CN116037944A - Method for preparing micron-scale/nano-scale graded spherical copper powder by using plasma - Google Patents

Abstract

The invention discloses a method for preparing micron/nanometer graded spherical copper powder by plasma. The raw material copper powder with irregular shape is placed in a vibrating powder feeder, and the raw material copper powder is fed through the vibrating powder feeder and carrier gas. Into the reaction chamber, the pressure of the reaction chamber is controlled at 10-15 psig, the raw copper powder is vaporized into copper vapor by the plasma flame moment emitted by the plasma generator located at the top center of the reaction chamber, and the copper vapor contacts the reaction with a temperature control device The chamber wall is cooled and spheroidized to obtain spherical copper powder, wherein the nano-scale spherical copper powder adheres to the wall of the reaction chamber, and the micron-scale spherical copper powder falls into the bottom collection tank located below the reaction chamber wall; the bottom The top side of the collection tank is provided with an exhaust port. The copper powder prepared by the present invention not only has two scales of micron scale/nano scale, but also has the characteristics of good sphericity, high spheroidization rate, and low impurity content. .

Description

A method for plasma preparation of micron/nanometer graded spherical copper powder

technical field

The invention belongs to the field of metal technology material preparation, and in particular relates to a method for preparing micron-level/nano-level graded spherical copper powder by plasma.

Background technique

Copper is an essential trace element for human life, and it participates in various physiological mechanisms, and metal copper has excellent plasticity, wear resistance, corrosion resistance and electrical and thermal conductivity, so copper has been widely used in transportation, aerospace, Electronic information, surgical biomaterials and energy fields. However, the traditional metal manufacturing method has a low material utilization rate and a simple product structure, which cannot meet the market demand brought about by technological progress. Therefore, additive manufacturing technology came into being, which provides a feasible way for low-cost and high-efficiency preparation of three-dimensional complex parts. The metal powder used for additive manufacturing requires high sphericity and good fluidity. Obviously, ordinary copper powder cannot meet the requirements.

As a special high-performance powder, spherical copper powder can eliminate the influence of agglomeration to the greatest extent, and the internal defects of the powder can be improved. At the same time, the spherical copper powder is evenly distributed, the surface morphology is regular, and the bulk density of the powder is significantly increased. . Among them, micron-sized spherical copper powder can be used in the field of additive manufacturing, and nano-sized spherical copper powder also plays a pivotal role in industrial production fields such as metal injection molding, ball grid electronic packaging, and thermal spraying. At present, the mainstream technologies for preparing micro/nano spherical copper powder at home and abroad are still chemical reduction, electrochemical, atomization and other methods. With the development of science and technology, in order to improve the comprehensive performance of spherical copper powder, various methods of preparing nano-copper powder emerge in an endless stream. Plasma is often used as a heat source due to its extremely high energy density, extremely high temperature, no electrode contamination, and flexible control, making it an excellent method for preparing spherical metal powders with stable composition, high sphericity, and good dispersion . The heating efficiency of the plasma is extremely high, and its central temperature can reach up to 10,000°C, which is enough to melt or even vaporize all refractory metal particles when passing through the heating zone. The cooling speed leaves the heating zone, so as to realize the rapid melting and rapid cooling of the particles, and finally obtain the spherical powder with high sphericity and good fluidity.

For example, the Chinese invention patent CN109513944A melts and forges a copper alloy with a certain chemical composition into a bar, and then uses a plasma rotating electrode powder making equipment to melt the alloy bar into droplets, and then breaks it into smaller particles under the action of centrifugal force. The liquid droplets are quickly solidified into spherical powder, and the desired high-purity, high-sphericity copper alloy powder is obtained. Chinese invention patent CN109824052A uses plasma as a heat source and high-purity gas MCl _x as a raw material. When the raw material gas passes through the plasma high-temperature zone, it undergoes a gas-phase reduction reaction with H ₂ . Quickly condense into the desired nanopowder.

