JP7212256B2 - Nickel powder manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing nickel powder used as an electrode material for laminated ceramic parts.

Nickel powder is used as a material for capacitors in electronic circuits, particularly as a material for thick-film conductors that constitute internal electrodes of multilayer ceramic components such as multilayer ceramic capacitors (MLCCs) and multilayer ceramic substrates. there is

In recent years, as the capacity of laminated ceramic capacitors has increased, the amount of internal electrode paste used to form internal electrodes of laminated ceramic capacitors has also increased significantly. Therefore, instead of using expensive noble metals, inexpensive base metals such as nickel are mainly used as metal powders for internal electrode pastes that constitute thick-film conductors.

In the process of manufacturing a laminated ceramic capacitor, an internal electrode paste prepared by kneading nickel powder, a binder resin such as ethyl cellulose, and an organic solvent such as terpineol is screen-printed onto a dielectric green sheet. Then, the dielectric green sheets on which the internal electrode paste is printed and dried are laminated so that the internal electrode paste printed layers and the dielectric green sheets are alternately overlapped, and then pressed to obtain a laminated body.

This laminate is cut into a predetermined size, then the binder resin is removed by heat treatment (binder removal treatment), and the laminate after the binder removal treatment is fired at a high temperature of about 1300 ° C. , a ceramic compact is obtained.

Then, external electrodes are attached to the obtained ceramic molded body to obtain a laminated ceramic capacitor. Since base metals such as nickel are used as the metal powder in the internal electrode paste that serves as the internal electrodes, the binder removal treatment of the laminate is carried out in an inert atmosphere or the like in which the oxygen concentration is low so that these base metals are not oxidized. It takes place in a very low atmosphere.

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.

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 by reducing nickel chloride vapor with hydrogen described in Patent Document 1, and a method of vaporizing nickel metal in plasma described in Patent Document 2, There are methods of making nickel powder. As a wet method, for example, there is a method of producing nickel powder by adding a reducing agent to a nickel salt solution, which is described in Patent Document 3.

The gas phase method is a high-temperature process of about 1000° C. or higher, so it is an effective means for obtaining nickel powder with excellent crystallinity and high properties. . 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. Therefore, in order to obtain such a nickel powder by the gas phase method, it is essential to classify the nickel powder by introducing an expensive classifier.

In the classification process, it is possible to remove coarse particles larger than the classification point with a classification point of an arbitrary value of about 0.6 μm to 2 μm in particle size, but some particles smaller than the classification point is also removed at the same time, there is also the problem that the actual yield of the product is greatly reduced. 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 having 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. It cannot cope with further thinning of the internal electrodes.

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, nickel powder is produced by crystallization in which a reduction reaction is performed in a reaction solution obtained by adding a solution containing hydrazine as a reducing agent to a solution containing a copper salt as a nickel salt, as described in Patent Document 3. In the method, a nickel salt (more precisely, a nickel ion (Ni ²⁺ ) or a nickel complex ion) is reduced with hydrazine in the presence of a salt of a metal more noble than nickel (nucleating agent). is controlled (that is, the particle size is controlled), and the nucleation and particle growth become uniform, resulting in fine nickel powder with a narrower particle size distribution (hereinafter, the nickel powder generated in the reaction solution is referred to as nickel crystallized powder). ) is known to be obtained. For reference, FIG. 1 shows a representative manufacturing process of nickel powder by a wet method.

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 of internal electrode layers (film thickness of about 0.5 μm to 1.0 μm) accompanying the recent increase in capacity of multilayer ceramic capacitors, the average particle size is 0.3 μm or less, preferably the average Fine nickel powder having a particle size of 0.2 μm or less is used, and coarse particles having a size (for example, 0.8 μm to 1.2 μm) similar to the film thickness of the internal electrode layer contained in the nickel powder are It is required to reduce it to the limit.

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 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.

JP-A-4-365806 Japanese Patent Publication No. 2002-530521 JP-A-2002-53904 Patent No. 6172413

By the way, in the nickel powder (wet nickel powder) obtained by the above-described conventional wet method, although the content of coarse particles (connected particles) in which nickel particles are connected to each other can be extremely reduced, nickel is not a little in the crystallization process. Linked bodies (connected particles) of nickel particles are generated in the crystallized powder. In addition, when passing through the washing/filtration process and the drying process, coarse particles (aggregated particles) are always generated between the nickel particles due to dry aggregation, so a crushing process is provided as a post-process after the drying process to It is generally practiced to divide (crushing) the connected particles and the coarse particles (aggregated particles) due to dry aggregation to reduce the coarse particles.

However, from the viewpoint of obtaining nickel powder at a lower cost, a wet method that does not require the crushing process as the post-process described above and reduces the generation of coarse particles (aggregated particles) due to dry aggregation of nickel crystallized powder generated in the drying process There is a need to produce nickel powder.

Therefore, the present invention uses a wet method in the particle size range (e.g., average particle size of 0.4 μm or less) that is the mainstream of nickel powder used in the internal electrode paste of laminated ceramic capacitors. Also, by effectively suppressing the formation of coarse particles (aggregated particles) due to dry aggregation, a high-performance nickel powder with a very small content of coarse particles can be obtained inexpensively and easily. The object is to provide a manufacturing method.

The present inventors have found that in a method for producing nickel powder by a wet method used for laminated ceramic capacitors, etc., nickel powder (nickel crystallized powder) is washed and washed from a strongly alkaline nickel powder slurry, which is the final solution of the crystallization reaction. In the course of the washing/filtration process in which the nickel powder cake is collected by filtration, a salt volatile at 40°C to 150°C is added to the nickel powder slurry or the nickel powder cake, and the nickel powder cake adhesion liquid is heated to 40°C. If a salt that is volatile at ~150°C or less is left behind, drying aggregation that occurs when nickel powder cake is dried by conventional wet drying means can be effectively suppressed even if conventional drying means is used. I found what I can do. This is because when a salt volatile at 40° C. to 150° C. is added, the nickel powder cake is dried to obtain nickel crystallized powder (nickel powder). Salts that are volatile at ~150°C are deposited and removed by volatilization at the same time, so trace amounts of non-volatile salts (NaCl, Na ₂ SO ₄ etc. ) is condensed and solidified, making it difficult to form strong bonds. The present invention has been completed based on such findings.

In order to solve the above-mentioned problems, the method for producing nickel powder of the present invention is a method for producing nickel powder by a wet method, in which nickel crystallized powder is filtered off while nickel powder slurry is washed to obtain a nickel powder cake. and a drying step of drying the nickel powder cake to obtain nickel powder. It is characterized by being added to the cake.

