JP2021155840A - Nickel particles, surface treatment method for nickel particles, and manufacturing method for nickel powder - Google Patents

Abstract

Kind Code: A1 Provided are nickel particles that suppress generation of coarse particles due to oxidation during storage, a surface treatment method for nickel particles, and a method for producing nickel powder. A Lewis base-containing nickel, wherein a nitrogen-containing Lewis base is present on the surface of nickel particles, and the mass ratio of the Lewis base to the nickel particles is 0.16 to 3.0:100. particle. [Selection drawing] Fig. 2

Description

The present invention relates to nickel particles, a method for treating the surface of nickel particles, and a method for producing nickel powder.

Nickel particles are used as a material for conductive paste for producing thick-film conductors, and are used for forming electric circuits and electrodes for multilayer ceramic parts such as multilayer ceramic capacitors (MLCCs) and multilayer ceramic substrates. It is used.

The MLCC in which this electrode is used is manufactured by the following method, for example, when nickel particles are used in the metal powder.

First, a conductive paste obtained by kneading nickel particles, a resin such as ethyl cellulose, and an organic solvent such as tarpineol is screen-printed on a dielectric green sheet (ceramic green sheet) having a thickness of 10 μm or less. Then, it is dried to prepare a nickel coating film for an internal electrode.

Next, the printed nickel coating film for the internal electrode and the dielectric green sheet are laminated so as to be alternately overlapped, and pressure-bonded to prepare a laminated body.

The prepared laminate is cut to a predetermined size, subjected to a binder removal treatment for burning and removing a resin such as ethyl cellulose used as an organic binder, and then a dielectric obtained by firing at a high temperature of about 1300 ° C. and an internal electrode. Sintering of the (nickel film) is advanced to obtain a ceramic body in which the dielectric layer and the internal electrode layer are laminated on each other. Then, an external electrode is attached to this ceramic body to form a multilayer ceramic capacitor.

The binder removal treatment of the laminate is performed in an atmosphere containing an extremely small amount of oxygen so that the nickel particles are not oxidized.

Generally, the nickel paste used for the internal electrode of MLCC is produced by kneading nickel powder in a vehicle and contains a large amount of agglomerates of nickel powder. In the nickel powder manufacturing process, a drying step is usually included at the final stage regardless of the nickel powder manufacturing method (gas phase method, liquid phase method). Since the drying treatment in this drying step promotes the agglomeration of nickel particles, the obtained nickel powder generally contains agglomerates generated during drying as coarse particles.

In recent years, MLCCs are required to increase the number of layers of ceramic green sheets with internal electrode layers from several hundred layers to about 1,000 layers in order to achieve small size and large capacity. For this reason, studies have been made to reduce the thickness of the internal electrode layer from the conventional several micron level to the submicron level, and along with this, the particle size of nickel powder of the electrode material for the internal electrode has been reduced. There is.

However, the smaller the particle size, the larger the surface area of the nickel powder, and the larger the surface energy, which makes it easier to form aggregates. Further, metal powders such as nickel powder have poor dispersibility, and if aggregates are present, the nickel powder penetrates the ceramic sheet layer when the nickel powder is sintered in the firing process during MLCC production, and the electrodes are short-circuited. There is a risk that defective products will be generated. Further, even if the ceramic sheet layer cannot be penetrated, a partial current concentration may occur due to the shortening of the distance between the electrodes in the MLCC, and this current concentration causes deterioration of the life of the multilayer ceramic capacitor. It was. As described above, in MLCC, it is important to produce a nickel paste containing a small amount of coarse particles including aggregates and to obtain a smooth internal electrode having no unevenness on the surface. Further, since there is a concern that the presence of agglomerates of nickel particles may cause product defects, it is desired to improve the surface condition of nickel particles so that agglomerates do not occur.

