JP2023001434A - Manufacturing method of nickel powder - Google Patents

Abstract

To provide a manufacturing method of nickel powder capable of obtaining nickel powder with less coarse particles.SOLUTION: A manufacturing method of nickel powder includes: a wet-disintegration step of wet-disintegrating, in a reaction liquid containing water-soluble nickel salt, metal salt of a metal nobler than nickel, hydrazine, alkali hydroxide and water, slurry of nickel crystallization powder obtained by crystallizing the water-soluble nickel salt by a reductive reaction by the hydrazine so as to obtain nickel powder slurry with a reduced amount of coarse particles; a solvent substitution step of substituting a solvent of the nickel powder slurry after the wet-disintegration step with a water-soluble organic solvent; a solid-liquid separation step of solid-liquid separating the nickel powder slurry after the solvent substitution step to obtain a nickel powder cake; and a desiccation step of desiccating the nickel powder cake after the solid-liquid separation step to obtain nickel powder.SELECTED DRAWING: Figure 3

Description

TECHNICAL FIELD The present invention relates to a method for producing inexpensive and high-performance nickel powder used as an electrode material for laminated ceramic parts, and more particularly to a method for producing inexpensive and high-performance nickel powder obtained by a wet method.

Conventionally, conductive pastes mainly composed of conductive powder, resin and organic solvent have been used to form conductive layers, electrode layers, interlayer connecting materials that constitute wiring boards of electric circuits, and electrode layers of electronic parts. ing. As these wiring boards and electronic components become smaller and more dense, the width and thickness of the conductive layers and electrode layers tend to be reduced. For this reason, it is also required to reduce the diameter of the conductive powder, which is the material of the conductive paste used as the material for forming these components. Coarse particles exceeding a specific particle size are usually present in the powder. The problem is the negative impact on Therefore, the conductive powder is required to have the property of containing no coarse particles or containing very few coarse particles.

The problem caused by the presence of coarse particles in the powder is a particular problem in the field of conductive pastes for internal electrodes of multilayer ceramic capacitors (MLCCs). In a multilayer ceramic capacitor, for example, internal electrodes are formed by screen-printing a conductive paste in which nickel powder is mainly dispersed as a conductive powder on a dielectric green sheet, and a plurality of greens on which the internal electrodes are printed is formed. The sheets are stacked so that the internal electrodes are alternately stacked and pressed to obtain a laminate, which is then cut into a predetermined size, subjected to binder removal treatment, and then fired at a high temperature of 1300°C. to obtain a ceramic sintered body, and finally to attach external electrodes to this ceramic sintered body.

Along with the miniaturization and increase in capacity of laminated ceramic capacitors, the thickness of both internal electrodes and dielectrics is being reduced. Along with this, the particle size of the nickel powder used in the internal electrode paste is also becoming finer, necessitating a nickel powder with an average particle size of 0.4 μm or less, especially a nickel powder with an average particle size of 0.3 μm or less. is predominantly used. In addition, although it depends on the film thickness of the internal electrode, the standard particle size of the conductive powder is usually three to five times the number average particle size of the entire powder. Large particles are considered coarse particles. Here, when the conductive powder is mainly composed of primary particles, the coarse particles include not only particles having a primary particle size larger than the standard, but also primary particles that are strongly connected or aggregated and cannot be easily crushed. Secondary particles that are in a state and have a particle size equal to or larger than the standard particle size are also included.

Methods for producing nickel powder are roughly classified into a vapor phase method and a wet method. As the gas phase method, for example, a method of producing nickel powder (gas phase nickel powder) by reducing nickel chloride vapor with hydrogen described in Patent Document 1, and a method of producing nickel metal described in Patent Document 2. There is a method of vaporizing in plasma to produce nickel powder (vapor phase nickel powder). In addition, as a wet method, for example, nickel powder obtained by adding a reducing agent to a nickel salt solution described in Patent Document 3 (hereinafter, nickel powder obtained by a wet method may be referred to as "wet nickel powder". There is a method to make

The vapor phase method is an effective means for obtaining nickel powder with excellent crystallinity and high characteristics because it is a high-temperature process of about 1000° C. or more, but there is a problem that the particle size distribution of the obtained nickel powder is widened. . As described above, nickel powder containing no coarse particles and having a relatively narrow particle size distribution and an average particle size of 0.4 μm or less is required for thinning the internal electrodes. In order to obtain nickel powder, classification treatment by introducing an expensive classifier is essential.

In the classification process, coarse particles larger than the classification point can be removed with the classification point of an arbitrary value of about 0.6 μm to 2 μm as a goal, but some particles smaller than the classification point are also removed at the same time. There is also the problem that the actual yield of the product drops significantly because the product is depleted. Therefore, the vapor phase method cannot avoid increasing the cost of the product, including the introduction of the above-mentioned expensive equipment.

Furthermore, in the vapor phase method, when using nickel powder with an average particle size of 0.2 μm or less, particularly 0.1 μm or less, it becomes difficult to remove coarse particles by classification treatment. cannot be applied to thin layers.

On the other hand, the wet method has the advantage that the resulting nickel powder has a narrower particle size distribution than the vapor phase method. In particular, in the method of producing nickel powder by adding a solution containing hydrazine as a reducing agent to a solution containing a nickel salt and a copper salt described in Patent Document 3, a metal salt of a metal nobler than nickel (copper salt ) serves as a nucleating agent, and nickel salt (more precisely, nickel ion (Ni ²⁺ ) or nickel complex ion) is reduced with hydrazine in the presence of this nucleating agent. Therefore, the particle size can be controlled by controlling the number of nuclei generated, and the generation of nuclei and the growth of nickel particles are uniform, so fine nickel powder can be obtained with a narrower particle size distribution than the vapor phase method. It is known.

By the way, when applying the nickel powder obtained by the wet method to a multilayer ceramic capacitor, in order to prevent short-circuiting between the electrodes in the laminate composed of the internal electrode layers and the dielectric layers described above, the nickel powder and the resin A nickel paste dry film (a dry film obtained by printing and drying a nickel paste) mainly composed of is required to have high flatness. In particular, in order to cope with the thinning (approximately 0.5 μm to 1.0 μm) of internal electrode layers accompanying the recent increase in capacity of multilayer ceramic capacitors, the average grain size is 0.3 μm or less, preferably 0.2 μm or less. of fine nickel powder is used, and coarse particles of the same size (for example, 0.8 μm to 1.2 μm) as the film thickness of the internal electrode layer contained in the nickel powder can be reduced to the limit. requested.

Therefore, in Patent Document 4, as a method for producing nickel powder using a wet method, in a crystallization step in which a reduction reaction is performed in a strongly alkaline reaction liquid in order to increase the reducing power of hydrazine, a specific amine is added to the reaction liquid. A very small amount of compound or sulfide compound is added to remarkably suppress the self-decomposition reaction of hydrazine and to make it difficult to form coarse particles that occur when nickel particles are connected to each other. A method for obtaining a nickel powder of high quality at low cost is shown.

As a means for reducing coarse particles in the nickel powder, removal of coarse particles by the above-described classification treatment is exemplified for gas phase nickel powder. Techniques such as using glutamic acid or the like in the slurry to suppress the formation of aggregates of the vapor phase nickel powder are also used. On the other hand, for wet nickel powder, a crushing treatment or the like has been proposed as a means for reducing coarse particles. For example, Patent Document 6 discloses a wet nickel powder having a specific particle size distribution and an average primary particle size within a specific range by a specific pulverization treatment, and a method for producing the same.

However, when the above-mentioned classification treatment and crushing treatment target nickel powder having an average particle size of 0.2 μm or less, particularly 0.1 μm or less, it becomes increasingly difficult to remove or crush coarse particles. come. In particular, when dry pulverization is applied to nickel powder of 0.15 μm or less, there is a risk of insufficient pulverization force due to a decrease in kinetic energy due to a decrease in the mass of individual nickel particles, and a new pulverization surface due to an increase in specific surface area. There is a risk of heat generation and ignition due to increased heat of oxidation. Therefore, it is becoming more and more difficult to cope with future thinning of internal electrodes by means of classification processing and crushing processing.

On the other hand, as a method for producing nickel powder having excellent dispersibility, for example, Patent Document 7 reports a method using a hydrothermal synthesis method. According to this proposed method, it is disclosed that the product after the hydrothermal reaction is washed with deionized water and ethanol, but the degree of agglomeration of the resulting nickel powder can be determined only by SEM observation. Quantitative evaluation is not performed on the content of coarse particles. Therefore, it is not clear whether the hydrothermal synthesis method is effective from the viewpoint of suppressing the generation of coarse particles.

Further, Patent Document 8 reports a method of diluting and removing the post-reaction liquid with water by decantation after crystallization by a wet method, and then similarly diluting and removing water with a water-soluble organic solvent. According to this proposed method, although it is described that the nickel powder obtained has a low oxygen content and that aggregation is suppressed, evaluation of coarse particles is only SEM observation, and quantification No results were reported. Therefore, it is not clear whether this method is effective from the viewpoint of suppressing the generation of coarse particles.

FIG. 1 shows the conventional wet nickel powder manufacturing process. As shown in FIG. 2, nickel particles are oxidized to form nickel hydroxide, and coarse particles 2 of about 1 μm or more in size enveloping a plurality of nickel particles (hereinafter referred to as this coarse particle). The particles are sometimes referred to as "nickel hydroxide-containing coarse particles"). In addition, as the nickel powder cake is dried, the nickel particles are strongly attracted to each other due to the high surface tension of the adhering liquid (mainly water), which often results in strong aggregation (dry aggregation). In these cases, nickel hydroxide-containing coarse particles and dry agglomeration not only increase the number of coarse particles in the wet nickel powder, but also affect the dispersibility of the nickel particles when producing a conductive paste using the wet nickel powder. There is also the problem of a decrease in

Patent Document 9 reports a method of obtaining nickel powder by performing solid-liquid separation after crystallization by a wet method, slurrying again with a water-soluble organic solvent, and then performing solid-liquid separation and drying. there is According to this proposed method, it is possible to suppress the formation of nickel hydroxide-containing coarse particles and the dry agglomeration of nickel particles. In addition, the obtained nickel powder can be processed by dry crushing methods such as spiral jet crushing and counter jet mill crushing, wet crushing such as high-pressure fluid impingement crushing, and other general-purpose crushing methods. It is stated that the crushing method is applicable. However, in the examples, only the dry crushing method is described. Although it is preferable, no mention is made of a specific method for obtaining dry nickel powder after crushing when a wet crushing method is applied.