The method for producing the nickel powder includes at least a water-soluble nickel salt, a salt of a metal nobler than nickel, a reducing agent, an alkali hydroxide, water, and optionally an amine compound and/or a sulfur-containing compound. It may have a crystallization step of performing a reduction reaction in the mixed strongly alkaline reaction liquid to obtain the strongly alkaline nickel powder slurry, which is the final reaction liquid containing the crystallized nickel powder.

In the washing/filtration step, washing of the crystallized nickel powder in the nickel powder slurry may be performed until the electric conductivity of the washing liquid reaches 30 μS/cm to 5000 μS/cm.

The salt having volatility at 40° C. to 150° C. may be a readily soluble salt having a solubility in water of 10 g to 200 g/100 g water (25° C.).

The salt volatile at 40° C. to 150° C. may be a salt volatile at 100° C. or lower.

The salt volatile at 40° C. to 150° C. is one selected from ammonium carbonate ((NH ₄ ) ₃ CO ₃ ), ammonium hydrogen carbonate (NH ₄ HCO ₃ ) and ammonium carbamate (NH ₂ COONH ₄ ). or more.

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 may have a structure of the following formula A bonded via a carbon chain having 2 carbon atoms. good.

When the amine compound is the alkyleneamine, the alkyleneamine is ethylenediamine (H ₂ NC ₂ H ₄ NH ₂ ), diethylenetriamine (H ₂ NC ₂ H ₄ NHC ₂ H ₄ NH ₂ ), triethylenetetramine ( _{H2N ( C2H4NH} ) _2C2H4NH2 ), _{tetraethylenepentamine ( H2N ( C2H4NH ) 3C2H4NH2} ) _{, pentaethylenehexamine ( H2N} (C ₂ H ₄ NH) ₄ C ₂ H ₄ NH ₂ ) and propylenediamine (CH ₃ CH(NH ₂ )CH ₂ NH ₂ ), and the amine compound is the alkyleneamine When a derivative, the alkyleneamine derivative is 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) , ethylenediamine-N,N'-diacetic _{acid ( HOOCCH2NHC2H4NHCH2COOH} ), N,N' _- diacetylethylenediamine _{( CH3CONHC2H4NHCOCH3} ) _, N,N' _- dimethylethylenediamine ( _CH3 NHC ₂ H ₄ NHCH ₃ ), N,N′-diethylethylenediamine (C ₂ H ₅ NHC ₂ H ₄ NHC ₂ H ₅ ), N,N′-diisopropylethylenediamine (CH ₃ (CH ₃ )CHNHC ₂ H ₄ NHCH ( CH ₃ )CH ₃ ) and 1,2-cyclohexanediamine (H ₂ NC ₆ H ₁₀ NH ₂ ).

The sulfur-containing compound has, in its molecule, a sulfide group (-S-), a sulfonyl group (-S(=O) ₂ -), a sulfonic acid group (-S(=O) ₂ -O-), a thioketone group ( -C(=S)-) may be one or more selected from compounds containing at least one or more.

The sulfur-containing compound is L (or D, or DL)-methionine (CH ₃ SC ₂ H ₄ CH(NH ₂ )COOH), L (or D, or DL)-ethionine (C ₂ H ₅ SC ₂ H ₄ CH(NH ₂ )COOH), N-acetyl-L (or D, or 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 ).

According to the method for producing nickel powder according to the present invention, in the washing/filtration step subsequent to the crystallization step, which is one step of the method for producing nickel powder by the wet method, By adding a salt volatile at 40°C to 150°C to an alkaline nickel powder slurry or nickel powder cake and leaving a small amount of the salt volatile at 40°C to 150°C in the adhering liquid of the nickel powder cake. Since it is possible to effectively suppress dry aggregation of the nickel powder that occurs when the nickel powder cake is dried by a drying means in the conventional wet method, the crushing step of the dried nickel powder is not necessary. Therefore, it is possible to produce a high-performance nickel powder containing very few coarse particles, which is suitable for use as internal electrodes of laminated ceramic capacitors, at a lower cost.

It is a schematic diagram which shows the typical manufacturing process in the manufacturing method of the nickel powder by a wet method. 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 of this invention.

Hereinafter, the nickel powder production method of the present invention and the nickel powder obtained by the production method will be described in the following order with reference to FIGS. 1 and 2 as a preferred example. However, the present invention is not limited to these, and can be arbitrarily changed without departing from the gist of the present invention.

1. Nickel powder2. Method for producing nickel powder using wet method 2-1. Crystallization step 2-1-1. Agent used in crystallization step 2-1-2. Crystallization procedure 2-1-3. Reduction reaction 2-1-4. Reaction initiation temperature 2-2. Washing/filtration process 2-2-1. Washing/filtration methods and procedures 2-2-2. Salts volatile at 40°C to 150°C 2-3. drying process

<1. Nickel powder>
The nickel powder obtained by the nickel powder production method of the present invention has a very low content of coarse particles (connected particles) in which nickel particles are connected to each other, and a dry film obtained by drying the nickel paste achieves high flatness. can. Therefore, it is possible to effectively prevent a short circuit between electrodes in a laminate composed of an internal electrode layer and a dielectric layer, and it is suitable for use as an internal electrode of a laminated ceramic capacitor.

The nickel powder has a substantially spherical particle shape, and its average particle size is 0.03 μm to 0.4 μm from the viewpoint of responding to the thinning of internal electrodes of multilayer ceramic capacitors in recent years. The substantially spherical shape includes not only a true sphere but also an ellipsoid whose predetermined cross section has an elliptical shape in which the ratio of the minor axis to the major axis (minor axis/major axis) is 0.8 to 1.0. In addition, the average particle size of the present invention is the number average particle size obtained from the scanning electron microscope image (SEM image) of the nickel powder.

Like the nickel powder described above, nickel powder that can be applied to internal electrodes of laminated ceramic capacitors usually contains a small amount of sulfur in some cases in order to suppress its catalytic activity. This is because the surface of the nickel particles has a high catalytic activity, and if it is used as it is without containing sulfur or the like, the heat of the binder resin such as the ethyl cellulose resin contained in the internal electrode paste may occur during the binder removal process during the manufacturing of the multilayer ceramic capacitor. This is because decomposition is accelerated, and the binder resin is decomposed from a low temperature, and the strength of the laminate is greatly reduced.

In order to contain sulfur in the nickel powder as described above, a surface treatment is performed to attach sulfur to the surface of the nickel particles, and the entire surface of the nickel particles is thinly and uniformly modified (coated) with sulfur. , from the viewpoint of exhibiting the effect of suppressing the decomposition of the binder resin and reducing the influence of sulfur as an impurity on the characteristics of the multilayer ceramic capacitor. However, as long as the effect of suppressing the decomposition of the binder resin can be exhibited, only a part of the surface of the nickel particles may be modified (coated) without modifying (coating) the entire surface. In the present invention, the term "surface treatment" is used as a concept encompassing the modification (coating) of the entire nickel particles and the modification (coating) of only a part of the nickel particles.

