Manufacturing method of metal powder and manufacturing apparatus of metal powder

Abstract

A method for manufacturing metal powder involves heating and melting at least a portion of a metal raw material placed in a sealed crucible within a reaction vessel. While storing the molten metal, at least a portion of the molten metal evaporates to generate metal vapor. This metal vapor, along with a carrier gas introduced into the crucible, moves from the crucible towards a cooling pipe for cooling. Alternatively, a method involves introducing gas from outside the reaction vessel into the reaction vessel, which absorbs heat from the crucible to cool it. Simultaneously, the gas is heated, and at least a portion of this heated gas is introduced into the crucible as the carrier gas. According to the present invention, a method and apparatus for manufacturing metal powder can be provided, which solves the problems of crucible deterioration and impurity contamination of the metal powder, and also helps to reduce the manufacturing cost of metal powder.

Description

Technical Field

[0001] This invention relates to a method and apparatus for manufacturing metal powder. Prior Technology

[0002] One known method for manufacturing fine metal powders is the use of plasma (see, for example, Patent Document 1). This method utilizes plasma to melt and evaporate a metal raw material in a sealed crucible. The metal vapor, along with a carrier gas (also called a dilution gas), is then transferred from the crucible to a cooling tube. In the cooling tube, the metal vapor is cooled and condenses into microparticles, thereby obtaining metal powder. To minimize localized condensation of the metal vapor, the carrier gas system is injected into the plasma chamber at a sufficiently high temperature (at least 1000 K) equivalent to the temperature of the metal vapor in the crucible.

[0003] Therefore, for crucibles storing molten metal at temperatures above the melting point of metals, high fire resistance and heat resistance are required. Thus, research has been conducted on using metals such as copper as the constituent materials of the crucible, and using water cooling or oil cooling mechanisms to cool the crucible in a way that the metal crucible is not molten.

[0004] However, when water-cooling or oil-cooling mechanisms are used in this way, the overall structure of the manufacturing equipment becomes more complex, equipment and maintenance costs increase, and it may even be related to the increase in the cost of the metal powder that is part of the manufactured product.

[0005] Furthermore, within the metal crucible, a large temperature difference arises between the parts cooled by the aforementioned cooling mechanism and the parts in direct contact with the molten metal, resulting in increased thermal stress between them. This causes problems even on the durability surface of the metal crucible. On the other hand, if the metal crucible is overcooled in a way that prioritizes durability and avoids the aforementioned thermal stress, the evaporation of the stored molten metal is suppressed, leading to a decrease in the efficiency of metal powder production.

[0006] Because of these issues, oxide-based ceramic crucibles (especially zirconium dioxide crucibles) with superior refractoriness and heat resistance compared to metal crucibles are generally used. While ceramic crucibles generally offer better refractoriness and heat resistance than metal crucibles, prolonged exposure to high temperatures accelerates their deterioration, increases the crucible's exchange frequency, and impacts productivity. Furthermore, components of the ceramic crucible can dissolve into the molten metal, becoming impurities that seep into the metal powder. Therefore, even with ceramic crucibles, cooling is preferable to extend their lifespan. This cooling is achieved by directly or indirectly exposing the crucible to cooling gas. [Previous Technical Documents] [Patent Literature]

[0007] [Patent Document 1] Japanese Patent No. 3541939 Summary of the Invention

[0008] (The problem the invention aims to solve)

[0009] On the other hand, as mentioned above, the carrier gas system that transfers metal vapor from the crucible to the cooling tube must be supplied to the crucible in order to heat (preheat) it to a high temperature of at least 1000K. Therefore, from the perspective of manufacturing cost, the energy required for heating the carrier gas cannot be ignored.

[0010] The purpose of this invention is to provide a method and apparatus for manufacturing metal powder, which efficiently implements the heating of the carrier gas and the cooling of the reaction vessel (especially the crucible), thereby solving the problems of crucible deterioration and impurity contamination of the metal powder, and also helps to reduce the manufacturing cost of metal powder. (Technical means to solve the problem)

[0011] The aforementioned problems can be solved by the following manufacturing method and apparatus. Specifically, the method for manufacturing metal powder according to the present invention (1) involves heating and melting at least a portion of the metal raw material fed into a sealed crucible within a reaction vessel. While storing the molten metal, at least a portion of the molten metal evaporates to generate metal vapor. This metal vapor, along with a carrier gas introduced into the crucible, moves from the crucible towards a cooling pipe and is cooled, thereby manufacturing metal powder. The gas introduced from outside the reaction vessel into the reaction vessel absorbs heat from the crucible, thereby cooling the crucible and simultaneously heating the gas. At least a portion of the heated gas is introduced into the crucible as the carrier gas.

