KR20090026512A - Method and apparatus for producing nickel nanopowder using arc plasma apparatus - Google Patents

Abstract

A manufacturing method of nano nickel powder using an arc plasma device and a device for manufacturing the same are provided to improve a vapor phase synthesis process for the nano metal powder manufacture. A device for manufacturing nano nickel powder comprises a metal evaporator(10), a cooling unit(20), and a collector(25). The metal evaporator has an outside heat insulation material(12) of a cover(11) and a crucible part(4). The crucible part has a crucible in which a ceramic coating layer is formed and a support part. The refrigerator includes a cooling gas inlet port on upper and lower and a porous cylinder pipe in inside. The material of the ceramics comprised over a one among zrO2, mgO, caO, zrB2, hfB, BN and TiB2.

Description

Method and apparatus for producing nickel nanopowder using arc plasma apparatus {Method and apparatus for producing nickel nanopowder using arc plasma apparatus}

The present invention relates to a method and apparatus for manufacturing nickel nanopowder using an arc plasma apparatus, wherein an arc plasma is generated between a tungsten anode and a nickel metal which acts as a consumable anode to evaporate nickel, and nickel vapor is used to produce excess nitrogen or argon. Cooling with gas produces spherical nickel nanopowders having excellent crystallinity. The present invention proposes a nickel melting crucible for continuously evaporating nickel lumps to produce high purity nickel nanopowders, and a method of preparing nickel nanopowders of 200 nm or less by rapidly cooling evaporated nickel vapor. The present invention also provides a method of forming an oxide film on the surface of the nickel nanopowder in order to improve the stability of the manufactured nickel nanopowder.

Nickel powder is a key material that is applied as electrode material of multilayer ceramic chip capacitors (MLCC) used as core parts in electronic and information communication devices. MLCC is a ceramic dielectric layer and internal electrodes are alternately stacked, and then applied under pressure, attached together, and co-fired to integrate them. Generally, ferroelectric barium titanate is applied as a material for the dielectric layer. Nickel is applied as the material. The characteristics required for the internal electrode material include good dispersibility, high electrical conductivity, and low oxidation and shrinkage during simultaneous firing. As a result, Pd, Ag-Pd, etc. Powders belonging to the noble metals were applied. Nickel has been applied to replace expensive precious metals since the mid-1990s. Currently, powders with an average particle size of 300nm-600nm are mainly applied for high-layered MLCCs. In addition, the miniaturization and ultra-high lamination of high-capacity MLCCs require nano-sized nickel nanopowders with very small particle sizes, and powders with excellent spherical crystallinity to solve shrinkage and oxidation problems during firing. It is required.

In general, submicro nickel powder is produced by a liquid phase method and a gas phase method. The liquid phase method is a wet chemical process, which is produced by reducing nickel sulfate (NiSO ₄ ) or nickel nitrate (Ni (NO ₃ ) ₂ ) aqueous solution, followed by precipitation, separation, washing and drying of nickel, and the mass production process is relatively easy. . While the powder produced by the liquid phase method has a relatively constant particle size, there is a problem in that the dispersibility is poor and the shrinkage rate during firing is excessively large.

The gas phase method has recently been expected to be a process for producing metal and ceramic nanopowders. In general, in the case of metal or oxide ceramics, the particles have a spherical shape, excellent dispersibility, and high powder crystallinity. There is this. In particular, the gas phase synthesis method using an ultra high temperature thermal plasma is capable of producing nanopowders at an extremely high speed, and it is reported that raw materials can also be easily used in a variety of solid, liquid and gaseous materials (Non-Patent Document 1).

