JP2022022743A - Method for producing metal powder - Google Patents

Abstract

To provide a method for producing metal powder by an atomization method utilizing metals comprising an organic compound, in which molten metal blur and the clogging of a tap nozzle are suppressed, and a long term continuous operation is possible.SOLUTION: A method for producing metal powder has a process where raw material metals are heated and melted into a molten metal, this molten metal is dropped, a fluid is blown on the flow of the dropping molten metal, and the molten metal is pulverized and solidified to obtain metal powder. The raw material metals includes a metal M including an organic compound, and, while holding the temperature of the molten metal to a temperature T satisfying specified conditions, an oxidizing gas is blown into the molten metal, and thereafter, the molten metal is dropped.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a metal powder.

Metal powder is an important material in the industry, and is used in various applications such as electronic materials, catalysts, battery active materials, tools, pharmaceuticals, and jewelry depending on its characteristics.

There are various methods for producing the metal powder, such as a wet reduction reaction, an atomizing method, and a plasma method, and the optimum production method is selected from the viewpoint of the use of the metal powder and the allowable cost.

Patent Document 1 describes in a metal powder manufacturing apparatus including a tundish that holds a molten metal and a spray fluid nozzle that injects a high-pressure fluid toward the molten metal that falls from the molten metal nozzle of the tundish. A device for producing a metal powder is disclosed, which comprises an elevating device for moving the tundish and the spray fluid nozzle up and down relative to each other.

Further, in Patent Document 1, when the molten metal nozzle is blocked due to the reverse injection of the molten metal, the tundish is moved upward by the elevating device, and the operator uses the oxygen blowing pipe to inject oxygen into the molten metal nozzle. Is disclosed to dissolve the substance clogged in the molten metal nozzle. The molten metal reverse injection is a phenomenon in which a part of the collision force of the fluid acts upward and a part of the molten metal is scattered upward at the site where the fluid and the molten metal (molten metal) collide in the atomizing method (Patent Documents). 2) (Part of the molten metal scattered upward adheres to and solidifies on the molten metal nozzle, blocking the nozzle. It is considered that oxygen is blown into the blocked substance (metal) as described above to oxidize the metal, and the heat generated by the oxidation reaction heats the blocked portion and the metal in the vicinity to the melting point or higher and melts the metal.

Further, Patent Document 3 describes the following method as a method for producing a high entropy alloy powder used for so-called 3D printing by gas atomizing this bullion after producing a high entropy alloy bullion by a smelting technique. The method is disclosed.

A melting step of melting a raw metal mass to generate a molten metal, a peroxide step of blowing oxygen gas into the molten metal to form slag, and a separation step of separating the slag floating on the liquid surface of the molten metal and the molten metal. A degassing step of blowing argon gas into the molten metal separated from the slag to degas the gas component in the molten metal, and a casting step of casting the degassed molten metal to form a cast alloy. In the method of manufacturing a cast alloy equipped with
The cast alloy includes a step of melting the cast alloy in a vacuum to form a molten alloy, and a powdering step of flowing the molten alloy and spraying an inert gas onto the flowing molten alloy to form an alloy powder. In the powder spreading step of spreading the alloy powder in layers, the spread alloy powder is locally heated and melted and then solidified to form a solidified structure, and the heated region by the local heating is described as described above. A plurality of layers of solidification are formed by alternately repeating the solidification layer forming step of moving the alloy powder parallel to the spread surface to form a solidified layer, and the powder spreading step and the solidifying layer forming step. Used in a series of steps to form a layer
The cast alloy contains Al, Co, Cr, Fe and Ni in the atomic concentration range of 5 at% or more and 30 at% or less, respectively, and the difference in atomic concentration of at least four of the above elements is less than 3 at%. As unavoidable impurities, P is 0.005 wt% or less, Si is 0.040 wt% or less, S is 0.002 wt% or less, Sn is 0.005 wt% or less, Sb is 0.002 wt% or less, A method for producing a cast alloy, characterized in that As is contained in an atomic concentration range of 0.005 wt% or less, Mn is 0.050 wt% or less, O is 0.001 wt% or less, and N is 0.002 wt% or less.

