JP2005256125A - Metal powder production apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal particulate production apparatus capable of preventing the occurrence of connected particles. <P>SOLUTION: In the range from a reaction part heated by a heating coil 34 in a reaction tube 20 to a cooling part cooled by a cooling apparatus 35, the inside diameter of the reaction tube is gradually made small to form a taper part. In the taper part, a gas circulation cross-sectional area is gradually made small, thus, a reduction in the linear flow rate of gas can be prevented, and the turbulence in the counter current, convection current, etc., of the gas can be prevented. Further, the temperature in the lower end of the taper part in the reaction tube 20 is controlled to ≤200°C which is lower than the sintering temperature of metal powder. Thus, the occurrence of connected particles in which metal particulates are connected is prevented, and the metal particulates with a particle diameter of 50 to 150 nm can be produced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a metal powder manufacturing apparatus and method capable of suppressing the formation of connected particles in metal fine particles obtained by reducing metal chloride gas, and more particularly to an internal electrode material of a multilayer ceramic capacitor and an electronic device. The present invention relates to an apparatus and a method for producing metal powder suitable for magnetic powder for magnetic storage media such as conductive paste fillers for parts and HDDs (Hard Disk Drives).

  Among metal powders, in particular, Ni and Cu powders have been used in large amounts as internal electrode materials for multilayer ceramic capacitors (hereinafter referred to as MLCC (Multilayer Ceramic Capacitor)). Conventionally, MLCC has used noble metal powders such as Pt powder, Pd powder, and Ag-Pd powder as internal electrode materials. However, since MLCC is used in large quantities on one electronic circuit board, there is a problem that the cost of the noble metal powder is high, and although it is a base metal, highly reliable Ni powder and Cu powder are used as electrode materials. It came to be.

  MLCC is a multilayer of ceramic dielectric layers and metal internal electrode layers, and the capacitance increases as the number of layers increases. On the other hand, the MLCC is required to be small in size as an electronic component. In order to meet these conflicting requirements, it is necessary to reduce the thickness of each layer. At present, the layer thickness of the internal electrode is 1 μm or less. For this reason, the particle size of the powder for internal electrodes is required to be 1 μm or less, and in recent years, the trend toward smaller diameters is increasingly spurred.

  In general, in MLCC manufacturing methods, dielectric powder is slurried, and paste-like metal powder of the internal electrode layer is printed on a ceramic green sheet prepared by coating it on a film, and they are stacked and pressure bonded. And then sintered. Therefore, in order to make the layer thickness thin and uniform, it is necessary that the Ni particles used in the paste-like metal powder have a small particle size and a narrow particle size distribution.

  In consideration of the sintering process, if there are many grain boundaries with high interface energy in the particles, sintering starts at a low temperature so that the dielectric does not sinter in order to relax the interface energy. End up. Thereby, destruction of the laminated structure called delamination occurs. For this reason, it is desirable that the crystallinity of the powder is high. In order to satisfy such required characteristics, the Ni fine particles are synthesized by gas phase hydrogen reduction of a metal halide gas having sublimation properties. As the metal halide gas, chloride gas is most often used.

Conventionally, as a method for producing Ni powder as described above, a gas phase hydrogen reduction method in which a nickel halide gas such as nickel chloride (NiCl ₂ ) gas and hydrogen are chemically reacted in a reactor is known. FIG. 5 is a cross-sectional view showing an example of an apparatus for producing Ni powder by the gas phase hydrogen reduction method (Patent Document 1: Utility Model Registration No. 2510932).