[0012] The method for manufacturing metal powder of the present invention (2) is as described in (1), wherein the crucible is provided with a vent hole at its upper part, and the heated gas is introduced into the crucible as the carrier gas through the vent hole.

[0013] The method for manufacturing metal powder of the present invention (3) is as described in (2), wherein the crucible is composed of a crucible body for storing the molten metal and a cover covering the crucible body, and the vent is formed on the cover.

[0014] The method for manufacturing metal powder of the present invention (4) is as described in (1), wherein at least a heat insulation portion is provided on the outer surface of the crucible, and the gas absorbs heat from the heat insulation portion to cool the crucible.

[0015] The method for manufacturing the metal powder of the present invention (5) is as described in (1), wherein the cooling gas is introduced into the reaction vessel at a position lower than the crucible in the reaction vessel.

[0016] The method for manufacturing the metal powder of the present invention (6) is the method described in any one of (1) to (5), wherein, The cover has a shape that includes an airflow guide that protrudes from the inner side of the crucible. The carrier gas introduced into the crucible by the airflow guide is induced to move toward the molten metal.

[0017] The metal powder manufacturing apparatus of the present invention (7) comprises: Reaction vessel; Plasma generation system, which generates plasma; The crucible is a sealed crucible disposed within the aforementioned reaction vessel, into which at least a portion of the aforementioned plasma generation system is embedded. At least a portion of the metal raw material fed into the crucible is melted by the aforementioned plasma and stored as molten metal. Simultaneously, at least a portion of the molten metal evaporates to generate metal vapor. A cooling pipe, connected from inside the crucible to the outside of the reaction apparatus, cools the metal vapor transported from the crucible by a carrier gas, thereby producing metal powder; and A gas inlet section introduces gas from outside the reaction vessel into the reaction vessel. The crucible is positioned within the flow path through which the gas introduced from the gas inlet is introduced and moves into the crucible. The gas is used to absorb heat from the crucible to cool it, while simultaneously heating the gas. At least a portion of the heated gas is introduced into the crucible as a carrier gas.

[0018] The metal powder manufacturing apparatus of the present invention (8) is the metal powder manufacturing apparatus described in (7). The crucible has a vent at its top, through which the heated gas is introduced into the crucible as a carrier gas.

[0019] The metal powder manufacturing apparatus of the present invention (9) is the metal powder manufacturing apparatus described in (8). The crucible is composed of a crucible body for storing the molten metal and a cover covering the crucible body, and the vent is formed in the cover.

[0020] The metal powder manufacturing apparatus of the present invention (10) is the metal powder manufacturing apparatus described in (7). The crucible is provided with a heat insulation part on at least a portion of its outer surface, and the crucible is cooled by the gas absorbing heat from the heat insulation part.

[0021] The metal powder manufacturing apparatus of the present invention (11) is the metal powder manufacturing apparatus described in (7). The gas inlet is located inside the reaction vessel at a position lower than the crucible.

[0022] The metal powder manufacturing apparatus of the present invention (12) is the metal powder manufacturing apparatus described in any one of (7) to (11). The aforementioned covering has a shape that includes an airflow guide portion protruding from the inner side of the crucible. The carrier gas introduced into the crucible by the airflow guide is induced to move toward the molten metal. (Compared to the effectiveness of previous technologies)

[0023] According to the present invention, a method and apparatus for manufacturing metal powder can be provided, which effectively implements the heating of the carrier gas and the cooling of the reaction vessel (especially the crucible), thereby solving the above-mentioned problems, namely, the problems of crucible deterioration and impurity contamination of metal powder, and also helping to reduce the manufacturing cost of metal powder. Simple Explanation of the Diagram