Japanese Unexamined Patent Publication No. 6-220508 Japanese Unexamined Patent Publication No. 62-151503 Japanese Unexamined Patent Publication No. 2016-28821

Generally, in the production of metal powder by the atomizing method, the raw metal is heated in a furnace to form a molten metal, and while the molten metal is dropped from a hot water nozzle provided at the bottom of the furnace, water or the like is added to the flow of the falling molten metal. The molten metal is crushed and solidified by spraying a fluid to form particles, and the obtained metal powder is recovered. Further, a classification process is carried out on the obtained metal powder to obtain a desired particle size distribution to obtain a final metal powder product. Then, as a by-product of classification, a metal powder excluded from the final product is produced. In the present specification, the metal powder on the side excluded from the final product is referred to as "classification residue".

In addition, in order to increase the fluidity of the metal powder, a surface treatment may be performed in which the surface of the particles is coated with an organic compound. If the fluidity of the powder is not increased, the classification process may not be successful. Therefore, the surface treatment is generally performed before the classification process.

Then, it is conceivable to dispose of the classification residue generated in the classification process (coated with the organic compound), but if this can be reused as a raw material for the molten metal, it will be an environmental burden in terms of the manufacturing cost of the metal powder. It is also advantageous in terms of. When the present inventors prepared a molten metal by reusing the classification residue and carried out continuous operation of atomization, hot water blurring and clogging of the hot water nozzle occurred in the middle, and long-term continuous operation of atomization could not be carried out. The hot water blur refers to a phenomenon in which at least a part of the molten metal discharged from the hot water nozzle does not fall in the vertical direction but scatters laterally.

The present invention is a method for producing a metal powder by an atomizing method using a metal containing an organic compound such as a residue of classification, and is a method for producing a metal powder capable of long-term continuous operation by suppressing hot water blurring and clogging of a hot water nozzle. The subject is to provide a manufacturing method.

In order to solve the above-mentioned problems, the present inventor first examined the causes of the above-mentioned hot water blurring and clogging of the hot water nozzle. Analysis of the substance clogged in the hot water nozzle revealed that it contained a large amount of carbon. The present inventor presumes that this is a carbide of the organic compound adhering to the surface of the unclassified particles, and in order to prevent this from occurring, the organic compound (decomposition) is reacted with oxygen in a high temperature environment called molten metal. The idea was to expel it as a gas such as carbon dioxide by making it, and after actual verification, the present invention was completed.

That is, the present invention is as follows.
[1] A method for producing a metal powder, in which a raw metal is heated and melted to form a molten metal, the molten metal is dropped, and a fluid is sprayed on the flowing molten metal to crush and solidify the molten metal to obtain a metal powder.
The raw material metal contains a metal M containing an organic compound, and while maintaining the temperature of the molten metal at a temperature T satisfying the following condition (1), the molten metal is dropped after blowing an oxidizing gas into the molten metal. , Metal powder manufacturing method:
(1) The free energy ΔGM of the oxide of the constituent metal of the molten metal at the temperature T is larger than the free energy _ΔGC of the oxide of the _carbon at the temperature T.

[2] A method for producing a metal powder, in which a raw metal is heated and melted to form a molten metal, the molten metal is dropped, and a fluid is sprayed on the flowing molten metal to crush and solidify the molten metal to obtain a metal powder.
The raw material metal contains a metal M containing an organic compound, and while maintaining the temperature of the molten metal at a temperature T satisfying the following condition (1), the molten metal is dropped after blowing an oxidizing gas into the molten metal. , Metal powder manufacturing method:
(1) For a metal having an amount of 92% by mass or more of the constituent metals of the molten metal, the free energy ΔGM of the oxide of the metal at the temperature T is larger than the free energy _ΔGC of the oxide of the _carbon at the temperature T.

[3] The method for producing a metal powder according to [1] or [2], wherein the ratio of the metal M to the raw metal is 5 to 100% by mass.

[4] The method for producing a metal powder according to any one of [1] to [3], wherein the metal M has a carbon content of 0.01 to 0.3% by mass.

[5] The method for producing a metal powder according to any one of [1] to [4], wherein the metal M is produced by a gas atomizing method or a water atomizing method.

According to the present invention, it is a method for producing a metal powder by an atomizing method using a metal containing an organic compound such as a classification residue, and is a metal capable of long-term continuous operation by suppressing hot water blurring and clogging of a hot water nozzle. A method for producing a powder is provided.