Thermal plasma is classified into RF plasma, transferred arc plasma, and non-transferred arc plasma according to the generation method. In the nano powder manufacturing process, transfer arc plasma is mainly used. Is applied. In the transfer arc plasma, an arc is generated between the tungsten electrode (cathode) and the anode, and the raw material metal of the target material and the crucible containing the raw material are connected to the anode to evaporate the metal raw material using the metal raw material itself as the anode. As the plasma generating gas, arc discharge is performed using argon, nitrogen, helium, hydrogen, oxygen, or a mixture thereof, and the target raw material is introduced into the arc plasma to evaporate, and a reactive gas or an inert gas is injected into the vaporized metal vapor. Cooling to produce a nano-sized ceramic or metal powder. In order to control the particle size and crystallinity in the process of manufacturing nanopowder using plasma, the concentration and temperature of the metal vapor, the residence time of the particles, and the cooling rate are known as the main variables.

Examples of synthesizing nanopowder using the thermal plasma are as follows. In patent document 1, the metal nanopowder was manufactured using hydrogen plasma, and in patent document 2, aluminum nitride ultrafine powder was manufactured by evaporating aluminum using nitrogen plasma. In these processes, the crucible material into which a reactor and a metal raw material are put is cooled by cooling water, and it becomes a problem that thermal efficiency becomes low. In order to improve the thermal efficiency of a thermal plasma process, the method of manufacturing a nano powder by making a reactor and a raw material crucible with graphite is also reported (nonpatent literature 2).

In addition, Patent Document 3 recently proposed a method for producing Cu, Ni powder having an average particle size of 0.8-1.7 µm by introducing a hot dilution gas of 1000 K or more into the reactor and the cooler. In this patent, graphite crucible is used as a metal melting crucible, and as a crucible material for metal raw materials in the process of manufacturing metal nanopowder using such a high temperature thermal plasma, it has excellent heat insulation and durability at an ultra-high temperature of more than 2000 degrees, and melts. There is a demand for non-reactivity with metals, and graphite crucibles are generally used. A transfer arc plasma was used, and a method and apparatus for producing metal fine particles by promoting the growth of metal particles while controlling the injection amount of hot dilution gas of 1000 K or more, the length of the cooling tube, and the flow rate of the cooling gas were described.

[Patent Document 1] US Patent No. 4,376,740

[Patent Document 2] Korean Patent No. 252590

[Patent Document 3] US Patent No. 6,379,419B1

[Non-Patent Document 1] "Thermal Plasma Process and Application", Dong Hwa Park, Seong Min Oh, pp.124-155, Inha University Press, ISBN 89-7404-169-X 93570, 2004

[Non-Patent Document 2] Ageorges et al., Plasma Chemistry and Plasma Processing, pp. 613-632, 1993

As described above, water-cooled copper crucibles or graphite crucibles are generally used to contain metal raw materials in the process of producing metal nanopowders using an arc plasma process. However, in the case of nickel, the evaporation point is very high, more than 2700 degrees, so the evaporation rate drops sharply when using the copper crucible, and there is a problem in the continuous mass production of high purity nickel powder with controlled carbon content because it reacts at high temperature with graphite. . In order to solve such a problem, the present invention proposes a crucible for continuously manufacturing high purity nickel nanopowder.

In addition, with respect to the particle size of the current metal powder, it is required to manufacture the particle size to 200nm or less by increasing the cooling rate rather than growing the particles by using a high-temperature dilution gas of 1000K or more proposed in Patent Document 3. Therefore, to improve the injection method of excess cooling gas to prepare a metal nano powder having an average particle size of 200nm or less. In addition, in order to control the explosion risk which is a problem in the practical handling of metal nanopowders and to improve the surface properties of the powder, a method of forming and passivating an appropriate surface oxide layer before collecting the powder is proposed.

In the present invention, a method and apparatus for manufacturing nickel nanopowder using an arc plasma apparatus, which generates an arc plasma between a tungsten cathode and a nickel metal which acts as a consumable anode to evaporate nickel, and nickel vapor in excess nitrogen or argon gas. It is characterized by producing a spherical nickel nanopowder excellent in crystallinity by cooling using. In addition, in the present invention, a nickel melting crucible for continuously evaporating the nickel lump to produce a high purity nickel nanopowder, a method of rapidly cooling the evaporated nickel vapor to produce a nickel nanopowder of 200 nm or less, and the manufactured nickel In order to improve the stability of the nano-powder is characterized by the method of forming an oxide film on the surface of the nickel nano-powder.

