicon powder after cooling; filtering the air flow containing the silicon powder through a filter, depositing the nanosilicon powder on the surface of the filter, and blowing it down with a periodic backflow to collect the nanosilicon powder. The present invention uses silane gas as raw material, adopts induced plasma as the main heat source, and adopts a general heating tube as the auxiliary heat source, and has the advantages of high pyrolysis rate, no electrode pollution, and long-term continuous production. The produced nanosilicon powder has high purity, high sphericity, narrow particle size distribution, excellent flowability, and extremely high quality.

Description

[Technical Field]

[0001] The present invention relates to the field of materials chemistry, and more particularly to a method for producing nanosilicon powder from induction plasma pyrolysis silane. [Background technology]

[0002] With the development of new energy-related industries and the widespread use of 3C electronic products, people are placing higher demands on lithium-ion batteries, including higher volumetric / mass energy density, faster charge / discharge rates, and improved safety. Silicon has an energy density approximately ten times higher than that of graphite, making it a strong contender for lithium-ion battery anode materials. However, silicon suffers from a serious drawback: after lithium absorption, it expands to approximately three times its original volume, limiting its application in this field. Nanosilicon powder, with its nano effect, can effectively mitigate this negative effect. The use of carbon-coated nanosilicon powder mixed with graphite effectively improves the capacity and service life of lithium-ion batteries and controls the expansion rate of the anode material within an acceptable range. Nanosilicon powder also has broad application prospects in other fields. For example, nanosilicon powder is mixed with diamond under high pressure to form silicon carbide, which is widely used in abrasives, grinding wheels, and cutting tools. Nanosilicon powder can react with organic materials to serve as a raw material for organosilicone polymer materials.

[0003] Currently, methods for producing nanosilicon powder include mechanical ball milling, chemical vapor deposition, molten salt electrolysis, and plasma evaporation and condensation. Mechanical ball milling typically uses zirconia as a milling medium to grind large silicon particles into small silicon powder. Its advantages include simple steps and low production costs. However, the resulting silicon powder has a high impurity content, making it difficult to control the particle shape and particle size range, and making it very difficult to obtain nanoscale products. Chemical vapor deposition involves heating silane in a diluted high-purity hydrogen atmosphere until it decomposes and then cooling to obtain nanosilicon powder. However, the production process involves high-pressure, high-concentration hydrogen gas and silane, posing significant safety risks. Molten salt electrolysis, which uses anhydrous CaCl2 as an electrolyte to electrolyze SiO2, produces silicon particles with nonuniform particle size, making it difficult to control the growth of silicon particles. The plasma evaporation and condensation method generally uses micron-scale silicon powder as the raw material, direct current arc plasma as the heat source to instantly vaporize the silicon raw material, and then cools the silicon vapor to produce nano-silicon powder. During the production process, contamination due to vaporization of the electrode material is likely to occur, and the thermal coupling efficiency between the micron-scale raw material powder and the plasma is low, making it difficult to ensure the purity and yield of the product.

[0004] Therefore, it is a technical problem that those skilled in the art must urgently solve to provide a method for producing nanosilicon powder from induced plasma pyrolysis silane, which has a high silane decomposition rate, is highly safe, and allows for continuous production. Summary of the Invention [Problem to be solved by the invention]

[0005] In view of this, the present invention provides a method for producing nanosilicon powder from induction plasma pyrolysis silane. [Means for solving the problem]

[0006] To achieve the above object, the present invention adopts the following technical solutions.

[0007] A method for producing nanosilicon powder from induction plasma pyrolysis silane includes the steps of exciting a working gas in an induction plasma reactor to form a stable high-temperature plasma, mixing silane gas with a dilution gas and injecting the mixture into a high-temperature plasma thermal field, decomposing the silane gas under the cooperative action of the hot air flow in the high-temperature plasma thermal field and the high-temperature circulating cooling air flow, and allowing the silicon atoms or silicon ions produced by the pyrolysis to condense into nanoscale spherical silicon powder after cooling; and directing the air flow containing the silicon powder into a collection chamber including a filter, depositing the nanosilicon powder on the surface of the filter after passing through the filter, and collecting the nanosilicon powder by blowing it down with a periodic backflow of air.