Hereinafter, embodiments of the present invention will be described.

[Manufacturing method of metal powder]
An embodiment of the method for producing a metal powder of the present invention is a method for obtaining a metal powder by a so-called atomizing method in which a fluid is sprayed on a molten metal, and a metal containing an organic compound is used as at least a part of a raw material for the molten metal. It is characterized by blowing an oxidizing gas into the molten metal under specific temperature conditions before blowing the fluid into the molten metal. The organic compound is typically attached to the particle surface in the classification residue, but a metal powder is produced, for example, by a wet synthesis reaction (the organic compound may be added to the reaction system for a desired effect). However, if a classification residue is generated from now on, it is considered that the organic compound may be caught inside the particles.

<Holding temperature T of molten metal>
In the present invention, for example, a specific raw material metal is charged into a normal atomizing furnace having a hot water nozzle at the bottom, and the raw material metal is heated and melted to prepare a molten metal. The raw material metal contains a metal M containing an organic compound. The molten metal may be prepared in another furnace such as a melting furnace, and the molten metal may be poured into the furnace having the hot water nozzle.

In the present invention, while maintaining the temperature of the prepared molten metal at a temperature T that satisfies the following condition (1), after blowing an oxidizing gas into the molten metal, the molten metal is dropped from the hot water nozzle to perform atomization. ..
(1) The free energy ΔGM of the oxide of the constituent metal of the molten metal at the temperature T is larger than the free energy _ΔGC of the oxide of the _carbon at the temperature T.

As a premise, the temperature T is a temperature at which the molten metal does not solidify (maintains the state of the molten metal). The "temperature at which the molten metal does not solidify" is a temperature equal to or higher than the melting point of the metal when the molten metal is composed of substantially a single metal. On the other hand, when the molten metal is an alloy molten metal composed of a plurality of kinds of metals, the temperature is higher than the melting point of the alloy. In the case of a molten metal in which a metal composed of a plurality of types of metals but not forming an alloy is present, the temperature is higher than the melting point of the metal having the highest melting point.

Regarding the above condition (1), the oxide free energy ΔG indicates that the oxide is more stable as the value thereof is smaller, and can be used as a guideline for the likelihood of reaction. If ΔG is a negative value, the oxide formation reaction occurs spontaneously.

In the present invention, when the molten metal is held at the high temperature T described above and an oxidizing gas is blown into the molten metal, the organic compound (or its decomposition product) contained in the metal M before the molten metal is oxidized and further. It is considered that the carbon-carbon bond of the carbon chain constituting the organic compound is cleaved to generate carbon dioxide or carbon monoxide, which is separated from the molten metal. It is considered that this prevents hot water blurring and clogging of the hot water nozzle due to the generation of carbides. Moreover, at the temperature T, carbon is more likely to be oxidized than the constituent metal of the molten metal. Therefore, it is considered that the generation of the above-mentioned two (1) carbon oxide is prioritized over the oxidation of the constituent metal. .. It is considered that this prevents unnecessary oxidation of the constituent metal. When the metal is oxidized, the melting point changes (in many cases, the melting point rises), and the viscosity of the molten metal also changes, which can cause hot water shake. Therefore, the above-mentioned oxidation prevention is also useful in terms of preventing hot water shake.

In the present invention, when the molten metal contains a plurality of constituent metals, it is not always necessary for all the constituent metals to satisfy the above condition (1) at the temperature T, but as described above, the oxidation of the metal causes the hot water to shake. Since it can be a cause, it is preferable that there are many constituent metals that satisfy the condition (1). Specifically, the proportion of the metal satisfying the above condition (1) among the constituent metals of the molten metal is preferably 92% by mass or more, and more preferably 96% by mass or more. Conversely, it is preferable to set the temperature T so that 92% by mass or more, more preferably 96% by mass or more of the constituent metals of the molten metal satisfy the condition (1).

Here, when the molten metal is an alloy molten metal, with respect to the oxidation of the constituent metals, the oxide of the alloy is formed, or the oxide of each constituent metal alone is generated without forming such an oxide. In some cases. In the former case, _ΔGM is the free energy for forming the oxide of the alloy, and in the latter case, there are a plurality of _ΔGMs , each of which is compared with _ΔGC .

