WO2014057735A1

WO2014057735A1 - Metal powder manufacturing method

Info

Publication number: WO2014057735A1
Application number: PCT/JP2013/072862
Authority: WO
Inventors: 祐也石田
Original assignee: 株式会社村田製作所
Priority date: 2012-10-11
Filing date: 2013-08-27
Publication date: 2014-04-17

Abstract

Provided is a metal powder manufacturing method capable of removing impurities in hydrazine, which is used as a reducing agent, on an industrial scale and with which, as a result, metal can be reduced with a small amount of hydrazine. Impurities in the hydrazine are removed using fibrous activated carbon. A hydrazine solution is prepared using the hydrazine from which impurities have been removed. A metal salt solution is prepared using a metal salt. Said metal salt solution and hydrazine solution are mixed and metal powder is deposited by a reduction reaction.

Description

Method for producing metal powder

The present invention relates to a method for producing metal powder, and more particularly, for example, to a method for producing metal powder used as an electrode material for electronic parts.

For example, a conductive paste is used to form internal electrodes of a multilayer ceramic capacitor. The conductive paste contains metal powder such as nickel powder as a conductive component. In order to obtain such a metal powder, a strong alkali is added to the nickel salt aqueous solution to adjust the pH to 10 or more, the temperature of the nickel salt aqueous solution is set to 55 to 70 ° C., and the temperature is 0 to 70 ° C. There is a method in which 2 to 10 mol of a reducing agent is added to 1 mol and nickel powder is precipitated by a reduction reaction. According to this method, a nickel powder having a narrow particle size distribution with an average primary particle size in the range of 0.4 to 0.6 μm can be obtained (see Patent Document 1).

Further, an organic compound composed of N, C, O and H and having an OH group in the molecule is added to a nickel salt solution and / or a hydrazine compound solution containing copper ions, and a nickel salt solution and a hydrazine compound solution Are mixed to obtain nickel powder by oxidation-reduction reaction. According to this method, nickel powder having a particle size of 100 to 300 nm can be obtained (see Patent Document 2).

Further, a nickel chloride solution and 1.2 to 2.5 mol of hydrazine are mixed with 1 mol of nickel in the nickel chloride solution to form a complex salt composed of nickel and hydrazine, and the pH of the solution is set to 12 or more. There is disclosed a method for producing nickel powder that is adjusted to cause hydrolysis at a reaction temperature in the range of 80 to 100 ° C. According to this method, the amount of hydrazine used per 1 mol of nickel can be reduced to 1.2 to 2.5 mol, and the particle diameter of the obtained nickel powder can be set to 0.1 to 1 μm. Yes (see Patent Document 3).

In addition, there is a method for producing nickel powder in which a sodium or potassium carbonate compound is added to a nickel sulfate solution, hydrazine or a hydrazine compound is added and mixed in the presence, and then heated to a temperature of 100 ° C. or lower to cause a reduction reaction. It is disclosed. According to this method, the reduction efficiency of hydrazine can be increased, and the amount of hydrazine used with respect to 1 mol of nickel can be reduced to 1.3 to 2.0 mol (see Patent Document 4).

Further, in a method of adding hydrated hydrazine to an aqueous solution of a water-soluble nickel salt and reducing it to metallic nickel, the production of nickel powder characterized by removing pyrazoles produced when producing hydrated hydrazine with an adsorption resin A method is disclosed. According to this method, the amount of hydrazine used can be reduced by removing pyrazoles that hinder the reduction of nickel (see Patent Document 5).

Also disclosed is a method of reducing TOC (total organic carbon) containing pyrazole in a hydrated hydrazine aqueous solution by distillation. Here, a method of reducing TOC in a hydrated hydrazine aqueous solution with activated carbon is also disclosed (see Patent Document 6).

Japanese Patent Application Laid-Open No. 07-278619 JP-A-2005-97729 JP-A-6-336601 JP-A-3-257106 JP 2004-263288 A JP 63-295408 A

The method described in Patent Document 1 is not suitable as a conductive paste for internal electrodes of a small-sized and large-capacity multilayer ceramic capacitor because the resulting nickel powder has a large particle size of 0.4 to 0.6 μm. Further, when producing nickel powder, 2 to 10 mol of hydrazine is required per 1 mol of nickel ions, and a large amount of hydrazine is required for producing nickel powder.