JP-A-4-365806 Japanese Patent Publication No. 2002-530521 JP-A-2002-53904 WO2017/069067 JP-A-2006-219688 Japanese Patent Application Laid-Open No. 2001-247903 Japanese Patent No. 5421339 Japanese Patent No. 6065699 JP 2019-44268 A

An object of the present invention is to provide a nickel powder production method for producing nickel powder with few coarse particles when producing nickel powder using an aqueous solution-based wet method.

In order to solve the above-mentioned problems, the method for producing nickel powder of the present invention comprises: a wet crushing step of wet crushing a slurry of nickel crystallized powder obtained by crystallizing the water-soluble nickel salt in a reduction reaction to obtain a nickel powder slurry with reduced coarse particles; and after the wet crushing step. A solvent replacement step of replacing the solvent of the nickel powder slurry with a water-soluble organic solvent, a solid-liquid separation step of solid-liquid separating the nickel powder slurry after the solvent replacement step to obtain a nickel powder cake, and the solid-liquid separation step and a subsequent drying step of drying the nickel powder cake to obtain nickel powder.

INDUSTRIAL APPLICABILITY As described above, according to the present invention, it is possible to provide a method for producing nickel powder that can obtain nickel powder with few coarse particles when nickel powder is produced using an aqueous wet method. .

It is a schematic diagram which shows an example of the manufacturing process of the conventional wet nickel powder. FIG. 2 is a schematic diagram showing nickel hydroxide-containing coarse particles found in conventional wet nickel powder. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows an example of the manufacturing process in the manufacturing method of the nickel powder which concerns on one Embodiment of this invention. 1 is a schematic diagram of a suction filtration device used for evaluating the content of coarse particles in wet nickel powders obtained by the production methods shown in Examples, Comparative Examples, and Reference Examples. FIG.

Hereinafter, the method for producing nickel powder according to the present invention will be described in the following order with reference to the drawings. The present invention is not limited to the following examples, and can be arbitrarily modified without departing from the gist of the present invention.

Method for producing nickel powder 1 . Crystallization step 1-1. Agents Used in Crystallization Step 1-2. Crystallization reaction procedure (crystallization procedure)
1-3. Crystallization reaction (reduction reaction, hydrazine autolysis reaction)
1-4. Crystallization conditions (reaction initiation temperature)
2. Wet crushing process 3 . Solvent replacement step 4. 5. Solid-liquid separation step; drying process

<Method for reducing coarse particles of wet nickel powder (manufacturing method)>
First, a method for producing nickel powder according to an embodiment of the present invention will be described. FIG. 3 shows a schematic diagram as an example of the production process in the method for producing nickel powder according to one embodiment of the present invention. A method for producing nickel powder according to an embodiment of the present invention includes a crystallization step, a wet pulverization step, a solvent replacement step, a solid-liquid separation step, and a drying step.

If desired, a sulfur compound is added to the reaction liquid containing the nickel crystallized powder or the cleaning liquid, and a surface treatment (sulfur coating treatment) is performed to modify the surface of the nickel crystallized powder with a sulfur component to obtain a wet nickel powder. (Nickel crystallized powder) may be obtained. By surface-treating the wet nickel powder in this way, it is possible to weaken the activity of nickel to decompose organic substances, and for example, it is possible to suppress the deterioration of the resin coexisting with the wet nickel powder in the conductive paste. . In the present invention, "powder" and "powder" are states in which a large number of particles are aggregated to form an aggregate, and crystallized nickel particles are dispersed in a slurry or dried. A solid aggregate corresponds to nickel powder or nickel powder. For example, "crystallized nickel powder" is nickel powder that has been reduced in the crystallization process.

(1. Crystallization step)
In the crystallization process, a nickel salt (more precisely, nickel ion or nickel complex ion ) can be reduced by a reduction reaction using a reducing agent such as hydrazine. In the present invention, when hydrazine is used, the reaction solution is mixed with an amine compound or a sulfur-containing compound, if necessary, in the presence of the amine compound or sulfur-containing compound to suppress the decomposition of hydrazine as a reducing agent. However, nickel salts can also be reduced.

(1-1. Agents used in the crystallization step)
In the crystallization step of the present invention, a reaction solution containing nickel salts, salts of metals nobler than nickel, reducing agents, alkali hydroxides, various chemicals such as amine compounds and sulfur-containing compounds, and water as necessary is used. It is From the viewpoint of reducing the amount of impurities in the resulting nickel powder, water as a solvent includes ultrapure water (conductivity: ≤ 0.06 μS / cm (micro Siemens per centimeter), pure water (conductivity: ≤ A high purity of 1 μS/cm) is preferred, and pure water, which is inexpensive and readily available, is preferably used.

(a) Water-soluble nickel salt The water-soluble nickel salt is not particularly limited as long as it is a nickel salt that is readily soluble in water. For example, one or more selected from nickel chloride, nickel sulfate, and nickel nitrate. can be used. Among these nickel salts, it is more preferable to use nickel chloride, nickel sulfate, or a mixture thereof.

(b) Metal Salts of Metals Noble to Nickel Salts of metals nobler than nickel have a lower ionization tendency than nickel, and thus are reduced before nickel when nickel is deposited by reduction. Therefore, when a salt of a metal nobler than nickel is contained in a nickel salt solution, the metal nobler than nickel is first reduced and acts as a nucleating agent to form initial nuclei when nickel is reduced and deposited. In the nickel crystallized powder (nickel powder) obtained by the particle growth of the initial nuclei, it becomes possible to easily perform particle size control and refinement.

The metal salt of a metal nobler than nickel may be a metal salt of a metal that is water-soluble and has a lower ionization tendency than nickel, such as water-soluble copper salts, gold salts, silver salts, platinum salts, and palladium salts. , rhodium salts, iridium salts, and other water-soluble noble metal salts. For example, water-soluble copper salts include copper sulfate, water-soluble silver salts include silver nitrate, and water-soluble palladium salts include sodium palladium(II) chloride, ammonium palladium(II) chloride, palladium(II) nitrate, Palladium (II) sulfate and the like can be used, but are not limited to these.

As the metal salt of a metal nobler than nickel, it is preferable to use the above-described palladium salt, because the particle size distribution of the obtained nickel powder can be more finely controlled, although the particle size distribution becomes somewhat wider. . When a palladium salt is used, the ratio [moles ppm] of the palladium salt and nickel (number of moles of palladium salt/number of moles of nickel×10 ⁶ ) is appropriately selected depending on the desired number average particle size of the wet nickel powder. be able to. For example, if the number average particle diameter of wet nickel powder is set to 0.05 μm to 0.5 μm, the ratio of palladium salt and nickel is within the range of 0.2 mol ppm to 100 mol ppm, preferably 0.5 It is preferably in the range of mol ppm to 80 mol ppm. If this ratio is less than 0.2 mol ppm, the number average particle size of the produced wet nickel powder may exceed 0.4 μm. On the other hand, if this ratio exceeds 100 mol ppm, a large amount of expensive palladium salt will be used, which may lead to an increase in cost for producing wet nickel powder.

(c) Reducing Agent The reducing agent used in the crystallization step of the present invention is not particularly limited, but hydrazine (N ₂ H ₄ , molecular weight: 32.05) can be mentioned, for example. In addition to anhydrous hydrazine, hydrazine includes hydrazine hydrate (N ₂ H ₄ ·H ₂ O, molecular weight: 50.06), which is a hydrazine hydrate, and either of them may be used. The reduction reaction of hydrazine is as shown in the formula (2) described later, but since it is particularly alkaline and has a high reducing power, and the by-products of the reduction reaction are nitrogen gas and water, impurity components due to the reduction reaction are reduced. It has the characteristics that it does not occur in the reaction solution, the amount of impurities in hydrazine is originally low, and it is easily available. Therefore, hydrazine is suitable as a reducing agent, and for example, commercially available industrial grade 60 mass % hydrazine hydrate can be used.

(d) Alkali hydroxide Since the reducing power of hydrazine increases as the alkalinity of the reaction solution increases (see formula (2) described later), alkali hydroxide is used as a pH adjuster to increase alkalinity in the crystallization step. can be done. Although the alkali hydroxide is not particularly limited, it is preferable to use an alkali metal hydroxide from the standpoint of availability and cost. Specifically, it is more preferable to use one or more selected from sodium hydroxide and potassium hydroxide.

The amount of the alkali hydroxide is such that the pH of the reaction solution at the reaction temperature is 9.5 or higher, preferably 10 or higher, and more preferably 10.5 or higher so that the reducing power of hydrazine as a reducing agent is sufficiently increased. should be determined so that When the pH of the reaction solution is compared at 25° C. and 70° C., for example, the high temperature of 70° C. is lower.

(e) Amine compound The amine compound of the present invention acts as a hydrazine self-decomposition inhibitor, a reduction reaction accelerator, and a linking inhibitor between nickel particles as described above. , may be included in the reaction solution. The amine compound is a compound containing two or more functional groups selected from a primary amino group (--NH.sub.2) or a _secondary amino group (--NH--) in the molecule. For example, alkyleneamines and/or alkyleneamine derivatives can be used. As an example, it is preferable to use an amine compound having at least the structure of the following formula A in which nitrogen atoms of amino groups in the molecule are bonded through a carbon chain having 2 carbon atoms.

