JP7340728B1 - Nickel particles and method for producing nickel particles - Google Patents

Abstract

These are nickel particles having a surface area containing an alloy of nickel and metal element M. The metal element M is at least one selected from bismuth, copper, iron, and molybdenum. The content of the metal element M with respect to the entire nickel particles is 0.09% by mass or more and 15.8% by mass or less. When a region from the outermost surface to a sputtering depth of 5 nm in terms of SiO2 is measured in the depth direction of a nickel particle by X-ray photoelectron spectroscopy, in this region, the metal element relative to the total number of atoms of nickel element and metal element M The maximum value of the ratio of the number of atoms of M is set as X (at%), and when nickel particles are measured by ICP emission spectrometry, 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 When Y (at%), the value of X/Y is 0.5 or more and 35 or less.

Description

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

Nickel particles are generally used to form internal electrodes of multilayer ceramic capacitors (hereinafter also referred to as "MLCC") used in electronic devices. When manufacturing a MLCC, when a stack of internal electrodes containing nickel particles and a dielectric layer is simultaneously fired, defects may occur in the internal electrodes due to differences in the sintering temperatures of the raw materials. In order to prevent such inconveniences, it is desired to improve the sintering resistance of nickel particles.

For example, Patent Document 1 discloses a technique in which nickel powder containing tin or bismuth obtained by PVD or CVD is used to form internal electrodes of MLCC. This document states that by adding a non-magnetic metal such as tin to nickel powder, the crystal structure of nickel is distorted, thereby increasing the sintering temperature of the nickel powder.

Patent Document 2 discloses a technique in which nickel powder having a substantially spherical particle shape and surface-treated with tin is used to form internal electrodes of an MLCC. The document also discloses surface treatment using bismuth in addition to tin. The document states that the nickel powder described in the document improves its sintering behavior.

International Publication No. 2014/080600 pamphlet Japanese Patent Application Publication No. 2018-104819

Incidentally, as the performance of electronic devices has improved in recent years, it has become necessary to further prevent inconveniences caused by defects that may occur in internal electrodes in MLCCs. In order to meet this demand, nickel particles have not only improved sintering resistance, but also prevent excessively increasing the electrical resistance of internal electrodes when the nickel particles are used to form internal electrodes. It is hoped that there will be no such thing.
Therefore, an object of the present invention is to provide nickel particles that have high sintering resistance without excessively increasing electrical resistance.

The present invention provides nickel particles having a surface area containing an alloy of nickel and a metal element M,
The metal element M is at least one selected from bismuth, copper, iron, and molybdenum,
The content of the metal element M with respect to the entire nickel particles is 0.09% by mass or more and 15.8% by mass or less,
When a region from the outermost surface to a sputtering depth of 5 nm in terms of SiO ₂ is measured in the depth direction of the nickel particles by X-ray photoelectron spectroscopy, it is found that the total number of atoms of nickel element and metal element M in this region is Let the maximum value of the ratio of the number of atoms of the metal element M be X (at%),
When the nickel particles are measured 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 Y (at%),
The present invention provides nickel particles having an X/Y value of 0.5 or more and 35 or less.

The present invention also provides a method for producing nickel particles by heating a liquid mixture containing nickel hydroxide particles, polyol, polyvinylpyrrolidone, and polyethyleneimine, comprising:
Using 30 parts by mass or more and 200 parts by mass or less of polyvinylpyrrolidone for 1 part by mass of polyethyleneimine,
reducing the nickel hydroxide particles to nickel base particles by the heating;
While some of the nickel hydroxide particles remain, the mixed liquid is mixed with a compound of metal element M, and the compound is reduced to metal M, so that nickel and metal element are added to the nickel mother particles. A method for producing nickel particles forming a surface region comprising an alloy with M, the method comprising:
The metal element M is at least one selected from bismuth, copper, iron, and molybdenum, and provides a method for producing nickel particles.

The present invention will be described below based on its preferred embodiments. The nickel particles of the present invention have a nickel base particle and a surface area containing an alloy of nickel and metal element M (hereinafter also referred to as "nickel/metal M alloy") located on the surface of the base particle. ing. The term "nickel mother particles" as used herein refers to particles that are substantially composed of nickel element and the remainder contains unavoidable elements. Unavoidable elements include, for example, oxygen elements and carbon elements derived from oxygen and carbon dioxide in the atmosphere, and nitrogen elements that may be mixed in during the manufacturing process of nickel particles.

The nickel base particles in the nickel particles have a surface region containing the nickel-metal M alloy on the surface thereof. In this specification, "nickel/metal M alloy" refers to a nickel-based alloy containing metal element M, which will be described later. The nickel/metal M alloy is substantially composed of an alloy of nickel element and metal element M, and the remainder contains unavoidable elements. In the surface region containing the nickel/metal M alloy, a part of the metal element M may exist in a simple state (that is, a metal state). Alternatively, a part of the metal element M may exist in a state of a compound of the metal element M. Alternatively, the metal element M may be present in a combination of two or more types thereof. When the metal element M is present in the surface area containing the nickel/metal M alloy in the form of a compound of the metal element M, the compound includes, for example, an oxide, hydroxide, sulfide, or sulfide containing the metal M. , borides, phosphides, etc., but are not limited to these. Of course, it is desirable that the metal element M in the surface region containing the nickel-metal M alloy consists essentially only of an alloy with nickel, from the viewpoint of maximizing the inherent advantages of the nickel particles of the present invention. In this specification, "substantially consisting only of an alloy with nickel" means intentionally excluding that the surface region contains a metal element M other than an alloy with nickel, and in the process of manufacturing the nickel particles. The purpose is to allow a trace amount of a single metal element M or a compound of a metal element M to be mixed in unavoidably.

The metal element M in the nickel particles is preferably at least one selected from bismuth, copper, iron, and molybdenum. When the metal element M is bismuth, copper, iron, or molybdenum, the sintering resistance can be further improved without excessively increasing the electrical resistance of the nickel particles. As the metal element M, only one of bismuth, copper, iron, and molybdenum may be used, or any combination of two or more thereof may be used. In the following description, the metal element M (or metal M) means bismuth, copper, iron, molybdenum, or a combination of two or more of these, depending on the context.

It can be confirmed by the following method that the nickel particles contain the nickel/metal M alloy in their surface region.
Specifically, first, the nickel particles contain a metal element M in the surface region, and it is determined that the metal element M is mainly in a metallic state by measurement using X-ray photoelectron spectroscopy (hereinafter also referred to as "XPS"). confirm. Next, it is confirmed that the a-axis length of the X-ray diffraction peak of the nickel particles is longer than the a-axis length of the obtained X-ray diffraction peak obtained by measuring only the nickel particles in advance. An increase in the a-axis length in the X-ray diffraction peak means that the substance is in solid solution. Therefore, in addition to the fact that the metal element M, which was confirmed by XPS measurement, exists in a metallic state in the surface area of the nickel particles, the metal element M, which was confirmed by the comparison of the a-axis lengths, and nickel are in solid solution. From this fact, it can be confirmed that the nickel particles contain a nickel/metal M alloy in their surface area.