In the method described in Patent Document 2, nickel powder having a particle size of 100 to 300 nm can be obtained. However, when nickel powder is produced, the amount of hydrazine needs to be 2 to 10 mol per mol of nickel ions. A large amount of hydrazine is required for the production of nickel powder.

In the method described in Patent Document 3, the obtained nickel powder has a fine particle size of 0.1 to 1 μm, and the amount of hydrazine to be used can be reduced. However, in order to compensate for the small amount of hydrazine, 80 ° C. Since the complex salt of nickel and hydrazine is hydrolyzed at the above temperature, it is difficult to control the particle diameter of the resulting nickel powder. Therefore, in this method, the particle size variation of the nickel powder becomes large.

In the method described in Patent Document 4, the particle diameter of the obtained nickel powder is 0.1 to 1 μm, the amount of hydrazine used is small, and the reaction can be performed at a low temperature up to 60 ° C. Since an alkali salt is used, the obtained nickel powder forms a lump of 50 μm or more derived from nickel carbonate.

In the method described in Patent Document 5, the amount of hydrazine used can be reduced when nickel powder is produced by removing pyrazoles in hydrazine. In order to remove pyrazoles in hydrazine, an adsorption resin having pores having an average pore diameter of 50 nm or more is used. However, in order to adsorb pyrazoles having a size of 1 nm or less, the pore diameter of the adsorption resin is large and the adsorption energy is low. Therefore, it takes time for the pyrazole to diffusely adsorb in the pores, and therefore it is necessary to limit the contact rate between hydrazine and the adsorbing resin to 0.6 g / h or less per mL of adsorbing resin. A large amount of adsorbent resin is required for processing. For example, 167 L of adsorbent resin is required to process 100 L of hydrazine in 1 hour. Therefore, it is uneconomical to remove pyrazole in hydrazine on an industrial scale using an adsorbent resin.

Patent Document 6 discloses a method of removing organic impurities containing pyrazole in hydrazine with activated carbon, but it is described that the efficiency is poor as in the case of the adsorption resin.

Therefore, a main object of the present invention is to produce a metal powder that can remove impurities in hydrazine used as a reducing agent on an industrial scale, thereby reducing metal with a small amount of hydrazine. Is to provide.
Another object of the present invention is to remove a pyrazole compound, which is an impurity in hydrazine, particularly when a nickel powder is produced using a water-soluble nickel salt and hydrazine. It is providing the manufacturing method of the metal powder which can obtain.

The present invention includes a step of removing impurities in hydrazine using fibrous activated carbon, a step of preparing a hydrazine solution using hydrazine from which impurities are removed, a step of adjusting a metal salt solution using a metal salt, A method for producing a metal powder, comprising mixing a metal salt solution and a hydrazine solution and precipitating the metal powder by a reduction reaction.
Since the pores on the surface of the fibrous activated carbon have a small average pore diameter, the adsorption energy for adsorbing impurities in hydrazine is high. Therefore, it is possible to diffuse and adsorb impurities in the pores of the fibrous activated carbon in a short time. Thus, by using hydrazine from which impurities have been removed, metal powder can be deposited without hindering metal reduction.

In such a method for producing metal powder, the pyrazole compound as an impurity is removed.
In such a production method, the impurity that hinders the reaction between the metal salt and hydrazine is a pyrazole compound, and by removing this pyrazole compound, the above-described effects can be obtained.

Moreover, the metal salt solution can use what was prepared using water-soluble nickel salt, and the metal powder to precipitate in this case is nickel powder.
When a solution prepared using a water-soluble nickel salt is used as the metal salt solution, nickel powder can be obtained. The nickel powder is useful as a material for a conductive paste for an internal electrode of a multilayer ceramic capacitor, for example.

Copper ions can be added when preparing a metal salt solution using a water-soluble nickel salt.
By adding copper ions when preparing the metal salt solution, the copper is first reduced to become nuclei and the effect of atomizing the nickel powder can be obtained.

The average pore radius of the fibrous activated carbon is preferably in the range of 0.84 to 1.54 nm.
Further, the specific surface area of the fibrous activated carbon is preferably 850 to 1300 m ² / g.
The pore volume of the fibrous activated carbon is preferably 0.35 to 0.97 mL / g.
When the average pore radius, specific surface area, and pore volume of the fibrous activated carbon are within such ranges, impurities in hydrazine can be efficiently removed.

