CN119816387A

CN119816387A - Nickel particles and method for producing nickel particles

Info

Publication number: CN119816387A
Application number: CN202380063344.4A
Authority: CN
Inventors: 西野光彦; 佐佐木隆史; 泽本裕树
Original assignee: Mitsui Mining and Smelting Co Ltd
Current assignee: Mitsui Metal Co ltd
Priority date: 2022-09-30
Filing date: 2023-06-28
Publication date: 2025-04-11
Anticipated expiration: 2043-06-28
Also published as: CN119816387B; JPWO2024070097A1; JP7340727B1; KR20250085713A

Abstract

A nickel particle having a surface region containing an alloy of nickel and a metal element M. The metal element M is at least one selected from tin and zinc. The content of the metal element M relative to the entire nickel particle is 0.16 mass % to 11.4 mass %. When measuring the region from the outermost surface to a sputtering depth of 5 nm in terms of SiO ₂ in the depth direction of the nickel particle by X-ray photoelectron spectroscopy, in this region, the maximum value of the ratio of the number of atoms of the metal element M to the total number of atoms of the nickel element and the metal element M is set to X (at%), and when measuring the nickel particle by ICP emission spectroscopy, when the ratio of the number of atoms of the metal element M to the total number of atoms of the nickel element and the metal element M is set to Y (at%), the value of X/Y is 1.5 to 30.

Description

Nickel particle and method for producing nickel particle

Technical Field

The present invention relates to nickel particles and a method for producing the same.

Background

Nickel particles are generally used for forming internal electrodes of a multilayer ceramic capacitor (hereinafter also referred to as "MLCC") used in electronic devices. In the production of MLCCs, when a laminate of a dielectric layer and an internal electrode including nickel particles is fired at the same time, defects may occur in the internal electrode due to the difference in sintering temperature of the raw materials. In order to prevent such a problem, it is required to improve the sintering resistance of nickel particles.

For example, patent document 1 discloses a technique for forming internal electrodes of an MLCC by using nickel powder containing tin or zinc obtained by a PVD method or a CVD method. This document describes that the sintering temperature of nickel powder is increased by adding a non-magnetic metal such as tin to the nickel powder to distort the crystal structure of nickel.

Patent document 2 discloses a technique for forming internal electrodes of an MLCC by using nickel powder having a particle shape of a substantially spherical shape and surface-treated with tin. In addition, it is disclosed in this document that zinc is used for surface treatment in addition to tin. In this document it is described that the sintering behaviour is improved according to the nickel powder described in this document.

Prior art literature

Patent literature

Patent document 1 International publication No. 2014/080600 pamphlet

Patent document 2 Japanese patent application laid-open No. 2018-104819

Disclosure of Invention

However, with the recent increase in performance of electronic devices, there is a demand for further preventing defects in MLCCs caused by defects that may occur in internal electrodes. In order to meet this demand, not only is the sintering resistance required to be further improved, but also the resistance of the electrode is required not to be excessively improved when the nickel particles are used to form the internal electrode.

Accordingly, an object of the present invention is to provide nickel particles having high sintering resistance without excessively increasing the electrical resistance.

The present invention provides a nickel particle having a surface region comprising an alloy of nickel and a metal element M,

The metal element M is at least 1 selected from tin and zinc,

The content of the metal element M relative to the whole nickel particles is 0.16-11.4 mass%,

When a region from the outermost surface to a sputtering depth of 5nm calculated by SiO ₂ conversion is measured in the depth direction of the nickel particles by X-ray photoelectron spectroscopy, the maximum value of the ratio of the atomic number of the metal element M to the total atomic number of the nickel element and the metal element M is set to X (at%), and when the ratio of the atomic number of the metal element M to the total atomic number of the nickel element and the metal element M is set to Y (at%) by ICP emission spectroscopy, the value of X/Y is 1.5 to 30.

The present invention also provides a method for producing nickel particles, comprising heating a mixed solution containing nickel hydroxide particles, a polyol, polyvinylpyrrolidone and polyethylenimine,

For 1 part by mass of polyethyleneimine, 30 to 200 parts by mass of polyvinylpyrrolidone is used,

The nickel hydroxide particles are reduced to nickel master particles by the heating,

Mixing the mixed solution with a compound of a metal element M in a state where a part of the nickel hydroxide particles remain, reducing the compound to the metal M, forming a surface region of an alloy containing nickel and the metal element M on the nickel master particles,

The metal element M is at least 1 selected from tin and zinc.

Drawings

Fig. 1 is a scanning electron microscope image of nickel particles obtained in example 3.

Fig. 2 is a scanning electron microscope image of nickel particles obtained in comparative example 2.

Detailed Description

The present invention will be described below based on preferred embodiments thereof. The nickel particles of the present invention have a nickel master particle and a surface region of an alloy containing nickel and a metal element M (hereinafter, also referred to as "nickel/metal M alloy") located on the surface of the master particle. The term "nickel master" as used herein refers to particles which are substantially composed of nickel element and contain unavoidable elements in the remainder. The unavoidable elements are, for example, oxygen and carbon elements originating from the atmosphere, carbon dioxide, nitrogen elements that may be mixed in during the production of nickel particles, and the like.

The nickel master particles in the nickel particles have a surface region comprising nickel/metal M alloy on the surface thereof. In the present specification, "nickel/metal M alloy" means a nickel-based alloy containing a metal element M described later. The nickel/metal M alloy is substantially composed of an alloy of a nickel element and a metal element M, and contains unavoidable elements in the remaining portion. In the surface region containing the nickel/metal M alloy, a part of the metal element M may also exist in an elemental state of the metal element M (i.e., a state of metal). Or a part of the metal element M may exist in the form of a compound of the metal element M. Or the metal element M may be present in a state in which two or more kinds thereof are combined. When the metal element M exists in the surface region containing the nickel/metal M alloy in the form of a compound of the metal element M, examples of the compound include, but are not limited to, oxides, hydroxides, sulfides, sulfur oxides, borides, phosphides, and the like containing the metal M. In particular, the fact that the metal element M in the surface region containing the nickel/metal M alloy substantially contains only an alloy with nickel is preferable from the viewpoint of maximizing the advantage that the nickel particles of the present invention have. In the present specification, "substantially only an alloy with nickel" means that the surface region is intentionally excluding a simple substance of a metal element M or a compound of a metal element M, which contains a metal element other than an alloy with nickel and is allowed to be inevitably mixed in a trace amount in the process of producing nickel particles.

