CN108046268A - The method that plasma enhanced chemical vapor synthetic method prepares high-purity nm boron carbide powder - Google Patents

Abstract

The method of preparing high-purity nano-boron carbide powder by plasma chemical vapor synthesis method firstly introduces argon gas into the plasma generator, starts the plasma generator power supply to generate arc discharge, and forms a stable argon plasma arc; then introduces hydrogen and methane into the plasma The generator is mixed with argon plasma to form a plasma jet; then the plasma jet is introduced into the reactor below the plasma generator, and at the same time, boron trichloride gas is introduced from the reactor to collide with the plasma jet and quickly mix to complete the gas phase synthesis Reaction, the space generates solid B ₄ C and gaseous HCl; solid B ₄ C is sprayed with the airflow to the cooling wall of the cooling powder collector to form nano-boron carbide powder; the process steps are simple, and the finished product is produced in one step; plasma reaction The efficiency is extremely high and the gas phase reaction has no foreign impurities. The boron carbide powder produced has high purity and uniform particle size, and can be used to prepare ceramic materials without post-processing, which has better comprehensive advantages.

Description

Method for preparing high-purity nano boron carbide powder by plasma chemical vapor phase synthesis

technical field

The invention relates to the technical field of preparation of inorganic non-metallic materials, in particular to a method for preparing high-purity nano boron carbide powder by a plasma chemical vapor phase synthesis method.

Background technique

Boron carbide has the characteristics of high hardness, high modulus, high melting point, low density, good wear resistance, strong acid and alkali corrosion resistance, etc., and has many advantages such as high neutron absorption capacity and semiconductor conductivity. Materials, hard materials, industrial ceramics, bulletproof ceramics, nuclear industry, aerospace and semiconductor industries and other fields are widely used. The main process of boron carbide ceramic material preparation is powder preparation, molding and sintering. Since boron carbide is a compound with strong covalent bonds, it is difficult to sinter. In order to improve the sintering quality, ultrafine, high-purity carbonization must be used. Boron powder, nanoscale boron carbide powder has the characteristics of easy sintering due to its small size effect, quantum effect, unsaturated valence effect and electron tunnel effect, which is an important direction for the development of boron carbide powder. Very great development value and application prospect.

The industrial preparation methods of boron carbide powder mainly include high-temperature self-propagating synthesis (SHS) and carbothermal reduction method. In recent years, laser chemical gas phase reaction method, sol-gel carbothermal reduction method, etc. Magnesium is mostly used as flux, also known as magnesia thermal method, which has the advantages of energy saving and rapid reaction, but the disadvantage is that the particle size of the synthesized boron carbide powder is only micron and the residual magnesium and magnesium oxide impurities in the reactant are extremely difficult Thorough removal; the carbothermal reduction method is to put boron-containing compounds and carbon powder or carbon-containing compounds into a carbon tube furnace or electric arc furnace, and synthesize boron carbide powder at a certain temperature with a protective gas. The disadvantage of this method is that it can High consumption, low efficiency, large particle size of the synthesized powder (20-40μm) and containing impurities such as carbon powder or boric anhydride that are difficult to remove, as a raw material for sintered boron carbide, a large number of post-processing procedures are required, which greatly increases the production cost; Laser Induced Chemical Vapor Deposition (LICVD) uses the absorption of specific wavelength laser beams by reaction gas molecules to generate thermal decomposition or chemical reaction, and form ultrafine powder through nucleation and growth. This method has low production capacity, expensive equipment and energy consumption. Large and high purity requirements for reaction raw materials; sol-gel (sol-gel) carbothermal reduction method is to solidify inorganic substances or metal alkoxides through solutions, sols, and gels, and then synthesize compounds by heat treatment. Since borides that provide boron sources are difficult to form gels with other inorganic or organic substances, the process of synthesizing boron carbide by this method is complex and costly.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for preparing high-purity nano boron carbide powder by plasma chemical vapor phase synthesis, so as to solve the above-mentioned shortcomings in the background technology.