More specifically, _{alkyleneamines} include _{ethylenediamine ( H2NC2H4NH2} ), _{diethylenetriamine ( H2NC2H4NHC2H4NH2} ), _{triethylenetetramine ( H2N ( C2H 4NH} ) _2C2H4NH2 ), _{tetraethylenepentamine ( H2N ( C2H4NH} ) _3C2H4NH2 ) _{, pentaethylenehexaamine ( H2N ( C2H4NH ) 4} C ₂ H ₄ NH ₂ ), propylenediamine (also known as 1,2-diaminopropane, 1,2-propanediamine) (CH ₃ CH(NH ₂ )CH ₂ NH ₂ ). be able to. Examples of alkyleneamine derivatives include tris(2-aminoethyl)amine (N(C ₂ H ₄ NH ₂ ) ₃ ), N-(2-aminoethyl)ethanolamine (also known as 2-(2-aminoethyl amino) ethanol (H ₂ NC ₂ H ₄ NHC ₂ H ₄ OH), N-(2-aminoethyl) propanolamine (also known as 2-(2-aminoethylamino) propanol) (H ₂ NC ₂ H ₄ NHC ₃ H ₆ OH), L (or D, DL)-2,3-diaminopropionic acid (also known as 3-amino-L (or D, DL)-alanine) (H ₂ NCH ₂ CH(NH) COOH), ethylenediamine-N,N'-diacetic acid (also known as ethylene-N,N'-diglycine) (HOOCCH ₂ NHC ₂ H ₄ NHCH ₂ COOH), N,N'-diacetylethylenediamine (also known as N, N′-ethylenebisacetamide) (CH ₃ CONHC ₂ H ₄ NHCOCH ₃ ), 1,2-cyclohexanediamine (also known as 1,2-diaminocyclohexane) (H ₂ NC ₆ H ₁₀ NH ₂ ), N,N′ -dimethylethylenediamine _{( CH3NHC2H4NHCH3} ), N,N' _- diethylethylenediamine _{( C2H5NHC2H4NHC2H5} ), _{N ,} N' _- diisopropylethylenediamine _{( CH3 ( CH3} ) CHNHC ₂ H ₄ NHCH(CH ₃ )CH ₃ ).These alkyleneamines and alkyleneamine derivatives are water-soluble, and among them, ethylenediamine and diethylenetriamine have the effect of inhibiting the self-decomposition of hydrazine. is relatively strong, readily available, and inexpensive.

The action of the amine compound as a reduction reaction accelerator is considered to be due to its action as a complexing agent that complexes nickel ions (Ni ²⁺ ) in the reaction solution to form nickel complex ions. In addition, regarding the action of hydrazine as an inhibitor of self-decomposition and an inhibitor of linkage between nickel particles, the primary amino group (—NH ₂ ) and the secondary amino group (—NH—) in the amine compound molecule. , is presumed to be expressed by interaction with the surface of hydrazine or nickel crystallized powder.

The alkyleneamine or alkyleneamine derivative, which is the amine compound, preferably has the structure of the above formula A in which nitrogen atoms of amino groups in the molecule are bonded through a carbon chain having 2 carbon atoms. This is because the effect of suppressing the decomposition of hydrazine molecules is increased. For example, if the nitrogen atoms of the amino group, which strongly adsorbs to the nickel crystallized powder, are bonded through a carbon chain with 3 or more carbon atoms, the length of the carbon chain increases the freedom of movement of the carbon chain portion of the amine compound molecule. degree (molecular flexibility) increases. As a result, it becomes impossible to effectively prevent hydrazine molecules from coming into contact with the nickel crystallized powder, and more hydrazine molecules undergo self-decomposition due to the catalytic activity of nickel. be done.

In fact, ethylenediamine (H ₂ NC ₂ H ₄ NH ₂ ) and propylenediamine (also known as 1,2-diaminopropane, 1,2-diaminopropane, 1,2-diaminopropane, 1,2-diaminopropane, 2-propanediamine) (CH ₃ CH(NH ₂ )CH ₂ NH ₂ ), trimethylenediamine (also known as 1 It has been confirmed that ,3-diaminopropane, 1,3-propanediamine) (H ₂ NC ₃ H ₆ NH ₂ ) is inferior in the autolysis inhibitory action of hydrazine.

Here, the ratio [mol%] of the amine compound and nickel in the reaction solution ((number of moles of amine compound/number of moles of nickel) × 100) is in the range of 0.01 mol% to 5 mol%, preferably A range of 0.03 mol % to 2 mol % is preferable. If the ratio is less than 0.01 mol%, the amount of the amine compound is too small, and it is not possible to obtain each action as a self-decomposition inhibitor of hydrazine, a reduction reaction accelerator, or a linking inhibitor between nickel particles. Sometimes you can't. On the other hand, if the above ratio exceeds 5 mol %, the amine compound acts too strongly as a complexing agent to form nickel complex ions, which may result in abnormal growth of particles of the crystallized nickel powder. The characteristics of the nickel powder may be degraded, for example, the nickel powder loses its granularity and sphericalness and becomes distorted, and a large number of coarse particles in which the nickel particles are connected to each other are formed.

(f) Sulfur-containing compound (auxiliary agent for inhibiting autolysis of hydrazine)
The reaction liquid may contain a sulfur-containing compound. The sulfur-containing compound used in the present invention is a compound that is applied as a brightening agent for nickel plating or a stabilizer for a plating bath. not big. However, it has an interaction such as adsorption with the nickel particle surface, and when used in combination with the above amine compound, it has the action of a hydrazine self-decomposition inhibitor auxiliary agent that can greatly strengthen the self-decomposition inhibitory action of hydrazine. there is Therefore, it may be added to the reaction solution as needed. The sulfur-containing compound contains a sulfide group (--S--), a sulfonyl group (--S(=O) ₂ --), a sulfonic acid group (--S(=O) ₂ --O--), and a thioketone group in the molecule. A compound containing at least one of (-C(=S)-). Furthermore, the sulfur-containing compound acts as an auxiliary agent for suppressing the self-decomposition of hydrazine, and also acts as a linking inhibitor for nickel particles. It is also possible to more effectively reduce the amount of coarse particles produced.

As the sulfur-containing compound, for example, a sulfide compound having a sulfide group (-S-) in the molecule should preferably have high water solubility. OH), carboxy group-containing sulfide compounds containing at least one amino group (primary: -NH ₂ , secondary: -NH-, tertiary: -N<), hydroxyl group-containing sulfide compounds , amino group-containing sulfide compounds, and thiazole ring-containing sulfide compounds containing at least one thiazole ring (C ₃ H ₃ NS) are also applicable, although they are not highly water-soluble. More specifically, L (or D, DL)-methionine (CH ₃ SC ₂ H ₄ CH(NH ₂ )COOH), L (or D, DL)-ethionine (C ₂ H ₅ SC ₂ H ₄ CH(NH ₂ )COOH), N-acetyl-L (or D, DL)-methionine (CH ₃ SC ₂ H ₄ CH(NH(COCH ₃ ))COOH), lanthionine (also known as 3,3′- _{thiodialanine} ) (HOOCCH( _NH2 ) _{CH2SCH2CH ( NH2} )COOH), thiodipropionic _acid (also known as 3,3'-thiodipropionic acid) _{( HOOCC2H4SC2H4COOH} ), Thiodiglycolic acid (also known as 2,2′-thiodiglycolic acid, 2,2′-thiodiacetic acid, 2,2′-thiobisacetic acid, mercaptodiacetic acid) (HOOCCH ₂ SCH ₂ COOH), Names: 3-methylthio-1-propanol) (CH ₃ SC ₃ H ₆ OH), thiodiglycol (also known as 2,2′-thiodiethanol) (HOC ₂ H ₅ SC ₂ H ₅ OH), thiomorpholine ( C ₄ H ₉ NS), thiazole (C ₃ H ₃ NS), and benzothiazole (C ₇ H ₅ NS) are preferred. Among these, methionine and thiodiglycolic acid are preferable because they are excellent in the autolysis-suppressing effect of hydrazine, are readily available, and are inexpensive. In addition, "L (or D, DL)-methionine" means "L-methionine, D-methionine or DL-methionine", and in other compounds with the notation of L (or D, DL) The same is true for

More specifically, sulfur-containing compounds other than sulfide compounds include saccharin (also known as o-benzoic acid sulfimide, o-sulfobenzimide) (C ₇ H ₅ NO ₃ S), sodium dodecyl sulfate (C ₁₂ H _{25OS (} O) _2ONa ), _{dodecylbenzenesulfonic acid} ( _C12H25C6H4S (O) _2OH ), sodium _{dodecylbenzenesulfonate ( C12H25C6H4S (} O) _2ONa ) ), bis(2-ethylhexyl) sodium sulfosuccinate (also known as di-2-ethylhexyl sodium sulfosuccinate, dioctyl sodium sulfosuccinate) (NaOS(O) ₂ CH(COOCH ₂ CH(C ₂ H ₅ )C ₄ H ₉ )CH ₂ (COOCH ₂ CH(C ₂ H ₅ )C ₄ H ₉ ), thiourea (H ₂ NC(S)NH ₂ ) These sulfur-containing compounds are water-soluble Among them, saccharin and thiourea are preferable because they are excellent in assisting the autolysis inhibition of hydrazine, are readily available, and are inexpensive.

The action of the sulfur-containing compound as an auxiliary agent for suppressing self-decomposition of hydrazine and as an agent for suppressing coupling between nickel particles can be presumed as follows. That is, the sulfur-containing compound has intramolecular sulfide group (-S-), sulfonyl group (-S(=O) ₂ -), sulfonic acid group (-S(=O) ₂ -O-), thioketone group ( -C(=S)-) is adsorbed on the nickel surface of the nickel particles by intermolecular force, but by itself, it does not increase the effect of covering and protecting the nickel crystallized powder like the amine compound molecules described above. On the other hand, when an amine compound and a sulfur-containing compound are used together, when the amine compound molecules strongly adsorb to the surface of the nickel crystallized powder and cover and protect it, a minute area that cannot be completely covered by the amine compound molecules may occur. However, since the sulfur-containing compound molecules cover the part by adsorption, the contact between the hydrazine molecules in the reaction solution and the nickel crystal powder is more effectively prevented, and furthermore, the nickel crystal powder It is said that it is possible to prevent the coalescence of comrades more strongly, and the above action is manifested.