As shown in FIG. 5, in this synthesis apparatus, a NiCl ₂ raw material is supplied from a raw material supply device 2 through a charging tube 9 into a vaporization crucible 11 installed in the vaporization section 6 of the reactor 3. Is heated by the coil 13 of the external heating unit 8 in the vaporizing unit 6 to vaporize the chloride gas. A carrier gas introduction pipe 10 having a double pipe structure and a reducing gas supplier 12 are inserted into the upper part of the reaction pipe 3. A carrier gas is supplied into the reaction tube 3 from between the carrier gas supply pipe 10 and the reducing gas supply pipe 12, and the vaporized chloride gas evaporated from the raw material in the crucible 11 is carried by the carrier gas to the reaction tube. 3 is supplied to the lower reaction section 7. The reducing gas is supplied from the reducing gas supply pipe 12 to the reaction unit 7 of the reaction tube 3 and heated by the coil 14 of the heating unit 8, while the vaporized gas is reduced by reacting with the reducing gas in the reaction unit 7. By this reduction reaction, the chloride gas is reduced to obtain metal fine particles. The metal fine particles are cooled in the cooling unit 4 and then collected in the collection unit 19 of the powder collector 5.

Utility Model Registration No. 2510932

  However, the conventional techniques described above have the following problems. When the above-mentioned conventional apparatus is used to synthesize fine Ni powder or Cu powder having a particle size of 200 nm or less, particularly 100 nm or less, many connected particles having a shape in which the particles are connected to each other are generated. And when this connection particle | grain exists in paste-form metal powder, an unevenness | corrugation will generate | occur | produce notably on the printing surface of a metal powder paste, and a film thickness will become non-uniform | heterogenous. If the film thickness is not uniform, pinholes are likely to be generated in the MLCC, so that the electrical resistance increases, and the protrusions may penetrate the dielectric layer, causing a short circuit.

  This invention is made | formed in view of this problem, Comprising: It aims at providing the metal powder manufacturing apparatus and method which can prevent generation | occurrence | production of a connection particle | grain.

  A metal powder production apparatus according to the present invention is an apparatus for producing metal fine particles by a gas phase hydrogen reduction method of metal chloride gas, and vaporizing by heating and vaporizing a reaction tube and the metal chloride disposed in the reaction tube. A reducing unit that reduces the metal chloride by reacting the metal chloride vaporized gas and the reducing gas in the reaction tube; A cooling unit that cools the gas and a recovery device that is connected to the reaction tube and collects the metal fine particles solidified from the vaporized gas, and is continuously vaporized, reduced, and cooled in the reaction tube The reaction tube is arranged so that the gas flow rate at the outlet of the cooling unit is greater than or equal to the gas flow rate at the rear of the heating region from the rear of the heating region in the reaction unit to the outlet of the cooling unit. Wherein the Tsuryudan area is small.

  In this metal powder production apparatus, for example, the metal chloride is nickel chloride, and the metal fine particles are Ni fine powder having an average particle diameter of 50 to 150 nm.

  Moreover, it is preferable that the temperature of the said vaporization gas in the said cooling part exit shall be 200 degrees C or less. Furthermore, the metal particles are, for example, a metal selected from the group consisting of Ni, Cu, Co, Fe, Ag, W, Mo, Nb, and Ta, or an alloy thereof.

  Furthermore, the cooling part of the reaction tube may be divided into a plurality of parts, and each divided part may be connected by a flange. Thereby, the cooling length in a cooling part can be adjusted by changing the connection aspect of a flange, for example, and changing the number of the division parts which comprise the cooling part of a reaction tube.

  The method for producing a metal powder according to the present invention includes a step of heating and vaporizing a metal chloride in a vaporization section in a reaction tube in a method for producing metal fine particles by a gas phase hydrogen reduction method of a metal chloride gas, Supplying a reducing gas to the reaction tube to react the vaporized gas of the metal chloride with the reducing gas to reduce the metal chloride, cooling the gas after the reduction reaction, and the vaporization Recovering the metal fine particles solidified from the gas, and the vaporization, reduction reaction and cooling are continuously performed in the reaction tube, and the reaction tube is inserted from the rear of the heating region in the reaction unit. The gas flow cross-sectional area decreases toward the cooling part outlet, and the gas flow rate at the cooling part outlet is equal to or higher than the gas flow rate at the rear part of the heating region.