The technical problem solved by the present invention adopts following technical scheme to realize:

A method for preparing high-purity nano-boron carbide powder by plasma chemical vapor synthesis, using a device for preparing high-purity nano-boron carbide powder by plasma chemical vapor synthesis to prepare high-purity nano-boron carbide powder, the specific steps are as follows:

1) Introduce argon gas into the plasma generator, start the plasma generating power supply to generate arc discharge, and form a stable argon plasma arc;

2) Then introduce hydrogen and methane into the plasma generator, and mix and discharge with argon plasma to form a plasma jet, which contains a large number of ionized ions and dissociated highly active hydrogen atoms and carbon atoms;

3) Then the plasma jet is introduced into the reactor below the plasma generator, and boron trichloride gas is introduced from the boron trichloride inlet hole of the reactor at the same time, and it is quickly mixed with the plasma jet and mixed evenly. Under the action of active particles, boron trichloride breaks bonds and reacts quickly with C and H atoms in the jet, and generates solid B ₄ C and gaseous HCl in space;

4) The solid B ₄ C generated in step 3) is sprayed with the airflow to the cooling wall of the cooling powder collector for quenching deposition to form nano boron carbide powder;

5) Part of the nano boron carbide powder in step 4) is driven by the airflow into the water absorption gas-solid separation powder collector, the powder is absorbed by water and the gas overflows, and finally the powder is collected and washed and dried to obtain nano boron carbide powder body.

In the present invention, in step 1), the flow rate of argon gas is 1.5-2m ³ /h, the pressure is 0.3-0.5MPa, the power of starting the plasma generating power supply to generate arc discharge is 10KW, the current is 105-115A, and the voltage is 90-100V .

In the present invention, in step 2), the volume flow ratio of hydrogen to methane is 4-6:1, the gas supply pressure is 0.3-0.5 MPa, and the power supply of the plasma generator is adjusted so that the output power is 10-100KW.

In the present invention, in step 3), the volume flow ratio of boron trichloride to methane is 4:1, the heating temperature of boron trichloride is 40-60° C., and the gas supply pressure of boron trichloride is 0.3-0.5 MPa.

In the present invention, the device for preparing high-purity nano-boron carbide powder by plasma chemical vapor synthesis method includes a plasma generating power supply, a plasma generator, a reactor, a cooling powder collector, a water absorption gas-solid separation powder collector, and an exhaust gas absorber. , argon gas source, hydrogen gas source, methane gas source and boron trichloride gas source, wherein, the plasma generator is a semi-closed container made of polytetrafluoro material insulation, the upper end of the semi-closed container is closed and the lower end is open, and in the semi-closed The upper part of the closed container is provided with a cathode made of cerium-tungsten material, and the lower part of the semi-closed container is provided with an anode made of copper material. The cathode is connected to the negative pole of the plasma generator power supply, and the anode is connected to the positive pole of the plasma generator power supply; There is an argon gas inlet hole at the bottom for introducing argon through the argon source, and a mixed gas inlet hole for introducing hydrogen through the hydrogen source and methane through the methane gas source at the top of the anode of the plasma generator; the plasma generator has a built-in The cooling circulating water system is used for cooling protection to cool down the plasma generator working at atmospheric pressure or higher pressure; the reactor is sealed and connected to the lower end of the plasma generator, and the top of the reactor is symmetrically arranged with two for the passage of boron trichloride The gas source is introduced into the boron trichloride inlet hole of the boron trichloride gas, and the boron trichloride heating source for heating and vaporizing the boron trichloride is arranged outside the boron trichloride gas source, and the lower port of the reactor is placed in a cooling and receiving port. In the powder collector, the outer jacket of the cooling powder collector is provided with a circulating cooling water system for cooling and cooling. The water absorbing gas-solid separation powder collector is connected to the outlet of the cooling powder collector, and is connected to the argon source, hydrogen source, The four gas source outlets of the methane gas source and the boron trichloride gas source are respectively provided with flowmeters, and the argon gas source is connected to the argon gas inlet hole at the bottom of the cathode of the plasma generator after being measured by the flowmeter. The methane gas source is measured by the flowmeter and connected to the hydrogen and methane mixture gas inlet hole on the top of the anode of the plasma generator. The boron trichloride gas source is heated and vaporized by the boron trichloride heating source and then measured by the flowmeter It is connected to the boron trichloride air inlet at the top of the reactor, and the water absorption gas-solid separation powder collector is connected to the tail gas absorber.