The proportion of the metal element M in the surface region of the nickel particles can be measured by XPS. Specifically, when measuring the region from the outermost surface to the sputtering depth of 5 nm in terms of SiO ₂ (hereinafter, this region is also referred to as "particle surface region") in the depth direction of the nickel particle by XPS. In the particle surface region, the value of X, which is 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 preferably 0.5 at % or more. The above-mentioned "maximum value" refers to the maximum value of the X values when a plurality of X values measured along the thickness direction of the particle surface region are different. It is preferable that the metal element M is present so as to have a portion where the value of X is 0.5 at % or more, from the viewpoint of further increasing the sintering resistance of the nickel particles described below.
When the metal element M is bismuth, from the same viewpoint as above, the value of X (at%) is more preferably 1 at% or more, even more preferably 2 at% or more, and even more preferably 3 at% or more. It is more preferably 7 at% or more, even more preferably 7 at% or more, and particularly preferably 14 at% or more. Further, the value of X (at%) is more preferably 70 at% or less, even more preferably 35 at% or less, even more preferably 30 at% or less, and even more preferably 20 at% or less. Preferably, it is particularly preferably 15 at% or less.
When the metal element M is copper, from the same viewpoint as above, the value of X (at%) is more preferably 1 at% or more, even more preferably 2 at% or more, and even more preferably 4 at% or more. More preferably, it is 8 at% or more, even more preferably 8 at% or more, and particularly preferably 12 at% or more. Moreover, the value of preferable.
When the metal element M is iron, from the same viewpoint as above, the value of X (at%) is more preferably 1 at% or more, even more preferably 2 at% or more, and even more preferably 4 at% or more. It is even more preferable that the content is 7 at% or more, and even more preferable that it is 7 at% or more. Further, the value of X (at%) is more preferably 70 at% or less, even more preferably 35 at% or less, even more preferably 30 at% or less, and even more preferably 20 at% or less. The content is preferably 9 at% or less, particularly preferably 9 at% or less.
When the metal element M is molybdenum, from the same viewpoint as above, the value of X (at%) is more preferably 1 at% or more, even more preferably 2 at% or more, and even more preferably 4 at% or more. It is even more preferable that the content is 8 at% or more, and even more preferable that it is 8 at% or more. Moreover, the value of preferable.
A method for measuring the value of X will be explained in the examples described later.
The above-mentioned "outermost surface of the nickel particle" refers to the outermost surface of the nickel particle containing the surface treatment agent, if a surface treatment agent such as an organic acid or amine is present on the surface of the nickel particle. refers to When no surface treatment agent is present on the surface of nickel particles, it refers to the surface of the particles themselves.

The nickel particles preferably contain 0.09% by mass or more and 15.8% by mass or less of the metal element M based on the entire nickel particles. When the content of the metal element M in the nickel particles is within this range, the sintering resistance can be further improved without excessively increasing the electrical resistance of the nickel particles.
When the metal element M is bismuth, from the same viewpoint as above, the content of the bismuth element relative to the entire nickel particle is more preferably 0.3% by mass or more, and preferably 0.4% by mass or more. The content is more preferably 1% by mass or more, even more preferably 6.7% by mass or more. Further, the content of bismuth element relative to the entire nickel particles is more preferably 15.8% by mass or less, even more preferably 13% by mass or less, even more preferably 11.4% by mass or less, It is even more preferable that the amount is 10% by mass or less.
When the metal element M is copper, from the same viewpoint as above, the content of the copper element relative to the entire nickel particle is more preferably 0.4% by mass or more, and even more preferably 1% by mass or more. , more preferably 2.1% by mass or more, and even more preferably 4.3% by mass or more. Further, the content of copper element relative to the entire nickel particles is more preferably 11.4% by mass or less, even more preferably 7.6% by mass or less, and even more preferably 6.5% by mass or less. It is preferably 6% by mass or less, even more preferably 5.4% by mass or less, and particularly preferably 5.4% by mass or less.
When the metal element M is iron, from the same viewpoint as above, the content of the iron element relative to the entire nickel particle is more preferably 0.09% by mass or more, and preferably 0.28% by mass or more. The content is more preferably 0.40% by mass or more, even more preferably 0.47% by mass or more. Further, the content of iron element relative to the entire nickel particles is more preferably 11.4% by mass or less, even more preferably 6% by mass or less, even more preferably 2.87% by mass or less, It is even more preferably 1.91% by mass or less, and particularly preferably 0.96% by mass or less.
When the metal element M is molybdenum, from the same viewpoint as above, the content of the molybdenum element relative to the entire nickel particle is more preferably 0.4% by mass or more, and even more preferably 1% by mass or more. , more preferably 1.1% by mass or more, and even more preferably 1.6% by mass or more. Further, the content of the molybdenum element relative to the entire nickel particles is more preferably 11.4% by mass or less, even more preferably 6.4% by mass or less, even more preferably 6% by mass or less, It is even more preferably 4.9% by mass or less, and particularly preferably 3.3% by mass or less.
The content of the metal element M in the entire nickel particles can be measured by ICP emission spectrometry described below.

The nickel particles of the present invention have atoms of the metal element M relative to the total number of atoms of the nickel element and the metal element M in the whole nickel particle, provided that the content of the metal element M in the whole nickel particle satisfies the above range. The value of Y (at%), which is a numerical ratio, is preferably 0.1 at% or more and 7 at% or less. It is preferable that the metal element M is present so that the value of Y is within this range, from the viewpoint of further increasing the sintering resistance without excessively increasing the electrical resistance of the nickel particles.
When the metal element M is bismuth, from the same viewpoint as above, the value of Y is more preferably 0.1 at% or more, even more preferably 0.2 at% or more, and even more preferably 0.3 at% or more. More preferably, it is 0.5 at% or more, even more preferably 0.5 at% or more, and particularly preferably 2 at% or more. Further, the value of Y is more preferably 6 at% or less, even more preferably 5 at% or less, even more preferably 4 at% or less, and even more preferably 3 at% or less.
When the metal element M is copper, from the same viewpoint as above, the value of Y is more preferably 0.2 at% or more, even more preferably 0.5 at% or more, and even more preferably 1 at% or more. It is more preferably 2 at% or more, even more preferably 2 at% or more, and particularly preferably 4 at% or more. Further, the value of Y is more preferably 7 at% or less, even more preferably 6 at% or less, and even more preferably 5 at% or less.
When the metal element M is iron, from the same viewpoint as above, the value of Y is more preferably 0.1 at% or more, even more preferably 0.2 at% or more, and even more preferably 0.3 at% or more. It is more preferable that it is, and even more preferable that it is 0.5 at% or more. Further, the value of Y is more preferably 6 at% or less, even more preferably 3 at% or less, even more preferably 2 at% or less, and even more preferably 1 at% or less.
When the metal element M is molybdenum, from the same viewpoint as above, the value of Y is more preferably 0.2 at% or more, even more preferably 0.3 at% or more, and even more preferably 0.5 at% or more. It is more preferably 0.7 at% or more, even more preferably 0.7 at% or more, and particularly preferably 1 at% or more. Further, the value of Y is more preferably 6 at% or less, even more preferably 4 at% or less, even more preferably 3 at% or less, and even more preferably 2 at% or less.

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 particle is measured by ICP emission spectroscopy, and the content ratio of nickel element and the content ratio of metal element M are determined. Next, the content ratio (mass %) of the nickel element is divided by the atomic weight (58.7) of the nickel element, and the content ratio is converted into the number of atoms A _Ni of the nickel element. In addition, the content ratio (mass%) of the metal element M is divided by the atomic weight of the metal element M (209 for bismuth, 63.6 for copper, 55.9 for iron, 96 for molybdenum), and the content ratio is calculated by dividing the content ratio (mass%) of the metal element M. Number of atoms of M A Convert to _M. Then, calculate the ratio of the number of atoms of the metal element _M to the number of atoms of the nickel element A _Ni and the number of atoms of the metal element M (A _M / (A _Ni + A _M ) × 100), and obtain the value of Y. .

As a result of studies conducted by the present inventors, it was found that the relationship between the value of X and the value of Y affects the sintering resistance of nickel particles. Specifically, it has been found that by setting the value of X/Y to 0.5 or more and 35 or less, the temperature at which nickel particles start shrinking due to sintering increases, that is, the sintering resistance increases. The nickel particles of the present invention, which have high sintering resistance, can be used to manufacture, for example, an MLCC, in the firing step, which is one of the manufacturing steps, by controlling the temperature at which the internal electrodes shrink due to sintering of the nickel particles to a dielectric material. By sintering the particles, the temperature at which the dielectric layer contracts can be brought as close as possible. It is advantageous to reduce the difference in temperature at which the internal electrodes and the dielectric layer contract, since the times at which the internal electrodes and the dielectric layer contract overlap in the temperature raising process of the firing process. Specifically, in the firing process of MLCC, structural defects such as cracks and delamination (layer separation at the interface between the internal electrode and dielectric layer) caused by differences in temperature and shrinkage rate at which the internal electrode and dielectric layer contract This is advantageous from the viewpoint of effectively preventing the occurrence of.

