Nickel particles, surface treatment method for nickel particles, and method for producing nickel powder

Abstract

To provide a nickel particle, a method for surface-treating a nickel particle and a method for producing a nickel powder whereby it is possible to prevent the occurrence of coarse particles due to oxidation during storage.SOLUTION: In a Lewis salt group-containing nickel particle, a nitrogen-containing Lewis base is present on the surface of a nickel particle, and a mass ratio between the Lewis base and the nickel particle is 0.16-3.0:100.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to nickel particles, a method for surface treatment of nickel particles, and a method for producing nickel powder. [Background technology]

[0002] Nickel particles are used as an ingredient in conductive pastes for producing thick-film conductors, and are used in the formation of electrical circuits and in the electrodes of multilayer ceramic components such as multilayer ceramic capacitors (MLCCs) and multilayer ceramic substrates.

[0003] An MLCC using this electrode is manufactured by the following method, for example, when nickel particles are used as the metal powder.

[0004] First, a conductive paste obtained by kneading nickel particles, a resin such as ethyl cellulose, and an organic solvent such as terpineol is screen-printed onto a dielectric green sheet (ceramic green sheet) with a thickness of 10 μm or less, and then dried to produce a nickel coating film for the internal electrodes.

[0005] Next, the printed nickel coatings for the internal electrodes and the dielectric green sheets are layered alternately and pressed together to produce a laminate.

[0006] The laminate thus produced is cut to a specified size, and after a binder removal process is performed to burn off the ethyl cellulose and other resins used as organic binders, the dielectric and internal electrodes (nickel films) are sintered by high-temperature firing at about 1300°C to obtain a ceramic body in which the dielectric layers and internal electrode layers are laminated together. External electrodes are then attached to this ceramic body to form a multilayer ceramic capacitor.

[0007] The binder removal treatment of the laminate is carried out in an atmosphere containing an extremely small amount of oxygen so as to prevent the nickel particles from being oxidized.

[0008] Generally, nickel paste used in the internal electrodes of MLCCs is manufactured by kneading nickel powder in a vehicle, and contains many nickel powder aggregates. The manufacturing process of nickel powder usually has a drying process at the final stage, regardless of the manufacturing method of nickel powder (gas phase method or liquid phase method). Since the drying process promotes the aggregation of nickel particles, the resulting nickel powder generally contains aggregates generated during drying as coarse particles.

[0009] In order to achieve small size and large capacity in recent MLCCs, there is a demand to increase the number of laminated ceramic green sheets with internal electrode layers from several hundred to around 1000. For this reason, there is a study being conducted to thin the thickness of the internal electrode layers from the conventional several microns level to the submicron level, and accordingly, progress is being made in reducing the particle size of nickel powder, the electrode material for the internal electrodes.

[0010] However, the smaller the particle size, the larger the surface area of ​​the nickel powder becomes, and the larger the surface energy becomes, making it easier to form aggregates. In addition, metal powders such as nickel powder have poor dispersibility, and if aggregates are present, the nickel powder may penetrate the ceramic sheet layer when sintered in the firing process during MLCC manufacturing, resulting in defective products with short-circuited electrodes. Even if the nickel powder does not penetrate the ceramic sheet layer, the distance between the electrodes in the MLCC may become shorter, causing partial current concentration, and this current concentration has been the cause of the deterioration of the life of the multilayer ceramic capacitor. Thus, in MLCC, it is important to manufacture a nickel paste with few coarse particles, including aggregates, and to obtain internal electrodes with a smooth surface without unevenness. In addition, since there is a concern that the presence of aggregates of nickel particles may cause product defects, it is desired to improve the surface condition of the nickel particles so that aggregates do not occur.

[0011] Patent Document 1 discloses a technique for the oxidation treatment of the surface of nickel particles, and discloses a technical matter of adding nickel powder produced by a liquid phase method to pure water to form a slurry, and then oxidizing it with hydrogen peroxide. However, surface oxidation treatment using hydrogen peroxide needs to be carried out in an aqueous system, and is not suitable when a non-aqueous organic compound is used as a surface treatment agent. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Publication No. 11-343501 Summary of the Invention [Problem to be solved by the invention]

[0013] When nickel powder is stored, it may be oxidized by oxygen in the air over time, forming nickel hydroxide on the surface. Coarse nickel particles may occur when adjacent nickel particles are firmly bound together by nickel hydroxide on the surface. Therefore, it is important to suppress the oxidation of nickel powder during storage, especially for nickel powder used in MLCCs, to prevent defects caused by the generation of coarse particles due to oxidation during storage.