In the present invention, the plasma generating power supply is a DC arc power supply with an output power of 10-100 kW.

In the present invention, the argon gas inlet and the mixed gas inlet are both annular tangent structures.

In the present invention, the reactor is a tubular reactor composed of a water-cooled outer jacket and a through-hole graphite tube.

In the present invention, the cooling powder collector is composed of a cylindrical barrel body with a symmetrical opening mirror on the upper part, a conical sedimentation barrel body in the middle part and a powder accumulation tank at the bottom.

In the present invention, the water absorption gas-solid separation powder collector is provided with a bottom extension pipe for connecting the outlet of the cooling powder collector and an air outlet pipe for connecting the tail gas absorber.

In the present invention, the bottom extension pipe extends 5cm below the water surface.

In the present invention, the flowmeter is an air calibrated rotameter.

In the present invention, the tail gas absorber is a tail gas spray absorption tower.

In the present invention, the argon gas is always used in the reaction, that is, as a purge replacement gas and as a protective gas, which can prolong the service life of the plasma generator.

In the present invention, the purity of the argon, hydrogen, methane and boron trichloride is all 99.99%.

Beneficial effects: the invention adopts the plasma reaction process with simple steps, and the finished product can be produced in one step; and the high temperature and a large number of active particles generated by the plasma make the synthesis reaction rate extremely high and the production efficiency high; at the same time, the non-product substances in the gas phase reaction system are all in the form of The gas overflows, there is no foreign impurity, and the boron carbide powder produced is of high purity; while the solid-phase product generated by the plasma gas-phase synthesis reaction has the characteristics of uniform nucleation in space, air jet dispersion and cold wall quenching deposition, which makes the prepared boron carbide powder The boron carbide powder is ultra-fine and has a uniform particle size distribution. The highest yield of boron carbide powder can reach more than 68%, the purity of the product can reach more than 99%, and its average particle size is about 30-80nm. It can be used for preparation without post-treatment Ceramic materials have better comprehensive advantages compared with traditional craft methods.

Description of drawings

Fig. 1 is a schematic structural diagram of a preferred embodiment of the present invention.

Fig. 2 is the SEM picture of the boron carbide powder product in the preferred embodiment of the present invention.

Fig. 3 is an X-ray diffraction (XRD) spectrum of the boron carbide powder product in a preferred embodiment of the present invention.

Detailed ways

In order to make the technical means, creative features, goals and effects achieved by the present invention easy to understand, the present invention will be further described below in conjunction with specific illustrations.