In summary, the above-mentioned methods generally have different problems such as the inability to prepare micron-scale/nano-scale spherical powders at the same time, and the prepared powders are easy to agglomerate and oxidize, and the product stability is poor. and diverse requirements. Therefore, it is necessary to develop a method that has a simple preparation process and can simultaneously prepare high-performance micron-scale/nano-scale spherical powders.

Contents of the invention

Aiming at the various problems existing in the above-mentioned technologies, the present invention aims to provide a method for preparing micron-scale/nano-scale graded spherical copper powder by plasma. The method of the present invention is simple and fast, and can simultaneously produce micron-scale and nano-scale powder, and the prepared micron-scale and nano-scale powders have high sphericity, good fluidity and high purity.

In order to achieve the above object, the present invention adopts the following technical solutions:

The invention discloses a method for preparing micron-level/nano-level graded spherical copper powder by plasma. The raw material copper powder of irregular shape is placed in a vibrating powder feeder, and the raw material copper powder is sent into the reaction through the vibrating powder feeder and carrier gas. Chamber, control the pressure of the reaction chamber to 10-15 psig, the raw copper powder is vaporized into copper vapor by the plasma flame moment emitted by the plasma generator located at the top center of the reaction chamber, and the copper vapor contacts the reaction chamber wall with a temperature control device Cooling spheroidization obtains spherical copper powder, wherein the nano-scale spherical copper powder adheres to the wall of the plasma reaction chamber, and the micron-scale spherical copper powder falls into the bottom collection tank located below the plasma reaction chamber wall; The top side of the bottom collection tank is provided with an exhaust port.

The present invention is based on the induction plasma spheroidization pulverizing system. The raw copper powder is usually axially transported to the center of the plasma discharge, and when the powder particles touch the plasma, they are instantly heated and melted or directly vaporized. The vaporized copper vapor contacts the low-temperature zone and the reactor wall with cooling water firstly liquefies into fine copper droplets, and then solidifies under the action of surface tension during the rapid condensation process. By adjusting the pressure in the reaction chamber and The flow rate of the gas makes most of the light-weight and high-viscosity nano-scale spherical copper powder adhere to the wall of the reactor chamber, and a small part of the light-weight nano-scale spherical copper powder is removed by the exhaust port, while the heavy and micron-scale copper powder The spherical copper powder falls into the bottom collection tank, first collects the micron-sized spherical copper powder in the bottom collection tank, and then obtains the nanometer-sized spherical copper powder on the cavity wall through the spiral scraping device added inside the reactor. The method can simultaneously prepare spherical powders of micron and nanometer levels.

The plasma gas at the exit of the plasma torch, which contains powder molten droplets or vapor, is further processed to remove the carrier gas from the gas stream before it enters the exhaust port to remove impurity gases. Since no electrode material is in contact with the plasma gas, the present invention provides a pollution-free powder processing method. This property is especially suitable for the preparation of high-purity powders, with almost no restrictions on the melting point of the powder. Inductively coupled high-frequency electrodeless plasma discharge can also reduce impurities through their volatilization or reactive volatilization. Impurities with lower boiling points escape from the granular matrix during preparation. This process can directly generate micron/nanometer spherical copper powder in one step from large particle size copper powder or reduced copper powder, while greatly reducing the impurity content in the powder.

In a preferred solution, the particle size of the raw copper powder is 100-400 mesh.

In a preferred solution, the raw copper powder is firstly reduced to obtain reduced copper powder, and then the reduced copper powder is placed in a vibrating powder feeder, and the oxygen content of the reduced copper powder is ≤ 800 ppm.

Further preferably, during the reduction treatment, the hydrogen flux is 500-2000mL/min, preferably 1000mL/min, the temperature of the reduction treatment is 200-400°C, preferably 250°C, and the reduction treatment time is 3~6h, preferably 4h.