When the metal element M is bismuth, the value of X/Y in the nickel particles is more preferably 1.5 or more, and more preferably 3.7 or more, from the viewpoint of making the above advantages even more remarkable. is more preferable, more preferably 4 or more, even more preferably 5 or more, particularly preferably 7 or more. The value of X/Y in the nickel particles is more preferably 30 or less, even more preferably 25 or less, and even more preferably 20 or less.
When the metal element M is copper, the value of X/Y in the nickel particles is more preferably 0.5 or more, and more preferably 1 or more, from the viewpoint of making the above advantages even more remarkable. It is preferably 1.5 or more, more preferably 2 or more, and even more preferably 2 or more. The value of X/Y in the nickel particles is more preferably 30 or less, even more preferably 15 or less, even more preferably 13 or less, even more preferably 10 or less, and 7 or less. It is particularly preferable that the number is 3 or less, and particularly preferably 3 or less.
When the metal element M is iron, the value of X/Y in the nickel particles is more preferably 1 or more, and more preferably 1.5 or more, from the viewpoint of making the above advantages even more remarkable. It is preferably 3.7 or more, more preferably 5 or more, even more preferably 10 or more. The value of X/Y in the nickel particles is more preferably 30 or less, even more preferably 25 or less, even more preferably 20 or less, and even more preferably 15 or less.
When the metal element M is molybdenum, the value of X/Y in the nickel particles is more preferably 1 or more, and more preferably 1.5 or more, from the viewpoint of making the above advantages even more remarkable. It is preferably 3 or more, more preferably 3.7 or more, even more preferably 3.7 or more, and particularly preferably 5 or more. The value of X/Y in the nickel particles is more preferably 30 or less, even more preferably 15 or less, even more preferably 13 or less, even more preferably 10 or less, and 7 or less. It is particularly preferable that there be.

In the particle surface region, 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 may be constant or may vary in the depth direction. When the value of the ratio is not constant in the depth direction, the value of the ratio may decrease continuously or stepwise, for example, from the surface of the nickel particle toward the center. In particular, when measuring the region from the outermost surface of a nickel particle to a sputtering depth of 20 nm in terms of SiO ₂ by XPS, it was found that the value of the ratio gradually decreased from the outermost surface toward a sputtering depth of 20 nm. , is preferable because the sintering resistance of the nickel particles becomes even higher. In this case, when the maximum value of the ratio in the region from the outermost surface of the nickel particle to the sputtering depth of 5 nm is X, and the maximum value of the ratio in the sputtering depth of 20 nm is X1, the value of X/X1 is 0. The number is preferably 1 or more and 15 or less from the viewpoint of further improving the sintering resistance of the nickel particles.
When the metal element M is bismuth, the value of preferable. Further, the value of X/X1 is more preferably 10 or less, even more preferably 7.8 or less, even more preferably 6.1 or less, even more preferably 4 or less, It is particularly preferably 3 or less, and even more preferably 2.5 or less.
When the metal element M is copper, the value of X/X1 is more preferably 0.1 or more, even more preferably 0.5 or more, and 1 or more, from the same viewpoint as above. is more preferable. Further, the value of X/X1 is more preferably 10 or less, even more preferably 7.8 or less, even more preferably 6.1 or less, even more preferably 5 or less, It is particularly preferable that it is 3 or less.
When the metal element M is iron, the value of X/X1 is more preferably 0.1 or more, even more preferably 0.5 or more, and 1 or more, from the same viewpoint as above. is more preferable. Further, the value of X/X1 is more preferably 10 or less, even more preferably 7.8 or less, even more preferably 6.1 or less, even more preferably 5 or less, It is particularly preferable that it is 2 or less.
When the metal element M is molybdenum, the value of X/X1 is more preferably 0.1 or more, still more preferably 1 or more, and even more preferably 2 or more, from the same viewpoint as above. preferable. Further, the value of X/X1 is more preferably 10 or less, even more preferably 7.8 or less, even more preferably 6.1 or less, even more preferably 5 or less, It is particularly preferable that it is 3 or less.
The method for measuring X1 will be explained in the Examples described later.

When the metal element M is bismuth, the value of X1 itself is preferably 0.2 or more, and more preferably 0.5 or more, from the viewpoint of further increasing the sintering resistance of the nickel particles. It is preferably 0.7 or more, more preferably 1.7 or more, even more preferably 2 or more, particularly preferably 5 or more. Further, the value of X1 itself is more preferably 15 or less, even more preferably 10 or less, and even more preferably 7 or less.
When the metal element M is copper, the value of X1 itself is preferably 0.2 or more, and more preferably 0.5 or more, from the viewpoint of further increasing the sintering resistance of the nickel particles. It is preferably 0.7 or more, more preferably 1 or more, even more preferably 1.7 or more, particularly preferably 3 or more, particularly preferably 5 or more. Particularly preferred. Further, the value of X1 itself is more preferably 20 or less, even more preferably 15 or less, and even more preferably 10 or less.
When the metal element M is iron, the value of X1 itself is preferably 0.2 or more, and more preferably 0.5 or more, from the viewpoint of further increasing the sintering resistance of the nickel particles. preferably 0.7 or more, even more preferably 1 or more, particularly preferably 1.7 or more, particularly preferably 2 or more, especially 4 or more. Particularly preferred. Further, the value of X1 itself is more preferably 15 or less, even more preferably 10 or less, and even more preferably 6 or less.
When the metal element M is molybdenum, the value of X1 itself is preferably 0.2 or more, and more preferably 0.5 or more, from the viewpoint of further increasing the sintering resistance of the nickel particles. preferably 0.7 or more, even more preferably 1 or more, particularly preferably 1.7 or more, particularly preferably 2 or more, especially 4 or more. Particularly preferred. Further, the value of X1 itself is more preferably 15 or less, even more preferably 10 or less, even more preferably 6 or less, and even more preferably 5 or less.

The nickel particles of the present invention preferably have a value of _D50 , which is the cumulative particle diameter at a cumulative number of 50% by number, of 20 nm or more and 200 nm or less. In other words, the nickel particles of the present invention are preferably fine particles. By having the particle size _D50 of the nickel particles within this range, when the nickel particles of the present invention are used for various purposes, for example, as internal electrodes of MLCC, there is an advantage that short circuits between the internal electrodes are less likely to occur. be. From the viewpoint of making this advantage even more remarkable, the particle size _D50 of the nickel particles is more preferably 20 nm or more and 150 nm or less, even more preferably 40 nm or more and 150 nm or less, and even more preferably 40 nm or more and 100 nm or less. More preferred. The particle size _D50 of the nickel particles is measured by observing the nickel particles with a scanning electron microscope (SEM). Specifically, a nickel particle is photographed using an SEM at a magnification of 50,000 times, and the area of the photographed nickel particle is determined. Calculate the equivalent circle diameter from the area. Particle size distribution is determined based on the calculated circle equivalent diameter. In the particle size distribution, the horizontal axis of the graph represents the equivalent circle diameter, and the vertical axis represents the number frequency. In the particle size distribution curve obtained in this manner, the number cumulative particle diameter at a cumulative number of 50% by number is defined as _D50 .

When obtaining the above-mentioned "particle size distribution curve", the equivalent circular diameters of 5000 or more nickel particles are determined. Image analysis particle size distribution measurement software (Mac-View, manufactured by Mountech Co., Ltd.) is used to calculate the equivalent circle diameter. The minimum unit of nickel particles to be observed is determined by whether a particle interface recognized as an independent particle is observed by SEM. Therefore, even if an aggregate consisting of a plurality of particles is observed, if a particle interface is observed in the aggregate, the area defined by the particle interface is recognized as one particle.

