JP2020100858A - Nickel powder and method for producing the same - Google Patents

Abstract

To provide nickel powder in which the content of coarse grains essentially consisting of nickel hydroxide is reduced, and a method for producing the same, particularly, a method for producing nickel by a wet process capable of more simply and easily producing nickel powder.SOLUTION: Nickel powder has an almost spherical grain shape, in which the number average grain size is 0.03 to 0.4 μm, the content of coarse grains essentially consisting of nickel hydroxide having a grain size exceeding 0.8 μm is 200 mass ppm or lower, and the content of coarse grains essentially consisting of nickel hydroxide having a grain size exceeding 1.2 μm is 100 mass ppm or lower.SELECTED DRAWING: Figure 3

Description

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

Nickel powder is used as a material for capacitors of electronic circuits, in particular, 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, the capacity of multilayer ceramic capacitors has increased, and the amount of internal electrode paste used for forming internal electrodes of multilayer ceramic capacitors has also increased significantly. Therefore, as the metal powder for the internal electrode paste forming the thick film conductor, an inexpensive base metal such as nickel is mainly used instead of the expensive noble metal.

In the process of manufacturing a monolithic 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 on 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 superposed, and further pressure-bonded to obtain a laminated body.

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

Then, external electrodes are attached to the obtained ceramic molded body to obtain a monolithic ceramic capacitor. Since the base metal such as nickel is used as the metal powder in the internal electrode paste to be the internal electrode, the binder removal treatment of the laminate is performed so that the oxygen concentration in an inert atmosphere or the like is adjusted so that these base metals are not oxidized. It is performed in an extremely low atmosphere.

With the miniaturization and increase in capacity of monolithic ceramic capacitors, the internal electrodes and dielectrics have been made thinner. Along with this, the particle size of the nickel powder used in the internal electrode paste has also become smaller, and nickel powder with an average particle size of 0.4 μm or less is required. In particular, nickel powder with an average particle size of 0.3 μm or less is required. Has become the mainstream.

The nickel powder manufacturing method is roughly classified into a vapor phase method and a wet method. Examples of the vapor phase method include 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 described in Patent Document 2 in plasma. There is a method of producing nickel powder. As a wet method, for example, there is a method described in Patent Document 3 in which a reducing agent is added to a nickel salt solution to produce nickel powder.

Since the vapor phase method is a high temperature process of about 1000° C. or higher, it is an effective means for obtaining nickel powder having excellent crystallinity and high characteristics, but there is a problem that the particle size distribution of the obtained nickel powder becomes wide. is there. As described above, in order to reduce the thickness of the internal electrode, nickel powder that does not contain coarse particles and has an average particle size of 0.4 μm or less, which has a relatively narrow particle size distribution, is required. Therefore, in order to obtain such nickel powder by the vapor phase method, it is necessary to classify the nickel powder by introducing an expensive classifier.

In the classification treatment, coarse particles larger than the classification point can be removed by aiming at the classification point having an arbitrary value of about 0.6 μm to 2 μm, but a part of particles smaller than the classification point can be removed. However, it is also removed at the same time, so there is also a problem that the actual product yield is significantly reduced. Therefore, the gas phase method inevitably raises the cost of the product including the above-mentioned expensive equipment introduction.

Further, in the vapor phase method, when nickel powder having an average particle size of 0.2 μm or less, particularly 0.1 μm or less is used, it becomes difficult to remove coarse particles by classification, and therefore it is difficult to remove It is not possible to cope with thinner internal electrodes.

On the other hand, the wet method has an advantage that the particle size distribution of the obtained nickel powder is narrower than that of the vapor phase method. In particular, nickel powder is prepared by crystallization described in Patent Document 3 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 copper salt as a nickel salt. In the method, since the nickel salt (more precisely, nickel ion (Ni ²⁺ ) or nickel complex ion) is reduced with hydrazine in the coexistence with a salt of a metal nobler than nickel (nucleating agent), the number of nucleation Is controlled (that is, the particle size is controlled), the nucleation and the particle growth are uniform, and a fine nickel powder having a narrower particle size distribution (hereinafter, nickel powder generated in the reaction solution is referred to as nickel crystallization powder). It is known to be obtained). For reference, FIG. 1 shows a typical manufacturing process of nickel powder by a wet method.

By the way, when the nickel powder obtained by the above-mentioned wet method is applied to a laminated ceramic capacitor, in order to prevent a short circuit (short circuit) between electrodes in the above-mentioned laminated body including the internal electrode layer and the dielectric layer, the nickel powder and the resin are used. High flatness is required for a nickel paste dry film containing as a main component (a dry film obtained by printing and drying a nickel paste). Particularly, in order to cope with the thinning of the internal electrode layers (the film thickness is about 0.5 μm to 1.0 μm) accompanying the recent increase in the capacity of the multilayer ceramic capacitor, the average particle diameter is 0.3 μm or less, preferably Fine nickel powder having an average 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. Is required to be reduced 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 strong alkaline reaction solution in order to enhance the reducing power of hydrazine, a specific amine is added in the reaction solution. Compounds and sulfide compounds are added in very small amounts to significantly suppress the hydrazine self-decomposition reaction, and to prevent the formation of coarse particles formed by the connection of nickel particles with each other. A method for inexpensively obtaining various nickel powders is shown.

JP-A-4-365806 Japanese Patent Publication No. 2002-530521 JP, 2002-53904, A WO2017/069067

In the method for producing nickel powder using the wet method as described above, hydrazine is often used as a reducing agent, and therefore, as is clear from Patent Document 4 and the like, the reaction solution is generally strongly alkaline. is there. As shown in FIG. 1 described above, in the crystallization step, a nickel powder slurry in which nickel crystallization powder is generated in the strongly alkaline reaction liquid is obtained by the reduction reaction of hydrazine, and the nickel crystallization powder is converted from the nickel powder slurry. A washing/filtering step in which the nickel powder cake is collected by filtration while washing with pure water, and a drying step in which the nickel powder cake is dried (vacuum drying, etc.) to obtain dried nickel crystallization powder (nickel powder). It is carried out subsequent to the crystallization process.

Since the above washing/filtering step is usually carried out in the atmosphere, the resulting nickel powder cake is more or less exposed to the atmosphere to some extent during the washing/filtering step and before the drying in the drying step. It is unavoidable that the crystallization powder is oxidized. In particular, when the crystallization reaction is carried out on a mass production scale, unlike the small-scale handling at the laboratory level, it takes time to handle the nickel powder cake, so the oxidation of the nickel crystallization powder is likely to proceed due to exposure to the atmosphere.

In the nickel powder cake obtained from the above strongly alkaline nickel powder slurry through the washing and filtration steps, when the nickel crystallization powder is oxidized, nickel crystallization powder 1 (particle size 0.4 μm or less) In some cases, coarse particles 10 (see FIG. 2) containing nickel hydroxide as a main component, which were solidified by nickel hydroxide 2 generated by oxidation of each other, were generated. In many cases, the coarse particles 10 have a particle size of 0.8 μm or more, which may cause troubles such as a monolithic ceramic capacitor. Therefore, effective suppression measures have been demanded.

Therefore, in the present invention, a nickel powder having a low content of coarse particles containing nickel hydroxide as a main component and a method for producing the same, in particular, a method for producing nickel powder by a wet method capable of producing the nickel powder more easily and easily is provided. The purpose is to provide.

In the method for producing nickel powder by a wet method used for a monolithic ceramic capacitor or the like, the inventors of the present invention wash nickel crystallization powder (nickel powder) from a strongly alkaline nickel powder slurry which is the final solution of the crystallization reaction. In the process of washing/filtering step of filtering and collecting as a nickel powder cake, if the strong alkali is neutralized with an inorganic acid or an organic acid to make the nickel powder slurry neutral to weakly alkaline, the above nickel hydroxide is removed. It was found that the formation of coarse particles as the main component can be effectively suppressed. The present invention has been completed based on such findings.

In order to solve the above problems, the nickel powder of the present invention has a substantially spherical particle shape, has a number average particle diameter of 0.03 μm to 0.4 μm, and a particle diameter of more than 0.8 μm. The content of coarse particles containing nickel as a main component is 200 mass ppm or less, and the content of coarse particles containing nickel hydroxide as a main component is 100 mass ppm or less.

The content of coarse particles containing nickel hydroxide as a main component is 100 mass ppm or less, the particle size is more than 0.8 μm, and the nickel hydroxide is a main component having a particle size of more than 1.2 μm. The content of the coarse particles may be 50 ppm by mass or less.

Further, in order to solve the above problems, a method for producing the nickel powder of the present invention is a production method for producing the nickel powder of the present invention, which is a water-soluble nickel salt, a salt of a metal nobler than nickel, or a reduction. A crystallization step of performing a reduction reaction in a reaction liquid in which an agent, an alkali hydroxide and water are mixed to obtain a nickel powder slurry as a reaction final liquid containing nickel crystallization powder, and a nickel crystallization powder in the nickel powder slurry A washing/filtering step of washing and filtering to obtain a nickel powder cake, and a drying step of drying the nickel powder cake to obtain nickel powder, wherein the washing/filtering step is the nickel powder slurry or the same. A neutralization step in which the diluted solution is neutralized with at least one selected from an inorganic acid and an organic acid so as to have a pH of 7.0 to pH 9.0; and the conductivity of the solution containing the nickel crystallization powder is 30 μS/cm. After performing the washing step of washing the nickel crystallization powder so as to be about 1000 μS/cm, the neutralization step and the washing step, the washed nickel crystallization powder is filtered from the liquid to obtain the nickel powder cake. It is characterized by including another step of obtaining

In the washing/filtering step, the washing step may be performed after the neutralizing step.

The strong alkaline reaction liquid may include an amine compound or a sulfur-containing compound.

The inorganic acid may include any of hydrochloric acid (HCl), nitric acid (HNO ₃ ), sulfuric acid (H ₂ SO ₄ ), and carbonic acid (H ₂ CO ₃ ).

The organic acid may include any one of acetic acid (CH ₃ COOH), citric acid (C(OH)(CH ₂ COOH) ₂ COOH), and ascorbic acid (C ₆ H ₈ O ₆ ).

The amine compound is at least one of an alkylene amine and an alkylene amine derivative, and has at least a structure of the following formula A in which a nitrogen atom of an amino group in the molecule is 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 ( _{H 2 N (C 2 H 4} NH) 2 C 2 H 4 NH 2), tetraethylene pentamine _{(H 2 N (C 2 H} 4 NH) 3 C 2 H 4 NH 2), pentaethylenehexamine _(H 2 N It may be one or more selected from (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 is the alkylene amine 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) , 1,2-cyclohexane diamine _{(H 2 NC 6 H 10 NH} 2), ethylenediamine -N, N'-diacetic acid _{(HOOCCH 2 NHC 2 H 4 NHCH} 2 COOH), N, N'- diacetyl ethylenediamine _(CH 3 CONHC _{2 H 4 NHCOCH 3), N} , N'- dimethylethylenediamine _{(CH 3 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 even _{(H 2 NC 6 H 10 NH} 2) from one or more selected Good.