With respect to the carbon oxide formation free energy _ΔGC under the condition (1), the carbon dioxide production free energy of the reaction in which carbon and oxygen react to generate carbon dioxide is approximately -390 kJ / molO at any temperature. It is constant at ₂ . On the other hand, the free energy for carbon monoxide formation in the reaction between carbon and oxygen to produce carbon monoxide decreases with increasing temperature, and the free energy for carbon dioxide formation (approximately -390 kJ / molO ₂ ) at about 700 ° C. ), And when the temperature rises further, it becomes smaller than the free energy of carbon dioxide production. In the present invention, the free energy ΔGC for producing carbon oxides is -390 kJ / molO ₂ at a temperature of 700 ° _C. or lower, and the free energy for producing carbon monoxide in a reaction in which carbon monoxide is produced at a temperature higher than 700 ° C. It shall be.

The difference between _ΔGM and _ΔGC at the temperature T ( _ΔGM − _ΔGC ) is preferably 80 kJ / molO ₂ or more, more preferably 150 kJ, from the viewpoint of effectively preventing the oxidation of the constituent metals of the molten metal. / MolO ₂ or more. Although there is no particular upper limit, the difference ( _{ΔGM −ΔGC} ) is preferably 240 to 700 kJ / molO ₂ . Among the constituent metals of the molten metal, the proportion of the metal satisfying such a difference ( _{ΔGM −ΔGC} ) is preferably 92% by mass or more, and more preferably 96% by mass or more.

Specific examples of metals to which the present invention can be suitably applied (metals in which the difference ( _ΔGM − _ΔGC ) falls within the above-mentioned preferable range in a relatively wide temperature range (particularly, the low temperature side capable of containing the melting point of the metal)) are silver. , Copper, iron, nickel and tin. The temperature at which _ΔGM is larger than ΔGC for each metal is about 750 ° _C. or higher for iron, 220 ° C. or higher for nickel, and about 650 ° C. or higher for tin. In addition, silver and copper have _ΔGM larger than _ΔGC in any temperature range.

Further, the temperature T is preferably 50 ° C. or higher higher than the melting point of the constituent metal of the molten metal from the viewpoint of surely preventing solidification of the molten metal, and is 50 higher than the melting point of the constituent metal in consideration of the burden on the furnace and the heat cost. It is more preferable that the temperature is higher by about 350 ° C. When the molten metal is a molten alloy, the "melting point of the constituent metal" is the melting point of the alloy.

<Metal M>
The raw material metal that is heated and melted and held at the temperature T includes a metal M containing an organic compound. Examples of the metal M include metal powder surface-treated with an organic compound to improve the fluidity of the powder, and a metal having an organic compound attached to the surface, such as a metal lump to which a resin is attached or coated. Be done.

The metal powder surface-treated with the organic compound is typically produced by the gas atomization method or the water atomization method described in the section [Problems to be solved by the invention], and the metal surface-treated with the organic compound. It is a classification residue excluded by classification in the powder, and the organic compound in this is, for example, an alcohol, an amine, a fatty acid or a thiol having 2 to 36 carbon atoms. Further, as an example of the aspect of the surface treatment, the embodiment is carried out by mixing the metal powder and the organic compound (which is a solid or liquid), or the embodiment is carried out by mixing the metal powder and the organic compound in the liquid. Alternatively, there is an embodiment in which the metal powder is reacted with the organic compound and the organic compound is chemically bonded to the metal powder.

Examples of metal ingots to which the resin adheres or is coated include those manufactured by recycling discarded electric products and electronic parts. These are called "nuggets" and the like, but they are suitable as raw materials for preparing molten metal because they are inexpensive. The resin is an organic compound, and even when this metal lump is used as a raw material for preparing a molten metal, hot water blurring and clogging of the hot water nozzle may occur. Long-term continuous operation is possible.

The carbon content of the metal M containing the organic compound described above is an index of the amount of the organic compound and is not particularly limited, but is, for example, 0.01 to 0.3% by mass, such as hot water blurring. Is likely to occur, and these can be suitably suppressed by applying the present invention, so that the content is preferably 0.02 to 0.2% by mass. Since the amount of the organic compound in the metal M is typically about this level (in terms of carbon), the amount of gas such as carbon dioxide generated by the implementation of the present invention is small.