[0024] Figure 1 is a schematic cross-sectional view showing the metal powder manufacturing apparatus of the first embodiment. Figure 2 is a schematic cross-sectional view showing the metal powder manufacturing apparatus of the second embodiment. Implementation

[0025] The following description, with reference to the drawings, outlines an apparatus for manufacturing metal powder and a method for manufacturing metal powder using the same apparatus. As an example, the metal powder manufacturing apparatus of the following embodiment employs a portable DC arc plasma system identical to that described in Patent Document 1. A metal block is melted to generate a molten metal solution, from which metal vapor is generated. This metal vapor, along with a carrier gas, is transported to a cooling tube and cooled, thereby manufacturing metal powder. Compared to other plasma systems, the portable DC arc plasma system effectively utilizes the energy generated during manufacturing, significantly reducing the cost of manufacturing metal powder. [First Implementation Form]

[0026] As shown in Figure 1, the metal powder manufacturing apparatus 11 includes: a reaction vessel 12; a plasma generation system 13 spanning the inside and outside of the reaction vessel 12 and capable of generating plasma 29 inside the reaction vessel 12; a crucible body 15 disposed inside the reaction vessel 12 and capable of storing molten metal raw materials 14; and a cover 16 covering the upper side of the crucible body 15. The crucible body 15 and the cover 16 constitute the sealed crucible of the present invention. Furthermore, the manufacturing apparatus 11 includes: a gas inlet 17 for introducing gas used for cooling the crucible (hereinafter, it may also be simply referred to as cooling gas) from the outside of the reaction vessel 12 to the inside; a vent 18 communicating between the inside of the reaction vessel 12 disposed on the cover 16 and the inside of the crucible; a cooling pipe 21 extending from the crucible to the outside of the reaction vessel 12; and a heat insulation part 22 that retains at least a portion of the outside of the crucible. Furthermore, although not shown in the figure, the manufacturing apparatus 11 has the same metal raw material input path as described in Patent Document 1, which is used to input the metal block, which will become a metal raw material, into the crucible. As a cooling gas, air, carbon dioxide, or even low-activity / inactive gases such as nitrogen and argon, or mixtures thereof, can be used appropriately.

[0027] The metal materials that can be put into the crucible can be silver, gold, cadmium, cobalt, copper, iron, nickel, palladium, platinum, rhodium, ruthenium, tantalum, titanium, tungsten, zirconium, molybdenum, niobium, and alloys thereof.

[0028] In this embodiment, the plasma generation system 13 is composed of a portable DC arc plasma system, but it can also be other types of plasma generation systems. In the case of a portable DC arc plasma system, the plasma generation system 13 is as well known in the art (see, for example, Patent Document 1), having a plasma torch 26, a first positive electrode and a negative electrode (not shown) inside the plasma torch 26, and a second positive electrode 27 on the crucible side. Plasma generating gas is supplied from a supply pipe (not shown). As for the plasma torch 26, after plasma is generated by using the negative electrode as the cathode and the first positive electrode as the anode, the anode is transferred to the second positive electrode 27, thereby generating plasma 29 between the plasma torch 26 and the second positive electrode 27. The reaction vessel 12 (storage container) can be formed of a metal material with good refractory and heat resistance, or it can be formed of ceramic material and other refractory materials.

[0029] The crucible comprises a crucible body 15 and a cover 16. The shape of the crucible body 15 is not particularly limited; for example, although not shown, it can be pot-shaped, with a second positive electrode 27 positioned at the center of its bottom, allowing it to communicate with the metal material inside the crucible body 15. Regarding the crucible body 15, a metal block, which is the metal material, is fed into it through the aforementioned metal material feeding path, while the cover 16 covers the crucible body 15, thus creating a nearly sealed crucible to the outside. The shape of the cover 16 is not particularly limited if it covers the crucible body 15; for example, it can be a deep concave dish inverted as shown in the figure. Furthermore, in this example, the crucible 15 and the cover 16 are constructed as separate components as indicated by the dotted lines in the figure; they can also be constructed as a single unit.