In the molecule, the sulfur-containing compound has a sulfide group (-S-), a sulfonyl group (-S(=O) _2- ), a sulfonic acid group (-S(=O) _2- O-), a thioketone group ( It may be one or more selected from compounds containing at least one or more of any one of -C(=S)-).

Said sulfur-containing compound, 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), thio diglycolic acid _{(HOOCCH 2} SCH ₂ COOH), Mechionoru _{(CH 3 SC 3 H 6 OH} ), thiodi glycol _{(HOC 2 H 5 SC 2 H} 5 OH), thiomorpholine _{(C 4} H 9 NS), thiazole _{(C 3} H ₃ NS), benzothiazole _{(C 7} H 5 NS), saccharin _{(C 7} H 5 NO ₃ S), sodium dodecyl sulfate _{(C 12 H 25 OS (O} ) 2 ONa), dodecylbenzene sulfonic acid _{(C 12 H 25 C 6 H} 4 S (O) 2 OH), sodium dodecyl benzene sulfonate _(C 12 _{H 25 C 6 H 4 S (O)} 2 ONa), sulfosuccinic di-2-ethylhexyl sodium _{(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 one or more selected from thiourea (H ₂ NC(S)NH ₂ ).

The washing/filtering step may include a supernatant removing step of decanting the nickel powder slurry and then removing the supernatant before the neutralizing step.

INDUSTRIAL APPLICABILITY The nickel powder according to the present invention has a very small content of coarse particles containing nickel hydroxide as a main component and can realize high flatness in a nickel paste dry film, and thus is suitable for use as an internal electrode of a laminated ceramic capacitor. is there.

Further, the method for producing a nickel powder according to the present invention has a strong reaction that is a final solution of crystallization in a washing/filtering step performed after the crystallization step, which is one step of the method for producing a nickel powder by the wet method. By neutralizing the alkaline nickel powder slurry from neutral to weakly alkaline, it is possible to effectively suppress the generation of coarse particles containing nickel hydroxide as a main component, and thus it is suitable for use as an internal electrode of a laminated ceramic capacitor. Suitable, high-performance nickel powder can be manufactured at low cost.

It is a schematic diagram which shows the typical manufacturing process in the manufacturing method of the nickel powder by a wet method. It is a schematic diagram which shows the coarse particle which has nickel hydroxide as a main component found in the nickel powder by a wet method. 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 according to the present invention will be described. As a preferable example of the method for producing nickel powder according to the present invention, a method for producing nickel powder using a wet method will be described in the following order with reference to FIGS. 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 powder 2. Manufacturing method of 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 start temperature 2-2. Washing/filtration step 2-2-1. Washing/Filtration Method and Procedure 2-2-2. Agent used for neutralization 2-3. Drying process 2-4. Crushing process (post-treatment process)

<1. Nickel powder>
INDUSTRIAL APPLICABILITY The nickel powder of the present invention is coarse particles having a particle size of more than 0.8 μm, and the content of coarse particles containing nickel hydroxide as a main component is very small at 200 mass ppm or less, which is high in a nickel paste dry film. Flatness can be realized. Therefore, it becomes possible to effectively prevent a short circuit between electrodes in a laminated body including an internal electrode layer and a dielectric layer, which is suitable for use as an internal electrode of a laminated ceramic capacitor.

The nickel powder of the present invention has a substantially spherical particle shape, and the average particle diameter thereof is 0.03 μm to 0.4 μm from the viewpoint of coping with the thinning of the internal electrodes of recent monolithic ceramic capacitors. The substantially spherical shape includes not only a true sphere but also an ellipsoid in which a predetermined cross section has an elliptical shape in which a ratio of a minor axis to a major axis (minor axis/major axis) is 0.8 to 1.0.

The average particle diameter of the present invention is a number average particle diameter obtained from a scanning electron micrograph (SEM image) of nickel powder. In addition, the nickel powder produced by the wet method of the present invention described later has a sufficiently narrow particle size distribution without classification treatment. That is, in this case, the CV value, which is the value obtained by dividing the standard deviation of the particle diameter by the average particle diameter, is 0.2 or less, and the nickel powder has a uniform particle diameter.

Here, the coarse particles containing nickel hydroxide as the main component, by the nickel hydroxide generated on the surface of the nickel crystallized powder in the process from the washing/filtration step to be described later to the drying step, the nickel crystallized powder is involved. It is a solid material that is tightly bound. These are not easily disentangled even if they are subjected to the disintegration treatment described later. The coarse particles containing nickel hydroxide as a main component are obtained by separating the coarse particles of the crushed nickel powder with a filter such as a membrane filter, and then separating the coarse particles with EDS (energy dispersive X-ray analysis) or It can be specified by analysis by XPS (X-ray photoelectron spectroscopy) or the like and shape observation by a scanning electron microscope (SEM) or the like.

The nickel powder of the present invention has a content of coarse particles whose main component is nickel hydroxide having a particle size of more than 0.8 μm is 200 mass ppm or less, more preferably 100 mass ppm or less. The content of coarse particles containing nickel hydroxide as a main component and having a particle size of more than 1.2 μm is 100 mass ppm or less, more preferably 50 mass ppm or less. Of course, the influence of coarse particles depends on the film thickness of the internal electrode layer of the multilayer ceramic capacitor in which nickel powder is used, but in the thinned internal electrode layer of recent years, nickel hydroxide having a particle size of more than 0.8 μm is used. If the content of coarse particles containing as a main component exceeds 200 mass ppm, or if the content of coarse particles containing nickel hydroxide having a particle size of more than 1.2 μm as a main component exceeds 100 mass ppm, a short circuit between electrodes occurs. May occur significantly. Needless to say, the smaller the content of the coarse particles containing nickel hydroxide as the main component, the better, and the content of the coarse particles containing nickel hydroxide as the main component whose particle size exceeds 0.8 μm is 100 mass ppm or less. Alternatively, if the content of coarse particles containing nickel hydroxide as a main component and having a particle size of more than 1.2 μm is 50 mass ppm or less, the occurrence rate of short circuits between electrodes can be sufficiently reduced. The particle size of the coarse particles containing nickel hydroxide as the main component may be the minor axis diameter obtained from the SEM image.

Usually, nickel powder may contain slight impurities. For example, nickel powder obtained by the wet method contains oxygen due to surface oxidation of nickel particles, chlorine considered to be due to nickel chloride which is a nickel raw material, and alkali metals such as sodium due to sodium hydroxide. May be contained in trace amounts. Further, the nickel powder obtained by the vapor phase method also contains a small amount of chlorine in the case of oxygen produced by the surface oxidation of nickel particles and the nickel powder obtained by the method of reducing nickel chloride vapor with hydrogen. May be included. Since these impurities may cause defects in the internal electrodes during the production of the monolithic ceramic capacitor, it is preferable to reduce them as much as possible. For example, for chlorine and alkali metals, 0% in the nickel powder is preferable. The content is preferably 0.01 mass% or less.

Like the nickel powder of the present invention, nickel powder applicable to the internal electrodes of a monolithic ceramic capacitor may usually contain a trace amount of sulfur in order to suppress its catalytic activity. This is because the surface of nickel particles has a high catalytic activity, and if they are used as they are without containing, for example, sulfur, the binder resin such as ethyl cellulose resin contained in the internal electrode paste will not be heated in the binder removal process during the production of multilayer ceramic capacitors. This is because the decomposition may be promoted, the binder resin may be decomposed at a low temperature, and the strength of the laminated body may be significantly reduced, and at the same time, a large amount of decomposed gas may be generated to easily cause cracks in the laminated body.

As described above, in order to add sulfur to the nickel powder, it is necessary to carry out a surface treatment for adhering sulfur to the surface of the nickel particles so that 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 laminated ceramic capacitor, it is most preferable. However, if the effect of suppressing the decomposition of the binder resin can be exhibited, the nickel particles may be in a modified (coated) state in which a part of the surface is modified (coated), without modifying (coating) the entire surface. .. In the present invention, "surface treatment" is used as a concept that includes the entire modification (coating) and the partial modification (coating) of such nickel particles. In the method for producing nickel powder using the wet method of the present invention, since the reaction liquor for crystallization contains an excessive amount of alkali hydroxide and exhibits strong alkalinity, surface treatment with sulfur as described above Even if the pH of the solution may be slightly lowered, the pH of the nickel powder slurry and its diluted solution will not be 7.0 to pH 9.0, and this surface treatment is not suitable for neutralization in the present invention. Not applicable.

If the sulfur content with respect to the nickel powder exceeds 0.5% by mass, internal electrode defects due to sulfur may occur, preferably 0.3% by mass or less, and more preferably 0.2% by mass or less. .. The lower limit of the sulfur content is not particularly limited, and it is an extremely small amount of content that results in a measurement result below the detection limit by an analytical instrument used in the analysis of the content, such as a sulfur analyzer by a combustion method or an ICP analyzer. It may be the amount.

<2. Manufacturing Method of Nickel Powder Using Wet Method>
First, a method for manufacturing 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 an embodiment of the present invention is at least a water-soluble nickel salt, a salt of a metal nobler than nickel, a reducing agent (for example, hydrazine), and an alkali hydroxide as a pH adjusting agent. In a strong alkaline reaction solution obtained by mixing water with water, a crystallization step for obtaining a strong alkaline nickel powder slurry that is a reaction final solution containing nickel crystallization powder by crystallizing nickel by a reduction reaction with hydrazine or the like, A washing/filtering step of separating nickel crystallization powder to obtain a nickel powder cake while washing the nickel powder slurry and a drying step of drying the nickel powder cake to obtain a nickel crystallization powder (nickel powder) are included. In addition, if necessary, an amine compound or a sulfur-containing compound may be added to the reaction solution to suppress the autolysis of hydrazine (amine compound, sulfur-containing compound) and reduction reaction accelerator (complexing agent) (amine compound). May act as. Moreover, you may add the disintegration process performed as needed as a post-processing process.

In addition, if desired, a very small amount of a sulfur compound is added to a strongly alkaline nickel powder slurry, which is a reaction end solution containing nickel crystallization powder, or a dilution liquid or a cleaning liquid thereof, so that the content in the nickel powder is 0.5. A surface treatment (sulfur coating treatment) for modifying the surface of the nickel particles with a sulfur component may be carried out so that the content is not more than mass %. Further, the obtained nickel powder can be subjected to a heat treatment at about 200° C. to 300° C. in an inert atmosphere or a reducing atmosphere to obtain a nickel powder. This sulfur coating treatment or heat treatment can control the debindering behavior of the internal electrodes and the sintering behavior of the nickel powder at the time of manufacturing the above-mentioned multilayer ceramic capacitor, and is therefore very effective when used within an appropriate range.

