Nano powder preparation system based on arc plasma

Abstract

The invention discloses a nano powder preparation system based on arc plasma, and relates to the field of production of carbon nano materials and nano silicon nitride, in particular to a production process for synthesizing silicon nitride. At present, the problems that continuous production of nano materials is difficult, the oxygen content of products is high, the production process is difficult to control, and the structure of a production line is single exist, and the problems can be well solved by adding a negative pressure pumping air tightness detection device, a process device cooling pipe and a tail gas detection device. The invention also provides a device for effectively solving the problem of negative pressure in the device, further improving the problems of negative pressure detection and sealing performance detection in the device, and carrying out gas washing to ensure that only a small amount of air is left in the device, so that the product is not oxidized or is slightly oxidized, and the product with lower oxygen content and higher quality is obtained. The method is suitable for various plasmas or combined plasmas, can be used for preparing various nano materials, and is simple and diversified in production line.

Description

Technical Field

[0001] The invention relates to the technical field of plasma preparation of nano powders, and in particular to a nano powder preparation system based on arc plasma. Background Art

[0002] Silicon nitride, as the most common silicon-nitrogen composite material, has good structural strength, thermal stability and conductivity, just like graphene and carbon black. Carbon black is an important auxiliary material for lithium batteries. Graphene and silicon nitride have good application potential in lithium-ion batteries with excellent performance. Silicon nitride has always been widely used in high-performance ceramics. Graphene and its derivatives have a wider range of applications and can be used in supercapacitors, fuel cells, batteries and water decomposition. There are also new applications in oxygen reduction reactions, hydrogen evolution reactions, lithium-ion batteries, field-effect transistors, etc., so they have been widely studied, and a series of production processes have been developed, such as chemical deposition, heat treatment and hydrolysis. The actual content of carbon nanomaterials sold on the market today is low and the quality is poor, so it is crucial to develop high-quality, high-yield, high-conversion and low-cost preparation methods. In addition, artificial regulation of single atoms / radicals at the nanoscale seems doubtful and almost impossible, unless the technology is made industrially unfeasible through a slow and laborious process. Therefore, the natural way to achieve synthesis by design is to create conditions that force atoms / radicals to self-assemble into target nanostructures. Arc plasma synthesis of nanomaterials has the advantages of simple precursors, easy to control product performance, high product yield and good product quality, so it is a very promising synthesis method.

[0003] Since silicon nitride is very easy to oxidize above 800℃, the presence of oxygen in the air during the reaction process poses a great threat to the production of silicon nitride, and the sealing and low-oxygen environment of the device must be ensured. The oxidation reaction is very weak below 800℃, so it is particularly important to add a cooling device to the device to ensure that the obtained nanopowder material can be effectively collected.

[0004] In the existing production technology, there are problems such as difficulty in continuous production, high oxygen content of products, difficult to control the production process, and single production line structure, so it is necessary to continuously improve the technology. To this end, a nano powder preparation system based on arc plasma is proposed. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, one purpose of the present invention is to provide a nano powder preparation system based on arc plasma, which effectively solves the problem of negative pressure inside the device, further improves the problem of negative pressure detection and sealing detection inside the device, and can perform air washing to ensure that only a small amount of air remains inside, ensure that the product is not oxidized or less oxidized, and obtain a product with lower oxygen content and higher quality.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A nano powder preparation system based on arc plasma, comprising a gas introduction unit, a gas flow control unit, a plasma reaction unit, an AC / DC arc ignition power supply system, a negative pressure extraction device, a chromatographic detection unit, a cooling device, a fluidized bed, a separation and dust removal device, and an air induction system;

[0008] The gas outlet end of the separation and dust removal device is connected to the tail gas treatment device of the induced draft system, and the material outlet end of the separation and dust removal device is connected to the collection device;

[0009] The improved process for preparing nanomaterials by arc discharge plasma of the nano powder preparation system based on arc plasma has the following steps:

[0010] S1. First, close all the valves of the device, open the valve of the negative pressure extraction device, and extract the air until the negative pressure value of the vacuum gauge remains stable for a period of time, then close the valve. When the reading remains stable at this moment, it proves that the air tightness is good;