[0030] At least a portion of the plasma torch 26 is inserted into the crucible through an opening (not shown) on the upper part of the cover 16, thereby generating plasma 29 from the front end of the plasma torch 26 within the sealed crucible. Then, the heat of the plasma 29 melts at least a portion of the metal material in the crucible, storing it in the crucible as molten metal. Simultaneously, at least a portion of the molten metal evaporates through further heating, becoming metal vapor within the sealed crucible.

[0031] As an example, both the crucible body 15 and the cover 16 can be formed of refractory ceramic materials. More specifically, the crucible 15 and the cover 16 can be carbides such as graphite, tantalum carbide, silicon carbide, and titanium carbide; oxides such as magnesium oxide, aluminum oxide, and zirconium dioxide; or nitrides such as titanium nitride, tantalum nitride, zirconium nitride, and boron nitride. Furthermore, they can be borides such as titanium diboride, tantalum diboride, and zirconium diboride; or refractory materials such as tungsten, tantalum, molybdenum, and niobium, or materials with high melting temperatures. Then, as shown in the figure, a vent 18 is provided on the upper part of the cover 16 to connect the inside of the reaction vessel 12 with the inside of the crucible.

[0032] The cooling gas system, introduced from the outside of the reaction vessel 12 through the gas inlet 17, enters the crucible through the vent 18 after being used for crucible cooling, ensuring a proper flow path within the reaction vessel. Once introduced into the crucible, this cooling gas acts as a carrier gas for transporting the metal vapor within the crucible.

[0033] There are no particular limitations on the location, shape, number, etc. of the vent holes 18. For example, the flow path (airflow) of the gas in the reaction vessel 12 can be obtained by using a simulator, thereby determining the location, shape, and number of vent holes that can be effectively introduced into the crucible.

[0034] Cooling tube 21 is connected to the crucible through the reaction vessel 12. Metal vapor generated in the crucible by the heat of the plasma 29 from the molten metal 14 is transported to cooling tube 21 by the aforementioned carrier gas. Then, the metal vapor is cooled in cooling tube 21. After metal condensation nuclei are generated in the gas phase (carrier gas), metal powder is produced by particle growth and collected by the collection part 23 outside cooling tube 21. As an example, cooling tube 21 is made of heat-resistant metal material, ceramic material, etc. Depending on the situation, a cooling mechanism can also be set around cooling tube 21 and cooled from the outside by a fluid such as water.

[0035] Other cooling pipe configurations, besides those implementing two-stage cooling as described in Patent Document 1, may also include those with two or more intervals having different inner diameters as described in Japanese Patent Application Publication 2013-112893, or those with protrusions and recesses on the inner wall as described in International Publication WO2013 / 084650.

[0036] While not strictly necessary in this invention, it is preferable to provide a heat insulation portion 22 to at least a portion of the outside of the crucible. By providing the heat insulation portion 22, the cooling gas from the gas inlet 17 can be prevented from directly contacting the outside of the crucible, thereby mitigating or preventing problems related to thermal stress generated on the crucible due to the aforementioned cooling.

[0037] The heat insulation portion 22, as shown in the figure, can be attached inside the reaction vessel 12 to almost completely cover the outside of the crucible, or it can only cover a portion of the outside. Alternatively, it can be attached to cover the entire outer surface of the cover 16. Furthermore, the heat insulation portion 22 can be attached only to the periphery of the crucible's exterior and held in place by other components not shown, thereby fixing the position of the crucible relative to the reaction vessel 12.

[0038] The material of the heat insulation section 22 (heat insulation material) is not particularly limited. Refractory materials such as alumina felt, graphite felt, zirconium dioxide felt, and graphite layers can be used. Furthermore, various shapes such as sand-like, granular, or felt-like materials can be used. It is preferable that the heat insulation section 22 has good ventilation, so that the cooling gas system can flow through the heat insulation section 22 into the reaction vessel 12.

[0039] Furthermore, in this invention, cooling where the cooling gas directly contacts the outside of the crucible is referred to as "direct cooling," while cooling where the cooling gas does not directly contact the outside of the crucible is referred to as "indirect cooling." For example, when a heat insulation part is attached to the outside of the crucible, it is usually indirect cooling. Even in this case, direct cooling can occur when a portion of the cooling gas passes through the interior of the heat insulation material and contacts the outside of the crucible due to the permeability of the heat insulation material. In this invention, whether it is direct or indirect cooling, the cooling gas can cool the crucible by absorbing heat from it. In addition, it is preferable to use direct cooling and indirect cooling separately based on the temperature of the molten metal, the material and shape of the crucible used, etc., but they can also be used in combination depending on the circumstances. Next, the method for manufacturing metal powder using the metal powder manufacturing apparatus 11 of this embodiment will be described.