The metal element M in the nickel particles is preferably at least 1 selected from tin and zinc. By using tin or zinc as the metal element M, the sintering resistance can be further improved without excessively increasing the resistance of the nickel particles. The metal element M may be any of tin and zinc, or may be both of tin and zinc. In the following description, when the metal element M (or the metal M) is referred to, tin or zinc or both tin and zinc are referred to depending on the context.

The fact that the nickel particles contain nickel/metal M alloy in the surface region thereof can be confirmed by the following method.

Specifically, first, it was confirmed by measurement by X-ray photoelectron spectroscopy (hereinafter also referred to as "XPS") that the nickel particles contained a metal element M in a surface region thereof, and that the metal element M was mainly in a metallic state. Next, it was confirmed that the a-axis length in the X-ray diffraction peak of the nickel particles was longer than the a-axis length in the X-ray diffraction peak obtained by measuring only nickel particles in advance. The elongation of the a-axis length in the X-ray diffraction peak means that the substance is solid-dissolved. Therefore, when the metal element M confirmed by XPS measurement exists in a metallic state in the surface region of the nickel particles and when the metal element M confirmed by a-axis length comparison dissolves in nickel, it can be confirmed that the nickel particles contain nickel/metal M alloy in the surface region.

The proportion of the nickel particles containing the metal element M in the surface region thereof can be determined by XPS. Specifically, when a region from the outermost surface to a sputtering depth of 5nm in terms of SiO ₂ conversion (hereinafter, this region is also referred to as "particle surface region") is measured by XPS in the depth direction of nickel particles, the value of X, which is the maximum value of the ratio of the atomic number of the metal element M to the total atomic number of the nickel element and the metal element M, in the particle surface region is preferably 0.5at% or more. The "maximum value" mentioned above refers to a maximum value of the value of X when a plurality of values of X measured along the thickness direction of the particle surface region are different. The presence of the metal element M in a region having an X value of 0.5at% or more is preferable from the viewpoint of further improving the sintering resistance of nickel particles described later. From the same viewpoint, the value (at%) of X is more preferably 0.5at% or more, still more preferably 1at% or more, and still more preferably 2at% or more. From the same viewpoint, the value (at%) of X is more preferably 70at% or less, still more preferably 30at% or less, and still more preferably 20at% or less. The method of measuring the value of X will be described in examples to be described later.

The term "outermost surface of nickel particles" as used herein refers to the outermost surface of nickel particles containing a surface treatment agent such as an organic acid or amine when the surface of nickel particles is provided with the surface treatment agent. When the surface treatment agent is not present on the surface of the nickel particles, the surface itself of the particles is referred to.

The nickel particles preferably contain 0.16 to 11.4 mass% of the metal element M relative to the whole nickel particles. When the content of the metal element M relative to the nickel particles is within this range, the sintering resistance can be further improved without excessively increasing the resistance of the nickel particles.

In the case where the metal element M is tin, the content of tin element relative to the entire nickel particles is more preferably 0.3 mass% or more, still more preferably 0.4 mass% or more, and still more preferably 1 mass% or more, from the same point of view as described above. The content of tin element relative to the entire nickel particles is more preferably 6 mass% or less.

In the case where the metal element M is zinc, the content of the zinc element relative to the entire nickel particles is more preferably 0.2 mass% or more, still more preferably 0.4 mass% or more, and still more preferably 0.5 mass% or more, from the same point of view as described above. The content of zinc element relative to the whole nickel particles is more preferably 6.7 mass% or less, and still more preferably 3.4 mass% or less.

The content of the metal element M in the whole nickel particles can be measured by ICP emission spectrometry described later.

The nickel particles of the present invention preferably have a value (at%) of Y, which is a ratio of the number of atoms of the metal element M to the total number of atoms of the nickel element and the metal element M, of 0.15at% to 6at%, provided that the content of the metal element M relative to the whole nickel particles satisfies the above-described range. The fact that the metal element M is present so that the value of Y falls within this range is preferable from the viewpoint of further improving the sintering resistance without excessively increasing the resistance of the nickel particles. From the same viewpoint, the value of Y is particularly preferably 0.2at% or more, and particularly preferably 0.5at% or more. The value of Y is particularly preferably not more than 6at%, and particularly preferably not more than 3 at%.

The value of Y, which is the ratio of the number of atoms of the metal element M contained in the entire nickel particle, is measured by ICP emission spectrometry. Specifically, first, the entire nickel particles were measured by ICP emission spectrometry to determine the content of nickel element and the content of metal element M. Next, the content ratio (mass%) of nickel element is divided by the atomic weight (58.7) of nickel element, and the content ratio is converted into atomic number a _Ni of nickel element. The content ratio (mass%) of the metal element M was divided by the atomic weight of the metal element M (tin: 118.7 and zinc: 65.4), and the content ratio was converted into the atomic number a _M of the metal element M. Then, the ratio (a _M/(A_Ni+A_M) ×100) of the atomic number of the metal element M to the atomic number a _Ni of the nickel element and the atomic number a _M of the metal element M was calculated, and the value of Y was obtained.

As a result of the study by the inventors of the present invention, it was found that the relation between the value of X and the value of Y affects the sintering resistance of nickel particles. Specifically, it was found that by setting the X/Y value to 1.5 to 30, the sintering temperature at which nickel particles begin to shrink increases, i.e., the sintering resistance increases. When the nickel particles of the present invention having high sintering resistance are used to manufacture, for example, an MLCC, the temperature at which the internal electrode is shrunk by sintering the nickel particles can be made as close as possible to the temperature at which the dielectric layer is shrunk by sintering the dielectric particles in the sintering step, which is one step of manufacture. The reduction of the difference between the temperatures at which the internal electrode and the dielectric layer shrink is advantageous in terms of overlapping the time at which the internal electrode and the dielectric layer shrink during the temperature increase in the firing step. Specifically, in the firing step of the MLCC, it is advantageous from the viewpoint that occurrence of structural defects such as cracks and delamination (delamination at the interface between the internal electrode and the dielectric layer) due to the difference in temperature and shrinkage rate between the internal electrode and the dielectric layer can be effectively prevented.

From the viewpoint of making the above advantages more remarkable, the value of X/Y in the nickel particles is more preferably 3.7 or more. The value of X/Y in the nickel particles is more preferably 20 or less, still more preferably 15 or less, still more preferably 13 or less, still more preferably 10 or less.