If the sulfur content in the nickel powder exceeds 0.5% by mass, internal electrode defects may occur due to sulfur, so it is preferably 0.3% by mass or less, more preferably 0.2% by mass or less. . The lower limit of the sulfur content is not particularly limited, and the content may be less than the detection limit by measurement using an analytical instrument used for content analysis, such as a sulfur analyzer using a combustion method or an ICP analyzer. .

<2. Method for producing nickel powder using wet method>
First, a method for producing nickel powder using a wet method according to an embodiment of the present invention will be described. A method for producing nickel powder using a wet method according to one embodiment of the present invention includes at least a water-soluble nickel salt, a salt of a metal nobler than nickel, a reducing agent (e.g., hydrazine), and an alkali hydroxide as a pH adjuster. Crystallization step of crystallizing nickel by a reduction reaction with hydrazine or the like in a strongly alkaline reaction liquid obtained by mixing and water to obtain a strongly alkaline nickel powder slurry, which is the final reaction liquid containing nickel crystallized powder. , a washing/filtration step of separating the crystallized nickel powder while washing the nickel powder slurry to obtain a nickel powder cake, and a drying step of drying the nickel powder cake to obtain a crystallized nickel powder (nickel powder). In addition, if necessary, an amine compound or a sulfur-containing compound may be blended into the reaction solution to act as a hydrazine self-decomposition inhibitor and reduction reaction accelerator (complexing agent).

If desired, a very small amount of a sulfur compound may be added to the strong alkaline nickel powder slurry, which is the final reaction solution containing the nickel crystallized powder, or its diluted solution or washing solution, so that the content in the nickel powder is 0.5%. A surface treatment (sulfur coating treatment) may be applied to modify the surface of the nickel particles with a sulfur component so that the content is not more than mass %. In addition, nickel powder can also be obtained by subjecting the obtained nickel powder to heat treatment at about 200° C. to 300° C. in an inert atmosphere or a reducing atmosphere, for example. This sulfur coating treatment and heat treatment can control the debindering behavior of the internal electrodes and the sintering behavior of the nickel powder during the manufacturing of the above-described laminated ceramic capacitor, and are very effective if used within an appropriate range.

(2-1. 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.

(2-1-1. Agent used in crystallization step)
In the crystallization step of the present invention, a reaction solution containing water and nickel salts, salts of metals nobler than nickel, reducing agents, alkali hydroxides, various chemicals such as amine compounds and sulfur-containing compounds, if necessary, is used. ing. From the viewpoint of reducing the amount of impurities in the resulting nickel powder, water as the solvent is ultrapure water (conductivity: ≤0.06 µS/cm) or pure water (conductivity: ≤1 µS/cm). High-purity water is preferable, and pure water, which is inexpensive and readily available, is preferably used. Each of the above-mentioned various agents will be described in detail below.

(a) Nickel salt The nickel salt used in the present invention 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) Salts of metals nobler than 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, it acts as a nucleating agent in which the metal nobler than nickel is first reduced to form initial nuclei when nickel is reduced and deposited. Therefore, in the nickel crystallized powder (nickel powder) obtained by particle growth of the initial nuclei, it becomes possible to easily perform particle size control and refinement of the nickel powder.

The 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. Examples include 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 salt of a metal nobler than nickel, it is preferable to use the above-mentioned palladium salt, because the particle size distribution of the resulting nickel powder can be more finely controlled, although the particle size distribution becomes somewhat wider. When a palladium salt is used, the ratio of palladium salt to nickel [moles ppm] (number of moles of palladium salt/number of moles of nickel×10 ⁶ ) can be appropriately selected depending on the target number average particle size of the nickel powder. can be done. For example, if the average particle size of nickel powder is set to 0.03 μm to 0.4 μm, the ratio of palladium salt and nickel is within the range of 0.2 mol ppm to 100 mol ppm, preferably 0.5 mol ppm It is preferable to be in the range of up to 25 molar ppm. If the above ratio is less than 0.2 mol ppm, the average particle size of the resulting 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 the cost of the 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 The reducing power of hydrazine increases as the alkalinity of the reaction solution increases, as shown in formula (2) described later. It can be used as a pH adjuster. 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 (NaOH) and potassium hydroxide (KOH).

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 Comparing the pH of the reaction solution at 25° C. and 70° C., for example, the high temperature of 70° C. is slightly smaller.

(e) Amine compound As described above, the amine compound acts as a hydrazine self-decomposition inhibitor, a reduction reaction accelerator, and a linking inhibitor between nickel particles. should be added. 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 (abbreviation: EDA) (H ₂ NC ₂ H ₄ NH ₂ ), diethylenetriamine (abbreviation: DETA) (H ₂ NC ₂ H ₄ NHC ₂ H ₄ NH ₂ ), triethylene _Tetramine (abbreviation: TETA) ₍ H2N _{( C2H4NH} ) _2C2H4NH2 ) _, Tetraethylenepentamine ₍ abbreviation: TEPA) _{( H2N ( C2H4NH} ) _{3C2H 4} NH ₂ ), pentaethylenehexamine (abbreviation: PEHA) (H ₂ N(C ₂ H ₄ NH) ₄ C ₂ H ₄ NH ₂ ), propylene diamine (also known as 1,2-diaminopropane, 1,2- Propanediamine) (abbreviation: PDA) (CH ₃ CH(NH ₂ )CH ₂ NH ₂ ) can be used. Examples of alkyleneamine derivatives include tris(2-aminoethyl)amine (abbreviation: TETA) (N(C ₂ H ₄ NH ₂ ) ₃ ), N-(2-aminoethyl)ethanolamine (also known as 2-( 2-aminoethylamino)ethanol (abbreviation: AEEA) (H ₂ NC ₂ H ₄ NHC ₂ H ₄ OH), N-(2-aminoethyl)propanolamine (also known as 2-(2-aminoethylamino)propanol ) (abbreviation: AEPA) (H ₂ NC ₂ H ₄ NHC ₃ H ₆ OH), L (or D, or DL)-2,3-diaminopropionic acid (also known as 3-amino-L (or D, or DL)-alanine) (abbreviation: DAPA) (H ₂ NCH ₂ CH(NH)COOH), ethylenediamine-N,N'-diacetic acid (also known as ethylene-N,N'-diglycine) (abbreviation: EDDA) ( HOOCCH ₂ NHC ₂ H ₄ NHCH ₂ COOH), N,N′-diacetylethylenediamine (also known as N,N′-ethylenebisacetamide) (abbreviation: DAEDA) (CH ₃ CONHC ₂ H ₄ NHCOCH ₃ ), N,N '-dimethylethylenediamine (alias: 1,2-bis(methylamino)ethane) (abbreviation: DMEDA) (CH ₃ NHC ₂ H ₄ NHCH ₃ ), N,N'-diethylethylenediamine (alias: 1,2- bis(ethylamino)ethane) (abbreviation: DEEDA) (C ₂ H ₅ NHC ₂ H ₄ NHC ₂ H ₅ ), N,N′-diisopropylethylenediamine (abbreviation: DIPEDA) (CH ₃ (CH ₃ )CHNHC ₂ H ₄ NHCH(CH ₃ )CH ₃ ), 1,2-cyclohexanediamine (also known as 1,2-diaminocyclohexane) (abbreviation: CHDA) (H ₂ NC ₆ H ₁₀ NH ₂ ). These alkyleneamines and alkyleneamine derivatives are water-soluble, and among them, ethylenediamine and diethylenetriamine are preferable because they are 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. , it is presumed that the action is expressed by the interaction with the surface of the nickel crystallized powder in the reaction solution.

