A method for preparing nano-nickel powder using plasma

Abstract

This invention provides a method for preparing nano-nickel powder using plasma. The method includes: using a nickel-containing material as the anode, passing a plasma working gas through a vacuum reaction chamber, conducting an arc discharge until the reaction is complete, evacuating the reaction chamber and introducing a passivation gas, and obtaining nano-nickel powder after passivation treatment. The plasma working gas is a mixture of oxygen, hydrogen, and a first gas, wherein the first gas is any one or more of argon, nitrogen, and helium. The nano-nickel powder prepared by this invention has good dispersibility and uniform particle size, overcoming the problem of severe agglomeration in nano-nickel powder prepared by the original growth path.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy, and more specifically, relates to a method for preparing nano-nickel powder using plasma. Background Technology

[0002] With the adjustment of the electronic product market structure, the rapid development of mobile communication devices and portable computers has created a huge market space for multilayer ceramic capacitors (MLCCs). Traditional MLCC electrode materials are Pd / Ag alloys or pure Pd. However, due to the high price of imported pastes for the most widely used Pd internal electrodes, replacing Pd / Ag electrodes with base metal materials is a significant trend in MLCC development. To balance high capacity and low cost, base metal nickel electrodes are the best choice. Based on current MLCC development trends, to meet the requirements of improved processes such as screen printing, stacking, and sintering, as well as the stability required for actual use, the nickel particles used in the electrodes must have high purity, small particle size, uniform particle size, high dispersion, and certain oxidation resistance.

[0003] There are two main categories of methods for preparing high-quality nano-nickel powder: chemical methods and physical methods. Chemical methods can be further divided into chemical vapor deposition (CVD) and liquid-phase methods. Currently, the industrially mass-produced CVD methods include nickel carbonyl pyrolysis and gaseous chloride hydrogen reduction, while the industrially mass-produced liquid-phase method is electrolysis. Chemical methods offer the advantage of high yield, but their widespread application is limited by drawbacks such as easy contamination, low product purity, and tendency to agglomerate. Physical methods utilize physical means such as electricity, heat, magnetism, and force to refine nickel metal into nanoparticles. These methods mainly include plasma methods, mechanical ball milling, electro-explosion methods, ultrasonic methods, and laser-induced evaporation methods. The physical methods that can be industrially mass-produced include plasma methods, mechanical ball milling, and electro-explosion methods. Currently, physical methods are widely used in the preparation of nano-nickel powder due to their environmental friendliness, uniform particle size, and high product purity. Among the many physical methods for preparing nano-nickel powder, the plasma method is highly favored in the field of preparing high-quality nano-nickel powder due to its advantages such as high chemical activity, controllable reaction atmosphere, high temperature gradient, high product purity, high sphericity, and ease of large-scale production. Therefore, the plasma method for preparing metal nanomaterials has irreplaceable advantages in the preparation of high-quality nano-nickel powder because of its high purity, high sphericity, and small average particle size. However, the poor dispersibility and wide particle size distribution of nano-nickel powder prepared by existing plasma methods prevent its direct application in MLCC electrodes. Summary of the Invention

[0004] In view of the shortcomings of the prior art, one of the objectives of this invention is to solve one or more problems existing in the prior art. For example, one objective of this invention is to provide a method for preparing nano-nickel powder with good dispersibility and uniform particle size distribution.

[0005] This invention discloses a method for preparing nano-nickel powder using plasma, which may include the following steps: using a nickel-containing material as the anode, passing a plasma working gas through a vacuum reaction chamber, arcing until the reaction is complete, evacuating the reaction chamber and introducing a passivation gas, and obtaining nano-nickel powder after passivation treatment. The plasma working gas is a mixture of oxygen, hydrogen and a first gas, wherein the first gas is any one or more of argon, nitrogen and helium.

[0006] Furthermore, in the plasma working gas, the volume ratio of hydrogen and the first gas to oxygen can be 95-99:1-5, and hydrogen can account for 1 / 10 to 1 / 2 of the total volume of hydrogen and the first gas.

[0007] Furthermore, the method may also include controlling the distance between the anode and the cathode to a constant value between 1 mm and 6 mm.

[0008] Furthermore, the distance between the anode and cathode can be controlled by adjusting the anode lifting position.

[0009] Furthermore, the arc discharge includes a control current of 20A to 300A and an arc discharge time of 1min to 60min.

[0010] Furthermore, the passivating gas can be air at a pressure of 5 kPa to 50 kPa, and the passivation time can be 1 h to 10 h.

[0011] Furthermore, the pressure of the plasma working gas can be 30 kPa to 80 kPa.