In the actual operation process, before the raw copper powder is sent into the reaction chamber, the reaction chamber is first replaced with gas, all impurity gases in the device are discharged, and a protective atmosphere is filled at the same time to prevent the outside air from entering, and the vacuum leak of the device and the high-pressure system are detected. leak test.

In a preferred solution, when the vibrating powder feeder and the carrier gas send the raw copper powder into the reaction chamber, the vibration frequency is controlled to be 90-120 Hz, preferably 115 Hz, and the vibration amplitude is 20-90 μm, preferably 60-68 μm; the powder feeding rate It is 1.5 to 80 g/min, preferably 6 to 7.5 g/min.

In a preferred solution, the carrier gas is selected from at least one of argon, nitrogen, and helium.

In a preferred solution, the reaction chamber is fed with a non-oxidizing atmosphere as the plasma gas, the non-oxidizing atmosphere is selected from argon, or a mixed atmosphere of argon and hydrogen, and the ratio of the flow rate of the carrier gas to the plasma gas is 1 ~12:4~35, preferably 1:2.

Further preferably, the hydrogen flow rate is 0-10 slpm, preferably 7.5 slpm, and the argon flow rate is 10-107 slpm, preferably 40-46 slpm.

In the actual operation process, when the plasma is in an excited state, the plasma gas is introduced, and the actual power of the equipment reaches the preset value.

Further preferably, when the copper powder is selected from non-reduced copper powder, the non-oxidizing atmosphere is selected from a mixed atmosphere of argon and hydrogen.

In a preferred solution, the power of the plasma generator is 10-15kw.

In a preferred solution, the inner wall of the reaction chamber is provided with a spiral powder scraping device. In the actual operation process, first collect the micron-sized spherical copper powder in the bottom collection tank, and then add a spiral powder scraping device inside the reactor to obtain nano-sized spherical copper powder on the cavity wall.

Principles and advantages

The present invention adopts reduced copper powder or performs hydrogenation reduction pretreatment on raw copper powder to obtain reduced copper powder with lower oxygen content. Under the action of the magnetic field generated by the applied current, the inert gas argon used is ionized to form a stable high-density plasma flow, and its temperature is extremely high, up to 11000 °C. When the pretreated reduced copper powder is transported by the vibrating powder feeder and the carrier gas, and reaches the high temperature range of the plasma flame moment, the copper powder with a low melting point will be vaporized instantly, and the copper vapor will instantly fill the entire reaction chamber. After contacting the wall of the reaction chamber with a temperature control device, the copper vapor is first converted into molten droplets, which are spheroidized under the action of surface tension. By adjusting the air pressure in the reaction chamber and the flow rate of various gases, most of the light-weight and high-viscosity nano-scale spherical copper powder adheres to the wall of the reactor cavity, and a small part of the light-weight nano-scale spherical copper powder is exhausted. The heavy, micron-sized spherical copper powder falls into the bottom collection tank, first collects the micron-sized spherical copper powder in the bottom collection tank, and then obtains nano Size of spherical copper powder.

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

1. The present invention can realize the simultaneous preparation of nano-scale and micron-scale spherical copper powder. The selected raw material powder has a wide particle size range and low impurity content requirements. The obtained powder has good sphericity and high spheroidization rate. Improves powder purity.

2. The technological process of the present invention is simple, and the "one-step" preparation method greatly shortens the experimental cycle and improves the powder collection rate. At the same time, the actual working power can be changed by changing the working current to achieve control of the plasma moment temperature and product particle size Effect.

Description of drawings

Fig. 1 is a schematic structural diagram of a device for preparing nano-spherical copper powder by plasma according to the present invention.

Fig. 2 is a scanning electron micrograph of copper powder before plasma spheroidization in Example 1 of the present invention.

Fig. 3 is a scanning electron micrograph of the micron-spherical copper powder prepared in Example 1 of the present invention.

FIG. 4 is a scanning electron micrograph of the nano-spherical copper powder prepared in Example 1 of the present invention.

