JP2021139031A - Manufacturing method of metal powder - Google Patents

Abstract

To provide a method of manufacturing a metal powder having a smaller average particle size, and a sharper particle size distribution.SOLUTION: A manufacturing method metal powder performs: a step of mixing a metal salt, basic amino acid, one or more valent carboxylic acids or salts thereof, and a noble metal catalyst with water to prepare a metal salt solution; a step of mixing an alkaline pH adjuster, a reducing agent and water to prepare a reducing agent solution; a step of adding the reducing agent solution to the metal salt solution to mix, in which a blending amount of the basic amino acid is 35 wt.% or smaller relative to a weight of the metal powder to be produced, a blending amount of the above monovalent or more carboxylic acid or its salt is 120 wt.% or smaller relative to the weight of the produced metal powder, and a ratio of the blending amount of the basic amino acid to the blending amount of the above monovalent or more carboxylic acid or its salt is larger than 0.2 and 1.0 or smaller.SELECTED DRAWING: None

Description

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

In a multilayer ceramic capacitor, dielectric layers and internal electrode layers are alternately laminated, and external electrodes are formed on both end faces of the laminated body obtained by firing treatment. With such a structure, it is possible to obtain a small size and a large capacity, and therefore, it is widely used in various applications with the recent increase in demand for mobile devices and the like.

Thinning the internal electrode layer is an important issue in order to increase the capacity and size of the multilayer ceramic capacitor. However, if the average particle size of the metal powder used to form the internal electrode layer is not small, the multilayer ceramic capacitor is laminated. The electrical characteristics of ceramic capacitors cannot be satisfied, and problems such as short-circuit defects and structural defects frequently occur.

As a method for producing a metal powder, a liquid phase synthesis method and a gas phase synthesis method are generally used, and in particular, the liquid phase synthesis method is a simple method for producing fine metal powder. As a method for producing fine metal powder by a liquid phase synthesis method, a method of adding a nucleating agent in order to increase nucleation energy is known. In the production of nickel metal powder, fine metal powder can be produced by using Pd, Pt, Au, Ag, Cu or the like as a nucleating agent and adjusting the amount of addition thereof.

For example, in Patent Document 1, a reduction reaction is started in a reaction solution containing a water-soluble nickel salt, a nucleating agent, a hydrazine, a carboxylic acid as a complexing agent, a pH adjuster, and water, and then hydrazine is further added. Discloses a method for producing nickel powder.

Japanese Unexamined Patent Publication No. 2017-171957

In the examples of Patent Document 1, nickel powder having an average particle size of 0.12 to 0.37 μm and a CV value of 25% or less is obtained. However, in order to reduce the size of the multilayer ceramic capacitor, the average grain size is further increased. Nickel powder with a small diameter is required.

In order to obtain a finer metal powder by using the method disclosed in Patent Document 1, it is conceivable to increase the amount of the nucleating agent and decrease the amount of the complexing agent. However, when the amount of the nucleating agent increases, the particle size distribution of the obtained metal powder becomes broad due to the deviation of the start of the nucleation reaction between the nucleating agent and the metal ion and the dispersion of the nucleating agent in the reaction field. If the particle size distribution of the metal powder is broad, there is a problem that when the metal powder is used for forming the internal electrode layer of a laminated ceramic capacitor, the electrode smoothness deteriorates and uneven sintering behavior occurs. ..

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for producing a metal powder having a smaller average particle size and a sharp particle size distribution.

The method for producing a metal powder of the present invention includes a step of mixing a metal salt, a basic amino acid, a monovalent or higher carboxylic acid or a salt thereof, and a noble metal catalyst in water to prepare a metal salt solution, and an alkaline method. It is a method for producing a metal powder, which comprises a step of mixing a pH adjuster and a reducing agent with water to prepare a reducing agent solution, and a step of adding the reducing agent solution to the metal salt solution and mixing them. The amount of the basic amino acid compounded is 35% by weight or less based on the weight of the produced metal powder, and the amount of the monovalent or higher carboxylic acid or its salt compounded is based on the weight of the produced metal powder. It is 120% by weight or less, and the ratio of the blending amount of the basic amino acid to the blending amount of the monovalent or higher carboxylic acid or a salt thereof is more than 0.2 and 1.0 or less.