[0014] The present invention has been proposed in consideration of the above-mentioned circumstances, and aims to provide nickel particles that suppress the generation of coarse particles due to oxidation during storage, a method for surface treatment of nickel particles, and a method for producing nickel powder. [Means for solving the problem]

[0015] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have found that coating nickel particles with a Lewis base compound can suppress the aggregation of nickel particles, thereby suppressing the generation of coarse particles, and have thus completed the present invention.

[0016] In order to solve the above problems, the Lewis base-containing nickel particles of the present invention have a nitrogen-containing Lewis base 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.

[0017] The Lewis base may be coordinated to the surface of the nickel particle.

[0018] The Lewis base may include a compound represented by the following formula (1):

[0019] [ka]

[0020] 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, R 3 and R 4 is H or CH 3 Shows.

[0021] The Lewis base may include one or more selected from N-oleoyl sarcosine, N-lauroyl sarcosine, and myristoylmethyl-β-alanine.

[0022] The Lewis base-containing nickel particles of the present invention may have a number average particle size of 0.03 μm to 0.4 μm, a content of particles having a particle size exceeding 0.8 μm of 400 mass ppm or less, and a content of particles having a particle size exceeding 1.2 μm of 200 mass ppm or less.

[0023] 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 with a nitrogen-containing Lewis base.

[0024] In order to solve the above problems, the method for producing nickel powder of the present invention also includes a drying step of drying the surface-treated nickel particles after the above mixing step. Effect of the Invention

[0025] According to the present invention, it is possible to provide nickel particles that suppress the generation of coarse particles due to oxidation during storage, a method for treating the surface of nickel particles, and a method for producing nickel powder. [Brief description of the drawings]

[0026] [Figure 1] FIG. 1 is a flow chart showing a surface treatment method for nickel particles and a method for producing nickel powder according to the present invention as a series of steps. [Diagram 2] 1 is a SEM photograph of nickel particles of Example 1 and Comparative Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. Fig. 1 is a flow diagram showing the surface treatment method of nickel particles and the manufacturing method of nickel powder of the present invention as a series of steps. However, the present invention is not limited to the following embodiments.

[0028] [Surface treatment method for nickel particles] Nickel particles to be surface treated As nickel particles to be surface-treated, various nickel powders can be used regardless of the manufacturing method such as wet method or dry method. For example, nickel powders produced by so-called dry methods such as CVD method, evaporation quenching method, and hydrogen reduction method using nickel salt, nickel hydroxide, etc. can be used as nickel particles to be treated. Nickel powders produced by so-called wet methods such as wet reduction method using a reducing agent such as hydrazine for a nickel salt solution can be used as nickel particles to be treated. Among them, nickel powders produced by so-called wet methods such as wet reduction method are suitable as materials for MLCCs because they are spherical and have small variation in particle size.

[0029] <Mixing process> The method for treating the surface of nickel particles includes a mixing step of mixing nickel particles with a nitrogen-containing Lewis base. By the mixing step, the surfaces of the nickel particles can be surface-treated with the nitrogen-containing Lewis base.

[0030] (Nickel Slurry) The method of surface treating nickel particles using the Lewis base includes a method of contacting nickel particles with Lewis base by wet mixing using various solvents containing alcohol as a medium. That is, nickel slurry in which nickel particles are dispersed in various solvents containing alcohol and Lewis base containing nitrogen are added and mixed in various solvents containing alcohol to form a slurry, thereby uniformly treating the particle surface of nickel particles.

[0031] In the mixing step, nickel particles to be surface-treated may be added to a solution in which the Lewis base is dissolved and mixed, or the Lewis base may be added to a nickel slurry and mixed. However, from the viewpoint of effectively and uniformly treating the surfaces of fine nickel particles, it is preferable to dissolve the Lewis base in advance in various solvents including alcohol.