The ceramic-coated graphite crucible proposed from the present invention does not react with molten nickel at an ultra-high temperature of more than 2000 degrees, and has good thermal insulation, so that it is possible to stably evaporate nickel by suppressing heat loss of arc plasma energy, and to produce nickel powder. It is useful to control the carbon content of the carbon dioxide.

In addition, it is possible to prevent the powder from adhering to the cooler wall and the like by the cooling gas injection method of the present invention, and it is possible to continuously manufacture a nano-powder of 30-170nm by introducing an excessive amount of cooling gas, the produced powder is collected The surface oxidation treatment was carried out before the process, thereby improving the gas phase synthesis process for producing metal nanopowders.

The present invention provides a method and apparatus for producing nickel nanopowder using non-conveying arc plasma.

In the method for producing nickel nanopowder using the arc plasma apparatus of the present invention, in the method of continuously producing the nickel nanopowder by vapor phase synthesis method by generating an arc plasma between the tungsten cathode and the nickel anode,

(a) heating nickel to a high temperature of at least 2000 degrees while generating nickel in a crucible continuously in electrical contact with the anode to generate nickel vapor; (b) rapidly cooling the resulting nickel vapor with an excess of cooling gas to produce a nickel nanopowder having an average particle size of 200 nm or less; (c) controlling the surface of the nickel powder by injecting a gas containing 0-1 wt% of oxygen into the prepared nickel nanopowder at 0-100 L / min.

Here, nickel nano powder having an average particle size of 30 to 200 nm by injecting argon, nitrogen, or a mixed gas containing one or more of these as the cooling gas into a cooler in a range of 500 L / min-10,000 L / min and cooling at a high speed. Manufacturing the

Argon or nitrogen gas containing 1% or less of oxygen as the cooling gas is injected into a cooler or a powder collector so that the thickness of the surface oxide layer of the metal powder is controlled to 10 nm or less.

In addition, the present invention is a nickel nano powder continuous production apparatus consisting of a metal evaporator, a cooler and a collector equipped with a torch and a raw material tank as a manufacturing apparatus applied to the method for producing the nickel nano powder.

The metal evaporator of the manufacturing apparatus is filled with a heat insulating material to the outside of the crucible portion and the cover, the crucible portion is composed of a crucible and a support portion formed with a ceramic coating layer, the cooler forms a cooling gas inlet in the upper and lower, and the porous inside The cylindrical tube is installed, and the collector is equipped with a metal filter inside and a powder collector is installed at the bottom.

Here, the crucible may be configured to be in electrical contact with a double overlap of a separate ceramic crucible instead of a ceramic coating layer, the ceramic material is composed of any one or more of ZrO ₂ , MgO, ZrB ₂ , HfB, BN, TiB ₂ Is characteristic.

As described above, the apparatus applied to the method of manufacturing nanopowders of the present invention is divided into an evaporator, a cooler, and a collector as an arc plasma system for producing metal nanopowders. In the evaporator, an arc plasma is generated using argon, nitrogen, hydrogen, or a mixed gas thereof to evaporate the metal at an extremely high temperature, and in the cooler, an excessive amount of argon or nitrogen is injected to collide with the metal particles from the evaporator to cool it. It is made of solid metal powder, and the collector separates the manufactured powder and gas to recover the powder and discharge the gas.

The non-conveying arc plasma apparatus of the present invention is composed of a non-consumable cathode and a consumable anode, and the cathode is processed by tungsten into a conical form to be cooled by water in a plasma torch, and the anode is nickel as an evaporation target material. It is used in the crucible and melted to serve as an anode.

Hereinafter, the configuration of the present invention through the accompanying drawings in more detail.