According to the present invention, it is possible to provide a method for producing a metal powder having a smaller average particle size and a sharp particle size distribution.

Hereinafter, the method for producing the metal powder of the present invention will be described. However, the present invention is not limited to the following configurations, and can be appropriately modified and applied without changing the gist of the present invention. It should be noted that a combination of two or more of the individual desirable configurations described below is also the present invention.

The method for producing a metal powder of the present invention uses a liquid phase synthesis method, and is made of an alkaline metal salt solution containing a metal salt, a basic amino acid and a monovalent or higher carboxylic acid or salt thereof, a noble metal catalyst, and water. A metal powder is precipitated in the mixed solution by preparing a reducing agent solution containing a pH adjuster, a reducing agent and water, respectively, and then adding the reducing agent solution to the metal salt solution and mixing them.
In particular, the production method of the present invention is characterized in that a basic amino acid and a monovalent or higher carboxylic acid or a salt thereof are used in combination as a complexing agent to be blended in a metal salt solution.

[Metal salt solution]
Examples of the metal to be the metal powder include metals that can be used as materials for forming the internal electrode layer of the multilayer ceramic capacitor, and specific examples thereof include Ni, Cu, Pt, and Ag.

The metal salt to be mixed with the metal salt solution is a metal salt that becomes a metal powder. The metal salt is not particularly limited as long as it is water-soluble, and examples thereof include chlorides such as Ni, Cu, Pt, and Ag, bromides, sulfates, and nitrates. Specific examples of the metal salt include nickel chloride, nickel sulfate, nickel nitrate, nickel acetate, copper (I) chloride, copper (II) chloride, copper (II) sulfate, copper (I) sulfate, and copper (II) acetate. ), Platinum chloride (II), platinum (IV) chloride, hexachloroplatinic acid, silver nitrate, silver acetate and the like. As the metal salt, one kind or two or more kinds may be used.
It may also be a hydrate of these salts.
When nickel powder is produced as a metal powder, nickel chloride, nickel sulfate, or a mixture thereof is preferable as the nickel salt from the viewpoint of being inexpensive and easily procured.

The blending amount of the metal salt is preferably 12% by weight or more and 50% by weight or less with respect to the total weight of the metal salt solution.

As the basic amino acid, at least one selected from the group consisting of lysine, arginine and histidine is preferable. The basic amino acid may be either L-form or D-form.
As the basic amino acid, one kind or two or more kinds may be used. L-arginine is more preferable as the basic amino acid because a metal powder having a small average particle size and a low CV value can be obtained.
The basic amino acid has an effect of suppressing the average particle size of the metal powder to a small value (metal particle growth suppressing effect) in the process of precipitating the metal powder, and has an effect of making the particle size distribution uniform.

The blending amount of the basic amino acid in the metal salt solution is 35% by weight or less based on the weight of the produced metal powder. The basic amino acid has an effect of suppressing the average particle size of the metal powder to be small and has an effect of making the particle size distribution uniform. However, when the amount of the basic amino acid compounded exceeds 35% by weight, the precipitation reaction does not proceed. , Metal powder cannot be obtained. The blending amount of the basic amino acid is preferably 10% by weight or more.

As a monovalent or higher carboxylic acid or a salt thereof (hereinafter, "monovalent or higher carboxylic acid or a salt thereof" is also referred to as "monovalent or higher carboxylic acid"), it has reducing property and is soluble in water. It is preferable to have. Examples of such monovalent or higher carboxylic acids include ascorbic acid, formic acid, acetic acid, citric acid, tartaric acid, malic acid, malonic acid, and succinic acid. Examples of the salt of the monovalent or higher carboxylic acid include trisodium citrate and sodium ascorbate. The monovalent or higher carboxylic acid may be added in the form of a hydrate (eg, trisodium citrate dihydrate). As the monovalent or higher carboxylic acid, one kind or two or more kinds may be used.
The monovalent or higher carboxylic acid or salt thereof is more preferably at least one selected from citric acid or a salt thereof, and ascorbic acid or a salt thereof.
Metal particles are precipitated by using a carboxylic acid having a valence of 1 or more.