Patent Document 1 discloses a technique for oxidizing the surface of nickel particles. Nickel powder produced by the liquid phase method is added to pure water to form a slurry, and then oxidized with hydrogen peroxide. The technical matters are disclosed. However, the surface oxidation treatment with hydrogen peroxide needs to be carried out in an aqueous system, and is not suitable when a non-aqueous organic compound is used as the surface treatment agent.

Japanese Unexamined Patent Publication No. 11-343501

If the nickel powder is stored, it may be oxidized by oxygen in the air over time to form nickel hydroxide on the surface. The coarse particles of nickel particles may be generated by firmly solidifying adjacent nickel particles with nickel hydroxide on the surface. Therefore, it is particularly important for the nickel powder used for MLCC to suppress the oxidation of the nickel powder during storage so that problems do not occur due to the generation of coarse particles due to the oxidation during storage.

The present invention has been proposed in view of such circumstances, and provides nickel particles, a method for surface-treating nickel particles, and a method for producing nickel powder, in which the generation of coarse particles due to oxidation during storage is suppressed. With the goal.

The present inventors have made extensive studies to solve the above-mentioned problems. As a result, they have found that by coating the nickel particles with a Lewis base compound, the aggregation of the nickel particles can be suppressed and the generation of coarse particles can be suppressed, and the present invention has been completed.

In order to solve the above problems, in the Lewis base-containing nickel particles of the present invention, the Lewis base containing nitrogen is present on the surface of the nickel particles, and the mass ratio of the Lewis base to the nickel particles is 0. 16 to 3.0: 100.

The Lewis base may be coordinated to the surface of the nickel particles.

The Lewis base may contain a compound represented by the following formula (1).

In formula (1), R ¹ represents an alkyl group having 1 to 18 carbon atoms or an alkenyl group having 1 to 18 carbon atoms, R ² represents an alkylene group having 1 to 6 carbon atoms, and R ³ and R. ⁴ indicates H or CH ₃ .

The Lewis base may contain one or more selected from N-oleoyl sarcosine, N-lauroyl sarcosine, and myristylmethyl-β-alanine.

The Lewis base-containing nickel particles of the present invention have a number average particle size of 0.03 μm to 0.4 μm, a particle content of particles having a particle size of more than 0.8 μm of 400 mass ppm or less, and a particle size of 1. The content of particles exceeding 2 μm may be 200 mass ppm or less.

Further, in order to solve the above problems, the surface treatment method for nickel particles of the present invention includes a mixing step of mixing nickel particles and a Lewis base containing nitrogen.

Further, in order to solve the above problems, the method for producing nickel powder of the present invention includes a drying step of drying the surface-treated nickel particles after the above mixing step.

According to the present invention, it is possible to provide nickel particles, a method for surface-treating nickel particles, and a method for producing nickel powder, in which the generation of coarse particles due to oxidation during storage is suppressed.

It is a flow chart which showed the surface treatment method of nickel particles of this invention and the manufacturing method of nickel powder as a series of steps. 3 is an SEM photograph of nickel particles of Example 1 and Comparative Example 2.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a flow chart showing a method for surface-treating nickel particles and a method for producing nickel powder of the present invention as a series of steps. However, the present invention is not limited to the following embodiments.

[Surface treatment method for nickel particles]
<Nickel particles to be surface treated>
As the nickel particles to be surface-treated, various nickel powders can be used regardless of the production method such as a wet method or a dry method. For example, nickel powder obtained by a so-called dry method such as a CVD method, an evaporation quenching method, or a hydrogen reduction method using a nickel salt or a nickel hydroxide can be used as the nickel particles to be treated. Further, nickel powder obtained by a so-called wet method such as a wet reducing method using a reducing agent such as hydrazine with respect to a nickel salt solution can be used as the nickel particles to be treated. Among them, nickel powder produced by a so-called wet method such as a wet reduction method is suitable as a material for MLCC because it is spherical and has a small variation in particle size.

<Mixing process>
The method for surface-treating nickel particles includes a mixing step of mixing the nickel particles with a nitrogen-containing Lewis base. By the mixing step, the surface of the nickel particles can be surface-treated with a nitrogen-containing Lewis base.