[0011] S2. The carrier gas of the gas introduction unit is then introduced into the plasma reaction unit, and the step in S1 is continued for 2-3 times for gas washing;

[0012] S3. Open the induced draft fan system to introduce cooling water, introduce the reaction gas and carrier gas of the gas introduction unit into the plasma reaction unit, open the valve after the settling chamber, control the gas flow to be stable, and turn on the AC and DC arc power supply system. At this moment, the raw gas is cracked through nucleation and growth, and continues to grow into nano powder materials. After the reaction continues to be stable, open the one-way valve of the chromatographic detection unit, and cool the sample tail gas through the cooling coil and enter the sample bag for detecting the occurrence of the reaction. After sampling, close the valve;

[0013] As the reaction proceeds, the reactant particles gradually deposit in the graphite tube and the subsequent separation section. The processed nanomaterial products enter the cooling tube device and the separation and dust removal device. The separated nanomaterial products enter the external collection device. After cooling, the nanomaterials are obtained, and the exhaust gas is sent out through the induced draft system.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The present invention optimizes the gas introduction and reaction process, uses a variety of reaction gases and carrier gases, and accurately controls the flow rate through a rotor flowmeter and a mass flowmeter to ensure the stability of reaction conditions and the diversity of material synthesis. Among them, plasma is used as a reaction unit, and the plasma can be a plasma composed of one or two plasmas in a combined form. The present invention takes arc plasma as the main body, and uses graphene rod electrodes inside, which optimizes the arc discharge effect and improves the plasma generation efficiency and material synthesis quality.

[0016] The tail gas cooling device in the present invention adopts a single-channel detachable water-cooled heat exchange tube, the interior of which can be used to collect part of the nanopowder material to reduce material loss. At the same time, the design of the chromatographic detection unit realizes real-time sampling and analysis of the reaction tail gas, which is helpful to monitor the reaction process and conversion rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of the nano powder preparation system based on arc plasma of the present invention;

[0018] Figure 2 It is the internal structure diagram of the arc plasma generating device in the present invention;

[0019] Figure 3 The SEM image of the product of Experimental Example 1 of the present invention and the image of silicon nitride nanopowder are shown.

[0020] In the figure: 10, gas introduction unit; 20, gas flow control unit; 30, plasma reaction unit; 40, AC / DC arc ignition power supply system; 50, negative pressure extraction device; 60, chromatographic detection unit; 70, cooling device; 80, sedimentation chamber; 90, separation and dust removal device; 100, air induction system;

[0021] 1. Ceramic tube; 2. Sealed threaded pipe cap; 3. Asbestos fiber; 4. Clay insulation layer; 5. Graphite electrode. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] See also Figure 1 , Figure 2 , the present invention provides a technical solution:

[0024] A nano powder preparation system based on arc plasma, comprising:

[0025] Cooling device;

[0026] A gas introduction unit, including a reaction gas and a carrier gas, wherein the reaction gas is one or more of methane, ethane, propane, and alkane gases, which can be used as a carbon precursor for preparing carbon nanomaterials, the reaction gas silane can be used as a silicon precursor for silicon nanomaterials, the reaction gas nitrogen, ammonia, or one or more can be used as a nitrogen precursor, and the reaction gas hydrogen can be used as an auxiliary reaction gas;

[0027] The carrier gas is one or more of nitrogen, argon and helium.

[0028] The gas flow control unit is a rotor flow meter and a mass flow meter, which are used to control the gas volume flow rate and mass flow rate;

[0029] The exhaust gas cooling device is a single-channel detachable water-cooled heat exchange tube, the interior of which is used to collect a portion of the nano-powder material.

[0030] The plasma reaction unit is one or more combinations of a high-frequency and high-voltage AC sliding discharge plasma device and an arc plasma generating device. The interior of the arc plasma generating device is composed of two graphene rods. The distance between the two graphene rods is 1-3 mm and they are in the same plane.