[0008] Furthermore, the above method specifically includes: (1) flushing the entire pyrolysis system using argon or nitrogen gas and conducting a leak test; (2) flowing a working gas into a plasma reactor, and exciting the working gas to form a stable high-temperature plasma with a predetermined power; and using a compressor to flow a high-temperature circulating cooling air flow into the first high-temperature cooling zone, and a low-temperature circulating cooling air flow and a nitrogen gas cooling air flow into the second low-temperature cooling zone; (3) using a feeding probe to inject silane gas wrapped in a dilution gas flow into a high-temperature plasma thermal field, decomposing the silane in the high-temperature plasma thermal field, and then cooling the silicon atoms or silicon ions generated by the pyrolysis in the first high-temperature cooling zone to form fine silicon powder; and further pyrolyzing the undecomposed silane gas to generate silicon powder and hydrogen gas, which are then transported by the mixed gas flow to a second low-temperature cooling zone for further cooling; The silicon powder cooled in the secondary low-temperature cooling region is transported to a collection chamber by the mixed gas flow, and after the gas passes through a filter in the collection chamber, a portion of the gas is treated and then discharged, while the remaining gas is repeatedly used as a circulating cooling gas. The nanosilicon powder is trapped by the filter and deposited on the surface of the filter, and then blown down by a periodic backflow of air, and the nanosilicon powder is collected. (4)

[0009] Furthermore, the working gas includes a center gas and a sheath gas.

[0010] Furthermore, the center gas is argon gas with a flow rate of 5 to 100 slpm, and the sheath gas is a mixed gas of argon gas and hydrogen gas, with the flow rate of the argon gas in the sheath gas being 20 to 250 slpm and the flow rate of the hydrogen gas in the sheath gas being 0 to 30 slpm.

[0011] The beneficial effects of adopting the above additional solution are as follows: By introducing an appropriate amount of hydrogen gas into the sheath gas, the thermal conductivity of the plasma thermal flow can be effectively improved, and the heating efficiency of the plasma thermal field can be further improved.

[0012] Furthermore, in step (2), the power of the plasma reactor is 15 to 80 kW, and the operating pressure of the system is 14 to 17 Psig.

[0013] The beneficial effects of adopting the above additional solution are as follows: By setting the working pressure of the system to about 1 atmosphere, the airtightness requirements of the system can be reduced, and the possibility of fire or explosion hazards caused by a relatively large leak in the system can be reduced.

[0014] Furthermore, the high-temperature circulating cooling airflow is a mixed gas of nitrogen gas, argon gas, and hydrogen gas, and the temperature of the high-temperature circulating cooling airflow is 420 to 650°C, and the flow rate is 1000 to 3000 slpm.

[0015] Furthermore, the volume ratio of nitrogen gas, argon gas, and hydrogen gas in the mixed gas of the high-temperature circulating cooling airflow is 50% nitrogen gas, 40% argon gas, and 10% nitrogen gas.

[0016] Furthermore, the low-temperature circulating cooling airflow is a mixed gas of nitrogen gas, argon gas, and hydrogen gas, the temperature of the low-temperature circulating cooling airflow is 18 to 35°C, the flow rate is 5000 to 15000 slpm, and the flow rate of the nitrogen gas cooling airflow is 150 to 450 slpm.

[0017] Furthermore, in the mixed gas of the low-temperature circulating cooling airflow, the volume ratio of nitrogen gas, argon gas, and hydrogen gas is 50% nitrogen gas, 40% argon gas, and 10% nitrogen gas.