[0040] First, to prepare the metal material inside the crucible body 15, the metal raw material can be directly added into the crucible body 15 by opening the cover 16, including the case where the cover 16 and the crucible body 15 are integrally formed. Alternatively, the metal raw material block can be added through the aforementioned metal raw material input path without opening the cover 16. Next, the plasma generation system 13 is activated to generate plasma 29 inside the crucible. By the heat generated by the plasma 29, at least a portion of the metal raw material melts, and molten metal 14 is generated inside the crucible body 15. At the same time, by the heat generated by the plasma 29, at least a portion of the molten metal 14 evaporates, generating metal vapor inside the crucible.

[0041] On the other hand, although not shown in the figure, cooling gas is introduced into the reaction vessel 12 via the gas inlet 17 through the gas inlet 17 in the direction of the arrow in the figure. The arrow in the figure indicates an example of the flow path of the cooling gas and / or the carrier gas. The crucible is cooled by the cooling gas directly or indirectly contacting at least a portion of the outside of the crucible through the flow path, absorbing heat from the crucible. At the same time, the cooling gas system is heated to a high temperature of 1000K or higher required for the carrier gas. Then, the heated cooling gas system can be introduced into the crucible through the vent 18 along the gas flow path inside the reaction vessel 12 and used as a carrier gas.

[0042] The gas system introduced into the crucible as a carrier gas transports the metal vapor generated from the molten metal 14 to the cooling tube 21, where the metal vapor is cooled. In this process, a large number of condensation nuclei in the carrier gas (in the gas phase) are generated from the metal vapor. These nuclei further grow, thereby producing metal powder with uniform particle size and high sphericity. The metal powder is then collected in the collection section 23.

[0043] The key feature of this invention is that the gas initially introduced through the gas inlet 17 to cool the crucible is heated by the cooling process, and then introduced into the crucible and used as a carrier gas. Conventionally, separate gases are prepared for crucible cooling (cooling gas) and metal powder transport (carrier gas). With this invention, it is unnecessary to prepare multiple gases, and the gas piping within the manufacturing apparatus can be simplified, even reducing the manufacturing cost of the metal powder. Furthermore, by cooling the crucible, its lifespan can be extended, further reducing the manufacturing cost of the metal powder, and contamination of the metal powder can be suppressed, contributing to improved powder quality. Moreover, since the carrier gas is heated through heat exchange with the crucible, the amount of energy used during manufacturing can be reduced. [Second Implementation]

[0044] The following description focuses on the parts that differ from the first embodiment described above, while the parts that are the same as the first embodiment are omitted. As shown in Figure 2, in the second embodiment, the cover 16 has an airflow guide 24 protruding from its inner side toward the inside of the crucible, and also has an exhaust section 25 that connects the inside and outside of the reaction vessel 12.

[0045] The airflow guide 24 is positioned to surround the vent 18, and is configured to guide the gas introduced into the crucible through the vent 18 as a carrier gas toward the molten metal 14. This increases the flow rate of the carrier gas toward the molten metal 14 within the crucible, promotes the evaporation of metal vapor from the molten metal 14, and facilitates the carrying of metal vapor onto the carrier gas flow, thereby increasing the yield of metal powder. Preferably, the airflow guide 24 is integrally formed using the same material as the cover 16, but it can also be separable.

[0046] The exhaust section 25 is provided to discharge a portion of the gas introduced from the gas inlet section 17 as cooling gas to the outside of the reaction vessel 12. In cases where the flow rate of cooling gas required to cool the crucible is greater than the flow rate of carrier gas needed to transport metal vapor, the reaction vessel 12 becomes clogged with gas. Therefore, a portion of the heated cooling gas is discharged from the exhaust section 25 to the outside of the reaction vessel 12, while the remaining cooling gas is utilized as carrier gas. Furthermore, when the heated cooling gas is discharged from the exhaust section 25, it is preferable to extract the heat energy from the cooling gas through a heat exchanger or similar means for reuse. The above-described embodiments can be implemented by applying various substitutions and changes. Furthermore, the invention can also be achieved by appropriately combining the above-described embodiments with each other.