[0012] Furthermore, the anode can be a nickel rod or a nickel block.

[0013] Furthermore, the cathode can be a tungsten rod.

[0014] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0015] (1) The method of the present invention uses a mixed gas containing hydrogen as plasma gas, which makes the arc region temperature high and the arc stability high, and has the advantages of high preparation efficiency and environmentally friendly process.

[0016] (2) By using a mixed gas containing oxygen and hydrogen as the working gas, this invention changes the original growth path of nano-nickel powder evaporation-coagulation-growth, and the growth path is evaporation-oxidation-reduction-growth, thereby reducing the temperature at which nano-nickel powder is prone to melting or agglomeration during the growth stage, resulting in good dispersibility of the prepared nano-nickel powder and overcoming the problem of severe agglomeration of nano-nickel powder prepared by the original growth path.

[0017] (3) The passivation treatment of the present invention can effectively reduce the activity and surface energy of nano nickel powder, making it difficult for nano nickel powder to sinter and grow under high temperature conditions. Attached Figure Description

[0018] The above and other objects and features of the present invention will become clearer from the following description taken in conjunction with the accompanying drawings, in which:

[0019] Figure 1 This is a scanning electron microscope image of the nickel nanoparticles prepared in Example 1;

[0020] Figure 2 This is a particle size distribution diagram of the nano-nickel powder prepared in Example 1;

[0021] Figure 3 The image shows a scanning electron microscope image of the nickel nanoparticles prepared in Example 2.

[0022] Figure 4 Scanning electron microscope image of the nickel nanoparticles prepared in Example 3;

[0023] Figure 5 This is a scanning electron microscope image of the nickel nanoparticles prepared in Comparative Example 1. Detailed Implementation

[0024] In the following, a method for preparing nano-nickel powder using plasma according to the present invention will be described in detail with reference to the accompanying drawings and exemplary embodiments.

[0025] Specifically, this invention utilizes DC arc plasma to prepare nano-nickel powder. The arc discharge between the electrodes generates a high temperature of 104 K, causing the gas in the reaction chamber to transform into a plasma state, and the metallic nickel anode rapidly sublimates into gaseous atoms. Oxygen in the reaction chamber first reacts with the vaporized nickel to form nickel oxide, which is then reduced and grown in a hydrogen-reducing gas environment to form nickel powder. The nickel powder produced through this reaction process is located at the lower temperature edge of the plasma, and the large temperature gradient within the arc plasma reaction chamber prevents the nickel powder from fusing or agglomerating, thus producing nano-nickel powder with good dispersibility and a narrow particle size distribution.

[0026] This invention provides a method for preparing nano-nickel powder using plasma. In an exemplary embodiment of the method for preparing nano-nickel powder using plasma according to this invention, the method may include:

[0027] Step 1: Using nickel-containing material as the anode, the reaction chamber is evacuated, and then plasma working gas is introduced. The current and voltage are set to perform arc discharge.

[0028] Step 2: After the arc discharge ends, the reaction chamber is evacuated, and then passivation gas is introduced for passivation treatment. The nano-nickel powder on the inner wall of the reaction chamber is collected to obtain nano-nickel powder with good dispersibility and uniform particle size distribution.

[0029] In some implementations, the plasma working gas can be a mixture of oxygen, hydrogen, and a first gas, wherein the first gas can be any one or more of argon, nitrogen, and helium. That is, the plasma working gas can be a mixture of oxygen, hydrogen, and argon; a mixture of oxygen, hydrogen, and nitrogen; or a mixture of oxygen, hydrogen, and helium.

[0030] In some implementations, the volume ratio of hydrogen to the first gas and oxygen in the plasma working gas can be 95–99:1–5, with hydrogen accounting for 1 / 10 to 1 / 2 of the total volume of hydrogen and the first gas. With the above-mentioned proportions of plasma working gas components, on the one hand, the preparation process can achieve an oxidation-reduction-growth process to prepare nano-nickel powder, ensuring that the final prepared nano-nickel powder is metallic nickel, not nickel oxide; on the other hand, the preparation safety can be guaranteed within the above-mentioned proportion range. For example, the volume ratio of hydrogen to the first gas and oxygen can be 96–98:2–4, with hydrogen accounting for 1 / 8 to 1 / 3 of the total volume of hydrogen and the first gas. As another example, the volume ratio of hydrogen to the first gas and oxygen can be 97:3, with hydrogen accounting for 1 / 5 of the total volume of hydrogen and the first gas.