[0018] The beneficial effects of adopting the above additional solution are as follows: Using relatively inexpensive nitrogen gas as the main cooling gas effectively reduces production costs, while nitrogen gas has a relatively high specific heat capacity, effectively improving cooling efficiency. Using a relatively high-temperature circulating cooling airflow (higher than the thermal decomposition temperature of silane gas) as the primary cooling gas not only cools silicon atoms or ions to generate silicon particles, but also acts as a supplementary heat source to provide energy and reaction atmosphere for the small amount of unreacted silane gas, significantly improving the thermal decomposition rate of silane gas (greater than 99%). Using an ultra-high-flow low-temperature circulating gas as the secondary cooling gas effectively prevents the silicon particles generated by the reaction from becoming larger. The gas temperature in the system can be controlled within a relatively low range as the main cooling means, effectively preventing powder from interfering with the cooling process and achieving the goal of long-term stable operation.

[0019] Furthermore, the flow rate of the silane gas flow is 15 to 120 slpm, and the dilution gas flow is argon gas with a flow rate of 50 to 200 slpm.

[0020] The beneficial effects of adopting the above additional solution are as follows: Using silane as the raw material gas allows molecular-level contact between the raw material and the plasma thermal field, improving thermal coupling efficiency; and at the same time, preventing the formation of large micron-scale particles caused by incomplete vaporization of crude silicon powder when crude silicon powder is used as the raw material. Introducing a dilution gas stream restricts the flow direction of the silane gas, preventing it from escaping before being injected into the high-temperature thermal field; and at the same time, the dilution gas stream can initially dilute the silane gas before injection, contributing to the production of nano-silicon powder products with smaller particle sizes.

[0021] Furthermore, the blowback gas is argon gas or nitrogen gas.

[0022] The beneficial effects of adopting the above additional solution are as follows: By using argon gas or nitrogen gas as the blowing gas, the blowing step can be completed without introducing more types of gas, and the complexity of the process conditions can be reduced. [Effects of the Invention]

[0023] The beneficial effects of the present invention are as follows: The present invention uses silane gas as a raw material, induction plasma as the main heat source, and a general electric heating tube as the auxiliary heat source, and produces nanosilicon powder through a multi-stage reaction and multi-stage cooling method. This method has the advantages of a high silane decomposition rate, strong safety, and continuous production.

[0024] By using induction plasma as the main heat source, the present invention can perform concentrated heating of the raw material gas under the condition that the raw material and the equipment do not come into contact with each other at all, which does not lead to electrode contamination and contributes to improving the purity of the product. It also prevents the powder generated by the reaction during the heating process from adhering to the surface of the heating device, improves heating efficiency, and reduces equipment maintenance costs, which is advantageous for industrial continuous production.

[0025] The present invention uses silane gas as a raw material, which allows the raw material to come into molecular-level contact with the plasma hot airflow, greatly improving the thermal coupling efficiency and energy utilization rate. At the same time, the use of silane gas as a raw material can avoid the generation of large micron-scale particles that are formed when crude silicon powder is used as a raw material and is not completely vaporized, which is beneficial to improving the quality of nano-silicon powder products in terms of particle size.

[0026] In this invention, a conventional electric heating tube is used as an auxiliary heat source, combined with an induction plasma heat source, and a multi-stage reaction and multi-stage cooling mode is newly introduced, fully utilizing the advantages of the two heating modes, greatly improving the thermal decomposition rate of silane gas. By adopting the method described in this invention, the thermal decomposition rate of silane can reach 99% or more, effectively improving the utilization rate of silane gas, reducing the environmental protection costs for treating exhaust gases, and further achieving the goal of reducing production costs.

[0027] In the manufacturing process of the present invention, approximately 90% of the working gas is reused and used as an ultra-high flow cooling gas, which not only effectively controls the particle size of the nanoparticles but also reduces the amount of working gas used and saves costs. At the same time, the relatively high flow rate of the working gas can dilute the total concentration of hydrogen gas and silane in the system to less than 10%, greatly reducing the possibility of system leaks and hazards in extreme cases.

