Method for preparing nano nickel powder by using plasma

Abstract

The invention provides a method for preparing nano nickel powder by using plasma. The method comprises the steps that a nickel-containing material serves as an anode, plasma working gas and arc discharge are conducted in a vacuum reaction chamber till the reaction is finished, the reaction chamber is vacuumized, passivation gas is introduced into the reaction chamber, the nanometer nickel powder is obtained after passivation treatment is completed, the plasma working gas is mixed gas composed of oxygen, hydrogen and first gas, and the first gas is mixed gas. The first gas is any one or more of argon, nitrogen and helium. The nanometer nickel powder prepared through the method is good in dispersity and uniform in granularity, and the problem that the nanometer nickel powder prepared through an original growth path is seriously agglomerated is solved.

Description

Technical Field

[0001] The invention belongs to the field of powder metallurgy, and more specifically, relates to a method for preparing nano nickel powder by utilizing plasma. Background Art

[0002] With the adjustment of the market structure of electronic complete products, mobile communication equipment and portable computers have developed rapidly, bringing huge market space for the development of multilayer ceramic capacitors (MLCC). The traditional MLCC electrode material is Pd / Ag alloy or pure Pd. Since the imported slurry of Pd inner electrode, which is currently the most used, is expensive, the use of base metal materials to replace Pd / Ag electrodes is an important trend in the development of MLCC. In order to take into account the requirements of large capacity and low cost, base metal nickel electrodes are the best choice. Based on the current development trend of MLCC, in order to meet the requirements of screen printing, stacking, sintering and other process improvements and actual use stability in the process, the metal nickel particles used in its electrodes must be high in purity, small in particle size, uniform in particle size, highly dispersed, and have certain antioxidant properties.

[0003] There are two main methods for preparing high-quality nano nickel powders: chemical method and physical method. The chemical method can be divided into chemical vapor deposition (CVD) method and liquid phase method. The current industrial mass production methods of CVD method are carbonyl nickel pyrolysis method and gaseous chloride hydrogen reduction method, and the current industrial mass production method of liquid phase method is electrolysis method. The chemical method for preparing high-quality metal nickel powder has the advantage of large output, but defects such as easy pollution, low product purity and easy agglomeration limit its wide application. The physical method refers to the use of physical methods such as electricity, heat, magnetism, and force to refine particles to make nickel metal nanoparticles, mainly including plasma method, mechanical ball milling method, electric explosion method, ultrasonic method, laser heating evaporation method, etc. The methods that can be industrially mass-produced by physical methods include plasma method, mechanical ball milling method and electric explosion method. At present, the physical method has been widely used in the field of preparing nano nickel powder because of its environmental friendliness, uniform particle size and high product purity. Among the many physical methods for preparing nano nickel powder, the plasma method has the advantages of high chemical activity, controllable reaction atmosphere, high temperature gradient, high product purity, high spheroidization rate and easy large-scale production, and is highly favored in the field of preparing high-quality nano nickel powder. Therefore, the plasma method for preparing metal nanomaterials has irreplaceable advantages in the preparation of high-quality nano nickel powder due to its advantages of high purity, high spheroidization rate and small average particle size. However, the nano nickel powder prepared by the existing plasma method has poor dispersibility and a wide particle size distribution range, which makes it impossible to directly use it in MLCC electrodes. Summary of the invention

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

[0005] The invention discloses a method for preparing nano nickel powder by using plasma, which can include the following steps: taking a nickel-containing material as an anode, passing a plasma working gas through a vacuum reaction chamber, arc discharge until the reaction is completed, evacuating the reaction chamber and passing a passivation gas, and obtaining the nano nickel powder after the passivation treatment is completed, wherein the plasma working gas is a mixed gas composed of oxygen, hydrogen and a first gas, and the first gas is any one or more of argon, nitrogen and helium.

[0006] Furthermore, in the plasma working gas, the volume ratio of the total volume of hydrogen and the first gas to oxygen can be 95-99:1-5, and hydrogen can account for 1 / 10-1 / 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 be a constant value between 1 mm and 6 mm.