In the embodiment of the method for producing a metal powder of the present invention, as the raw material metal, only the metal M containing the organic compound described above may be used, or a metal containing substantially no organic compound is mixed with the metal M. It may be a thing. The ratio of the metal M used in the molten metal raw material (ratio to the total raw material metal) is preferably 5 to 100% by mass, more preferably 10 to 100% by mass, and further, from the viewpoint of cost merit due to the use of the metal M. It is preferably 30 to 100% by mass.

<Blowing in oxidizing gas>
By blowing an oxidizing gas into the molten metal while keeping the molten metal at the temperature T described above, the organic compound (or its decomposition product) becomes a gas such as carbon dioxide and separates from the molten metal as described above. It is thought that it will continue. As a result, in atomization using a metal M containing an organic compound such as a classification residue as a raw material for molten metal, the occurrence of hot water blurring and clogging of the hot water nozzle is suppressed, and long-term continuous operation becomes possible.

Oxidizing gas contains oxygen. The oxidizing gas may be a gas containing 100% oxygen or a mixed gas of oxygen and another gas. Other gases do not interfere with the oxidizing action of oxygen and are not particularly limited as long as they are inert to the molten metal. In some cases, carbon is used as the material of the furnace for preparing and discharging the molten metal (carbon crucible) from the viewpoint of heat resistance and reactivity with the raw metal. In this case, if 100% oxygen gas is used. , Gas can wear the inner surface of the furnace. The oxidizing gas preferably contains 5 to 50% by volume of oxygen from the viewpoint of removing the organic compound from the molten metal and from the viewpoint of preventing its wear when a furnace made of a material containing carbon is used. It is more preferable to contain ~ 40% by volume. The atmosphere is very preferable because it meets this requirement and is inexpensive.

From the viewpoint of removing all the organic compounds, the amount of the oxidizing gas used may be 100% or more when the theoretical amount required to oxidize the entire amount of the organic compounds contained in the metal M is 100%. preferable. When the constituent metal of the molten metal is a metal that is extremely difficult to oxidize, such as silver, if an excessive amount of oxidizing gas is blown with respect to the theoretical amount, the organic compounds can be completely removed (oxidation). There is no particular upper limit to the amount of sex gas used). On the other hand, when the constituent metal is a metal that is easily oxidized (although it is less likely to be oxidized than carbon at a temperature T), an amount of 80 to 120% of an oxidizing gas is blown when the theoretical amount is 100%. It is preferable, and it is more preferable to blow an amount of 90 to 110% of the oxidizing gas. It is desirable that the amount of blown water is 100% or more of the theoretical amount when it is important to suppress hot water blurring and clogging of the hot water nozzle, and when it is important to prevent oxidation of the constituent metals, the amount of blown water should be 100% or less of the theoretical amount. Is desirable.

The theoretical amount is determined by measuring the carbon content of the metal M in advance and determining the amount required to convert all of the carbon into carbon monoxide or carbon dioxide. As described above, the free energy for producing carbon monoxide becomes smaller as the temperature rises, becomes the same as the free energy for producing carbon dioxide at about 700 ° C., and becomes smaller than the free energy for producing carbon dioxide at a higher temperature. From the above, the above theoretical amount is the amount required to convert all the carbon contained in the metal M into carbon dioxide when the temperature T is 700 ° C. or lower, and the metal M when the temperature T exceeds 700 ° C. The amount required to convert all of the carbon contained in carbon monoxide.

The preparation of the molten metal and the blowing of the oxidizing gas may be carried out under any of the conditions of atmospheric pressure, pressurization, and decompression. From the viewpoint of cost, it is preferable to carry out under atmospheric pressure.

<Spraying fluid>
A molten metal blown with an oxidizing gas at a predetermined temperature T is dropped from, for example, a hot water nozzle of a furnace, and a fluid is blown onto the flow of the falling molten metal to crush and solidify the molten metal to obtain a metal powder.

If the gas is present in the space above the molten metal after the oxidizing gas is blown in, it may dissolve in the molten metal to form a metal oxide. After purging with an inert gas such as Ar or N ₂ or a reducing gas such as H ₂ or CO), the molten metal may be dropped.

Examples of the fluid to be blown on the flowing molten metal include water and a gas having a temperature lower than the melting point of the molten metal. The gas needs to be inert to the molten metal.