According to this invention, by using fibrous activated carbon, impurities in hydrazine can be efficiently removed, and hydrazine from which impurities have been removed on an industrial scale can be obtained. By using hydrazine from which impurities are removed, a metal powder can be obtained by reacting a metal salt and hydrazine at a low temperature using a small amount of hydrazine. Therefore, it is not necessary to add a carbonic acid compound that causes coarsening of the metal powder particles, and a metal powder having a small particle size can be obtained. In addition, since the metal salt and hydrazine can be reacted at a low temperature, the particle size of the metal powder can be controlled well, and a metal powder with small variation in particle size can be obtained.

The above-mentioned object, other objects, features, and advantages of the present invention will become more apparent from the following description of the embodiments for carrying out the invention with reference to the drawings.

It is a conceptual diagram which shows the surface of granular activated carbon. It is a conceptual diagram which shows the surface of fibrous activated carbon.

For example, a conductive paste is used for forming an electrode of an electronic component such as a multilayer ceramic capacitor. The conductive paste contains metal powder as a conductive material. In order to obtain a metal powder, a metal salt solution and a hydrazine solution are mixed, and the metal powder is precipitated by a reduction reaction. For example, a reaction in which a nickel salt and a hydrazine solution are mixed and nickel powder is precipitated by a reduction reaction is expressed as follows.
Ni ²⁺ + 2e ^- → Ni
N ₂ H ₄ + 2OH ⁻ → N ₂ + 2H ₂ O + H ₂ + 2e ⁻
The present invention relates to a method for producing such a metal powder, and can be applied to metals that can be reduced with hydrazine such as nickel, cobalt, copper, platinum, palladium, silver, and gold as the metal species.

There are many organic impurities in hydrazine such as alcohols, ketones, amines, amides, oximes, hydrazones, hydrazides, pyrazines, pyrazoles, pyrazolines, pyrroles, pyridines, pyridazines, triazoles, and imidazoles due to production by-products. Exists. Among them, a compound having a lone electron pair may coordinate with a metal ion and hinder its reduction. In particular, a heterocyclic compound having two or more lone electron pairs having N as an element, such as pyrazine, pyrazole, pyridazine, triazole, and imidazole, cross-links with a metal ion to make reduction more difficult.

Due to the presence of such a compound in hydrazine, for example, when nickel ions are made into nickel powder, hydrazine needs to be added in a large amount of 2 to 10 mol per mol of nickel. In order to reduce 1 mol of nickel, it can theoretically be reduced with 1 mol of hydrazine, so in practice, 2 to 10 times the theoretical amount of hydrazine is added.

In order to bring the amount of hydrazine used close to the theoretical amount, it is possible to react at a reaction temperature of 80 ° C. or higher, or to add a carbonic acid compound, but these methods increase the particle size variation of nickel powder. . In addition, during the production of nickel powder, the nickel powder can be atomized by adding copper ions to the nickel salt and reducing the copper first to make it a core. Therefore, it is difficult to atomize the nickel powder.

Therefore, by passing hydrazine through a filter using fibrous activated carbon having pores with an average pore radius of 1.6 nm or less (diameter of 3.2 nm or less), organic impurities that prevent reduction of metal ions are caused by fibrous activated carbon. To be removed by adsorption. Note that most of the organic impurities that crosslink and coordinate with metal ions present in hydrazine are considered to have a radius of 1.5 nm or less. In order to remove such organic impurities, it is preferable to use fibrous activated carbon having pores having an average pore radius in the range of 0.84 to 1.54 nm. The specific surface area of the fibrous activated carbon is preferably in the range of 850 to 1300 m ² / g. Further, the pore volume of the fibrous activated carbon is preferably in the range of 0.35 to 0.97 mL / g.

In addition, as shown in FIG. 1, the conventional granular activated carbon has macropores of 50 nm or more, small-diameter trajectory pores are formed therein, and micro-pores of smaller diameters are further formed therein. It has a configuration. In this way, the macropores on the surface of the granular activated carbon use an adsorbent resin that has a pore diameter that is too large to adsorb organic impurities having a radius of 1.5 nm or less and that has a pore diameter of 50 nm or more. The removal efficiency of organic impurities is poor as in the case of As shown in FIG. 2, the fibrous activated carbon has a large number of micropores having an optimal size of 1 to 2 nm (10 to 20 angstroms) in radius on the fiber surface. Can be removed.