(Nickel slurry)
Examples of the method of surface-treating the nickel particles using the Lewis base include a method of bringing the nickel particles into contact with the Lewis base by wet mixing using various solvents including alcohol as a medium. That is, by adding and mixing a nickel slurry in which nickel particles are dispersed in various solvents containing alcohol and a Lewis base containing nitrogen in various solvents containing alcohol to form a slurry, the particle surface of the nickel particles is made uniform. Can be processed into.

In the mixing step, the nickel particles to be surface-treated may be added and mixed with the solution in which the Lewis base is dissolved, or the Lewis base may be added and mixed with the nickel slurry. However, from the viewpoint of effectively and uniformly treating the surface of fine nickel particles, it is preferable to dissolve the Lewis base in various solvents including alcohol in advance.

Specifically, the nickel slurry can be agitated, a Lewis base solution in which the Lewis base is dissolved is dropped and mixed, and then the mixed solution is agitated to perform surface treatment.

For example, a Lewis base solution is prepared so that the content of the Lewis base is 0.1 to 30% by mass, and the Lewis base solution is added dropwise to a nickel slurry being stirred at a peripheral speed of 5 to 10 m / sec at a dropping rate of 2 ml / min. Can be dropped with. For stirring the nickel slurry, a stirring blade having a shape such as a soft cross, a paddle cross, or a four-sheet inclined paddle can be used.

The temperature of the mixed solution of the nickel particles and the Lewis base during the surface treatment is preferably 20 to 50 ° C. If the temperature of the mixed solution is lower than 20 ° C., the rate of adhesion of the Lewis base to the nickel particles may decrease, and the stirring time of the mixed solution in the surface treatment may become long. Further, if the temperature of the mixed solution is higher than 50 ° C., the volatilization of the solvent is promoted and the surface treatment may be difficult.

Further, the stirring time of the mixed solution in the surface treatment is preferably 0.5 to 24 hours. If the stirring time is less than 0.5 hours, the amount of Lewis base attached to the nickel particles is reduced, and the effect of suppressing the generation of coarse particles due to the surface treatment may not be sufficiently obtained. Further, even if the stirring time is longer than 24 hours, the amount of Lewis base adhered hardly increases, and the longer the treatment time, the longer the surface treatment time of the nickel particles, and the higher the cost. there is a possibility. The stirring of the mixed solution may be carried out under the condition of a peripheral speed of 5 to 10 m / sec as in the mixing step.

<Lewis base containing nitrogen>
As the compound used for the surface treatment, a Lewis base containing nitrogen is used. According to the surface treatment method according to the present invention, it is conceivable that a lone electron pair of a Lewis base containing nitrogen gives an electron to the surface of nickel particles to form a coordinate bond. The Lewis base compound containing nitrogen can be efficiently adsorbed on the surface of nickel particles and coordinate-bonded, and the generation of coarse particles due to the aggregation of nickel particles can be suppressed.

The amount of the Lewis base containing nitrogen added is such that the mass ratio of the Lewis base and the nickel particles is 0.16 to 3.0: 100 in the state of the Lewis base-containing nickel particles after the surface treatment. do. Specifically, as a rule of thumb, it is preferable to add nickel particles in a range of 0.2% by mass or more and 4.0% by mass or less with respect to 100% by mass of nickel particles. When the amount of the Lewis base derived from nitrogen added is 0.2% by mass or more with respect to 100% by mass of the nickel particles, the amount of adsorption to the nickel particles can be increased, and as a result, the dispersibility of the nickel fine particles can be further enhanced. Can be done. On the other hand, when the amount of the nitrogen-derived Lewis base added is 4.0% by mass or less, it is possible to prevent the change in the viscosity of the nickel paste due to the increase in the amount of the nitrogen-derived Lewis base.

Examples of the nitrogen-containing Lewis base include those containing a compound represented by the following formula (1).