FIG. 5 is a scanning electron micrograph of the micron-spherical copper powder prepared in Comparative Example 1 of the present invention.

Detailed ways

In order to facilitate the understanding of the present invention, the invention will be described more comprehensively and in detail below in conjunction with the accompanying drawings and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

Unless otherwise defined, all technical terms used hereinafter have the same meanings as commonly understood by those skilled in the art. The terminology used herein is only for the purpose of describing specific embodiments, and is not intended to limit the protection scope of the present invention.

Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

Example 1

Preparation of spherical copper powder (reduced copper powder, without adding hydrogen):

Firstly, the raw copper powder with a purity of 99.9% and a particle size of 300 mesh (48 μm) was placed in a tubular hydrogen furnace. According to the hydrogenation process route, the temperature in the furnace was controlled at 250 °C, the hydrogen flux was set at 1000 mL/min, and the temperature was constant. 4 hours; second, put the obtained reduced copper powder into the vibrating powder feeder, turn on the cooling water of the equipment, discharge all impurities and gases in the device through the gas purification system, and fill in an inert protective atmosphere of argon at the same time to control the argon The flow rate is 17slpm; thirdly, after the system self-test has no vacuum leakage and the air and other impurity gases in the reaction chamber are exhausted, turn off the argon gas and turn on the vacuum pump; thirdly, adjust the vibration frequency to 115Hz and the vibration amplitude to 68μm to control the actual powder feeding rate of copper powder in this state is 6g/min; Fourth, open the argon gas source and adjust the carrier gas pressure regulating valve to 60mm (5slpm), the plasma gas pressure regulating valve to 40mm (10slpm), Argon pressure regulating valve to 80mm (28slpm), manually set the pressure in the reaction chamber to 3.80psig; fifth, switch to high frequency mode, increase the voltage value to 4V, after the actual current stabilizes to 2.2A, increase the pressure in the reaction chamber to While stabilizing the actual current value at 7.0 psig, the pressure is increased by 2.0 psig each time and repeat the above steps until the pressure reaches 15 psig; sixth, when the actual power and the pressure in the reaction chamber are stabilized, the temperature of the plasma flame moment tends to be stable at this time, and start to The set powder feeding rate is constant; seventh, after the powder feeding is completed, turn off the high-frequency mode, turn off all air sources, and the system will automatically turn off and stop. After the whole device cools down to room temperature, take out the powder in the collection tank and pass the reaction The spiral powder scraping device added inside the device collects the nano-spherical copper powder adhering to the wall of the reaction chamber.

Fig. 1 is a schematic structural diagram of a device for preparing nano-spherical copper powder by plasma according to the present invention. FIG. 2 is a SEM microscopic photo of the raw copper powder in this embodiment. Fig. 3 is the SEM microscopic appearance photograph of the micron spherical copper powder prepared in the present embodiment, as can be seen from Fig. 3, the spherical degree of micron spherical copper powder is good, and surface finish is good, and particle size distribution is uniform, and most of powder particle diameters are in 20 Between -50μm. Fig. 4 is the SEM microscopic topography photo of the nano-spherical copper powder prepared in this embodiment, as can be seen from 4, the nano-spherical copper powder has good sphericity, good surface finish, and particle size distribution is within 100nm.

Example 2

Preparation of spherical copper powder (non-reduced copper powder, hydrogenation):