1 is a schematic diagram of a thermal plasma apparatus for manufacturing nickel nanopowder of the present invention, comprising a plasma torch power source 1 and a torch 2, a metal evaporator 10, a cooler 20, and a metal powder collector 25. The evaporator 10 and the cooler 20 are water cooled by a double tube (not shown).

The arc plasma torch 2 is composed of a water-cooled copper nozzle and a rod-shaped tungsten cathode protected by an insulator in the center thereof, and is connected to the copper cathode 3 while flowing argon or nitrogen gas through the nozzle to serve as an anode. An ultra high temperature plasma 5 of 10,000 degrees or more is generated between the crucible 16 (see FIG. 2 to be described later) of the crucible part 4.

The metal lump raw material is continuously fed from the raw material tank 6 to the metal melting crucible 16 through the injection pipe 7 and is melted at a rapid time by the ultra-high temperature of the arc plasma 5. The molten metal 8 melted inside the anode crucible 16 acts as a consumable anode that itself is consumed and plasma energy is concentrated so that the molten metal surface rapidly evaporates.

The distance between the plasma torch 2 and the consumable anode molten metal 8 is controlled by a torch positioner 9 located above the evaporator 10 to control the plasma conditions.

In order to increase the evaporation efficiency of the molten metal (8), the lid 11 of the crucible part 4 is composed of a high temperature heat insulator and heat insulating material in the space between the crucible part 4 and the cover 11 and the inner wall of the metal evaporator 10. Filled with 12. The cover 11 and the heat insulating material 12 around the crucible portion 4 mainly use porous graphite, and other oxides, nitrides, carbides, and boride ceramics may be used.

The metal vapor evaporated from the molten metal surface is mixed with the conveying gas 14 introduced through the spacer 13 and flows to the cooler 20 through the metal vapor pipe 15. Argon or nitrogen may be used as the transfer gas 14, and the spacer 13 may form a hole in a portion of the crucible cover 11, or a porous material may use a ceramic material.

In addition, the pipe 15 through which the metal vapor escapes from the evaporator 10 is coated with a high temperature heat insulating material therein to promote particle growth, or inject a quench gas to suppress particle growth. The metal vapor particles coming out of the evaporator 10 collide with the cooling gas 18 such as excess argon or nitrogen injected into the cooler 20 to be cooled at a high speed and become nano-sized solid metal powder particles. The metal powder and gas are separated at 25) using a porous metal filter 26.

Here, the transfer pipe 21 is injected with a surface oxidation gas 22 to oxidize the surface of the nickel powder to passivate the powder.

The metal nanopowder separated from the surface of the filter 26 and dropped down is accumulated in the powder collecting container 27, and gas passes through the metal filter 26 and is discharged out using a blower.

FIG. 2 is an enlarged explanatory view of the crucible part 4 of FIG. 1, showing the structure of the metal melting crucible.

As shown in the figure, the crucible part 4 includes a crucible 16 and a support part 23 on which a ceramic coating layer 17 is formed.

The crucible 16 may be made of graphite or a high-temperature ceramic material, and in the present invention, a ceramic coating layer 17 is formed inside the crucible 16 of graphite material and manufactured in a double overlapped structure to allow electricity to be melted. To suppress the reaction between metal and graphite crucible. If the target metal is Ag, Au, Pt, Cu, Al, Mg, etc., the ceramic coating layer 17 is not necessary and it is easy to manufacture these metal nanopowders using the crucible 16 made of graphite, but Ni, Ti In the case of manufacturing a nano powder, such as Si, because it reacts with the crucible 16 of graphite material at high temperature, it is possible to use a high-temperature ceramic crucible or a crucible coated with a ceramic on a graphite crucible. As such a material that can be used as the coating layer of the ultra-high temperature metal melting crucible or the crucible 16 made of graphite, oxides such as ZrO ₂ , MgO, and CaO, and borides such as ZrB ₂ , HfB, BN, and TiB ₂ are suitable. In addition, the crucible 16 may be configured to be in electrical contact with a double overlap of a separate ceramic crucible instead of the ceramic coating layer 17.