Here, the ratio [mol%] of the sulfur-containing compound and nickel in the reaction solution ((number of moles of sulfur-containing compound/number of moles of nickel) × 100) is in the range of 0.01 mol% to 5 mol%, The range is preferably 0.03 mol % to 2 mol %, more preferably 0.05 mol % to 1 mol %. If the above ratio is less than 0.01 mol %, the amount of the sulfur-containing compound is too small, and there is a risk that the effects of the auxiliary agent for suppressing self-decomposition of hydrazine and the agent for suppressing linking between nickel particles cannot be obtained. On the other hand, even if the above ratio exceeds 5 mol %, the above effects are not improved, so the amount of the sulfur-containing compound used is simply increased, which increases the chemical cost and at the same time adds organic components to the reaction solution. increases the chemical oxygen demand (COD) of the reaction waste liquid in the crystallization process, resulting in an increase in waste liquid treatment costs.

(g) Other Contents In addition to the above, various additives such as a dispersant, a complexing agent, and an antifoaming agent may be added to the reaction liquid in the crystallization step. For example, dispersing agents and complexing agents can improve the granularity (sphericity) of nickel crystallized powder, improve the surface smoothness of nickel crystallized powder, and reduce coarse particles if they are used in an appropriate amount. it may be possible to Also, if an appropriate antifoaming agent is used in an appropriate amount, foaming in the crystallization process caused by the nitrogen gas generated in the crystallization reaction (see formulas (2) to (4) below) can be suppressed. Thus, for example, it is possible to prevent the reaction liquid from overflowing from the container. As the dispersant, known substances can be used, for example, alanine (CH ₃ CH(COOH)NH ₂ ), glycine (H ₂ NCH ₂ COOH), triethanolamine (N(C ₂ H ₄ OH) ₃ ), diethanolamine (another name: iminodiethanol) (NH(C ₂ H ₄ OH) ₂ ), and the like. As the complexing agent, known substances can be used, and hydroxycarboxylic acids, carboxylic acids (organic acids containing at least one carboxyl group), hydroxycarboxylic acid salts and hydroxycarboxylic acid derivatives, carboxylic acid salts and carboxylic acid derivatives. Acid derivatives, specifically tartaric acid, citric acid, malic acid, ascorbic acid, formic acid, acetic acid, pyruvic acid, and salts and derivatives thereof. Further, the antifoaming agent is not particularly limited as long as it has excellent foam breakability under alkaline conditions, and an oil-type or solvent-type silicone or non-silicone antifoaming agent can be used.

(1-2. Procedure of crystallization reaction (crystallization procedure))
In the crystallization step, a nickel salt solution in which at least a water-soluble nickel salt and a salt of a metal nobler than nickel are dissolved in water, a reducing agent solution in which a reducing agent (for example, hydrazine) is dissolved in water, and hydroxylation An alkali hydroxide solution is prepared by dissolving an alkali in water, and these are added and mixed to prepare a reaction solution. Then, a crystallization reaction for obtaining crystallized nickel powder by crystallizing nickel particles in the reaction liquid is performed by a reduction reaction. The amine compound and sulfur-containing compound to be added as necessary are added and mixed with any of the above solutions or a mixture thereof before preparing the reaction solution, or after preparing the reaction solution. can be added and mixed. In addition, in a room temperature environment, the reduction reaction starts when the reaction solution is prepared.

Here, as a specific crystallization procedure, a reducing agent solution and an alkali hydroxide solution are mixed in advance with a nickel salt solution containing a nickel salt to be reduced and a salt of a metal nobler than nickel. A procedure of adding and mixing a reducing agent (e.g. hydrazine) and a reducing agent/alkali hydroxide solution containing alkali hydroxide to prepare a reaction solution, and adding and mixing a reducing agent solution (e.g. hydrazine solution) to the nickel salt solution. There are two methods of preparing a reaction solution by adding and mixing an alkali hydroxide solution to the resulting nickel salt/reducing agent solution. In the former, a reducing agent (e.g., hydrazine) that is highly alkaline and has enhanced reducing power due to alkali hydroxide is added to and mixed with a nickel salt solution containing the substance to be reduced. There is a difference in that the pH is adjusted (increased) with alkali hydroxide to increase the reducing power after being mixed in advance with a nickel salt solution containing

In the former case (when the nickel salt solution and the reducing agent/alkali hydroxide solution are added and mixed), the temperature at the time the reaction solution is prepared, that is, at the time the reduction reaction starts (hereinafter referred to as the reaction start temperature Nickel salt solution (solution containing nickel salt and a salt of a metal nobler than nickel) and alkali hydroxide to increase the alkalinity and reduce power of the reducing agent/alkali hydroxide solution When the time required for addition and mixing (hereinafter sometimes referred to as the raw material mixing time) becomes longer, the alkalinity increases locally in the addition and mixing region of the nickel salt solution and the reducing agent/alkali hydroxide solution from the middle of the addition and mixing. As a result, the reducing power of hydrazine increases, and nuclei are generated due to salts of metals nobler than nickel, which is the nucleating agent. Therefore, toward the end of the raw material mixing time, the nucleation effect of the added nucleating agent weakens, and the dependence of nucleation on the raw material mixing time increases. tend to be difficult. This tendency is more pronounced when an alkaline reducing agent/alkali hydroxide solution is added to and mixed with a weakly acidic nickel salt solution. Since the above tendency can be suppressed as the mixing time of the raw materials is shortened, it is desirable to mix for a short period of time. 20 seconds to 120 seconds, more preferably 30 seconds to 80 seconds.

On the other hand, in the latter case (when an alkali hydroxide solution is added and mixed with a nickel salt/reducing agent solution obtained by adding and mixing a nickel salt solution and a reducing agent solution), a nickel salt and a salt of a metal nobler than nickel are mixed. In the nickel salt/reducing agent solution containing the reducing agent, hydrazine as the reducing agent is added and mixed in advance so as to have a uniform concentration. Therefore, the dependence of the raw material mixing time of the alkali hydroxide on the nucleus generation that occurs when adding and mixing the alkali hydroxide solution is not as large as in the former case, and the nickel crystallized powder can be made finer and a narrow particle size distribution can be obtained. It is characterized by the fact that it is easy to However, for the same reason as the former case, the mixing time of the alkali hydroxide solution is preferably short, and considering the restrictions on mass production equipment, the mixing time is preferably 10 seconds to 180 seconds, or more. It is preferably 20 to 120 seconds, more preferably 30 to 80 seconds.

Regarding the addition and mixing of the amine compound and the sulfur-containing compound of the present invention, as described above, the procedure of preliminarily blending the reaction solution before the reaction solution is prepared, and the addition after the reaction solution is prepared and the reduction reaction is started. There are two types of mixed procedures.

In the former case (when the reaction solution is mixed in advance before the reaction solution is prepared), an amine compound or a sulfur-containing compound is added to the reaction solution in advance, so a salt of a metal nobler than nickel (nucleating agent) is used. ), there is an advantage that various actions of the amine compound and the sulfur-containing compound are exhibited from the start of nucleation caused by ). On the other hand, interactions with nickel particle surfaces, such as adsorption of amine compounds and sulfur-containing compounds, may be involved in nucleation and affect the particle size and particle size distribution of the resulting nickel crystallized powder.

Conversely, in the latter case (when the reaction solution is added and mixed after the start of the reduction reaction), after passing through the very initial stage of the crystallization process in which nucleation due to the nucleating agent occurs, the amine compound or sulfur-containing compound is added to the reaction solution and mixed. Therefore, although the action of the above-described amine compound and sulfur-containing compound is somewhat delayed, since the amine compound and sulfur-containing compound do not participate in nucleation, the particle size and particle size distribution of the obtained nickel crystallization powder are different from those of the amine compound. and sulfur-containing compounds, making them easier to control. Here, the mixing time for adding and mixing the amine compound and the sulfur-containing compound to the reaction solution in this procedure may be added at once within a few seconds, or may be added in portions or added dropwise over a period of about several minutes to 30 minutes. good too. As described above, the amine compound acts as a reduction reaction accelerator (complexing agent). For this reason, the slower the addition, the slower the crystal growth and the higher the crystallinity of the nickel crystallized powder, but the gradual suppression of hydrazine self-decomposition also reduces the effect of reducing hydrazine consumption. , the above-mentioned mixing time may be appropriately determined while considering the balance between the two. The timing of addition and mixing of the amine compound and the sulfur-containing compound in the former procedure can be comprehensively judged according to the purpose and appropriately selected.

The addition and mixing of the nickel salt solution and the reducing agent/alkali hydroxide solution, the addition and mixing of the nickel salt solution and the reducing agent solution, and the addition and mixing of the alkali hydroxide solution to the nickel salt/reducing agent solution are carried out while stirring the solution. Agitation to mix is preferred. If the stirring and mixing property is good, the non-uniformity is reduced, depending on the location of nucleation, and the dependence of the nucleation on the raw material mixing time and the alkali hydroxide mixing time as described above is reduced. It becomes easy to refine the particles and obtain a narrow particle size distribution. A well-known method may be used for stirring and mixing, and it is preferable to use a stirring blade from the viewpoint of stirring and mixing property control and facility cost.

(1-3. Crystallization reaction (reduction reaction, hydrazine autolysis reaction))
In the crystallization step, crystallized nickel powder is obtained by reducing a nickel salt with hydrazine in the presence of an alkali hydroxide and a salt of a metal nobler than nickel in a reaction solution. In addition, if necessary, the action of a very small amount of a specific amine compound or sulfur-containing compound can significantly suppress the self-decomposition of hydrazine to cause a reductive reaction.