Thus, a hydrazine solution is prepared using hydrazine from which organic impurities such as pyrazole and its compounds are removed using fibrous activated carbon. A metal salt solution is prepared using a metal salt such as a water-soluble nickel salt. Then, the metal salt solution and the hydrazine solution can be mixed and the metal powder can be precipitated by a reduction reaction. Here, if a water-soluble nickel salt is used as the metal salt, nickel powder useful as a material for a conductive paste for an electrode such as a multilayer ceramic capacitor can be obtained. When preparing a metal salt solution using a water-soluble nickel salt, copper ions that act as a atomizing agent can be added.

The amount of hydrazine used per mole of nickel ions is reduced to 1.3-2 moles by removing hydrazine from which organic impurities that hinder the reduction of metal ions, such as nickel ions and copper ions, which are atomizing agents, are removed. can do. Moreover, since reduction of copper ions is not hindered, a nucleation effect by copper ions appears and a metal powder having a small particle size can be obtained. Furthermore, by removing organic impurities that hinder the reduction of metal ions, it is not necessary to react the metal salt solution with the hydrazine solution at a high temperature. Therefore, the metal salt solution and the hydrazine solution can be reacted at a low temperature of 50 to 70 ° C., and the particle size can be controlled, so that a metal powder having a small particle size and small particle size variation can be obtained.

In addition, by removing organic impurities in hydrazine, it is not necessary to add a carbonic acid compound during the reaction between the metal salt and hydrazine, it is possible to prevent coarsening of the metal powder, there is no lump, and there is no variation in particle size. Small metal powder can be obtained. In order to remove organic impurities contained in hydrazine, a large amount of hydrazine can be treated in a short time by using fibrous activated carbon with many pores on the surface, and organic impurities are removed on an industrial scale. Hydrazine can be obtained.

(Example 1)
The amount of TOC (total organic carbon) was 98 ppm, and quantitative analysis using the peak area of the GC-MS (gas chromatography) spectrum revealed that it contained 65 ppm of 1,3,5-trimethylpyrazole. 10 L of hydrazine (this hydrazine is referred to as hydrazine A) was prepared.

19650 g of this hydrazine A was applied to a 1 L activated carbon filter filled with unitary carbon fiber W-15W manufactured by Unitika Co., Ltd. having a specific surface area of 1250 m ² / g, a pore volume of 0.97 mL / g and an average pore radius of 1.54 nm Passing treatment was performed at a flow rate of / h. The obtained hydrazine had a TOC amount of 20 ppm, and a peak of 1,3,5-trimethylpyrazole could not be confirmed by GC-MS. The hydrazine thus obtained is designated as hydrazine B.

In addition, hydrazine A was applied to a 1 L activated carbon filter filled with fibrous activated carbon A-10 manufactured by Unitika Ltd. having a specific surface area of 1300 m ² / g, a pore volume of 0.55 mL / g, and an average pore radius of 0.86 nm. The passing treatment was carried out at a flow rate of 19650 g / h. The obtained hydrazine had a TOC amount of 20 ppm, and a peak of 1,3,5-trimethylpyrazole could not be confirmed by GC-MS. The hydrazine thus obtained is designated as hydrazine C.

In addition, a 1 L activated carbon filter filled with hydrazine A filled with fibrous activated carbon A-7 manufactured by Unitika Ltd. having a specific surface area of 850 m ² / g, a pore volume of 0.35 mL / g, and an average pore radius of 0.84 nm. The passing treatment was carried out at a flow rate of 19650 g / h. The obtained hydrazine had a TOC amount of 20 ppm, and a peak of 1,3,5-trimethylpyrazole could not be confirmed by GC-MS. The hydrazine thus obtained is designated as hydrazine D.

As described above, it was confirmed that 1,3,5-trimethylpyrazole was removed by fibrous activated carbon. If the pore diameter of the activated carbon is larger than the molecular size of the impurity to be removed, 1 Not only, 3,5-trimethylpyrazole, but also other impurities can be removed.

Further, hydrazine A was passed through a 1 L activated carbon filter filled with commercially available coconut shell activated carbon at a flow rate of 19650 g / h. The obtained hydrazine had a TOC amount of 60 ppm, and GC-MS contained 43 ppm of 1,3,5-trimethylpyrazole. The hydrazine thus obtained is designated as hydrazine E.

Further, hydrazine A was passed through a 1 L column packed with adsorption resin Diaion HP20 at a flow rate of 19650 g / h. The obtained hydrazine had a TOC content of 50 ppm, and GC-MS contained 35 ppm of 1,3,5-trimethylpyrazole. The hydrazine thus obtained is designated as hydrazine F.

Table 1 shows data on specific surface area, pore volume and average pore radius for the adsorbent used in the filter used in the above-described hydrazine treatment.