Referring to the method for preparing high-purity nano-boron carbide powder by plasma chemical vapor synthesis in Fig. 1 to Fig. 3, the device for preparing high-purity nano-boron carbide powder by plasma chemical vapor The device for preparing high-purity nano-boron carbide powder by bulk chemical vapor synthesis method includes plasma power supply 1, plasma generator 2, reactor 3, cooling powder collector 4, water absorption gas-solid separation powder collector 5, argon gas source 6 , hydrogen source 7, methane gas source 8, boron trichloride gas source 9, flow meter 10, boron trichloride heating source 11, tail gas spray absorption tower 12, bottom extension pipe 13 and outlet pipe 14, wherein, the The plasma generating power supply 1 is a DC arc power supply with an adjustable output power of 10-100kW. The upper part of the plasma generator 2 is a rod-shaped cathode made of cerium-tungsten material, and the lower part is a ring-shaped anode made of copper material, and the cathode and The anode is insulated by PTFE material to form a container with the upper end closed and the lower end open. The cathode is connected to the negative pole of the DC arc power supply, and the anode is connected to the positive pole of the DC arc power supply. Argon gas is introduced through the argon gas source 6, and a ring-shaped tangential hydrogen gas inlet hole is provided on the top of the anode, which is used to respectively introduce the mixed gas gas inlet hole of hydrogen and methane through the hydrogen gas source 7 and the methane gas source 8; the plasma generator 2 adopts a built-in The cooling circulating water system is used for cooling protection to cool down the DC arc thermal plasma generator working at atmospheric pressure or higher pressure, so it does not need to be carried out under vacuum conditions; A tubular reactor composed of a water-cooled outer jacket and a through-hole graphite tube. The top of the reactor 3 is symmetrically provided with boron trichloride air intake holes for introducing boron trichloride gas through the boron trichloride gas source 9. The reactor The lower port of 3 is placed in the cooling powder collector 4. The cooling powder collector 4 is composed of a cylindrical barrel body with a symmetrical opening mirror on the upper part, a conical barrel body for sedimentation in the middle, and a powder accumulation tank at the bottom. The outer jacket circulating cooling water system is used for cooling, and the water absorption gas-solid separation powder collector 5 is a sealed container including a bottom extension pipe 13 and an air outlet pipe 14 connected to the outlet of the cooling powder collector 4, wherein the bottom extension pipe extends into the water surface Below 5cm, the argon gas source 6 is connected to the argon gas inlet hole at the bottom of the cathode of the plasma generator 2 after being metered by the flow meter 10, and the hydrogen gas source 7 and the methane gas source 8 are respectively connected to the plasma generator after being metered by the flow meter 10 The mixed gas inlet hole at the top of the anode of the reactor, the boron trichloride gas source 9 is heated and vaporized by the boron trichloride heating source 11 and then connected to the boron trichloride gas inlet at the top of the reactor 3 after being metered by the flow meter 10 The flowmeter 10 is a rotameter calibrated with air, and the tail gas spray absorption tower 12 is connected to the gas outlet pipe 14; argon is ionized into a plasma arc by a plasma generator, and hydrogen and methane are introduced into the plasma at the same time The arc is mixed and discharged to form a high-temperature plasma jet. This jet is introduced into the reactor, and then the raw material BCl ₃ gas is also introduced into the reactor through the oppositely symmetrical boron trichloride gas inlet holes to mix with the penetrating plasma jet. High-temperature hydrogen, Methane and BCl ₃ rapidly Mix and dissociate for spatial recombination, complete the gas phase synthesis reaction, and obtain boron carbide powder products. The specific steps are as follows:

First, argon gas is introduced into the plasma generator 2, and the plasma generator power supply 1 is started to generate an argon plasma arc, and then hydrogen and methane are introduced into the plasma generator 2 and mixed with the argon plasma to form a plasma jet; then the plasma jet is It is introduced into the reactor 3 below the plasma generator 2, and at the same time, the boron trichloride gas is introduced from the boron trichloride inlet hole of the reactor 3, and it is rapidly mixed with the plasma jet to complete the gas-phase synthesis reaction, and the space generates solid B ₄ C and Gaseous HCl; solid B ₄ C is sprayed with the airflow to the cooling wall of the cooling powder collector 4 and quenched and deposited to form nano-boron carbide powder; part of the nano-boron carbide powder enters the water absorption gas-solid separation powder collector driven by the airflow 5. The powder is absorbed by water and the gas overflows, and finally the powder is collected and washed and dried to obtain nano-boron carbide powder; the tail gas HCl is treated by the tail gas spray absorption tower 12; specific examples are as follows:

Example 1

First turn on the cooling circulating water to supply to the plasma generator 2, the reactor 3, and the cooling powder collector 4, then turn on the argon gas source 6, keep the pressure of the gas cylinder at 0.3MPa, feed in the argon gas with a flow rate of 1.6m ³ /h, blow Scan the replacement system for 10 minutes; turn on the plasma generator power supply 1, rotate the current regulator to make the current value at 105A, press the start switch, and generate an argon plasma torch. At this time, the voltage value shows about 90V, and the argon gas can be seen from the observation window Stabilize the plasma arc for 1 min; then rotate the current regulator to increase the current to 130 A, turn on the hydrogen source 7 and the methane gas source 8, maintain the pressure of the gas cylinder at 0.3 MPa, and slowly feed it from the flow meter 10 (air calibration) Hydrogen is 0.6 m ³ /h, methane is 0.6 m ³ /h. At this time, the voltage is raised to 130 V, and then the current regulator is rotated to adjust the current to 200A. At this time, the plasma jet discharge power is 25KW, and the mixed discharge forms a plasma jet; Open the boron trichloride gas source 9, heat the system to a constant temperature of 40°C by the boron trichloride heating source 11, and the boron trichloride gas supply pressure is 0.3MPa, and slowly feed in about 2.5kg/h of boron trichloride; Boron is sprayed into the plasma jet, and the ionized and dissociated hydrogen and methane in it undergo plasma gas phase synthesis reaction, and the space generates solid B ₄ C and gaseous HCl; solid B ₄ C is sprayed with the air flow to the cooling of the cooling powder collector 4 The nano boron carbide powder is formed by quenching and depositing on the wall and is deposited into the powder accumulation tank for collection; part of the nano boron carbide powder enters the water absorption gas-solid separation powder collector 5 driven by the air flow, the powder is absorbed by water and the gas overflows, and is collected The powder is washed and dried to obtain nano-boron carbide powder, and the tail gas HCl is processed by the tail gas spray absorption tower 12; the reaction lasts for 30 minutes, and the total amount of boron carbide powder collected by the powder accumulation tank and the water absorption gas-solid separation powder collector 5 is 70g; Calculated according to the supply-output ratio of boron trichloride, the yield is greater than 60%. The obtained boron carbide powder product is qualitatively analyzed by XRD and detected by SEM, EDS and ICP. % (of which: the oxygen content is less than 0.5%, the total metal ion content is less than 300ppm).

Example 2

First turn on the cooling circulating water to supply to the plasma generator 2, the reactor 3, and the cooling powder collector 4, then turn on the argon gas source 6, keep the pressure of the gas cylinder at 0.4MPa, feed in the argon gas with a flow rate of 1.8m ³ /h, blow Scan the replacement system for 10 minutes; turn on the plasma generator power supply 1, rotate the current regulator to make the current value at 110 A, press the start switch, and generate an argon plasma torch. At this time, the voltage value shows about 95V, and the argon can be seen from the observation window Gas plasma arc, stable for 1min; then rotate the current regulator to increase the current to 200A, turn on the hydrogen source 7 and methane gas source 8, maintain the pressure of the gas cylinder at 0.4MPa, and slowly feed it from the flow meter 10 (air calibration) Hydrogen 0.8m ³ /h, methane 0.8 m ³ /h, at this time the voltage rises to 200V, then turn the current regulator to adjust the current to 220A, at this time the plasma jet discharge power is 45KW, mixed discharge forms a plasma jet; open The boron trichloride gas source 9 is heated by the boron trichloride heating source 11 to a constant temperature of 50°C, and the boron trichloride gas supply pressure is 0.4MPa, and slowly feeds in about 4.5kg/h of boron trichloride; Boron is sprayed into the plasma jet, and the ionized and dissociated hydrogen and methane in it undergo plasma gas-phase synthesis reaction, and the space generates solid B ₄ C and gaseous HCl; solid B ₄ C is sprayed to the cooling wall of the cooling powder collector 4 along with the air flow The upper quenching deposition forms nano-boron carbide powder and settles to the powder accumulation tank for collection; part of the nano-boron carbide powder enters the water absorption gas-solid separation powder collector 5 driven by the airflow, the powder is absorbed by water and the gas overflows, and the powder is collected And after washing and drying, nano boron carbide powder is obtained, tail gas HCl is processed by tail gas spray absorption tower 12; reaction continues for 30min, and the boron carbide powder collected by powder accumulation tank and water absorption gas-solid separation powder collector 5 is 130g in total; According to the calculation of the supply-output ratio of boron trichloride, the recovery rate is greater than 65%. The obtained boron carbide powder product is qualitatively analyzed by XRD and detected by SEM, EDS and ICP. It shows that the boron carbide powder has a particle size of 30-80nm and a purity of more than 99% (of which: the oxygen content is less than 0.5%, and the total metal ion content is less than 300ppm).