In the particle surface region, the value of the ratio of the atomic number of the metal element M to the total atomic number of the nickel element and the metal element M may be constant or may vary in the depth direction. In the case where the value of the ratio is not constant in the depth direction, the value of the ratio may be continuously or stepwise decreased from the surface of the nickel particles toward the center, for example. In particular, when the region from the outermost surface of the nickel particles to the sputtering depth of 20nm calculated by SiO ₂ conversion is measured by XPS, the above ratio is preferable in terms of further increasing the sintering resistance of the nickel particles from the outermost surface toward the sputtering depth of 20 nm. In this case, when the maximum value of the ratio in the region from the outermost surface of the nickel particles to the sputtering depth of 5nm is set to X and the maximum value of the ratio at the sputtering depth of 20nm is set to X1, the value of X/X1 is preferably 3.0 to 15, from the viewpoint of further improving the sintering resistance of the nickel particles. From the same viewpoint, the value of X/X1 is more preferably 3.8 or more, and still more preferably 4.3 or more. The value of X/X1 is more preferably 10 or less, still more preferably 7.8 or less, and still more preferably 6.1 or less. The method of measuring X1 will be described in examples to be described later.

The value of X1 itself is preferably 0.2 to 10, more preferably 0.5 to 6, still more preferably 0.7 to 4.1, and still more preferably 1.7 to 4.1, from the viewpoint of further improving the sintering resistance of nickel particles.

The number-cumulative particle diameter D ₅₀, which is the cumulative number of nickel particles of the present invention is 50% by number, is preferably 20nm to 200nm. In other words, the nickel particles of the present invention are preferably fine particles. When the particle diameter D ₅₀ of the nickel particles is within this range, there is an advantage that when the nickel particles of the present invention are used as internal electrodes of various applications, for example, MLCCs, short circuits between the internal electrodes are less likely to occur. From the viewpoint of further remarkable advantages, the particle diameter D ₅₀ of the nickel particles is more preferably 20nm to 170nm, still more preferably 20nm to 150nm, still more preferably 40nm to 100nm. The particle diameter D ₅₀ of the nickel particles was measured by observing the nickel particles with a Scanning Electron Microscope (SEM). Specifically, nickel particles were photographed at a magnification of 50000 times by SEM, and the area of the photographed nickel particles was determined. From this area, the equivalent circle diameter was calculated. The particle size distribution was obtained based on the calculated equivalent circle diameter. The particle size distribution is obtained by taking the equivalent circle diameter on the horizontal axis and the number frequency on the vertical axis of the graph. In the particle size distribution curve obtained in this way, the number cumulative particle diameter at which the cumulative number is 50% by number is defined as D ₅₀.

When the "particle size distribution curve" described above was obtained, the equivalent circle diameter was obtained for 5000 or more nickel particles. For calculation of the equivalent circle diameter, image analysis particle size distribution measurement software (Mac-View, manufactured by MOUNTECH Co., ltd.) was used. The minimum unit of nickel particles as an observation target was determined by whether or not the particle interface confirmed as an independent one particle was observed by SEM. Therefore, even if an agglomerate including a plurality of particles is observed, when a particle interface is observed in the agglomerate, a region defined by the particle interface is regarded as one particle.

The nickel particles of the present invention are preferably not only fine particles but also coarse particles in a small proportion. When the nickel particles of the present invention are used for, for example, the internal electrodes of MLCCs, the presence of coarse particles may cause short-circuiting between the internal electrodes. By reducing the presence ratio of coarse particles in the nickel particles, the short circuit can be effectively prevented. From this viewpoint, in the nickel particles of the present invention, the proportion of particles having a particle diameter of 1.5 times or more the D ₅₀ (hereinafter also referred to as "coarse particle existing proportion") is preferably 0.5% by number or less, more preferably 0.3% by number or less, and still more preferably 0.1% by number or less.

The more effective the coarse particle presence ratio is in preventing the occurrence of short-circuiting between the internal electrodes as the coarse particle presence ratio approaches 0%, but the more effective the prevention of short-circuiting between the internal electrodes can be achieved as long as the coarse particle presence ratio is as low as about 0.01%.

The reason why the particle having a particle size of 1.5 times or more of D ₅₀ is selected as the size of coarse particles is that the inventors of the present invention found that, when the particle size is 1.5 times or more of D ₅₀, the surface of the conductive film becomes rough when the conductive film is formed, which is closely related to the occurrence of short-circuiting between the internal electrodes of the MLCC.

The nickel particles of the present invention are preferably not only small in the presence ratio of fine particles and coarse particles, but also as uniform in particle size as possible. In other words, the particle size distribution curve is preferably sharp. The sharpness of the particle size distribution curve can be evaluated by the coefficient of variation of the particle size. The coefficient of variation is a value defined by (σ/D ₅₀) ×100 (%) when the standard deviation of the particle diameter in the particle size distribution is set to σ (nm). The value of the coefficient of variation of the nickel particles of the present invention is preferably 14% or less from the viewpoint of reducing the surface roughness of the conductive film formed of the nickel particles. The coefficient of variation is more preferably 13% or less, and still more preferably 12% or less, from the viewpoint of further reducing the surface roughness of the conductive film.

The closer the coefficient of variation is to 0%, the more contributes to the reduction of the surface roughness of the conductive film, but if the coefficient of variation is as low as about 8%, the surface roughness of the conductive film can be reduced to a level that is sufficiently satisfied.

The nickel particles of the present invention preferably have high crystallinity of nickel. The high crystallinity of nickel means that the nickel particles of the present invention undergo sintering and start to shrink at an elevated temperature. In other words, the high crystallinity of nickel means that the nickel particles exhibit high sintering resistance as described above.

The method of evaluating the crystallinity of nickel by Cs/D ₅₀, which is a ratio of the crystallite size Cs (nm) to the particle diameter D ₅₀ (nm), is often employed in the technical field of metal powders. The larger the Cs/D ₅₀ value, the higher the crystallinity of nickel can be evaluated. From this viewpoint, in the nickel particles of the present invention, the Cs/D ₅₀ value is preferably 0.3 or more, more preferably 0.34 or more, and even more preferably 0.37 or more.

The higher the Cs/D ₅₀ value, the higher the temperature at which the nickel particles start to shrink by sintering, but in the present invention, the Cs/D ₅₀ value is more preferably 0.55 or less, and still more preferably 0.52 or less, since the Cs/D ₅₀ value is preferably 0.6 or less, the temperature can be sufficiently increased.

The value of the crystallite size Cs itself is preferably 15nm to 70nm, more preferably 18nm to 70nm, and even more preferably 20nm to 70nm, from the viewpoint of sufficiently increasing the temperature at which the nickel particles start to shrink by sintering.