The nickel particles of the present invention preferably have a small proportion of coarse particles in addition to being fine particles. The presence of coarse particles may cause a short circuit between the internal electrodes of an MLCC, for example, when the nickel particles of the present invention are used in the internal electrodes of the MLCC. This short circuit can be effectively prevented by reducing the proportion of coarse particles in the nickel particles. From this point of view, in the nickel particles of the present invention, the abundance ratio of particles having a particle size of 1.5 times or more than _D50 (hereinafter also referred to as "coarse particle abundance ratio") is 0.5 number % or less. The content is preferably 0.3% by number or less, more preferably 0.1% by number or less, and even more preferably 0.1% by number or less.
The closer the coarse particle abundance ratio is to 0%, the more effective it is in preventing short circuits between internal electrodes, but if the coarse particle abundance ratio is as low as about 0.01%, it is more effective in preventing short circuits between internal electrodes. can be prevented.
The reason why we selected particles with a particle size of 1.5 times or more of _D50 as a measure of coarse particles is that if the particle size is 1.5 times or more of _D50 , the surface of the conductive film will be damaged when the conductive film is formed. This is because the present inventor has discovered that this is a cause of roughness, and that this is extremely closely involved in the occurrence of short circuits between internal electrodes of MLCC.

The nickel particles of the present invention are preferably fine particles with a low proportion of coarse particles, and in addition, the particle size is preferably as uniform as possible. In other words, it is preferable that the particle size distribution curve is sharp. The sharpness of the particle size distribution curve can be evaluated by the coefficient of variation of particle size. The coefficient of variation is a value defined by (σ/D ₅₀ )×100(%), where σ (nm) is the standard deviation of particle diameter in the particle size distribution. The nickel particles of the present invention preferably have a coefficient of variation of 14% or less from the viewpoint of reducing the surface roughness of a conductive film formed from the nickel particles. From the viewpoint of further reducing the surface roughness of the conductive film, the coefficient of variation is more preferably 13% or less, and even more preferably 12% or less.
The closer the coefficient of variation is to 0%, the more it contributes to reducing 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 is reduced to a sufficiently satisfactory level. can be done.

The nickel particles of the present invention preferably have high nickel crystallinity. High crystallinity of nickel means that the temperature at which the nickel particles of the present invention sinter and begin to shrink increases. In other words, the high crystallinity of nickel means that the nickel particles exhibit high sintering resistance, as described above.
A method of evaluating the crystallinity of nickel using Cs/D ₅₀ , which is the ratio of crystallite size Cs (nm) to particle size D ₅₀ (nm), is often used in the technical field of metal powders. It can be evaluated that the larger the value of Cs/D ₅₀ , the higher the crystallinity of nickel. From this point of view, 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 larger the value of Cs/D ₅₀ , the higher the temperature at which nickel particles sinter and start shrinking. In the present invention, if the value of Cs/D ₅₀ is preferably 0.6 or less, It is possible to raise the temperature sufficiently, and from this point of view, the value of Cs/D ₅₀ is more preferably 0.55 or less, and even more preferably 0.52 or less.

The value of the crystallite size Cs itself is preferably 15 nm or more and 70 nm or less, and more preferably 18 nm or more and 70 nm or less, from the viewpoint of sufficiently increasing the temperature at which the nickel particles sinter and start shrinking. , more preferably 20 nm or more and 70 nm or less.

Various methods for measuring crystallite size are known in the technical field of metal powders, and in this specification, crystallite size refers to a value measured by the WPPF (whole powder pattern fitting) method. be. In addition to the WPPF method, the Scherrer method is known as a method for measuring crystallite size. However, if the degree of crystal distortion is large, the crystallite size value determined based on the Scherrer method may be unreliable. Therefore, in the present invention, the WPPF method, which is less likely to cause such a risk, is adopted.
Details of the method for measuring the nickel crystallite size based on the WPPF method will be explained in the Examples described later.

It is preferable that the nickel particles of the present invention do not excessively increase electrical resistance. When such nickel particles are used, for example, in the internal electrodes of an MLCC, the performance of the MLCC can be further improved. Therefore, in order to prevent the electrical resistance from increasing excessively, it is necessary to control the crystal structure of the nickel particles so that the pure nickel component in the nickel particles having a surface area containing the nickel/metal M alloy increases. preferable. From this point of view, in the nickel particles of the present invention, the a-axis length of the crystal lattice in the nickel crystal structure is preferably 3.520 Å or more and 3.529 Å or less, and preferably 3.522 Å or more and 3.526 Å or less. More preferably, the thickness is 3.523 Å or more and 3.526 Å or less, even more preferably 3.524 Å or more and 3.526 Å or less.

The a-axis length of the crystal lattice in the crystal structure of the nickel particles can be measured by an X-ray diffraction device using CuKα1 rays, as described in Examples below. The analysis is performed using the WPPF method as described in the Examples below.

The crystallite size and the a-axis length of the crystal lattice in the crystal structure of the nickel of the present invention can be determined, for example, by adjusting the proportion of the metal element M in the surface area of the nickel particles, or by adjusting the nickel-metal M alloy that the nickel particles have. This can be achieved by reducing the thickness of the surface area involved. In addition to this, or instead of this, it can also be achieved by appropriately adjusting the conditions in the method for producing nickel particles, which will be described later.

The degree of sintering resistance of the nickel particles of the present invention can be evaluated by thermomechanical analysis (TMA) of the nickel particles. In the present invention, the temperature at which the TMA shrinkage rate (%) is 5% based on room temperature (25° C.) is defined as the shrinkage start temperature. It is preferable that the temperature is 400° C. or higher in order to further improve the sintering resistance of the nickel particles. From the viewpoint of making this advantage even more remarkable, the temperature is more preferably 450°C or higher, even more preferably 500°C or higher, even more preferably 550°C or higher, and even more preferably 570°C or higher. More preferred.

Next, a preferred method for producing nickel particles of the present invention will be explained. In this manufacturing method, nickel particles are manufactured by a so-called polyol method. The polyol method is a method in which a polyol is used as a solvent that also serves as a reducing agent. In the polyol method, a chemical species of nickel is heated in a state in which it is present in a polyol to cause a reduction reaction to nickel mother particles, and a compound of the metal element M is mixed before the end of the reduction reaction. , further heating is performed to cause a reduction reaction to metal M, and a surface region containing a nickel/metal M alloy is formed on the nickel mother particles.

In this production method, it is preferable to use nickel hydroxide as the chemical species of nickel for producing nickel particles, from the viewpoint of successfully obtaining the desired nickel particles. Nickel hydroxide is added to a liquid mixture containing polyol, polyvinylpyrrolidone (hereinafter also referred to as "PVP"), and polyethyleneimine (hereinafter also referred to as "PEI"). From the viewpoint of ease of handling, it is preferable to use nickel hydroxide having a particulate form.

As described above, the polyol contained in the mixed liquid is used as a solvent and also as a reducing agent for nickel hydroxide.
Examples of polyols 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, polyethylene glycol, and the like can be used. These polyols can be used alone or in combination of two or more. Among these polyols, ethylene glycol is preferable because it has a high reducing performance due to a large proportion of hydroxyl groups relative to the molecular weight, and is liquid at room temperature and is easy to handle.

Considering the polyol as a reducing agent, the amount of polyol to be used may be appropriately adjusted depending on the amount of nickel hydroxide in the mixed solution, so there is no need to set any particular limitations on the amount of polyol used. On the other hand, when attempting to function as a solvent, the properties of the mixed liquid change depending on the concentration of polyol in the mixed liquid, so a certain appropriate concentration range exists. From this point of view, it is preferable to set the concentration of the polyol in the mixed liquid in a range of 50% by mass or more and 99.8% by mass or less.

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 these PVPs may be appropriately adjusted depending on the degree of water solubility and dispersibility. The amount of PVP in the mixed liquid is preferably 0.01 parts by mass or more and 30 parts by mass or less based on 100 parts by mass of nickel hydroxide converted to nickel. By setting it within this range, the dispersion effect can be sufficiently exhibited without making the viscosity of the liquid mixture excessively high.

PEI has the function of reducing the number of nickel ions in the mixed liquid while nickel nuclei are being generated in the mixed liquid, so that nucleation and growth do not proceed at the same time. The reason for this is that (a) PEI has lone pairs of electrons that interact with nickel ions and can form a coordinate bond with nickel ions, and (b) PEI has lone pairs of electrons that interact with nickel ions. and (c) PEI has a hydrogen bonding site that can interact with the surface of nickel hydroxide present in an undissolved state in the mixed liquid. It is.