In addition, the supporting portion 23 for supporting the crucible 16 is preferably made of graphite or a high-temperature ceramic material, such as the crucible 16, but preferably porous than the crucible 16, the crucible 16 is adiabatic For the structure is wrapped around the crucible cover 11, but without the cover 11 it is possible to manufacture a continuous metal nanopowder.

3 is a view illustrating the inlet and injection method of the cooling gas of FIG. 1, wherein argon or nitrogen, which is the cooling gas 18, is attached to the wall of the cooler 20 while the metal particles coming from the evaporator are cooled. (18-a, 18-b) In addition, the porous cylindrical tube 19 of ceramic, graphite, or metal in the form of a cylinder having a plurality of pores is cooled. Injecting the excess cooling gas 18 through the pores, the metal particles from the evaporator 10 is attached to the wall of the cooler 20 to prevent the passage from being blocked.

Hereinafter, the present invention will be described in detail by Examples, Comparative Examples and Experimental Examples. However, the following examples are merely to illustrate the invention, but the content of the present invention is not limited by the following examples.

Example 1

Nitrogen plasma was generated at 30 kW while flowing nitrogen gas at 20 L / min between the tungsten anode and the graphite anode crucible, and nickel balls having a diameter of about 10 mm were continuously supplied to the graphite anode crucible. Nitrogen was injected into the cooling gas through a cooler at a flow rate of 500 L / min, and nickel powder was obtained at a rate of 0.5 kg / hr.

Example 2

Nitrogen gas is generated at 30 kW while flowing nitrogen gas at 20 L / min between the tungsten cathode and the ZrO ₂ coated graphite crucible, and nickel balls of diameter 10 mm are continuously supplied to the ZrO ₂ coated graphite crucible. I was. Nitrogen was injected into the cooling gas through a cooler at a flow rate of 500 L / min to obtain nickel powder at a rate of 0.6 kg / hr. Compared with the graphite crucible, the evaporation amount of nickel was slightly increased, and the prepared nickel powder was obtained as nano-sized spherical particles as shown in FIG. 4.

Example 3

Nitrogen plasma is generated at 30 kW while flowing nitrogen gas at 20 L / min between the tungsten anode and the ZrO ₂ coated graphite crucible, and nickel balls of diameter 10 mm are continuously supplied to the ZrO ₂ coated graphite crucible. I was. Nitrogen was injected into the cooling gas through a cooler at a flow rate of 1,500 L / min to obtain nickel powder at a rate of 0.5 kg / hr.

Example 4

Nitrogen plasma was generated at a rate of 30 kW while flowing nitrogen gas at 20 L / min between the tungsten cathode and the ZrO ₂ coated graphite crucible, and nickel balls having a diameter of about 10 mm were continuously supplied to the ZrO ₂ coated graphite crucible. . Nitrogen was injected into the cooling gas through a cooler at a flow rate of 500 L / min, and nitrogen gas containing 0.1 wt% of oxygen was injected at a flow rate of 50 L / min between the cooler and the collector for surface oxidation of the prepared powder. The prepared nickel particles were obtained as spherical nickel nano powders whose surface was oxidized at several nm as shown in FIG. 5.

Experimental Example 1 (particle size analysis, carbon content analysis, XRD and oxygen content analysis results)

Nickel powders prepared from Examples 1, 2, 3 and 4 are obtained as spherical nanopowders with smooth surfaces in the form equivalent to that shown in FIG. 4, and the average size of the particles decreases as the flow rate of the cooling gas increases. appear. When the flow rate of nitrogen as the cooling gas is 500 L / min as in Examples 1, 2, and 4, the average particle diameter is measured as 150 nm, 170 nm, and 160 nm, respectively, and in Example 3, the cooling gas flow rate is 1,500 L / min. In one case, the average particle size of the nickel powder was rapidly reduced to 70 nm.