As a method for measuring the crystallite size, various methods are known in the art of metal powders, but the crystallite size in the present specification means a value obtained by measurement by WPPF (full spectrum fitting; white powder PATTERN FITTING) method. As a method for measuring the crystallite size, a scherrer method is known in addition to WPPF method, but when the degree of distortion of the crystal is large, the value of the crystallite size obtained by the scherrer method becomes less reliable, and therefore, WPPF method with less concern as described above is employed in the present invention.

Details of the method for measuring the crystallite size of nickel by WPPF method will be described in examples described later.

The nickel particles of the present invention preferably do not excessively increase the resistance. When such nickel particles are used for, for example, an internal electrode of an MLCC, the performance of the MLCC can be further improved. Thus, for the purpose of not excessively increasing the resistance, it is preferable to control the crystal structure of the nickel particles in such a manner that the pure nickel component in the nickel particles having the surface region containing the nickel/metal M alloy becomes large. From this point of view, in the nickel particles of the present invention, the a-axis length of the crystal lattice in the crystal structure of nickel is preferablyMore preferablyFurther preferred is

The a-axis length of the crystal lattice in the crystal structure of the nickel particles can be measured by an X-ray diffraction apparatus using cukα1 rays as described in examples described later. The analysis was obtained by WPPF method as described in examples described later.

The crystallite size and the a-axis length of the crystal lattice in the crystal structure of nickel of the present invention are achieved, for example, by adjusting the proportion of the nickel particles containing the metal element M in the surface region thereof and by thinning the thickness of the surface region containing the nickel/metal M alloy possessed by the nickel particles. In addition to or instead of this, the method may be achieved by appropriately adjusting the conditions in the method for producing nickel particles described later.

The degree of the sintering resistance of the nickel particles of the present invention can be evaluated by a thermo-mechanical analysis (TMA) with respect to the nickel particles. In the present invention, the temperature at which the TMA shrinkage (%) based on room temperature (25 ℃) becomes 5% is defined as the shrinkage start temperature. The temperature of 500 ℃ or higher is preferable from the viewpoint of further improving the sintering resistance of the nickel particles. From the viewpoint of making this advantage more remarkable, it is more preferably 530 ℃ or higher, still more preferably 550 ℃ or higher, and still more preferably 570 ℃ or higher.

Next, a preferred method for producing the nickel particles of the present invention will be described. In the present production method, nickel particles are produced by a so-called polyol method. The polyol method refers to a method using a polyol as a solvent which also serves as a reducing agent. In the polyol method, a reduction reaction to a nickel master is generated by heating in a state where a chemical species of nickel is present in a polyol, a compound of a metal element M is mixed before the completion of the reduction reaction, and further, a reduction reaction to a metal M is generated by heating, and a surface region including nickel/metal M alloy is formed on the nickel master.

In the present production method, nickel hydroxide is preferably used as a chemical species of nickel for producing nickel particles from the viewpoint of obtaining target nickel particles smoothly. Nickel hydroxide is added to a mixed solution containing a polyol, polyvinylpyrrolidone (hereinafter also referred to as "PVP"), and polyethylenimine (hereinafter also referred to as "PEI"). From the viewpoint of operability, nickel hydroxide having a particulate form is preferably used.

The polyol contained in the mixed solution is used as a solvent as described above and also as a reducing agent for nickel hydroxide.

Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1, 2-propanediol, dipropylene glycol, 1, 2-butanediol, 1, 3-butanediol, 1, 4-butanediol, 2, 3-butanediol, 1, 5-pentanediol, and polyethylene glycol. These polyols may be used alone or in combination of 2 or more. The ethylene glycol in these polyols is preferable because it has a high ratio of hydroxyl groups to molecular weight, and therefore has high reducing performance, is liquid at ordinary temperature, and is excellent in handleability.

The amount of the polyhydric alcohol to be used is not particularly limited as long as it is appropriately adjusted according to the amount of nickel hydroxide in the mixed solution, from the viewpoint of using the polyhydric alcohol as a reducing agent. On the other hand, when the solvent is intended to function, the properties of the mixed solution change depending on the concentration of the polyol in the mixed solution, and thus, there is a certain proper concentration range. From this viewpoint, the concentration of the polyol in the mixed solution is preferably set to a range of 50 mass% to 99.8 mass%.

PVP is used as a dispersant for nickel hydroxide. PVP is preferable because it has a remarkable effect as a dispersant and can sharpen the particle size distribution of nickel particles produced by reduction. The molecular weight of the PVP may be appropriately adjusted according to the degree of water solubility and dispersibility. The amount of PVP in the mixed solution is preferably set to 0.01 to 30 parts by mass per 100 parts by mass of nickel converted from nickel hydroxide. By setting the viscosity to this range, the dispersion effect can be sufficiently exhibited without excessively increasing the viscosity of the mixed solution.

PEI has an effect of reducing the number of nickel ions in the mixed solution during the formation of nuclei of nickel in the mixed solution, and making the nuclei formation and the nuclei growth not proceed simultaneously. The reason for this is that (a) PEI has a non-covalent electron pair that interacts with nickel ions and is capable of coordinate bonding with nickel ions, (b) PEI has a large number of the non-covalent electron pairs, and (c) PEI has hydrogen bond sites that interact with the surface of nickel hydroxide that is present in an undissolved state in the mixed solution.

The presence of PEI in the mixed solution enables the sequential formation of nickel nuclei and the growth of the nuclei formed. As a result, nickel particles having a uniform particle diameter can be smoothly obtained. In contrast, in the production of conventional nickel particles by reduction, since the nucleation and the nucleation are simultaneously generated, coarse particles are easily generated and the particle size is easily uneven.

From the above viewpoints, it is advantageous to use branched PEI as the PEI as compared with the linear PEI. From the same point of view, PEI having a number average molecular weight of 600 to 10000, particularly PEI having a number average molecular weight of 800 to 5000, and particularly PEI having a number average molecular weight of 1000 to 3000 is preferably used.

In particular, in the present production method, by setting the ratio of PVP to PEI contained in the mixed solution to a specific range, the nucleation and the nuclear growth of nickel are successively performed, and thus the reliability is improved. Specifically, 30 to 200 parts by mass of PVP is preferably used, 40 to 150 parts by mass of PVP is more preferably used, and 50 to 130 parts by mass of PVP is more preferably used, per 1 part by mass of PEI.