The blending amount of the monovalent or higher carboxylic acid in the metal salt solution is 120% by weight or less with respect to the weight of the produced metal powder. When the blending amount of the monovalent or higher carboxylic acid exceeds 120% by weight, the particle size of the obtained metal powder is large and the CV value (particle size distribution) is larger than 25%. When such a metal powder is used as a material for forming an internal electrode layer of a multilayer ceramic capacitor, the electrode smoothness may be deteriorated or uneven sintering behavior may occur. The blending amount of the monovalent or higher carboxylic acid is preferably 10% by weight or more.

The ratio of the blending amount of the basic amino acid to the blending amount of the monovalent or higher carboxylic acid (basic amino acid / carboxylic acid of monovalent or higher) is larger than 0.2 and 1.0 or less. When this ratio is 0.2 or less, the effect of suppressing the growth of metal particles of basic amino acids is not sufficient, and the average particle size of the metal powder becomes large. When this ratio exceeds 1.0, the effect of suppressing the growth of metal particles of basic amino acids exceeds the reducing action of monovalent or higher carboxylic acids, and the precipitation reaction of metal particles does not proceed. The ratio of the above blending amounts is preferably 0.3 or more and 0.6 or less.

The noble metal catalyst is added to the metal salt solution in order to function as a nucleating agent for generating crystal nuclei in the process of precipitating the metal powder. The metal ions of the noble metal catalyst are reduced before the metal ions of the metal powder to be produced to become initial nuclei, and the initial nuclei grow particles to obtain fine metal powder.
The noble metal catalyst is a salt of a metal that is more noble than the metal that becomes the metal powder to be produced, and examples thereof include water-soluble noble metal salts such as gold salt, copper salt, silver salt, palladium salt, platinum salt, rhodium salt, and iridium salt. Be done. Specific examples of the noble metal catalyst include copper sulfate, silver nitrate, sodium palladium (II) chloride, palladium (II) chloride, palladium (II) nitrate, palladium (II) sulfate, hexachloroplatinic acid and the like. Hydrate of these salts may be used. One kind or two or more kinds of noble metal catalysts can be used.

As one aspect, in the case of producing nickel powder, the particle size of the obtained nickel powder can be controlled more finely or the particle size can be controlled by using a plurality of noble metal salts of metals nobler than nickel exemplified above as the noble metal catalyst. It is possible to narrow the distribution. In particular, if a noble metal catalyst composed of two or more components, which is a combination of a copper salt and one or more selected from gold salt, silver salt, platinum salt, palladium salt, rhodium salt, iridium salt, etc., is used, the nickel powder can be used. The particle size control becomes easier, and the particle size distribution can be narrowed.
When producing nickel powder, copper sulfate or palladium chloride is preferable as the noble metal catalyst.

The amount of the noble metal catalyst is preferably 30 ppm by weight or more and 120 wt ppm or less with respect to the weight of the metal powder to be produced, that is, the weight of the metal in the metal salt contained in the metal salt solution. When the amount of the noble metal catalyst is within the above range, the average particle size of the metal powder can be reduced, but the average particle size of the metal powder does not decrease even if 120% by weight ppm or more is blended. More preferably, it is 50% by weight or more and 100% by weight or less.

As the water to be blended in the metal salt solution, pure water is preferably used from the viewpoint of reducing the amount of impurities in the metal powder. Further, in order to increase the solubility of solutes such as basic amino acids to be blended in the metal salt solution, a water-soluble organic solvent such as alcohol may be blended together with water.

A dispersant may be further added to the metal salt solution for the purpose of controlling the particle size and particle size distribution of the metal powder. Known components can be used as the dispersant, and specifically, triethanolamine (N (C ₂ H ₄ OH) ₃ ) and diethanolamine (also known as iminodiethanol) (NH (C ₂ H ₄ OH)). ₂ ), amines such as oxyethylenealkylamine, and salts and derivatives thereof; or _{amino acids such as alanine (CH 3} CH (COOH) NH ₂ ), glycine (H ₂ NCH ₂ COOH), and salts thereof. And derivatives.