Example 3

Turn on the cooling circulating water to supply to the plasma generator 2, reactor 3, and cooling powder collector 4, then turn on the argon gas source 6, keep the pressure of the gas cylinder at 0.5 MPa, feed in argon gas with a flow rate of 2m ³ /h, and purge and replace System for 10 minutes; turn on the plasma generator power supply 1, rotate the current regulator to make the current value at 115A, press the start switch, and generate an argon plasma torch. At this time, the voltage value shows about 100V, and the argon plasma can be seen from the observation window Body arc, stable for 1min; then rotate the current regulator to increase the current to 220A, turn on the hydrogen source 7 and the methane gas source 8, maintain the pressure of the gas cylinder at 0.5MPa, and slowly send in hydrogen gas 1.2 from the flow meter 10 (air calibration) m ³ /h, methane 1.2m ³ /h, at this time, the voltage rises to 220V, and then rotate the current regulator to adjust the current to 260A, at this time, the plasma jet discharge power is 60KW, and the mixed discharge forms a plasma jet; turn on the trichloro Boron trichloride gas source 9, the system is heated by boron trichloride heating source 11 to a constant temperature of 60°C, boron trichloride gas supply pressure is 0.5MPa, slowly feed boron trichloride at about 6kg/h; boron trichloride is sprayed into Plasma jet, and the ionized and dissociated hydrogen and methane in the plasma gas phase synthesis reaction, space to generate solid B ₄ C and gaseous HCl; solid B ₄ C is jetted to the cooling wall of the cooling powder collector 4 along with the air flow for quenching Deposit to form nano-boron carbide powder and deposit it to the powder accumulation tank for collection; part of the nano-boron carbide powder enters the water absorption gas-solid separation powder collector 5 driven by the airflow, the powder is absorbed by water and the gas overflows, the powder is collected and washed , obtain nanometer boron carbide powder after drying; Tail gas HCl is processed by tail gas spray absorption tower 12; Reaction continues 30min, the boron carbide powder totaling 185g that powder accumulation tank and water absorption gas-solid separation powder collector 5 collect; Based on the boron supply-output ratio calculation, the recovery rate is greater than 68%. The obtained boron carbide powder product is qualitatively analyzed by XRD and detected by SEM, EDS and ICP. It shows that the boron carbide powder has a particle size of 30-80nm and a purity of more than 99% (of which: the oxygen content is less than 0.5%, and the total metal ion content is less than 300ppm).

In the above examples, argon is used to start the arc and mixed with hydrogen and methane to form an arc plasma jet with a temperature higher than 4000°C. At this temperature, most of hydrogen and methane are dissociated into hydrogen atoms with extremely high reduction activity. and carbon atoms (partially ionized into ions); gaseous BCl ₃ is quickly mixed with the plasma jet to form a reaction system with a temperature greater than 2000°C, and under the action of temperature radiation and a large number of high-energy active particles, boron trichloride quickly breaks bonds and Collision and recombination with hydrogen atoms and carbon atoms in space completes the reduction reaction to generate HCl and boron carbide; because hydrogen, methane, and boron trichloride systems can generally break bonds at 1150 ° C to generate boron carbide, therefore, in the plasma generation Due to the ultra-high temperature and a large number of high-energy active particles, the efficiency and speed of the plasma gas phase synthesis reaction are much higher than the traditional method. The reaction carried out in the reactor 3 is as follows:

_4BCl3 + _4H2 + _CH4 → _B4C +12HCl;

_4BCl3 +8H+C→ _B4C +12HCl;

Argon and "hydrogen and methane" mixed gas are respectively fed from the bottom of the cathode and the top of the anode of the plasma generator 2 in a circular tangential manner, which can ensure the stability of the plasma arc and plasma jet; The top of the device 3 is fed in a symmetrical manner to increase the uniformity of reaction gas mixing while ensuring the cutting kinetic energy of boron trichloride.