Furthermore, if necessary, a crushing step (post-treatment step) of crushing nickel crystallization powder is added to increase the size of coarse particles due to the connection of nickel particles generated during the nickel particle generation process in the crystallization step. It is preferable to obtain a nickel powder that reduces

By performing such a crystallization step, a washing/filtering step, a drying step, and a crushing step as necessary, it has a substantially spherical particle shape and its average particle diameter is 0.03 μm to 0.4 μm. A nickel powder can be obtained.

(2-1. Crystallization step)
In the crystallization process, at least a water-soluble nickel salt, a salt of a metal nobler than nickel, a reducing agent, an alkali hydroxide, and a nickel salt (more precisely, a nickel ion or a nickel complex ion) in a reaction solution mixed with water. ) Can be reduced by a reduction reaction using a reducing agent such as hydrazine. In the present invention, in the case of using hydrazine, the reaction solution is mixed with an amine compound or a sulfur-containing compound as necessary, and in the presence of the amine compound or the sulfur-containing compound, it is possible to suppress the decomposition of hydrazine as a reducing agent. However, the nickel salt can also be reduced.

(2-1-1. Agent used in crystallization step)
In the crystallization step of the present invention, a reaction solution containing nickel salt, a salt of a metal nobler than nickel, a reducing agent, an alkali hydroxide, and if necessary, various agents such as an amine compound and a sulfur-containing compound and water is used. Has been. Water as a solvent is ultrapure water (electrical conductivity: ≦0.06 μS/cm (microsiemens per centimeter)) or pure water (electrical conductivity) from the viewpoint of reducing the amount of impurities in the obtained nickel powder. : ≦1 μS/cm) with high purity is preferable, and it is preferable to use pure water which is inexpensive and easily available. Hereinafter, each of the above-mentioned various drugs will be described in detail.

(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 easily soluble in water, and for example, one or more selected from nickel chloride, nickel sulfate and nickel nitrate can be used. Can be used. Among these nickel salts, it is more preferable to use nickel chloride, nickel sulfate, or a mixture thereof.

(B) Salt of Noble Metal than Nickel The salt of a metal nobler than nickel has a lower ionization tendency than nickel, and thus is reduced before nickel during the reduction and precipitation of nickel. Therefore, when a salt of a metal that is more precious than nickel is contained in the nickel salt solution, when nickel is reduced and precipitated, the metal that is more precious than nickel is reduced first and acts as a nucleating agent that becomes an initial nucleus. Therefore, in the nickel crystallized powder (nickel powder) obtained by grain growth of the initial nuclei, it becomes possible to easily control the grain size of the nickel powder and make it finer.

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

As the salt of a metal nobler than nickel, it is preferable to use the above-mentioned palladium salt, since the particle size distribution is somewhat broadened, but the particle size of the obtained nickel powder can be controlled more finely. When using a palladium salt, the ratio [mol ppm] of the palladium salt and nickel (mol number of palladium salt/mol number of nickel×10 ⁶ ) should be appropriately selected according to the intended number average particle size of the nickel powder. You can For example, if the average particle size of the nickel powder is set to 0.03 μm to 0.4 μm, the ratio of the 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 -25 mol ppm. If the above ratio is less than 0.2 mol ppm, the average particle size of the obtained 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 is used, which may increase 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, and examples thereof include hydrazine (N ₂ H ₄ , molecular weight: 32.05). 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, but either one may be used. The reduction reaction of hydrazine is as shown in the formula (2) described later, but it is particularly alkaline and has a high reducing power, and since the byproducts of the reduction reaction are nitrogen gas and water, the impurity components due to the reduction reaction are It is characterized in that it does not occur in the reaction solution, that impurities in hydrazine are small in the first place, and that 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, as shown in the formula (2) described later, in the present invention, alkali hydroxide is used in the crystallization step. It can be used as a pH adjuster to enhance. The alkali hydroxide is not particularly limited, but it is preferable to use an alkali metal hydroxide in terms of availability and price. Specifically, it is more preferable to use one or more selected from sodium hydroxide (NaOH) and potassium hydroxide (KOH).

The amount of alkali hydroxide to be added is such that the pH of the reaction solution is 9.5 or more, preferably 10 or more, more preferably 10.5 or more at the reaction temperature so that the reducing power of hydrazine as a reducing agent is sufficiently enhanced. You should decide so that For example, when the temperature of the reaction solution is about 25° C. and about 70° C., the temperature at a high temperature of 70° C. is somewhat lower.

(E) Amine Compound As described above, the amine compound acts as a hydrazine self-decomposition inhibitor, a reduction reaction accelerator, and a nickel particle-linking inhibitor, so that the reaction solution may be added as necessary. Should be added to. Examples of the amine compounds, there at the primary amino group (-NH ₂₎ or a compound having two or more together either functional group selected from a secondary amino group (-NH-) in the molecule For example, at least one of alkylene amine and alkylene amine derivative 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 the nitrogen atom of the amino group in the molecule is bonded via a carbon chain having 2 carbon atoms.

More specifically, as the alkyleneamine, ethylenediamine (H ₂ NC ₂ H ₄ NH ₂ ), diethylenetriamine (H ₂ NC ₂ H ₄ NHC ₂ H ₄ NH ₂ ), triethylenetetramine (H ₂ N(C ₂ H _{4 NH) 2 C 2 H 4 NH} 2), tetraethylene pentamine _{(H 2 N (C 2 H} 4 NH) 3 C 2 H 4 NH 2), pentaethylenehexamine _{(H 2 N (C 2 H} 4 NH) 4 One or more selected from C ₂ H ₄ NH ₂ ) and propylenediamine (CH ₃ CH(NH ₂ )CH ₂ NH ₂ ) can be used. Further, as the alkylene amine derivative, 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- cyclohexane diamine _{(H 2 NC 6 H 10 NH} 2), ethylenediamine -N, N'-diacetic acid (another name: ethylene -N, _{N'diglycine, HOOCCH 2 NHC 2 H 4 NHCH} 2 COOH), N, N'- diacetylethylenediamine _{(CH 3 CONHC 2 H 4 NHCOCH} 3), N, N'- dimethylethylenediamine _{(CH 3 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), 1 selected from 1,2-cyclohexanediamine _{(H 2 NC 6 H 10 NH} 2) More than one species can be used. These alkyleneamines and alkyleneamine derivatives are water-soluble, and among them, ethylenediamine and diethylenetriamine are preferable because they are easily available and inexpensive.

It is considered that the action of the amine compound as a reduction reaction accelerator is due to the action as a complexing agent that complexes nickel ions (Ni ²⁺ ) in the reaction solution to form nickel complex ions. Further, regarding the action of the hydrazine as a self-decomposition inhibitor or a coupling inhibitor between nickel particles, it may be combined with a primary amino group (-NH ₂ ) or a secondary amino group (-NH-) in the amine compound molecule. It is assumed that the action is manifested by the interaction with the surface of the nickel crystallized powder in the reaction solution.

In addition, it is preferable that the alkyleneamine or the alkyleneamine derivative which is an amine compound has a structure of the above formula A in which the nitrogen atom of the amino group in the molecule is bonded via a carbon chain having 2 carbon atoms. This is because the effect of suppressing the decomposition of hydrazine molecules becomes large. For example, if the nitrogen atom of the amino group strongly adsorbed to the nickel crystallized powder is bound via a carbon chain having 3 or more carbon atoms, the carbon chain becomes long, and the movement of the carbon chain portion of the amine compound molecule becomes free. It is thought that the degree (flexibility of the molecule) increases. As a result, it is thought that the contact of hydrazine molecules to the nickel crystallized powder cannot be effectively prevented, and the number of hydrazine molecules that self-decompose due to the catalytic activity of nickel increases, reducing the effect of suppressing hydrazine self-decomposition. To be

Actually, ethinediamine (H ₂ NC ₂ H ₄ NH ₂ ) and propylenediamine (other names: 1,2-diaminopropane, 1, 1, in which the nitrogen atom of the amino group in the molecule is bonded via a carbon chain having 2 carbon atoms) 2-Propanediamine) (CH ₃ CH(NH ₂ )CH ₂ NH ₂ ) compared to trimethylenediamine (other name: 1) in which the nitrogen atom of the amino group in the molecule is bonded via a carbon chain having 3 carbon atoms. , 3-diaminopropane, _{1,3-propanediamine) (H 2 NC 3 H 6} NH 2) , it has been confirmed that autolysis inhibitory effect of the hydrazine is inferior.

Here, the ratio [mol %] of the amine compound and nickel in the reaction solution ((mol number of amine compound/mol number of nickel)×100) is in the range of 0.01 mol% to 5 mol %, preferably The range of 0.03 mol% to 2 mol% is preferable. If the above ratio is less than 0.01 mol %, the amount of the amine compound may be too small to obtain each action as a hydrazine self-decomposition inhibitor, a reduction reaction accelerator, or a nickel particle interlocking inhibitor. is there. On the other hand, when the above-mentioned ratio exceeds 5 mol %, the amine compound becomes too strong as a complexing agent for forming nickel complex ions, and as a result, the particle growth of the nickel crystallization powder may be abnormal. There is a possibility that the characteristics of the nickel powder may be deteriorated, such that the granularity or spherical property of the powder is lost and the powder has a distorted shape, or a large number of coarse particles in which nickel particles are connected to each other are formed.

(F) Sulfur-containing compound (auxiliary agent for suppressing autolysis of hydrazine)
The sulfur-containing compound is a compound applied to a brightener for nickel plating and a stabilizer for a plating bath, and unlike the above amine compound, when used alone, the hydrazine self-decomposition inhibiting effect is not so great. However, it has an interaction such as adsorption with the surface of nickel particles, and when used in combination with the above amine compound, it has the effect of an auxiliary agent for suppressing hydrazine self-degradation, which can significantly enhance the effect of hydrazine self-decomposition. There is. Therefore, it may be added to the reaction solution if necessary. The sulfur-containing compound has 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. It is a compound containing at least one of (-C(=S)-). Furthermore, the sulfur-containing compound, in addition to the action of the hydrazine self-decomposition inhibitor, also acts as a coupling inhibitor between nickel particles, and when used in combination with the amine compound, the nickel particles are linked to each other. It is also possible to more effectively reduce the amount of generated coarse particles.