[0032] Specifically, the nickel slurry is stirred, and the Lewis base solution in which the Lewis base is dissolved is dropped and mixed therein, and then the mixed solution is stirred to perform the surface treatment.

[0033] For example, a Lewis base solution is prepared so that the Lewis base content is 0.1 to 30 mass%, and the Lewis base solution can be added dropwise at a rate of 2 ml / min to nickel slurry being stirred at a peripheral speed of 5 to 10 m / sec. For stirring the nickel slurry, stirring blades in the shape of a soft cross, a paddle cross, a four-blade inclined paddle, or the like can be used.

[0034] The temperature of the mixed solution of nickel particles and Lewis base during surface treatment is preferably 20 to 50° C. If the temperature of the mixed solution is lower than 20° C., the adhesion rate of the Lewis base to the nickel particles may decrease, and the stirring time of the mixed solution during surface treatment may become longer. If the temperature of the mixed solution is higher than 50° C., the evaporation of the solvent is promoted, which may make the surface treatment difficult.

[0035] Furthermore, 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 small, and the effect of suppressing the generation of coarse particles due to the surface treatment may not be sufficiently obtained. Even if the stirring time is longer than 24 hours, the amount of Lewis base attached hardly increases, and if the treatment time is longer, the surface treatment time of the nickel particles will also be longer, which may increase the cost. The stirring of the mixed solution may be performed under the condition of a peripheral speed of 5 to 10 m / sec, similar to the mixing process.

[0036] <Nitrogen-containing Lewis bases> A nitrogen-containing Lewis base is used as the compound used for the surface treatment. It is believed that the surface treatment method of the present invention allows the lone electron pair of the nitrogen-containing Lewis base to donate electrons to the surface of the nickel particles to form a coordinate bond, forming a structure. The nitrogen-containing Lewis base compound is capable of efficiently adsorbing to the surface of the nickel particles and forming a coordinate bond, and can suppress the generation of coarse particles due to the aggregation of the nickel particles.

[0037] The amount of the nitrogen-containing Lewis base is added so that the mass ratio of the Lewis base to the nickel particles is 0.16 to 3.0:100 in the state of the Lewis base-containing nickel particles after the surface treatment. Specifically, based on experience, it is preferable to add the Lewis base in the range of 0.2 mass% to 4.0 mass% with respect to 100 mass% of the nickel particles. By adding the amount of the nitrogen-derived Lewis base of 0.2 mass% or more with respect to 100 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 improved. On the other hand, by adding the amount of the nitrogen-derived Lewis base of 4.0 mass% or less, it is possible to prevent a change in the viscosity of the nickel paste due to an increase in the amount of the nitrogen-derived Lewis base.

[0038] Examples of the nitrogen-containing Lewis base include those containing a compound represented by the following formula (1).

[0039] [ka]

[0040] 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, R 3 and R 4 is H or CH 3 Shows.

[0041] In particular, as a Lewis base that can be dissolved in a solvent capable of forming a slurry of nickel particles, one or more types selected from N-oleoyl sarcosine, N-lauroyl sarcosine, and myristoylmethyl-β-alanine can be used as the Lewis base. The structures of N-oleoyl sarcosine, N-lauroyl sarcosine, and myristoylmethyl-β-alanine are shown in the following general formulas (2) to (4).

[0042] [ka]

[0043] [ka]

[0044] [ka]

[0045] (solvent) The solvent for dispersing nickel particles to be surface-treated to form a slurry and the solvent for dissolving the nitrogen-containing Lewis base are not particularly limited as long as they can disperse nickel particles and dissolve the Lewis base.Specific examples include terpineol, dihydroterpineol, dihydroterpineol acetate, isobornyl propionate, isobornyl isobutyrate, mineral spirits, No. 0 solvent, butyl carbitol, isobutyl acetate, methyl ethyl ketone, cyclohexane, hexane, ethanol, nonane, nonanol, decanol, etc.Furthermore, aliphatic hydrocarbons, aromatic hydrocarbons, etc. can also be used, and specific examples include dimethyloctane, ethylmethylcyclohexane, methylpropylcycloheptane, trimethylhexane, butylcyclohexane, tridecane, tetradecane, methylnonane, ethylmethylheptane, trimethyldecane, pentylcyclohexane, decane, undecane, dodecane, toluene, etc.These organic solvents can be used alone or in combination of two or more.