The amount of PEI in the mixed solution is appropriately set according to the amount of PVP, provided that the ratio of PVP to PEI satisfies the above-described range.

The mixed solution may contain a noble metal catalyst. This allows fine noble metal nuclei to be produced in the early stage of the reduction, and nickel is smoothly reduced with the nuclei as starting points. As the noble metal catalyst, for example, a noble metal compound such as a water-soluble salt of a noble metal can be used. Examples of the water-soluble salts of noble metals include water-soluble salts of palladium, silver, platinum, gold, and the like. In the case of using palladium as the noble metal, for example, palladium chloride, palladium nitrate, palladium acetate, ammonium palladium chloride, or the like can be used. In the case of using silver, for example, silver nitrate, silver lactate, silver oxide, silver sulfate, silver cyclohexanoate, silver acetate, or the like can be used. In the case of using platinum, for example, platinic chloride, potassium platinate chloride, sodium platinate chloride, or the like can be used. In the case of gold, for example, gold acid chloride, sodium gold chloride, or the like can be used. Among them, palladium nitrate, palladium acetate, silver nitrate and silver acetate are preferably used because they are inexpensive and economical. The noble metal catalyst may be used in the form of the above-mentioned compound or in the form of an aqueous solution obtained by dissolving the compound in water. The amount of the noble metal catalyst contained in the mixed solution is preferably 0.01 to 5 parts by mass, particularly preferably 0.01 to 1 part by mass, based on 100 parts by mass of nickel converted from nickel hydroxide.

The mixture containing the above components was heated while stirring, and nickel hydroxide was reduced. The heating temperature varies depending on the type of the polyhydric alcohol used, but the nickel hydroxide can be smoothly reduced to the nickel master particles by heating at atmospheric pressure preferably at 150 to 200 ℃, more preferably at 170 to 200 ℃, still more preferably at 190 to 200 ℃.

Then, before the reduction reaction of nickel hydroxide is completed, a compound of the metal element M is mixed in the above mixed solution. In other words, the compound of the metal element M is mixed in the mixed solution in a state where a part of nickel hydroxide remains. The term "before the completion of the reduction reaction of nickel hydroxide" as used herein means before 80mol% or more of the nickel hydroxide is reduced with respect to the amount of nickel hydroxide charged. When the metal element M is tin, at least one compound selected from sodium stannate 3 hydrate, tin (II) chloride, and tin (IV) chloride is preferably used as the compound, and sodium stannate 3 hydrate is particularly preferably used, from the viewpoint of smoothly forming a surface region including nickel/metal M alloy on the nickel master particles in a reduction reaction of a compound of the metal element M to be described later. In the case where the metal element M is zinc, from the same viewpoints as described above, at least one compound selected from zinc sulfate, zinc nitrate, zinc chloride, zinc hydroxide and zinc oxide is preferably used, and zinc hydroxide is particularly preferably used.

When the metal element M is tin, the amount of the tin compound in the mixed solution is preferably set to 0.016 parts by mass or more, more preferably 0.003 parts by mass or more, still more preferably 0.004 parts by mass or more, and even more preferably 0.01 parts by mass or more, based on 1 part by mass of the amount of nickel to be charged, from the viewpoint of smoothly forming the surface region of the alloy containing nickel and tin on the nickel master particles. The amount of the tin compound in the mixed solution is preferably set to 0.12 parts by mass or less, more preferably 0.06 parts by mass or less, based on 1 part by mass of nickel to be charged, in terms of tin.

When the metal element M is zinc, the amount of the zinc compound in the mixed solution is preferably set to 0.016 parts by mass or more, more preferably 0.002 parts by mass or more, still more preferably 0.004 parts by mass or more, and even more preferably 0.005 parts by mass or more, based on 1 part by mass of the amount of nickel to be charged, in terms of successfully forming the surface region of the alloy containing nickel and zinc on the nickel master particles. The amount of the zinc compound in the mixed solution is preferably set to 0.12 parts by mass or less, more preferably 0.070 parts by mass or less, and even more preferably 0.034 parts by mass or less, based on 1 part by mass of nickel to be added, in terms of zinc.

Next, the mixed solution containing the compound of the metal element M is heated while stirring, and nickel hydroxide in the mixed solution and the compound are reduced. By this reduction reaction, nickel hydroxide remaining in the mixed solution is reduced to nickel, and in the case where the metal element M is tin, the compound of the metal element M is reduced to tin, and in the case where the metal element M is zinc, the compound of the metal element M is reduced to zinc. In this reduction reaction, nickel hydroxide and a compound of metal element M are simultaneously reduced, whereby a surface region containing a nickel/metal M alloy in which nickel element and metal M are homogeneously dissolved is formed on the surface of nickel master particles. The metal element M may be partially present in a simple substance state of the metal element M, a compound state of the metal element M, or a combination of two or more thereof, as long as the effects of the present invention can be exhibited.

The heating temperature of the above-mentioned mixed solution varies depending on the type of the polyhydric alcohol and the compound of the metal element M used, but is preferably 150 to 200 ℃, more preferably 170 to 200 ℃, and even more preferably 190 to 200 ℃ under atmospheric pressure. By setting the heating temperature to be within this range, the nickel hydroxide and the compound of the metal element M can be reduced simultaneously, and a surface region including nickel/metal M alloy can be smoothly formed on the surface of the nickel master particle.

Thereafter, if necessary, the polyol in the obtained nickel particle dispersion is replaced with water, and then the replaced water is replaced with methanol again to wash the nickel particles, followed by vacuum drying. The nickel particles of the present invention can be produced by doing so.

In the case of producing nickel particles containing the metal element M, a PVD method or a CVD method may be performed by adding a raw material of the metal element M to a nickel raw material. The nickel particles in this case become nickel/metal M alloy in their entirety. However, when the sintering resistance of the nickel particles is to be improved, the content of tin and/or zinc, which are metal elements M in the whole nickel particles, becomes too high, and as a result, there is a problem that the electrical resistance becomes high. In addition, since the particle size of nickel particles becomes uneven, the surface of the conductive film becomes rough when the conductive film is formed using the nickel particles, and there is a problem that it is one of the causes of occurrence of short-circuits between internal electrodes of MLCCs. As another method for producing nickel particles containing a metal element M, as described in patent document 2, a method of reducing the entire amount of nickel hydroxide and then adding a compound of the metal element M is known. In this case, a layer of elemental tin and/or zinc, which is a metal element M having a lower melting point than nickel, is formed on the surface of the nickel particles. However, the sintering resistance of the nickel particles is caused by the surface of the particles being formed of a layer of an elemental tin and/or zinc and not becoming high. In contrast, according to the nickel particles of the present invention including the nickel master particles and the nickel/metal M alloy disposed on the surface thereof, the sintering resistance can be improved without excessively increasing the resistance. Further, if the nickel particles of the present invention are used to form a conductive film, the surface of the conductive film can be smoothed. For these reasons, as described above, it is preferable to produce nickel particles by reducing the nickel hydroxide and the compound of the metal element M simultaneously in a state where a part of the nickel hydroxide remains.