First, the reduction reaction in the crystallization step will be described. The reaction in which nickel ions (Ni ²⁺ ) crystallize to form nickel (Ni) is a two-electron reaction represented by the following formula (1). Also, the reaction of hydrazine (N ₂ H ₄ ) is a four-electron reaction represented by the following formula (2). For example, as described above, when nickel chloride (NiCl ₂ ) is used as the nickel salt and sodium hydroxide (NaOH) is used as the alkali hydroxide, the overall reduction reaction is represented by the following formula (3), nickel chloride and nickel hydroxide (Ni(OH) ₂ ) produced by the neutralization reaction of sodium hydroxide is reduced by hydrazine. Stoichiometrically (as a theoretical value), nickel (Ni) 1 0.5 moles of hydrazine (N ₂ H ₄ ) are required per mole.

Here, from the reduction reaction of hydrazine in Formula (2), it can be seen that the stronger the alkalinity of hydrazine, the greater its reducing power. The above-mentioned alkali hydroxide is used as a pH adjuster for increasing alkalinity and has a function of promoting the reduction reaction of hydrazine.

[Chemical 2]
Ni ²⁺ +2e ⁻ →Ni↓ (two-electron reaction) (1)

N ₂ H ₄ →N ₂ ↑ +4H ⁺ +4e ⁻ (4-electron reaction) (2)

2NiCl2 _{+ N2H4 +} 4NaOH
→2Ni(OH) ₂ + _{N2H4 +} 4NaCl
→2Ni↓+ _N2 ↑+4NaCl ₊ 4H2O (3)

As described above, in the conventional crystallization process, the active surface of the nickel crystallized powder acts as a catalyst to promote the self-decomposition reaction of hydrazine represented by the following formula (4), and hydrazine as a reducing agent is reduced. Others were consumed in large quantities. Therefore, depending on the crystallization conditions such as the reaction initiation temperature, for example, about 2 mols of hydrazine per 1 mol of nickel, which is about 4 times the theoretical value required for the reduction, was generally used. Furthermore, as shown in formula (4), a large amount of ammonia is by-produced in the autolysis of hydrazine, and a high concentration of ammonia is contained in the reaction solution, resulting in a nitrogen-containing waste liquid. Thus, the use of an excessive amount of hydrazine, which is an expensive chemical, and the cost of treating the nitrogen-containing waste liquid are factors that increase the cost of producing nickel powder by the wet method (wet nickel powder).

[Chemical 3]
3N ₂ H ₄ →N ₂ ↑ +4NH ₃ (4)

In the wet nickel powder production method of the present invention, a very small amount of a specific amine compound or a sulfur-containing compound is added to the reaction solution to significantly suppress the self-decomposition reaction of hydrazine and significantly reduce the amount of hydrazine, which is expensive as a chemical. Reduction is preferred. The specific amine compound can suppress the self-decomposition of hydrazine because (I) the molecules of the specific amine compound and sulfur-containing compound are adsorbed on the surface of the nickel crystallization powder in the reaction solution, and nickel (II) Molecules of specific amine compounds and sulfur-containing compounds, which physically interfere with the contact between the active surface of the crystallized powder and the hydrazine molecules, act on the surface of the nickel crystallized powder, reducing the catalytic activity of the surface. is inactivated.

In the crystallization process of the conventional wet method, nickel ions (Ni ²⁺ ) such as tartaric acid and citric acid and complex ions are added in order to shorten the reduction reaction time (crystallization reaction time) to a practical range. A complexing agent that forms to increase the concentration of ionic nickel is generally used as a reduction accelerator. However, these complexing agents such as tartaric acid and citric acid do not have the action of hydrazine self-decomposition inhibitors such as the above-mentioned specific amine compounds and sulfur-containing compounds.

On the other hand, the above-mentioned specific amine compound also functions as a complexing agent like tartaric acid, citric acid, etc., and has the advantage of acting both as a hydrazine self-decomposition inhibitor and as a reduction reaction accelerator.

(1-4. Crystallization conditions (reaction initiation temperature))
In the crystallization reaction in the crystallization step, for example, a solution (nickel salt solution) containing at least a water-soluble nickel salt and a salt of a metal nobler than nickel is added to a solution containing a reducing agent (such as hydrazine) and an alkali hydroxide (reduction It starts with a reaction solution in which an agent and an alkali hydroxide solution) are added and mixed. In this case, the reaction initiation temperature of the crystallization reaction is preferably 40°C to 95°C, more preferably 50°C to 80°C, even more preferably 60°C to 70°C. The temperatures of the nickel salt solution and the reducing agent/alkali hydroxide solution are not particularly limited as long as the temperature of the mixed solution obtained by premixing them, that is, the reaction initiation temperature is within the above temperature range. can be set.

The higher the reaction initiation temperature, the more the reduction reaction is accelerated, and the nickel crystallized powder tends to be highly crystallized. As the consumption increases, the foaming of the reaction liquid tends to increase. Therefore, if the reaction initiation temperature is too high, hydrazine consumption may increase significantly, or the crystallization reaction may not be continued due to a large amount of foaming. On the other hand, if the reaction start temperature is too low, the crystallinity of the crystallized nickel powder will be significantly reduced, or the reduction reaction will be slowed down, resulting in a significant extension of the crystallization process time and a decrease in the productivity of the nickel powder. Tend. For the above reasons, by setting the temperature within the above range, high-performance nickel powder can be produced at low cost while suppressing hydrazine consumption and maintaining high productivity.

The crystallization step is not an essential step in the production method of the present invention. A nickel crystal powder obtained by crystallizing a water-soluble nickel salt in a reduction reaction is obtained by purchasing the nickel crystal powder and making it into a slurry, or a slurry of the nickel crystal powder obtained after the crystallization process is purchased. Then, a wet crushing step, which will be described later, may be performed.

In addition, in the slurry of the crystallized nickel powder obtained in the crystallization step and the slurry of the obtained nickel crystallized powder, the number average particle diameter of the nickel crystallized powder is 0, considering that it is used as a material for MLCC. It is preferably between 0.03 μm and 0.15 μm.

(2. Wet crushing process)
Although the content of coarse particles in the nickel crystallization powder produced in the reaction solution by the above reduction reaction with hydrazine can be kept low, if it is desired to reduce coarse particles to the limit, or depending on the crystallization procedure and crystallization conditions, If the content of coarse particles increases somewhat due to the connection of particles during crystallization and becomes a problem, a wet pulverization step is provided, and the coarse particles to which the nickel particles are connected are divided at the connection portion. It is necessary to reduce coarse particles by As for the crushing process, as described above, it is difficult to apply the dry crushing method to nickel powder with an average particle size of 0.15 μm or less, so the raw material on the slurry pressurized to an ultrahigh pressure is jetted and collided at high speed to break it. Wet crushing methods such as high-pressure fluid impingement crushing, supersonic droplet collision dispersal, and other general-purpose crushing methods, in which raw material slurry is supplied to a gas stream exceeding the speed of sound and crushed by collision. should be applied. Specific examples of wet atomization devices include starburst used for high-pressure fluid collision pulverization and G-smasher used for supersonic droplet collision dispersion. In addition, as described above, the nickel crystallized powder before the wet pulverization step is subjected to a sulfur coating treatment with a sulfur compound such as a mercapto compound or a disulfide compound, if necessary, and then pure water (conductivity: ≤ 1 μS / cm) or other high-purity water to remove remaining unreacted substances, impurities, and the like. The slurry used in the wet crushing step has a nickel concentration of 13% by mass or more, preferably 17% by mass or more, and more preferably 23% by mass or more in order to suppress oxidation of nickel due to dissolved oxygen in the slurry. desirable.

(3. Solvent replacement step)
The solvent replacement step is a step of replacing the water contained in the slurry with the water-soluble organic solvent by replacing the solvent of the nickel powder slurry with the water-soluble organic solvent. The replacement method may be carried out by a known procedure such as repeating decantation and diluting the nickel powder with a solvent containing a water-soluble organic solvent, or using solid-liquid separation equipment in the post-process.

When the crystallized nickel powder is dried as it is as a nickel powder cake containing water, the crystallized nickel powder causes dry agglomeration due to the high surface tension of the water (approximately 73 mN/m; 20°C) and becomes coarse. In addition, the nickel powder cake comes into contact with air during its handling, oxidizing the nickel crystallization powder and facilitating the formation of nickel hydroxide-containing coarse particles. may lead to a decrease in the dispersibility of the Therefore, the water contained in the nickel powder cake is diluted with a water-soluble organic solvent by solvent replacement, and the water-soluble organic solvent containing water is filtered and removed in the solid-liquid separation process, which is a post-process. By forming a nickel powder cake containing a solvent, most of the moisture can be removed from the nickel powder cake.

As a result, in the subsequent drying step of drying the nickel powder cake mainly containing a water-soluble organic solvent, since the nickel powder cake contains almost no water, drying aggregation due to the high surface tension of water is suppressed, Furthermore, even when the crystallized nickel powder is exposed to air and oxidized, the nickel hydroxide does not grow in a water-soluble organic solvent so that the nickel hydroxide particles envelop a plurality of the crystallized nickel powder. Since nickel hydroxide-containing coarse particles can also be suppressed, it is possible to prevent an increase in coarse particles and a decrease in the dispersibility of the wet nickel powder.

At this time, in order to reduce the amount of water-soluble organic solvent used, the nickel powder cake is washed in advance with high-purity water such as pure water (conductivity: ≤ 1 μS / cm), and a certain percentage of water is removed by solid-liquid separation. After removal, replacement with a water-soluble organic solvent may be performed. Furthermore, water can be efficiently replaced with the water-soluble organic solvent by repeating the solid-liquid separation and replacement with the water-soluble organic solvent a plurality of times.