First, put copper powder with a purity of 99.9% and a particle size of 300 mesh (48 μm) into the vibrating powder feeder, turn on the cooling water of the equipment, discharge all impurity gases in the device through the gas purification system, and fill it with an inert protective atmosphere of argon , control the flow rate of argon gas to 17slpm; secondly, after the system self-checks that there is no vacuum leak and the impurity gas such as air in the reaction chamber is exhausted, turn off the argon gas and turn on the vacuum pump; thirdly, adjust the vibration frequency to 115Hz through the powder feeding controller , The vibration amplitude is 68μm to control the actual powder feeding rate of copper powder in this state to 6g/min; Fourth, turn on the argon gas source and adjust the carrier gas pressure regulating valve to 60mm (5slpm), the plasma gas pressure regulating valve to 40mm (10slpm), argon pressure regulating valve to 80mm (28slpm), manually set the pressure in the reaction chamber to 3.80psig; fifth, switch to high frequency mode, increase the voltage value to 4V, after the actual current stabilizes to 2.2A, increase When the pressure in the reaction chamber reaches 7.0 psig, the actual current value is stabilized, and the pressure is increased by 2.0 psig each time. Repeat the above steps. When the pressure in the reaction chamber increases to 11.0 psig, turn on the hydrogen gas source and adjust the hydrogen pressure regulating valve to 15 mm (7.5 slpm). Maintain the actual current to 2.23A, and then repeat the above steps by increasing the pressure value by 1.0 psig each time. The specific power, pressure and hydrogen flow comparison table are shown in Table 1; sixth, when the actual power and the pressure in the reaction chamber are stable, the plasma flame moment The temperature tends to be stable, and start to feed powder at the previously set powder feeding rate; seventh, after the powder feeding is completed, turn off the high-frequency mode, turn off all air sources, and the system will automatically turn off and stop. After the whole device cools down to room temperature, take it out The micron-spherical copper powder in the collection tank is collected by the spiral powder scraping device added inside the reactor to collect the nano-spherical copper powder adhering to the wall of the reaction chamber.

Because the copper powder is easy to oxidize and the hydrogenation reduction treatment was not carried out before the spheroidization experiment, and a large amount of hydrogen gas was introduced in the experiment, resulting in high humidity, high viscosity and easy agglomeration of the prepared powder, but the micron and nanometer spherical copper powder was still obtained. Among them, the spherical copper powder has a good sphericity, the particle size of most micron-sized copper powder is about 50 μm, and the particle size distribution of the nano-spherical copper powder is within 100 nm.

Table 1 Power and air pressure and hydrogen flow comparison table

Comparative example 1

Preparation of spherical copper powder (reduce plasma spheroidizing power to 9KW, reaction chamber pressure to 9.0psig):

First, put copper powder with a purity of 99.9% and a particle size of 300 mesh (48 μm) into the vibrating powder feeder, turn on the cooling water of the equipment, discharge all impurity gases in the device through the gas purification system, and fill it with an inert protective atmosphere of argon , control the flow rate of argon gas to 17slpm; secondly, after the system self-checks that there is no vacuum leak and the impurity gas such as air in the reaction chamber is exhausted, turn off the argon gas and turn on the vacuum pump; thirdly, adjust the vibration frequency to 110Hz through the powder feeding controller , The vibration amplitude is 60μm to control the actual powder feeding rate of copper powder in this state to 8g/min; Fourth, turn on the argon gas source and adjust the carrier gas pressure regulating valve to 60mm (5slpm), the plasma gas pressure regulating valve to 40mm (10slpm), the argon pressure regulating valve to 80mm (28slpm), manually set the pressure in the reaction chamber to 3.80psig; fifth, switch to high frequency mode, increase the voltage value to 4V, after the actual current stabilizes to 2.15A, increase When the pressure of the reaction chamber reaches 7.0 psig, the actual current value is stabilized, and the pressure is increased by 2.0 psig to repeat the above steps. When the pressure of the reaction chamber increases to 9.0 psig, the pressure is stopped, and the plasma spheroidizing power is adjusted to 9KW; sixth, when the actual After the power and the air pressure in the reaction chamber are stabilized, the temperature of the plasma flame moment tends to be stable at this time, and the powder feeding rate starts to be constant at the previously set powder feeding rate; seventh, after the powder feeding is completed, turn off the high-frequency mode, turn off all gas sources, and the system After the whole device is cooled to room temperature, the powder in the collection tank is taken out, and the nano-spherical copper powder adhering to the wall of the reaction chamber is collected through the spiral powder scraping device added inside the reactor.