[0046] [Method of manufacturing nickel powder] <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.

[0047] For example, nickel powder can be obtained by drying the surface-treated nickel particles at 50 to 300°C, preferably 80 to 150°C, using a general-purpose drying device such as an inert gas atmosphere dryer or a vacuum dryer so as not to oxidize the particles.

[0048] If necessary, a washing and filtration process described below may be carried out to produce a nickel powder hydrous cake, and the adhering water in this cake may be replaced with a low-temperature volatile organic solvent such as ethanol, and then the cake may be dried in the above-mentioned inert gas atmosphere dryer or vacuum dryer to weaken the drying aggregation between nickel particles that occurs during drying due to the large surface tension of water.

[0049] (Washing and filtration process) In the method for producing nickel powder of the present invention, a washing and 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 is obtained, and this slurry is first filtered under reduced pressure using a suction filter. Then, the nickel particles remaining on the filter paper after filtration are mixed with the above-mentioned solvent and washed by stirring at a peripheral speed of 2 to 5 m / sec for 0.5 to 3 hours. By repeating this washing and filtering process, unreacted Lewis bases and impurities can be removed from the nickel particles. Furthermore, infrared spectroscopy of the obtained filtrate is performed to confirm that no unreacted Lewis bases are detected, and the washing process can be terminated.

[0050] For filtering the nickel particles, a general-purpose solid-liquid separation device can be used, and specific examples thereof include, but are not limited to, a Denver filter, a filter press, a centrifuge, a decanter, etc. After the washing operation, the solvent may be removed by blowing it off from the nickel particles using a spray dryer or the like.

[0051] (Crushing / classification process) In addition, in the method for producing nickel powder of the present invention, a crushing and classification process may be performed after the drying process. For example, when nickel particles are weakly aggregated due to dry aggregation in the drying process, a crushing process can be provided during or at the end of the production process to crush the nickel particles. For example, dry crushing methods such as spiral jet crushing and counter jet mill crushing, wet crushing methods such as high-pressure fluid collision crushing, and other general-purpose crushing methods can be applied.

[0052] Furthermore, the nickel powder may be classified by any method such as dry classification, wet classification, or sieving classification to remove extremely coarse particles.

[0053] [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 of nickel particles of the present invention or the manufacturing method of nickel powder. However, the manufacturing method is not limited to these.

[0054] In the Lewis base-containing nickel particles of the present invention, a nitrogen-containing Lewis base 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. If the mass ratio is less than 0.16:100, there is a risk that an oxidizable region remains on the surface of the nickel particles, which may generate nickel hydroxide over time, resulting in the generation of coarse particles. In addition, it is difficult to make the Lewis base exist when the mass ratio exceeds 3.0:100, and the mass ratio of 3.0:100 is considered to be the upper limit of the amount of the Lewis base present.

[0055] It is believed that the lone electron pair of the nitrogen-containing Lewis base provides an electron to the surface of the nickel particle to form a coordinate bond, and the Lewis base is coordinated to the surface of the nickel particle. The nitrogen-containing Lewis base compound can efficiently adsorb to the surface of the nickel particle and form a coordinate bond, and can suppress the generation of coarse particles due to the aggregation of the nickel particles.

[0056] Examples of the nitrogen-containing Lewis base include those containing a compound represented by the following formula (1).

[0057] [ka]

[0058] 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, R 3 and R 4 is H or CH 3 Shows.

[0059] In particular, as a Lewis base that can be dissolved in a solvent capable of forming a slurry of nickel particles, one or more types selected from N-oleoyl sarcosine, N-lauroyl sarcosine, and myristoylmethyl-β-alanine can be used as the Lewis base. The structures of N-oleoyl sarcosine, N-lauroyl sarcosine, and myristoylmethyl-β-alanine are shown in the following general formulas (2) to (4).

[0060] [ka]

[0061] [ka]

[0062] [ka]

[0063] From the viewpoint of responding to the recent trend of thinner internal electrodes of multilayer ceramic capacitors, 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. The number average particle size is the number average particle size determined from a scanning electron microscope (SEM image) of the nickel particles.