The solvent used in the solvent replacement step is desirably a solvent containing 90% by mass or more, preferably 95% by mass or more of a water-soluble organic solvent. When the content of the water-soluble organic solvent in the solvent is 90% by mass or more, the surface tension of the solvent can be suppressed at a low level, and nickel hydroxide-containing coarse particles and dry aggregation can be effectively suppressed. can. If the purity of the water-soluble organic solvent in the solvent is low, the effect of suppressing nickel hydroxide-containing coarse particles and dry aggregation may be insufficient. The solvent used in the solvent replacement step may be a solvent composed of water and a water-soluble organic solvent component.

The water-soluble organic solvent should preferably have a boiling point of 50°C to 120°C, preferably 50°C to 100°C, more preferably 50°C to 90°C. If the boiling point is less than 50°C, the volatility is too high and it becomes difficult to handle, and at the same time, it is not preferable because the danger of volatile ignition increases. It becomes difficult to volatilize. If the boiling point of the water-soluble organic solvent is too high, the drying process will take too long, resulting in a significant deterioration in drying efficiency and a cost disadvantage.

It is not preferable to use a non-water-soluble organic solvent in place of the water-soluble organic solvent because it becomes difficult to replace the water with the organic solvent. Depending on the water-soluble organic solvent, an azeotropic mixture with water may be formed. It is desired to be less than 20% by weight, more preferably less than 10% by weight (for example, the concentration of water in a water-ethanol azeotrope composition is 4% by weight). Specific examples of water-soluble organic solvents that can be removed by volatilization at relatively low temperatures include acetone (boiling point: 56.5°C) and methanol (boiling point: 64.7°C), which are water-soluble and can be removed by volatilization. Ethanol (boiling point: 78.3°C), 1-propanol (also known as n-propyl alcohol) (boiling point: 97.2°C), and 2-propanol (also known as isopropyl alcohol) (boiling point: 82.4°C) , 1,4-dioxane (boiling point: 102° C.), 1,2-dimethoxyethane (boiling point: 82° C.), tetrahydrofuran (boiling point: 65° C.), or one or more temporary solvents selected from them, or containing them as main components Contained organic solvents (eg, various denatured alcohols, etc.) can be used. Among these, alcohol-based organic solvents are preferable in consideration of volatility and safety (harmfulness and flammability). In consideration of cost, denatured alcohol, which is a mixed solvent containing ethanol as a main component and two or more of methanol, isopropyl alcohol, n-propyl alcohol and water, is most preferable. Also, the water-soluble organic solvent is preferably a solvent containing alcohol, ketone or ether as a main component. Also, the water-soluble organic solvent preferably contains any one of methanol, ethanol, 1-propanol, 2-propanol, acetone, 1,4-dioxane, 1,2-dimethoxyethane, tetrahydrofuran and denatured alcohol.

(4. Solid-liquid separation step)
In the solid-liquid separation step, the nickel slurry may be separated from the solvent using known procedures to form a nickel powder cake. Specific methods include, but are not limited to, Denver filters, filter presses, centrifuges, decanters, and the like.

(5. Drying process)
The drying step is a step of drying the nickel powder cake after the solid-liquid separation step to obtain wet nickel powder. Specifically, using a general-purpose drying apparatus such as an inert gas atmosphere dryer and a vacuum dryer, the drying temperature is set to 30°C to 300°C, preferably 50°C to 200°C, more preferably 80°C to 150°C. By drying the nickel powder cake for a predetermined time, moisture in the nickel powder cake is removed to obtain dried nickel powder. In the case of drying at about 200° C. to 300° C. in an inert atmosphere, a reducing atmosphere, or a vacuum atmosphere, it is possible to obtain a heat-treated wet nickel powder in addition to simple drying. The heat treatment can change the surface composition (for example, the ratio of nickel metal, nickel oxide, and nickel hydroxide) in the oxide film formed on the surface of the nickel particles. Specifically, the proportion of nickel oxide in the oxide film increases and the proportion of nickel hydroxide decreases. In addition, since the heat treatment promotes crystal growth, the higher the drying temperature, the larger the crystallite diameter of the wet nickel powder obtained.

EXAMPLES The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples. The evaluation items and methods used in the examples are as follows.

(Example 1)
<Production of wet nickel powder>
[Preparation of solutions of nickel salts and metal salts of metals nobler than nickel]
Nickel chloride hexahydrate (NiCl ₂ .6H ₂ O, molecular weight: 237.69) was dissolved so that 100 g of Ni metal was present in 1 L of pure water (“100 g-Ni/L aqueous solution”). and palladium (II) ammonium chloride (also known as ammonium tetrachloropalladium (II)) ((NH ₄ ) ₂ PdCl ₄ , molecular weight: 284.31) as a metal salt of a metal nobler than nickel. , 1.2 g of Pd metal dissolved in 1 L of pure water (referred to as “1.2 g-Pd/L aqueous solution”). Then, 1000 mL of 100 g-Ni/L aqueous solution and 4.17 mL of 1.2 g-Pd/L aqueous solution, L- 1.27 g of methionine (CH ₃ SC ₂ H ₄ CH(NH ₂ )COOH, molecular weight: 149.21) was dissolved in 881 mL of pure water, and nickel salts, sulfur-containing compounds, and nickel-noble A solution containing a nickel salt nucleating agent, which is an aqueous solution containing a nucleating agent that is a metal salt of a metal, was prepared. Here, in the nickel salt nucleating agent-containing solution, L-methionine, which is a sulfide compound, is a very small amount of 0.005 (0.5 mol %) in molar ratio to nickel, and palladium (Pd) is in nickel (Ni). 50 ppm by mass (27.58 mol ppm).

[Preparation of reducing agent solution]
Commercially available industrial grade 60% hydrazine hydrate (MGC Otsuka Chemical Co., Ltd.) obtained by diluting hydrazine hydrate (N ₂ H ₄ ·H ₂ O, molecular weight: 50.06) with pure water to 1.67 times as a reducing agent. ) was weighed out to prepare a reducing agent solution, which is an aqueous solution containing hydrazine as a main component and containing no alkali hydroxide.

[Alkali hydroxide solution]
As an alkali hydroxide, sodium hydroxide (NaOH, molecular weight: 40.0) was dissolved in pure water, and 757 mL of an alkali hydroxide solution, which was an aqueous solution containing sodium hydroxide at a concentration of 382 g/L, was prepared.

[Amine compound solution]
Ethylenediamine (abbreviation: EDA) (H ₂ NC ₂ H ₄ NH ₂ , molecular weight: 60.1), which is an alkyleneamine containing two primary amino groups (—NH ₂ ) in the molecule, as the amine compound1. 02 g was dissolved in 18 mL of pure water to prepare an amine compound solution, which is an aqueous solution containing ethylenediamine.

The materials used in the nickel salt nucleating agent-containing solution, the reducing agent solution, the alkali hydroxide solution, and the amine compound solution are reagents manufactured by Wako Pure Chemical Industries, Ltd., except for 60% hydrazine hydrate. board.

[Crystallization step]
The nickel salt nucleating agent-containing solution was placed in a Teflon (registered trademark)-coated stainless steel container with stirring blades and heated with stirring so that the liquid temperature reached 85°C. and hydrazine hydrate at a molar ratio of 1:1.46, adding and mixing for a mixing time of 10 seconds to obtain a nickel salt/reducing agent-containing solution. An alkali hydroxide solution at a liquid temperature of 27° C. was added to the nickel salt/reducing agent-containing liquid so that the molar ratio of Ni metal and sodium hydroxide was 1:3.54, and the mixing time was 120 seconds. A reaction solution (nickel chloride+palladium salt+hydrazine+sodium hydroxide) having a liquid temperature of 70° C. was prepared, and a reduction reaction (crystallization reaction) was initiated (reaction initiation temperature 70° C.). Over 20 minutes from 8 minutes to 28 minutes after the start of the reaction, the amine compound solution was added to the reaction solution so that the molar ratio of Ni metal and ethylenediamine was 1:0.01 (1.0 mol%). , and the reduction reaction was allowed to proceed while suppressing the self-decomposition of hydrazine to deposit crystallized nickel powder in the reaction solution. The reduction reaction was completed within 60 minutes from the start of the reaction, and the supernatant liquid of the reaction solution was transparent. Therefore, it was confirmed that all the nickel components in the reaction solution were reduced to metallic nickel and crystallized nickel powder was obtained. bottom.

The reaction liquid containing the crystallized nickel powder is in the form of a slurry, and an aqueous solution of mercaptoacetic acid (thioglycolic acid) (HSCH ₂ COOH, molecular weight: 92.12) is added to the slurry containing the crystallized nickel powder to obtain the crystallized nickel powder. surface treatment (sulfur coating treatment).

[Wet crushing process]
After the surface treatment, decantation and addition of pure water (electrical conductivity: 1 μS/cm) are repeated to wash the slurry containing the nickel-crystallized powder until the electric conductivity in the slurry is 15 μS/cm or less, and the nickel concentration is 25 mass. % nickel crystal powder containing slurry was subjected to wet pulverization.

[Solvent replacement step, solid-liquid separation step]
After the wet pulverization step, a filter paper is placed on a Nutsche, the slurry containing the nickel crystallization powder is added thereto and filtered, and then methanol with a purity of 99.5% or more (boiling point: 64.7 ° C.) is added to the Nutsche. The solvent in the nickel slurry was replaced from water to methanol. The concentration of methanol contained in the solvent of the nickel slurry after solvent replacement was 99.0% by mass, and the remaining 1.0% by mass was water. Here, the methanol concentration was obtained by collecting the final filtrate (last 50 mL) of the solid-liquid separation step, measuring the Karl Fischer moisture content (150 ° C.), and determining "100 - moisture content (%) = solvent in the filtrate The solvent concentration in the filtrate obtained by the calculation of "concentration (%)" was taken as the methanol concentration. It was calculated in the same manner in other examples. After the solvent replacement, solid-liquid separation was continued until the solid content concentration reached 40% by mass or more to obtain a nickel powder cake.