Next, 253 g of nickel sulfate, 23.3 g of trisodium citrate, and copper sulfate pentahydrate were dissolved in 620 mL of pure water to prepare a nickel salt aqueous solution. Here, the amount of copper ions in the copper sulfate pentahydrate was 20 ppm relative to the amount of nickel. Meanwhile, 108 g of hydrazine B, 104 g of sodium hydroxide and 17 g of triethanolamine were dissolved in 670 mL of pure water to prepare a hydrazine solution. At this time, the amount of hydrazine with respect to 1 mol of nickel ions was 1.3 mol.

Next, the nickel salt solution and the hydrazine solution were heated to a liquid temperature of 60 ° C., and then the two liquids were mixed and stirred for 60 minutes to obtain a nickel powder slurry. When the supernatant was collected after stirring the two liquids and the remaining nickel ions were confirmed by an ion checker, no nickel ions were detected. The obtained nickel powder slurry is filtered and washed until the filtrate has a conductivity of 10 μS / cm or less, and then water is replaced with acetone, followed by drying in an oven set at a temperature of 80 ° C. Got.

Next, the obtained nickel powder was observed at a magnification of 5000 to 10,000 times using an electrolytic emission scanning electron microscope. And the particle size of nickel powder was calculated | required by image-analyzing the observed image, and the average particle size and the particle size dispersion | variation were computed from the result. The particle size variation is a CV value, which is calculated based on an equation of (standard deviation / average value) × 100 (%). An average particle size of 0.4 μm or less and a CV value of 25% or less are preferable as nickel powder for use in a multilayer ceramic capacitor having a small maximum capacity. The average particle diameter of the obtained nickel powder was 0.15 μm, and the CV value was 20%.

In Example 1, even if the amount of hydrazine is as small as 1.3 mol of hydrazine with respect to 1 mol of nickel ions, nickel ions do not remain after the reaction, the average particle size is 0.15 μm, and the CV value is 25% or less. Nickel powder having a uniform particle size can be obtained.

(Example 2)
Nickel powder was obtained in the same manner as in Example 1 except that the amount of hydrazine was 135 g. At this time, the amount of hydrazine with respect to 1 mol of nickel ions was 1.6 mol. Nickel ions were not detected from the supernatant after stirring the nickel salt solution and the hydrazine solution for 60 minutes. The obtained nickel powder had an average particle size of 0.15 μm and a CV value of 20%. In Example 2, the same effect as in Example 1 could be obtained.

(Example 3)
Nickel powder was obtained in the same manner as in Example 1 except that the amount of hydrazine was 158 g. At this time, the amount of hydrazine with respect to 1 mol of nickel ions was 2 mol. Nickel ions were not detected from the supernatant after stirring the nickel salt solution and the hydrazine solution for 60 minutes. The obtained nickel powder had an average particle size of 0.15 μm and a CV value of 20%. In Example 3, the same effect as in Example 1 could be obtained.

Example 4
Nickel powder was obtained in the same manner as in Example 3 except that the amount of copper ions was changed to 0 ppm. Nickel ions were not detected from the supernatant after stirring the nickel salt solution and the hydrazine solution for 60 minutes. The resulting nickel powder had an average particle size of 0.24 μm and a CV value of 24%. In Example 4, since no copper ion was added, a nickel powder controlled to have a larger particle size than that of Example 3 was obtained.

(Example 5)
Nickel powder was obtained in the same manner as in Example 1 except that the amount of copper ions was 1 ppm. Nickel ions were not detected from the supernatant after stirring the nickel salt solution and the hydrazine solution for 60 minutes. The resulting nickel powder had an average particle size of 0.35 μm and a CV value of 15%. In Example 5, since the copper ion was reduced to 1 ppm, a nickel powder controlled to have a larger particle size than that of Example 1 was obtained.

(Example 6)
Nickel powder was obtained in the same manner as in Example 1 except that the reaction temperature was 50 ° C. Nickel ions were not detected from the supernatant after stirring the nickel salt solution and the hydrazine solution for 60 minutes. The resulting nickel powder had an average particle size of 0.20 μm and a CV value of 19%. In Example 6, since the reaction temperature was 50 ° C., nickel powder controlled to have a larger particle size than that of Example 1 was obtained.