[0028] The present invention uses a feed probe with a double-layer coaxial tube structure to feed the raw material, and the silane gas is surrounded by an argon gas curtain and injected directly into the high-temperature plasma thermal field. This not only prevents the silane gas from escaping before entering the plasma thermal field, but also allows the argon gas to be used to initially dilute the silane gas, which contributes to improving heating efficiency and reducing the particle size of the nanosilicon powder.

[0029] The present invention performs gas-solid separation using a long, cylindrical filter bank made of porous cermet material, and by blowing back the filters one by one with a periodic backflow of air, it achieves higher filtration efficiency and a longer usage cycle than conventional bug catchers, enabling long-term continuous production.

[0030] The nanosilicon powder produced by the present invention has an average particle size of 30-120 nm, which is adjustable, and is characterized by high purity, narrow distribution, spherical shape, easy dispersion, excellent fluidity, large specific surface area, and high surface activity.

[0031] The present invention further provides an apparatus for producing nanosilicon powder from the above-mentioned induction plasma pyrolysis silane, the apparatus including a plasma generator, a feed probe, a primary high-temperature cooling zone, a secondary low-temperature cooling zone, a collection chamber, a filter, a compressor, an electric heating tube, a water-cooled heat exchanger, and an exhaust gas treatment device.

[0032] wherein the plasma generator and the feed probe are both fixed to the primary high-temperature cooling area, the secondary low-temperature cooling area is fixed to a bottom end of the primary high-temperature cooling area, the bottom end of the secondary low-temperature cooling area is connected to one side of a collection chamber, the other side of the collection chamber is connected to a water-cooled heat exchanger, a compressor is installed between the collection chamber and the water-cooled heat exchanger, an electric heating pipe is installed between the compressor and the water-cooled heat exchanger, and an exhaust gas treatment device is installed between the compressor and the collection chamber, a high-temperature circulating cooling air inlet is provided on the surface of the first high-temperature cooling area; a low-temperature circulating cooling air inlet is provided in the second low-temperature cooling area; and a nitrogen gas cooling air inlet is further provided in the low-temperature circulating cooling air inlet; A powder collection tank is provided at the bottom end of the collection chamber, and a filter is provided inside the collection chamber.

[0033] Furthermore, the structure of the feed probe is a double-layered coaxial tube, the inner tube being a silane gas channel, and the middle layer between the inner and outer tubes being a dilution gas flow channel. Three to four of the feed probes are provided.

[0034] Furthermore, 10 to 30 filters are provided in the collection chamber, and the material of the filters is porous cermet, and the shape of the filters is a long cylinder. [Brief explanation of the drawings]

[0035] [Figure 1] 1 is a flow chart schematic diagram of the apparatus structure and method for producing nanosilicon powder from induction plasma pyrolysis silane of the present invention. [Figure 2] 1 is an electron microscope photograph of a nanosilicon powder sample produced in Example 1 according to the present invention. [Figure 3] 1 is an electron microscope photograph of a nanosilicon powder sample produced in Example 2 according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0036] The following clearly and completely describes the technical solutions in the embodiments of the present invention, in conjunction with the drawings in the embodiments of the present invention, and of course, the described embodiments are only some of the embodiments of the present invention, and do not represent all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments in this application without any creative effort are within the scope of protection of this application.

[0037] The purity of silane used in the present embodiment is 99.9999%, the purity of hydrogen gas is 99.999%, the purity of argon gas is 99.999%, and the purity of nitrogen gas is >99.99%. [Example]

[0038] 1) Preparation process: The system was flushed for 10 minutes using argon gas at a flow rate of 300 slpm, and then a leak test was performed. The leak test process was divided into a high-pressure leak test and a low-pressure leak test. The pass criteria were as follows: when the system was at a high pressure of 18 psi, the leak rate was 5 slpm or less; when the system was at a low pressure of 2 psi, the leak rate was 2 slpm or less. 30 slpm of center gas (argon gas) and sheath gas (a mixture of 90 slpm argon gas and 10 slpm hydrogen gas) were flowed into the induction plasma generator. The induction plasma was excited, the system pressure was adjusted to 14.5 psi, and the power of the induction plasma generator was adjusted to 40 kW. Then, the compressor was started, and a 1500 slpm high-temperature circulating cooling airflow at 430°C was flowed into the primary high-temperature cooling zone, and a 6500 slpm low-temperature circulating cooling airflow at 28°C and a 250 slpm nitrogen gas cooling airflow were flowed into the secondary low-temperature cooling zone.