In formula (1), R ¹ represents an alkyl group having 1 to 18 carbon atoms or an alkenyl group having 1 to 18 carbon atoms, R ² represents an alkylene group having 1 to 6 carbon atoms, and R ³ and R. ⁴ indicates H or CH ₃ .

In particular, one or more selected from N-oleoyl sarcosine, N-lauroyl sarcosine, and myristylmethyl-β-alanine can be used as the Lewis base as a Lewis base that can be dissolved in a solvent capable of slurrying nickel particles. .. The structures of N-oleoyl sarcosine, N-lauroyl sarcosine, and myristylmethyl-β-alanine are shown in the following general formulas (2) to (4).

(solvent)
As a solvent for dispersing nickel particles to be surface-treated and making them into a slurry, and a solvent for dissolving a Lewis base containing nitrogen, nickel particles can be dispersed and the Lewis base can be dissolved. If there is, there is no particular limitation. Specifically, for example, tarpineol, dihydroterpineol, dihydroterpineol acetate, isobornylpropionate, isobornylisobutyrate, mineral spirit, No. 0 solvent, butyl carbitol, isobutyl acetate, methyl ethyl ketone, cyclohexane, hexane, etc. Examples thereof include ethanol, nonane, nonanol, decanol and the like. Furthermore, aliphatic hydrocarbons, aromatic hydrocarbons and the like can also be used. Specifically, dimethyloctane, ethylmethylcyclohexane, methylpropylcycloheptane, trimethylhexane, butylcyclohexane, tridecane, tetradecane, methylnonane and ethylmethyl Examples thereof include heptane, trimethyldecane, pentylcyclohexane, decane, undecane, dodecane and toluene. These organic solvents may be used alone or in combination of two or more.

[Nickel powder manufacturing method]
<Drying process>
Next, a method for producing nickel powder will be described. This method includes a drying step of drying the surface-treated nickel particles after the mixing step described in the above-mentioned method for surface-treating nickel particles.

For example, the nickel powder is dried at 50 to 300 ° C., preferably 80 to 150 ° C. using a general-purpose drying device such as an inert gas atmosphere dryer and a vacuum dryer so that the surface-treated nickel particles are not oxidized. Can be obtained.

If necessary, a washing / filtering step described later is performed to obtain a nickel powder-containing cake, and the adhering water in the cake is replaced with a low-temperature volatile organic solvent such as ethanol, and then the above-mentioned inert gas atmosphere drying is performed. It is also possible to dry in a machine or vacuum dryer to weaken the drying agglomeration between nickel particles that occurs during drying due to the high surface tension of water.

(Washing / filtration process)
In the method for producing nickel powder of the present invention, a washing / filtering step may be performed before the drying step. Specifically, after carrying out the above-mentioned surface treatment method for nickel particles, a slurry in which nickel particles surface-treated with a Lewis base are dispersed can be obtained. Therefore, first, this slurry is depressurized using a suction filter. Filter. Then, the nickel particles remaining on the filter paper by filtration are mixed with the above solvent, and the mixture is stirred and washed at a peripheral speed of 2 to 5 m / sec for 0.5 to 3 hours. By repeating this cleaning operation and the filtration operation, unreacted Lewis bases and impurities can be removed from the nickel particles. Further, infrared spectroscopic analysis of the obtained filtrate can be performed to confirm that no unreacted Lewis base is detected, and the cleaning operation can be completed.

A general-purpose solid-liquid separator can be used for filtering nickel particles, and specific examples thereof include, but are not limited to, a Denver filter, a filter press, a centrifuge, and a decanter. Further, after the cleaning operation, the solvent may be further removed from the nickel particles by using a spray dryer or the like.

(Crushing / classification process)
Further, in the method for producing nickel powder of the present invention, a crushing / classification step may be performed after the drying step. For example, when nickel particles are aggregated with a weak force due to drying aggregation in the drying step, a crushing step can be provided during or at the end of the manufacturing process to crush the nickel particles. For example, dry crushing methods such as spiral jet crushing treatment and counter jet mill crushing treatment, wet crushing methods such as high-pressure fluid collision crushing treatment, and other general-purpose crushing methods can be applied. ..