Further, the mixing order of each component to be blended in the metal salt solution is not particularly limited.

[Reducing agent solution]
The reducing agent solution contains an alkaline pH regulator, a reducing agent and water.
The pH adjuster is not particularly limited, but an alkali metal hydroxide can be used from the viewpoint of availability and price. Examples of the alkali metal hydroxide include sodium hydroxide, potassium hydroxide, lithium hydroxide and the like. As the alkaline pH adjuster, one kind or two or more kinds can be used.

As the reducing agent, for example, hydrazine, sodium borohydride, alcohol, ascorbic acid or a salt thereof and the like can be used. As the hydrazine, in addition to the anhydrous hydrazine, there is a water-holding hydrazine (N ₂ H ₄ · H ₂ O) which is a hydrazine hydrate, and any of them may be used. Hydrazine is suitable as a reducing agent because it has the characteristics of high reducing power, no by-products of the reducing reaction being generated in the reaction solution, few impurities, and easy availability.
As the hydrazine, specifically, a commercially available industrial grade 60% by mass hydrazine containing water can be used.

As the water to be blended in the reducing agent solution, it is preferable to use pure water as in the metal salt solution from the viewpoint of reducing the amount of impurities in the metal powder. Further, a water-soluble organic solvent such as alcohol may be blended together with water.
The mixing order of each component to be blended in the reducing agent solution is not particularly limited.

The step of preparing the metal salt solution and the step of preparing the reducing agent solution may be performed first or at the same time.

[Precipitation process]
Next, a step of adding the reducing agent solution to the metal salt solution and mixing is performed. By mixing the metal salt solution and the reducing agent solution, metal powder is precipitated by the reducing reaction of the reducing agent in the mixed solution containing the metal salt solution and the reducing agent solution. Hereinafter, the "step of adding the reducing agent solution to the metal salt solution and mixing" is also referred to as a "precipitation step".
The reducing agent solution may be added to the metal salt solution all at once, may be divided into a plurality of times, or the reducing agent solution may be continuously added dropwise.

The temperature of the mixed solution at the time when the mixed solution is prepared and the metal precipitation starts, that is, the reaction starting temperature is preferably 40 ° C. or higher and 95 ° C. or lower, and 50 ° C. or higher and 90 ° C. or lower. More preferred. Since the metal precipitation starts immediately after the reducing agent solution is added to the metal salt solution, the reaction start temperature can be considered to be the temperature of the mixed solution at the time of preparation. The higher the reaction start temperature, the higher the reduction reaction rate can be increased, but if it exceeds 95 ° C., it becomes difficult to control the particle size of the metal crystallization powder, or the reaction rate cannot be controlled and the mixed solution is discharged from the reaction vessel. It can cause problems such as spills. Further, when the reaction start temperature is lowered to less than 40 ° C., the reduction reaction rate becomes low, the time required for the precipitation step becomes long, and the productivity decreases. For the above reasons, if the reaction start temperature is set to the temperature range of 40 ° C. or higher and 95 ° C. or lower, the metal powder can be produced by facilitating the control of the particle size and the CV value while maintaining high productivity. ..

For the above reasons, it is preferable to heat at least one of the metal salt solution and the reducing agent solution to the reduction temperature of the reducing agent before the step of adding and mixing the reducing agent solution to the metal salt solution. The "reduction temperature with a reducing agent" refers to a temperature at which a metal salt is reduced with a reducing agent to precipitate a metal, and is preferably 40 ° C. or higher and 95 ° C. or lower.
If the metal salt solution and the reducing agent solution are heated to the reduction temperature before mixing, the temperature does not change suddenly during mixing, and the reaction start temperature of precipitation that starts immediately after mixing can be maintained at the same level as the reduction temperature. ..

In the precipitation step, it is preferable that the pH of the mixed solution obtained by adding the reducing agent solution to the metal salt solution is 11 or more. For example, when the reducing agent is hydrazine, 4 is an electron reaction _{N 2 H 4 → N 2 ↑} + 4H + + 4e - As is evident from such a reduction reaction, the reducing power of the highly alkaline as hydrazine increases.
In the precipitation step, it is preferable to make the mixed solution highly alkaline with a pH of 11 or higher to increase the reducing power of the reducing agent and generate nuclei of noble metals in the mixed solution. When the pH of the mixed solution is 11 or more, many initial nuclei can be uniformly formed, and atomization of the metal powder and narrowing of the particle size distribution can be achieved.
The pH is prepared by adding a reducing agent solution containing the above-mentioned pH adjuster.