[0039] 2) Reaction process: A total of 30 slpm of silane gas was flowed through the inner tubes of the three feed probes, and a total of 90 slpm of argon gas was flowed as a dilution gas through the intermediate layer between the inner and outer tubes. The silane gas was enveloped and diluted by the argon gas and then directly injected into the plasma hot stream, whose core temperature reached 10,000°C, where it rapidly decomposed into atomic and ionic silicon and hydrogen. As it passed through the primary high-temperature cooling zone, the silicon atoms and ions rapidly cooled to form fine silicon particles. At the same time, the small amount of undecomposed silane gas further decomposed in this zone, producing fine silicon particles and hydrogen gas. The mixed gas then carried the silicon powder into the secondary low-temperature cooling zone. After cooling, the temperature of the gas and silicon powder rapidly dropped below 200°C.

[0040] 3) Collection Process: The silicon powder produced in the reaction zone was transported by airflow to the collection chamber. Here, the gas passed through multiple filters suspended within the collection chamber. A portion was burned and cleaned by an exhaust gas treatment system before being discharged. The remaining gas was compressed by a compressor and reused. A portion was heated by an electric heating tube and sent to the primary high-temperature cooling zone. Another portion was cooled by a water-cooled heat exchanger and sent to the secondary low-temperature cooling zone. The nanosilicon powder was blocked by the filters and deposited on their surfaces. Argon gas was used as a backflow, periodically blowing back the multiple filters one by one, blowing the deposited nanosilicon powder into a powder collection tank at the bottom of the collection chamber. The reaction process continued for 8 hours, and the powder collection tank was replaced online. After stopping and collecting, a total of 15.8 kg of nanosilicon powder was obtained.

[0041] The nanosilicon powder obtained in this example is a pale yellow powder, with a BET average particle size of 61 nm, and the particle shape is spherical or approximately spherical, as shown in FIG. [Example]

[0042] Example 1 is repeated with the following differences:

[0043] In step 1), 40 slpm of center gas (argon gas) and sheath gas (a mixture of 120 slpm argon gas and 15 slpm hydrogen gas) were flowed into the induction plasma generator. The induction plasma was excited, the system pressure was adjusted to 14.7 psi, and the power of induction plasma generator 1 was adjusted to 60 kW. Then, the compressor was started, and a 1700 slpm, 450°C high-temperature circulating cooling airflow was flowed into the primary high-temperature cooling zone, and a 7500 slpm, 30°C low-temperature circulating cooling airflow and a 300 slpm nitrogen gas cooling airflow were flowed into the secondary low-temperature cooling zone.

[0044] In step 2), a total of 60 lpm of silane gas was flowed through the inner tubes of the three feed probes, and a total of 150 slpm of argon gas was flowed as a dilution gas through the intermediate layer between the inner and outer tubes.

[0045] In step 3), the reaction process was continued for 24 hours, and the powder collection tank 14 was replaced online and collected after stopping, thereby obtaining a total of 86.2 kg of nanosilicon powder.

[0046] The nanosilicon powder obtained in this example is a dark yellow powder, with a BET average particle size of 98 nm, and the particle shape is spherical or nearly spherical, as shown in FIG.