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

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

[0010] Furthermore, the passivation gas may be air at 5 kPa to 50 kPa, and the passivation time may be 1 h to 10 h.

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

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

[0013] Furthermore, the cathode may 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 the plasma gas, so that the arc region temperature is high and the arc stability is high, and has the advantages of high preparation efficiency and environmentally friendly process;

[0016] (2) The present invention uses a mixed gas containing oxygen and hydrogen as the working gas, thereby changing the original growth path of the nano-nickel powder from evaporation-condensation-growth to evaporation-oxidation-reduction-growth, thereby reducing the temperature at which the nano-nickel powder is easily fused or agglomerated during the growth stage, making the prepared nano-nickel powder have good dispersibility, and overcoming the problem of serious agglomeration of the 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 the nano-nickel powder, making it difficult for the nano-nickel powder to sinter and grow under high temperature conditions. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0020] Figure 2 The particle size distribution diagram of the nano nickel powder prepared in Example 1;

[0021] Figure 3 This is a scanning electron microscope image of the nano nickel powder prepared in Example 2;

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

[0023] Figure 5 This is a scanning electron microscope image of the nano nickel powder prepared in Comparative Example 1. DETAILED DESCRIPTION

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

[0025] Specifically, the present invention uses direct current arc plasma to prepare nano nickel powder. The arc discharge between the electrodes generates a high temperature of up to 104K, which converts the gas in the reaction chamber into a plasma state, and the metal nickel anode quickly sublimates into gaseous atoms. The oxygen in the reaction chamber first reacts with the gasified nickel to form nickel oxide, and then in a hydrogen reducing gas environment, the nickel oxide is reduced and grown to form nickel powder. The nickel powder through the above reaction process is at the edge of the plasma with a relatively low temperature, and the temperature gradient in the arc plasma reaction chamber is large, so the formed nickel powder cannot be fused or agglomerated, thereby preparing nano nickel powder with good dispersibility and narrow particle size distribution.

[0026] The present 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 of the present invention, the method may include:

[0027] Step 1, using the nickel-containing material as the anode, evacuating the reaction chamber, then introducing the plasma working gas, setting the current and voltage to perform arc discharge;

[0028] Step 2, after the arc discharge is completed, the reaction chamber is evacuated, and then a passivation gas is introduced for passivation treatment, and 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 embodiments, the plasma working gas may be a mixed gas of oxygen, hydrogen and a first gas, and the first gas may be any one or more of argon, nitrogen and helium. That is, the plasma working gas may be a mixed gas of oxygen, hydrogen and argon, a mixed gas of oxygen, hydrogen and nitrogen, or a mixed gas of oxygen, hydrogen and helium.

[0030] In some embodiments, in the plasma working gas, the volume ratio of the total volume of hydrogen and the first gas to oxygen can be 95-99:1-5, and hydrogen accounts for 1 / 10-1 / 2 of the total volume of hydrogen and the first gas. Under the above-mentioned proportion of plasma working gas components, on the one hand, the preparation process can realize the oxidation-reduction-growth process to prepare nano-nickel powder, and it can be ensured 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 ratio range. For example, the volume ratio of the total volume of hydrogen and the first gas to oxygen can be 96-98:2-4, and hydrogen accounts for 1 / 8-1 / 3 of the total volume of hydrogen and the first gas. For another example, the volume ratio of the total volume of hydrogen and the first gas to oxygen can be 97:3, and hydrogen accounts for 1 / 5 of the total volume of hydrogen and the first gas.

[0031] In some embodiments, the preparation method further comprises controlling the spacing between the anode and the cathode to maintain a constant value. The spacing between the anode and the cathode can be controlled between 1 mm and 6 mm. By controlling the electrode spacing between the anode and the cathode to be constant, it is beneficial to stabilize the arc, so that the refractory metal nano nickel powder has a more regular spherical structure, and the particle size of the nano nickel powder is small and the particle size distribution is uniform. For example, the spacing between the anode and the cathode can be 2 mm, 3 mm, 4 mm or 5 mm. In certain embodiments, the spacing between the anode and the cathode can be constant by controlling the anode to rise at a uniform speed.