  In this metal powder manufacturing method, the temperature of the vaporized gas at the outlet of the cooling section is preferably 200 ° C. or lower.

  According to the present invention, since the gas flow cross-sectional area is small so that the flow rate of the vaporized gas becomes constant from the rear part of the heating area in the vaporization part toward the cooling part outlet, It is possible to reliably reduce the abundance of connected particles, which is a problem in the synthesis of micron metal powder. Thereby, the uniformity of the thin film obtained can be improved when this metal fine particle is contained in the mounting material for electronic components. For this reason, an electronic component can be reduced in size and high-density mounting of an electronic component can be performed at low cost. A metal or alloy such as Co or Ni can also be used as a high-quality magnetic medium storage powder. Furthermore, even if there is a straight pipe part on the downstream side of the throttle part where the flow cross-sectional area is small by setting the temperature of the vaporized gas at the outlet of the cooling part to 200 ° C. or less, the connected particles in this straight pipe part Can be suppressed.

Hereinafter, a metal fine particle manufacturing apparatus and method according to an embodiment of the present invention will be described. FIG. 1 is a cross-sectional view schematically showing a metal fine particle manufacturing apparatus according to this embodiment. In the upper part of the reaction tube 20, a metal chloride 21 such as NiCl ₂ is housed and installed in a housing part 22. The storage portion 22 is provided with a lid 24 at the upper end thereof, and encloses the internal metal chloride 21. The storage portion 22 has an opening 23 formed in the upper portion thereof so that the internal gas can be discharged. A pipe 25 for introducing carrier gas into the storage unit 22 is inserted into the lid 24.

A housing 26 is provided in an airtight manner with respect to the outer surface of the storage portion 22 so as to cover the substantially lower half of the storage portion 22, and partitions 27 and 28 having a triple concentric cylindrical structure are provided on the lower surface of the housing 26. , 29 are provided with their axial directions vertical. The space between the housing 26 and the storage portion 22 communicates with the central partition 27, so that the gas discharged from the storage portion 22 into the housing 26 through the opening 23 passes through the partition 27. To be fed into the reaction tube. A pipe 30 communicates with a space between the central partition 27 and the outer partition 28, and sheath Ar gas is supplied to the space through the pipe 30. Further, a pipe 31 communicates with the space between the partition 28 and the outermost partition 29, and H ₂ gas as a reducing gas is supplied to the space through the pipe 31. Therefore, the vaporized gas that has been carried by the Ar gas is supplied from the inside of the partition 27 into the reaction tube 20, and the sheath Ar gas is supplied from the space between the partition 27 and the partition 28 into the reaction tube 20. A reducing H ₂ gas is supplied into the reaction tube 20 from the space between the partition 29 and the partition 29.

  Further, a pressurized Ar gas inlet 32 is provided on the upper peripheral surface of the reaction tube 20. Heating coils 33 and 34 are installed on the outside of the reaction tube 20 aligned with the storage portion 22 and on the outside of the reaction tube 20 aligned in the vicinity of the gas discharge holes of the partitions 27 to 29, respectively. A cooling device 35 for cooling the reaction tube by circulating cooling water is installed below the heating coil 34. A region in the reaction tube in which the heating coil 33 is installed is a vaporization unit where the metal chloride gas is vaporized, a region in the reaction tube in which the heating coil 34 is installed is a reaction unit in which the metal chloride gas and the reducing gas are reacted, A region where the cooling device 35 is installed is a cooling unit. A powder collection container 36 is installed at the lower end of the reaction tube 20, and a bag-like filter 37 for collecting powder is provided in the container 36. The remaining gas whose powder has been collected in the bag-shaped filter 37 is discharged to the outside from the discharge port 38.