(Example 7)
Nickel powder was obtained in the same manner as in Example 1 except that the reaction temperature was 70 ° C. Nickel ions were not detected from the supernatant after stirring the nickel salt solution and the hydrazine solution for 60 minutes. The obtained nickel powder had a particle size of 0.15 μm and a CV value of 20%. In Example 7, the same effect as in Example 1 was obtained at a reaction temperature of 70 ° C.

(Example 8)
Nickel powder was obtained in the same manner as in Example 1 except that hydrazine C was used and the reaction temperature was 70 ° C. Nickel ions were not detected from the supernatant after stirring the nickel salt solution and the hydrazine solution for 60 minutes. The obtained nickel powder had an average particle size of 0.15 μm and a CV value of 20%. In Example 8, the same effect as Example 1 was able to be acquired with the reaction temperature of 70 degreeC.

Example 9
Nickel powder was obtained in the same manner as in Example 1 except that hydrazine D was used and the reaction temperature was 70 ° C. Nickel ions were not detected from the supernatant after stirring the nickel salt solution and the hydrazine solution for 60 minutes. The obtained nickel powder had an average particle size of 0.15 μm and a CV value of 20%. In Example 9, the same effect as in Example 1 could be obtained at a reaction temperature of 70 ° C.

(Comparative Example 1)
Nickel powder was obtained in the same manner as in Example 1 except that the amount of hydrazine was changed to 158 g using hydrazine A. At this time, the amount of hydrazine with respect to 1 mol of nickel ions was 2 mol. Nickel ions were not detected from the supernatant after stirring the nickel salt solution and the hydrazine solution for 60 minutes. The obtained nickel powder had an average particle size of 0.6 μm and a CV value of 20%. In Comparative Example 1, the amount of hydrazine was sufficient, but since the pyrazole was not removed, the nickel particle size exceeded 0.4 μm.

(Comparative Example 2)
Nickel powder was obtained in the same manner as in Example 1 except that hydrazine E was used. Nickel ions were detected from the supernatant after stirring the nickel salt solution and the hydrazine solution for 60 minutes. The resulting nickel powder had an average particle size of 0.6 μm and a CV value of 18%. Hydrazine E used in Comparative Example 2 is obtained by treating hydrazine A with coconut shell activated carbon, and since pyrazole has not been removed, nickel ions remain in the liquid after the reaction, and the nickel particle size is 0.1. It exceeded 4 μm.

(Comparative Example 3)
Nickel powder was obtained in the same manner as in Example 1 except that hydrazine F was used. Nickel ions were detected from the supernatant after stirring the nickel salt solution and the hydrazine solution for 60 minutes. The obtained nickel powder had a particle size of 0.5 μm and a CV value of 20%. Hydrazine F used in Comparative Example 3 is obtained by treating hydrazine A with an adsorbent resin, and since pyrazole is not removed, nickel ions remain in the liquid after the reaction, and the nickel particle size exceeds 0.4 μm. It was.
The above results are shown in Table 2.

As can be seen from these examples and comparative examples, when hydrazine from which pyrazole has not been removed is used, the particle size of nickel powder exceeds 0.4 μm, but by using hydrazine from which pyrazole has been removed, the particle size can be reduced. Nickel powder having a CV value of 25% or less can be obtained at 0.4 μm or less. Moreover, nickel powder with a small average particle diameter can be obtained by adding a copper ion when mixing a nickel salt solution and a hydrazine solution.

Claims

Removing impurities in hydrazine using fibrous activated carbon,
A step of preparing a hydrazine solution using the hydrazine from which impurities have been removed,
A method for producing a metal powder, comprising a step of adjusting a metal salt solution using a metal salt, and a step of mixing the metal salt solution and the hydrazine solution and depositing a metal powder by a reduction reaction.
The method for producing a metal powder according to claim 1, wherein the impurity is a pyrazole compound.
The method for producing a metal powder according to claim 1 or 2, wherein the metal salt solution is prepared using a water-soluble nickel salt, and the deposited metal powder is a nickel powder.
The method for producing a metal powder according to claim 3, wherein copper ions are added when the metal salt solution is prepared using the water-soluble nickel salt.
The method for producing metal powder according to any one of claims 1 to 4, wherein an average pore radius of the fibrous activated carbon is in a range of 0.84 to 1.54 nm.
6. The method for producing metal powder according to claim 1, wherein the specific surface area of the fibrous activated carbon is 850 to 1300 m 2 / g.
The method for producing metal powder according to any one of claims 1 to 6, wherein the pore volume of the fibrous activated carbon is 0.35 to 0.97 mL / g.