The presence of PEI in the mixed solution makes it possible to sequentially perform the nucleation of nickel and the growth of the generated nuclei. As a result, fine nickel particles having a uniform particle size can be successfully obtained. In contrast, in the conventional production of nickel particles by reduction, nucleation and growth occur simultaneously, which tends to produce coarse particles and, moreover, tends to cause variations in particle size.
From the above viewpoint, it is more advantageous to use a branched PEI than a linear PEI. From the same viewpoint, it is also preferable to use PEI having a number average molecular weight of 600 or more and 10,000 or less, particularly 800 or more and 5,000 or less, particularly 1,000 or more and 3,000 or less.

In particular, in this manufacturing method, by setting the ratio of PVP and PEI contained in the liquid mixture within a specific range, it is ensured that nickel nucleation and nucleation are performed sequentially. Specifically, it is preferable to use 30 parts by mass or more and 200 parts by mass or less of PVP, more preferably 40 parts by mass or more and 150 parts by mass or less, and 50 parts by mass or more and 130 parts by mass or less, per 1 part by mass of PEI. It is more preferable to use

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

The mixed solution can also contain a noble metal catalyst. As a result, fine core particles of the noble metal are generated in the initial stage of reduction, and nickel is smoothly reduced from the core particles as a starting point. 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 water-soluble salts of noble metals include water-soluble salts of palladium, silver, platinum, gold, and the like. When using palladium as the noble metal, for example, palladium chloride, palladium nitrate, palladium acetate, ammonium palladium chloride, etc. can be used. When using silver, for example, silver nitrate, silver lactate, silver oxide, silver sulfate, silver cyclohexanoate, silver acetate, etc. can be used. When using platinum, for example, chloroplatinic acid, potassium chloroplatinate, sodium chloroplatinate, etc. can be used. When using gold, for example, chloroauric acid, sodium chloroaurate, etc. can be used. Among these, palladium nitrate, palladium acetate, silver nitrate, and silver acetate are preferably used because they are cheap and economical. The noble metal catalyst can be added and used in the form of the above-mentioned compound or in the form of an aqueous solution in which the compound is dissolved in water. The amount of the noble metal catalyst to be contained in the mixed solution should be 0.01 parts by mass or more and 5 parts by mass or less, particularly 0.01 parts by mass or more and 1 part by mass or less, per 100 parts by mass of nickel hydroxide converted to nickel. is preferred.

A mixed solution containing the above components is heated while stirring to reduce nickel hydroxide. The heating temperature depends on the type of polyol used, but heating is preferably performed at 150°C or more and 200°C or less, more preferably 170°C or more and 200°C or less, and even more preferably 190°C or more and 200°C or less under atmospheric pressure. By this method, nickel hydroxide can be successfully reduced to nickel mother particles.

Next, before the reduction reaction of nickel hydroxide is completed, a compound of the metal element M is mixed into the mixed liquid. In other words, the compound of the metal element M is mixed into the liquid mixture while some nickel hydroxide remains. Here, "before the reduction reaction of nickel hydroxide is completed" means before 80 mol% or more of the charged amount of nickel hydroxide is reduced.
When the metal element M is bismuth, from the viewpoint of successfully forming a surface area containing a nickel/metal M alloy on the nickel base particles in the reduction reaction of the compound of the metal element M described later, the compound may be bismuth nitrate or chloride. It is preferable to use at least one selected from the group consisting of bismuth, bismuth nitrate pentahydrate, bismuth hydroxide, bismuth oxide, and bismuth carbonate, and it is particularly preferable to use bismuth chloride.
When the metal element M is copper, from the same viewpoint as above, the compounds include copper nitrate trihydrate, copper sulfate pentahydrate, copper acetate monohydrate, copper hydroxide, cuprous oxide, and copper oxide. It is preferable to use at least one selected from the group consisting of copper, and it is particularly preferable to use copper sulfate pentahydrate.
When the metal element M is iron, from the same viewpoint as above, the compound is a group consisting of iron nitrate nonahydrate, iron chloride hexahydrate, iron sulfate heptahydrate, iron hydroxide, and iron oxide. It is preferable to use at least one selected from the following, and it is particularly preferable to use iron sulfate heptahydrate.
When the metal element M is molybdenum, from the same viewpoint as above, it is preferable to use at least one member selected from the group consisting of sodium molybdate, potassium molybdate, calcium molybdate, and ammonium molybdate. Particular preference is given to using sodium chloride.

When the metal element M is bismuth, from the viewpoint of successfully forming a surface area containing an alloy of nickel and bismuth on the nickel base particles, the amount of bismuth compound in the mixed liquid is 1 mass of the charged bismuth. The amount of nickel is preferably 0.003 parts by mass or more, more preferably 0.004 parts by mass or more, even more preferably 0.01 parts by mass or more, and 0.02 parts by mass. It is more preferable that the amount is more than 1 part. Further, the amount of bismuth compound in the mixed liquid is preferably 0.20 parts by mass or less, and 0.16 parts by mass or less, in terms of bismuth, per 1 part by mass of nickel in the mixture. is more preferable, more preferably 0.13 parts by mass or less, even more preferably 0.12 parts by mass or less.

When the metal element M is copper, from the viewpoint of successfully forming a surface area containing an alloy of nickel and copper on the nickel base particles, the amount of copper compound in the mixed solution is 1 mass of copper in terms of copper. The amount of nickel per part is preferably 0.004 parts by mass or more, more preferably 0.01 parts by mass or more, even more preferably 0.022 parts by mass or more, and 0.045 parts by mass. It is more preferable that the amount is more than 1 part. In addition, the amount of copper compound in the mixed liquid is preferably 0.12 parts by mass or less, and 0.082 parts by mass or less, in terms of copper, per 1 part by mass of nickel in the mixture. is more preferable, it is still more preferably 0.07 parts by mass or less, and even more preferably 0.06 parts by mass or less.

When the metal element M is iron, from the viewpoint of successfully forming a surface area containing an alloy of nickel and iron on the nickel base particles, the amount of iron compound in the mixed liquid is 1 mass of iron in terms of iron. The amount of nickel is preferably 0.0009 parts by mass or more, more preferably 0.0028 parts by mass or more, even more preferably 0.004 parts by mass or more, and 0.0047 parts by mass. It is more preferable that the amount is more than 1 part. In addition, the amount of iron compound in the mixed liquid is preferably 0.12 parts by mass or less, and 0.08 parts by mass or less, in terms of iron, per 1 part by mass of nickel in the mixture. is more preferable, it is still more preferably 0.06 parts by mass or less, even more preferably 0.030 parts by mass or less, and even more preferably 0.020 parts by mass or less.

When the metal element M is molybdenum, from the viewpoint of successfully forming a surface area containing an alloy of nickel and molybdenum on the nickel base particles, the amount of molybdenum compound in the mixed solution is calculated as 1 mass of molybdenum. The amount of nickel is preferably 0.004 parts by mass or more, more preferably 0.01 parts by mass or more, even more preferably 0.013 parts by mass or more, and 0.016 parts by mass. It is more preferable that the amount is more than 1 part. In addition, the amount of molybdenum compound in the mixed liquid is preferably 0.12 parts by mass or less, and 0.07 parts by mass or less, in terms of molybdenum, relative to 1 part by mass of nickel charged. It is more preferably 0.06 parts by mass or less, even more preferably 0.051 parts by mass or less, and even more preferably 0.034 parts by mass or less.

Next, the mixture containing the compound of the metal element M is heated while stirring to reduce the nickel hydroxide and the compound in the mixture. By this reduction reaction, the nickel hydroxide remaining in the mixed liquid is reduced to nickel, and when the metal element M is bismuth, the compound of the metal element M is reduced to bismuth. Alternatively, when the metal element M is copper, the compound of the metal element M is reduced to copper. Alternatively, when the metal element M is iron, the compound of the metal element M is reduced to iron. Alternatively, when the metal element M is molybdenum, the compound of the metal element M is reduced to molybdenum. In this reduction reaction, by simultaneously reducing nickel hydroxide and a compound of metal element M, a surface area containing a nickel/metal M alloy in which nickel element and metal M are homogeneously dissolved on the surface of the nickel mother particles is formed. is formed. Note that, as long as the effects of the present invention are achieved, a part of the metal element M may exist in the form of a single metal element M, a compound of the metal element M, or a combination of two or more of these. Permissible.