  Thus, in this embodiment, the reaction tube 20 is a straight tube (straight tube portion 20a) in a part of the vaporization part and the reaction part, but from the rear part of the heating region of the reaction part toward the outlet of the cooling part. The tube diameter is reduced, and the cross-sectional area of the gas flowing through the reaction tube 20 decreases from the rear part of the heating region of the reaction part toward the outlet of the cooling part (tapered part 20b). And the connection part with the collection | recovery apparatus 36 of the lower end part of the reaction tube 20 is the straight pipe part 20d with a small diameter. The tapered portion 20b in which the gas flow cross-sectional area of the reaction tube 20 is small is such that the inner surface of the reaction tube is inclined by, for example, 5 ° with respect to the inner surface of the straight tube portion in the cross section passing through the axial center of the reaction tube 20. . Further, as is clear from the above description, the boundary 20c between the straight pipe portion 20a extending from the vaporization portion to a part of the reaction portion and the tapered portion 20b having a reduced cross-sectional area is a heating coil 34 of the reaction portion. Is in the heating zone of the reaction zone where is located. Further, the tapered portion 20b of the inner surface of the reaction tube below the boundary 20c only needs to be such that the inner surface of the tube is inclined with respect to the axial center in the tube cross section and the gas flow cross-sectional area is gradually reduced. It does not necessarily have to be inclined.

Next, the operation of the metal fine particle manufacturing apparatus configured as described above will be described. After the cover 24 is opened and the NiCl ₂ raw material is stored in the storage unit 22 and the cover 24 is installed in the storage unit 22, pressurized Ar gas is introduced into the reaction tube 20 from the inlet 32, and carrier Ar gas, sheath Ar gas and H ₂ gas are introduced into the reaction tube, respectively. And it supplies with electricity to the heating coils 33 and 34, and the heating of the metal chloride 21 in a reaction tube is started. The heating of the metal chloride 21 in the vaporizing section by the heating coil 33 is, for example, 1000 ° C. when the metal chloride is NiCl ₂ and CuCl. The vaporized gas vaporized from the metal chloride 21 is carriered by Ar gas and introduced from the partition 27 into the reaction section in the reaction tube 20. Then, in the reaction section inside the reaction tube 20, the vaporized gas of NiCl ₂ metal chloride is reduced by the H ₂ gas while being heated by the heating coil 34, and Ni fine powder is generated. The Ni fine powder is carried by the carrier gas and reaches the cooling unit 35, where it is cooled by the cooling device 35. The Ni fine powder is blocked by a bag-like filter and collected in the filter 37. The gas is discharged from the discharge port 38.

  In the present embodiment, the diameter of the inner surface of the reaction tube is gradually reduced at the tapered portion 20b that goes downstream from the boundary 20c in the reaction portion surrounded by the heating coil 34, and the flow gas is reduced while being restricted in the reaction tube. It is supplied to the recovery device 36 from the pipe part 20d. Thus, since the inner diameter of the reaction tube 20 becomes smaller toward the downstream side, the gas containing the metal powder after hydrogen reduction is in the temperature drop region of the cooling part following the soaking region by the heating coils 33 and 34. , Its volume shrinks. If the entire reaction tube has a straight tube shape as in the prior art, the linear flow rate of the gas decreases as the temperature drops. When the linear flow velocity of the gas decreases, countercurrent and convection are likely to occur, so that the upstream gas is disturbed by the downstream gas. The metal fine particles in the turbulent flow field are significantly more likely to come into contact with each other than the fine particles in the field where the flow is not turbulent. For this reason, particles are connected to generate connected particles.