[Drying process]
The nickel powder cake was dried in a vacuum dryer set at a temperature of 120° C. for 6 hours to obtain a wet nickel powder.

<Evaluation and its results>
(number average particle size)
The obtained wet nickel powder is observed with a scanning electron microscope (SEM, manufactured by JEOL Ltd., JSM-7100F), and the overall shape can be confirmed by image processing the SEM image. Area of 100 to 200 particles was measured, the diameter of each particle was calculated from the measured area by conversion into a perfect circle, and the average value of the calculated diameters was calculated, which was taken as the number average particle diameter. From the viewpoint of coping with the thinning of internal electrodes of multilayer ceramic capacitors in recent years, the number average particle size of the nickel powder was set to be 0.15 μm or less. As a result, as shown in Table 1, the number average particle diameter in each example, comparative example and reference example was 82 nm.

(Content of coarse particles)
For the crushed wet nickel powder, particles having a particle size exceeding 0.4 μm, which is about five times the number average particle size, were defined as coarse particles.

First, in the evaluation of coarse particles, a dispersion step was performed to obtain a slurry in which nickel particles were dispersed in a dispersion medium. Specifically, 0.03 g of nickel powder and 100 ml of a 0.1% by mass sodium hexametaphosphate aqueous solution as a dispersion medium were stirred and mixed in a 250 ml capacity glass beaker. Next, the beaker was placed in a bath of an ultrasonic cleaner, and ultrasonic waves (26 kHz, 300 W) were applied for 3 minutes to disperse the wet nickel powder in the sodium hexametaphosphate aqueous solution. A slurry in which the nickel particles were dispersed in the dispersion medium was obtained by the dispersion process described above.

Next, the slurry was subjected to a filtration step using a suction filtration device having the same configuration as the suction filtration device 100 schematically shown in FIG. For the crushed wet nickel powder, a membrane filter made of regenerated cellulose with a diameter of 90 mm and a pore size of 0.4 μm (MICRO FILTER manufactured by Fujifilm Corporation) was used. A membrane filter 1 is placed on a filter folder 2, a suction cup 3 as a slurry charging container is attached to the filter folder 2, the filter folder 2 is further installed in a filtrate collection container 4, and a decompression pump 5 is operated. In this state, slurry 10 in which nickel particles 10b are dispersed in dispersion medium 10a is poured into suction cup 3, and suction filtration is performed. Furthermore, 50 ml of 0.1% by mass aqueous solution of sodium hexametaphosphate used as a dispersion medium was poured into the suction cup 3 so as to wash away the wall surface of the 250 ml beaker containing the slurry, and suction filtration was performed. went. Through the above filtration process, the filter 1 with coarse particles having a filter pore size larger than 0.4 μm attached as residue, and the filtrate 20 containing the dispersion medium 20a and the nickel particles 20b were obtained.

The nickel particles constituting the residue were calculated using a high frequency inductively coupled plasma atomic emission spectrometry (ICP method) as coarse particles having a size larger than the filter pore size, and the content of coarse particles contained in the nickel powder was obtained. . Specifically, after air-drying the membrane filter with the residue obtained by the above filtration step, it was boiled with aqua regia to dissolve coarse particles, and then the membrane filter was removed. and This sample solution was subjected to ICP spectroscopic analysis using an ICP spectroscopic analyzer (ICP720, manufactured by Agilent Technologies) to quantify nickel. Furthermore, from the quantitative value of nickel, the total mass of residual nickel collected as coarse particles was calculated, and the content of coarse particles contained in the wet nickel powder (0.03 g) subjected to evaluation was calculated. As a result, the content of coarse particles in the wet nickel powder used for evaluation was 180 ppm by mass with a size exceeding 0.4 μm after crushing treatment.

(Evaluation of coarse particles containing nickel hydroxide)
The presence or absence of nickel hydroxide-containing coarse particles (see FIG. 2) in the wet nickel powder was evaluated by the method shown below. That is, the membrane filter to which the coarse particles adhered as residue, obtained in the process of measuring the content of the coarse particles described above, was observed with a scanning electron microscope (SEM) in five different fields of view at a magnification of 10,000 times. When evaluated by the average number of nickel hydroxide-containing coarse particles of 4 μm or more per field of view (less than 1: ○, 1 or more and less than 3: △, 3 or more: ×), the evaluation result was “○”. rice field.

(Example 2)
In the solvent replacement step, ethanol having a purity of 99.9% or more (boiling point: 78.3 ° C.) is used as the replacement solvent to be passed, and the ethanol concentration contained in the solvent of the nickel slurry after solvent replacement is 98.6% by mass, The same operation as in Example 1 was performed, except that the remaining 1.4% by mass was water. The obtained wet nickel powder had a number average particle size of 82 nm, and a content of coarse particles having a size exceeding 0.4 μm was 220 mass ppm. In addition, the evaluation result of the nickel hydroxide-containing coarse particles was "Good".

(Example 3)
In the solvent replacement step, the replacement solvent to be passed is an ethanol aqueous solution, the ethanol concentration contained in the solvent of the nickel slurry after solvent replacement is 91.1% by mass, and the remaining 8.9% by mass is water. The same operation as in Example 1 was performed. The obtained wet nickel powder had a number average particle diameter of 82 nm, and a content of coarse particles having a size exceeding 0.4 μm was 120 mass ppm. In addition, the evaluation result of the nickel hydroxide-containing coarse particles was "Good".

(Example 4)
In the solvent replacement step, denatured alcohol (Neoethanol P-7, manufactured by Daishin Chemical Co., Ltd., boiling point: 78 to 97 ° C.) is used as the replacement solvent, and the concentration of denatured alcohol contained in the solvent of the nickel slurry after solvent replacement is The same operation as in Example 1 was performed except that 99.2% by mass of was used and the remaining 0.8% by mass was water. The obtained wet nickel powder had a number average particle size of 82 nm, and the content of coarse particles having a size exceeding 0.4 μm was 100 mass ppm. In addition, the evaluation result of the nickel hydroxide-containing coarse particles was "Good".

(Example 5)
In the solvent replacement step, 1-propanol with a purity of 99.5% or higher (boiling point: 97.2° C.) is used as the replacement solvent, and the concentration of 1-propanol contained in the solvent of the nickel slurry after solvent replacement is 98.5%. The same operation as in Example 1 was performed except that 5% by mass and the remaining 1.5% by mass was water. The obtained wet nickel powder had a number average particle size of 82 nm, and the content of coarse particles with a size exceeding 0.4 μm was 240 mass ppm. In addition, the evaluation result of the nickel hydroxide-containing coarse particles was "Good".

(Example 6)
In the solvent replacement step, 2-propanol with a purity of 99.5% or higher (boiling point: 82 ° C.) is used as the replacement solvent, and the 2-propanol concentration contained in the solvent of the nickel slurry after solvent replacement is 99.1 mass. %, and the remaining 0.9% by mass was water. The obtained wet nickel powder had a number average particle size of 82 nm, and the content of coarse particles with a size exceeding 0.4 μm was 260 mass ppm. In addition, the evaluation result of the nickel hydroxide-containing coarse particles was "Good".

(Example 7)
In the solvent replacement step, acetone with a purity of 99.0% or more (boiling point: 56.5°C) is used as the replacement solvent to be passed, and the acetone concentration contained in the solvent of the nickel slurry after solvent replacement is 87.1% by mass, The same operation as in Example 1 was performed except that the remaining 12.9% by mass was water. The obtained wet nickel powder had a number average particle size of 82 nm, and a content of coarse particles having a size exceeding 0.4 μm was 200 mass ppm. In addition, the evaluation result of the nickel hydroxide-containing coarse particles was "Good".

(Example 8)
In the solvent replacement step, 1,4-dioxane with a purity of 99.5% or more (boiling point: 102° C.) is used as the replacement solvent to be passed, and the concentration of 1,4-dioxane contained in the solvent of the nickel slurry after solvent replacement is The same operation as in Example 1 was performed except that 99.4% by mass and the remaining 0.6% by mass were water. The obtained wet nickel powder had a number average particle size of 82 nm, and a content of coarse particles having a size exceeding 0.4 μm was 280 mass ppm. In addition, the evaluation result of the nickel hydroxide-containing coarse particles was "Good".

(Example 9)
In the solvent replacement step, 1,2-dimethoxyethane with a purity of 99.0% or higher (boiling point: 82°C) is used as the replacement solvent, and the concentration of 1,2-dimethoxyethane contained in the solvent of the nickel slurry after solvent replacement is The same operation as in Example 1 was performed except that 98.8% by mass of was used and the remaining 1.2% by mass was water. The obtained wet nickel powder had a number average particle diameter of 82 nm, and a content of coarse particles having a size exceeding 0.4 μm was 160 mass ppm. In addition, the evaluation result of the nickel hydroxide-containing coarse particles was "Good".

(Example 10)
In the solvent replacement step, tetrahydrofuran having a purity of 99.5% or more (boiling point: 65 ° C.) is used as the replacement solvent to be passed, and the tetrahydrofuran concentration contained in the solvent of the nickel slurry after solvent replacement is 99.0% by mass, and the remaining The same operation as in Example 1 was performed, except that 1.0% by mass was water. The obtained wet nickel powder had a number average particle diameter of 82 nm, and a content of coarse particles having a size exceeding 0.4 μm was 150 mass ppm. In addition, the evaluation result of the nickel hydroxide-containing coarse particles was "Good".

(Reference example)
In the production of wet nickel powder, the same operations as in Example 1 were performed up to the wet crushing step, and the nickel powder slurry obtained in the wet crushing step was neither dried nor exposed to air. A slurry containing 0.03 g of nickel powder in the state of is dispersed in 100 ml of a 0.1% by mass sodium hexametaphosphate aqueous solution, and wet nickel powder (nickel crystallization The content of coarse particles in powder) was determined. The content of coarse particles was 120 ppm by mass with a size exceeding 0.4 μm, and the evaluation result of nickel hydroxide-containing coarse particles was “◯”. Further, the nickel powder slurry obtained in the wet pulverization step is dried in a vacuum dryer set at a temperature of 120° C. for 6 hours to obtain wet nickel powder. When the number average particle diameter was measured by observing with a microscope (SEM, manufactured by JEOL Ltd., JSM-7100F), the number average particle diameter was 82 nm.