As the sulfur-containing compound, for example, a sulfide compound having a sulfide group (-S-) in the molecule preferably has high water solubility, and therefore, a carboxy group (-COOH) and a hydroxyl group (- OH), amino group (primary: -NH _2, secondary: -NH-, tertiary: -N <) or a carboxy group-containing sulfide compound containing at least one or more hydroxyl-containing sulfide compound , And an amino group-containing sulfide compound is preferred, and a thiazole ring-containing sulfide compound containing at least one thiazole ring (C ₃ H ₃ NS) is also applicable although it is not highly water-soluble. is there. 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 (another name: 3,3' _{Chiojiaranin) (HOOCCH (NH 2) CH} 2 SCH 2 CH (NH 2) COOH), thiodipropionic acid (another name: 3,3'-thiodipropionic _{acid) (HOOCC 2 H 4 SC 2} H 4 COOH), Thiodiglycolic acid (other name: 2,2′-thiodiglycolic acid, 2,2′-thiodiacetic acid, 2,2′-thiobisacetic acid, mercaptodiacetic acid) (HOOCCH ₂ SCH ₂ COOH), methionol (other name: _{3-methylthio-1-propanol) (CH 3 SC 3 H 6} OH), thiodiglycol (another name: 2,2'-thio _{diethanol) (HOC 2 H 5 SC 2} H 5 OH), thiomorpholine ( One or more selected from C ₄ H ₉ NS), thiazole (C ₃ H ₃ NS) and benzothiazole (C ₇ H ₅ NS) are preferable. Among these, methionine and thiodiglycolic acid are preferable because they have an excellent effect of suppressing the autolysis of hydrazine, are easily available, and are inexpensive.

As the sulfur-containing compound other than the sulfide compound, more specifically, saccharin (another name: o-benzoic acid sulfimide, o-sulfobenzimide) (C ₇ H ₅ NO ₃ S), sodium dodecyl sulfate (C ₁₂ H ₂₅ OS(O) ₂ ONa), dodecylbenzenesulfonic acid (C ₁₂ H ₂₅ C ₆ H ₄ S(O) ₂ OH), sodium dodecylbenzenesulfonate (C ₁₂ H ₂₅ C ₆ H ₄ S(O) ₂ ONa) ), sodium bis(2-ethylhexyl) sulphosuccinate (other names: sodium 2-diethylhexyl sulfosuccinate, dioctyl sodium sulfosuccinate) (NaOS(O) ₂ CH(COOCH ₂ CH(C ₂ H ₅ )C ₄ One or more selected from H ₉ )CH ₂ (COOCH ₂ CH(C ₂ H ₅ )C ₄ H ₉ ) and thiourea (H ₂ NC(S)NH ₂ ) are preferable. Among them, saccharin and thiourea are preferable because they are water-soluble and have an excellent effect of suppressing hydrazine self-decomposition, are easily available, and are inexpensive.

The action of the above-mentioned sulfur-containing compound as a hydrazine self-decomposition suppression auxiliary agent and a nickel particle mutual connection suppressing agent can be presumed as follows. That is, the sulfur-containing compound is a sulfide group (-S-), a sulfonyl group (-S(=O) _2- ), a sulfonic acid group (-S(=O) _2- O-), a thioketone group (-) in the molecule. -C(=S)-) is adsorbed on the nickel surface of the nickel particles by intermolecular force, but by itself, it does not have a large effect of covering and protecting the nickel crystallization powder like the amine compound molecule described above. On the other hand, when an amine compound and a sulfur-containing compound are used together, when the amine compound molecule strongly adsorbs onto the surface of the nickel crystallization powder to protect it, a minute area that cannot be completely covered by the amine compound molecules may occur. However, since the sulfur-containing compound molecule covers the part by adsorption, the contact between the hydrazine molecule and the nickel crystallized powder in the reaction solution is more effectively prevented, and the nickel crystallized powder is further added. It is said that coalescence between them can be more strongly prevented and the above-mentioned action is exhibited.

Here, the ratio [mol%] of the above-mentioned sulfur-containing compound and nickel in the reaction liquid ((mol number of sulfur-containing compound/mol number of nickel)×100) is in the range of 0.01 mol% to 5 mol%, The range of 0.03 mol% to 2 mol% is preferable, and the range of 0.05 mol% to 1 mol% is more preferable. When the above-mentioned ratio is less than 0.01 mol%, the above-mentioned sulfur-containing compound is too small, and there is a possibility that the respective actions of the hydrazine self-decomposition suppression auxiliary agent and the nickel particle-coupling suppression agent cannot be obtained. On the other hand, even if the above ratio exceeds 5 mol %, the above-mentioned respective actions are not improved, so that only the amount of the sulfur-containing compound used is increased, the chemical cost is increased, and at the same time, the organic component is added to the reaction liquid. The chemical oxygen demand (COD) of the reaction waste liquid in the crystallization step increases and the cost of waste liquid treatment increases.

(G) Other inclusions In the reaction liquid of the crystallization step, in addition to the above-mentioned nickel salt, a salt of a metal nobler than nickel, a reducing agent (for example, hydrazine), an alkali hydroxide, an amine compound, a dispersant, A small amount of various additives such as complexing agents and defoaming agents may be contained. For example, when the appropriate amount of dispersant or complexing agent is used, it is possible to improve the graininess (sphericity) and surface smoothness of the nickel crystallization powder, or to reduce coarse particles. There is. Further, as for the defoaming agent, if an appropriate amount of defoaming agent is used, it is possible to suppress the foaming in the crystallization step due to the nitrogen gas (see the following formulas (2) to (4)) generated in the crystallization reaction. Thus, for example, it is possible to prevent the aqueous solution from overflowing the container. As the dispersant, a known substance can be used, and examples thereof include alanine (CH ₃ CH(COOH)NH ₂ ), glycine (H ₂ NCH ₂ COOH), and triethanolamine (N(C ₂ H ₄ OH) ₃ ), diethanolamine (alias: iminodiethanol) (NH(C ₂ H ₄ OH) ₂ ), and the like. Known substances can be used as the complexing agent, such as hydroxycarboxylic acid, carboxylic acid (organic acid containing at least one carboxyl group), hydroxycarboxylic acid salt, hydroxycarboxylic acid derivative, carboxylic acid salt or carboxylic acid. Examples thereof include acid derivatives, specifically tartaric acid, citric acid, malic acid, ascorbic acid, formic acid, acetic acid, pyruvic acid, and salts and derivatives thereof. Further, the defoaming agent is not particularly limited as long as it has excellent defoaming property under alkaline conditions, and an oil type or solvent type silicone or non-silicone defoaming agent can be used.

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

Here, a specific crystallization procedure is obtained by previously mixing a reducing agent solution and an alkali hydroxide solution with a nickel salt solution containing a nickel salt that is a substance to be reduced and a salt of a metal nobler than nickel. A procedure for preparing a reaction solution by adding and mixing a reducing agent (eg, hydrazine) and a reducing agent/alkali hydroxide solution containing an alkali hydroxide, and adding and mixing a reducing agent solution (eg, hydrazine solution) to the nickel salt solution. There are two types of procedures for 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 (for example, hydrazine) having a high alkalinity and an increased reducing power by alkali hydroxide is added to and mixed with a nickel salt solution containing a substance to be reduced, whereas in the latter, the reducing agent (for example, hydrazine) is mixed. There is a difference in that the pH is adjusted (increased) with alkali hydroxide to enhance the reducing power after being mixed in advance with a nickel salt solution containing a reduced product.

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 when the reaction solution is prepared, that is, when the reduction reaction starts (hereinafter referred to as the reaction start temperature) However, it depends on the nickel salt solution (a solution containing nickel salt and a salt of a metal that is more precious than nickel) and a reducing agent/alkali hydroxide solution whose alkalinity is increased by alkali hydroxide to increase the reducing power. When the time required for additive mixing (hereinafter sometimes referred to as the raw material mixing time) becomes longer, the alkalinity increases locally in the additive mixed region of the nickel salt solution and the reducing agent/alkali hydroxide solution from the stage during the additive mixing. As a result, the reducing power of hydrazine increases, and nucleation occurs due to a salt of a metal that is more precious than nickel that is a nucleating agent. Therefore, the closer to the end of the raw material mixing time the weaker the nucleation action of the added nucleating agent becomes, the greater the dependence of the nucleation on the raw material mixing time becomes, resulting in a finer nickel crystallization powder or a narrow particle size distribution. Tends to be difficult. This tendency is more remarkable 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 shorter, it is desirable to mix for a short time. However, considering the restrictions of the mass production facility, the mixing time of the raw materials is preferably 10 seconds to 180 seconds, and more preferably 20 seconds to 120 seconds, and more preferably 30 seconds to 80 seconds.

On the other hand, in the latter case (when adding an alkali hydroxide solution to a nickel salt/reducing agent solution in which a nickel salt solution and a reducing agent solution have been added and mixed), a nickel salt and a salt of a metal nobler than nickel is used. In the nickel salt/reducing agent solution containing the reducing agent, the reducing agent hydrazine is added and mixed in advance to obtain a uniform concentration. Therefore, the nucleation that occurs when the alkali hydroxide solution is added and mixed, the dependency of the alkali hydroxide on the raw material mixing time is not so large as in the former case, and the nickel crystallization powder is made finer or a narrow particle size distribution is obtained. There is a feature that it becomes easy. However, for the same reason as in the former case, it is desirable that the mixing time of the alkali hydroxide solution is short, and in consideration of the restrictions of the mass production facility, the mixing time is preferably 10 seconds to 180 seconds, It is preferably 20 seconds to 120 seconds, more preferably 30 seconds 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 premixing the reaction liquid before the reaction liquid is prepared, and the addition after the reaction liquid is prepared and the reduction reaction is started. There are two types of mixing 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 the sulfur-containing compound is added to the reaction solution in advance. There is an advantage that various actions of the amine compound and the sulfur-containing compound are manifested from the start point of the nucleation caused by the salt of a different metal (nucleating agent). On the other hand, the interaction of the amine compound or the sulfur-containing compound with the surface of the nickel particles, such as adsorption, may be involved in the nucleation and affect the particle size and particle size distribution of the obtained nickel crystallization powder.

On the contrary, in the latter case (when the reaction liquid is prepared and the amine compound or the sulfur-containing compound is added and mixed after the reduction reaction is started), after the very initial stage of the crystallization process in which nucleation caused by the nucleating agent occurs, , An amine compound and a sulfur-containing compound are added to and mixed with the reaction solution. Therefore, although the action of the amine compound or the sulfur-containing compound described above is somewhat delayed, the involvement of the amine compound or the sulfur-containing compound in the nucleation of the amine compound is eliminated, and the particle size or particle size distribution of the obtained nickel crystallization powder is the amine compound. It has the advantage that it is less susceptible to the effects of sulfur and sulfur-containing compounds, making it easier to control them. Here, the mixing time in the addition and mixing of the amine compound and the sulfur-containing compound to the reaction solution in this procedure may be added all at once within a few seconds, or may be performed by divided addition or dropwise addition over a few minutes to about 30 minutes. Good. As described above, the amine compound acts as a reduction reaction accelerator (complexing agent). Therefore, the slow addition causes the crystal growth to proceed slowly and the nickel crystallized powder becomes highly crystalline, but it also gradually acts on the suppression of hydrazine self-decomposition, which reduces the effect of reducing hydrazine consumption. The above-mentioned mixing time may be appropriately determined while considering the balance between them. The timing of addition and mixing of the amine compound and the sulfur-containing compound in the former procedure can be appropriately determined by comprehensively judging according to the purpose.