  However, as in the present invention, when the inner diameter of the reaction tube decreases from the lower part of the soaking part to the temperature drop part, the gas flow cross-sectional area is reduced toward the downstream side in the gas flow direction. The decrease in the gas volume is compensated by the reduction in the cross-sectional area of the flow passage, and the reduction in the linear flow velocity of the gas can be prevented. For this reason, countercurrent and convection do not occur, and the generation of connected particles can be suppressed. Moreover, it is preferable that the lower end temperature of this taper part 20b is lower than the temperature which metal powder sinters. Otherwise, there is a possibility that connected particles are generated in the straight pipe portion 20d below the tapered portion 20b where the inner diameter decreases. For this reason, it is preferable that the cooling device 35 sufficiently cools so that the lower end temperature of the tapered portion 20b (upper end temperature of the straight pipe portion 20d) is 200 ° C. or lower, preferably 100 ° C. or lower.

  The reason why the boundary 20c is the lower part in the reaction part (soaking part) heated by the heating coil 34 as in the present invention is that there is a temperature drop at the outlet of the soaking part. This is because there is a decrease in the linear flow rate due to a temperature drop even in the region where is arranged.

  The tapered portion 20b in which the flow cross-sectional area of the reaction tube 20 is continuously reduced is such that the tube inner surface of the tapered portion 20b is inclined by 1 to 5 ° with respect to the tube inner surface of the straight tube portion 20a. It is preferable. As a result, the counter-current and convection described above can be more reliably prevented, and a decrease in the linear flow velocity of the flow gas can be reliably prevented.

  FIG. 2 is a view showing a metal fine particle manufacturing apparatus and method according to another embodiment of the present invention. The apparatus of the present embodiment is different from the apparatus shown in FIG. 1 in that the tapered portion 20b of the reaction tube 20 is divided into a plurality of portions 20b1, 20b2, and 20b3, and the portions 20b1 and 20b2 are separated by the flange 40. That is, the portion 20 b 2 and the portion 20 b 3 are connected by the flange 41. These parts 20b1 to 20b3 are connected, the diameter of the pipe is reduced from the rear part of the heating area of the reaction part toward the outlet of the cooling part, and the flow cross-sectional area of the gas flowing through the reaction pipe 20 is the reaction part. It becomes small toward the exit of a cooling part from the rear part of a heating area | region.

  In the present embodiment, the cooling part (tapered part 20b) of the reaction tube 20 is divided into a plurality of parts, and the divided parts 20b1 to 20b3 are connected by the flanges 40 and 41, so the connection mode of the flanges is changed. For example, if the flange 41 is directly connected to the recovery device 36, the cooling length of the cooling portion (taper portion 20b) can be shortened. Conversely, if the number of divided parts is increased, the cooling length of the cooling part (tapered part 20b) can be increased. Since the cooling length can be adjusted in this way, according to the present embodiment, it is easy to control the cooling unit outlet temperature to a predetermined value.

Hereinafter, the effects of the examples satisfying the claims of the present invention will be specifically described in comparison with comparative examples that are out of the scope of the present invention. Metal fine particles were produced using the production apparatus shown in FIG. 1, and the material of the reaction tube 20 was made of quartz, alumina, or metal made of metal. Further, hydrogen gas was used as the reducing gas. The raw material metal chloride 21 is Ni chloride and Cu chloride. And the metal powder of Ni microparticles and Cu microparticles | fine-particles was produced | generated on the conditions shown in following Table 1.

  Further, as a comparative example, a straight tubular reaction tube was used, and the other fine particles of Ni, Cu, and Ag were produced by the production apparatus shown in FIG. 1 under the same conditions as in the example. The evaluation results of the metal powders of Examples 1 to 4 and Comparative Examples 1 to 4 are summarized in Table 2 below.

  Regarding the metal powders of the examples and comparative examples manufactured under the above conditions, surface morphology observation by FE-SEM (Field Emission-Scanning Electron Microscope), TEM (Transmission Electron Microscope: transmission electron microscope) As a result of observing the metal powders of Examples 1 to 12 with FE-SEM, no connection of particles was observed, so that the metal powders of Examples 1 to 12 were used for MLCC internal electrodes. It was suitable as.