[0047] 11: Manufacturing equipment 12: Reaction Vessel 13: Plasma Generation System 14: Molten Metal 15: Crucible body 16: Cover 17: Gas Inlet Section 18: Vent hole 21: Cooling pipe 22: Insulation section 23:Collection Department 24: Airflow guide 25: Exhaust section 26: Plasma torch 27: Second positive electrode 29: Plasma

Claims

1. A method for manufacturing metal powder, comprising heating and melting at least a portion of a metal raw material fed into a sealed crucible disposed within a reaction vessel, storing the molten metal while evaporating at least a portion of the molten metal to generate metal vapor, and moving the metal vapor together with a carrier gas introduced into the crucible from the crucible toward a cooling tube for cooling, thereby manufacturing metal powder; wherein a gas introduced from outside the reaction vessel into the reaction vessel absorbs heat from the crucible to cool the crucible, and simultaneously heats the gas, and at least a portion of the heated gas is introduced into the crucible as the carrier gas.

2. The method for manufacturing the metal powder as described in claim 1, wherein, The crucible has a vent at its top, through which the heated gas is introduced into the crucible as a carrier gas.

3. The method for manufacturing the metal powder as described in claim 2, wherein, The crucible is composed of a crucible body for storing the molten metal and a cover covering the crucible body, and the vent is formed on the cover.

4. A method for manufacturing metal powder as described in claim 1, wherein, A heat insulation portion is attached to at least a portion of the outer surface of the crucible, and the gas absorbs heat from the heat insulation portion to cool the crucible.

5. A method for manufacturing metal powder as described in claim 1, wherein, At a position below the crucible within the aforementioned reaction vessel, the aforementioned gas used to cool the aforementioned crucible is introduced into the aforementioned reaction vessel.

6. A method for manufacturing metal powder as described in claim 3, wherein, The aforementioned cover has a shape with an airflow guide protruding from the inner side of the aforementioned crucible. The carrier gas introduced into the aforementioned crucible through the airflow guide is induced to move toward the aforementioned molten metal.

7. An apparatus for manufacturing metal powder, comprising: a reaction vessel; a plasma generation system for generating plasma; a crucible disposed within the reaction vessel, a sealed crucible into which at least a portion of the plasma generation system is inserted, wherein at least a portion of a metal raw material fed into the crucible is melted by the plasma and stored as molten metal, while at least a portion of the molten metal evaporates to generate metal vapor; a cooling pipe communicating from the inside of the crucible to the outside of the reaction vessel for cooling the metal vapor transported from the crucible by a carrier gas to manufacture metal powder; and a gas inlet for introducing gas from the outside of the reaction vessel into the reaction vessel; wherein the crucible is disposed within a flow path in which the gas introduced from the gas inlet is introduced and moves into the crucible, the gas is used to absorb heat from the crucible to cool the crucible, and the gas is simultaneously heated, and at least a portion of the heated gas is introduced into the crucible as a carrier gas.

8. The apparatus for manufacturing metal powder as described in claim 7, wherein, The crucible has a vent at its top, through which the heated gas is introduced into the crucible as a carrier gas.

9. The apparatus for manufacturing metal powder as described in claim 8, wherein, The crucible is composed of a crucible body for storing the molten metal and a cover covering the crucible body, and the vent is formed in the cover.

10. The apparatus for manufacturing metal powder as described in claim 7, wherein, At least a portion of the outer surface of the crucible is provided with a heat insulation portion, through which the gas absorbs heat from the heat insulation portion to cool the crucible.

11. The apparatus for manufacturing metal powder as described in claim 7, wherein, The gas inlet is located inside the reaction vessel at a position lower than the crucible.

12. The apparatus for manufacturing metal powder as described in claim 9, wherein, The aforementioned cover has a shape with an airflow guide protruding from the inner side of the aforementioned crucible. The carrier gas introduced into the crucible through the airflow guide is induced to move toward the aforementioned molten metal.

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