[0031] Specifically, the arc plasma generating device includes a ceramic tube 1, a sealed threaded pipe cap 2, asbestos fibers 3, a graphite electrode 5, a clay insulation layer 4 and a stainless steel shell, and a heat insulation layer made of clay heat-insulating refractory material is used in the reaction chamber.

[0032] Specifically, since the graphene rod will generate a lot of heat during the power-on process, asbestos fiber and ceramic tube are used for heat insulation. The ceramic tube 1, the sealing threaded cap 2, the asbestos fiber 3, and the graphite electrode 5 are all provided with sealing rings to ensure good sealing performance. The reaction chamber uses a heat insulation layer made of clay heat-insulating refractory material, which not only prevents the high temperature generated during the reaction from causing damage and danger to the reactor and the experimenters, but also appropriately increases the gas flow rate, and the use of a narrow upper and wide lower channel is conducive to preventing carbon deposition.

[0033] AC / DC arc striking power supply system, which is a high-frequency AC power supply and a single-phase or three-phase DC or AC power supply.

[0034] The negative pressure extraction device includes a negative pressure vacuum pressure gauge and an air extraction pump or a vacuum pump. A one-way valve is provided at the front end pipeline inlet of the air extraction pump to extract air and the carrier gas for washing. The negative pressure vacuum pressure gauge is used to indicate the negative pressure value inside the reaction device, and the negative pressure value is maintained at 80-100kPa.

[0035] The chromatographic detection unit includes a gas collection hole, a one-way valve, a gas cooling coil, and a gas aluminum foil sampling bag. The collection bag has a specification of 0.2L. The gas collection hole is arranged at the lower end of the plasma reaction unit and the front end of the tail gas cooling tube. The gas cooling coil is used for cooling the sample reaction tail gas. The collected gas is used for qualitative and quantitative analysis of gas chromatography detection and the conversion rate of the analysis reaction.

[0036] A separation and dust removal device, including a cyclone separator and a dust removal bag connected thereto;

[0037] The induced draft system includes an induced draft fan structure and an exhaust pipe, and a one-way valve is provided between the separation and dust removal device 90 and the settling chamber 80 .

[0038] Specifically, the nanopowder is carbon black particles, graphene nanosheets and nano silicon nitride particles or other composite nanomaterials.

[0039] The ratio of reaction gas to carrier gas and the type of carrier gas used control the type, quality and yield of carbon nanomaterials according to the different nanopowder preparation methods. The ratio of silicon nitride raw gas to carrier gas controls the product form. As the carrier gas flow rate increases, the product will tend to change in the direction of particle size reduction and dispersion.

[0040] Depending on the preparation of nanopowders, the raw gas for preparing carbon black can be methane, ethane, ethylene and other alkane gases as carbon sources, and the carrier gas can be argon or helium, with argon being the most commonly used carrier gas. When the raw gas is methane and the carrier gas is argon, the volume flow ratio of methane to argon in DC arc or AC / DC arc is controlled at 1:3-1:15, the DC power is 5.5kW-10kW, and the volume flow ratio of methane to argon in AC arc is 1:3-1:13, the power is 3.8kW-7.6kW, and the reaction temperature range is controlled at 3000K-4500K.

[0041] The raw material gas used in the preparation of graphene is the same as that of carbon black. It should be noted that in order to obtain graphene sheets, the C:H atomic ratio of the gas entering the reaction must be greater than 1:4, so an appropriate amount of hydrogen or ammonia needs to be added to control the morphology. The carrier gas can be nitrogen, helium, or argon, and the ratio of the carrier gas flow rate to the alkane gas is controlled to be <1:2.

[0042] The improved process for preparing nanomaterials by arc discharge plasma of the nano powder preparation system based on arc plasma has the following steps:

[0043] S1. First, close all the valves of the device, open the valve of the negative pressure extraction device, and extract the air until the negative pressure value of the vacuum gauge remains stable for a period of time, then close the valve. When the reading remains stable at this moment, it proves that the air tightness is good;

[0044] S2. The carrier gas of the gas introduction unit is then introduced into the plasma reaction unit, and the step in S1 is continued for 2-3 times for gas washing;