Further, the nickel powder may be classified by any method such as dry classification, wet classification, sieving classification, etc. to remove extremely coarse particles.

[Lewis base-containing nickel particles]
Next, the Lewis base-containing nickel particles of the present invention will be described. The nickel particles can be obtained, for example, by the above-mentioned surface treatment method for nickel particles of the present invention or the method for producing nickel powder. However, the manufacturing method is not limited to these.

In the Lewis base-containing nickel particles of the present invention, the Lewis base containing nitrogen is present on the surface of the nickel particles, and the mass ratio of the Lewis base to the nickel particles is 0.16 to 3.0: 100. When the mass ratio is less than 0.16: 100, a region that can be oxidized remains on the surface of the nickel particles, nickel hydroxide is generated over time, and coarse particles may be generated. Further, it is difficult for the Lewis base to be present in such a mass ratio exceeding 3.0: 100, and the mass ratio of 3.0: 100 is considered to be the upper limit of the abundance of the Lewis base.

It is considered that the Lewis base is coordinated to the surface of the nickel particle by adopting a structure in which the lone electron pair of the Lewis base containing nitrogen gives an electron to the surface of the nickel particle and is coordinated. The Lewis base compound containing nitrogen can be efficiently adsorbed on the surface of nickel particles and coordinate-bonded, and the generation of coarse particles due to the aggregation of nickel particles can be suppressed.

Examples of the nitrogen-containing Lewis base include those containing a compound represented by the following formula (1).

In formula (1), R ¹ represents an alkyl group having 1 to 18 carbon atoms or an alkenyl group having 1 to 18 carbon atoms, R ² represents an alkylene group having 1 to 6 carbon atoms, and R ³ and R. ⁴ indicates H or CH ³ .

In particular, one or more selected from N-oleoyl sarcosine, N-lauroyl sarcosine, and myristylmethyl-β-alanine can be used as the Lewis base as a Lewis base that can be dissolved in a solvent capable of slurrying nickel particles. .. The structures of N-oleoyl sarcosine, N-lauroyl sarcosine, and myristylmethyl-β-alanine are shown in the following general formulas (2) to (4).

The Lewis base-containing nickel particles of the present invention preferably have a number average particle size of 0.03 μm to 0.4 μm from the viewpoint of corresponding to the recent thinning of the internal electrodes of the multilayer ceramic capacitor. The number average particle size is a number average particle size obtained from a scanning electron micrograph (SEM image) of nickel particles.

Similarly, from the viewpoint of corresponding to thinning, the particle shape is preferably substantially spherical, and the substantially spherical shape includes not only a true sphere but also a predetermined cross section (for example, a cross section passing through the center of the particle). Also includes an ellipsoid having an ellipsoidal shape in which the ratio of the minor axis to the major axis (minor axis / major axis) is 0.8 to 1.0.

Further, in the Lewis base-containing nickel particles of the present invention, the content of particles having a particle size of more than 0.8 μm is 200% by mass or less, and the content of particles having a particle size of more than 1.2 μm is 100% by mass or less. It is preferable to have.

The influence of the coarse particles of the nickel particles depends on the thickness of the internal electrode layer of the multilayer ceramic capacitor in which the nickel particles are used, but the particle size of the thinned internal electrode layer in recent years exceeds 0.8 μm. If the content of the coarse particles exceeds 400 mass ppm or the content of the coarse particles having a particle size of more than 1.2 μm exceeds 200 mass ppm, the short circuit between the electrodes may become remarkable. Needless to say, the smaller the content of the coarse particles is, the better the nickel particles are. When the content of is 100% by mass or less, the occurrence rate of short circuit between electrodes can be sufficiently reduced. The particle size of the coarse particles may be the minor axis diameter obtained from the SEM image.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