[0031] In some embodiments, the preparation method further includes controlling the distance between the anode and cathode to remain constant. The distance between the anode and cathode can be controlled between 1 mm and 6 mm. Maintaining a constant electrode distance between the anode and cathode is beneficial for arc stability, resulting in a more regular spherical structure for the refractory metal nanoparticles, with small particle size and uniform particle size distribution. For example, the distance between the anode and cathode can be 2 mm, 3 mm, 4 mm, or 5 mm. In some embodiments, a constant distance between the anode and cathode can be achieved by controlling the anode to rise at a uniform rate.

[0032] In some implementations, the arc discharge includes a controlled current of 20A to 300A and an arc discharge time of 1 min to 60 min. Under these current and arc discharge times, the nickel reaction process can be achieved as evaporation-oxidation-reduction-growth, which can reduce the temperature at which the nano-nickel powder is prone to melting or agglomeration during the growth stage, resulting in well-dispersed nano-nickel powder. For example, the arc discharge includes a controlled current of 50A to 280A and an arc discharge time of 5 min to 55 min; or an arc discharge includes a controlled current of 100A to 260A and an arc discharge time of 20 min to 40 min; or an arc discharge includes a controlled current of 200A to 255A and an arc discharge time of 22 min to 34 min, or combinations thereof.

[0033] In some implementations, the passivating gas can be air at a pressure of 5 kPa to 50 kPa, and the passivation time can be 1 h to 10 h. Under these passivating gas pressures and passivation times, the activity and surface energy of the nano-nickel powder can be effectively reduced, making it less prone to sintering and growth at high temperatures. For example, the passivating gas can be air at a pressure of 10 kPa to 40 kPa, and the passivation time can be 2 h to 7 h; or the passivating gas can be air at a pressure of 15 kPa to 28 kPa, and the passivation time can be 4 h to 6 h, or a combination of these ranges.

[0034] In some implementations, the pressure of the plasma working gas can be 30 kPa to 80 kPa. For example, the pressure of the plasma working gas can be a combination of 40 kPa to 75 kPa, 45 kPa to 63 kPa, 51 kPa to 59 kPa or above.

[0035] In some implementations, the anode can be a nickel rod or a nickel block.

[0036] In some implementations, the cathode can be a tungsten rod.

[0037] To better understand the present invention, specific examples are provided below to further illustrate the content of the present invention, but the content of the present invention is not limited to the examples below.

[0038] Example 1

[0039] A method for preparing nano-nickel powder using plasma, the specific steps of which are as follows:

[0040] Step 1: Using a pure tungsten rod as the cathode (20mm in diameter) and a nickel rod as the anode, fix the nickel rod anode in the slot of the water-cooled copper crucible.

[0041] Step 2: Evacuate the reaction chamber, then introduce plasma gas, set the current and voltage to perform arc discharge, and simultaneously control the anode to rise at a uniform speed and control the arc spacing to be 3 mm; the plasma gas is an O2 / Ar / H2 mixed gas system, the total pressure of the plasma gas is 60 kPa, O2:(Ar / H2)=1:99 (volume ratio), the volume of H2 in Ar / H2 is 1 / 2 (Ar / H2 represents the total volume of Ar and H2), the current is 200 A, and the arc discharge time is 5 min.

[0042] Step 3: After the arc discharge in Step 2 ends, the reaction chamber is evacuated and a passivating gas is introduced for passivation treatment. Metal nanoparticles (nano-tungsten powder) on the inner wall of the reaction chamber are collected. The passivating gas is air at 15 kPa and the passivation time is 1 hour.

[0043] Scanning electron microscope image of the nano-nickel powder in this embodiment ( Figure 1 ) and particle size distribution diagram of nano-nickel powder ( Figure 2 As can be seen from the figure, the prepared nano-nickel powder has a regular spherical structure, and the nickel powder has a narrow particle size distribution range and good dispersibility, which can meet the requirements of MLCC for nano-nickel powder.

[0044] Example 2

[0045] A method for preparing nano-nickel powder using plasma, the specific steps of which are as follows:

[0046] Step 1: Using a pure tungsten rod as the cathode (150mm in diameter) and a nickel block as the anode, fix the nickel block anode inside a water-cooled copper crucible.

[0047] Step 2: Evacuate the reaction chamber, then introduce plasma gas, set the current and voltage to initiate arc discharge, and simultaneously control the anode to rise at a uniform speed and maintain the arc spacing at 6 mm; the plasma gas is an O2 / N2 / H2 mixture system with a total pressure of 50 kPa, O2:(Ar / H2) = 3:97, and H in N2 / H2... 2 The volume occupies 1 / 3 of the total volume, the current is 150A, and the arc discharge time is 10min.