The nickel particles produced by the above method, although being fine particles and uniform in particle diameter, can be used in various fields by utilizing the feature that the surface area containing nickel/metal M alloy is provided on the surface of the nickel particles. In particular, the method is suitable for forming internal electrodes of MLCC.

The present invention has been described based on preferred embodiments thereof, but the present invention is not limited to the above embodiments. For example, the present inventors have studied the fact that the nickel particles of the present invention have a surface region containing nickel/tin alloy on the surface thereof, and have found that the above-described advantages can be sufficiently exhibited even when the nickel particles are produced using zinc element instead of tin element. In other words, the inventors of the present invention have found that the above-described advantages can be sufficiently exhibited even when the nickel particles have a surface region containing nickel/zinc alloy, the content of zinc element relative to the entire nickel particle is within a predetermined range, and when the region from the outermost surface to a sputtering depth of 5nm calculated by SiO ₂ conversion is measured by X-ray photoelectron spectroscopy in the depth direction of the nickel particle, the maximum value of the ratio of the atomic number of zinc element to the total atomic number of nickel element and zinc element in the region is set to X2, and when the nickel particles are measured by ICP emission spectrometry, the value of X2/Y1 is within a predetermined range. Such nickel particles can be easily produced by using zinc element instead of tin element in the above-described preferred production method of nickel particles of the present invention. Further, in the above-described production method, even when nickel particles having a surface region containing nickel/tin/zinc alloy are produced by using zinc together with tin, the above-described advantages can be fully exhibited.

The present invention has been described based on preferred embodiments thereof, but the present invention is not limited to the above embodiments.

The following nickel particles and the method for producing the same are further disclosed with respect to the above embodiments.

[ 1] A nickel particle having a surface region comprising an alloy of nickel and a metal element M,

The metal element M is at least 1 selected from tin and zinc,

The nickel particles according to item [ 2 ], wherein, in the particle size distribution obtained based on the equivalent circle diameter calculated by measurement using a scanning electron microscope, D ₅₀ is 20nm to 200nm when the number cumulative particle diameter at 50% by number is set to D ₅₀,

When the standard deviation of the particle diameter in the particle size distribution is set to σ (nm), the variation coefficient (σ/D ₅₀) (%) is 14% or less.

Coefficient of variation (%) = (σ/D ₅₀) ×100

The nickel particles according to [1] or [ 2], wherein the proportion of particles having a particle diameter of 1.5 times or more of D ₅₀ is 0.5% by number or less, when the number-cumulative particle diameter at 50% by number of cumulative particles is set to D ₅₀, based on the particle size distribution obtained by measuring the equivalent circle diameter by a scanning electron microscope.

The nickel particles according to any one of [1 ] to [ 3], wherein, in the particle size distribution obtained based on the equivalent circle diameter calculated by measurement using a scanning electron microscope, the number cumulative particle diameter at 50% by number is set to D ₅₀, and the crystallite size measured by WPPF method is set to Cs (nm), and the value of Cs/D ₅₀ is 0.3 to 0.6.

[ 5 ] A method for producing nickel particles, wherein a mixed solution containing nickel hydroxide particles, a polyol, polyvinylpyrrolidone and polyethylenimine is heated to produce nickel particles,

The metal element M is at least 1 selected from tin and zinc.

A multilayer ceramic capacitor wherein the nickel particles of any one of [ 1] to [ 4 ] are used as the internal electrode.

Examples

Hereinafter, the present invention will be described in more detail with reference to examples. The scope of the invention is not limited to the embodiments described. Unless otherwise specified, "%" means "% by mass".

[ Example 1]

A500 ml beaker was charged with 445g of ethylene glycol, 64g of nickel hydroxide particles, 12g of polyvinylpyrrolidone, 0.14g of polyethylenimine and 0.13ml of an aqueous palladium nitrate solution (concentration: 100 g/l) to prepare a mixed solution. The polyethyleneimine was branched polyethyleneimine, and the number average molecular weight was 1800. The mixture was heated with stirring, and the reduction reaction was carried out at 198℃under atmospheric pressure for 5 hours. At this time, 80mol% of nickel hydroxide was reduced with respect to the amount of nickel hydroxide charged. Then, 0.5g of sodium stannate 3 hydrate was added thereto, and the reduction reaction was further carried out at 198℃for 10 hours under atmospheric pressure. Stopping heating to finish the reduction, and naturally cooling to room temperature. In this way, a large amount of nickel particles were obtained.

A magnet was placed at the bottom of a beaker containing the obtained dispersion of nickel particles, and the nickel particles were attracted to the magnet. In this state, the supernatant of the dispersion was removed.

After removing the magnet from the bottom of the beaker, 50g of pure water was added and the dispersion was stirred for 10 minutes. Thereafter, the magnet was again disposed at the bottom of the beaker to attract the nickel particles to the magnet. In this state, the supernatant of the dispersion was removed. A series of operations were repeated 5 times.

Next, 50g of methanol was added and the dispersion was stirred for 10 minutes. The removal of the supernatant was repeated 3 times by using a magnet, and the solvent in the dispersion was replaced with methanol. Thereafter, vacuum drying was performed at 80 ℃ to obtain nickel particles.

[ Examples 2 to 6]

The amounts of palladium nitrate aqueous solution and sodium stannate 3 hydrate added and the time from the start of heating the mixed solution to the addition of sodium stannate 3 hydrate to the mixed solution were set as shown in table 1. Except for these, nickel particles were obtained in the same manner as in example 1.

[ Examples 7 to 12 ]

Zinc hydroxide was added instead of sodium stannate 3 hydrate. The amount of palladium nitrate aqueous solution and the amount of zinc hydroxide added were set as shown in table 1. Except for these, nickel particles were obtained in the same manner as in example 1.