The heating temperature of the liquid mixture depends on the type of the polyol used and the compound of the metal element M, but is preferably 150°C or more and 200°C or less, more preferably 170°C or more and 200°C or less, and even more preferably 170°C or more and 200°C or less, under atmospheric pressure. is 190°C or more and 200°C or less. By setting the heating temperature within this range, the compound of nickel hydroxide and metal element M can be simultaneously reduced, and a surface region containing a nickel/metal M alloy can be successfully formed on the surface of the nickel mother particles.

Thereafter, if necessary, the polyol in the resulting dispersion of nickel particles is replaced with water, and then the replaced water is replaced again with methanol to wash the nickel particles, followed by vacuum drying. In this way, the nickel particles of the present invention can be manufactured.

When manufacturing nickel particles containing the metal element M, the raw material for the metal element M can be added to the nickel raw material and then a PVD method or a CVD method can be performed. In this case, a nickel/metal M alloy is formed over the entire nickel particle. However, when trying to increase the sintering resistance of the nickel particles, the content of metal elements M such as bismuth, copper, iron, and/or molybdenum in the entire nickel particles becomes excessively high, resulting in high electrical resistance. There was a problem. In addition to this, the particle size of the nickel particles is non-uniform, so when a conductive film is formed using the nickel particles, the surface of the conductive film becomes rough, which can lead to short circuits between the internal electrodes of the MLCC. The issue was that this could be one of the causes. Furthermore, as another method for manufacturing nickel particles containing metal element M, there is a known method in which a compound of metal element M is added after reducing the entire amount of nickel hydroxide, as described in Patent Document 2. There is. In this case, when bismuth and/or copper is used as the metal element M, a single layer of bismuth and/or copper having a melting point lower than that of nickel is formed on the surface of the nickel particles. However, the sintering resistance of these nickel particles was not high because the surface of the particles consisted of a single layer of bismuth and/or copper. In addition, when using iron and/or molybdenum as the metal element M, a layer containing iron oxide and/or molybdenum oxide is formed on the surface of the nickel particles due to the fact that iron and molybdenum are easily oxidized. It is formed. If nickel particles on which such a layer is formed are fired during the production of MLCC, the oxide contained in the layer will be absorbed into the dielectric layer, so the sintering resistance of the nickel particle will not be high. Ta. On the other hand, according to the nickel particles of the present invention, which are composed of a nickel base particle and a nickel/metal M alloy disposed on the surface thereof, the sintering resistance can be increased without excessively increasing the electrical resistance. Furthermore, when a conductive film is formed using the nickel particles of the present invention, the surface of the conductive film can be made smooth. For these reasons, as described above, it is preferable to manufacture nickel particles by simultaneously reducing the nickel hydroxide and the compound of the metal element M while some of the nickel hydroxide remains.

The nickel particles produced by the above method are used in various fields by taking advantage of the characteristic that the nickel particles have a surface area containing nickel/metal M alloy on the surface of the nickel particles while being fine and uniform in size. It is particularly suitable for forming internal electrodes of MLCC.

Although the present invention has been described above based on its preferred embodiments, the present invention is not limited to the above embodiments.

Regarding the above embodiment, the following nickel particles and a method for producing the same are further disclosed.
[1] Nickel particles having a surface region containing an alloy of nickel and metal element M,
The metal element M is at least one selected from bismuth, copper, iron, and molybdenum,
The content of the metal element M with respect to the entire nickel particles is 0.09% by mass or more and 15.8% by mass or less,
When a region from the outermost surface to a sputtering depth of 5 nm in terms of SiO ₂ is measured in the depth direction of the nickel particles by X-ray photoelectron spectroscopy, it is found that the total number of atoms of nickel element and metal element M in this region is Let the maximum value of the ratio of the number of atoms of the metal element M be X (at%),
When the nickel particles are measured 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 Y (at%),
Nickel particles having an X/Y value of 0.5 or more and 35 or less.
[2] In the particle size distribution based on the equivalent circle diameter calculated from measurement with a scanning electron microscope, when the number cumulative particle size at a cumulative number of particles of 50% is _D50 , _D50 is 20 nm or more and 200 nm or less,
The nickel particles according to [1], wherein the value of the coefficient of variation (σ/D ₅₀ ) (%) is 14% or less, where σ (nm) is the standard deviation of the particle size in the particle size distribution.
Coefficient of variation (%) = (σ/D ₅₀ ) x 100
[3] In the particle size distribution based on the equivalent circle diameter calculated from measurements using a scanning electron microscope, when the number cumulative particle size at a cumulative number of 50 pieces is _D50 , the particle size is 1.5 times or more of _D50 . The nickel particles according to [1] or [2], wherein the proportion of particles having the following is 0.5% by number or less.
[4] In the particle size distribution based on the equivalent circle diameter calculated from measurements using a scanning electron microscope, the number cumulative particle size at a cumulative number of 50% by number is taken as D ₅₀ , and the crystallite size measured by the WPPF method is Cs (nm ), the nickel particles according to any one of [1] to [3], have a Cs/D ₅₀ value of 0.3 or more and 0.6 or less.
[5] A method for producing nickel particles by heating a liquid mixture containing nickel hydroxide particles, polyol, polyvinylpyrrolidone, and polyethyleneimine, comprising:
Using 30 parts by mass or more and 200 parts by mass or less of polyvinylpyrrolidone for 1 part by mass of polyethyleneimine,
reducing the nickel hydroxide particles to nickel base particles by the heating;
While some of the nickel hydroxide particles remain, the mixed liquid is mixed with a compound of metal element M, and the compound is reduced to metal M, so that nickel and metal element are added to the nickel mother particles. A method for producing nickel particles forming a surface region comprising an alloy with M, the method comprising:
The method for producing nickel particles, wherein the metal element M is at least one selected from bismuth, copper, iron, and molybdenum.
[6] A multilayer ceramic capacitor using the nickel particles according to any one of [1] to [4] as an internal electrode.

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

[Example 1]
Add 445 g of ethylene glycol, 64 g of nickel hydroxide particles, 12 g of polyvinylpyrrolidone, 0.14 g of polyethyleneimine, and 0.13 ml of palladium nitrate aqueous solution (concentration: 100 g/l) to a 500 ml beaker to make a mixed solution. Prepared. Polyethyleneimine was branched and had a number average molecular weight of 1,800. The mixture was heated while stirring, and a reduction reaction was carried out at 198° C. for 5 hours under atmospheric pressure. At this point, the reduction of nickel hydroxide had progressed to 80 mol% relative to the charged amount of nickel hydroxide. Then, 0.3 g of bismuth chloride was added thereto, and the reduction reaction was further carried out at 198° C. for 10 hours under atmospheric pressure. Heating was stopped to complete the reduction, and the mixture was allowed to cool naturally to room temperature. In this way, a large number of nickel particles were obtained.
A magnet was placed at the bottom of the beaker containing the resulting dispersion of nickel particles, and the nickel particles were attracted to the magnet. Under this condition, the supernatant of the dispersion was removed.
After removing the magnet from the bottom of the beaker, 50 g of pure water was added and the dispersion was stirred for 10 minutes. The magnet was then repositioned at the bottom of the beaker to attract the nickel particles to the magnet. Under this condition, the supernatant of the dispersion was removed. The series of operations was repeated 5 times.
Then, 50 g of methanol was added and the dispersion was stirred for 10 minutes. Removal of the supernatant was repeated three times using a magnet, and the solvent in the dispersion was replaced with methanol. Thereafter, vacuum drying was performed at 80° C. to obtain nickel particles.

[Example 2 to 6]
The amount of palladium nitrate aqueous solution added, the amount of bismuth chloride added, and the time from the start of heating the mixed solution until the addition of bismuth chloride to the mixed solution were as shown in Table 1. Nickel particles were obtained in the same manner as in Example 1 except for the above.

[Example 7]
Copper sulfate pentahydrate was added in place of bismuth chloride. The amount of palladium nitrate aqueous solution added and the amount of copper sulfate pentahydrate added were as shown in Table 1. Nickel particles were obtained in the same manner as in Example 1 except for the above.