[0032] In some embodiments, the arc discharge includes a controlled current of 20A to 300A, and the arc discharge time can be 1min to 60min. Under the above current and arc discharge time, the reaction process of nickel can be evaporation-oxidation-reduction-growth, which can reduce the temperature at which the nano-nickel powder is easily fused or agglomerated during the growth stage, so that the prepared nano-nickel powder has good dispersibility. For example, the arc discharge includes a controlled current of 50A to 280A, and the arc discharge time can be 5min to 55min; or the arc discharge includes a controlled current of 100A to 260A, and the arc discharge time can be 20min to 40min, or the arc discharge includes a controlled current of 200A to 255A, and the arc discharge time can be 22min to 34min, or a combination of the above ranges.

[0033] In some embodiments, the passivation gas may be air at 5 kPa to 50 kPa, and the passivation time may be 1 h to 10 h. Under the above passivation gas pressure and passivation time, the activity and surface energy of the nano-nickel powder can be effectively reduced, so that the nano-nickel powder is not easy to sinter and grow under high temperature conditions. For example, the passivation gas may be air at 10 kPa to 40 kPa, and the passivation time may be 2 h to 7 h; or the passivation gas may be air at 15 kPa to 28 kPa, and the passivation time may be 4 h to 6 h or a combination of the above ranges.

[0034] In some embodiments, 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 40 kPa to 75 kPa, 45 kPa to 63 kPa, 51 kPa to 59 kPa, or a combination of the above ranges.

[0035] In some embodiments, the anode may be a metal nickel rod or block.

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

[0037] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with specific examples, but the content of the present invention is not limited to the following examples.

[0038] Example 1

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

[0040] Step 1: Use a pure tungsten rod as the cathode, the tungsten rod is 20 mm long, and a metal nickel rod as the anode. Fix the nickel rod anode in the hole of a water-cooled copper crucible.

[0041] Step 2: evacuate the reaction chamber, then introduce plasma gas, set the current and voltage for arc discharge, and control the anode to rise at a uniform speed and control the arc spacing to be 3 mm; wherein the plasma gas is O 2 / Ar / H 2 Mixed gas system, the total pressure of plasma gas is 60kPa, O 2 :(Ar / H 2 )=1:99(volume ratio),Ar / H 2 Medium H 2 The volume of Ar / H 2 Indicates Ar and H 2 The total volume of the battery is 200A, the current is 200A, and the arc discharge time is 5min.

[0042] Step 3: After the arc discharge in step 2 is completed, the reaction chamber is evacuated, a passivation gas is introduced for passivation treatment, and the metal nanopowder (nano-tungsten powder) on the inner wall of the reaction chamber is collected; wherein the passivation gas is 15 kPa of air, and the passivation time is 1 hour.

[0043] The scanning electron microscope image of the nano nickel powder in this example ( Figure 1 ) and the particle size distribution of nano nickel powder ( Figure 2 ), it can be seen from the figure that the prepared nano nickel powder has a regular spherical structure, and the nickel powder particle size distribution range is narrow and the dispersibility is good, 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 are as follows:

[0046] Step 1: Use a pure tungsten rod as the cathode, the tungsten rod is 150 mm long, and a metal nickel block as the anode. Fix the nickel block anode in a water-cooled copper crucible.

[0047] Step 2: evacuate the reaction chamber, then introduce plasma gas, set the current and voltage for arc discharge, and control the anode to rise at a uniform speed and control the arc spacing to be 6 mm; wherein the plasma gas is O 2 / N 2 / H 2 Mixed gas system, the total pressure of plasma gas is 50kPa, O 2 :(Ar / H 2 )=3:97,N 2 / H 2 Medium H 2 The volume is 1 / 3, the current is 150A, and the arc discharge time is 10min.