The amount of the reducing agent added to the mixed solution in the precipitation step is appropriately adjusted depending on the type of metal salt, the type of reducing agent, and the like. In one embodiment, when the metal salt is a nickel salt and the reducing agent is hydrazine, the amount of hydrazine added is preferably in the range of 2.0 or more and 3.25 or less in terms of the molar ratio to the nickel powder. If the amount of hydrazine added is less than 2.0 in terms of molar ratio to nickel powder, the entire amount of nickel in the reaction solution may not be reduced. On the other hand, if the amount of hydrazine exceeds 3.25 in terms of molar ratio to nickel powder, no further effect can be obtained, and the use of excess hydrazine is economically disadvantageous.

When mixing the metal salt solution and the reducing agent solution, it is preferable to stir each solution. By this stirring, the metal precipitation reaction can be made uniform, and a metal powder having a narrow particle size distribution can be obtained. As the stirring method, a known method may be used, and it is preferable to use a stirring blade from the viewpoint of controllability and equipment manufacturing cost. Commercially available products such as paddle blades, turbine blades, max blend blades, and full zone blades may be used as the stirring blades. Measures can also be taken.

[Recovery of metal powder]
Only the metal powder is separated from the metal powder slurry containing the metal powder obtained in the above precipitation step by a known procedure, for example, a procedure of washing, solid-liquid separation, and drying.

In order to separate the metal powder from the metal powder slurry, solid-liquid separation is performed by a known means such as a Denver filter, a filter press, a centrifuge, and a decanter, and pure water or ultrapure water having a conductivity of 1 μS / cm or less is used. Thoroughly wash with high-purity water such as water. Here, sufficient cleaning means that, for example, when pure water having a conductivity of about 1 μS / cm is used, the conductivity of the filtrate obtained when the metal powder is filtered and cleaned and filtered is 10 μS / cm or less. It means cleaning to a certain extent. In this way, after solid-liquid separation and washing, a range of 50 ° C. or higher and 200 ° C. or lower is preferable using a general-purpose drying device such as an air dryer, a hot air dryer, an inert gas atmosphere dryer, and a vacuum dryer. Is dried in the range of 80 ° C. or higher and 150 ° C. or lower to obtain a metal powder.

As one aspect, a metal powder surface-modified with sulfur can be obtained by adding a sulfur coating agent, which is a water-soluble sulfur compound, to the metal powder slurry. Examples of the sulfur coating agent include thiolic acid (HOOCCH (SH) CH ₂ COOH), L-cysteine (HSCH ₂ CH (NH ₂ ) COOH), thioglycerol (HSCH ₂ CH (OH) CH ₂ OH), and dithiodi. Examples thereof include water-soluble sulfur compounds containing either a mercapto group (-SH) such as glycolic acid (HOOCH ₂ S-SCH _{2 COOH) or a disulfide group (-S-S-).}

[Crushing process (post-treatment process)]
The metal powder obtained in the precipitation step can be used as it is as the metal powder of the final product, but by performing a crushing treatment as necessary, coarse particles formed in the process of metal precipitation and connections are formed. It is more preferable to reduce particles and the like. As the crushing treatment, dry crushing methods such as spiral jet crushing treatment and counter jet mill crushing treatment, wet crushing methods such as high-pressure fluid collision crushing treatment, and other general-purpose crushing methods should be applied. Is possible.

Hereinafter, examples in which the method for producing the metal powder of the present invention is more specifically disclosed will be shown. The present invention is not limited to these examples.

[Evaluation method]
In Examples and Comparative Examples, the mixed solution 60 minutes after the start of the precipitation reaction was examined to determine whether the precipitation reaction was completed. In addition, the average particle size (nm) and particle size distribution (CV value) of the obtained metal powder were measured and calculated by the following methods.