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 enhanced. 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, the contact of hydrazine molecules with the nickel crystallized powder cannot be effectively prevented, and more hydrazine molecules self-decompose due to the catalytic activity of nickel, which is thought to reduce the effect of suppressing the self-decomposition of hydrazine. .

In fact, ethyne diamine (H ₂ NC ₂ H ₄ NH ₂ ) and propylene diamine (also known as 1,2-diaminopropane, 1,2-diaminopropane, 1, 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 may not be possible to obtain the effects of hydrazine as a self-decomposition inhibitor, a reduction reaction accelerator, or as an inhibitor of linkage between nickel particles. be. 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 particle growth of the nickel crystallized powder. There is a possibility that the characteristics of the nickel powder may be degraded, for example, the granularity and sphericalness of the powder may be lost, resulting in an distorted shape, and a large number of coarse particles in which nickel particles are connected to each other may be formed.

(f) Sulfur-containing compound (auxiliary agent for inhibiting autolysis of hydrazine)
Sulfur-containing compounds are compounds that are applied as brighteners for nickel plating and stabilizers for plating baths, and unlike the above amine compounds, when used alone, hydrazine's self-decomposition inhibitory action is not so great. 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 effect of a hydrazine self-decomposition inhibitor auxiliary agent that can greatly strengthen the self-decomposition inhibitory action of hydrazine. ing. 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)-OH), a thioketone group (- 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. be. More specifically, L (or D, or DL)-methionine (CH ₃ SC ₂ H ₄ CH(NH ₂ )COOH), L (or D, or DL)-ethionine (C ₂ H ₅ SC ₂ H ₄ CH(NH ₂ )COOH), N-acetyl-L (or D, or 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.

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 preferably Among them, saccharin and thiourea are preferred because they are water-soluble, and are excellent in assisting the autolysis inhibition of hydrazine, and are easily available and 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 a sulfide group (-S-), a sulfonyl group (-S(=O) ₂ -), a sulfonic acid group (-S(=O)-OH), a 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 crystallized nickel powder, unlike 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 to cover and protect it, a minute region that cannot be completely covered by the amine compound molecules is generated. Although it is highly possible, the adsorption of the sulfur-containing compound molecules assists the coverage of that portion, which effectively prevents the contact between the hydrazine molecules in the reaction solution and the nickel crystallization powder, and furthermore, the nickel crystallization It is said that the coalescence of powders can be more strongly prevented, and the above effect is exhibited.

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 cost.

(g) Other Contents In addition to the above-mentioned nickel salts, salts of metals nobler than nickel, reducing agents (e.g., hydrazine), alkali hydroxides, and amine compounds, dispersing agents, A small amount of various additives such as a complexing agent and an antifoaming agent may be added. For example, if an appropriate dispersant or complexing agent is used in an appropriate amount, it is possible to improve the graininess (sphericity) and surface smoothness of the crystallized nickel powder, as well as reduce coarse particles. Sometimes. 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 aqueous solution 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, salts and derivatives thereof, and the like. 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.

(2-1-2. Crystallization procedure)
In the crystallization step, a nickel salt solution obtained by dissolving at least a water-soluble nickel salt and a salt of a metal nobler than nickel in water, a reducing agent solution obtained by dissolving a reducing agent (such as hydrazine) in water, and an alkali hydroxide is dissolved in water to prepare an alkali hydroxide solution, 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 (e.g., hydrazine) and an alkali hydroxide solution are mixed in advance with a nickel salt solution containing a nickel salt, which is the substance to be reduced, and a salt of a metal nobler than nickel. a procedure for preparing a reaction solution by adding and mixing the reducing agent/alkali hydroxide solution obtained by the above, and a nickel salt/reducing agent solution obtained by adding and mixing a reducing agent solution (e.g., hydrazine solution) to the nickel salt solution. (2) includes two procedures of adding and mixing an alkali hydroxide solution to prepare a reaction 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 a substance to be reducible. There is a difference in that the reducing power is increased by pre-mixing with a nickel salt solution containing a reduced product and then adjusting (increasing) the pH with alkali hydroxide.

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 a reducing agent/alkali hydroxide solution that has increased alkalinity and reduced power with alkali hydroxide If the time required for the addition and mixing of the nickel salt solution and the reducing agent/alkali hydroxide solution becomes longer, the local alkalinity of the nickel salt solution and the reducing agent/alkali hydroxide solution in the addition/mixing region starts from the middle of the addition/mixing. increases, 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 nucleating action of the added nucleating agent becomes weaker, and the dependence of the nucleus generation on the raw material mixing time increases, making the nickel crystallized powder finer and obtaining a narrow particle size distribution. 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 in a short time. However, considering restrictions on mass production equipment, etc., the mixing time of the raw materials is preferably more than 10 seconds and within 180 seconds. , more preferably over 10 seconds and within 120 seconds, more preferably over 10 seconds and within 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, it is desirable that the mixing time of the alkali hydroxide solution is short. Seconds or less, more preferably over 10 seconds and within 120 seconds, more preferably over 10 seconds and within 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 an amine compound or a sulfur-containing compound is added to the reaction solution before the reaction solution is prepared), the amine compound or sulfur-containing compound is added to the reaction solution in advance, so nickel is more noble than nickel. 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 the salt of such a metal (nucleating agent). On the other hand, interaction with the surface of nickel particles, 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 an amine compound or a sulfur-containing compound is added and mixed after the reaction solution has been prepared and the reduction reaction has started), the , an amine compound or a sulfur-containing compound is added to and mixed with the reaction solution. 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 effect of suppressing the self-decomposition of hydrazine also acts gradually, and the effect of reducing hydrazine consumption decreases. Therefore, the 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 properties are good, the frequency of non-uniform nucleus generation decreases, depending on the location of nucleation, and the dependence of nucleation on the mixing time of raw materials and the alkali hydroxide mixing time as described above decreases. Therefore, it becomes easy to refine the crystallized nickel powder 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.