The temperature of the molten metal when spraying the fluid is 50 to 800 ° C. from the melting point of the molten metal from the viewpoint of lowering the viscosity and increasing the crushing power of the fluid to obtain fine metal powder, and from the viewpoint of the burden on the furnace and the heat cost. It is preferably high, and more preferably 100 to 700 ° C. Regarding the melting point of the molten metal, if the molten metal is an alloy molten metal, the melting point of the molten metal shall be the melting point of the alloy.

The fluid may be sprayed in an atmospheric atmosphere, but it is preferably performed in a non-oxidizing gas atmosphere from the viewpoint of suppressing the oxidation of the molten metal and the formed metal powder. Examples of the non-oxidizing gas atmosphere include an inert gas such as He, Ar and N ₂ , and a reducing gas such as H ₂ and CO.

<Other processes>
In the method for producing a metal powder of the present invention, the following optional steps may be carried out on the metal powder obtained by spraying the fluid described above.

(Solid-liquid separation process)
When the fluid is a liquid such as water, a slurry in which the metal powder is dispersed in the liquid is obtained. Metal powder is recovered by solid-liquid separation of this slurry. As a method for solid-liquid separation, a conventionally known method can be adopted without particular limitation, and the slurry may be pressure-filtered using, for example, a filter press or the like. The recovered metal powder may be washed.

(Drying process)
The metal powder obtained in the solid-liquid separation step may be dried. Drying may be carried out at room temperature (25 ° C.) or at a high temperature (40 to 120 ° C.) from the viewpoint of improving the drying speed. Further, the drying may be carried out under atmospheric pressure, but from the viewpoint of improving the drying speed, drying may be carried out in a reduced pressure environment of −0.05 MPa or less with respect to atmospheric pressure. Drying may be carried out in a vacuum environment (-0.095 MPa or less).

(Crushing process, surface treatment process, classification process)
The particle size distribution may be adjusted by crushing or classifying the metal powder. The metal powder may be surface-treated with an organic compound at the same time as crushing or before and after crushing. Examples of organic compounds include alcohols, amines, fatty acids and thiols having 2-36 carbon atoms.

Although the embodiments of the present invention have been described above, the present invention is not limited to such examples. It is clear that a person skilled in the art can come up with various modifications or modifications within the scope of the technical ideas described in the claims, and of course, the technical scope of the present invention also includes them. It is understood that it belongs to.

[Example 1]
<Generation of classification residue (metal M)>
While the molten metal melted by heating Shot Silver to 1600 ° C in the atmosphere is dropped from the hot water nozzle at the bottom of the carbon crucible, atomizing water is sprayed in the atmosphere with a water pressure of 103 MPa and a water volume of 160 L / min to quench it. It was coagulated. The obtained slurry was separated into solid and liquid, and the solid was washed with water and dried.

Oleic acid (0.06 parts by mass with respect to 100 parts by mass of the solid material) was added to the dried solid material as a surface treatment agent, and the surface treatment agent was mixed with the solid material while crushing the solid material. A silver powder surface-treated with oleic acid was obtained.

Then, the surface-treated silver powder was classified to obtain a silver powder having an average particle diameter of 3 μm as the powder on the fine powder side. The average particle size was measured at a dispersion pressure of 5 bar using a laser diffraction type particle size distribution measuring device (a hellos particle size distribution measuring device (HELOS & RODOS (air flow type dispersion module)) manufactured by SYMPATEC). Cumulative 50% particle size.

On the other hand, as a by-product of classification, silver powder with a large particle size on the coarse powder side (classification residue (metal M)) was also generated. The carbon content of this classification residue was 0.08% by mass. The carbon content was measured by a carbon / sulfur analyzer (EMIA-22V manufactured by HORIBA, Ltd.).

<Reused water atomizing of the remaining classification>
25.675 kg of shot silver and 14.325 kg of the classification residue (metal M) generated in the above operation are charged in a carbon crucible (the ratio of metal M to the total raw metal is about 35.8 mass%) in the air atmosphere. Was heated to 1260 ° C. and melted. While maintaining the temperature of this molten metal at 1260 ° C. (silver melting point is 962 ° C.), air is blown to a place deeper than half the depth of the molten metal in the molten metal at a flow rate of 2 L / min using a heat-resistant sleeve. Blowed in for 15 minutes. The carbon crucible used here is a new product replaced from the carbon crucible used in the above <generation of classification residue>. The temperature of the molten metal was actually measured with an optical fiber thermometer.