Comparative example 1

A500 ml beaker was charged with 445g of ethylene glycol, 64g of nickel hydroxide particles, 8g of polyvinylpyrrolidone, 0.14g of polyethyleneimine and 0.13ml of an aqueous palladium nitrate solution (concentration: 100 g/l) to prepare a mixed solution. The polyethyleneimine was branched polyethyleneimine, and the number average molecular weight was 1800. The mixture was heated with stirring, and the reduction reaction was performed at 198℃for 6.5 hours. Stopping heating to finish the reduction, and naturally cooling to room temperature. In this way, a large amount of nickel particles were obtained.

Next, 50g of methanol was added and the dispersion was stirred for 10 minutes. The removal of the supernatant was repeated 3 times by using a magnet, and the solvent in the dispersion was replaced with methanol. Thereafter, vacuum drying was performed at 80 ℃ to obtain a powder of nickel particles.

Comparative example 2

Nickel particles were obtained in the same manner as in example 1, except that sodium stannate 3 hydrate was added before the reduction reaction of nickel hydroxide was performed.

[ Comparative example 3]

After 300g of pure water and hydrazine 1 hydrate were added to the dispersion and the temperature was raised to 60 ℃, 1g of sodium stannate 3 hydrate was added thereto, and stirring was performed for 5 hours, to surface-treat nickel particles with tin.

Next, 50g of methanol was added and the dispersion was stirred for 10 minutes. The removal of the supernatant was repeated 3 times by using a magnet, and the solvent in the dispersion was replaced with methanol. Thereafter, vacuum drying was performed at 80 ℃ to obtain a powder of nickel particles surface-treated with tin. As described in [ evaluation 1] described later, it was confirmed that the surface region of the nickel particles was free of nickel-tin alloy and a tin surface layer was formed.

[ Evaluation 1]

The values of X and X1 were obtained by the following XPS analysis method for the nickel particles obtained in examples 1 to 12 and comparative examples 1 to 3.

Further, the content of tin element and zinc element relative to the whole nickel particles and the value of Y were obtained by ICP emission spectrometry.

The particle size distribution was measured by the above method, and the particle diameter D ₅₀, the coarse particle presence ratio, and the coefficient of variation were obtained.

The a-axis length and crystallite size Cs of nickel by WPPF method were determined by the following method.

Further, it was confirmed by the above-described method whether or not an alloy of nickel and tin, and further, an alloy of nickel and zinc was contained in the surface region of the nickel particles.

The results are shown in table 1 below. SEM images of the nickel particles obtained in example 3 and comparative example 2 are shown in fig. 1 and 2.

[ X-ray photoelectron Spectrometry (XPS) measurement ]

As the sample to be measured for XPS, a sample obtained by forming nickel particles into particles by a press machine was used. Specifically, a particle sample of about 10mg was added to an aluminum container having a dimension of phi 5.2mm and a height of 2.5 mm. Then, the aluminum container was pressurized with a predetermined stroke (25 mm) using a press (model: 1-312-01, manufactured by AS ONE) and an adapter (model: 1-312-03). Then, the particle-shaped product of nickel particles supported by the aluminum container was taken out.

The obtained particle molded product was subjected to the outermost surface measurement and the depth direction measurement from the sample surface toward the inside by sputtering with Ar monomer ions. The measurement conditions were as follows.

Measuring apparatus, ULVAC-PHI Co., ltd VersaProbeIII

Exciting X-rays monochromatization of Al-K alpha rays (1486.7 eV)

Output power 50W

Accelerating voltage of 15kV

X-ray irradiation diameter 200 μm phi

X-ray scanning area 1000 μm X300 μm

Detection angle of 45 DEG

Band pass energy 26.0eV

Energy step size 0.1eV/step

Sputtering ion species Ar monomer ion

Sputtering rate 3.3nm/min (SiO ₂ conversion)

Sputtering interval of 20s

Measuring element C _1s、Ni_2p3、Sn_3d5、Zn_2p3

Energy correction value C-C bond and C-H bond in C _1s (284.8 eV)

[ Analysis of XPS data ]

XPS data was analyzed using data analysis software (ULVAC-PHI company, "MultiPak Ver9.9"). Background mode Shirley was used.

[ Value of X ]

In examples 1 to 6, the ratio of the atomic number of Sn _3d5 to the total atomic number of the total 2 elements of Ni _2p3 and Sn _3d5 was set to X (at%). In examples 7 to 12, the ratio of the atomic number of Zn _2p3 to the total atomic number of the total 2 elements of Ni _2p3 and Zn _2p3 was set to X (at%).

[ Measurement of a Axis Length and crystallite size Cs ]

The a-axis length and crystallite size Cs of the nickel particles obtained in examples and comparative examples were calculated from the diffraction peak derived from nickel obtained by X-ray diffraction measurement using WPPF method.

Device name SmartLab (9 KW): rigaku Corporation system

< Device Structure >

Wavelength of

Target Cu

Wavelength type Kα1

·Kα1:

·Kα2:

·Kβ:

Kα12 intensity ratio 0.4970

Horizontal polarization ratio of 0.500

Diffraction device

Goniometer SmartLab

Accessory base Z-stage alone

Accessory ASC 6-reflection

< Measurement conditions >

Optical system Property, concentration method

CBO selection slit BB

Incident parallel slit: soller_slot_5.0 deg

Entrance slit 2/3deg

Length limiting slit 10.0mm

Light receiving slit 1:20.000mm

Light-receiving parallel slit Soller_slit_5.0deg

Light receiving slit 2:20.000mm

Attenuator: on

Detector D/teX Ultra250,250

Scanning axis 2 theta/theta

Scan mode: continuous

Scanning range 5.0000-140.0000deg

Step size 0.0100deg

Scanning speed/measurement time 2.015572deg/min

Data Point number 13501 Point

Guan Dianya:45 kV

Guan Dianliu:200 mA

·HV:0.00

< Preparation of sample for X-ray diffraction >

The measurement holder was filled with nickel particles to be measured, and the measurement holder was smoothed by using a glass plate so that the thickness of the layer formed of nickel particles became 0.5mm and the measurement surface was smoothed.

The X-ray diffraction pattern obtained under the above measurement conditions was analyzed by analysis software under the following conditions. In the analysis, data obtained from lanthanum hexaboride powder (SRM 660 series), which is a standard substance supplied by National Institute of Standards and Technology (NIST), was used for correction. The a-axis length and crystallite size Cs were calculated using WPPF method.