(2-1-3. Reduction 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 and cause a reductive reaction.

First, the reduction reaction in the crystallization step will be explained. 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. Alkali hydroxide is used as a pH adjuster to increase the alkalinity of the reaction solution, and has the function of promoting the reduction reaction of hydrazine.

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

Therefore, in the method for producing nickel powder 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 used as an expensive chemical. should be reduced to 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 liquid, (II) Molecules of specific amine compounds and sulfur-containing compounds, which physically interfere with the contact between the active surface of the nickel crystallization powder and hydrazine molecules, act on the surface of the nickel crystallization powder to catalyze the surface. It is conceivable that the activity is inactivated.

Conventionally, in the wet crystallization process, in order to shorten the reduction reaction time (crystallization reaction time) to a practical range, nickel ions (Ni ²⁺ ) such as tartaric acid and citric acid and complex ions are added. 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 act as inhibitors for hydrazine self-decomposition, such as the above-mentioned specific amine compounds and sulfur-containing compounds, or they cause coarse particles to occur when nickel particles are linked to each other during crystallization. It does not act as a coupling inhibitor that makes it difficult to form

On the other hand, the above-mentioned specific amine compound also has the advantage of acting as a complexing agent in the same way as tartaric acid, citric acid, etc., and acting as a hydrazine self-decomposition inhibitor, linkage inhibitor, and reduction reaction accelerator. there is

(2-1-4. 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 to

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, it is possible to inexpensively produce a high-performance nickel powder with a very low content of coarse particles while maintaining high productivity while suppressing the consumption of hydrazine. can be done.

(2-2. Washing/filtration step)
In the nickel powder production method using the wet method as described above, hydrazine is often used as a reducing agent. Therefore, as is clear from Patent Document 4 and the like, the reaction solution is generally strongly alkaline. be. As shown in FIG. 1, in the crystallization process, nickel powder (nickel crystallized powder) is produced in the strongly alkaline reaction liquid by the reduction reaction of hydrazine to obtain a nickel powder slurry. A washing/filtration step of obtaining a nickel powder cake by filtering and collecting the nickel powder cake while washing is successively carried out.

In the nickel powder cake obtained through a washing and filtering process in which a slurry of strongly alkaline nickel powder (for example, about pH 14) is filtered and collected while washing with pure water, alkali hydroxides exhibiting strong alkalinity are washed away. However, alkali salts (NaCl, etc.) generated by neutralization of alkali hydroxides and nickel salts remain in a small to very small amount depending on the degree of washing, and remain on the nickel powder cake as a weakly alkaline adhesion liquid. Therefore, if heat drying is performed in this state in the drying process, the nickel crystallized powder (for example, particle size of 0.4 μm or less) is strongly solidified by the dry aggregation action of the remaining alkali hydroxide or alkali salt. Particles (in many cases, agglomerated particles having a particle size of 1.0 μm or more) are likely to occur.

On the other hand, the residue of alkali hydroxide and alkali salt in the nickel powder cake is washed to the limit (for example, when pure water with a conductivity of 1 μS / cm is used, the conductivity of the washing liquid becomes 10 μS / cm or less. However, in this case, the efficiency of the washing/filtration process may be significantly reduced, leading to an increase in cost. In addition, there is also the problem that the nickel crystallized powder is oxidized during heat drying in the drying process, and drying agglomeration caused by strengthening of bonding between nickel hydroxides formed on the particle surface is unavoidable.

Therefore, in the present invention, a salt having volatility at 40° C. to 150° C. is added to the nickel powder slurry or the nickel powder cake, which is a strongly alkaline reaction liquid, in the washing process of the washing/filtration process, so that the nickel powder cake adheres to the liquid. A small amount of salt volatile at 40°C to 150°C remains in the solution. By leaving a small amount of this salt remaining in this way, the salt volatile at 40° C. to 150° C. is once deposited between the nickel particles in the drying process, and at the same time, it is volatilized and removed. Even if the degree of washing is low, the formation of coarse particles (aggregated particles) due to dry aggregation as described above can be greatly suppressed.

(2-2-1. Washing/filtration method and procedure)
In the present invention, as shown in FIG. 2, a nickel powder cake is obtained by separating and recovering the crystallized nickel powder from the nickel powder slurry while washing the strongly alkaline nickel powder slurry obtained in the crystallization step. be able to. The timing of addition of the salt volatile at 40° C. to 150° C. to the nickel powder slurry or nickel powder cake is not particularly limited, and the reaction final solution (nickel powder slurry) containing the Ni crystallized powder obtained by the crystallization step (nickel powder slurry) or , the nickel powder slurry in this step, and the nickel powder cake after filtration. For example, if a salt volatile at 40°C to 150°C is added after the strong alkaline component in the nickel powder slurry is washed away to some extent, the water of the salt volatile at 40°C to 150°C or less in the nickel powder cake is added. It is preferable because the proportion of alkali oxide or alkali salt is increased, and the effect of suppressing dry aggregation is enhanced.

Specific methods for separating the nickel crystallized powder from the nickel powder slurry include a method using a Denver filter, a filter press, a centrifugal separator, a decanter, or the like. For example, it is possible to obtain a nickel powder cake by solid-liquid separation of the crystallized nickel powder from the reaction solution and thorough washing with high-purity water such as pure water (conductivity: ≦1 μS/cm). . Then, for example, after sufficiently repeating washing with pure water, a salt volatile at 40° C. to 150° C. is added, and if the conductivity of the final filtrate is 100 μS / cm or more, the salt is present in the nickel powder cake, and it can be judged that it has the effect of suppressing aggregation of the nickel powder due to drying. The upper limit of the conductivity of the final filtrate has no technical upper limit because the greater the amount of such salt, the higher the aggregation suppression effect, but for example, the conductivity is 1000 μS / cm as a guideline. be able to.

(2-2-2. Salt having volatility at 40 ° C to 150 ° C)
The salt volatile at 40° C. to 150° C. used for neutralization of the strongly alkaline nickel powder slurry or its diluted solution of the present invention is preferably a salt volatile at 100° C. or less from the viewpoint of ease of handling. There is no particular limitation as long as it is readily soluble in water. Salts that are volatile at 40°C to 150°C include those that change from liquid to gas at 40°C to 150°C, as well as those that decompose at 40°C to 150°C, and the decomposed products produced by such decomposition volatize ( It also includes those that change from liquid to gas).