[0064] Similarly, from the viewpoint of accommodating thin layers, it is preferable that the particle shape is approximately spherical, and the approximately spherical shape includes not only a true sphere but also an ellipsoid having a ratio of the minor axis to the major axis (minor axis / major axis) of 0.8 to 1.0 in a specified cross section (e.g., a cross section passing through the center of the particle) and the like.

[0065] Moreover, the Lewis base-containing nickel particles of the present invention preferably contain no more than 200 ppm by mass of particles having a particle size exceeding 0.8 μm, and no more than 100 ppm by mass of particles having a particle size exceeding 1.2 μm.

[0066] The effect of coarse particles in nickel particles depends on the film thickness of the internal electrode layer of the multilayer ceramic capacitor in which nickel particles are used. In recent thin internal electrode layers, if the content of coarse particles with a particle size exceeding 0.8 μm exceeds 400 mass ppm, or if the content of coarse particles with a particle size exceeding 1.2 μm exceeds 200 mass ppm, the occurrence of short circuits between electrodes may become significant. It goes without saying that the lower the content of coarse particles in nickel particles, the better. If the content of coarse particles with a particle size exceeding 0.8 μm is 200 mass ppm or less and the content of coarse particles with a particle size exceeding 1.2 μm is 100 mass ppm or less, the occurrence rate of short circuits between electrodes can be sufficiently reduced. The particle size of the coarse particles may be the minor axis diameter obtained from the SEM image. EXAMPLES

[0067] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0068] [Example 1] 10g of nickel particles was added to 100g of dihydroterpineol, and a soft cross-shaped stirring blade was attached to a three-one motor, and the mixture was stirred at 300 rpm for 1 hour to obtain a nickel slurry at a peripheral speed of 8 m / sec. While maintaining the stirring conditions, a Lewis base solution in which 0.2g of N-oleoyl sarcosine was dissolved in 10g of dihydroterpineol as a Lewis base was added dropwise to the nickel slurry at a rate of 2ml / min. After that, the mixture was stirred at room temperature of 25°C for 3 hours without changing the stirring conditions to obtain a slurry of surface-treated nickel particles. The slurry was separated into solid and liquid by suction filtration, and the separated nickel particles were added with 100g of dihydroterpineol to form a slurry, which was repeated three times to wash the nickel particles. After washing, the nickel particles were separated into solid and liquid by suction filtration, and the separated nickel particles were dried at 120°C under a nitrogen atmosphere to obtain a powder of nickel particles after the intended surface treatment.

[0069] [Example 2] Surface treatment was carried out in the same manner as in Example 1, except that N-lauroyl sarcosine was used as the Lewis base, to obtain a powder of surface-treated nickel particles.

[0070] [Example 3] Surface treatment was carried out in the same manner as in the Example, except that myristoylmethyl-β-alanine was used as the Lewis base, to obtain a powder of surface-treated nickel particles.

[0071] Comparative Example 1 Except for the step of dropping the Lewis base solution, the conditions were the same as in Example 1. That is, the slurrying of nickel particles, solid-liquid separation, washing, and drying treatment were performed in the same manner as in Example 1, without using a Lewis base.

[0072] Comparative Example 2 The nickel particles themselves used as the raw material in Examples 1 to 3 and Comparative Example 1 were used as Comparative Example 2. That is, unlike Comparative Example 1, the nickel particles were not subjected to any of the following treatments: slurrying, solid-liquid separation, washing, or drying.

[0073] [Evaluation of nickel particles] Evaluation of the amount of carbon on the surface of nickel particles The carbon content was measured using a carbon-sulfur analyzer (LECO CS844).

[0074] <Analysis of nickel particle surface treatment state> The dihydroterpineol after solid-liquid separation by suction filtration and the dihydroterpineol after washing the nickel particles were recovered, and these were diluted with methanol to adjust the concentration for analysis, and the content of the Lewis base not consumed in the surface treatment was quantified using a liquid chromatography-mass spectrometry device (Agilent 1290 infinity2-Agilent 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).

[0075] [Number 1] Lewis base content of Ni particles after surface treatment = (total amount of Lewis base used − amount of Lewis base not consumed in surface treatment) (5)

[0076] [Number 2] Lewis base content in Ni particles after surface treatment (mass%) = (amount of Lewis base contained in Ni particles after surface treatment / amount of Ni particles after surface treatment) × 100 (6)

[0077] Measurement of average particle size The average particle size of the nickel particles was calculated as the number average particle size by measuring the particle size obtained from the results of image analysis of the observation image (SEM image) of the nickel powder using a scanning electron microscope (SEM, JSM-6360, manufactured by JEOL Ltd.).