[0048] Step 3: After the arc discharge in Step 2 ends, the reaction chamber is evacuated and a passivating gas is introduced for passivation treatment. Metal nanoparticles (nano-nickel powder) on the inner wall of the reaction chamber are collected. The passivating gas is air at 30 kPa and the passivation time is 1 hour.

[0049] The scanning electron microscope image of the nano-nickel powder in this embodiment is shown below. Figure 3 As shown, the nano-nickel powder has a regular spherical structure, and the nickel powder has a narrow particle size distribution range and good dispersibility, which can meet the requirements of MLCC for nano-nickel powder.

[0050] Example 3

[0051] A method for preparing nano-nickel powder using plasma, the specific steps of which are as follows:

[0052] Step 1: Using a pure tungsten rod as the cathode (10mm in diameter) and a nickel block as the anode, fix the nickel block anode inside a water-cooled copper crucible.

[0053] Step 2: Evacuate the reaction chamber, then introduce plasma gas, set the current and voltage to perform arc discharge, and simultaneously control the anode to rise at a uniform speed and control the arc spacing to be 4 mm; wherein the plasma gas is an O2 / He / H2 mixed gas system, the total pressure of the plasma gas is 80 kPa, O2:(He / H2)=5:95, and the volume of H2 in He / H2 is 1 / 5; the current is 100 A, and the arc discharge time is 30 min.

[0054] Step 3: After the arc discharge in Step 2 ends, the reaction chamber is evacuated and a passivating gas is introduced for passivation treatment. Metal nanoparticles (nano-nickel powder) on the inner wall of the reaction chamber are collected. The passivating gas is air at 50 kPa and the passivation time is 5 hours.

[0055] The scanning electron microscope image of the nano-nickel powder in this embodiment is shown below. Figure 4 As shown, the nano-nickel powder has a regular spherical structure, and the nickel powder has a narrow particle size distribution range and good dispersibility, which can meet the requirements of MLCC for nano-nickel powder.

[0056] Example 4

[0057] A method for preparing nano-nickel powder using plasma, the specific steps of which are as follows:

[0058] Step 1: Using a pure tungsten rod as the cathode (20mm in diameter) and a metallic nickel rod as the anode, fix the nickel rod anode inside a water-cooled copper crucible.

[0059] Step 2: Evacuate the reaction chamber, then introduce plasma gas, set the current and voltage to perform arc discharge, and simultaneously control the anode to rise at a uniform speed and control the arc spacing to be 1 mm; wherein the plasma gas is an O2 / N2 / H2 mixed gas system, the total pressure of the plasma gas is 30 kPa, O2:(Ar / H2)=3:97, and the volume of H2 in N2 / H2 is 1 / 10; the current is 300 A, and the arc discharge time is 60 min.

[0060] Step 3: After the arc discharge in Step 2 ends, the reaction chamber is evacuated and a passivation gas is introduced for passivation treatment. Metal nanoparticles (nano nickel powder) on the inner wall of the reaction chamber are collected. The passivation gas is air at 5 kPa and the passivation time is 10 h.

[0061] The nano-nickel powder obtained in this embodiment has a regular spherical structure, and the nickel powder has a narrow particle size distribution range and good dispersibility, which can meet the requirements of MLCC for nano-nickel powder.

[0062] Example 5

[0063] A method for preparing nano-nickel powder using plasma, the specific steps of which are as follows:

[0064] Step 1: Using a pure tungsten rod as the cathode (10mm in diameter) and a metallic nickel rod as the anode, fix the nickel anode in a water-cooled copper crucible.

[0065] Step 2: Evacuate the reaction chamber, then introduce plasma gas, set the current and voltage to perform arc discharge, and simultaneously control the anode to rise at a uniform speed and control the arc spacing to be 5 mm; the plasma gas is an O2 / N2 / H2 mixed gas system, the total pressure of the plasma gas is 80 kPa, O2:(Ar / H2)=4:96, and H2 accounts for 1 / 4 of the volume in N2 / H2; the current is 20 A, and the arc discharge time is 50 min.

[0066] Step 3: After the arc discharge in Step 2 ends, the reaction chamber is evacuated and a passivation gas is introduced for passivation treatment. Metal nanoparticles (nano-nickel powder) on the inner wall of the reaction chamber are collected. The passivation gas is air at 20 kPa and the passivation time is 5 hours.

[0067] The nano-nickel powder obtained in this embodiment has a regular spherical structure, and the nickel powder has a narrow particle size distribution range and good dispersibility, which can meet the requirements of MLCC for nano-nickel powder.

[0068] Example 6

[0069] A method for preparing nano-nickel powder using plasma, the specific steps of which are as follows:

[0070] Step 1: Using a pure tungsten rod as the cathode (15mm in diameter) and a nickel block as the anode, fix the nickel block anode inside a water-cooled copper crucible.