For example, in the case of a salt that is volatile at a temperature of less than 40 ° C., it may volatilize before being added to the nickel powder slurry or nickel powder cake, and the effect of suppressing the aggregation of nickel particles may not be sufficiently obtained. There is In addition, in the case of a salt that is volatile at a temperature higher than 150 ° C., it will remain without volatilizing even if it is added to the nickel powder slurry or nickel powder cake, thereby suppressing the aggregation of nickel particles. may not be obtained, and problems may occur in subsequent steps such as sintering and printing.

Moreover, the salt having volatility at 40° C. to 150° C. is preferably a readily soluble salt having a solubility in water of 10 g to 200 g/100 g water (25° C.). Since such a salt dissolves in water at the molecular level from the time it is added, the salt uniformly precipitates and intervenes between the fine nickel particles during the drying process of the nickel powder, resulting in an effect of suppressing dry aggregation. can be effectively used.

As such a salt, specifically, one or more selected from ammonium carbonate ((NH ₄ ) ₂ CO ₃ ), ammonium hydrogen carbonate (NH ₄ HCO ₃ ), and ammonium carbamate (NH ₂ COONH ₄ ). can be used. As shown in the following formulas ( ₅ ) to (7), these salts exhibit respective decomposition reactions. , carbon dioxide (CO ₂ ), water vapor (H ₂ O), etc., and these decomposition products volatilize. These salts having volatility at 40° C. to 150° C. may be added to the nickel powder slurry or nickel powder cake as they are, but they are preferably used in the form of an aqueous solution in consideration of ease of handling.

[Chemical 5]
(NH4) _2CO3- > _2NH3 ↑+ _CO2 ↑ _{+ H2O} ↑ ( ₅ )
_NH4HCO3- > _NH3 ↑+ _CO2 ↑+ _H2O ↑ ( ₆ )
_H2NCOONH4- > _2NH3 ↑ _{+ CO2} ↑ (7)

(2-3. Drying process)
The nickel powder cake is dried at 50° C. to 300° C., preferably 80° C. to 150° C. using a general-purpose drying apparatus such as an air dryer, a hot air dryer, an inert gas atmosphere dryer and a vacuum dryer. , nickel powder can be obtained. In addition, when the nickel powder cake is dried at about 200°C to 300°C in an inert atmosphere, a reducing atmosphere, or a vacuum atmosphere using a drying apparatus such as an inert gas atmosphere dryer or a vacuum dryer, simple drying is performed. In addition, it is possible to obtain heat-treated nickel powder.

EXAMPLES The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples. As the physical properties of the nickel powder, the average particle size and coarse particle content are evaluated as follows.

<Average particle size>
The nickel powder obtained in the present invention has a substantially spherical particle shape. It is the number average particle size based on the particle size obtained from the result of image analysis of (SEM image).

<Coarse particle content>
If coarse particles are contained in the nickel powder, when it is used for the internal electrodes of a multilayer ceramic capacitor, the continuity of the internal electrode layers may be reduced, and the adjacent dielectric layers may be pressed to cause short-circuit defects. Coarse particles are defined as particles having a diameter of 2 to 4 times or more the average particle diameter, and particles exceeding 0.8 μm are defined as coarse particles. The content of coarse particles in the nickel powder is obtained by photographing an image (SEM image) (magnification of 10000 times) with a scanning electron microscope in 20 fields of view, and in the SEM image of 20 fields of view, nickel particles are mainly formed by connecting. The content (% by mass) of coarse particles having a particle size of more than 0.8 μm, that is, mass of all coarse particles/mass of all particles×100, is obtained by measuring. The content of coarse particles is 5.0% by mass or less, preferably 4.0% by mass or less, more preferably 3.0% by mass or less, from the viewpoint of corresponding to thinning of the internal electrodes of the multilayer ceramic capacitor. is desirable.

(Example 1)
[Preparation of solutions of nickel salts and salts of metals nobler than nickel]
405 g of nickel chloride hexahydrate (NiCl ₂ .6H ₂ O, molecular weight: 237.69) as a nickel salt, and a sulfide group (-S-) in the molecule as a sulfur-containing compound as an auxiliary agent for suppressing autolysis of hydrazine. 1.271 g of L-methionine containing one (CH ₃ SC ₂ H ₄ CH(NH ₂ )COOH, molecular weight: 149.21), palladium (II) ammonium chloride (also known as tetra 0.134 mg of ammonium chloropalladium (II)) ((NH ₄ ) ₂ PdCl ₄ , molecular weight: 284.31) was dissolved in 1880 mL of pure water to obtain nickel salt, a sulfur-containing compound, and nickel as main components. A nickel salt solution, which is an aqueous solution containing a nucleating agent, which is a salt of a noble metal, was prepared. Here, in the nickel salt solution, L-methionine, which is a sulfide compound, is a very small amount of 0.5 mol % (0.005 in molar ratio) with respect to nickel, and palladium is 0.28 mol ppm (0.50 mol ppm) with respect to nickel. mass ppm).

[Preparation of reducing agent solution]
As a reducing agent, hydrazine hydrate (N ₂ H ₄ ·H ₂ O, molecular weight: 50.06) was diluted 1.67 times with pure water to obtain commercially available industrial grade 60 mass% hydrazine hydrate (MGC Otsuka Chemical Co., Ltd. (manufactured by the company) was weighed to prepare a reducing agent solution, which is an aqueous solution containing hydrazine as a main component and containing no alkali hydroxide. Hydrazine contained in the reducing agent solution was adjusted to have a molar ratio of 1.46 to nickel in the nickel salt solution.

[Alkali hydroxide solution]
As an alkali hydroxide, 230 g of sodium hydroxide (NaOH, molecular weight: 40.0) was dissolved in 672 mL of pure water to prepare an alkali hydroxide solution, which is an aqueous solution containing sodium hydroxide as the main component. Sodium hydroxide contained in the alkali hydroxide solution was adjusted to have a molar ratio of 5.75 to nickel in the nickel salt solution.

[Amine compound solution]
Ethylenediamine (abbreviation: EDA), which is an alkyleneamine containing two primary amino groups (—NH ₂ ) in the molecule, is used as an amine compound as a hydrazine autolysis inhibitor and reduction reaction accelerator (complexing agent). 1.024 g of (H ₂ NC ₂ H ₄ NH ₂ , molecular weight: 60.1) was dissolved in 19 mL of pure water to prepare an amine compound solution, which is an aqueous solution containing ethylenediamine as a main component. The amount of ethylenediamine contained in the amine compound solution was as small as 1.0 mol % (molar ratio: 0.01) with respect to nickel in the nickel salt solution. The nickel salt solution, the reducing agent solution, the alkali hydroxide solution, and the amine compound solution were all reagents manufactured by Wako Pure Chemical Industries, Ltd., except for 60 mass % hydrazine hydrate.