[Example 1]
10 g of nickel particles were added to 100 g of dihydroterpineol, a soft cross-shaped stirring blade was attached to a three-one motor, and the mixture was stirred at 300 rpm for 1 hour so as to have a peripheral speed of 8 m / sec to obtain a nickel slurry. While maintaining stirring under these conditions, a Lewis base solution prepared by dissolving 0.2 g of N-oleoyl sarcosine as a Lewis base in 10 g of dihydroterpineol was added dropwise to the nickel slurry at a rate of 2 ml / min. Then, the mixture was stirred at room temperature of 25 ° C. for 3 hours without changing the stirring conditions to obtain a surface-treated nickel particle slurry. This slurry was solid-liquid separated by suction filtration, and the operation of adding 100 g of dihydroterpineol to the separated nickel particles to form a slurry was repeated three times to wash the nickel particles. After washing, solid-liquid separation was performed by suction filtration, and the separated nickel particles were dried at 120 ° C. in a nitrogen atmosphere to obtain the desired surface-treated nickel particle powder.

[Example 2]
A surface treatment was carried out in the same manner as in Example 1 except that N-lauroyl sarcosine was used as a Lewis base, and a powder of nickel particles after the surface treatment was obtained.

[Example 3]
A surface treatment was carried out in the same manner as in Examples except that myristylmethyl-β-alanine was used as a Lewis base, and a powder of nickel particles after the surface treatment was obtained.

(Comparative Example 1)
The conditions were the same as in Example 1 except for the step of dropping the Lewis base solution. That is, the nickel particles were slurried, solid-liquid separated, washed, and dried in the same manner as in Example 1 without using a Lewis base.

(Comparative Example 2)
The nickel particles themselves used as raw materials in Examples 1 to 3 and Comparative Example 1 were designated as Comparative Example 2. That is, unlike Comparative Example 1, none of the nickel particles was slurried, solid-liquid separated, washed, and dried.

[Evaluation of nickel particles]
<Evaluation of carbon content on the surface of nickel particles>
The amount of carbon was measured by a carbon / sulfur analyzer (CS844 manufactured by LECO).

<Analysis of nickel particle surface treatment state>
Dihydroterpineol after solid-liquid separation by suction filtration and dihydroterpineol after washing nickel particles were recovered, diluted with methanol for concentration adjustment for analysis, and liquid chromatography-mass spectrometer (Agilent). The content of Lewis bases not consumed in the surface treatment was quantified by 1290 Infinity 2-Agilent Co., Ltd. 6530)). Using this value, the Lewis base content contained in the nickel particles after the surface treatment was calculated from the following formulas (5) and (6).

[Number 1]
Amount of Lewis base contained in Ni particles after surface treatment = (total amount of Lewis base used-amount of Lewis base not consumed in surface treatment) ... (5)

[Number 2]
Lewis base content (mass%) contained in Ni particles after surface treatment
= (Amount of Lewis base contained in Ni particles after surface treatment / Amount of Ni particles after surface treatment) × 100 ... (6)

<Measurement of average particle size>
The average particle size of the nickel particles is obtained by measuring the particle size obtained from the result of image analysis of the observation image (SEM image) using a scanning electron microscope (SEM, JSM-6360, manufactured by JEOL Ltd.) of the nickel powder, and the number average. It was calculated as the particle size of.

<Measurement of coarse particle content>
Regarding the nickel particles of Examples 1 to 3 and Comparative Example 1 after the nickel powder after the surface treatment operation was placed in a 100 ml high vessel container (BHB-100 manufactured by Kinki Container Co., Ltd.) and left at room temperature for 1 day in an air atmosphere. Using a scanning electron microscope (SEM, JSM-6360, manufactured by JEOL Ltd.), a photograph of an SEM image at a magnification of 5000 was obtained. Then, using the image analysis software Mac-View (manufactured by Mountech Co., Ltd.), the area and number of particles in which the entire shape of the particles in the photograph of the obtained SEM image can be seen are measured, and the diameter of each particle is calculated from these. The particles having a diameter of 0.8 μm or more and 1.2 μm or more were counted as coarse particles. Then, the content of the coarse particles contained in the nickel powder (when the particle size exceeds 0.8 μm and when the particle size exceeds 1.2 μm) was determined as an initial value.