While adding the nickel salt solution and the reducing agent/alkali hydroxide solution, mixing and mixing the nickel salt solution and the reducing agent solution, and adding and mixing the nickel salt/reducing agent solution with the alkali hydroxide solution, stir the solution. Stir mixing is preferred. If the stirring and mixing property is good, the frequency of non-uniform nucleation will decrease depending on the location of nucleation, and the dependence of the nucleation on the raw material mixing time and alkali hydroxide mixing time as described above will decrease. Therefore, it becomes easy to miniaturize the nickel crystallized powder and obtain a narrow particle size distribution. As a method of stirring and mixing, a known method may be used, and it is preferable to use a stirring blade in terms of control of stirring and mixing properties and equipment cost.

(2-1-3. Reduction reaction)
In the crystallization step, nickel crystallized powder is obtained by reducing the nickel salt with hydrazine in the reaction solution in the presence of an alkali hydroxide and a salt of a metal nobler than nickel. In addition, if necessary, a very small amount of a specific amine compound or a sulfur-containing compound can act to significantly suppress the autolysis of hydrazine and cause a reduction reaction.

First, the reduction reaction in the crystallization step will be described. The reaction when nickel ions (Ni ²⁺ ) are crystallized to nickel (Ni) is a two-electron reaction of the following formula (1). Moreover, the reaction of hydrazine (N ₂ H ₄ ) is a four-electron reaction of 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 entire reduction reaction is represented by the following formula (3): And nickel hydroxide (Ni(OH) ₂ ) produced by the neutralization reaction of sodium hydroxide with sodium hydroxide are represented by the reaction of being reduced with hydrazine. Stoichiometrically (theoretical value), nickel (Ni) 1 0.5 mol of hydrazine (N ₂ H ₄ ) is required per mol.

Here, from the reduction reaction of hydrazine of the formula (2), it is understood that the stronger the alkalinity of hydrazine, the greater its reducing power. Alkali hydroxide is used as a pH adjuster for increasing the alkalinity of the reaction solution, and has a 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)

2NiCl ₂ +N ₂ H ₄ +4NaOH
→ 2Ni(OH) ₂ +N ₂ H ₄ +4NaCl
→2Ni↓+N ₂ ↑+4NaCl+4H ₂ O ・・・(3)

As described above, in the conventional crystallization step, the active surface of the nickel crystallization powder serves as a catalyst to promote the autolysis reaction of hydrazine represented by the following formula (4) and reduce hydrazine as a reducing agent. Besides, it was consumed in large quantities. Therefore, although depending on the crystallization conditions such as the reaction starting temperature, for example, about 2 moles of hydrazine to 1 mole of nickel, which is about four times the theoretical value required for the above reduction, is generally used. Further, as shown in the formula (4), a large amount of ammonia is by-produced in the autolysis of hydrazine, and ammonia is contained in the reaction liquid at a high concentration to generate a nitrogen-containing waste liquid. As described above, the use of an excessive amount of hydrazine, which is an expensive drug, and the cost of treating the nitrogen-containing waste liquid are factors that increase the production cost of nickel powder (wet nickel powder) by the wet method.

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

Therefore, in the method for producing a 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 autolysis reaction of hydrazine and significantly reduce the amount of expensive hydrazine used as a drug. It is preferable to reduce to. The specific amine compound can suppress the autolysis of hydrazine, (I) the molecules of the specific amine compound or the sulfur-containing compound are adsorbed on the surface of the nickel crystallization powder in the reaction solution, (II) A molecule of a specific amine compound or a sulfur-containing compound that physically interferes with the contact between the active surface of the nickel crystallized powder and the hydrazine molecule acts on the surface of the nickel crystallized powder to form a catalyst on the surface. It is considered that the activity is inactivated.

Conventionally, in the crystallization process by the wet method, 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 used. A complexing agent that is formed to increase the ionic nickel concentration is generally used as a reduction reaction promoter. However, these complexing agents such as tartaric acid and citric acid act as a self-decomposition inhibitor of hydrazine such as the above-mentioned specific amine compounds and sulfur-containing compounds, or coarse particles produced by the coupling of nickel particles with each other during crystallization. It does not act as a ligation inhibitor that makes it difficult to form

On the other hand, the specific amine compound has an advantage that it also functions as a complexing agent similarly to tartaric acid, citric acid, etc., and has the functions of a hydrazine autolysis inhibitor, a coupling inhibitor, and a reduction reaction accelerator. There is.

(2-1-4. Reaction start temperature)
The crystallization reaction in the crystallization step is, for example, a solution containing at least a water-soluble nickel salt or a salt of a metal nobler than nickel (nickel salt solution), a solution containing a reducing agent (eg hydrazine) and an alkali hydroxide (reduction It starts in the reaction liquid in which the agent/alkali hydroxide solution) is 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, and further preferably 60°C to 70°C. The temperature of each of the nickel salt solution and the reducing agent/alkali hydroxide solution is not particularly limited as long as the temperature of the mixed solution obtained by premixing them, that is, the reaction initiation temperature falls within the above temperature range, and is freely set. Can be set.

The higher the reaction initiation temperature is, the more the reduction reaction is promoted, and the nickel crystallized powder tends to be highly crystallized. On the other hand, however, the autolysis reaction of hydrazine is further promoted. As the consumption increases, the foaming of the reaction liquid tends to become severe. Therefore, if the reaction initiation temperature is too high, the amount of hydrazine consumed may significantly increase, or a large amount of foaming may prevent the crystallization reaction from continuing. On the other hand, if the reaction start temperature becomes too low, the crystallinity of the nickel crystallization powder will be significantly reduced, or the reduction reaction will be delayed and the crystallization process time will be greatly extended, decreasing the nickel powder productivity. Tend. For the above reasons, by setting the temperature range as described above, it is possible to inexpensively produce a high-performance nickel powder while suppressing the consumption of hydrazine and maintaining high productivity.

(2-2. Washing/filtration process)
In the method for producing nickel powder using the wet method as described above, hydrazine is often used as a reducing agent, so that the reaction solution becomes strongly alkaline (for example, about pH 14) as is clear from Patent Document 4 and the like. Is common. As shown in FIG. 1, in the crystallization step, a nickel powder slurry in which nickel crystallization powder was generated in the strongly alkaline reaction liquid was obtained by the reduction reaction of hydrazine, and the nickel crystallization powder was purified from the nickel powder slurry with pure water. The washing and filtering steps to obtain a nickel powder cake by filtering and collecting while washing with, and the drying step to obtain nickel crystallization powder (nickel powder) by drying (vacuum drying etc.) the nickel powder cake are the crystallization steps. It will be carried out subsequently.

Since the above washing/filtering step is usually carried out in the atmosphere, the resulting nickel powder cake is more or less exposed to the atmosphere to some extent during the washing/filtering step and before the drying in the drying step. It is unavoidable that oxidation of the crystallization powder occurs, and especially when carrying out the crystallization reaction on a mass production scale, it takes time to handle the nickel powder cake, unlike the handling of a small amount at the laboratory level. Oxidation of nickel crystallized powder due to exposure tends to proceed.

In the nickel powder cake obtained through the washing/filtering step in which the strongly alkaline nickel powder slurry (for example, about pH 14) is filtered and collected while being washed with pure water, the alkaline hydroxide having strong alkaline property is removed by washing. However, a small amount of alkali hydroxide may remain and remain in the nickel powder cake as a weakly alkaline deposit (for example, about pH 11). Therefore, when the nickel crystallized powder is oxidized in this state, the nickel ions (Ni ²⁺ ) generated by the oxidation easily form nickel hydroxide (Ni(OH) ₂ ) according to the equation (5). .. In a place where a large amount of nickel hydroxide is formed, as a result, the coarse particles 10 (having nickel hydroxide as a main component) in which nickel crystallization powders 1 (particle size 0.4 μm or less) are firmly solidified with nickel hydroxide 2 Coarse particles) (in many cases, particle diameters of 0.8 μm or more, see FIG. 2) are likely to occur.

[Chemical 5]
Ni ²⁺ +2OH ⁻ →Ni(OH) ₂ (5)

Therefore, in the present invention, in the washing process of the washing/filtering step, a step of neutralizing the strongly alkaline nickel powder slurry or its diluted solution with an inorganic acid or an organic acid to pH 7.0 to pH 9.0 (neutralization step ) And nickel crystallization powder having a conductivity of 30 μS/cm to 1000 μS/cm, preferably 30 μS/cm to 500 μS/cm, and more preferably 30 μS/cm to 100 μS/cm. The crystallization step is performed by performing a step of washing the powder with pure water (washing step), and then separating the nickel crystallization powder from the liquid to obtain a nickel powder cake containing the neutralized adherent liquid (filtering step). At the same time, the residual amount of impurities (Na, Cl, etc.) due to the chemical agent used in step 1 is significantly reduced, and at the same time, the alkalinity of the nickel powder cake attachment liquid is weakened, making it difficult to form nickel hydroxide (Ni(OH) ₂ ). Even if the degree of cleaning is low, the generation of coarse particles containing nickel hydroxide as a main component as described above is significantly suppressed.

(2-2-1. Washing/Filtration Method and Procedure)
In the present invention, as shown in FIG. 3, a strong alkaline nickel powder slurry (for example, about pH 14) obtained in the crystallization step is washed with nickel in a process of washing the nickel crystallization powder using a general-purpose washing method. The alkaline nickel powder slurry or its diluted solution is neutralized with an inorganic acid or an organic acid to pH 7.0 to pH 9.0, and finally the nickel crystallization powder is a nickel powder cake containing the neutralized adhesion liquid. Is collected by filtration using a general-purpose solid-liquid separator.

The pH of the nickel powder slurry or its diluted solution when neutralized with an inorganic acid or an organic acid is preferably 7.0 to 9.0. When the pH is less than 7.0 in the neutralization process, that is, when an excessive amount of an inorganic acid or an organic acid is added, coarse particles containing nickel hydroxide as a main component may often be generated. Generation of coarse particles containing nickel hydroxide as a main component is suppressed as the pH is lowered by neutralizing the nickel powder slurry in a strongly alkaline state or its diluted solution, but the pH is adjusted to 9.0 by the neutralization treatment. The content below can sufficiently reduce the content of coarse particles containing nickel hydroxide as a main component in the nickel powder.