[Example 8]
Iron sulfate heptahydrate was added in place of bismuth chloride. The amount of palladium nitrate aqueous solution added and the amount of iron sulfate heptahydrate added were as shown in Table 1. Nickel particles were obtained in the same manner as in Example 1 except for the above.

[Example 9]
Sodium molybdate was added instead of bismuth chloride. The amount of palladium nitrate aqueous solution added and the amount of sodium molybdate added were as shown in Table 1. Nickel particles were obtained in the same manner as in Example 1 except for the above.

[Comparative example 1]
Add 445 g of ethylene glycol, 64 g of nickel hydroxide particles, 8 g of polyvinylpyrrolidone, 0.14 g of polyethyleneimine, and 0.13 ml of palladium nitrate aqueous solution (concentration: 100 g/l) to a 500 ml beaker to make a mixed solution. Prepared. Polyethyleneimine was branched and had a number average molecular weight of 1,800. The mixture was heated while stirring, and a reduction reaction was carried out at 198° C. for 6.5 hours. Heating was stopped to complete the reduction, and the mixture was allowed to cool naturally to room temperature. In this way, a large number of nickel particles were obtained.
A magnet was placed at the bottom of the beaker containing the resulting dispersion of nickel particles, and the nickel particles were attracted to the magnet. Under this condition, the supernatant of the dispersion was removed.
After removing the magnet from the bottom of the beaker, 50 g of pure water was added and the dispersion was stirred for 10 minutes. The magnet was then repositioned at the bottom of the beaker to attract the nickel particles to the magnet. Under this condition, the supernatant of the dispersion was removed. The series of operations was repeated 5 times.
Then, 50 g of methanol was added and the dispersion was stirred for 10 minutes. Removal of the supernatant was repeated three times using a magnet, and the solvent in the dispersion was replaced with methanol. Thereafter, vacuum drying was performed at 80° C. to obtain a powder of nickel particles.

[Comparative example 2]
Nickel particles were obtained in the same manner as in Example 1, except that bismuth chloride was added before performing the reduction reaction of nickel hydroxide.

[Comparative example 3]
Add 445 g of ethylene glycol, 64 g of nickel hydroxide particles, 8 g of polyvinylpyrrolidone, 0.14 g of polyethyleneimine, and 0.13 ml of palladium nitrate aqueous solution (concentration: 100 g/l) to a 500 ml beaker to make a mixed solution. Prepared. Polyethyleneimine was branched and had a number average molecular weight of 1,800. The mixture was heated while stirring, and a reduction reaction was carried out at 198° C. for 6.5 hours. Heating was stopped to complete the reduction, and the mixture was allowed to cool naturally to room temperature. In this way, a large number of nickel particles were obtained.
A magnet was placed at the bottom of the beaker containing the resulting dispersion of nickel particles, and the nickel particles were attracted to the magnet. Under this condition, the supernatant of the dispersion was removed.
After removing the magnet from the bottom of the beaker, 50 g of pure water was added and the dispersion was stirred for 10 minutes. The magnet was then repositioned at the bottom of the beaker to attract the nickel particles to the magnet. Under this condition, the supernatant of the dispersion was removed. The series of operations was repeated 5 times.
After adding 300 g of pure water and hydrazine monohydrate to this dispersion and raising the temperature to 60°C, 1 g of sodium stannate trihydrate was added and stirred for 5 hours to surface-treat the nickel particles with tin. provided.
A magnet was placed at the bottom of the beaker containing the resulting dispersion of nickel particles, and the nickel particles were attracted to the magnet. Under this condition, the supernatant of the dispersion was removed.
After removing the magnet from the bottom of the beaker, 50 g of pure water was added and the dispersion was stirred for 10 minutes. The magnet was then repositioned at the bottom of the beaker to attract the nickel particles to the magnet. Under this condition, the supernatant of the dispersion was removed. The series of operations was repeated 5 times.
Then, 50 g of methanol was added and the dispersion was stirred for 10 minutes. Removal of the supernatant was repeated three times using a magnet, and the solvent in the dispersion was replaced with methanol. Thereafter, vacuum drying was performed at 80° C. to obtain a powder of nickel particles that had been surface-treated with tin. As described in [Evaluation 1] below, it was confirmed that the surface area of the nickel particles did not contain an alloy of nickel and tin, and a tin surface layer was formed.

[Rating 1]
Regarding the nickel particles obtained in Examples 1 to 9 and Comparative Examples 1 to 3, the values of X and X1 were determined by the following XPS analysis method.
Further, the content of bismuth element, copper element, iron element, and molybdenum element and the value of Y with respect to the whole nickel particles were determined by ICP emission spectrometry.
In addition, the particle size distribution was measured by the method described above, and the particle size D ₅₀ , the proportion of coarse particles present, and the coefficient of variation were determined.
Further, the a-axis length and crystallite size Cs of nickel were determined based on the WPPF method using the following method.
In addition, the method described above determines whether the surface area of the nickel particles contains an alloy of nickel and bismuth, an alloy of nickel and copper, an alloy of nickel and iron, and nickel particles. It was confirmed whether or not it contained an alloy of and molybdenum.

[X-ray photoelectron spectroscopy (XPS) measurement]
As a measurement target sample for XPS, nickel particles formed into pellets using a press were used. Specifically, approximately 10 mg of the particle sample was placed in an aluminum container having dimensions of 5.2 mm in diameter and 2.5 mm in height. Next, using a press machine (manufactured by As One, product number: 1-312-01) and an adapter (product number: 1-312-03), it was pressurized together with the aluminum container at a predetermined stroke (25 mm). Next, the pellet molded product of nickel particles supported in the aluminum container was taken out.
Regarding the obtained pellet molded product, the outermost surface measurement and the depth direction measurement from the sample surface toward the inside by sputtering with Ar monomer ions were performed. The measurement conditions are as follows.

・Measuring device: VersaProbe III manufactured by ULVAC-PHI Co., Ltd.
・Excited X-ray: Monochromatic Al-Kα ray (1486.7eV)
・Output: 50W
・Acceleration voltage: 15kV
・X-ray irradiation diameter: 200μmφ
・X-ray scanning area: 1000μm x 300μm
・Detection angle: 45°
・Pass energy: 26.0eV
・Energy step: 0.1eV/step
・Sputter ion species: Ar monomer ion ・Sputter rate: 3.3 nm/min (SiO ₂ equivalent)
・Sputter interval: 20s
・Measurement elements: C _1s , Ni _2p3 , Sn _3d5 , Bi _4f , Cu _2p , Fe _3p , Mo _3d
・Energy correction value: C-C bond and C-H bond in C _1s (284.8eV)

[Analysis of XPS data]
XPS data was analyzed using data analysis software ("Multipack Ver. 9.9" manufactured by ULVAC-PHI). Shirley was used as the background mode.

[Value of X]
In Examples 1 to 6, the ratio of the number of atoms of Bi _4f to the total number of atoms of two elements, Ni _2p3 and Bi _4f, was defined as X (at%). In Example 7, the ratio of the number of atoms of Cu _2p to the total number of atoms of two elements, Ni _2p3 and Cu _2p , was defined as X (at%). In Example ₈ , the ratio of the number of atoms of Fe 3p to the total number of atoms of two elements, Ni _2p3 and Fe _3p, was defined as X (at%). In Example ₉ , the ratio of the number of atoms of Mo 3d to the total number of atoms of two elements, Ni _2p3 and Mo _3d , was defined as 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 using the WPPF method from the diffraction peak derived from nickel obtained by X-ray diffraction measurement.