< Analysis conditions of measurement data >

Analysis software, manufactured by Rigaku system PDXL2

Analysis method WPPF method

Data processing automatic profile processing

(Rigaku Corporation PDXL instruction for use p.305)

[ Evaluation 2]

The shrinkage initiation temperature of the nickel particles, the resistivity of the sintered film containing the nickel particles, and the surface roughness Rz were measured for the nickel particles obtained in examples 1 to 12 and comparative examples 1 to 3 by the following methods. The results are shown in table 1 below.

[ Measurement of shrinkage onset temperature ]

As a measurement device for TMA, TMA/SS 6000 manufactured by Seiko Instruments Co., ltd was used. 0.2to 0.3g of nickel particles are placed in a stainless steel mold container having a diameter of 5.0mm, and the nickel particles are pressed and molded so as to exert a pressure of 92MPa thereon, thereby producing particles. The particle length of the obtained particles was measured and used as a sample to be measured. This was set in a measuring apparatus, and the temperature of the sample was raised at 5℃per minute under an atmosphere of 1% hydrogen by volume/99% nitrogen by volume at a load of 49 mN. Measurement was started from room temperature (25 ℃) to obtain a graph showing the relationship between temperature and shrinkage (%). The shrinkage start temperature was determined from the obtained graph.

[ Measurement of resistivity ]

0.1G of ethylcellulose was dissolved in 4g of terpineol, followed by adding 5g of nickel particles to obtain a mixture. The mixture was mixed with a rotation/revolution mixer (a-awa, registered trademark, manufactured by thin corporation). The mixture was then crushed in a three-roll mill 4 times. The gap of the three-roll mill was set to 8 μm. The coating liquid was obtained in this manner.

The coating liquid is applied to an alumina substrate to form a coating film. The thickness of the coating film was 30. Mu.m. The film was sintered at 800 ℃ for 60 minutes in an atmosphere of 1% hydrogen by volume/99% nitrogen by volume to obtain a sintered film. For this sintered film, loresta MCP-T600, manufactured by Mitsubishi Analytech, was used as a four-probe resistivity measuring device to measure resistivity (Ω. Cm).

[ Measurement of surface roughness Rz ]

The surface roughness Rz of the sintered film was measured using SURFCOM 130A. The measurement conditions were set so that the evaluation length was 6.0mm and the measurement speed was 0.6mm/s.

TABLE 1

As is evident from the results shown in table 1, it was confirmed by XPS measurement that the nickel particles obtained in examples 1 to 6 contained tin element in a metallic state in the surface region thereof. Further, the a-axis length of the nickel particles obtained in the examples was longer than that of the nickel particles obtained in comparative example 1 in which no tin compound was used. From these results, it is known that the nickel particles obtained in examples 1 to 6 contain an alloy of nickel and tin in the surface region thereof.

Further, as shown by the results shown in table 1, it was confirmed by XPS measurement that the nickel particles obtained in examples 7 to 12 contained zinc element in a metallic state in the surface region thereof. Further, the a-axis length of the nickel particles obtained in the examples was longer than that of the nickel particles obtained in comparative example 1 in which no zinc compound was used. From these results, it is known that the nickel particles obtained in examples 7 to 12 contain an alloy of nickel and zinc in the surface region thereof.

Further, as shown by the results shown in table 1, the nickel particles obtained in examples 1 to 12 exhibited a higher shrinkage start temperature than the nickel particles obtained in comparative examples 1 to 3. It was found that the nickel particles obtained in examples 1 to 12 exhibited high sintering resistance.

In particular, as is evident from comparison of examples 1 to 5 with example 6, it is known that the resistivity of the sintered film obtained from the nickel particles can be controlled by controlling the amount of tin contained in the nickel particles.

In addition, examples 1 to 6, in which nickel particles having a surface region in which an alloy of nickel and tin was formed, were produced, and the surface of the sintered film was smoother than comparative example 2, in which an alloy of nickel and tin was formed in the whole nickel particles. From these, it is known that the surface roughness of the sintered film becomes low according to nickel particles having a surface region containing an alloy of nickel and tin.

Further, when fig. 1 corresponding to example 3 and fig. 2 corresponding to comparative example 2 are compared, it can be seen that the nickel particles of fig. 1 have a uniform particle size, whereas the nickel particles of fig. 2 have a non-uniform particle size.

Industrial applicability

According to the present invention, nickel particles having high sintering resistance without excessively increasing the electrical resistance can be provided.

Claims

1. Nickel particles having a surface region comprising an alloy of nickel and a metallic element M,

The metal element M is at least 1 selected from tin and zinc,

When a region from the outermost surface to a sputtering depth of 5nm calculated by SiO ₂ conversion is measured in the depth direction of the nickel particles by X-ray photoelectron spectroscopy, the maximum value of the ratio of the atomic number of the metal element M to the total atomic number of the nickel element and the metal element M is set as X in at%, and when the nickel particles are measured by ICP emission spectroscopy, the value of X/Y is set as Y in at%, the maximum value of the ratio of the atomic number of the metal element M to the total atomic number of the nickel element and the metal element M is set as 1.5-30.

2. The nickel particles according to claim 1, wherein D ₅₀ is 20nm to 200nm when the number cumulative particle diameter at 50% by number of cumulative particles is D ₅₀ based on the particle size distribution obtained by measuring the equivalent circle diameter by a scanning electron microscope,

When the standard deviation of particle diameters in the particle size distribution is set to sigma in nm, the variation coefficient (sigma/D ₅₀) has a value of 14% or less,

Coefficient of variation (%) = (σ/D ₅₀) ×100.

3. The nickel particles according to claim 1, wherein, in the particle size distribution obtained based on the equivalent circle diameter calculated by measurement using a scanning electron microscope, when the number cumulative particle diameter at which the cumulative number is 50% is set to D ₅₀, the proportion of particles having a particle diameter of 1.5 times or more of D ₅₀ is 0.5% by number or less.

4. The nickel particles according to claim 1, wherein, in the particle size distribution obtained based on the equivalent circle diameter calculated by measurement using a scanning electron microscope, the number cumulative particle diameter when the cumulative number is 50% is set to D ₅₀, and the crystallite size measured by WPPF method is set to Cs in nm, the Cs/D ₅₀ value is 0.3 to 0.6.

5. A method for producing nickel particles, comprising heating a mixed solution containing nickel hydroxide particles, a polyol, polyvinylpyrrolidone and polyethyleneimine,

Reducing the nickel hydroxide particles to nickel master particles by the heating,

The metal element M is at least 1 selected from tin and zinc.

6. A multilayer ceramic capacitor using the nickel particles according to any one of claims 1 to 4 as an internal electrode.