The above-mentioned general-purpose cleaning method is, specifically, repeated decantation and deionized water dilution, concentration of nickel crystallization powder by a solid-liquid separation device (concentration of slurry or cake formation), and deionized pulp (added deionized water). Re-slurrying) and repeated washing of pure water to the concentrate (cake) of the nickel crystallization powder in the solid-liquid separator, but not limited thereto. Specific examples of the general-purpose solid-liquid separator include, but are not limited to, Denver filter, filter press, centrifuge, decanter, and the like.

The pure water used for the above cleaning is generally of high purity with a conductivity of 1 μS/cm or less. Distilled water or ultrapure water (conductivity: ≦0.06 μS/cm) can be used instead of pure water, but it is preferable to use pure water that is inexpensive and easily available.

As a concrete procedure for neutralizing the nickel powder slurry with an inorganic acid or an organic acid, it is also possible to directly mix and add the inorganic acid or the organic acid and an aqueous solution thereof to the strongly alkaline nickel powder slurry (for example, about pH 14). However, in that case, a large amount of inorganic acid or organic acid is required for neutralization, which may be disadvantageous in terms of cost and workability. Therefore, preferably, the supernatant liquid of the nickel powder slurry is once removed by a method such as decantation to reduce the amount of alkali components in the nickel powder slurry, and then the inorganic acid or organic acid and their aqueous solution are mixed and added. It's good to mix.

If the nickel powder slurry is, for example, strongly alkaline with a pH of about 14, even if the conductivity of the cleaning solution is reduced to about 100 μS/cm by washing with pure water as it is, the pH of the cleaning solution remains strongly alkaline with about 11 However, in the method of neutralizing with an inorganic acid or an organic acid of the present invention, when the conductivity of the cleaning liquid is reduced to about 100 μS/cm, the pH of the cleaning liquid is reduced to about 9 or less even if it is high. It is possible to

(2-2-2. Drug used for neutralization)
The chemical used for neutralizing the nickel powder slurry or its diluted solution may be one or more selected from inorganic acids and organic acids, and is not particularly limited as long as it is easily soluble in water. Specifically, hydrochloric acid (HCl), nitric acid (HNO ₃ ), sulfuric acid (H ₂ SO ₄ ), carbonic acid (H ₂ CO ₃ ), and the like can be used as the inorganic acid, and acetic acid ( CH ₃ COOH), citric acid (C(OH)(CH ₂ COOH) ₂ COOH), ascorbic acid (C ₆ H ₈ O ₆ ) and the like can be used. These inorganic acids and organic acids may be used for neutralization as they are, but from the viewpoint of easy handling, it is more preferable to use them in the form of an aqueous solution. For example, in the case of using carbonic acid, carbon dioxide (CO ₂ ) may be blown into a liquid (a nickel powder slurry or a diluted liquid thereof) so as to act as carbonic acid in the liquid for neutralization. Further, if an organic acid that forms a complex ion with nickel, such as citric acid, is used, an effect of preventing oxidation of the nickel crystallized powder can be expected.

In the present invention, in the washing/filtering step, the washing step can be performed after the neutralization step. Also, the neutralization step may be performed after the washing step.

(2-3. Drying process)
The nickel powder cake containing the neutralized adhesion liquid obtained in the washing/filtration step is heated to 50 to 50 using a general-purpose drying device such as an air dryer, a hot air dryer, an inert gas atmosphere dryer and a vacuum dryer. It is possible to obtain a nickel crystallization powder (nickel powder) by drying at 300°C, preferably 80 to 150°C. If necessary, after substituting the water adhered in the nickel powder cake with a low temperature volatile organic solvent such as ethanol, it is dried with the above inert gas atmosphere dryer or vacuum dryer, resulting in a large surface tension of water. It is also possible to weaken the dry agglomeration between the nickel particles which occurs during the drying.

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 device such as an inert gas atmosphere dryer or a vacuum dryer, it is simply dried. In addition, it is possible to obtain heat-treated nickel powder.

(2-4. Crushing process (post-treatment process))
As described above, the nickel crystallized powder (nickel powder) obtained through the crystallization step, the washing/filtration step, and the drying step, if an amine compound or a sulfur-containing compound is added as necessary, those It acts as a coupling inhibitor for nickel particles during nickel crystallization. Therefore, coarse particles formed by the nickel particles being connected to each other in the process of reduction precipitation (hereinafter, sometimes referred to as “coarse coarse particles” in order to distinguish them from “coarse particles containing nickel hydroxide as a main component”). .) is not so large in the first place. However, depending on the crystallization procedure and crystallization conditions, the content ratio of the connected coarse particles may be somewhat large, which may cause a problem. In this case, a crushing step is provided subsequent to the crystallization step, and the connected coarse particles in which the nickel particles are connected can be divided at the connecting portion to reduce the connected coarse particles. In the crushing process, apply dry crushing methods such as spiral jet crushing and counter jet mill crushing, wet crushing such as high-pressure fluid collision crushing, and other general-purpose crushing methods. Is possible.

In addition, the above-mentioned coarse particles mainly composed of nickel hydroxide in which nickel crystallized powders (particle size 0.4 μm or less) are firmly solidified with nickel hydroxide are prepared by using the above-mentioned various general-purpose crushing methods. Since it cannot be easily crushed, effective measures for suppressing coarse particles containing nickel hydroxide as a main component are very important, and the present invention is extremely useful from this point of view.

Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to the following Examples. In addition, as the characteristics of the nickel powder, the average particle diameter and the content of coarse particles are evaluated as follows.

(Average particle size)
The nickel powder obtained in the present invention has a substantially spherical particle shape, but its average particle size is an observation image of the nickel powder using a scanning electron microscope (SEM, manufactured by JEOL Ltd., JSM-7100F) ( It is the number average particle size based on the particle size obtained from the image analysis result of (SEM image).

(Content of coarse particles)
0.05 g of the nickel powder obtained in Examples and Comparative Examples was ultrasonically dispersed in 100 mL of a 0.1 mass% sodium hexametaphosphate oxide aqueous solution to obtain a nickel powder dispersion. The dispersion liquid is filtered through a membrane filter having a pore size of 0.8 μm or a pore size of 1.2 μm, and a size larger than the pore size of each membrane filter (size exceeding 0.8 μm, or exceeding 1.2 μm is present on the filter). Size) coarse particles are supplemented, and the amount of the coarse particles is calculated by ICP emission spectroscopy (high-frequency inductively coupled plasma emission spectroscopy) of a solution in which all of the coarse particles are dissolved in acid, and contained in the nickel powder. The content of coarse particles (when the particle size exceeds 0.8 μm and when the particle size exceeds 1.2 μm) was determined.

In principle, the content of the coarse particles includes (1) coarse nickel particles having a particle size of 0.8 μm or 1.2 μm alone, and (2) nickel particles having a particle size of 0.4 μm or less ( Coarse coarse particles in which nickel crystallization powders) are connected to each other on the surface of nickel particles in the crystallization process (reduction precipitation process) to have a size exceeding 0.8 μm or 1.2 μm, (3) particle size 0.4 μm or less Coarse particles containing nickel hydroxide as a main component, whose size is 0.8 μm or more than 1.2 μm due to solidification of nickel particles (nickel crystallization powder) in Example 2 by nickel hydroxide generated by oxidation (see FIG. 2). ), in all cases, the coarse particles of ((1) to (3)) are included.

However, in this example, as described above, the nickel powder manufactured by the wet method that can obtain the nickel powder having a narrow particle size distribution was used. Therefore, coarse nickel particles having a particle size of 0.8 μm or 1.2 μm alone are not generated, and it is not necessary to consider the case of (1) above. Furthermore, the connected coarse particles produced by the nickel particles (nickel crystallization powder) having a particle size of 0.4 μm or less that are connected on the nickel particle surface during the crystallization process (reduction precipitation process) adopt appropriate crystallization conditions. If so, the content is not so large in the first place, and the connection strength between nickel particles is not so strong. Therefore, as described above, if crushing treatment is performed after crystallization, even if the content ratio of the connected coarse particles becomes somewhat large, the connected coarse particles are divided at the connecting portion to form the connected coarse particles. Can be set to 0.8 μm or less, so that the case of (2) above need not be considered. Therefore, the coarse particles calculated by the ICP emission spectroscopy are only in the case of (3), and the content of the coarse particles exceeding the particle diameter of 0.8 μm (or the particle diameter of 1.2 μm) in the present invention is It may be considered as the content of coarse particles containing nickel hydroxide as a main component and having a particle size of 0.8 μm (or a particle size of 1.2 μm). Coarse particles containing nickel hydroxide having a size of 0.8 μm or more than 1.2 μm as a main component are formed by encapsulating a plurality of nickel particles (nickel crystallization powder) by nickel hydroxide generated on the surface of the nickel crystallization powder. This is because, since the coarse particles are firmly bonded, they will not be loosened even if the above-mentioned crushing treatment is performed, and they will remain in the nickel powder as coarse particles of the same size.

(Coarse particles containing nickel hydroxide as the main component)
The coarse particles having a size of more than 0.8 μm or 1.2 μm captured on the membrane filter as described above are, as shown in FIG. 2, a plurality of nickel particles (nickel particles (nickel nickel) entrapped in a matrix made of nickel hydroxide. The crystallized powder) has a structure in which it is firmly bonded via a nickel hydroxide matrix. The matrix (reference numeral 2 in FIG. 2) having nickel hydroxide (Ni(OH) ₂ ) as a main component means that coarse particles having a size of 0.8 μm or more than 1.2 μm captured on the membrane filter. In (a) SEM-EDX measurement of the matrix portion, many locations where the molar ratio of nickel and oxygen is about Ni:O=1:2 are observed, and (b) 0.8 μm recovered from above the membrane filter. It has been confirmed that nickel hydroxide (Ni(OH) ₂ ) is detected as the main component in the measurement result of coarse particles having a size of 1.2 μm or more by XPS.

(Example 1)
[Preparation of solution of nickel salt and salt of metal 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 the autolysis of hydrazine. 1.271 g of L-methionine (CH ₃ SC ₂ H ₄ CH(NH ₂ )COOH, molecular weight: 149.21) containing one, palladium (II) ammonium chloride (also known as tetra 0.134 mg of ammonium chloropalladium(II) acid ((NH ₄ ) ₂ PdCl ₄ , molecular weight: 284.31) was dissolved in 1880 mL of pure water to obtain a nickel salt as a main component, a sulfur-containing compound, and nickel. A nickel salt solution, which is an aqueous solution containing a nucleating agent which is a metal salt of a noble metal, was prepared. Here, in the nickel salt solution, the amount of L-methionine, which is a sulfide compound, was as small as 0.5 mol% (0.005 in molar ratio) with respect to nickel, and palladium was 0.28 mol ppm (0.50) with respect to nickel. Mass ppm).