[0048] Step 3: After the arc discharge in step 2 is completed, the reaction chamber is evacuated, a passivation gas is introduced for passivation treatment, and the metal nanopowder (nano-nickel powder) on the inner wall of the reaction chamber is collected; wherein the passivation gas is 30 kPa of air, and the passivation time is 1 hour.

[0049] The scanning electron microscope image of the nano nickel powder of this embodiment is as follows Figure 3 As shown, nano nickel powder has a regular spherical structure, and the nickel powder particle size distribution range is narrow and the dispersion is good, 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 are as follows:

[0052] Step 1: Use a pure tungsten rod as the cathode, the tungsten rod is 10 mm long, and a metal nickel block as the anode. Fix the nickel block anode in a water-cooled copper crucible.

[0053] Step 2: evacuate the reaction chamber, then introduce plasma gas, set the current and voltage for arc discharge, and control the anode to rise at a uniform speed and control the arc spacing to be 4 mm; wherein the plasma gas is O 2 / He / H 2 Mixed gas system, the total pressure of plasma gas is 80kPa, O 2 :(He / H 2 )=5:95,He / H 2 Medium H 2 The volume of the device is 1 / 5; the current is 100A and the arc discharge time is 30min.

[0054] Step 3: After the arc discharge in step 2 is completed, the reaction chamber is evacuated, a passivation gas is introduced for passivation treatment, and the metal nanopowder (nano-nickel powder) on the inner wall of the reaction chamber is collected, wherein the passivation gas is 50 kPa of air and the passivation time is 5 h.

[0055] The scanning electron microscope image of the nano nickel powder of this embodiment is as follows Figure 4 As shown, nano nickel powder has a regular spherical structure, and the nickel powder particle size distribution range is narrow and the dispersion is good, 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 are as follows:

[0058] Step 1: Use a pure tungsten rod as the cathode, the tungsten rod is 20 mm long, and a metal nickel rod as the anode. Fix the nickel rod anode in a water-cooled copper crucible.

[0059] Step 2: evacuate the reaction chamber, then introduce plasma gas, set the current and voltage for arc discharge, and control the anode to rise at a uniform speed and control the arc spacing to be 1 mm; wherein the plasma gas is O 2 / N 2 / H 2 Mixed gas system, the total pressure of plasma gas is 30kPa, O 2 :(Ar / H 2 )=3:97,N 2 / H 2 Medium H 2 The volume of the device is 1 / 10; the current is 300A and the arc discharge time is 60min.

[0060] Step 3: After the arc discharge in step 2 is completed, the reaction chamber is evacuated, a passivation gas is introduced for passivation treatment, and the metal nanopowder (nano-nickel powder) on the inner wall of the reaction chamber is collected; wherein the passivation gas is 5 kPa of air, 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 particle size distribution range is narrow and the dispersibility is good, 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 are as follows:

[0064] Step 1: Use a pure tungsten rod as the cathode, the tungsten rod is 10 mm in diameter, and a metal nickel rod as the anode. Fix the nickel block anode in a water-cooled copper crucible.

[0065] Step 2: evacuate the reaction chamber, then introduce plasma gas, set the current and voltage for arc discharge, and control the anode to rise at a uniform speed and control the arc spacing to be 5 mm; wherein the plasma gas is O 2 / N 2 / H 2 Mixed gas system, the total pressure of plasma gas is 80kPa, O 2 :(Ar / H 2 )=4:96,N 2 / H 2 Medium H 2 The volume of the device occupies 1 / 4; the current is 20A and the arc discharge time is 50min.

[0066] Step 3: After the arc discharge in step 2 is completed, the reaction chamber is evacuated, a passivation gas is introduced for passivation treatment, and the metal nanopowder (nano-nickel powder) on the inner wall of the reaction chamber is collected; wherein the passivation gas is 20 kPa of air, 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 particle size distribution range is narrow and the dispersibility is good, 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 are as follows:

[0070] Step 1: Use a pure tungsten rod as the cathode, the tungsten rod is 15 mm in diameter, and a metal nickel block as the anode. Fix the nickel block anode in a water-cooled copper crucible.