Example When using a graphite crucible as in the first, the carbon content in the produced nickel powder was analyzed to be increased to more than 1.0 wt%, in Examples 2, 3 and 4 using a graphite crucible coated with ZrO ₂ This lowered the carbon content to 0.1%.

Figure 6 shows a comparison of the X-ray diffraction results of the powder prepared when injecting the oxygen-containing gas in Example 4. In the case of the powder prepared in Example 4, a peak corresponding to NiO was clearly observed, which is due to the oxide layer on the surface of the nickel particles, as shown in the photograph of FIG. 5, indicating that a NiO layer having a thickness of 3 to 5 nm was formed.

1 is a schematic diagram of a thermal plasma device for producing nickel nanopowder of the present invention

2 is an enlarged explanatory diagram of the crucible part of FIG. 1;

3 is a view for explaining an injection port and a method of injection of the cooling gas of FIG.

Figure 4 is a scanning electron microscope (FE-SEM) photograph of the prepared nickel powder

5 is a transmission electron microscope (TEM) photograph of the prepared nickel powder

6 is an X-ray diffraction pattern (XRD) graph of the prepared nickel powder

* Explanation of symbols for the main parts of the drawings

1: torch power supply 2: torch 3: cathode

4: Crucible Part 5: Plasma 6: Raw Material Tank

7 injection tube 8 molten metal 9 torch position regulator

10 metal evaporator 11 cover 12 insulation

13 spacer 14 transfer gas 15 piping

16 crucible 17 coating layer 18 cooling gas

19: porous cylindrical tube 20: cooler 21: transfer tube

22: gas for surface oxidation 25: collector 26: metal filter

27: powder collector

Claims (6)

In the method for producing nickel nanopowder continuously by vapor phase synthesis method by generating an arc plasma between the tungsten cathode and the nickel anode, (a) heating nickel to a high temperature of at least 2000 degrees while generating nickel in a crucible continuously in electrical contact with the anode to generate nickel vapor; (b) rapidly cooling the resulting nickel vapor with an excess of cooling gas to produce a nickel nanopowder having an average particle size of 200 nm or less; (c) controlling the surface of the nickel powder by injecting a gas containing an oxygen content of 0-1 wt% into the prepared nickel nanopowder; a method of manufacturing the nickel nanopowder using an arc plasma apparatus comprising the The method of claim 1, Nickel nano powder using an arc plasma apparatus, characterized in that the cooling gas is injected into a cooler in the range of 500 L / min-10,000 L / min as argon, nitrogen, or at least one of them as the cooling gas and cooled at a high speed. Manufacturing Method The method of claim 1, An argon or nitrogen gas containing 1% or less of oxygen as the cooling gas is injected into a cooler or a powder collector at 0-1,000 L / min so that the thickness of the surface oxide layer of the metal powder is controlled to 10 nm or less. Manufacturing method of nickel nano powder using plasma apparatus In the nickel nano powder continuous manufacturing apparatus which consists of the metal evaporator 10, the cooler 20, and the collector 25 which installed the torch 2 and the raw material tank 6, The metal evaporator 10 fills the insulator 12 to the outside of the crucible part 4 and the cover 11, wherein the crucible part 4 is a crucible 16 and a support part on which a ceramic coating layer 17 is formed. 23) The cooler 20 forms a cooling gas injection hole in the upper and lower portions, and installs a porous cylindrical tube 19 therein. The collector 25 is equipped with a metal filter 26 therein and a powder collector 27 is installed in the lower portion of the nickel nano-powder manufacturing apparatus of claim 1 characterized in that The method of claim 4, wherein The crucible 16 is a device for manufacturing nickel nanopowder, characterized in that configured to be in electrical contact with a double overlap of a separate ceramic crucible instead of the ceramic coating layer 17 The method according to claim 4 or 5, The ceramic material is ZrO ₂ , MgO, CaO, ZrB ₂ , HfB, BN, TiB _{2 The} apparatus for producing nickel nano powder, characterized in that composed of any one or more

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