[Preparation of reducing agent solution]
Commercially available industrial-grade 60 mass% hydrazine hydrazine (Mc Otsuka Chemical Co., Ltd.) prepared by diluting hydrazine hydrate (N ₂ H ₄ ·H ₂ O, molecular weight: 50.06) with pure water 1.67 times as a reducing agent. 207 g (manufactured by the company) was weighed to prepare a reducing agent solution which is an aqueous solution containing no hydrazine as a main component and containing no alkali hydroxide. Hydrazine contained in the reducing agent solution was prepared so that the molar ratio to nickel in the nickel salt solution was 1.46.

[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 a main component. Sodium hydroxide contained in the alkali hydroxide solution was prepared so that the molar ratio to nickel in the nickel salt solution was 5.75.

[Amine compound solution]
Ethylenediamine (abbreviation: EDA), which is an alkyleneamine containing two primary amino groups (—NH ₂ ) in the molecule, as an amine compound as an inhibitor of hydrazine self-decomposition and a 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 was 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% (0.01 in molar ratio) with respect to nickel in the nickel salt solution. The materials used in 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% by mass hydrazine hydrate.

[Crystallization process]
A nickel salt solution obtained by dissolving nickel chloride and a palladium salt in pure water was placed in a Teflon (registered trademark)-coated stainless steel container with stirring blades, heated while stirring to a liquid temperature of 85°C, and then a liquid temperature of 25°C. The reducing agent solution containing hydrazine and water was added and mixed at a mixing time of 20 seconds to obtain a nickel salt/reducing agent-containing liquid. To the nickel salt/reducing agent-containing liquid, the alkali hydroxide solution having a liquid temperature of 25° C. and water is added and mixed at a mixing time of 80 seconds, and a reaction liquid having a liquid temperature of 70° C. (nickel chloride+palladium salt) is added. +hydrazine+sodium hydroxide) was prepared and the reduction reaction (crystallization reaction) was started. The reaction start temperature was 63°C. After the start of the reaction, the above amine compound solution was added dropwise to the above reaction solution for 10 minutes from 8 minutes to 18 minutes, and the reduction reaction was promoted while suppressing the autolysis of hydrazine to react the nickel crystallized powder. It was crystallized in the liquid. It was confirmed that the reduction reaction of the above formula (3) was completed within 60 minutes from the start of the reaction, the supernatant of the reaction solution was transparent, and all the nickel components in the reaction solution were reduced to metallic nickel. ..

The amount of 60% by mass hydrazine hydrate consumed in the crystallization reaction was 171 g, and the molar ratio to nickel was 1.20 with respect to 207 g of 60% by mass hydrazine hydrate blended in the reducing agent solution. Here, since the molar ratio of hydrazine consumed in the reduction reaction to nickel is assumed to be 0.5 from the above formula (3), the molar ratio of hydrazine consumed in autolysis to nickel is 0.70. It is estimated that there was.

[Washing/filtration process]
In the crystallization step, a strong alkaline (pH: 14.1) nickel powder slurry in the form of a slurry is obtained as a reaction final solution containing nickel crystallized powder, and this nickel powder slurry contains mercaptoacetic acid (thioglycolic acid) ( After adding an aqueous solution of HSCH ₂ COOH and a molecular weight of 92.12) to the surface treatment (sulfur coating treatment) of the nickel crystallization powder, the nickel crystallization powder is allowed to settle by allowing it to stand, and the supernatant liquid is used as a reaction liquid. Of about 50% was decanted. Pure water having a conductivity of 1 μS/cm was added to the nickel powder slurry in the same amount as the removed supernatant liquid to dilute (pH: 13.8), and then a 20 mass% sulfuric acid (H ₂ SO ₄ ) aqueous solution was added. In addition, the solution was neutralized and the pH of the solution was adjusted to 8.0. Then, using the above pure water, suction is performed using a Buchner funnel (filter paper: 5C) until the conductivity of the filtrate obtained by filtering the surface-treated slurry containing nickel crystallization powder is 100 μS/cm. After filtering and washing, solid-liquid separation was performed to obtain a nickel powder cake. Table 1 shows the agents used for neutralization and the pH of the solution after neutralization. Similarly, Table 1 shows the chemicals used for neutralization and the pH of the liquid after neutralization in Examples 2 to 10 and Comparative Examples 1 to 3 described later.

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

[Crushing process (post-process)]
The crystallization step, the washing/filtration step, and the drying step were followed by a crushing step to reduce the coarse particles formed mainly by the connection of nickel particles in the nickel powder. Specifically, the nickel crystallized powder (nickel powder) obtained in the crystallization step was subjected to a spiral jet disintegration treatment which is a dry disintegration method. Through the above steps, the nickel powder according to Example 1 produced using the wet method was obtained.

(Physical properties of nickel powder)
The average particle size of the obtained nickel powder was 0.20 μm. Further, the content of coarse particles containing nickel hydroxide as a main component having a particle size of 0.8 μm is 40 mass ppm, and the content of coarse particles containing nickel hydroxide having a particle size of 1.2 μm as a main component is It was 10 mass ppm or less. Table 1 shows the content of coarse particles containing nickel hydroxide having a particle size of more than 0.8 μm as a main component and the content of coarse particles containing nickel hydroxide having a particle size of more than 1.2 μm as a main component. Similarly, Table 1 also shows the content of coarse particles in Examples 2 to 10 and Comparative Examples 1 to 3 described later.

(Example 2)
In the washing/filtering step, nickel crystallization powder (nickel crystallization powder (nickel nickel) was used as in Example 1 except that a 20 mass% sulfuric acid (H ₂ SO ₄ ) aqueous solution was added for neutralization to adjust the pH of the solution to 7.0. Powder) was obtained. Then, the above nickel crystallization powder (nickel powder) was subjected to the same spiral jet disintegration treatment as in Example 1. Through the above steps, the nickel powder according to Example 2 produced using the wet method was obtained.

(Physical properties of nickel powder)
The average particle size of the obtained nickel powder was 0.20 μm. Further, the content of coarse particles containing nickel hydroxide as a main component having a particle size of 0.8 μm is 40 mass ppm, and the content of coarse particles containing nickel hydroxide having a particle size of 1.2 μm as a main component is It was 10 mass ppm or less.

(Example 3)
In the washing/filtering step, nickel crystallization powder (nickel crystallization powder (nickel nickel) was used as in Example 1 except that a 20% by mass aqueous solution of sulfuric acid (H ₂ SO ₄ ) was added for neutralization to adjust the pH of the solution to 9.0. Powder) was obtained. Then, the above nickel crystallization powder (nickel powder) was subjected to the same spiral jet disintegration treatment as in Example 1. Through the above steps, the nickel powder according to Example 3 produced using the wet method was obtained.

(Physical properties of nickel powder)
The average particle size of the obtained nickel powder was 0.20 μm. In addition, the content of coarse particles containing nickel hydroxide as a main component having a particle size of more than 0.8 μm is 60 mass ppm, and the content of coarse particles containing nickel hydroxide having a particle size of more than 1.2 μm as a main component is It was 15 mass ppm or less.

(Example 4)
In the washing/filtering step, nickel crystallization powder (nickel powder) was obtained in the same manner as in Example 1 except that 10% by mass hydrochloric acid (HCl) aqueous solution was added for neutralization to adjust the pH of the solution to 8.0. Obtained. Then, the above nickel crystallization powder (nickel powder) was subjected to the same spiral jet disintegration treatment as in Example 1. Through the above steps, the nickel powder according to Example 4 produced using the wet method was obtained.

(Physical properties of nickel powder)
The average particle size of the obtained nickel powder was 0.20 μm. Further, the content of coarse particles containing nickel hydroxide as a main component having a particle size of 0.8 μm is 40 mass ppm, and the content of coarse particles containing nickel hydroxide having a particle size of 1.2 μm as a main component is It was 10 mass ppm or less.

(Example 5)
In the washing/filtering step, nickel crystallization powder (nickel powder) was obtained in the same manner as in Example 1 except that a 10 mass% nitric acid (HNO ₃ ) aqueous solution was added for neutralization to adjust the pH of the solution to 8.0. Got Then, the above nickel crystallization powder (nickel powder) was subjected to the same spiral jet disintegration treatment as in Example 1. Through the above steps, the nickel powder according to Example 5 produced using the wet method was obtained.

(Physical properties of nickel powder)
The average particle size of the obtained nickel powder was 0.20 μm. Further, the content of coarse particles containing nickel hydroxide as a main component having a particle size of 0.8 μm is 40 mass ppm, and the content of coarse particles containing nickel hydroxide having a particle size of 1.2 μm as a main component is It was 10 mass ppm or less.

(Example 6)
In the washing/filtering step, nickel crystallization powder (nickel powder) was obtained in the same manner as in Example 1 except that 10% by mass acetic acid aqueous solution was added for neutralization to adjust the pH of the solution to 8.0. Then, the above nickel crystallization powder (nickel powder) was subjected to the same spiral jet disintegration treatment as in Example 1. Through the above steps, the nickel powder according to Example 6 produced using the wet method was obtained.

(Physical properties of nickel powder)
The average particle size of the obtained nickel powder was 0.20 μm. Further, the content of coarse particles containing nickel hydroxide as a main component having a particle size of 0.8 μm is 40 mass ppm, and the content of coarse particles containing nickel hydroxide having a particle size of 1.2 μm as a main component is It was 10 mass ppm or less.

(Example 7)
In the washing/filtration step, nickel crystallization powder (nickel powder) was obtained in the same manner as in Example 1 except that 10% by mass citric acid aqueous solution was added for neutralization to adjust the pH of the solution to 8.0. .. Then, the above nickel crystallization powder (nickel powder) was subjected to the same spiral jet disintegration treatment as in Example 1. Through the above steps, the nickel powder according to Example 7 produced using the wet method was obtained.

(Physical properties of nickel powder)
The average particle size of the obtained nickel powder was 0.20 μm. Further, the content of coarse particles containing nickel hydroxide as a main component having a particle size of 0.8 μm is 40 mass ppm, and the content of coarse particles containing nickel hydroxide having a particle size of 1.2 μm as a main component is It was 10 mass ppm or less.

(Example 8)
In the washing/filtering step, nickel crystallization powder (nickel powder) was obtained in the same manner as in Example 1 except that 10% by mass ascorbic acid aqueous solution was added to neutralize the solution to adjust the pH to 8.0. .. Then, the above nickel crystallization powder (nickel powder) was subjected to the same spiral jet disintegration treatment as in Example 1. Through the above steps, the nickel powder according to Example 8 produced using the wet method was obtained.

(Physical properties of nickel powder)
The average particle size of the obtained nickel powder was 0.20 μm. Further, the content of coarse particles containing nickel hydroxide as a main component having a particle size of 0.8 μm is 40 mass ppm, and the content of coarse particles containing nickel hydroxide having a particle size of 1.2 μm as a main component is It was 10 mass ppm or less.