Fig. 5 is the SEM microscopic topography photo of the micron spherical copper powder prepared in the present embodiment, as can be seen from Fig. 5, due to insufficient air pressure, the falling nanoparticles cannot be completely removed by the exhaust port, and fall in the bottom collecting tank. As a result, some nanopowder exists in the prepared micron spherical copper powder.

Claims (10)

1. A method for preparing micron-scale/nano-scale graded spherical copper powder by using plasma is characterized by comprising the following steps: placing raw copper powder in an irregular form into a vibration powder feeder, feeding the raw copper powder into a reaction chamber through the vibration powder feeder and carrier gas, controlling the pressure of the reaction chamber to be 10-15 psig, enabling the raw copper powder to be gasified into copper vapor by plasma flame moment emitted by a plasma generator positioned at the center of the top of the reaction chamber, enabling the copper vapor to contact with a reaction chamber wall with a temperature control device to be cooled and spheroidized to obtain spherical copper powder, wherein nano-scale spherical copper powder is adhered to the wall of the plasma reaction chamber, and enabling the micro-scale spherical copper powder to fall into a bottom collecting tank positioned below the wall of the plasma reaction chamber; the top side of the bottom collecting tank is provided with an exhaust port.

2. The method for preparing micron/nanometer grade graded spherical copper powder by using the plasma according to claim 1, wherein the method comprises the following steps: the grain diameter of the raw copper powder is 100-400 meshes.

3. A method for preparing micron/nanometer grade graded spherical copper powder by using plasma according to claim 1 or 2, wherein: the raw copper powder is subjected to reduction treatment to obtain reduced copper powder, and then the reduced copper powder is placed in a vibration powder feeder, wherein the oxygen content of the reduced copper powder is less than or equal to 800ppm.

4. A method for preparing micron/nanometer grade graded spherical copper powder by using plasma according to claim 3, wherein: during the reduction treatment, the hydrogen flux is 500-2000 mL/min, the temperature of the reduction treatment is 200-400 ℃, and the time of the reduction treatment is 3-6 h.

5. The method for preparing micron/nanometer grade graded spherical copper powder by using the plasma according to claim 1, wherein the method comprises the following steps: when the vibration powder feeder and carrier gas feed the raw copper powder into the reaction chamber, the vibration frequency is controlled to be 90-120 Hz, the vibration amplitude is 20-90 mu m, and the powder feeding speed is 1.5-80 g/min.

6. A method for preparing micron/nanometer grade graded spherical copper powder by using plasma according to claim 1 or 5, wherein the method comprises the following steps: the carrier gas is selected from at least one of argon, nitrogen and helium.

7. The method for preparing micron/nanometer grade graded spherical copper powder by using the plasma according to claim 1, wherein the method comprises the following steps: the non-oxidizing atmosphere is introduced into the reaction chamber as plasma gas, wherein the non-oxidizing atmosphere is selected from argon or a mixed atmosphere of argon and hydrogen, the flow ratio of carrier gas to plasma gas is 1-12:4-35, the flow of hydrogen is 0-10 slpm, and the flow of argon is 10-107 slpm.

8. The method for preparing micron/nanometer grade graded spherical copper powder by using the plasma according to claim 7, wherein the method comprises the following steps: when the raw copper powder is selected from non-reducing copper powder, the non-oxidizing atmosphere is selected from a mixed atmosphere of argon and hydrogen.

9. The method for preparing micron/nanometer grade graded spherical copper powder by using the plasma according to claim 1, wherein the method comprises the following steps: the power of the plasma generator is 10-15 kw.

10. The method for preparing micron/nanometer grade graded spherical copper powder by using the plasma according to claim 1, wherein the method comprises the following steps: the inner wall of the reaction chamber is provided with a spiral powder scraping device.

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