  On the other hand, when the metal powders of Comparative Examples 1 to 6 using a reaction tube having a straight tubular region were observed with FE-SEM, the particles were connected. For this reason, the particle size was not measured. Since the metal powder used for MLCC is required to be spherical, the metal powders of Comparative Examples 1 to 6 were unsuitable for MLCC internal electrodes.

  3 shows an FE-SEM photograph of the Ni powder of Example 2, and FIG. 4 shows an FE-SEM photograph of the Ni powder of Comparative Example 2. In FIG. 4, frozen particles were observed.

It is sectional drawing which shows typically the metal powder manufacturing apparatus which concerns on embodiment of this invention. It is sectional drawing which shows typically the metal powder manufacturing apparatus which concerns on other embodiment of this invention. 4 is an FE-SEM photograph of Ni powder of Example 2. 4 is an FE-SEM photograph of Ni powder of Comparative Example 2. It is sectional drawing which shows the Ni powder manufacturing apparatus by the conventional gaseous-phase hydrogen reduction method.

Explanation of symbols

20; reaction tube 21; metal chloride (NiCl ₂ )
22; storage 23; opening 24; lids 25, 30, 31; pipe 26; housings 27 to 29; partition 30; cooling mechanism 31; straight pipe 32; gas inlet 33, 34; Recovery device 37; bag-like filter 38; outlet

Claims (7)

In an apparatus for producing metal fine particles by a gas phase hydrogen reduction method of a metal chloride gas, a reaction tube, a vaporization section for heating and vaporizing the metal chloride disposed in the reaction tube, and a reducing gas in the reaction tube A supply device for supplying, a reducing section for reducing the metal chloride by reacting the vaporized gas of the metal chloride with the reducing gas in the reaction tube, a cooling section for cooling the gas after the reduction reaction, A recovery device connected to a reaction tube for recovering solid metal particles solidified from the vaporized gas, wherein vaporization, reduction reaction, and cooling are continuously performed in the reaction tube, and the reaction tube includes the reaction The gas flow cross-sectional area is small so that the gas flow rate at the outlet of the cooling unit is greater than or equal to the gas flow rate at the rear of the heating region, from the rear of the heating region to the cooling unit outlet. Metal powder production apparatus according to claim and. The metal powder production apparatus according to claim 1, wherein the metal chloride is nickel chloride, and the metal fine particles are Ni fine powder having an average particle diameter of 50 to 150 nm. The metal powder production apparatus according to claim 1 or 2, wherein the temperature of the vaporized gas at the outlet of the cooling unit is 200 ° C or lower. 4. The metal particles according to claim 1, wherein the metal particles are a metal selected from the group consisting of Ni, Cu, Co, Fe, Ag, W, Mo, Nb, and Ta, or an alloy thereof. The metal powder manufacturing apparatus of 1 item | term. The metal powder production apparatus according to any one of claims 1 to 4, wherein the reaction tube is connected by a flange in the middle of the cooling unit. In a method for producing metal fine particles by a gas phase hydrogen reduction method of a metal chloride gas, a step of heating and vaporizing the metal chloride in a vaporization section in the reaction tube, and supplying a reducing gas into the reaction tube to supply the inside of the reaction tube The step of reacting the metal chloride vaporized gas with the reducing gas to reduce the metal chloride, the step of cooling the gas after the reduction reaction, and the step of recovering solid metal particles from the vaporized gas And the vaporization, reduction reaction, and cooling are continuously performed in the reaction tube, and the gas flow from the rear part of the heating region in the reaction part toward the outlet of the cooling part. A method for producing metal powder, characterized in that the cross-sectional area is small, and the gas flow rate at the outlet of the cooling unit is equal to or higher than the gas flow rate at the rear part of the heating region. The method for producing metal powder according to claim 6, wherein the temperature of the vaporized gas at the outlet of the cooling unit is 200 ° C. or less.

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