[0045] S3. Open the induced draft fan system to introduce cooling water, introduce the reaction gas and carrier gas of the gas introduction unit into the plasma reaction unit, open the valve after the settling chamber, control the gas flow to be stable, and turn on the AC and DC arc power supply system. At this moment, the raw gas is cracked through nucleation and growth, and continues to grow into nano powder materials. After the reaction continues to be stable, open the one-way valve of the chromatographic detection unit, and cool the sample tail gas through the cooling coil and enter the sample bag for detecting the occurrence of the reaction. After sampling, close the valve;

[0046] As the reaction proceeds, the reactant particles gradually deposit in the graphite tube and the subsequent separation section. The processed nanomaterial products enter the cooling tube device and the separation and dust removal device. The separated nanomaterial products enter the external collection device. After cooling, the nanomaterials are obtained, and the exhaust gas is sent out through the induced draft system.

[0047] Among them, the raw material gas is divided into a carbon source and a silicon source, and the carrier gas can be an inert gas such as argon, nitrogen, and helium.

[0048] Experimental Example 1

[0049] The raw material gas used for silicon nitride is silane as the silicon source, nitrogen and ammonia as the nitrogen source, argon as the carrier gas, and the volume flow ratio of silane to carrier gas is controlled at 10:1-4:1. Silicon nitride is used as an example for detailed description, and the following steps are included:

[0050] S1. First, ensure that the experimental device is well sealed and confirm that all valves are in a closed state; then turn on the vacuum pump to vacuum the reactor body and the cooling section. After vacuuming, open the valve to introduce high-purity argon gas. After the vacuum degree drops, close the argon gas inlet valve to perform gas washing operations. Repeat this process 2-3 times to ensure that the air in the pores inside the device is completely removed.

[0051] S2. After completing the cleaning work, close the vacuum pump and the vacuum pump valve, turn on the induced draft fan, open the argon valve, and use argon to flush the reaction device for 3-5 minutes. During the flushing period, turn on the power to start the arc. If a blue-white arc is successfully generated, the experiment can begin.

[0052] S3. Open the valve of the hydrogen cylinder and adjust its flow rate. Adjust the argon cylinder appropriately to keep the target flow rate of argon. Pass silane and ammonia or nitrogen and adjust to the reaction flow rate. Enter the reaction chamber for reaction. When the reaction is stable, open the valve at the gas sample collection point during this period. The sample gas enters the sample bag after passing through the cooling coil. After obtaining the sample gas, close the valve.

[0053] After a certain period of reaction, turn off the power, then keep the argon and hydrogen open, and close the valves of the silane and nitrogen source cylinders. At this moment, after the reaction is completed, the temperature in the reactor is high, and the reactants still have a certain reaction activity, and oxidation may occur. This situation can be avoided after purging and cooling with cooling pipes. After the temperature of the device drops to room temperature, the device is disassembled to obtain the product in the product collection area, and the exhaust gas is sent out through the induced draft system.

[0054] The experimental results are as follows Figure 3 As shown, a, b, c, d, and e are SEM images of products obtained under different ratios of raw gas to carrier gas, and f is an image of silicon nitride nanopowder.