In addition, the amount of oxygen supplied by blowing air is the amount of oxygen required for the conversion, assuming that all of the carbon (0.08% by mass) contained in the above classification residue is converted to carbon monoxide. It is a large excess amount. The difference ( _ΔGM − _ΔGC ) between the free energy for producing silver oxide _ΔGM and the free energy for producing carbon oxide ΔGC at 1260 ° _C. is about 500 kJ / molO ₂ . The _ΔGM at 1260 ° C. is about 0 kJ / molO ₂ , and the free energy ΔGC for carbon oxide formation at 1260 ° _C. is carbon monoxide free energy, which is about −500 kJ / molO ₂ .

The blowing of air was stopped, N ₂ gas was blown into the space above the molten metal at a flow rate of 10 L / min, and this N ₂ purge was carried out for 5 minutes, and then the following water atomization was started.

While the molten metal (temperature: 1260 ° C.) was dropped from the hot water nozzle at the bottom of the carbon crucible, atomized water was sprayed in an atmospheric atmosphere with a water atomizing device at a water pressure of 103 MPa and a water volume of 160 L / min to quench and solidify. The obtained slurry was subjected to solid-liquid separation, washing with water, drying, surface treatment while crushing, and classification in the same manner as described above.

When the above series of operations was repeated with the same one without replacing the carbon crucible (the amount of shot silver and classification residue (metal M) used was 25.675 kg and 14.325 kg each time), 4 times (4). (Batch) It was possible to carry out without practical problems (although there was slight blurring of hot water, all the molten metal could be discharged from the hot water nozzle at the bottom of the carbon crucible).

[Examples 2 to 4]
Repeated water atomization operations using the same carbon crucible were carried out in the same manner as in Example 1 except that the amounts of shot silver and classification residue (metal M) used were changed as shown in Table 1 below. As a result, in each of the cases, the water atomizing operation could be carried out four times without any substantial problem.

[Comparative Example 1]
The amount of shot silver used was 26.1 kg, the amount of unclassified residue (metal M) used was 13.9 kg, and water atomization (melt temperature: 1260 ° C, water pressure: 150 MPa) was immediately performed without blowing air into the melt. , Water volume: 160 L / min), and repeated water atomization operations using the same carbon crucible were carried out in the same manner as in Example 1. As a result, hot water blurring and clogging of the hot water nozzle occurred at the 4th time.

Claims (5)

A method for producing metal powder, in which a raw metal is heated and melted to form a molten metal, the molten metal is dropped, and a fluid is sprayed on the flowing molten metal to crush and solidify the molten metal to obtain a metal powder.
The raw material metal contains a metal M containing an organic compound, and while maintaining the temperature of the molten metal at a temperature T satisfying the following condition (1), the molten metal is dropped after blowing an oxidizing gas into the molten metal. , Metal powder manufacturing method:
(1) The free energy ΔGM of the oxide of the constituent metal of the molten metal at the temperature T is larger than the free energy _ΔGC of the oxide of the _carbon at the temperature T. A method for producing metal powder, in which a raw metal is heated and melted to form a molten metal, the molten metal is dropped, and a fluid is sprayed on the flowing molten metal to crush and solidify the molten metal to obtain a metal powder.
The raw material metal contains a metal M containing an organic compound, and while maintaining the temperature of the molten metal at a temperature T satisfying the following condition (1), the molten metal is dropped after blowing an oxidizing gas into the molten metal. , Metal powder manufacturing method:
(1) For a metal having an amount of 92% by mass or more of the constituent metals of the molten metal, the free energy ΔGM of the oxide of the metal at the temperature T is larger than the free energy _ΔGC of the oxide of the _carbon at the temperature T. The method for producing a metal powder according to claim 1 or 2, wherein the ratio of the metal M to the raw metal is 5 to 100% by mass. The method for producing a metal powder according to any one of claims 1 to 3, wherein the metal M has a carbon content of 0.01 to 0.3% by mass. The method for producing a metal powder according to any one of claims 1 to 4, wherein the metal M is produced by a gas atomizing method or a water atomizing method.