(Example 9)
In the washing/filtering process, the same procedure as in Example 1 was carried out except that carbon dioxide (CO ₂ ) was blown into the liquid to neutralize it with carbonic acid (H ₂ CO ₃ ) and the pH of the liquid was adjusted to 8.0. Crystallized powder (nickel powder) was obtained. Then, the above nickel crystallization powder (nickel powder) was subjected to the same spiral jet disintegration treatment as in Example 1. Through the above steps, the nickel powder according to Example 9 produced using the wet method was obtained.

(Physical properties of nickel powder)
The average particle size of the obtained nickel powder was 0.20 μm. Further, the content of coarse particles containing nickel hydroxide as a main component having a particle size of 0.8 μm is 40 mass ppm, and the content of coarse particles containing nickel hydroxide having a particle size of 1.2 μm as a main component is It was 10 mass ppm or less.

(Example 10)
In the washing/filtering step, carbonated water (water in which carbonic acid (H ₂ CO ₃ ) was dissolved) was added to the solution to neutralize the solution, and the procedure was performed in the same manner as in Example 1 except that the pH of the solution was adjusted to 8.0. A nickel crystallized powder (nickel powder) was obtained. Then, the above nickel crystallization powder (nickel powder) was subjected to the same spiral jet disintegration treatment as in Example 1. Through the above steps, the nickel powder according to Example 10 produced using the wet method was obtained.

(Physical properties of nickel powder)
The average particle size of the obtained nickel powder was 0.20 μm. Further, the content of coarse particles containing nickel hydroxide as a main component having a particle size of 0.8 μm is 40 mass ppm, and the content of coarse particles containing nickel hydroxide having a particle size of 1.2 μm as a main component is It was 10 mass ppm or less.

(Comparative Example 1)
In the washing/filtering process, after the surface treatment (sulfur coating) of the nickel crystallization powder was performed, neutralization was not performed, and the pH of the nickel powder slurry was 14.1 and the conductivity was 1 μS/cm pure water. Is filtered and washed until the conductivity of the filtrate filtered from the slurry containing the nickel-crystallized powder subjected to the surface treatment reaches 100 μS/cm (the pH of the liquid is 10.8), and solid-liquid separation is performed. A nickel powder cake was obtained. Other than this was performed in the same manner as in Example 1 to obtain a nickel crystallized powder (nickel powder). Then, the above nickel crystallization powder (nickel powder) was subjected to the same spiral jet disintegration treatment as in Example 1. Through the above steps, the nickel powder according to Comparative Example 1 produced using the wet method was obtained.

(Physical properties of nickel powder)
The average particle size of the obtained nickel powder was 0.20 μm. Further, the content of coarse particles containing nickel hydroxide as a main component having a particle size of 0.8 μm is 340 mass ppm, and the content of coarse particles containing nickel hydroxide having a particle size of 1.2 μm as a main component is It was 160 mass ppm.

(Comparative example 2)
In the washing/filtering step, nickel crystallization powder (nickel powder) was performed in the same manner as in Example 1 except that a 20 mass% sulfuric acid (H ₂ SO ₄ ) aqueous solution was added to neutralize the solution to adjust the pH to 6.0. ) Got. Then, the above nickel crystallization powder (nickel powder) was subjected to the same spiral jet disintegration treatment as in Example 1. Through the above steps, the nickel powder according to Comparative Example 2 produced using the wet method was obtained.

(Physical properties of nickel powder)
The average particle size of the obtained nickel powder was 0.20 μm. In addition, the content of coarse particles containing nickel hydroxide as a main component having a particle size of 0.8 μm is 520 mass ppm, and the content of coarse particles containing nickel hydroxide having a particle size of 1.2 μm as a main component is It was 200 mass ppm.

(Comparative example 3)
In the washing/filtering step, nickel crystallization powder (nickel powder) was carried out in the same manner as in Example 1 except that a 20% by mass aqueous solution of sulfuric acid (H ₂ SO ₄ ) was added to neutralize and the pH of the solution was adjusted to 10.0. ) Got. Then, the above nickel crystallization powder (nickel powder) was subjected to the same spiral jet disintegration treatment as in Example 1. Through the above steps, the nickel powder according to Comparative Example 3 produced using the wet method was obtained.

(Physical properties of nickel powder)
The average particle size of the obtained nickel powder was 0.20 μm. In addition, the content of coarse particles containing nickel hydroxide as the main component having a particle size of 0.8 μm is 260 mass ppm, and the content of coarse particles containing nickel hydroxide having a particle size of 1.2 μm as the main component is It was 120 mass ppm.

[Summary]
As is clear from the examples, according to the present invention, the content of coarse particles containing nickel hydroxide having a particle size of more than 0.8 μm as a main component is very small, and high flatness in a nickel paste dry film can be realized. It is obvious that a method for producing nickel powder and nickel particles can be provided. In particular, according to the present invention, it is possible to provide a method for producing nickel particles by a wet method, which can easily and easily produce nickel powder having a very small content of coarse particles containing nickel hydroxide as a main component. it can.

1 Nickel particles (nickel crystallization powder)
2 Nickel hydroxide produced by oxidation of nickel crystallization powder 10 Coarse particles containing nickel hydroxide as a main component

Claims (12)

It has a substantially spherical particle shape,
The number average particle diameter is 0.03 μm to 0.4 μm,
The content of coarse particles having a particle size of more than 0.8 μm and containing nickel hydroxide as a main component is 200 mass ppm or less,
Nickel powder, characterized in that the content of coarse particles containing nickel hydroxide as a main component and having a particle size of more than 1.2 μm is 100 mass ppm or less. The content of coarse particles containing nickel hydroxide as a main component is 100 mass ppm or less, the particle size is more than 0.8 μm, and the nickel hydroxide is a main component having a particle size of more than 1.2 μm. 2. The nickel powder according to claim 1, wherein the content of the coarse particles is 50 mass ppm or less. The method for producing the nickel powder according to claim 1 or 2, wherein
A reduction reaction is carried out in a reaction solution in which a water-soluble nickel salt, a salt of a metal nobler than nickel, a reducing agent, an alkali hydroxide and water are mixed to obtain a nickel powder slurry as a reaction final solution containing nickel crystallization powder. A crystallization process,
A washing/filtering step of washing and filtering nickel crystallization powder in the nickel powder slurry to obtain a nickel powder cake,
A step of drying the nickel powder cake to obtain nickel powder,
A neutralization step in which the washing/filtering step neutralizes the nickel powder slurry or a diluted solution thereof with one or more kinds selected from inorganic acids or organic acids to pH 7.0 to pH 9.0;
A washing step of washing the nickel crystallization powder so that the conductivity of the liquid containing the nickel crystallization powder is 30 μS/cm to 1000 μS/cm,
A method for producing nickel powder, comprising a step of filtering the washed nickel crystallization powder from the liquid to obtain the nickel powder cake after performing the neutralization step and the washing step. The method of claim 3, wherein the washing/filtering step includes performing the washing step after the neutralizing step. The method for producing nickel powder according to claim 3, wherein the strongly alkaline reaction liquid contains an amine compound or a sulfur-containing compound. The inorganic acid contains any one of hydrochloric acid (HCl), nitric acid (HNO ₃ ), sulfuric acid (H ₂ SO ₄ ), and carbonic acid (H ₂ CO ₃ ), any one of claims 3 to 5. The method for producing the nickel powder according to item 1. The organic acid comprises any one of acetic acid (CH ₃ COOH), citric acid (C(OH)(CH ₂ COOH) ₂ COOH), and ascorbic acid (C ₆ H ₈ O ₆ ). Item 7. A method for producing a nickel powder according to any one of Items 3 to 6. The amine compound is at least one of an alkyleneamine and an alkyleneamine derivative, and has at least a structure represented by the following formula A in which a nitrogen atom of an amino group in the molecule is bonded via a carbon chain having 2 carbon atoms. The method for producing a nickel powder according to any one of claims 5 to 7, wherein:
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 ( _{H 2 N (C 2 H 4} NH) 2 C 2 H 4 NH 2), tetraethylene pentamine _{(H 2 N (C 2 H} 4 NH) 3 C 2 H 4 NH 2), pentaethylenehexamine _(H 2 N (C ₂ H ₄ NH) ₄ C ₂ H ₄ NH ₂ ) and one or more selected from propylenediamine (CH ₃ CH(NH ₂ )CH ₂ NH ₂ ),
When the amine compound is the alkylene amine derivatives, the alkylene amine 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 _{2 CH (NH) COOH),} 1,2- cyclohexanediamine _{(H 2 NC 6 H 10 NH} 2), ethylenediamine -N, N'-diacetic acid _{(HOOCCH 2 NHC 2 H 4 NHCH} 2 COOH), N, N ' - diacetylethylenediamine _{(CH 3 CONHC 2 H 4 NHCOCH} 3), N, N'- dimethylethylenediamine _{(CH 3 NHC 2 H 4 NHCH} 3), N, N'- diethylethylenediamine _{(C 2 H 5 NHC 2 H} 4 NHC 2 H _5), N, are selected from 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 method for producing nickel powder according to claim 8, wherein the nickel powder is one or more kinds. In the molecule, the sulfur-containing compound has a sulfide group (-S-), a sulfonyl group (-S(=O) _2- ), a sulfonic acid group (-S(=O) _2- O-), a thioketone group ( The method for producing nickel powder according to claim 5, wherein the nickel powder is at least one selected from compounds containing at least one of -C(=S)-). Said sulfur-containing compound, 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), thio diglycolic acid _{(HOOCCH 2} SCH ₂ COOH), Mechionoru _{(CH 3 SC 3 H 6 OH} ), thiodi glycol _{(HOC 2 H 5 SC 2 H} 5 OH), thiomorpholine _{(C 4} H 9 NS), thiazole _{(C 3} H ₃ NS), benzothiazole _{(C 7} H 5 NS), saccharin _{(C 7} H 5 NO ₃ S), sodium dodecyl sulfate _{(C 12 H 25 OS (O} ) 2 ONa), dodecylbenzene sulfonic acid _{(C 12 H 25 C 6 H} 4 S (O) 2 OH), sodium dodecyl benzene sulfonate _(C 12 _{H 25 C 6 H 4 S (O)} 2 ONa), sulfosuccinic di-2-ethylhexyl sodium _{(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 the production of nickel powder according to any one of claims 5 to 10, characterized in that it thiourea _{(H 2 NC (S) NH} 2) from one or more selected Method. 12. The washing/filtering step includes a supernatant liquid removing step of decanting the nickel powder slurry and then removing the supernatant liquid before the neutralization step, according to any one of claims 3 to 11. A method for producing the nickel powder described.