<Reaction completion judgment>
It was examined whether metal ions remained in the mixed solution by checking the liquid color of the mixed solution 60 minutes after the start of the precipitation reaction and the presence or absence of discoloration by the ion detection paper. The liquid color of the mixed solution was visually confirmed. As the ion detection paper, a nickel check manufactured by ADVANTEC was used.
Judgment is "○" when the liquid color of the mixed solution is colorless and transparent and there is no change in the color of the ion detection paper, and "x" when the liquid color of the mixed solution is colored and the color of the ion detection paper has changed. Marked.

<Average particle size and CV value>
With respect to the obtained metal powder, 1000 or more metal powders were observed (magnification: 20000 times) using a scanning electron microscope (SEM: JEOL Ltd., JSM-7100F), and an image of the observation image (SEM image) was observed. From the results of the analysis, the average particle size (nm) obtained by number averaging and its standard deviation (σ) were calculated, and the CV value [%), which is the value (%) obtained by dividing the standard deviation of the average particle size by the average particle size. Standard deviation (σ) of average particle size / average particle size (nm)) × 100] was obtained.
Judgment was made by marking "○" for those with an average particle size of 100 nm or less and CV value of 25% or less, and "x" for those with an average particle size of more than 100 nm or a CV value of more than 25%. ..

(Example 1)
[Preparation of metal salt solution]
Nickel sulfate hexahydrate as the metal salt _(NiSO 4 · _6H 2 O, molecular weight: 262.85), copper sulfate pentahydrate as a noble metal catalyst _(CuSO 4 · _5H 2 O, molecular weight: 249.7) 1.52 mg , L- arginine as the basic amino acid, monovalent or polyvalent carboxylic acid or trisodium citrate dihydrate salt thereof _{(Na 3 (C 3 H 5} O (COO) 3) · 2H 2 O), molecular weight: 294 1) was dissolved in pure water so as to have the ratio shown in Table 1 to prepare a metal salt solution.

[Preparation of reducing agent solution]
_{As a reducing agent, 65 g of 60% hydrazine hydrate (N 2} H ₄ · H ₂ O, molecular weight: 50.06) purified by removing organic impurities such as pyrazole, and as a pH adjuster, sodium hydroxide (NaOH, molecular weight:: 40.0) 57 g was dissolved in 280 mL of pure water to prepare a reducing agent solution.

[Precipitation process]
The metal salt solution and the reducing agent solution were each heated to a liquid temperature of 60 ° C., and then the two liquids were stirred and mixed to form a mixed solution, and the precipitation reaction was started. The reaction start temperature was 65 ° C. because the temperature of the mixed solution rose to 65 ° C. due to the heat generated during stirring and mixing of the metal salt solution and the reducing agent solution, each of which had a liquid temperature of 60 ° C. The pH of the mixed solution at the start of the precipitation reaction was 13. About 2 to 3 minutes after the start of the reaction (stirring and mixing of the two liquids), the reaction liquid discolors (yellowish green → gray) due to the generation of nuclei by the action of the noble metal catalyst, but the reduction reaction is carried out while further stirring. Nickel precipitate powder was obtained. The supernatant of the reaction solution after the reduction reaction is transparent, and the presence of nickel in the reaction solution is confirmed using ion detection paper, and it is confirmed that all the nickel components in the reaction solution are reduced to metallic nickel. bottom.

The reaction solution containing the obtained nickel-precipitated powder is in the form of a slurry (nickel-precipitated powder slurry), and the nickel-precipitated powder slurry is added with thioannic acid (also known as mercapto-succinic acid) (HOOCCH) as a sulfur coating agent (S-coating agent). (SH) CH ₂ COOH, molecular weight: 150.15) An aqueous solution was added, and the nickel precipitate powder was surface-treated. After the surface treatment, pure water having a conductivity of 1 μS / cm is used to filter and wash the filtrate filtered from the nickel precipitate powder slurry until the conductivity becomes 10 μS / cm or less, and after solid-liquid separation, 150 The mixture was dried in a vacuum dryer set at a temperature of ° C. to obtain a nickel precipitate powder (nickel powder) surface-treated with sulfur (S).