[Crystallization step]
A nickel salt solution obtained by dissolving nickel chloride and palladium salt in pure water is placed in a Teflon (registered trademark)-coated stainless steel container with a stirring blade, heated while stirring to a liquid temperature of 85°C, and then heated to a liquid temperature of 25°C. The reducing agent solution containing hydrazine and water was added and mixed for a mixing time of 20 seconds to obtain a nickel salt/reducing agent-containing solution. To this nickel salt/reducing agent-containing liquid, the above-mentioned alkali hydroxide solution containing alkali hydroxide and water at a liquid temperature of 25 ° C. was added and mixed for a mixing time of 80 seconds, and the reaction liquid (nickel chloride + palladium salt) at a liquid temperature of 70 ° C. + hydrazine + sodium hydroxide) were prepared to initiate a reduction reaction (crystallization reaction). The reaction initiation temperature was 70°C. Over 10 minutes from 8 minutes to 18 minutes after the start of the reaction, the amine compound solution was added dropwise to the reaction solution, and the reduction reaction proceeded while suppressing the self-decomposition of hydrazine to react the crystallized nickel powder. Crystallized in the liquid. Within 60 minutes from the start of the reaction, the reduction reaction of formula (3) was completed, the supernatant liquid of the reaction solution was transparent, and it was confirmed that all the nickel components in the reaction solution were reduced to metallic nickel. .

[Washing/filtration process]
In the crystallization step, a strongly alkaline ₍ pH: 14.1) nickel powder slurry is obtained as the reaction final solution containing nickel crystallized powder. , molecular weight: 92.12) was added to surface-treat the crystallized nickel powder (sulfur coating treatment). After that, using pure water with an electrical conductivity of 1 μS/cm, the slurry containing the surface-treated nickel crystallized powder is suction-filtered and washed using a Buchner funnel (filter paper: mesh size 5 type C), When the conductivity of the filtrate reached about 1000 μS/cm, ammonium carbonate (components: ammonium hydrogen carbonate (NH ₄ HCO ₃ , molecular weight: 79.06) and carbamin as salts volatile at 40° C. to 150° C. were added. A 0.05% aqueous solution (conductivity: about 500 μS/cm, pH: about 9.0 μS/cm) of an approximately equimolar mixture or double salt of ammonium acid ammonium (NH ₂ COONH ₄ , molecular weight: 78.07; manufactured by Kanto Kagaku Co., Ltd.). 4) was added and suction filtration washing was continued. When the conductivity of the filtrate reaches about 500 μS/cm, suction filtration and washing is terminated, solid-liquid separation is performed, and ammonium hydrogen carbonate (NH ₄ HCO ₃ ) and ammonium carbamate (NH ₂ COONH ₄ ) are the main components. A nickel powder cake was obtained containing an adherent liquid. In the suction filtration cleaning using a Buchner funnel, stop the suction while the nickel powder cake is wet and check the conductivity of the filtrate so that the nickel powder cake is not exposed to the air and oxidized. It was carried out by repeating suction filtration using pure water.

[Drying process]
The nickel powder cake was dried in a vacuum dryer set at 150° C. to obtain crystallized nickel powder (nickel powder).

[Evaluation of physical properties of nickel powder]
The obtained nickel powder was approximately spherical and had an average particle size of 0.20 μm. The content of particles larger than 0.8 μm in the nickel powder was 2.4% by weight. In addition, the nitrogen and carbon content in the nickel powder was measured using an oxygen/nitrogen analyzer (LECO ON836) and a carbon/sulfur analyzer (LECO CS844). As a result, no increase in the nitrogen and carbon contents was observed in the nickel powder to which the volatile _salt was added. HCO ₃ ) and ammonium carbamate (NH ₂ COONH ₄ ) did not remain, confirming that they were all decomposed and volatilized during the drying process.

(Example 2)
A salt volatile at 40° C. to 150° C. was ammonium carbonate ((NH ₄ ) ₃ CO ₃ , molecular weight: 96.09; a reagent manufactured by Sigma-Aldrich Japan G.K. was dissolved in saturated aqueous ammonia (NH ₄ ) ₃ CO. _{3.H 2} O crystals were used.) was changed to a 0.05% aqueous solution (conductivity: about 500 μS/cm, pH: about 9.3), suction filtration was performed, and the conductivity of the filtrate was washed. When the rate reached about 500 μS/cm, solid-liquid separation was performed to obtain a nickel powder cake containing an adhering liquid containing ammonium carbonate as the main component. A crystallized nickel powder (nickel powder) was obtained.

The obtained nickel powder was approximately spherical and had an average particle size of 0.20 μm. The content of coarse particles exceeding 0.8 µm in the nickel powder was 2.9% by mass. In addition, the nitrogen and carbon content in the nickel powder was measured using an oxygen/nitrogen analyzer (LECO ON836) and a carbon/sulfur analyzer (LECO CS844). As a result, no increase in the nitrogen and carbon contents was observed in the nickel powder to which the volatile salt was added. Therefore, the ammonium carbonate ((NH ₄ ) ₃ CO ₃ ) did not remain, and it was confirmed that it was all decomposed and volatilized during the drying process.

(Example 3)
A 0.05% aqueous solution of ammonium hydrogen carbonate (NH ₄ HCO ₃ , molecular weight: 79.06; manufactured by Kanto Kagaku Co., Ltd.) (conductivity: about 500 μS/cm, pH: Changed to about 8), suction filtration and washing were performed, and solid-liquid separation was performed when the conductivity of the filtrate reached about 500 μS / cm to obtain a nickel powder cake containing an adhering liquid mainly composed of ammonium hydrogen carbonate. A crystallized nickel powder (nickel powder) according to Example 3 was obtained in the same manner as in Example 1 except for the above.

The obtained nickel powder was approximately spherical and had an average particle size of 0.20 μm. The content of coarse particles exceeding 0.8 µm in the nickel powder was 3.0% by mass. In addition, the nitrogen and carbon content in the nickel powder was measured using an oxygen/nitrogen analyzer (LECO ON836) and a carbon/sulfur analyzer (LECO CS844). As a result, no increase in the nitrogen and carbon contents was observed in the nickel powder to which the volatile _salt was added. HCO ₃ ) did not remain, and it was confirmed that it was all decomposed and volatilized during the drying process.

(Example 4)
A 0.05% aqueous solution ₍ conductivity: about 500 μS/cm _, pH: 9.7), suction filtration and washing, solid-liquid separation when the conductivity of the filtrate reaches about 500 μS/cm, and a nickel powder cake containing ammonium carbamate as the main component. A crystallized nickel powder (nickel powder) according to Example 4 was obtained in the same manner as in Example 1 except for the above.