In the above examples, the flow rate of argon is 1.5-2 m ³ /h, and the gas supply pressure of argon, hydrogen, methane, and boron trichloride is 0.3-0.5 MPa. This condition is to ensure that the plasma arc (jet) continues The stability and sufficient efficiency of the gas phase synthesis reaction are the basis for ensuring the gas injection rate related to the particle size; at the same time, the volume flow ratio of hydrogen, methane, and boron trichloride is 4 to 6:1:4; a slight excess of hydrogen is helpful In order to improve the conversion rate of boron; while the volume flow ratio of methane and boron trichloride is kept at 1:4, so as to avoid free boron or free carbon in boron carbide powder.

When the ratio and flow rate of the working gas remain unchanged, the discharge power of the plasma generating power supply is increased, and the plasma temperature will inevitably rise, and the degree of ionization and dissociation of hydrogen and methane will also increase accordingly, and the high-energy active particles produced in the plasma will Therefore, the efficiency of the reaction under high power and the yield of boron carbide are also greatly increased; after the reaction gas completes the gas phase synthesis reaction in the reactor 3, the generated solid B ₄ C nucleates and grows uniformly in the space, and grows with the The air flow is sprayed onto the cooling wall of the cooling powder collector 4 to quench the deposition and stop the crystallization growth, thereby forming nano-sized boron carbide powder, and sinking along the conical barrel body to the powder accumulation tank at the bottom of the powder collector; if necessary , the sight glass window on the cooling powder collector 4 can be opened to brush the powder adhered to the inner wall into the powder accumulation tank for collection;

After the reactant is sprayed out from the reactor 3, some powder overflows the cooling powder collector 4 driven by the gas, and is introduced into the water absorption gas-solid separation powder collector 5 for gas-solid separation, and the bottom extension pipe 14 extends into the 5cm below the water surface can effectively absorb the overflowing boron carbide powder, and can easily overflow the gas, so as to achieve the purpose of gas-solid separation efficiently without causing resistance to the reaction flow. Compared with the commonly used screen type and cloth bag type gas solid separator, with better effect and smoother reaction; the boron carbide powder absorbed by water is collected, washed with deionized water and dried in vacuum at 100°C for 2 hours; the HCl treated by the tail gas spray absorption tower 12 The gas can be used as a by-product of hydrochloric acid.

The basic principles and main features of the present invention and the advantages of the present invention have been shown and described above. Those skilled in the industry should understand that the present invention is not limited by the above-mentioned embodiments. What are described in the above-mentioned embodiments and the description only illustrate the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will also have Variations and improvements all fall within the scope of the claimed invention. The protection scope of the present invention is defined by the appended claims and their equivalents.

Claims (10)