[Crushing process (post-processing process)]
The nickel precipitate powder obtained in the precipitation step was subjected to a spiral jet crushing treatment, which is a dry crushing method, to obtain a nickel powder according to Example 1 having a uniform particle size and a substantially spherical shape.
The reaction completion was determined by the above procedure, and the average particle size and CV value of the obtained nickel powder were measured and calculated. The results are shown in Table 1.

(Comparative Examples 1 to 3)
The precipitation reaction was carried out in the same manner as in Example 1 except that the addition amounts of the noble metal catalyst and the basic amino acid were changed as shown in Table 1. The results are shown in Table 1.

As shown in Table 1, in Example 1 using a basic amino acid and a monovalent or higher carboxylic acid, the reaction was completed within 60 minutes to obtain a metal powder having an average particle size of 97 nm and a CV value of 20%. I was able to do it. This is probably because the basic amino acids were effective in suppressing the growth of nickel particles.
On the other hand, as shown in Comparative Examples 1 to 3, if basic amino acids were not mixed, a nickel powder having an average particle size of 100 nm or less and a CV value of 25% or less could be obtained even if only the noble metal catalyst as a nucleating agent was increased. There wasn't.

(Comparative Examples 4 to 7)
The reaction was carried out in the same manner as in Example 1 except that the carboxylic acid having a valence of 1 or more was not added and the amount of the basic amino acid added was changed as shown in Table 2. However, the precipitation reaction did not start in any of the comparative examples. The results are shown in Table 2.

As shown in Table 2, the precipitation reaction did not start unless a monovalent or higher carboxylic acid was added, and the metal powder could not be produced.

(Comparative Examples 8 and 9)
The precipitation reaction was carried out in the same manner as in Example 1 except that no basic amino acid was added and the amount of monovalent or higher carboxylic acid added was changed to the ratio shown in Table 3. The results are shown in Table 3.

As shown in Table 3, the precipitation reaction was started when a monovalent or higher carboxylic acid was added. However, when the amount of monovalent or higher carboxylic acid added increases, particle growth proceeds, and when the amount of monovalent or higher carboxylic acid added is 120% by weight or more based on the weight of the produced nickel powder, the nickel powder The average particle size was 200 nm or more.
On the other hand, since energy is used for particle growth of nickel powder, the CV value decreased as the amount of monovalent or higher carboxylic acid added increased. However, a nickel powder having an average particle size of 100 nm or less and a CV value of 25% or less could not be obtained only by adjusting the addition amount of a monovalent or higher carboxylic acid without adding a basic amino acid.

(Examples 2 to 7, Comparative Examples 10 to 16)
The precipitation reaction was carried out in the same manner as in Example 1 except that the amount of the basic amino acid added and the amount of the monovalent or higher carboxylic acid added were changed as shown in Table 4. The results are shown in Table 4.

As shown in Table 4, in Comparative Examples 11 and 12 in which the amount of the basic amino acid added exceeded 35% by weight, the precipitation reaction did not proceed and the metal powder could not be obtained.
Further, in Comparative Examples 13 to 15 in which the addition amount of the monovalent or higher carboxylic acid exceeded 120% by weight, the CV value was larger than 25%.
Further, even if the addition amount of the basic amino acid is 35% by weight or less, the addition amount of the monovalent or higher carboxylic acid is large, and the (basic amino acid addition amount) / (monovalent or higher carboxylic acid addition amount) is 0.2 or less. The effect of suppressing particle growth of basic amino acids was not sufficiently exhibited, and the average particle size was 100 nm or less and the CV value was not 25% or less (Comparative Examples 10, 13, 15).
On the other hand, even if the amount of the basic amino acid added is 35% by weight or less, the amount of the monovalent or higher carboxylic acid added is small, and (the amount of the basic amino acid added) / (the amount of the monovalent or higher carboxylic acid added) is greater than 1.0. The effect of suppressing the particle growth of the basic amino acid was greater than the reducing effect of the monovalent or higher carboxylic acid, and the precipitation reaction did not proceed (Comparative Example 16).
From these results, the amount of basic amino acid added was 35% by weight or less based on the weight of the metal powder, and the amount of monovalent or higher carboxylic acid added was 120% by weight or less based on the weight of the metal powder (addition of basic amino acid). Amount) / (amount of carboxylic acid added having a valence of 1 or more) is greater than 0.2 and in the range of 1.0 or less in order to produce a metal powder having a smaller average particle size and a sharp particle size distribution. is necessary.