[0055] Parts not involved in the present invention are the same as the prior art or can be implemented by the prior art. Although the embodiments of the present invention have been shown and described, it is understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A nano powder preparation system based on arc plasma, characterized in that: It comprises a gas introduction unit (10), a gas flow control unit (20), a plasma reaction unit (30), an AC / DC arc ignition power supply system (40), a negative pressure extraction device (50), a chromatographic detection unit (60), a cooling device (70), a separation and dust removal device (90), and an air induction system (100); The gas outlet end of the separation and dust removal device (90) is connected to the tail gas treatment device of the induced draft system (100), and the material outlet end of the separation and dust removal device (90) is connected to the collection device; The plasma reaction unit (30) is a combination of one or more of a high-frequency high-voltage AC sliding discharge plasma device and an arc plasma generating device. The interior of the arc plasma generating device is composed of two graphene rods, the graphite rods are 15-10 mm long, the distance between the two graphene rods is 1-3 mm and they are in the same plane. The AC / DC arc striking power supply system (40) is a high-frequency AC power supply and a single-phase or three-phase DC or AC power supply. The arc plasma generating device comprises a ceramic tube (1), a sealed threaded tube cap (2), asbestos fibers (3), a graphite electrode (5), a clay insulation layer (4) and a stainless steel shell, wherein a heat insulation layer made of clay heat-insulating refractory material is used in the reaction chamber; The improved process for preparing nanomaterials by arc discharge plasma of the nano powder preparation system based on arc plasma has the following steps: S1. First, close all valves of the device, open the valve of the negative pressure extraction device (50), extract air until the negative pressure value of the vacuum gauge remains stable for a period of time, then close the valve. When the reading remains stable at this moment, it proves that the air tightness is good; S2. Then the carrier gas of the gas introduction unit (10) is introduced into the plasma reaction unit (30), and the step of S1 is continued for 2-3 times for gas washing; S3. Open the induced draft fan system to introduce cooling water, introduce the reaction gas and carrier gas of the gas introduction unit (10) into the plasma reaction unit (30), open the valve behind the settling chamber (80), control the gas flow to be stable, and then open the AC / DC arc power supply system (40). At this moment, the raw gas undergoes cracking through nucleation and growth, and continues to grow into nano-powder materials. After the reaction continues to be stable, open the one-way valve of the chromatographic detection unit (60), cool the sample tail gas through the cooling coil and then enter the sample bag for detecting the occurrence of the reaction. After sampling, close the valve; As the reaction proceeds, reactant particles gradually deposit in the graphite tube and the subsequent separation section, and the processed nanomaterial product enters the cooling tube device and the separation and dust removal device (90). The separated nanomaterial product enters the external collection device, and the nanomaterial is obtained after cooling. The tail gas is sent out through the induced draft system (100).

2. The arc plasma-based nanopowder preparation system according to claim 1, characterized in that: The gas introduction unit (10) comprises a reaction gas and a carrier gas, wherein the reaction gas is one or more of methane, ethane, propane, and alkane gas, which can be used as a carbon precursor for preparing carbon nanomaterials, the reaction gas silane can be used as a silicon precursor for silicon nanomaterials, and the reaction gas nitrogen and ammonia can be used as a nitrogen precursor. The carrier gas is one or more of nitrogen, argon and helium.

3. The arc plasma-based nanopowder preparation system according to claim 1, characterized in that: The gas flow control unit (20) is a rotor flow meter and a mass flow meter, which is used to control the gas volume flow rate and mass flow rate; The tail gas cooling device is a single-channel detachable water-cooled heat exchange tube, the interior of which is used to collect a portion of the nano powder material.

4. The arc plasma-based nanopowder preparation system according to claim 1, characterized in that: The negative pressure extraction device (50) comprises a negative pressure vacuum pressure gauge and an air extraction pump or a vacuum pump. A one-way valve is provided at the front end pipeline inlet of the air extraction pump for extracting air and carrier gas for washing. The negative pressure vacuum pressure gauge is used to indicate the negative pressure value inside the reaction device. The negative pressure value is maintained at 80-100 kPa.

5. The arc plasma-based nanopowder preparation system according to claim 1, characterized in that: The chromatographic detection unit (60) comprises a gas collection hole, a one-way valve, a gas cooling coil, and a gas aluminum foil sampling bag. The size of the collection bag is 0.2L. The gas collection hole is arranged at the lower end of the plasma reaction unit (30) and the front end of the tail gas cooling pipe. The gas cooling coil is used for cooling the sample reaction tail gas. The collected gas is used for qualitative and quantitative analysis of gas chromatography detection and the conversion rate of the analysis reaction.

6. The arc plasma-based nanopowder preparation system according to claim 1, characterized in that: The separation and dust removal device (90) comprises a cyclone separator and a dust removal bag connected to each other; The induced draft system (100) comprises an induced draft fan structure and an exhaust pipe, and a one-way valve is provided between the separation and dust removal device (90) and the settling chamber (80).

7. The arc plasma-based nanopowder preparation system according to claim 3, characterized in that: The nano powder is carbon black particles, graphene nano sheets and nano silicon nitride particles or other composite nano materials.

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