[0071] Step 2: evacuate the reaction chamber, then introduce plasma gas, set the current and voltage for arc discharge, and control the anode to rise at a uniform speed and control the arc spacing to be 4 mm; wherein the plasma gas is O 2 / He / H 2 Mixed gas system, the total pressure of plasma gas is 30kPa, O 2 :(He / H 2 )=2:98,He / H 2 Medium H 2 The volume is 1 / 5, the current is 300A, and the arc discharge time is 10min.

[0072] Step 3: After the arc discharge in step 2 is completed, the reaction chamber is evacuated, a passivation gas is introduced for passivation treatment, and the metal nanopowder (nano-nickel powder) on the inner wall of the reaction chamber is collected; wherein the passivation gas is 20 kPa of air, 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 particle size distribution range is narrow and the dispersibility is good, which can meet the requirements of MLCC for nano nickel powder.

[0074] Comparative Example 1

[0075] A method for preparing nano nickel powder by using plasma. Compared with Example 1, the plasma gas in Comparative Example 1 is Ar / H 2 Mixed gas system, does not contain O 2 , the specific steps are as follows:

[0076] Step 1, use a pure tungsten rod as the cathode, the tungsten rod is 20 mm thick, and a metal nickel rod as the anode, and fix the nickel rod anode in the hole groove of the water-cooled copper crucible;

[0077] Step 2: evacuate the reaction chamber, then introduce plasma gas, set the current and voltage for arc discharge, and control the anode to rise at a uniform speed and control the arc spacing to 3 mm; the plasma gas is Ar / H 2 Mixed gas system, the total pressure of plasma gas is 60kPa, and H2 The volume of the arc discharge chamber is 1 / 2; the current is 200A, and the arc discharge time is 5min;

[0078] Step 3: After the arc discharge in step 2 is completed, the reaction chamber is evacuated, a passivation gas is introduced for passivation treatment, and the metal nanopowder (nano-nickel powder) on the inner wall of the reaction chamber is collected; wherein the passivation gas is 15 kPa of air, and the passivation time is 1 hour.

[0079] The scanning electron microscope image of the nano nickel powder prepared in this comparative example 1 is as follows 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 has serious adhesion and agglomeration, which cannot meet the requirements of MLCC for nano-nickel powder.

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

Claims

1. A method for preparing nano nickel powder using plasma, characterized in that: The following steps are involved: The nickel-containing material is used as the anode, and the plasma working gas is passed through the vacuum reaction chamber, arc discharge is performed until the reaction is completed, the reaction chamber is evacuated and the passivation gas is introduced, and nano nickel powder is obtained after the passivation treatment is completed, wherein: The plasma working gas is a mixed gas consisting of oxygen, hydrogen and a first gas, and the first gas is any one or more of argon, nitrogen and helium.

2. The method for preparing nano nickel powder by plasma according to claim 1, characterized in that: In the plasma working gas, 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.

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

4. The method for preparing nano nickel powder by plasma according to claim 3, characterized in that: The distance between the anode and cathode is controlled by adjusting the anode lift.

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

6. The method for preparing nano nickel powder by utilizing plasma according to claim 1, 2 or 3, characterized in that: The passivation gas is air at 5kPa to 50kPa, and the passivation time is 1h to 10h.

7. The method for preparing nano nickel powder by utilizing plasma according to claim 1, 2 or 3, characterized in that: The pressure of the plasma working gas is 30kPa~80kPa.

8. The method for preparing nano nickel powder by utilizing plasma according to claim 1, 2 or 3, characterized in that: The anode is a metal nickel rod or nickel block.

9. The method for preparing nano nickel powder by utilizing plasma according to claim 1, 2 or 3, characterized in that: The cathode is a tungsten rod.

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