(Example 8)
The precipitation reaction was carried out in the same manner as in Example 2 except that the metal salt was changed to copper (II) sulfate pentahydrate and the noble metal catalyst was changed to palladium (II) ammonium chloride. The results are shown in Table 5.

(Example 9)
The precipitation reaction was carried out in the same manner as in Example 2 except that the metal salt was changed to silver nitrate and the noble metal catalyst was changed to palladium (II) ammonium chloride. The results are shown in Table 5.

(Example 10)
The precipitation reaction was carried out in the same manner as in Example 2 except that the metal salt was changed to hexachloroplatinic acid and the noble metal catalyst was changed to palladium (II) ammonium chloride. The results are shown in Table 5.

As shown in Table 5, even if the metal species to be produced is changed, the amount of basic amino acid added is 35% by weight or less based on the weight of the metal powder, and the amount of monovalent or higher carboxylic acid added is the metal powder. If it is 120% by weight or less based on the weight and the (addition amount of basic amino acid) / (addition amount of monovalent or higher carboxylic acid) is in the range of more than 0.2 and 1.0 or less, the average particle size is 100 nm or less and A metal powder having a CV value of 25% or less was obtained.

(Examples 11-12, Comparative Examples 17-18)
The precipitation reaction was carried out in the same manner as in Example 2 except that L-arginine was changed to the amino acid shown in Table 6. The results are shown in Table 6.

As shown in Table 6, even in Examples 11 and 12 in which other basic amino acids (lysine, histidine) were used instead of L-arginine, a metal powder having an average particle size of 100 nm or less and a CV value of 25% or less was obtained. rice field.
On the other hand, in Comparative Examples 17 and 18 in which the acidic amino acids L-aspartic acid or L-glutamic acid were used instead of L-arginine, the growth inhibitory effect of the metal powder was not exhibited, and the average particle size of the metal powder was 100 nm or less. Did not become.

Claims (7)

A step of mixing a metal salt, a basic amino acid, a monovalent or higher carboxylic acid or a salt thereof, and a noble metal catalyst in water to prepare a metal salt solution.
A step of mixing an alkaline pH adjuster and a reducing agent with water to prepare a reducing agent solution, and
A method for producing a metal powder, wherein the reducing agent solution is added to the metal salt solution and mixed, and the process is performed.
The blending amount of the basic amino acid is 35% by weight or less based on the weight of the produced metal powder.
The blending amount of the monovalent or higher carboxylic acid or a salt thereof is 120% by weight or less with respect to the weight of the produced metal powder.
A method for producing a metal powder, wherein the ratio of the blending amount of the basic amino acid to the blending amount of the monovalent or higher carboxylic acid or a salt thereof is greater than 0.2 and 1.0 or less. A claim comprising a step of heating at least one of the metal salt solution and the reducing agent solution to the reduction temperature by the reducing agent before the step of adding and mixing the reducing agent solution to the metal salt solution. Item 2. The method for producing a metal powder according to Item 1. The method for producing a metal powder according to claim 1 or 2, wherein the pH of the mixed solution obtained by adding the reducing agent solution to the metal salt solution is 11 or more. The method for producing a metal powder according to any one of claims 1 to 3, wherein the basic amino acid is at least one selected from the group consisting of lysine, arginine and histidine. The method for producing a metal powder according to any one of claims 1 to 4, wherein the monovalent or higher carboxylic acid or a salt thereof has reducibility and solubility in water. The method for producing a metal powder according to any one of claims 1 to 5, wherein the monovalent or higher carboxylic acid or salt thereof is at least one selected from citric acid or a salt thereof, and ascorbic acid or a salt thereof. .. The method for producing a metal powder according to any one of claims 1 to 6, wherein the metal to be the metal powder is at least one selected from the group consisting of Ni, Cu, Pt and Ag.