(Comparative example 1)
In the solvent replacement step, the replacement solvent to be passed is an ethanol aqueous solution, the ethanol concentration contained in the solvent of the nickel slurry after solvent replacement is 85.0% by mass, and the remaining 15.0% by mass is water. The same operation as in Example 1 was performed. The obtained wet nickel powder had a number average particle size of 82 nm, and a content of coarse particles having a size exceeding 0.4 μm was 760 mass ppm. In addition, the evaluation result of the nickel hydroxide-containing coarse particles was "Δ".

(Comparative example 2)
In the solvent replacement step, the replacement solvent to be passed is an ethanol aqueous solution, the ethanol concentration contained in the solvent of the nickel slurry after solvent replacement is 47.0% by mass, and the remaining 53.0% by mass is water. The same operation as in Example 1 was performed. The obtained wet nickel powder had a number average particle diameter of 82 nm, and a content of coarse particles having a size exceeding 0.4 μm was 2200 mass ppm. In addition, the evaluation result of the nickel hydroxide-containing coarse particles was "x".

(Comparative Example 3)
In the production of wet nickel powder, the same operation as in Example 1 was performed except that the solvent replacement step was omitted, the wet pulverization step was followed by the solid-liquid separation step without solvent replacement, and then the drying step was performed. went. As a result, the number average particle diameter was 82 nm, and the content of coarse particles with a size exceeding 0.4 μm was 3440 mass ppm. In addition, the evaluation result of the nickel hydroxide-containing coarse particles was "x".

(Evaluation results)
Table 1 shows the solvent substitution rate, the content of coarse particles, the evaluation results of nickel hydroxide-containing coarse particles, and the number average particle diameter of the obtained nickel powder in Examples 1 to 12, Comparative Examples, and Reference Examples. .

In each of Examples 1 to 12, Comparative Example, and Reference Example, crystallized nickel powder was obtained by the crystallization process under the same conditions, and the number average particle diameter was the same. By performing a solvent replacement step as in Examples 1 to 12 to replace the solvent of the nickel powder slurry with a water-soluble organic solvent, the generation of nickel hydroxide-containing coarse particles and the dry aggregation of nickel particles are suppressed. It was possible to maintain the content of coarse particles at almost the same level as in the reference example in which nickel hydroxide-containing coarse particles and nickel particles did not dry agglomerate immediately after the wet pulverization step.

[summary]
The method for producing nickel powder according to the present invention is a method for producing nickel powder by a wet method using hydrazine as a reducing agent, wherein a water-soluble organic solvent is used in a solvent replacement step after a wet crushing step, which is one step of the wet method. By performing a solvent replacement treatment of the nickel powder slurry in, the formation of nickel hydroxide-containing coarse particles is effectively prevented, and the amount and bonding strength of coarse particles formed by dry aggregation of nickel particles are suppressed. Therefore, a wet nickel powder having excellent dispersibility and less coarse particles can be obtained. Therefore, high-performance wet nickel powder suitable for internal electrodes of laminated ceramic capacitors can be produced at low cost.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention belongs can conceive of various modifications or modifications within the scope of the technical idea described in the claims. It is understood that these also naturally belong to the technical scope of the present invention.

1 Membrane Filter 2 Filter Folder 3 Suction Cup 4 Filtrate Recovery Container 5 Decompression Pump 10 Slurry 10a Dispersion Medium 10b Nickel Particles 20 Filtrate 20a Dispersion Medium 20b Nickel Particles 100 Suction Filtration Device

Claims (12)

Nickel crystallization obtained by crystallizing the water-soluble nickel salt through a reduction reaction with hydrazine in a reaction solution containing a water-soluble nickel salt, a metal salt of a metal nobler than nickel, hydrazine, an alkali hydroxide, and water. a wet pulverizing step of wet pulverizing the powder slurry to obtain a nickel powder slurry with reduced coarse particles;
a solvent replacement step of replacing the solvent of the nickel powder slurry after the wet pulverization step with a water-soluble organic solvent;
A solid-liquid separation step of solid-liquid separating the nickel powder slurry after the solvent replacement step to obtain a nickel powder cake;
and a drying step of drying the nickel powder cake after the solid-liquid separation step to obtain nickel powder. A crystallization step of obtaining the crystallized nickel powder by a reduction reaction with hydrazine in a reaction liquid containing a water-soluble nickel salt, a metal salt of a metal nobler than nickel, hydrazine, an alkali hydroxide and water. 2. The method for producing nickel powder according to 1. The method for producing nickel powder according to claim 2, wherein the reaction liquid contains an amine compound or a sulfur-containing compound. The method for producing nickel powder according to any one of claims 1 to 3, wherein the crystallized nickel powder has a number average particle size of 0.03 µm to 0.15 µm. The solvent replacement step is a step of replacing the solvent of the nickel powder slurry with a water-soluble organic solvent using a solvent containing 90% by mass or more of the water-soluble organic solvent. of nickel powder. The method for producing nickel powder according to any one of claims 1 to 5, wherein the water-soluble organic solvent has a boiling point of 50°C to 120°C. The method for producing nickel powder according to any one of claims 1 to 6, wherein the water-soluble organic solvent is mainly composed of alcohol, ketone or ether. Claims 1 to 7, wherein the water-soluble organic solvent includes any one of methanol, ethanol, 1-propanol, 2-propanol, acetone, 1,4-dioxane, 1,2-dimethoxyethane, tetrahydrofuran and denatured alcohol. A method for producing a nickel powder according to any one of the above. The reaction liquid contains an amine compound,
The amine compound is at least one of an alkyleneamine or an alkyleneamine derivative, and the nitrogen atom of the amino group in the molecule is bonded via a carbon chain having 2 carbon atoms.

The method for producing nickel powder according to any one of claims 1 to 8, which has at least the structure of _{The alkyleneamine} is _{ethylenediamine ( H2NC2H4NH2} ), _{diethylenetriamine ( H2NC2H4NHC2H4NH2} ), _{triethylenetetramine ( H2N ( C2H4NH ) 2C2 H4NH2} ), _{tetraethylenepentamine ( H2N ( C2H4NH} ) _{3C2H4NH2 )} , _{pentaethylenehexamine ( H2N ( C2H4NH ) 4C2H4NH 2} ), and one or more selected from propylenediamine (CH ₃ CH(NH ₂ )CH ₂ NH ₂ ),
The alkyleneamine derivatives are tris(2-aminoethyl)amine (N(C ₂ H ₄ NH ₂ ) ₃ ), N-(2-aminoethyl)ethanolamine (H ₂ NC ₂ H ₄ NHC ₂ H ₄ OH). , N-(2-aminoethyl)propanolamine (H ₂ NC ₂ H ₄ NHC ₃ H ₆ OH), 2,3-diaminopropionic acid (H ₂ NCH ₂ CH(NH)COOH), 1,2-cyclohexanediamine _{( H2NC6H10NH2} ), ethylenediamine _- N,N' _- diacetic _{acid ( HOOCCH2NHC2H4NHCH2COOH} ), _N ,N' _- diacetylethylenediamine _{( CH3CONHC2H4NHCOCH3} ) _, N,N' _- dimethylethylenediamine _{( CH3NHC2H4NHCH3} ), N,N' _{- diethylethylenediamine ( C2H5NHC2H4NHC2H5} ), and _N ,N' _- diisopropylethylenediamine ₍ CH ₃ (CH ₃ )CHNHC ₂ H ₄ NHCH(CH ₃ )CH ₃ ), the method for producing nickel powder according to claim 9 . The sulfur-containing compound contains a sulfide group (-S-), a sulfonyl group (-S(=O) ₂ -), a sulfonic acid group (-S(=O) ₂ -O-), and a thioketone group in the molecule. The method for producing a nickel powder according to claim 3, which is one or more selected from compounds containing at least one of (-C(=S)-). The sulfur-containing compounds are L (or D, DL)-methionine (CH ₃ SC ₂ H ₄ CH(NH ₂ )COOH), L (or D, DL)-ethionine (C ₂ H ₅ SC ₂ H ₄ CH(NH ₂ )COOH), N-acetyl-L (or D, DL)-methionine (CH ₃ SC ₂ H ₄ CH(NH(COCH ₃ ))COOH), lanthionine (HOOCCH(NH ₂ )CH ₂ SCH ₂ CH(NH ₂ )COOH), thiodipropionic acid (HOOCC ₂ H ₄ SC ₂ H ₄ COOH), thiodiglycolic acid (HOOCCH ₂ SCH ₂ COOH), methionol (CH ₃ SC ₃ H ₆ OH), thiodi Glycol _{( HOC2H5SC2H5OH} ), Thiomorpholine _{( C4H9NS} ), Thiazole _{( C3H3NS} ) _, Benzothiazole _{( C7H5NS} ) _{, Saccharin ( C7H5NO3} S), sodium dodecyl sulfate ( _{C12H25OS (} O) _2ONa ), _{dodecylbenzenesulfonic acid ( C12H25C6H4S} (O) _2OH ), sodium _{dodecylbenzenesulfonate} ( _C12H25 C ₆ H ₄ S(O) ₂ ONa), di-2-ethylhexyl sodium sulfosuccinate (NaOS(O) ₂ CH(COOCH ₂ CH(C ₂ H ₅ )C ₄ H ₉ )CH ₂ (COOCH ₂ CH(C ₂ H ₅ )C ₄ H ₉ ), and thiourea (H ₂ NC(S)NH ₂ ), the method for producing a nickel powder according to claim 11 .

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