1. The method for preparing high-purity nano-boron carbide powder by plasma chemical vapor-phase synthesis is characterized in that the device for preparing high-purity nano-boron carbide powder by plasma chemical vapor-phase synthesis is used to prepare high-purity nano-boron carbide powder, and the specific steps are as follows: 1) Introduce argon gas into the plasma generator, start the plasma generating power supply to generate arc discharge, and form a stable argon plasma arc; 2) Then introduce hydrogen and methane into the plasma generator, and mix and discharge with argon plasma to form a plasma jet; 3) Then the plasma jet is introduced into the reactor below the plasma generator, and at the same time, boron trichloride gas is introduced from the boron trichloride inlet hole of the reactor, and the gas-phase synthesis reaction is completed by colliding with the plasma jet and quickly mixed to form a solid state in space. B ₄ C and gaseous HCl; 4) The solid B ₄ C generated in step 3) is sprayed with the airflow to the cooling wall of the cooling powder collector for quenching deposition to form nano boron carbide powder; 5) Part of the nano boron carbide powder in step 4) is driven by the airflow into the water absorption gas-solid separation powder collector, the powder is absorbed by water and the gas overflows, and finally the powder is collected and washed and dried to obtain nano boron carbide powder body. 2. The method for preparing high-purity nano-boron carbide powder by plasma chemical vapor synthesis according to claim 1, characterized in that, in step 1), the flow rate of argon gas is 1.5-2m ³ /h, the pressure is 0.3-0.5MPa, The power of starting the plasma generating power supply to generate arc discharge is 10KW, the current is 105-115A, and the voltage is 90-100V. 3. The method for preparing high-purity nano-boron carbide powder by plasma chemical vapor synthesis according to claim 1, characterized in that, in step 2), the volume flow ratio of hydrogen to methane is 4 to 6:1, and the gas supply The pressure is 0.3-0.5MPa, and the power supply of the plasma generator is adjusted so that the output power is 10-100KW. 4. The method for preparing high-purity nano-boron carbide powder by plasma chemical vapor synthesis according to claim 1, characterized in that, in step 3), the volume flow ratio of boron trichloride and methane is 4:1, three The boron chloride heating temperature is 40-60°C, and the boron trichloride gas supply pressure is 0.3-0.5MPa. 5. the method for preparing high-purity nano-boron carbide powder by plasma chemical vapor synthesis according to claim 1, is characterized in that the device for preparing high-purity nano-boron carbide powder by plasma chemical vapor synthesis comprises plasma generation power supply, Plasma generator, reactor, cooling powder collector, water absorption gas-solid separation powder collector, tail gas absorber, argon gas source, hydrogen gas source, methane gas source and boron trichloride gas source, the plasma generator is composed of A semi-closed container made of PTFE insulation, the upper end of the semi-closed container is closed and the lower end is open, and a cathode made of cerium-tungsten material is installed on the upper part of the semi-closed container, and an anode made of copper material is installed on the lower part of the semi-closed container. The negative electrode of the plasma generator power supply is connected, and the anode is connected to the positive electrode of the plasma generator power supply; at the same time, an argon inlet hole is provided at the bottom of the cathode of the plasma generator for introducing argon gas through an argon source, and an argon inlet hole is provided at the top of the anode of the plasma generator for passing hydrogen gas. The mixed gas inlet hole of introducing hydrogen from the source and introducing methane through the methane source; the plasma generator has a built-in cooling circulating water system for cooling protection; the reactor is sealed and connected with the lower end of the plasma generator, and two A boron trichloride air inlet hole for introducing boron trichloride gas through a boron trichloride gas source, a boron trichloride heating source for heating and vaporizing boron trichloride is arranged outside the boron trichloride gas source, The lower port of the reactor is placed in the cooling powder collector, and the outer jacket of the cooling powder collector is provided with a circulating cooling water system. The water absorbing gas-solid separation powder collector is connected to the outlet of the cooling powder collector, and the The outlets of the four gas sources, hydrogen source, methane gas source and boron trichloride gas source are respectively provided with flowmeters, and the water absorption gas-solid separation powder collector is connected with the tail gas absorber. 6 . The method for preparing high-purity nano boron carbide powder by plasma chemical vapor synthesis according to claim 5 , wherein the plasma generating power supply is a DC arc power supply with an output power of 10-100 kW. 7. The method for preparing high-purity nano-boron carbide powder by plasma chemical vapor synthesis according to claim 5, wherein the argon gas inlet and the mixed gas inlet are all ring-shaped tangent structures. 8. the method for preparing high-purity nanometer boron carbide powder by plasma chemical vapor synthesis according to claim 5, is characterized in that, described reactor is the tubular reactor that contains water-cooled outer jacket and through-hole graphite tube constitutes . 9. plasma chemical vapor synthesis according to claim 5 prepares the method for high-purity nanometer boron carbide powder, it is characterized in that, described cooling powder collection device is by the cylinder barrel body that the top contains symmetrical opening mirror, the middle part is The sedimentation conical barrel body and the bottom are composed of powder accumulation tanks. 10. the method for preparing high-purity nano-boron carbide powder by plasma chemical vapor synthesis according to claim 5, is characterized in that, the described water absorption gas-solid separation powder collector is provided with for connecting cooling powder collector outlet Outrigger pipe and outlet pipe for connecting exhaust absorber.