Device name SmartLab (9KW): Manufactured by Rigaku <Device configuration>
Wavelength ・Target: Cu
・Wavelength type: Kα1
・Kα1: 1.54059 (Å)
・Kα2: 1.54441 (Å)
・Kβ: 1.39225 (Å)
・Kα12 intensity ratio: 0.4970
・Horizontal polarization rate: 0.500
Diffraction device ・Goniometer: SmartLab
・Attachment base: Z stage alone ・Attachment: ASC6-Reflection <Measurement conditions>
・Optical system attribute: Concentration method ・CBO selection slit: BB
・Incidence parallel slit: Soller_slit_5.0deg
・Incidence slit: 2/3deg
・Longitudinal limit slit: 10.0mm
・Light receiving slit 1: 20.000mm
・Light receiving parallel slit: Soller_slit_5.0deg
・Light receiving slit 2: 20.000mm
・Attenuator: Open
・Detector: D/teX Ultra250
・Scan axis: 2θ/θ
・Scan mode: Continuous ・Scan range: 5.0000~140.0000deg
・Step width: 0.0100deg
・Scan speed/measurement time: 2.015572deg/min
・Number of data points: 13501 points ・Tube voltage: 45kV
・Tube current: 200mA
・HV:0.00

<Preparation of sample for X-ray diffraction>
Nickel particles to be measured were placed in a measurement holder and smoothed using a glass plate so that the layer of nickel particles had a thickness of 0.5 mm and the measurement surface was smooth.

Using the X-ray diffraction pattern obtained under the above measurement conditions, analysis was performed using analysis software under the following conditions. The analysis was corrected using data obtained from lanthanum hexaboride powder (SRM660 series), which is a standard material provided by the US National Institute of Standards and Technology (NIST). The a-axis length and crystallite size Cs were calculated using the WPPF method.

<Measurement data analysis conditions>
・Analysis software: Rigaku PDXL2
・Analysis method: WPPF method ・Data processing: Automatic profile processing (Rigakusha PDXL user manual p. 305)

[Evaluation 2]
Regarding the nickel particles obtained in Examples 1 to 9 and Comparative Examples 1 to 3, the shrinkage start temperature of the nickel particles, the specific resistance of the sintered film containing the nickel particles, and the surface roughness Rz were measured by the following methods. The above results are shown in Table 1 below.

[Measurement of contraction start temperature]
TMA/SS6000 manufactured by Seiko Instruments Inc. was used as a TMA measuring device. 0.2 to 0.3 g of nickel particles were placed in a stainless steel mold container with a diameter of 5.0 mm, and the nickel particles were press-molded so that a pressure of 92 MPa was applied to produce pellets. The pellet length of the obtained pellet was measured and used as a sample to be measured. This was set in a measuring device, and the temperature of the sample was raised at 5° C./min under a load of 49 mN and an atmosphere of 1% hydrogen/99% nitrogen by volume. Measurement was started from room temperature (25° C.), and a graph showing the relationship between temperature and shrinkage rate (%) was obtained. From the obtained graph, the shrinkage start temperature was determined.

[Measurement of specific resistance]
A mixture was obtained by dissolving 0.1 g of ethyl cellulose in 4 g of terpineol and then adding 5 g of nickel particles. This mixture was mixed using a rotation/revolution mixer (“Awatori Rentaro (registered trademark)” manufactured by Shinky Co., Ltd.). The mixture was then crushed by passing it through three rolls four times. The gap between the three rolls was set to 8 μm. A coating liquid was thus obtained.
This coating liquid was applied to an alumina substrate to form a coating film. The thickness of the coating film was 30 μm. This coating film was sintered at 800° C. for 60 minutes in a 1 volume % hydrogen/99 volume % nitrogen atmosphere to obtain a sintered film. The specific resistance (Ω·cm) of this sintered film was measured using Loresta MCP-T600, a four-probe resistivity measuring device manufactured by Mitsubishi Analytech.

[Measurement of surface roughness Rz]
The surface roughness Rz of the sintered film was measured using SURFCOM 130A. The measurement conditions were an evaluation length of 6.0 mm and a measurement speed of 0.6 mm/s.

As is clear from the results shown in Table 1, it was confirmed by XPS measurements that the nickel particles obtained in Examples 1 to 9 contained bismuth element, copper element, iron element, or molybdenum element in the metallic state in their surface regions. It was done. Furthermore, the a-axis length of the nickel particles obtained in the examples was longer than the a-axis length of the nickel particles obtained in Comparative Example 1, which did not use a compound of bismuth element, copper element, iron element, and molybdenum element. Ta. These results show that the nickel particles obtained in Examples 1 to 6 contain an alloy of nickel and bismuth in their surface regions. Further, it can be seen that the nickel particles obtained in Example 7 contain an alloy of nickel and copper in the surface region. Further, it can be seen that the nickel particles obtained in Example 8 contain an alloy of nickel and iron in the surface region. Further, it can be seen that the nickel particles obtained in Example 9 contain an alloy of nickel and molybdenum in the surface region.
Furthermore, as is clear from the results shown in Table 1, the nickel particles obtained in Examples 1 to 9 exhibited higher shrinkage start temperatures than the nickel particles obtained in Comparative Examples 1 to 3. This shows that the nickel particles obtained in Examples 1 to 9 exhibit high sintering resistance.
In particular, as is clear from the comparison between Examples 1 to 5 and Example 6, it can be seen that by controlling the amount of bismuth contained in the nickel particles, the specific resistance of the sintered film obtained from the nickel particles can be controlled.
In addition, Examples 1 to 6, in which nickel particles were produced having a surface region in which an alloy of nickel and bismuth was formed, were more sintered than Comparative Example 2, in which an alloy of nickel and bismuth was formed in the entire nickel particle. The surface of the conjunctiva became smooth. From these results, it can be seen that the surface roughness of the sintered film is reduced by using nickel particles having a surface region containing an alloy of nickel and bismuth.

According to the present invention, nickel particles with high sintering resistance are provided without excessively increasing electrical resistance.

Claims (6)

Nickel particles having a surface area containing an alloy of nickel and a metal element M,
The metal element M is at least one selected from bismuth, copper, iron, and molybdenum,
The content of the metal element M with respect to the entire nickel particles is 0.09% by mass or more and 15.8% by mass or less,
When a region from the outermost surface to a sputtering depth of 5 nm in terms of SiO ₂ is measured in the depth direction of the nickel particles by X-ray photoelectron spectroscopy, it is found that the total number of atoms of nickel element and metal element M in this region is Let the maximum value of the ratio of the number of atoms of the metal element M be X (at%),
When the nickel particles are measured 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 Y (at%),
Nickel particles having an X/Y value of 0.5 or more and 35 or less. In the particle size distribution based on the circle equivalent diameter calculated from measurement with a scanning electron microscope, when the number cumulative particle size at a cumulative number of 50 pieces is _D50 , _D50 is 20 nm or more and 200 nm or less,
The nickel particles according to claim 1, wherein the value of the coefficient of variation (σ/D ₅₀ ) (%) is 14% or less, where σ (nm) is the standard deviation of particle diameter in the particle size distribution.
Coefficient of variation (%) = (σ/D ₅₀ ) x 100 In the particle size distribution based on the equivalent circle diameter calculated from measurement with a scanning electron microscope, particles having a particle size 1.5 times or more of _D50 , where _D50 is the number cumulative particle size at a cumulative number of 50 pieces. The nickel particles according to claim 1, wherein the abundance ratio of nickel particles is 0.5% by number or less. In the particle size distribution based on the equivalent circle diameter calculated from measurement with a scanning electron microscope, the number cumulative particle size at a cumulative number of 50 number% was taken as D ₅₀ , and the crystallite size measured by the WPPF method was taken as Cs (nm). The nickel particles according to claim 1, wherein the Cs/D ₅₀ value is 0.3 or more and 0.6 or less. A method for producing nickel particles by heating a liquid mixture containing nickel hydroxide particles, polyol, polyvinylpyrrolidone and polyethyleneimine, the method comprising:
Using 30 parts by mass or more and 200 parts by mass or less of polyvinylpyrrolidone for 1 part by mass of polyethyleneimine,
reducing the nickel hydroxide particles to nickel base particles by the heating;
While some of the nickel hydroxide particles remain, the mixed liquid is mixed with a compound of metal element M, and the compound is reduced to metal M, so that nickel and metal element are added to the nickel mother particles. A method for producing nickel particles forming a surface region comprising an alloy with M, the method comprising:
The method for producing nickel particles, wherein the metal element M is at least one selected from bismuth, copper, iron, and molybdenum. A multilayer ceramic capacitor using the nickel particles according to any one of claims 1 to 4 as an internal electrode.