[0071] Step 2: Evacuate the reaction chamber, then introduce plasma gas, set the current and voltage to perform arc discharge, and simultaneously control the anode to rise at a uniform speed and control the arc spacing to be 4 mm; wherein the plasma gas is an O2 / He / H2 mixed gas system, the total pressure of the plasma gas is 30 kPa, O2:(He / H2)=2:98, the volume of H2 in He / H2 is 1 / 5, the current is 300 A, and the arc discharge time is 10 min.

[0072] Step 3: After the arc discharge in Step 2 ends, the reaction chamber is evacuated and a passivating gas is introduced for passivation treatment. Metal nanoparticles (nano-nickel powder) on the inner wall of the reaction chamber are collected. The passivating gas is air at 20 kPa and the passivation time is 2 hours.

[0073] The nano-nickel powder obtained in this embodiment has a regular spherical structure, and the nickel powder has a narrow particle size distribution range and good dispersibility, which can meet the requirements of MLCC for nano-nickel powder.

[0074] Comparative Example 1

[0075] A method for preparing nano-nickel powder using plasma, in Comparative Example 1 compared to Example 1, uses an Ar / H2 mixed gas system as the plasma gas, which does not contain O2. The specific steps are as follows:

[0076] Step 1: Using a pure tungsten rod as the cathode (20mm in diameter) and a metallic nickel rod as the anode, fix the nickel rod anode in the slot of the water-cooled copper crucible.

[0077] Step 2: Evacuate the reaction chamber, then introduce plasma gas, set the current and voltage to perform arc discharge, and simultaneously control the anode to rise at a uniform speed and control the arc spacing to be 3 mm; wherein the plasma gas is an Ar / H2 mixed gas system, the total pressure of the plasma gas is 60 kPa, and the volume of H2 in the plasma gas is 1 / 2; the current is 200 A, and the arc discharge time is 5 min;

[0078] Step 3: After the arc discharge in Step 2 ends, the reaction chamber is evacuated and a passivation gas is introduced for passivation treatment. Metal nanoparticles (nano-nickel powder) on the inner wall of the reaction chamber are collected. The passivation gas is air at 15 kPa and the passivation time is 1 hour.

[0079] The scanning electron microscope image of the nickel nanoparticles prepared in Comparative Example 1 is shown below. Figure 5 As shown, the nano-nickel powder has a relatively regular spherical structure, but the particle size distribution range is wide, and the nano-nickel powder is severely adhered and agglomerated, which cannot meet the requirements of MLCC for nano-nickel powder.

[0080] Although the invention has been described above in conjunction with exemplary embodiments, those skilled in the art will understand that various modifications and changes can be made to the exemplary embodiments of the invention without departing from the spirit and scope defined by the claims.

Claims

1. A method for preparing nano-nickel powder using plasma, characterized in that, Includes the following steps: Using nickel-containing material as the anode, an arc discharge is performed in a vacuum reaction chamber using plasma working gas until the reaction is complete. The reaction chamber is then evacuated and passivating gas is introduced. After passivation treatment, nano-nickel powder is obtained. The anode is a nickel rod or nickel block; The plasma working gas is a mixture of oxygen, hydrogen, and a first gas, wherein the first gas is any one or more of argon, nitrogen, and helium; the volume ratio of the total volume of hydrogen and the first gas to the volume of oxygen is 95~99:1~5, and hydrogen accounts for 1 / 10~1 / 2 of the total volume of hydrogen and the first gas.

2. The method for preparing nano-nickel powder using plasma according to claim 1, characterized in that, The method also includes controlling the distance between the anode and cathode to a constant value between 1 mm and 6 mm.

3. The method for preparing nano-nickel powder using plasma according to claim 2, characterized in that, The distance between the anode and cathode is controlled by adjusting the anode lifting position.

4. The method for preparing nano-nickel powder using plasma according to claim 1, 2, or 3, characterized in that, Arc discharge includes a control current of 20 A to 300 A and an arc discharge time of 1 min to 60 min.

5. The method for preparing nano-nickel powder using plasma according to claim 1, 2, or 3, characterized in that, The passivating gas is air at a pressure of 5 kPa to 50 kPa, and the passivation time is 1 h to 10 h.

6. The method for preparing nano-nickel powder using plasma according to claim 1, 2, or 3, characterized in that, The pressure of the plasma working gas is 30 kPa to 80 kPa.

7. The method for preparing nano-nickel powder using plasma according to claim 1, 2, or 3, characterized in that, The cathode is a tungsten rod.

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