The obtained nickel powder was approximately spherical and had an average particle size of 0.20 μm. The content of coarse particles exceeding 0.8 µm in the nickel powder was 2.9% by mass. In addition, the nitrogen and carbon content in the nickel powder was measured using an oxygen/nitrogen analyzer (LECO ON836) and a carbon/sulfur analyzer (LECO CS844). As a result, no increase in the nitrogen and carbon contents was observed in the nickel powder to which the volatile _salt was added. COONH ₄ ) did not remain, and it was confirmed that it was all decomposed and volatilized during the drying process.

(Comparative example 1)
In the washing/filtration process, after applying the surface treatment (sulfur coating treatment) to the nickel crystallized powder, suction filtration washing using pure water is continued without adding salts that are volatile at 40°C to 150°C. The nickel powder cake was obtained by filtering and washing until the conductivity of the filtrate reached about 500 μS/cm, followed by solid-liquid separation. Other than this, the procedure was carried out in the same manner as in Example 1 to obtain a crystallized nickel powder (nickel powder) according to Comparative Example 1.

The obtained nickel powder was approximately spherical and had an average particle size of 0.20 μm. The content of coarse particles exceeding 0.8 μm in the nickel powder was 6.0% by mass.

Table 1 shows the salts having volatility at 40° C. to 150° C. used in Examples 1 to 4 and Comparative Example 1, and the content of coarse particles in the obtained nickel powder. From Table 1, in the washing/filtration process, by adding a salt volatile at 40°C to 150°C or less to the strongly alkaline nickel powder slurry or nickel powder cake, which is the final solution of the crystallization reaction, dry flocculation It can be seen that the formation of coarse particles in the nickel powder can be effectively suppressed.

[summary]
As is clear from the results of Examples and Comparative Examples, according to the production method of the present invention, by using a salt that is volatile at 40°C to 150°C, coarse particles in which nickel particles are connected to each other (connected particles ) is clearly obtained. A nickel paste using such a nickel powder can achieve high flatness in a dry film of the nickel paste. In particular, according to the present invention, a nickel powder with a very low content of coarse particles can be produced simply and easily by a wet method.

Claims (10)

In the method for producing nickel powder by a wet method,
a washing/filtration step of obtaining a nickel powder cake by filtering out the crystallized nickel powder while washing the nickel powder slurry;
a drying step of drying the nickel powder cake to obtain nickel powder,
In the washing/filtration step, a salt volatile at 40° C. to 150° C. is added to the nickel powder slurry or the nickel powder cake to make the conductivity of the washing liquid 100 μS/cm or more . How to make powder. In a strongly alkaline reaction solution obtained by mixing at least a water-soluble nickel salt, a salt of a metal nobler than nickel, a reducing agent, an alkali hydroxide, water, and optionally an amine compound and/or a sulfur-containing compound 2. The method for producing a nickel powder according to claim 1, further comprising a crystallization step of performing a reduction reaction to obtain the strongly alkaline nickel powder slurry, which is the reaction final solution containing the crystallized nickel powder. 3. The method according to claim 1 or 2, wherein in the washing/filtration step, washing of the crystallized nickel powder in the nickel powder slurry is performed until the electric conductivity of the washing liquid reaches 100 μS/cm to 5000 μS/cm. A method for producing the described nickel powder. 4. The salt having volatility at 40° C. to 150° C. is a readily soluble salt having a solubility in water of 10 g to 200 g/100 g water (25° C.). The method for producing the nickel powder according to 1. The method for producing nickel powder according to any one of claims 1 to 4, wherein the salt volatile at 40°C to 150°C is a salt volatile at 100°C or lower. The salt volatile at 40° C. to 150° C. is at least one selected from ammonium carbonate ((NH4) ₃ CO ₃ ), ammonium hydrogen carbonate (NH ₄ HCO ₃ ) and ammonium carbamate (NH ₂ COONH ₄ ). The method for producing nickel powder according to any one of claims 1 to 5, characterized in that The amine compound is at least one of an alkyleneamine and an alkyleneamine derivative, and has a structure represented by the following formula A in which the nitrogen atoms of the amino groups in the molecule are bonded via a carbon chain having 2 carbon atoms. The method for producing nickel powder according to any one of claims 2 to 6, characterized in that:

When the amine compound is the alkyleneamine, the alkyleneamine is ethylenediamine (H ₂ NC ₂ H ₄ NH ₂ ), diethylenetriamine (H ₂ NC ₂ H ₄ NHC ₂ H ₄ NH ₂ ), triethylenetetramine ( _{H2N ( C2H4NH} ) _2C2H4NH2 ), _{tetraethylenepentamine ( H2N ( C2H4NH ) 3C2H4NH2} ) _{, pentaethylenehexamine ( H2N} (C ₂ H ₄ NH) ₄ C ₂ H ₄ NH ₂ ) and propylenediamine (CH ₃ CH(NH ₂ )CH ₂ NH ₂ ),
When the amine compound is the alkyleneamine derivative, the alkyleneamine derivative is tris(2-aminoethyl)amine (N(C ₂ H ₄ NH ₂ ) ₃ ), N-(2-aminoethyl)ethanol Amine (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 2CH(NH)COOH), ethylenediamine _- N,N' _- diacetic _{acid ( HOOCCH2NHC2H4NHCH2COOH} ), N,N' _- diacetylethylenediamine _{( CH3CONHC2H4NHCOCH3} ) _, N,N '-dimethylethylenediamine _{( CH3NHC2H4NHCH3} ), N,N' _- diethylethylenediamine _{( C2H5NHC2H4NHC2H5} ), _{N ,} N' _- diisopropylethylenediamine _{( CH3 ( CH3} )CHNHC ₂ H ₄ NHCH(CH ₃ )CH ₃ ) and 1,2-cyclohexanediamine (H ₂ NC ₆ H ₁₀ NH ₂ ). Method for producing nickel powder. The sulfur-containing compound has, in its molecule, a sulfide group (-S-), a sulfonyl group (-S(=O) ₂ -), a sulfonic acid group (-S(=O) ₂ -O-), a thioketone group ( -C(=S)-) is one or more selected from compounds containing at least one of -C(=S)-), The method for producing nickel powder according to any one of claims 2 to 8. The sulfur-containing compound is L (or D, or DL)-methionine (CH ₃ SC ₂ H ₄ CH(NH ₂ )COOH), L (or D, or DL)-ethionine (C ₂ H ₅ SC ₂ H ₄ CH(NH ₂ )COOH), N-acetyl-L (or D, or 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 _2H5 ) _C4H9 ) and thiourea _{( H2NC (} S) _NH2 ). Production method.

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