After taking the SEM image, the nickel particles of Examples 1 to 3 and Comparative Example 1 were left at room temperature in an air atmosphere for 180 days, and then the content of coarse particles was measured in the same manner. The results of the content of coarse particles after being left for 180 days are shown in Table 1.

Regarding the nickel particles of Comparative Example 2, SEM images were similarly obtained for the nickel particles immediately before being used as raw materials in Examples 1 to 3 and Comparative Example 1, and the content of coarse particles was similarly set as the initial value. I asked. Further, after obtaining the initial SEM image, the nickel particles of Comparative Example 2 are stored in the same place and environment as in Examples 1 to 3 and Comparative Example 1, so that the nickel particles of Comparative Example 2 can be stored in an air atmosphere at room temperature. After leaving it for 180 days, the content of coarse particles was measured in the same manner.

The results for the carbon content, average particle size and coarse particle content on the surface of the nickel particles are shown in Table 1. In addition, FIG. 2 shows SEM photographs of nickel particles in the initial stage and after being left for 180 days in Example 1 and Comparative Example 2.

From the results of Examples 1 to 3 and Comparative Example 2, the average particle size of the nickel particles did not change significantly due to the surface treatment, and no coarse particles were observed (Tables 1 and 2). In addition, the surface treatment was able to suppress the increase of coarse particles after 180 days in the air atmosphere.

However, from the results of the nickel particles of Comparative Example 1, when the nickel particles were slurried, solid-liquid separated, washed, and dried without using the Lewis base, they were compared with the nickel particles of Comparative Example 2. , The content of coarse particles increased. In addition, the result was that the coarse particles further increased after 180 days in the atmospheric atmosphere (Table 1).

Further, in the SEM image of Comparative Example 2 in FIG. 2 180 days later, a dark-colored mass region in which a plurality of particles appeared to be crushed and adhered was observed in the central portion. This region can be counted as one coarse particle due to oxidation.

[summary]
As described above, it is clear that the nickel particles of the present invention are surface-treated with a nitrogen-containing Lewis base to suppress the generation of coarse particles due to oxidation during storage.

Claims (7)

A nitrogen-containing Lewis base is present on the surface of the nickel particles and
Lewis base-containing nickel particles having a mass ratio of the Lewis base to the nickel particles of 0.16 to 3.0: 100. The Lewis base-containing nickel particle according to claim 1, wherein the Lewis base is coordinated to the surface of the nickel particle. The Lewis base-containing nickel particle according to claim 1 or 2, wherein the Lewis base contains a compound represented by the following formula (1).

(In the formula (1), R ¹ represents an alkyl group having 1 to 18 carbon atoms or an alkenyl group having 1 to 18 carbon atoms, R ² represents an alkylene group having 1 to 6 carbon atoms, and R ³ and R ⁴ indicates H or CH ₃ ) The Lewis base-containing nickel particle according to any one of claims 1 to 3, wherein the Lewis base contains one or more selected from N-oleoyl sarcosine, N-lauroyl sarcosine, and myristylmethyl-β-alanine. The number average particle size is 0.03 μm to 0.4 μm.
The content of particles having a particle size of more than 0.8 μm is 400 mass ppm or less.
The Lewis base-containing nickel particle according to any one of claims 1 to 4, wherein the content of the particles having a particle size of more than 1.2 μm is 200 mass ppm or less. A method for surface-treating nickel particles, which comprises a mixing step of mixing nickel particles with a nitrogen-containing Lewis base. A method for producing nickel powder, which comprises a drying step of drying the surface-treated nickel particles after the mixing step according to claim 6.

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