[0078] <Measurement of the content of coarse particles> The nickel powder after the surface treatment was placed in a 100 ml high vessel container (BHB-100 manufactured by Kinki Yoki Co., Ltd.), and the nickel particles of Examples 1 to 3 and Comparative Example 1 were left at room temperature for 1 day in an air atmosphere. A scanning electron microscope (SEM, JSM-6360, manufactured by JEOL Ltd.) was used to obtain SEM images at a magnification of 5000 times. Then, using image analysis software Mac-View (manufactured by Mountec Co., Ltd.), the area and number of particles in which the entire particle shape can be seen in the obtained SEM images were measured, and the diameter of each particle was calculated from these, and particles with diameters of 0.8 μm or more and 1.2 μm or more were counted as coarse particles. The content of 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 calculated as an initial value.

[0079] In addition, after taking the SEM images, 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 leaving for 180 days are shown in Table 1.

[0080] For the nickel particles of Comparative Example 2, an SEM image was similarly obtained for the nickel particles immediately before use as a raw material in Examples 1 to 3 and Comparative Example 1, and the content of coarse particles was similarly determined as an initial value. After obtaining the initial SEM image, the nickel particles of Comparative Example 2 were stored in the same place and environment as Examples 1 to 3 and Comparative Example 1, and the nickel particles of Comparative Example 2 were left at room temperature in an air atmosphere for 180 days, after which the content of coarse particles was similarly measured.

[0081] The results regarding the carbon amount on the nickel particle surface, the average particle size, and the content of coarse particles are shown in Table 1. Also, Fig. 2 shows SEM photographs of nickel particles in Example 1 and Comparative Example 2 at initial stage and after standing for 180 days.

[0082] [Table 1]

[0083] 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 generation of coarse particles was observed (Table 1, FIG. 2). In addition, the surface treatment was able to suppress the increase in coarse particles after 180 days in the air atmosphere.

[0084] However, the results for the nickel particles of Comparative Example 1 showed that when the nickel particles were subjected to slurrying, solid-liquid separation, washing, and drying treatments without using a Lewis base, the content of coarse particles increased compared to the nickel particles of Comparative Example 2. In addition, the amount of coarse particles further increased after 180 days in the air atmosphere (Table 1).

[0085] In addition, in the SEM image of Comparative Example 2 after 180 days in Figure 2, a dark mass was observed in the center where multiple particles seemed to have been crushed and adhered together. This area can be counted as one coarse particle caused by oxidation.

[0086] [summary] As described above, it is clear that the nickel particles of the present invention are surface-treated with a nitrogen-containing Lewis base, thereby suppressing the generation of coarse particles due to oxidation during storage.

Claims

1. A nitrogen-containing Lewis base is present on the surface of the nickel particles, a mass ratio of the Lewis base to the nickel particles is 0.16 to 3.0:100; A dry nickel powder comprising Lewis base-containing nickel particles, wherein the Lewis base is a compound represented by the following formula (1): 【Chemistry 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 represent H or CH 3 .)

2. 2. The nickel powder of claim 1, wherein the Lewis base is coordinated to the surface of the nickel particles.

3. The nickel powder according to claim 1 or 2, wherein the Lewis base comprises one or more selected from N-oleoyl sarcosine, N-lauroyl sarcosine, and myristoyl methyl-β-alanine.

4. The number average particle size of the Lewis base-containing nickel particles is 0.03 μm to 0.4 μm; The content of particles having a particle size exceeding 0.8 μm is 400 ppm by mass or less, The nickel powder according to any one of claims 1 to 3, wherein the content of particles having a particle size exceeding 1.2 µm is 200 mass ppm or less.

5. 5. The method for surface treatment of nickel particles containing a Lewis base according to claim 1, further comprising a mixing step of mixing nickel particles with a nitrogen-containing Lewis base.

6. A method for producing nickel powder, comprising the step of drying the surface-treated nickel particles after the mixing step according to claim 5.

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