[0047] Although the embodiments of the present invention have been shown and described above, it should be understood that the above embodiments are illustrative and should not be construed as limiting the present invention, and that those skilled in the art may make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention. [Explanation of symbols]

[0048] 1 - induction plasma generator, 2 - center gas, 3 - sheath gas, 4 - feeding probe, 5 - silane airflow, 6 - dilution airflow, 7 - first-stage high-temperature cooling area, 8 - second-stage low-temperature cooling area, 9 - high-temperature circulating cooling airflow inlet, 10 - low-temperature circulating cooling airflow inlet, 11 - nitrogen gas cooling airflow inlet, 12 - collection chamber, 13 - filter, 14 - powder collection tank, 15 - compressor, 16 - electric heating tube, 17 - water-cooled heat exchanger, 18 - exhaust gas treatment device

Claims

1. (1) flushing the entire pyrolysis system using argon or nitrogen gas and conducting a leak check; (2) flowing a working gas into a plasma reactor, and exciting the working gas to form a stable high-temperature plasma with a predetermined power; and using a compressor to flow a high-temperature circulating cooling air flow into a first high-temperature cooling zone, and a low-temperature circulating cooling air flow and a nitrogen gas cooling air flow into a second low-temperature cooling zone; (3) using a feeding probe to inject silane gas wrapped in dilution gas into the high-temperature plasma thermal field, decomposing the silane in the high-temperature plasma thermal field, and cooling the silicon atoms or silicon ions generated by the pyrolysis in the first high-temperature cooling zone to form fine silicon powder; and further pyrolyzing the undecomposed silane gas to generate silicon powder and hydrogen gas, and transporting the silicon powder to the second low-temperature cooling zone by the mixed gas flow for further cooling; and (4) transporting the silicon powder cooled in the secondary low-temperature cooling region to a collection chamber by the mixed gas flow, and after the gas passes through a filter in the collection chamber, blocking the nanosilicon powder with the filter and causing it to adhere to the surface of the filter, and then blowing it down with a periodic backflow of gas, thereby collecting the nanosilicon powder.

2. 2. The method for producing nanosilicon powder from induction plasma pyrolysis silane as claimed in claim 1, wherein the working gas comprises a center gas and a sheath gas.

3. 3. The method for producing nanosilicon powder from silane by induction plasma pyrolysis according to claim 2, wherein the center gas is argon gas and has a flow rate of 5 to 100 slpm, the sheath gas is a mixed gas of argon gas and hydrogen gas, the flow rate of the argon gas in the sheath gas is 20 to 250 slpm, and the flow rate of the hydrogen gas in the sheath gas is 0 to 30 slpm.

4. 2. The method for producing nanosilicon powder from induction plasma pyrolysis silane according to claim 1, wherein in step (2), the power of the plasma reactor is 15-80 kW, and the operating pressure of the system is 14-17 Psig.

5. 2. The method for producing nanosilicon powder from induction plasma pyrolysis silane according to claim 1, wherein the high-temperature circulating cooling airflow is a mixed gas of nitrogen gas, argon gas, and hydrogen gas, and the temperature of the high-temperature circulating cooling airflow is 420-650°C, and the flow rate of the high-temperature circulating cooling airflow is 1000-3000 slpm.

6. 2. The method for producing nanosilicon powder from induction plasma pyrolysis silane according to claim 1, wherein the low-temperature circulating cooling airflow is a mixed gas of nitrogen gas, argon gas, and hydrogen gas, the temperature of the low-temperature circulating cooling airflow is 18-35°C, and the flow rate of the low-temperature circulating cooling airflow is 5,000-15,000 slpm, and the flow rate of the nitrogen gas cooling airflow is 150-450 slpm.

7. 2. The method for producing nanosilicon powder from induction plasma pyrolysis silane according to claim 1, wherein the flow rate of the silane gas is 15 to 120 slpm, and the dilution gas is argon gas and has a flow rate of 50 to 200 slpm.

8. 2. The method for producing nanosilicon powder from induction plasma pyrolysis silane according to claim 1, wherein the blowback gas is argon gas or nitrogen gas.

Images